Method and device for determining an amount of carbon dioxide taken up by a soil infiltrate

Abstract

The present disclosure relates to a device, a system, a use and a method of determining an amount of carbon dioxide taken up by a soil infiltrate (1 ). The method comprises positioning a device (3) in a measurement position (7) in a soil (2). An alkalinity storage layer (6) of the device (3) is arranged underneath an upstream wall (5), wherein the alkalinity storage layer (6) is formed by a material bearing on its surface a plurality of acidic groups. The method further comprises allowing minerals (4) to react during a measurement time period with water and carbon dioxide to form a soil infiltrate (1 ) infiltrating through the soil (2) and through the alkalinity storage layer (6), thereby causing at least some of the acidic groups of the material forming the alkalinity storage layer (6) to be deprotonated. The method further comprises determining a total alkalinity taken up by the alkalinity storage layer (6), and determining based on the determined total alkalinity taken up by the alkalinity storage layer (6) a total amount of carbon dioxide taken up by the soil infiltrate (1 ).

Description

[0001] Method and Device for determining an amount of carbon dioxide taken up by a soil infiltrate

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a method of determining an amount of carbon dioxide taken up by a soil infiltrate.

[0004] BACKGROUND OF THE INVENTION

[0005] The measuring, reporting, and verification (MRV) of carbon removal in field settings poses a complex challenge due to their ‘open system’ nature. Using enhanced weathering (EW) as an example, the full system boundary would enclose the planet's atmosphere, the project area (typically the land plot where weathering materials are employed), and further riverine networks, aquifers transporting CO2, ground- and ocean waters. Considering the length and timescales of these different components, the project area and duration stand out as a spatiotemporal bottleneck where the holistic detection of carbon dioxide removal (CDR) signals or related signals is most feasible. At present, the accurate quantification of the EW process still poses significant challenges to scientists and project developers alike. Different methods focusing on the gas, liquid, or solid phase (or combinations thereof) of the project area are employed, all with their respective tradeoffs.

[0006] Gas phase measurements aim to capture the net CO2flux from the atmosphere into the soil, which would give direct evidence of carbon removal. So far, these methods still suffer from high uncertainty due to the comparably large in- and outflows from simultaneously occurring processes, such as biological activity.

[0007] Soil-based approaches aim to follow changes in the cation inventory of the solid phase. Base cation concentrations (e.g., Na, K, Mg, Ca) can then be used to infer the production and flow of removed CO2. Highly accurate cation concentrations can be determined, yet the indirect nature of the measurement diminishes its utility in carbon removal MRV. Solution-phase approaches can track, e.g., the total amount of chemical species representing the capacity of binding CO2as bicarbonate and carbonate in the liquid phase, commonly referred to as the total alkalinity (TA). Similar observations can be made based on dissolved inorganic carbon - the sum of dissolved CO2, carbonic acid, bicarbonate, and carbonate - as bicarbonate commonly represents the majority of active components within TA. Currently, TA measurements are routinely conducted due to their utility, however commonly on manually collected samples in a laboratory setting requiring skilled labor. Additionally, while precision is high, accuracy concerns persist due to representativeness concerns of the samples taken through, e.g., suction cups. Determining the concentration of TA in soil pore waters this way and then using a water balance to infer TA efflux from the field is a common approach that, however, relies on several assumptions about the hydrological conditions of the area of study. This approach severely limits the applicability of TA measurements in large-scale, high-fidelity MRV efforts. Thus, there is a need to provide a method that allows the reliable and accurate determination of the amount of captured carbon dioxide with high fidelity.

[0008] SUMMARY OF THE INVENTION

[0009] It is therefore the general object of the present invention to advance the state of the art with respect to quantifying the amount of captured carbon dioxide. In particular, it is an object of at least some variants to provide a method and a device that allow to determine the amount of carbon dioxide taken up by a soil infiltrate with high accuracy and fidelity. It is a further object of at least some variants to reduce the effort required for determining the amount of carbon dioxide taken up by a soil infiltrate and optionally to reduce interference or intrusion with nature during the measurement process. For example, it is an object of at least some variants to provide a method and device of quantifying the amount of carbon dioxide captured in enhanced weathering processes.

[0010] The general object is achieved in a first aspect of the disclosure by a method of determining an amount of carbon dioxide taken up by a soil infiltrate. The method comprises a) positioning a device in a measurement position in a soil such that a upstream wall of the device is arranged underneath a soil surface, preferably arranged at least 10 mm underneath the soil surface. An alkalinity storage layer of the device is typically arranged in a vertical direction underneath the upstream wall, wherein the alkalinity storage layer is formed by a material bearing on its surface a plurality of acidic group. In some variants, the alkalinity storage layer of the device is a buffer layer, e.g. a buffer layer having an initial pH from 3 to 7. In some variants, the device that is being positioned is the device according to any of the embodiments described herein, in particular any of the embodiments described herein in the context of the third aspect of the present disclosure. The upstream wall may in some variants be labelled as “top wall”.

[0011] The method further comprises b) allowing solids, e.g. minerals, to react during a measurement time period with water and carbon dioxide to form a soil infiltrate infiltrating through the soil and through the alkalinity storage layer, thereby causing at least some of the acidic groups of the material forming the alkalinity storage layer to be deprotonated over the measurement time period. In some variants, e.g. in variants in which the alkalinity storage layer is a buffer layer, in step b), the soil infiltrate infiltrating through the buffer layer may cause a change in pH of the buffer layer over the measurement time period.

[0012] The method further comprises c) determining a total alkalinity taken up by the alkalinity storage layer over at least a portion of the measurement time period.

[0013] The method further comprises d) determining, based on the determined total alkalinity taken up by the alkalinity storage layer, a total amount of carbon dioxide taken up by the soil infiltrate during the measurement time period.

[0014] By providing an alkalinity storage layer whose acidic groups are at least partially deprotonated as a result of the soil infiltrate passing through the alkalinity storage layer, the method allows determining the amount of carbon dioxide taken up by the soil infiltrate with high accuracy and little interference with nature. In particular, the quantity and nature of the chemical species formed by reaction of carbon dioxide with water may effectively be stored in the device in the form of a change in the degree of deprotonation (respectively the degree of protonation) of the alkalinity storage layer over the measurement period. This is advantageous because the chemical species formed from carbon dioxide (including bicarbonate (HCO3), carbonate (CO32) and hydroxide (OH ), respectively salts thereof) have limited stability, which means that the direct measurement of these species leads to measurement inaccuracies. Furthermore, attempts to measure the cation inventory of the soil infiltrate relies on doubtful and error-prone assumptions about the cation composition of the soil infiltrate, and is therefore not an accurate proxy to determine the amount of carbon dioxide captured. By contrast, the method of the present disclosure effectively allows to store information about the quantity of carbon dioxide taken up by soil infiltrate in the alkalinity storage layer in an accurate and stable manner.

[0015] For an illustrative example, a certain quantity of carbon dioxide may react with water to form a soil infiltrate having a certain concentration of chemical species (e.g. bicarbonate and carbonate), and these chemical species may on contact with the acidic groups of the material forming the alkalinity storage layer deprotonate these acidic groups. If the alkalinity storage layer is a buffer layer, the soil infiltrate leaving the alkalinity storage layer may e.g. have essentially the same pH as the alkalinity storage layer. The degree of deprotonation of the alkalinity storage layer is indicative of the amount of carbon dioxide taken up by the soil infiltrate in the first place. Over time, the alkalinity storage layer may take up a total alkalinity, commensurate with the amount of carbon dioxide taken up by the soil infiltrate. Consequently, the total alkalinity taken up by the alkalinity storage layer may be used to determine the total amount of carbon dioxide taken up by the soil infiltrate. Optionally, the total amount of carbon dioxide taken up by the soil infiltrate may be used to determine the amount of carbon dioxide captured in an enhanced weathering process. Moreover, carbon dioxide removal may in turn be quantified as well.

[0016] Depending on the application, different alkalinity storage layers may be used. For example, in some variants, the material forming the alkalinity storage layer is a material that changes its volumetric expansion upon infiltration of a soil infiltrate having a pH of higher than 5, preferably upon infiltration of a soil infiltrate having a pH of higher than 7, more preferably upon infiltration of a soil infiltrate having a pH of 8 or higher, more preferably from 8 to 14. In some variants, the material forming the alkalinity storage layer is a material that changes its volumetric expansion upon infiltration of a soil infiltrate comprising aqueous bicarbonate ions and / or aqueous carbonate ions through the alkalinity storage layer. For example, the alkalinity storage layer may in some variants comprise a resin, preferably an ion-exchange resin. The resin may e.g. be swellable and / or shrinkable upon contact with an aqueous solution having a pH of higher than 7, preferably upon contact with an aqueous solution having a pH of 8 higher. In some variants, the resin is swellable and / or shrinkable upon contact with aqueous bicarbonate ions and / or aqueous carbonate ions (respectively in contact with respective salts of these ions). In some variants, the alkalinity storage layer is made of a material that is swellable and / or shrinkable upon contact with an aqueous solution having a pH of higher than 7, preferably of 8 or higher. In some variants, the alkalinity storage layer is made of a material that is swellable and / or shrinkable upon contact with an aqueous solution of bicarbonate ions and / or carbonate ions.

[0017] In several variants described herein, the material forming the alkalinity storage layer or the resin are described to be swellable and / or shrinkable. In these variants, the material forming the alkalinity storage layer or the resin are preferably swellable.

[0018] It is understood that typically, when a material is said to change its volumetric expansion (e.g. by swelling or shrinking) upon contact with a given substance (e.g. a soil infiltrate or an aqueous solution having a certain pH or containing certain species), this means, at least in preferred variants, that the material displays a change in its volumetric expansion that is different from a possible change in volumetric expansion displayed upon contact with water in the absence of the given substance. For example, in some variants, the alkalinity storage layer may be made of a material that is swellable and / or shrinkable (respectively that changes its volumetric expansion) upon contact with water, e.g. due to absorption of water. However, the material may swell (respectively change its volumetric expansion) more strongly when contacted with water having a pH of 8 or higher (respectively in some variants soil infiltrate comprising aqueous bicarbonate and / or carbonate ions) than it would otherwise swell when contacted with the same amount of water having a neutral pH (e.g. water free of aqueous bicarbonate and carbonate ions). Thus, in some variants, the material forming the alkalinity storage layer is a material that changes its volumetric expansion upon infiltration of a soil infiltrate having a pH of higher than 7 (preferably pH of 8 or higher) through the alkalinity storage layer, wherein the change in volumetric expansion is at least partially due to the basic species in the soil infiltrate (e.g. due to the species contributing to the pH of higher than 7, preferably of 8 or higher, in the soil infiltrate). In some variants, the material forming the alkalinity storage layer is a material that changes its volumetric expansion upon infiltration of a soil infiltrate comprising aqueous bicarbonate ions and / or aqueous carbonate ions through the alkalinity storage layer, wherein the change in volumetric expansion is at least partially due to the aqueous bicarbonate ions and / or aqueous carbonate ions comprised in the soil infiltrate. In particular, the change in volumetric expansion may e.g. be due to a chemical reaction of the plurality of acidic groups with the aqueous bicarbonate ions and / or aqueous carbonate ions comprised in the soil infiltrate. In some variants, the alkalinity storage layer comprises a resin that is swellable and / or shrinkable upon contact with an aqueous solution having a pH of higher than 7 (preferably upon contact with an aqueous solution having a pH of 8 or higher), wherein the swelling or shrinking is at least partially due to the basic species in the soil infiltrate (e.g. due to the species contributing to the pH of higher than 7, preferably of 8 or higher, in the soil infiltrate). In some variants, the alkalinity storage layer comprises a resin that is swellable and / or shrinkable upon contact with aqueous bicarbonate ions and / or aqueous carbonate ions, wherein the swelling or shrinking is at least partially due to the aqueous bicarbonate ions and / or aqueous carbonate ions comprised in the soil infiltrate.

[0019] In some variants, the alkalinity storage layer contacts a first side of a detection wall, such that a change in the volumetric expansion of the material forming the alkalinity storage layer leads to a strain on the detection wall and / or to a physical deformation of the detection wall. The detection wall may e.g. be elastically deformable, preferably by elastic outward bulging of the detection wall on a second side opposite the first side of the detection wall, such that a change in the volumetric expansion of the material forming the alkalinity storage layer leads to a physical deformation of the detection wall. In these variants, the infiltration of the soil infiltrate through the alkalinity storage layer may e.g. lead to a change in volumetric expansion of the material forming the alkalinity storage layer, which may ultimately be used to infer the amount of carbon dioxide taken up. In some variants, the detection wall is arranged at least partially inside the housing. In particular, at least the first side of the detection wall may in some variants be arranged inside the housing. In some variants, the second side of the detection wall faces away from the alkalinity storage layer. In some variants, the step of determining the total alkalinity taken up by the alkalinity storage layer includes determining a change in volumetric expansion, preferably swelling, of the material forming the alkalinity storage layer over at least a portion of the measurement time period. In some variants, the step of c) determining the total alkalinity taken up by the alkalinity storage layer (6) over at least a portion of the measurement time period includes c.i) determining (e.g. measuring) a change in the volumetric expansion of the material forming the alkalinity storage layer over at least the portion of the measurement time period; and c.ii) determining, based on the measured change in the volumetric expansion of the material forming the alkalinity storage layer over at least the portion of the measurement time period, the total alkalinity taken up by the alkalinity storage layer over at least the portion of the measurement time period. In some variants, the change in the volumetric expansion of the material forming the alkalinity storage layer is a swelling and / or shrinking of the material forming the alkalinity storage layer occurring upon infiltration through the alkalinity storage layer of the soil infiltrate formed by reaction of the solids with water and carbon dioxide. In some variants, the change in the volumetric expansion of the material forming the alkalinity storage layer is a swelling and / or shrinking of the material forming the alkalinity storage layer occurring upon infiltration of the soil infiltrate comprising aqueous bicarbonate ions and / or aqueous carbonate ions through the alkalinity storage layer.

[0020] In some variants, the alkalinity storage layer is formed by a material bearing on its surface a plurality of acidic groups and a plurality of basic groups. For example, the material may include carboxylic acid groups and carboxylate groups.

[0021] In some variants, the alkalinity storage layer is arranged inside the housing.

[0022] In some variants, the solids comprise or consist of minerals. For example, the solids may be minerals. The solids are allowed to react during the measurement time period with water and carbon dioxide to form the soil infiltrate, which infiltrates into the soil and through the alkalinity storage layer. Thus, the solids are typically configured to undergo a chemical reaction with carbon dioxide and water to form a soil infiltrate comprising aqueous bicarbonate ions and / or aqueous carbonate ions. The solids, preferably minerals, are typically arranged on or in the soil. Thus, when the solids, preferably minerals, are allowed to react with water and carbon dioxide, the formed soil infiltrate infiltrates into the soil and through the alkalinity storage layer. In some variants, the solids, preferably minerals, are arranged on the soil surface and / or in a top soil layer. For example, the solids, preferably minerals, may be arranged on the soil surface and / or within 300 mm, preferably within 80 mm, more preferably within 30 mm, even more preferably within 10 mm, of the soil surface. It is understood that the solids, preferably minerals, are typically arranged between the soil surface and the upstream wall of the device. Depending on the application, it may also be possible to arrange the solids, preferably minerals, in an elevated location, with the soil infiltrate dripping from the elevated location onto the soil surface and further infiltrating into the soil. Typically, the solids, preferably minerals, are arranged such that they are in direct contact with ambient air. This allows capturing of carbon dioxide from the air. Alternatively or in combination, the solids, preferably minerals, may be arranged to be in contact with soil pore gases. One potential advantage of this is that the soil pore gases may contain significantly higher concentrations of carbon dioxide due to respiration processes occurring within the soil. It is also possible to expose the solids, preferably minerals, to carbon dioxide by e.g. using additional gas flows of carbon dioxide, which may optionally be arranged underground. Depending on the application, the solids, preferably minerals, may be provided, e g. on a flat soil or on a plowed soil.

[0023] In some variants, the method further comprises during the measurement time period controlling an inside flow rate of the soil infiltrate infiltrating through the device such that the inside flow rate has a known or determinable flow rate ratio with respect to an outside flow rate of the soil infiltrate infiltrating through a first reference segment of the soil arranged outside the device. For example, in some variants, the inside flow rate of the soil infiltrate infiltrating through the device is controlled such that the inside flow rate essentially maintains a predetermined flow rate ratio with respect to the outside flow rate of the soil infiltrate infiltrating through a first reference segment of the soil arranged outside the device. The predetermined flow rate ratio may e.g. lie within a ratio from 1 :5 to 5:1 , preferably from 1 :2.5 to 2.5:1 . In some variants, the method further comprises during the measurement time period controlling an inside flow rate of the soil infiltrate infiltrating through the device such that the inside flow rate essentially corresponds to an outside flow rate of the soil infiltrate infiltrating through a first reference segment of the soil arranged outside the device. Essentially corresponds, in this context, means that the inside flow rate is within 25%, preferably within 15%, more preferably within 5%, of the outside flow rate. In some variants, the step of controlling the inside flow rate comprises controlling a vacuum pressure inside the device. As an example, when the inside flow rate is lower than the outside flow rate, an underpressure may be applied inside the device in order to draw in more soil infiltrate. By contrast, if the inside flow rate is higher than the outside flow rate, for example, an overpressure may be applied inside the device in order to draw in less soil infiltrate. Controlling the inside flow rate to essentially correspond to the outside flow rate allows a measurement of the amount of captured carbon dioxide that is representative across an entire field of study, compared to a small section of that field where the device may be positioned. The first reference segment of the soil may for example be arranged adjacent to the device in a horizontal direction orthogonal to the vertical direction. The first reference segment may be directly adjacent to the device, or it may be spaced apart from the device. In some variants, the first reference segment of the soil is arranged in a horizontal direction orthogonal to the vertical direction adjacent to the device.

[0024] Depending on the application, different solids may be used. Since the solids, which may for example be minerals, primarily serve to react with water and carbon dioxide to form the soil infiltrate infiltrating through the soil, it is understood that the solids may be minerals, but are not limited to minerals. Instead, it is possible to use solids in general. The solids are capable of reacting with water and carbon dioxide, typically to form bicarbonate and / or carbonate. This reaction typically takes place spontaneously at room temperature and 1 bar. It is sufficient for the reaction to form an equilibrium with gaseous carbon dioxide. Though a full or quantitate conversion of carbon dioxide may be desirable, it is not necessarily required for the purposes of the present disclosure. The solids typically have a pH of 7 or higher, preferably from 7 to 12. The solids may for example comprise one or more of the following: industrial byproducts such as steel slags, cement kiln dust, fly ash, concrete or concrete-derived solids, such as recycled concrete aggregate, concrete particles or concrete-derived particles (wherein each concrete or concrete-derived particle may for example have a particle size of less than 1 cm3).

[0025] Depending on the application, the solids preferably comprise or consist of minerals. For example, in some variants, the solids comprise at least 50 wt%, preferably at least 75 wt%, more preferably at least 90 wt%, minerals. The minerals may, but do not have to be, crystalline. Typically, the minerals are basic minerals. For example, an aqueous solution (100 g / L) or, if the mineral is poorly soluble, an aqueous suspension (100 g / L) of the mineral may preferably have a pH at room temperature of 7 or higher, preferably from 7 to 12. In some variants, the minerals include one or more of the following: alkaline oxides, earthalkaline oxides, silicate-containing minerals. In some variants, the minerals are selected from a list consisting of alkaline oxides, earthalkaline oxides and silicate- containing minerals. In some variants, the minerals comprise or consist of silicate-containing minerals. For example, in some variants, the minerals include basalt and / or wollastonite.

[0026] The soil infiltrate infiltrates through the soil and through the alkalinity storage layer. As such, the soil infiltrate is typically the water on or above the soil surface that infiltrates into the soil. The soil infiltrate typically includes all water-based solutions, suspensions and dispersions which infiltrate through the soil. The soil infiltrate may in some variants be a soil leachate.

[0027] Water and carbon dioxide are allowed to react with solids, preferably minerals, during a measurement time period to form the soil infiltrate infiltrating through the soil. As a result of this reaction, the soil infiltrate comprises chemical species that are formed from this chemical reaction. The chemical species typically include bicarbonate (HCO3), carbonate (CO32-) and hydroxide (OH-), respectively salts of these anions. Thus, it may be said that a soil infiltrate having additional alkalinity is formed (i.e. “additional alkalinity” compared to soil infiltrate formed without contacting solids, preferably minerals). Depending on the nature of the chemical species and on the concentration of the chemical species in the soil infiltrate, the soil infiltrate has a certain total alkalinity. The total alkalinity of the soil infiltrate is defined as the capacity of the soil infiltrate to neutralize acids. In some variants, the total alkalinity of the soil infiltrate TA(I) may be provided as wherein [xyz] denotes the concentration of the respective species xyz. In particular, [SiO(OH)3 ] refers at least in some embodiments to the concentration of orthosilicic acid and derivatives thereof (e.g. derivatives formed through condensation and / or deprotonation of orthosilicic acid). [CH3COO ]* refers at least in some embodiments to the concentration of acetic acid and all other organic carboxylic acids. It is understood that out of all chemical species contributing to total alkalinity, some are associated more strongly than others with the reaction of carbon dioxide with water. In particular, when carbon dioxide is allowed to react with water in the presence of a solid, e.g. a mineral such as an oxide, bicarbonate, carbonate and hydroxide ion concentrations may be affected more strongly than the concentration of some of the other species. Additionally, when measuring total alkalinity at different points in time, some of the chemical species may be essentially unchanged and may cancel out when comparing two or more total alkalinity measurements.

[0028] In some variants, the total alkalinity of the soil infiltrate TA(I) may be provided as

[0029] TA(I) = [HCO3-] + 2 x [CO32] + [OH ] wherein [HCO3 ] denotes the concentration of bicarbonate ions, [CO32] denotes the concentration of carbonate ions and [OH ] denotes the concentration of hydroxide ions in the soil infiltrate, typically at 25 °C and 1 bar. In a further approximation, the total alkalinity may be approximated as being composed of the bicarbonate ion concentration and the carbonate ion concentration.

[0030] The chemical species that are formed from the reaction of water and carbon dioxide in the presence of the solids, preferably minerals, are typically basic. As such, the soil infiltrate that is formed may be described to have additional alkalinity. The term “additional alkalinity” may describe an excess of alkalinity of the soil infiltrate formed in the presence of the solids, preferably minerals, compared to soil infiltrate formed in the absence of the solids, preferably minerals.

[0031] When the soil infiltrate infiltrates through the alkalinity storage layer, this typically changes the protonation / deprotonation profile of the acidic groups of the material forming the alkalinity storage layer. For example, in variants in which the alkalinity storage layer is a buffer layer, the infiltration of the soil infiltrate leads to a change in pH of the buffer layer over the measurement time period. Typically, deprotonation occurs, i.e. e.g. the pH of the buffer layer is increased as a result of the soil infiltrate infiltrating through the buffer layer. For example, an overall increase in pH may be observed over the measurement time period. Depending on the application, the pH may increase steadily, or the pH may fluctuate over time, for example as a result of intermittent acidic portions of soil infiltrate.

[0032] The total alkalinity of the soil infiltrate is taken up by the alkalinity storage layer over the measurement time period. In some variants in which the alkalinity storage layer is a buffer layer, the total alkalinity taken up by the buffer layer over the measurement time period corresponds to a change in pH of the buffer layer over the measurement time period. The total alkalinity taken up by the buffer layer over the measurement time period may for example be defined as a capacity of the buffer layer after the measurement time period to neutralize acids until the initial pH of the buffer layer is restored. As the skilled person understands, the acids used for neutralization typically have a lower pH than the initial pH of the buffer layer. In some variants, the total alkalinity taken up by the buffer layer over the measurement time period may be defined as an excess molar amount of basic buffer group equivalents, wherein the excess amount of basic buffer group equivalents corresponds to a difference in the amount of basic buffer group equivalents after the measurement time period and the amount of basic buffer group equivalents before the measurement time period (i.e. at the initial pH). Thus, the total alkalinity taken up by the buffer layer over the measurement time period may be defined as the molar amount of basic buffer group equivalents formed during the measurement time period.

[0033] The term “amount of basic buffer group equivalents” as used herein may in some variants be defined as the amount of basic buffer groups multiplied by n(eq), wherein n(eq) is the number of protons which the basic buffer group has less compared to the number of protons which the corresponding acidic buffer group has. For buffers comprising only monoprotic acids (e.g. carboxylic acids), n(eq) is 1 . By contrast, if the acidic buffer groups may be deprotonated twice, then n(eq) of the doubly deprotonated basic buffer groups is 2 and n(eq) of the singly deprotonated basic buffer groups is 1 .

[0034] In some variants, e.g. when using a carboxylate-carboxylic acid buffer, the total alkalinity taken up by the buffer layer over the measurement time period may in some variants be defined as the molar amount of carboxylate groups formed during the measurement time period by deprotonation of carboxylic acid groups. Thus, the total alkalinity taken up by the buffer layer over the measurement time period TA(taken up) may in this variant be defined as:

[0035] TA(taken up) = n(carboxylate groups) - n(carboxylate groups)0wherein n(carboxylate groups)7is the molar amount of carboxylate groups present after the measurement time period and n(carboxylate groups)0is the molar amount of carboxylate groups present before the measurement time period, i.e. at the initial pH.

[0036] Typically, the total alkalinity of the soil infiltrate is taken up at least partially, preferably fully, by the alkalinity storage layer. Fully may for example mean that more than 80%, such as more than 90%, preferably more than 95%, more preferably more than 99%, of the total alkalinity of the soil infiltrate before contacting the alkalinity storage layer may be taken up by the alkalinity storage layer. In some variants, the soil infiltrate exiting the alkalinity storage layer (e.g. buffer layer) has the same pH as the alkalinity storage layer (e.g. buffer layer). Additionally or alternatively, the soil infiltrate exiting the alkalinity storage layer may have a pH from 4 to 7, preferably from 4 to 6, e.g. from 4.5 to 5.5.

[0037] In some variants, the total alkalinity of the soil infiltrate taken up over the measurement time period TA(taken up) may be provided by:

[0038] TA(taken up) = TA(I) x Q(LW) x T wherein TA(I) is the total alkalinity of the soil infiltrate (typically as a concentration e.g. in mol / L), Q(LW) is the average flow rate with which the soil infiltrate infiltrates through the buffer layer and T is the duration of the measurement time period.

[0039] The total alkalinity taken up by the alkalinity storage layer may be determined in different ways. For example, in some variants, the step of determining the total alkalinity taken up by the alkalinity storage layer over the measurement time period comprises determining for a plurality of intervals within the measurement time period a total interval alkalinity taken up by the alkalinity storage layer during the respective interval; and determining the total alkalinity taken up by the alkalinity storage layer over the measurement time period based on the total interval alkalinities determined for the plurality of intervals. The total interval alkalinity could for example be determined by measuring a volumetric expansion (e.g. swelling and / or shrinking) of the alkalinity storage layer that ensued over the respective interval. Alternatively or in combination, e.g. in variants in which the alkalinity storage layer comprises or consists of a buffer layer, the total interval alkalinity could for example be determined by measuring a pH difference of the buffer layer that ensued over the respective interval (i.e. pH of the buffer layer at the end of the respective interval minus pH of the buffer layer at the beginning of the respective interval). In some variants, the obtained pH differences for all of the intervals may be summed up to provide a total alkalinity taken up by the buffer layer during the measurement time period.

[0040] It is also possible to distinguish whether the total interval alkalinity values are positive or negative. As an example, it is possible that the soil infiltrate may for the most part be basic but may include sporadic acidic intervals during which it may be slightly acidic. If the acidity during these sporadic acidic intervals exceeds the acidity of the buffer layer (i.e. if the pH of the soil infiltrate is smaller than the pH of the buffer layer), this could distort the measurement because it may intermittently lead to protonation rather than deprotonation of the buffer layer. This could potentially lead to inaccuracies in the projected amount of captured carbon dioxide. To address this challenge, the total interval alkalinity could be examined and only positive total interval alkalinity values could be considered. In some variants, the step of determining the total alkalinity taken up by the buffer layer over the measurement time period is provided by summing up the total interval alkalinities of all intervals for which a positive total interval alkalinity was determined. Optionally, the total interval alkalinities of all intervals for which a negative total interval alkalinity was determined are discarded. Positive interval alkalinity, as used in this context, means that the pH of the buffer layer was increased over the respective interval (i.e. the buffer layer was rendered more basic). By contrast, negative interval alkalinity, as used in this context, means that the pH of the buffer layer was decreased over the respective interval (i.e. the buffer layer was rendered more acidic over the interval).

[0041] In some variants, the measurement time period comprises at least three, preferably at least five, more preferably from 10 to 1 ’000 intervals. The total interval alkalinity may be determined for each of these intervals, or for a selection of intervals, such as at least 30% of the intervals. In some variants, the total interval alkalinity is determined for a plurality of at least ten intervals during the measurement time period. Depending on the application, the interval may have a different duration. For example, in some variants, each interval may last at least 10 minutes, preferably from 1 hour to 10 days.

[0042] When measuring the total alkalinity taken up by the alkalinity storage layer, the whole alkalinity storage layer may be subjected to a measurement, or only a part, e.g. a sublayer and / or a sub-segment, of the alkalinity storage layer may be subjected to a measurement. For example, in some variants, the step of determining the total alkalinity taken up by the alkalinity storage layer over the measurement time period includes determining for at least some of a plurality of sub-layers arranged in the vertical direction underneath each other a total alkalinity taken up by the respective sub-layer; and, subsequently, determining the total alkalinity taken up by the alkalinity storage layer over the measurement time period based on the determined total alkalinities taken up by the respective sub-layers. It is understood that the sub-layers are sub-layers of the alkalinity storage layer. In other words, the alkalinity storage layer comprises the plurality of sub-layers. In some variants, the total alkalinity may be determined for at least 10% of all sub-layers, preferably for at least 30% of all sub-layers. Depending on the application, the buffer layer may comprise at least three, such as at least five sub-layers.

[0043] Depending on the application (e.g. in variants in which the alkalinity storage layer comprises or consists of a buffer layer), the pH profile across the thickness of the buffer layer may be uniform, or it may fluctuate or deviate across the thickness. In some variants, the pH decreases from a top sub-layer to a bottom sub-layer, wherein the top sub-layer is arranged in the vertical direction nearest to the upstream wall and the bottom sub-layer is in the vertical direction arranged nearest to the bottom wall. The pH may for example decrease steadily, i.e. it may decrease from each sub-layer to each subsequent sublayer (i.e. in the vertical direction subsequent sub-layer), or it may intermittently increase, but display an overall decrease from the top sub-layer to the bottom sub-layer. When the pH does not decrease steadily, this could in some variants be indicative of undesired backflow, which may render the measurement inaccurate.

[0044] In some variants, if the determined total alkalinities taken up by the respective sub-layers decrease in the vertical direction from each sub-layer to each downstream (i.e. e.g. in the vertical direction subsequent) sub-layer, the total alkalinity taken up by the alkalinity storage layer is provided as a sum of the total alkalinities taken up by all sub-layers. Additionally, in those variants, if the total alkalinity of at least one sub-layer is lower than the total alkalinity of a downstream sub-layer arranged in the vertical direction directly underneath said at least one sub-layer, the total alkalinity of said at least one sub-layer (i.e. the at least one sub-layer having a lower total alkalinity) is not included in the determination of the total alkalinity taken up by the alkalinity storage layer. In some variants, the total alkalinity of said at least one sub-layer is included only partially, e.g. with a correction factor. In some variants, if the total alkalinity of the at least one sub-layer is lower than the total alkalinity of a downstream sub-layer arranged in the vertical direction directly underneath said at least one sub-layer, the total alkalinity taken up by the alkalinity storage layer is provided as a sum of the total alkal i n it ies taken up by the sub-layers upstream and / or downstream of the said at least one sub-layer having a lower total alkalinity. In some variants, if the total alkalinity of an intermediate sub-layer is lower than the total alkalinity of a downstream (i.e. e.g. in the vertical direction subsequent) sublayer (which is e.g. arranged in the vertical direction directly underneath the intermediate sub-layer), the total alkalinity taken up by the alkalinity storage layer is provided as a sum of the total alkalinities taken up by the intermediate sub-layer and by all sub-layers arranged upstream of (i.e. e.g. in the vertical direction above) the intermediate sub-layer. The total alkalinity taken up by the sub-layers arranged downstream of (i.e. e.g. in the vertical direction below) the intermediate sub-layer is optionally discarded. In some variants, “lower than the total alkalinity of a subsequent sub-layer arranged directly downstream of (i.e. e.g. in the vertical direction directly underneath) the intermediate sublayer” means that the pH of the subsequent sub-layer is at least 1 %, preferably at least 3%, more preferably at least 10%, higher than the pH of the intermediate sub-layer. The variants described in this paragraph may relate to determining the total alkalinity taken up by the alkalinity storage layer over the measurement time period and / or over one or more intervals within the measurement time period.

[0045] The total alkalinity taken up by the buffer layer (respectively by a sub-layer) may be determined in different ways. Since the total alkalinity taken up by the buffer layer (respectively by a sub-layer) typically corresponds to an increase in pH of the buffer (respectively of a sub-layer), pH measurements may be used to determine the total alkalinity taken up by the buffer layer (respectively by a sub-layer). Thus, in some variants, the step of determining the total alkalinity taken up by the buffer layer over the measurement time period includes measuring the change in pH of the buffer layer over the measurement time period. In some variants, the total alkalinity taken up by the buffer layer (respectively by a sub-layer) is determined by measuring a difference in pH of the buffer layer (respectively a sub-layer) between two points in time, for example an end point marking the end of the measurement time period and a start point marking the beginning of the measurement time period. It is also possible to determine the pH difference for a plurality of intervals within the measurement time period. In this case, for example, the pH differences may e.g. be summed up to provide an overall change in pH. Optionally, intervals showing a negative pH difference (i.e. intervals with net acidification) may be discarded and not be included in the sum, which allows for a more accurate determination of the total alkalinity taken up during the measurement time period. Based on a pH difference for the measurement time period, for example, a total amount of base or base equivalents taken up may be calculated, e.g. by considering a total volume of the buffer.

[0046] In some variants, the total alkalinity taken up by the buffer layer (respectively by a sublayer) may be determined by titration, for example, by titrating at least a portion of the buffer layer (respectively a sub-layer) to a target pH. In some variants, the step of determining the total alkalinity taken up by the buffer layer over the measurement time period includes titrating at least a portion of the buffer layer at the end of the measurement time period to a target pH. Typically, a difference between the target pH and the initial pH is at least 0.4, preferably at least 1 , more preferably at least 2. Additionally or alternatively, the target pH may be from 6.5 to 9.5, preferably from 7 to 9.

[0047] As an illustrative example, the total alkalinity taken up by the buffer layer over the measurement time period may for example be determined as follows:

[0048] - at least a portion of the buffer layer may at the beginning of the measurement time period (i.e. in an initial state, i.e. before taking up the total alkalinity) be titrated to a target pH to provide a first measurement;

[0049] - at least a portion of the buffer layer may at the end of the measurement time period (i.e. after taking up the total alkalinity) be titrated to a target pH to provide a second measurement; a difference between the first measurement and the second measurement may provide the total alkalinity taken up by the buffer layer over the measurement time period.

[0050] Determining the total alkalinity taken up by the buffer layer typically involves detection of a signal and different signal detections may be envisioned. For example, signal detection can be enabled through the on-demand addition of pH-responsive indicator dyes. Additionally or alternatively, signal detection can occur spectroscopically, e.g., through the measurement of absorption in the visible, IR, or through Raman signals, either of the species of interest directly or through added dye molecules. Additionally or alternatively, signal detection can occur electrochemically, through the measurement of electrode potential differences between the sample solution and a reference. ISFET-based detectors may for example be used.

[0051] As outlined herein, determining the total alkalinity taken up by the buffer may involve titration. The titration may for example occur through acids provided from pre-loaded compartments within the device. Additionally or alternatively, the titration may occur through anodic pulses generating H+ in situ, without the need for additional chemicals. Additionally or alternatively, the titration and detection may happen in a thin layer sandwiched between a proton pump and a detector. Additionally or alternatively, plasmonic surfaces may be used for signal amplification, e.g. through surface-enhanced Raman spectroscopy (SERS).

[0052] The total alkalinity taken up by the buffer layer may also be determined by measuring the total alkalinity taken up by a sub-segment of the buffer layer and subsequently projecting over the entire buffer layer. For example, the step of determining the total alkalinity taken up by the sub-segment of the buffer layer may comprise measuring the pH of a plurality of buffer sub-segments arranged adjacent to each other in a horizontal direction orthogonal to the vertical direction, and subsequently providing an average change in pH for all buffer sub-segments.

[0053] Depending on the application, different alkalinity storage layers (e.g. buffer layers) may be used. When using a buffer layer, the buffer layer typically comprises a buffer having a plurality of acidic buffer groups and basic buffer groups. The acidic buffer groups and the basic buffer groups are in an equilibrium with each other and the position of the equilibrium determines the pH of the buffer. Thus, at an initial pH, the buffer has an initial acidic buffer group concentration and an initial basic buffer group concentration and, with regards to the total molar amounts, an initial molar amount of acidic buffer groups and an initial molar amount of basic buffer groups.

[0054] In some variants, the alkalinity storage layer comprises or consists of a buffer layer. The buffer layer may e.g. have an initial pH ranging from 2 to 6, e.g. from 4 to 6. In some variants, the initial pH ranges from 4 to 5, preferably from 4.5 to 4.7. In some variants, the buffer layer comprises a plurality of carboxylic acid groups and a plurality of carboxylate groups.

[0055] In some variants, the alkalinity storage layer (e.g. the buffer layer) comprises an immobilized buffer. In some variants, the alkalinity storage layer (e.g. the buffer layer) comprises beads having on a bead surface a plurality of carboxylic acid groups and a plurality of carboxylate salt groups. The alkalinity storage layer may for example comprise a DuPont AmberLite MAC-3 H resin or a DuPont AmberLite IRC83 H resin, preferably a DuPont AmberLite IRC83 H resin.

[0056] Depending on the application, the buffer layer may have different buffer capacities. The buffer capacity may for example be chosen such that it is at least 10%, preferably at least 100%, more preferably at least 500%, higher than a target total alkalinity to be taken up by the buffer layer over the measurement time period. In some variants, the buffer capacity may for example be at least 2 mol / m2, preferably from 4.4 mol / m2to 568 mol / m2, more preferably from 10 mol / m2to 100 mol / m2, even more preferably 44 mol / m2. The buffer capacity describes the amount of moles of alkalinity that may be taken up by the buffer per surface area (in mm2) sampled by the buffer layer. The surface area sampled by the buffer layer is typically the surface area of the soil surface from which soil infiltrate infiltrates into the device, which is typically the surface area of the soil surface underneath which in the vertical direction the device is arranged. In some variants, the surface area sampled by the buffer layer corresponds to the surface area of the upstream wall of the device.

[0057] Depending on the application, different measurement time periods may be chosen. For example, the measurement time period may be at least 3 months, preferably from 5 to 60 months, more preferably from 6 to 24 months. The measurement position may be chosen in accordance with the application. Typically, the measurement position is chosen such that the upstream wall of the device is arranged at least 10 mm underneath the soil surface. In some variants, the upstream wall of the device is in the measurement position arranged from 30 mm to 3’000 mm, preferably from 50 mm to 1 ’000 mm, underneath the soil surface.

[0058] The device used in the method disclosed herein may in some variants be labelled as buffer device. The device includes an upstream wall and a buffer layer arranged in the vertical direction underneath the upstream wall. In other words, the buffer layer may be described to be arranged downstream of the upstream wall. In some variants, the device further includes a bottom wall arranged opposite the upstream wall, typically opposite with respect to the vertical direction. The buffer is typically arranged between the upstream wall and the bottom wall. The upstream wall is permeable for water and, if realized, the bottom wall is typically also permeable for water. In some variants, the upstream wall and / or the bottom wall each comprise a membrane. The upstream wall and / or the bottom wall may each be impermeable to roots and / or insects. Additionally, the upstream wall and / or the bottom wall may each be impermeable to soil. In some variants, the upstream wall and / or the bottom wall have through-holes smaller than 100 mm2, preferably smaller than 10 mm2, more preferably smaller than 1 mm2.

[0059] In some variants, the device further comprises a first interspacing layer arranged in the vertical direction between the upstream wall and the alkalinity storage layer. For example, the first interspacing layer may be directly adjacent in the vertical direction to the alkalinity storage layer, e.g. contacting the alkalinity storage layer. The first interspacing layer may for example comprise sand, e.g. quartz sand. The first interspacing layer may for example have a thickness in the vertical direction of at least 2 mm, preferably at least 5 mm. In some variants, the first interspacing layer has a higher hydraulic conductivity (e.g. water permeability) than the alkalinity storage layer.

[0060] In some variants, the device further comprises a second interspacing layer (e.g. a lower interspacing layer) arranged in downstream of the alkalinity storage layer. For example, the second interspacing layer may be arranged in the vertical direction underneath the alkalinity storage layer, e.g. in the vertical direction between the bottom wall and the alkalinity storage layer. In some variants, the second interspacing layer may be directly adjacent to the vertical direction to the alkalinity storage layer, e.g. contacting the alkalinity storage layer. The second interspacing layer may for example comprise sand, e.g. quartz sand. The second interspacing layer may for example have a thickness in the vertical direction of at least 2 mm, preferably at least 5 mm. In some variants, the second interspacing layer has a higher hydraulic conductivity (e.g. water permeability) than the alkalinity storage layer, such that backflow of soil infiltrate from the second interspacing layer to the alkalinity storage layer is minimized.

[0061] In some variants, the first interspacing layer may be an upstream interspacing layer, e.g. an upper interspacing layer. Alternatively or in combination, the second interspacing layer may be a downstream interspacing layer, e.g. a lower interspacing layer. Notably, the device may comprise a second interspacing layer independently of whether or not it also comprises a first interspacing layer.

[0062] The device typically further comprises a circumferential side wall essentially impermeable for liquids and extending in the vertical direction from the upstream wall to the bottom wall. The circumferential side wall is arranged circumferentially around the alkalinity storage layer and, if realized, the first interspacing layer and the second interspacing layer. Depending on the application, the circumferential side wall may be coated with an insect repellent and / or a root repellent. The circumferential side wall is typically essentially impermeable to liquids.

[0063] In some variants, the side wall extends in the vertical direction beyond the upstream wall. For example, the side wall may extend into the soil column arranged in the vertical direction above the upstream wall. This may enable guiding the soil infiltrate and may contribute to an even and representative flow of soil infiltrate into the device.

[0064] In some embodiments, the device can comprise a cylindrical tube filled with a buffer layer. The buffer layer may for example contain a resin acting as a buffer to solutions in contact with it. The buffer resin may for example contain chemical be buffered to a pH of interest, e.g. 4.5. As an example, the buffer layer may comprise carboxylic acid groups and sodium carboxylate salts grafted onto polymer (e.g., acrylic, divinyl benzene, or styrene) beads, e.g. with an effective pH of 4.5. The upstream (e.g. upper) and / or downstream (e.g. lower) interspacing layer, which could be composed of quartz sand, may be used to separate the buffer medium from the surrounding soil enough to prevent diffusion back into the device. The membrane is typically permeable to any infiltrate coming from the topsoil while ensuring the mechanical integrity of the device. Additional functions of the membrane could be to prevent the intrusion of animals and plant roots.

[0065] The device may be designed such that it allows soil infiltrate flow through interior layers in accordance with the surrounding soil. In some variants, a passive device is used (i.e. e.g. no flow management), in other variants, active flow management is used. For example, in some variants, the water pressure acting on the water column above the device can be controlled to ensure representative soil infiltrate flow through the device.

[0066] In some variants, the device comprises a flux adjustment manifold, for example in the form of a suction plate. The flux adjustment manifold may be used to adjust the suction actively, increasing the accuracy of the measurement. Additionally or alternatively, a tensiometer can be used, and a pump system can adjust the vacuum within the device to reflect the surrounding water table.

[0067] Depending on the application, the device may be placed in different measurement positions and / or in different soils. In some variants, the step of positioning the device in the measurement position comprises ensuring that the hydrological properties of a soil column arranged vertically above the upstream wall match the hydrological properties of a second reference segment of the soil arranged in the horizontal direction adjacent to the soil column. For example, the step of positioning the device in the measurement position may comprise controlling one or more hydrological parameters of the soil column such that the soil column corresponds to the second reference segment with respect to one or more hydrological parameters. “Correspond to”, in this context, may for example mean that the respective hydrological parameter determined for the soil column is within 25%, preferably within 15%, more preferably within 5%, of the same hydrological parameter determined for the second reference segment. The one or more hydrological parameters may for example comprise hydraulic conductivity, water potential, water saturation, soil density and / or the soil temperature.

[0068] In some variants, the soil is plowed after positioning the device in the measurement position. The soil could be plowed before and / or during the measuring time period. In some variants, positioning the device in the measurement position comprises inserting the device into the measurement position through a lateral installation tunnel. Typically, the device is inserted into the measurement position through the lateral installation tunnel such that the soil column arranged in the measurement position above the upstream wall is essentially unchanged during placement of the device. In particular, the soil column does not need to be fully or partially removed for positioning the device in the measurement position.

[0069] The method disclosed herein may for example be used to quantify an amount of carbon dioxide captured in a total area of interest, for example by performing a measurement in a sample area of the total area of interest. Thus, more broadly, the present disclosure relates in a second aspect to a method of determining an amount of carbon dioxide taken up by a soil infiltrate in a total area of interest. This method may comprise determining an amount of carbon dioxide taken up by a soil infiltrate in a sample area according to any one of the embodiments of the method of the first aspect disclosed herein. In particular, the measurement position may be arranged in the vertical direction underneath the sample area. Typically, the sample area has a same sample surface area as a surface area of the upstream wall of the device. The total amount of carbon dioxide taken up by a soil infiltrate in the total area of interest may for example be determined based on a determined amount of carbon dioxide taken up by the soil infiltrate in the sample area. As an example, the total amount of carbon dioxide taken up in the sample area may be multiplied by a field factor to provide the total amount of carbon dioxide taken up in the total area of interest. In some variants, the field factor is a ratio between a surface area of the total area of interest and the surface area of the sample area. Depending on the application, the field factor may also represent further influences, such as an amount of minerals deposited on the soil surface, differences in surface topology, etc. In some variants, multiple sample areas are used to determine the amount of carbon dioxide taken up by the soil infiltrate in the total area of interest.

[0070] The method of the present disclosure may for example be used to determine an amount of carbon dioxide removed from the atmosphere during the measurement time period. The amount of carbon dioxide removed from the atmosphere during the measurement time period may for example be determined based on the total amount of carbon dioxide taken up by the soil infiltrate during the measurement time period. In some variants, the amount of carbon dioxide removed from the atmosphere during the measurement time period may essentially correspond to the total amount of carbon dioxide taken up by the soil infiltrate during the measurement time period. In further variants, depending on the application, the total amount of carbon dioxide taken up by the soil infiltrate during the measurement time period may be multiplied by a correction factor to provide the amount of carbon dioxide removed from the atmosphere during the measurement time period. Depending on the application, the correction factor may for example take into account a ratio between carbon dioxide taken up in solid form and an amount of carbon dioxide taken up by the soil infiltrate. For example, solid precipitates containing carbon dioxidebased salts may be formed, which may in some applications only partially be solubilized and enter into the soil as part of the soil infiltrate.

[0071] The disclosure relates in a third aspect to a device, in particular a device for determining an amount of carbon dioxide taken up by a soil infiltrate, typically over a measurement time period. In some embodiments, the device may be used for determining a total alkalinity taken up by a soil infiltrate over a measurement time period.

[0072] Different embodiments of the device have been disclosed in the context of the method according to any one of the embodiments of the first aspect of the disclosure. These embodiments also apply to the third aspect of the disclosure, i.e. they also constitute possible embodiments of the device. For example, the device may comprise a first wall (which may e.g. be a upstream wall), a second wall (which may e.g. be a bottom wall) opposite the first wall and a buffer layer arranged in a first direction (which may e.g. be a vertical direction) between the first wall and the second wall. The device may further comprise a first interspacing layer (which may e.g. be an upstream interspacing layer, e.g. an upper interspacing layer) arranged in the first direction between the first wall and the buffer layer. Additionally or alternatively, the device may further comprise a second interspacing layer (which may e.g. be a downstream interspacing layer, e.g. a lower interspacing layer) arranged in the first direction between the second wall and the buffer layer. In the present disclosure, when reference is made to a “device”, this device is typically the device for determining an amount of carbon dioxide taken up by a soil infiltrate, unless specifically indicated otherwise or unless the context clearly dictates otherwise.

[0073] In some variants, the device comprises a housing comprising a water-permeable upstream wall and a water-permeable downstream wall both defining an infiltration flow path. The water-permeable upstream wall and a water-permeable downstream are typically arranged opposite each other. The infiltration flow path may e.g. extend parallel to a vertical direction. It is understood that the microscopic infiltration flow path may be winding. However, on a macroscopic scale, the infiltration flow path may be essentially linear and may, in some variants, be essentially parallel to a vertical direction. In some variants, the water-permeable upstream wall may be labelled as water-permeable entry wall of the housing, and the water-permeable downstream wall may be labelled as water- permeable exit wall of the housing. Typically, the flow path extends through the housing.

[0074] In some variants, the device further comprises an alkalinity storage layer being arranged along the infiltration flow path between the upstream wall and the downstream wall. The alkalinity storage layer is formed by a material bearing on its surface a plurality of acidic groups, such that when a soil infiltrate comprising aqueous bicarbonate ions and / or aqueous carbonate ions infiltrates through the alkalinity storage layer, at least some of the acidic groups are deprotonated.

[0075] Typically, the alkalinity storage layer is configured such that soil infiltrate may infiltrate and / or trickle through the alkalinity storage layer. Typically, the soil infiltrate is able to pass through the alkalinity storage layer, but is still retained long enough to allow that at least some of the acidic groups are deprotonated upon contact with the soil infiltrate comprising aqueous bicarbonate ions and / or aqueous carbonate ions. For example, in some variants, the alkalinity storage layer has a hydraulic conductivity similar to sand (e.g. coarse sand, fine sand or silty sand), soil, loam, clay loam or clay. In some variants, the alkalinity storage layer has a hydraulic conductivity that is at least 10%, preferably at least 50%, more preferably at least 70%, higher than a hydraulic conductivity of sand (e.g. coarse sand, fine sand or silty sand), soil, loam, clay loam or clay. In some variants, the soil (e.g. the soil in which the device is positioned in the method according to the present disclosure) has a hydraulic conductivity (Ks) from 1 to 1500 cm / day, preferably from 5 to 500 cm / day, more preferably from 10 to 100 cm / day, as determined e.g. according to ASTM D2434-22. Alternatively or in combination, in some variants, the alkalinity storage layer has a hydraulic conductivity (Ks) from 1 to 4000 cm / day, preferably from 100 to 2000 cm / day, more preferably from 1000 to 1500 cm / day, as determined e.g. according to ASTM D2434-22. Typically, the hydraulic conductivity is determined under standard conditions, including at room temperature.

[0076] The device described herein may be used for several applications. For example, the device may be configured for quantifying the amount of carbon dioxide taken up by a soil infiltrate over the measurement time period. For example, the amount of carbon dioxide taken up in an enhanced weathering process may be quantified. In some variants, the device is an underground device, i.e. the device is configured to be installed and maintained underground at least during the measurement time period, preferably permanently.

[0077] In some variants, the device comprises a second sensor interconnected with the alkalinity storage layer and configured to measure a protonation state of the acidic groups over at least a portion of the measurement time period. Depending on the application, the protonation state of the acidic groups may be measured directly or indirectly. For example, a pH meter may be used to measure the protonation state, or other, more indirect sensors are used to measure the protonation state of the acidic groups. Depending on the application, the protonation state of the acidic groups over at least a portion of the measurement time period may be measured in different ways. For example, a degree or extent of deprotonation may be measured across the entire measurement time period or across the entire portion, or a deprotonation profile may be measured over time.

[0078] In some variants, the material forming the alkalinity storage layer is a material that changes its volumetric expansion upon infiltration of a soil infiltrate comprising aqueous bicarbonate ions and / or aqueous carbonate ions through the alkalinity storage layer. For example, in some variants, the material forming the alkalinity storage layer is a swellable and / or shrinkable material, in particular a material that is swellable and / or shrinkable upon infiltration of a soil infiltrate comprising aqueous bicarbonate ions and / or aqueous carbonate ions through the alkalinity storage layer. More preferably, in some variants, the material forming the alkalinity storage layer is swellable and / or shrinkable upon deprotonation of at least some of the acidic groups.

[0079] It is understood that as used herein, the term “material forming the alkalinity storage layer” typically refers to a main material forming the alkalinity storage layer, i.e. the material that mainly determined the physical characteristics of the alkalinity storage layer and / or that makes up the majority by weight (e.g. more than 50 wt.-%, preferably more than 75 wt.-%, more preferably more than 90 wt.-%, even more preferably more than 95 wt.-%, even more preferably essentially 100 wt.-%) of the alkalinity storage layer. For example, the alkalinity storage layer may in some variants exclusively consist of the material forming the alkalinity storage layer. In other variants, the alkalinity storage layer may further comprise one or more other materials, which preferably make up less than 25 wt.-%, more preferably less than 20 wt.-%, more preferably less than 5 wt.-%, of the alkalinity storage layer.

[0080] In some variants, the alkalinity storage layer contacts a first side of a detection wall, such that a change in the volumetric expansion of the material forming the alkalinity storage layer leads to a strain on the detection wall and / or to a physical deformation of the detection wall. These variants allow determining the amount of carbon dioxide with high precision. Depending on the application, different detection walls may be used. For example, the detection wall may in some variants be a detection membrane and / or a detection sheet and / or a detection membrane and / or a detection plate. Typically, the detection wall is essentially water impermeable.

[0081] Typically, the alkalinity storage layer contacts the first side of the detection wall with a side surface of the alkalinity storage layer. In some variants, the detection wall extends at an angle from -30° to +30°, preferably -15° to +15°, with respect to the direction of flow of the infiltration flow path. In some variants, the detection wall extends essentially parallel to the direction of flow of the infiltration flow path. The variants described in this paragraph may refer in particular to the macroscopic direction of flow.

[0082] In some variants, the detection wall circumferentially encompasses the alkalinity storage layer fully or partially. For example, in some variants, the detection wall circumferentially encompasses the alkalinity storage layer fully. In further variants, at least a circumferen- tial segment of the alkalinity storage layer is contacted by the detection wall. For example, in some variants, the device comprises a circumferential boundary wall circumferentially encompassing the alkalinity storage layer. The circumferential boundary wall may include a detection portion forming the detection wall and a non-detection portion. The non-detection portion typically has a higher binding stiffness than the detection portion forming the detection wall. Upon swelling and / or shrinking (or other changes in the volumetric expansion) of the alkalinity storage layer, the detection portion forming the detection wall may be physically deformed or strained, while the non-detection portion is essentially unaffected. In some variants, the circumferential boundary wall has an oval, preferably a circular, cross-section. For example, the detection portion forming the detection wall may have a cross-section forming a circular segment.

[0083] The detection wall may optionally be connected to a support frame. For example, an upper edge and / or a lower edge of the detection wall may be connected to a support frame, e.g. to control the physical deformation of the detection wall.

[0084] Depending on the application, different alkalinity storage layers may be used. In some variants, the detection wall is elastically deformable. Thus, a change in the volumetric expansion of the material forming the alkalinity storage layer may lead to a physical deformation of the detection wall. In some variants, the detection wall is elastically deformable by elastic outward bulging of the detection wall on a second side of the detection wall opposite the first side of the detection wall. In some variants, the detection wall is an elastomeric membrane. In some variants, the detection wall has a lower bending stiffness than a side wall of the housing.

[0085] In some variants, the device comprises a first sensor for measuring a change in volumetric expansion of the material forming the alkalinity storage layer over at least a portion of the measurement time period. The first sensor may for example comprise a sensor for measuring a strain on the detection wall and / or a physical deformation of the detection wall. The first sensor could for example be an optical sensor for measuring a physical deformation (e g. outward bulging) of the detection wall. Depending on the application, the device may include multiple first sensor. For example, the device may include two different optical sensors, e.g. measuring the physical deformation from different angles, for example to increase accuracy. It is also possible for the device to include two different types of first sensors, e.g. mechanical and optical sensors.

[0086] In some variants, the first sensor comprises a strain gauge interconnected to the detection wall. Alternatively or in combination, the first sensor may comprise a piezo sensor interconnected to the detection wall.

[0087] In some variants, the alkalinity storage layer comprises a plurality of sub-layers arranged along the infiltration flow path behind each other. Thereby, the sub-layers are typically arranged such that when the soil infiltrate infiltrates through the alkalinity storage layer, the soil infiltrate successively infiltrates through the different sub-layers. For example, the sub-layers may be arranged in vertical direction underneath each other. Depending on the application, the different sub-layers are either made of the same material or of different materials.

[0088] In some variants, the device comprises a plurality of first sensors, wherein each sublayer is interconnected with a respective first sensor, for measuring a change in volumetric expansion of the material forming the respective sub-layer over at least a portion of the measurement time period. These variants may advantageously be used to increase accuracy of the measurement result. Furthermore, additional information about the infiltration profile and infiltration depth over time may be reached.

[0089] Depending on the application, different alkalinity storage layers may be used. For example, in some variants, the plurality of acidic groups have a pKa of less than 6.35, preferably from 2 to 6, more preferably from 3 to 6. In some variants, the plurality of acidic groups have a pKa of higher than 2. As used herein, pKa values generally refer to hydrous conditions, unless expressly stated otherwise or unless the context clearly dictates otherwise. In some variants, the plurality of acidic groups are carboxylic acid groups and / or sulfonic acid groups, preferably carboxylic acid groups.

[0090] In some variants, the housing further comprises an essentially water-impermeable side wall circumferentially surrounding the alkalinity storage layer. In some variants, the side wall circumferentially surrounds the alkalinity storage layer along an entire height of the alkalinity storage layer. The height of the storage layer typically refers to a maximum extension of the alkalinity storage layer in vertical direction. In some variants, the water- impermeable side wall extends from the upstream wall to the downstream wall. Depending on the application, the side wall may contact the alkalinity storage layer fully or partially, or not at all.

[0091] In some variants, the side wall has an oval, preferably a circular cross section. The side wall may for example have a hollow cylindrical shape. In some variants, the side wall has a compressive strength of at least 0.1 MPa, preferably from 0.2 to 20 MPa, more preferably from 0.5 to 10 MPa, more preferably from 1 to 5 MPa, as determined e.g. according to ISO 604, version of 2002.

[0092] In some variants, the alkalinity storage layer comprises a buffer. For example, in some variants, the alkalinity storage layer is a buffer layer having an initial pH from 3 to 7. The buffer layer may for example be arranged in a vertical direction underneath the upstream wall, e.g. the top wall. The buffer layer may for example be configured to change its pH over the measurement time period upon infiltration of a soil infiltrate comprising aqueous bicarbonate ions and / or aqueous carbonate ions through the buffer layer.

[0093] In some variants, the initial pH of the buffer ranges from 4 to 5, preferably from 4.5 to 4.7. Alternatively or in combination, the buffer layer may comprise beads having on a bead surface a plurality of carboxylic acid groups and a plurality of carboxylate salt groups. In some variants, the buffer layer has a buffer capacity of at least 2 mol / m2, preferably from 4.4 mol / m2to 568 mol / m2, more preferably from 10 mol / m2to 100 mol / m2, even more preferably 44 mol / m2.

[0094] In some variants, the device further comprises a pH detector configured for measuring a pH and / or a change in pH of the alkalinity storage layer over at least a portion of the measurement time period.

[0095] In some variants, the alkalinity storage layer comprises a resin, preferably an ion-ex- change resin, wherein the resin is swellable and / or shrinkable upon contact with aqueous bicarbonate ions and / or aqueous carbonate ions. In some variants, the resin comprises a plurality of microbeads (e.g. radius of less than 10 mm, such as less than 2 mm). The resin may for example comprise a plurality of pores, which are typically randomly arranged. The pores may e.g. allow the infiltrate to infiltrate through the alkalinity storage layers. The pores may e.g. have a slit width of less than 1 ’000 nm, preferably less than 500 nm, more preferably less than 100 nm. In some variants, the pores have a slit width from 0.01 nm to 100 nm, such as from 0.5 nm to 70 nm.

[0096] Depending on the application, the housing may have different sizes, geometric properties and shapes. In some variants, the upstream wall and / or the downstream wall have through-holes having a cross section smaller than 100 mm2, preferably smaller than 10 mm2, more preferably smaller than 1 mm2. It is understood that in at least some embodiments, all of the through-holes in the upstream wall and / or in the downstream wall each have a cross section smaller than 100 mm2, preferably smaller than 10 mm2, more preferably smaller than 1 mm2.

[0097] In some variants, the device further comprises a first infiltration flow guide structure arranged on an upstream side of the upstream wall and configured for guiding an infiltrate flow towards the upstream wall. The first infiltration flow guide structure may e.g. be arranged on an upstream side of the upstream wall and may optionally face away from the alkalinity storage layer. Thus, the first infiltration flow guide structure may e.g. in some variants be used to feed and / or channel a representative infiltration flow to the upstream wall of the device. In some variants, the first infiltration flow guide structure comprises a water-impermeable wall extending essentially parallel to the side wall of the housing. The first infiltration flow guide structure may e.g. extend essentially parallel to the vertical direction. For example, the first infiltration flow guide structure may extend from the upstream wall in a vertical direction away from the alkalinity storage layer.

[0098] In some variants, the first infiltration flow guide structure extends away from the upstream wall. The first infiltration flow guide structure may in some variants circumferentially encompasses the upstream wall.

[0099] In some variants, the infiltration flow guide structure has essentially the same cross-sectional profile as the side wall of the housing. In some variants, a cross-sectional area of the infiltration flow guide structure is essentially identical to a cross-sectional area of the upstream wall. These variants may e.g. be advantageous to ensure that the infiltration flow to which the device is exposed is representative and essentially corresponds to the cross-section of a soil portion that is being examined by the device. In other words, the infiltration flow guide structure may be used to minimize or even prevent undesired lateral flow of the infiltrate upstream of the upstream end. Such lateral flows may lead to distorted measurements, e.g. causing an infiltration flow reaching the device that is either too small or too large than would be appropriate for the given soil cross-section.

[0100] In some variants, the device further comprises a second infiltration flow guide structure, which may e.g. be configured for guiding an infiltrate flow towards and / or away from the alkalinity storage layer. For example, the second infiltration flow guide structure may e.g. be arranged adjacent to and / or near the upstream wall. For example, the second infiltration flow guide structure may be configured for controlling a ratio between the infiltrate flow entering through the upstream wall and the infiltrate flow infiltrating through the alkalinity storage layer. The second infiltration flow guide structure may e.g. extend at an angle from 1 ° to 90°, preferably from 5° to 75°, more preferably from 5° to 45°, with respect to a horizontal direction. In some variants, the second infiltration flow guide structure may comprise a ramp or another feed structure arranged along the infiltration flow path between the upstream wall and the alkalinity storage layer. For example, an inclination angle of the ramp may be used to feed the infiltration flow to the alkalinity storage layer, e.g. in instances where the alkalinity storage layer may have a smaller and / or different cross-section than the upstream wall. In some variants, the inclination angle of the ramp may also be set such that at least a portion of the infiltration flow is guided away from the alkalinity storage layer, e.g. to a bypass channel bypassing the alkalinity storage layer. This may e.g. be used to prevent overfilling of the alkalinity storage layer. In some variants, the second infiltration flow guide structure is arranged in the vertical direction above and / or below a dry compartment of the device. In some variants, the second infiltration flow guide structure is arranged between the upstream wall and the dry compartment. The dry compartment may e.g. be configured for housing one or more of the following: the second sensor, the first sensor, the first communication unit, sensor processing unit or power supply. The dry compartment may be configured such that the soil infiltrate does not enter (e.g. infiltrate) into the dry compartment. The dry compartment may e.g. be arranged adjacent (such as adjacent in a horizontal direction) to a wet compartment housing at least the alkalinity storage layer. In some variants, the detection wall is arranged between the dry compartment and the wet compartment. In some variants, the dry compartment comprises a maintenance door. More broadly, in some variants, the device comprises a bypass channel bypassing at least a portion of the alkalinity storage layer. In some variants, the bypass channel bypasses the alkalinity storage layer fully. The bypass channel may e.g. extend parallel to the alkalinity storage layer with respect to the direction of the infiltration flow path. For example the bypass channel may extend from an upstream side of the alkalinity storage layer to a downstream side of the alkalinity storage layer.

[0101] In some variants, the device comprises a downstream interspacing layer (e.g. lower interspacing layer) arranged along the flow path downstream of the buffer layer and having a higher hydraulic conductivity than the alkalinity storage layer, such that backflow of soil infiltrate from the downstream interspacing layer to the alkalinity storage layer is minimized.

[0102] In some variants, the device further comprises a wick drain layer arranged in the infiltration flow path downstream of the alkalinity storage layer. The wick drain layer may for example be configured for consolidating the soil infiltrate.

[0103] In some variants, the device further comprises a root inhibition layer, which may e.g. comprise trifluralin. In some variants, the device further comprises a first barrier layer, which may e.g. be configured to prevent insects from passing and / or configured to prevent silting up. The first barrier layer may for example consist of a power and / or fine particles, preferably having a particle size of no more than 3 mm, preferably no more than 1 mm, more preferably no more than 0.1 mm. In some variants, the first barrier layer comprises or consists of diatomaceous earth. Preferably, the root inhibition layer and / or the first barrier layer are arranged upstream of the alkalinity storage layer.

[0104] In some variants, the device further comprises a first fiberglass filter layer and optionally also a second fiberglass filter layer. Preferably, the first fiberglass filter layer is arranged upstream of the alkalinity storage layer. Alternatively or in combination, the first fiberglass filter layer may be arranged upstream of the root inhibition layer.

[0105] In some variants, the device further comprises a maintenance door for allowing access to the device, preferably to the alkalinity storage layer. The maintenance door may e.g. be arranged in the side wall of the housing. The maintenance door may e.g. be realized as a maintenance hatch. In some variants, the device may further comprise a flow control unit configured for controlling an inside flow rate of the soil infiltrate infiltrating through the device such that the inside flow rate has a known or determinable flow rate ratio with respect to an outside flow rate of the soil infiltrate infiltrating through a first reference segment of the soil arranged outside the device. For example, in some variants, the flow control unit is configured for controlling the inside flow rate of the soil infiltrate infiltrating through the device such that the inside flow rate essentially maintains a predetermined flow rate ratio with respect to the outside flow rate of the soil infiltrate infiltrating through a first reference segment of the soil arranged outside the device. The predetermined flow rate ratio may e.g. lie within a ratio from 1 :5 to 5:1 , preferably from 1 :2.5 to 2.5:1 . In some variants, the device may comprise a flow control unit configured for controlling an inside flow rate of the soil infiltrate infiltrating through the device such that the inside flow rate essentially corresponds to an outside flow rate of the soil infiltrate infiltrating through a first reference segment of the soil arranged outside the device. Further embodiments of this variant are disclosed hereinbefore. For example, the flow control unit may comprise a pump for controlling a vacuum pressure inside the device. Additionally or alternatively, the flow control unit may comprise a tensiometer.

[0106] The disclosure relates in a fourth aspect to a system for determining an amount of carbon dioxide taken up by a soil infiltrate. The system comprises any of the embodiments of the device described herein, i.e. of the device for determining an amount of carbon dioxide taken up by a soil infiltrate. When used in the system, a variant of the device is used in which the device further comprises a first communication unit configured for sending underground measurement data measured over at least a portion of the measurement time period. Typically, the device is also configured to be installed underground in a soil.

[0107] The system further comprises a second communication unit configured for receiving the underground measurement data. The second communication unit is typically configured to be installed aboveground. The second communication unit may optionally be configured for transmitting the received underground measurement data, e.g. to a further unit such as a processing unit. In some variants, the second communication unit is a transceiver unit. The second communication unit may e.g. be installed locally to transmit the underground measurement data to a remotely located processing unit, e.g. a server. The system further comprises a processing unit configured for determining a total alkalinity taken up by the alkalinity storage layer over the measurement time period based on the underground measurement data. Typically, the processing unit is configured to be installed aboveground.

[0108] The system may e.g. be used to permanently install the device underground, without the need to unearth or excavate the device to determine the amount of carbon dioxide taken up by the soil infiltrate. This is particularly advantageous because it is less labor-intensive and because unearthing or excavating may jeopardize the soil and may jeopardize the accuracy of the measurements.

[0109] The system described herein may e.g. be a carbon capture quantification system, for example for quantifying the amount of carbon dioxide captured in an enhanced weathering process.

[0110] The disclosure relates in a fifth aspect to a use of the device or the system for determining an amount of carbon dioxide taken up by a soil infiltrate, preferably in an enhanced weathering process. More specifically, any of the embodiments of the device described herein, i.e. of the device for determining an amount of carbon dioxide taken up by a soil infiltrate, may be used. Similarly, any of the embodiments of the system described herein, i.e. of the system for system for determining an amount of carbon dioxide taken up by a soil infiltrate, may be used.

[0111] It is to be understood that both the foregoing general description and the following detailed description present embodiments, and are intended to provide an overview or framework for understanding the nature and character of the disclosure. The accompanying drawings are included to provide a further understanding, and are incorporated into and constitute a part of this specification. The drawings illustrate various embodiments, and together with the description serve to explain the principles and operation of the concepts disclosed.

[0112] In the present disclosure, for reasons of clarity and conciseness, directional references are at least in part provided in terms of vertical and horizontal directions. These typically refer to the direction of the compass, i.e. horizontal typically means parallel to a flat section of the surface of the earth and vertical typically means towards the sky. In vertical direction, typically, indications such as "up", “upper” or “top” refer to the vertical direction towards the sky and indications such as “down", “lower” or “bottom” refer to the vertical direction towards the core of the earth. Relative indications (i.e. indications designating a relative arrangement in the vertical direction) may optionally be specified with respect to a hypothetical flow of soil filtrate, which hypothetically may flow in the vertical direction towards the core of the earth. Relative indications such as “upper” or “in the vertical direction above” may optionally be replaced by the indication “upstream”, and relative indications such as “lower”, “in the vertical direction below”, “in the vertical direction beneath” or “in the vertical direction underneath” may optionally be replaced by the indication “downstream”. It is understood that the terms “upstream” and “downstream” refer to the infiltration flow path, unless expressly stated otherwise or unless the context clearly dictates otherwise. In particular, they typically refer to the macroscopic flow path of the soil infiltrate.

[0113] BRIEF DESCRIPTION OF THE DRAWINGS

[0114] The invention described herein will be more fully understood from the detailed description given herein below and the accompanying drawings which should not be considered limiting to the invention described in the appended claims. The drawings show:

[0115] Fig. 1 shows an embodiment of a method of determining an amount of carbon dioxide taken up by a soil infiltrate;

[0116] Fig. 2 shows a flow diagram to the embodiment shown in fig. 1 ;

[0117] Fig. 3 illustrated a change in pH of the alkalinity storage layer in the presence of soil infiltrate having a higher pH than the alkalinity storage layer (arrow B), respectively having a lower pH than the alkalinity storage layer (arrow A);

[0118] Fig. 4 shows simulated data of pH differences between soil infiltrate flow compared to alkalinity storage layer (e.g. buffer resin) (Fig. 4A) and integrated signal over time (Fig. 4B);

[0119] Fig. 5 shows an embodiment of the device with active flow control; Fig. 6 shows an embodiment of the device comprising a sensor for measuring a change in volumetric expansion of the material forming the alkalinity storage layer;

[0120] Fig. 7 shows a variant of the device illustrated in figure 6, which further comprises a plurality of sub-layers of the alkalinity storage layer;

[0121] Fig. 8 illustrates a swelling of the alkalinity storage layer as a result of infiltration of the soil infiltrate through the alkalinity storage layer;

[0122] Fig. 9 illustrates an embodiment of the device comprising a dry compartment arranged outside the side wall of the housing;

[0123] Fig. 10 illustrates an embodiment of the system for determining an amount of carbon dioxide taken up by a soil infiltrate.

[0124] DESCRIPTION OF THE EMBODIMENTS

[0125] Reference will now be made in detail to certain embodiments, examples of which are illustrated in the accompanying drawings, in which some, but not all features are shown. Indeed, embodiments disclosed herein may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Whenever possible, like reference numbers will be used to refer to like components or parts.

[0126] Figures 1 and 2 show an embodiment of the method disclosed herein. Specifically, in a first step (S1 , cf. Fig. 1 A), a device 3 is placed within the project area, right underneath a soil surface 21 , typically 30 cm underneath the soil surface 21 . The device 3 is oriented with a permeable upstream wall 5 and an opposite permeable downstream wall 8 (which may e.g. be a bottom wall) parallel to the ground to ensure an adequate and representative flow profile. The surrounding medium that may have been altered in the process of device installation is backfilled in such a way that it mimics the hydrological properties of the surrounding soil 2 (e.g., by embedding the device 3 in sand / silt). Further, the device 3 comprises a buffer layer 6 sandwiched between an upper interspacing layer 12 and a lower interspacing layer 1 1 .

[0127] Furthermore, minerals 4 are provided on or near the soil surface 21 . The minerals 4 can already be present before installation of the device 3, or the minerals are provided separately. It is also possible to increase an amount of pre-existing minerals 4. The minerals 4 may consequently be provided before, simultaneously with or subsequently to device installation.

[0128] In a second step (S2, cf. Fig. 2A), over the course of a project, soil infiltrate 1 is transported through the device 3. During this time, the pH of the soil infiltrate 1 is buffered to the target pH (4.5) by the active components on the bead surface of the buffer layer 6. As illustrated in Figure 3, in the process, the relative ratio of acidic (AH) and basic (A-) sites on the bead surface of the buffer layer 6 changes in accordance with exchanged species. Fig. 3 illustrates in the middle the buffer layer 6 before the project start. For most agricultural fields, soil infiltrate 1 has a pH > 4.5, leading to gradual deprotonation of acidic surface groups, as illustrated by process (B) in Fig. 3. By contrast, in theory, if the pH of the soil infiltrate 1 is lower than the pH of the buffer layer 6, this would lead to protonation of the buffer layer 6, as illustrated by process (A) in Fig. 3.

[0129] Referring again to Figs. 1 and 2, over the course of a project, the buffer layer 6 is typically rendered increasingly basic. More specific, the alkalinity of the soil infiltrate 1 , which derives at least in part from the capturing of carbon dioxide from the air, is effectively taken up and stored by the buffer layer 6. Taking into account the direction of flow of the soil infiltrate 1 , the buffer layer 6 may have a complex pH profile across its volume. For example, a top sub-layer 6a of the buffer layer 6 may have the highest (i.e. most alkaline) pH compared to the other sub-layers 6a, 6b of the buffer layer 6. In some variants, the pH decreases from the top sub-layer 6a to a bottom sub-layer.

[0130] In a third step (S3, cf. Fig. 1 C), after the project, or at the latest 12 months after installation, the device 3 is recovered from the soil 2. The buffer layer 6 within the device is separated into several vertical slices (i.e. e.g. sub-layers 6a, 6b). A given slice is homogenized, and an aliquot is withdrawn for quantification. The aliquot is dispersed in approx, four times the amount of DI water and the pH continuously measured through a pH me- ter. An aqueous solution of NaOH is then titrated into the mixture until it reaches a reference pH (e.g., pH = 7). The consumption of NaOH is compared to a reference slice that has been prepared without being exposed to soil infiltrate 1 . The difference between the two is then the amount of TA previously captured within the aliquot. This process is repeated for slices from the top until no more additional TA is detected. Should this not occur, the device 3 has been oversaturated and only provides a lower bound on the infiltrated total alkalinity. Should the pH profile within the device, as determined through the pH of the slices, not be monotonically decreasing from top to bottom, upward flow may have carried solutes into the device 3 from below. In such a case, the device 3 may be compromised and may have to be discarded. For intact devices 3, summation over the analyzed slices may provide the total alkalinity taken up by the buffer layer over the area covered by the device 3. Projecting the total alkalinity taken up over the associated project area then gives the total alkalinity infiltrated on that project site.

[0131] Optionally, to quantify carbon capture of an enhanced weathering activity, subtracting any total alkalinity captured by the same method in an appropriate control field yields the additional total alkalinity produced through the enhanced weathering project activities. The so-determined total alkalinity value a first quantification of the carbon removal originating from the project activities. Additional corrections can be undertaken for processes such as outgassing.

[0132] It is understood that the total alkalinity taken up by the buffer layer 6 during the project may be determined in many different ways and is not limited to pH measurement. For example, electrical conductivity measurements are also possible. As an example, the aliquot may be dispersed and the electrical conductivity may be measured. Reference to a calibration curve may then provide an accurate determination of ionic concentrations. In some variants, the aliquot is dispersed and excess salt (e.g., NaCI) is added. The Na+ ions displace any other ions bound to the bead surface. After draining and repeated rinsing of the bead solids with DI water, the aliquot is redispersed and the electrical conductivity measured.

[0133] In a further variant, the aliquot may be digested, for example using hydrochloric and nitric acid, and the liberated ions are measured using ICP-MS. Additional cations captured compared to reference devices directly correspond to additional TA produced through EW.

[0134] Figure 4 shows simulated data of pH differences between soil infiltrate flow compared to buffer resin (Fig. 4A) and integrated signal over time (Fig. 4B). Effectively, the fidelity of measurements may be increased by integrating a signal (e.g. pH difference) over the project duration. Specifically, while measuring the pH differences occurring over time in an instantaneous fashion may be difficult and prone to measurement errors, accumulating the pH differences over time (e.g. by allowing the buffer layer 6 to take up the alkalinity of the infiltrate flow and to effectively store it over time) allows the pH differences to be integrated over time, which allows a more accurate determination of a total alkalinity of a soil infiltrate flow over time. In Fig. 4A, the horizontal x-axis denotes the time (in a.u.) and the vertical y-axis denotes the change in pH (ApH, in a.u.). In Fig. 4B, the horizontal x-axis denotes the time (in a.u.) and the vertical y-axis denotes the integrated alkalinity (a.u.).

[0135] In some variants, ions flowing through in the device 3 may be stored and then released in intervals in order to turn a continuous stream of low concentrations into pulses of increased concentrations. This may allow for greater measurement accuracy.

[0136] In some variants, signals caused by ions of interest may be measured through absorption, either in the visible or infrared, potentially using interferometry, plasmonic enhancement, evanescent wave, or other signal amplification.

[0137] Figure 5 shows a variant in which a pressure acting on the water column inside the soil column 9 arranged above the device is adjusted through a soil infiltrate collection component (e.g. a suction plate) arranged in topsoil, based on moisture sensor 13 (e.g. tensiometer) and a pump 14. This ensures that the soil infiltrate 1 infiltrating through the device is representative of covered surface area.

[0138] Figure 6 shows a further variant of the device 3 that also includes a second sensor 30 interconnected with the alkalinity storage layer 6. The second sensor 30 is configured to measure a protonation state of the acidic groups of the alkalinity storage layer 6 over at least a portion of the measurement time period. In the illustrated embodiment, the second sensor 30 is a pH meter. Figure 7 shows an embodiment of the device 3, wherein Fig. 7B shows a close-up of an excerpt of the device 3 shown in Fig. 7 A. The device 3 comprises a housing 15 having a hollow cylindrical shape with a circular cross section. The device 3 further comprises an upstream wall 5 and a downstream wall 8 arranged downstream of the upstream wall 5, namely in the vertical direction underneath the upstream wall 5. Between the upstream wall 5 and the downstream wall 8, an alkalinity storage layer 6 is arranged. The alkalinity storage layer 6 is circumferentially surrounded by a side wall 18 of the housing 15. Within the hollow cylindrical housing 15, a dry compartment 27 is arranged, which houses electronic components of the device 3. The dry compartment 27 is thus configured for housing electronic components in order to protect the electronic components from the infiltration water. More specifically, a detection wall 16 is arranged within the housing, which on a first side 161 contacts the alkalinity storage layer 6. On an opposite second side 162 facing the dry compartment 27, a plurality of first sensors 17a, 17b are arranged, which in the illustrated embodiment are Piezo sensors. Furthermore, the dry compartment 27 also houses a first communication unit 20 interconnected with the Piezo sensors 17a, 17b, and configured for transmitting raw sensor data from these sensors to another communication unit, e.g. a communication unit arranged outside of the device, preferably aboveground (not illustrated). The dry compartment 27 further houses a power supply 24 and a sensor processing unit 25 for processing the raw sensor data. Above the dry compartment 27, a second infiltration flow guide structure 29 feeds the incoming infiltrate to the alkalinity storage layer 27 in order to ensure that the alkalinity storage 27 captures the entire cross-section of the soil, i.e. the soil infiltrate from the entire column that, in the operative state, is encompassed by an upstream portion of the side wall 18. In the illustrated embodiment, the second infiltration flow guide structure 29 is realized as a ramplike structure.

[0139] An upstream interspacing layer 12 and a downstream interspacing layer 11 are arranged upstream and downstream of the alkalinity storage layer 6, respectively. They separate the alkalinity storage layer from the adjacent soil, thereby minimizing the risk of contamination of the alkalinity storage layer 6. Furthermore, the upstream and downstream interspacing layer 12, 1 1 each have a hydraulic conductivity that is higher than that of the alkalinity storage layer 6, which prevents backflow of the infiltrate in an upstream direction. In the illustrated embodiment, the alkalinity storage layer 6 is made of a swellable resin. More specifically, the resin includes a plurality of carboxylic acid groups and carboxylate groups on its surface, and the resin is swellable upon contact with soil infiltrate comprising aqueous bicarbonate ions and / or aqueous carbonate ions (respectively corresponding salts thereof). When a soil filtrate comprising aqueous bicarbonate ions and / or aqueous carbonate ions (more specifically respective salts thereof) infiltrates through the resin, the resin swells. The swelling of the resin may be measured using a first sensor 17, specifically by the plurality of first sensors 17a, 17b, which in the illustrated embodiment are Piezo sensors. The Piezo sensors gauge a strain on a detection wall 16, which is caused by swelling of the resin, which in turn occurs upon infiltration of the soil infiltrate comprising aqueous bicarbonate ions and / or aqueous carbonate ions (more specifically respective salts thereof) through the resin. In particular, since the bending stiffness of the detection wall 16 is significantly lower than the bending stiffness of the side wall 18 of the housing 15, the swelling of the resin leads almost exclusively to strain on the detection 16. The degree of strain can therefore be used to determine the degree of swelling. Thus, by measuring the degree of strain through the plurality of first sensors 17a, 17b, the degree of swelling is determined, which in turn is used to determine the total alkalinity of the soil infiltrate, which in turn is used to determine the amount of carbon dioxide captured.

[0140] Fig. 7B shows a close-up of a selected excerpt of the device 3. In particular the close-up shows the detection wall 16 which on its first side 161 contacts the alkalinity storage layer 6. On the second side 162 of the detection wall 16, the first sensors 17a, 17b are arranged, which are able to gauge the strain on the detection wall 16 generated as a result of swelling of the alkalinity storage layer 6.

[0141] It is understood that the swelling of the alkalinity storage layer 6 may lead to a strain on the detection wall 16, as explained above, and / or to an outward bulging of the detection wall 16. For example, when the detection wall 16 has a low bending stiffness, outward bulging may prevail, such that the swelling primarily leads to outward bulging. In some variants, the detection wall 16 experiences both a strain and an outward bulging as a result of the swelling of the alkalinity storage layer 6. Thus, it is understood that the sensors 17a, 17b may be configured to determine a strain on and / or an outward bulging of the detection wall 16. Depending on the application, the detection wall 16 may be chosen accordingly. For example, in the illustrate embodiment, the detection wall 16 is made of an elastic membrane.

[0142] Figure 8 shows an embodiment of the device 3 similar to the embodiment illustrated in fig. 7. Additionally, fig. 8 illustrates that the alkalinity storage layer 6 comprises a plurality of sub-layers 6a, 6b arranged adjacent to each other along the infiltration flow path. More specifically, as illustrated, the sub-layers 6a, 6b are arranged in the vertical direction behind each other, such that the soil infiltrate consecutively infiltrates through the sublayers 6a, 6b. For each of the sub-layers 6a, 6b, the device 3 further comprises a corresponding first sensor 17a, 17b, which is configured to detect the strain on and / or outward bulging of the detection wall 16 as a result of swelling of the respective sub-layer 6a, 6b. Accordingly, the first sensors 17a, 17b are also arranged in the vertical direction behind each other. Similar to fig. 7, fig. 8 also illustrates in fig. 8B a close-up of an excerpt of the device shown in full in fig. 8A.

[0143] Figure 9 illustrates a swelling of the alkalinity storage layer 6 as a result of infiltration of the soil infiltrate through the alkalinity storage layer. More specifically, a close-up of the device 3 illustrated in Fig. 7 is illustrated in Fig. 9. In Fig. 9A, the alkalinity storage layer 6, which is made of a swellable resin, is shown in an unswollen state. As carbon dioxide reacts with water on a mineral surface, a soil infiltrate comprising aqueous bicarbonate ions and / or aqueous carbonate ions (respectively corresponding salts thereof) is formed, which infiltrates through the soil and eventually through the alkalinity storage layer 6. As the soil infiltrate starts infiltrating into the alkalinity storage layer 6 on an upstream side, the acidic groups on the surface of the alkalinity storage layer 6 are deprotonated, which leads to swelling of the resin, as illustrated in Fig. 9B. Since the side wall 18 of the housing 15 has a higher bending stiffness than the detection wall 16, the detection wall 16 is caused to bulge outwardly due to the swelling of the resin, as shown in Fig. 9B. The outward bulging is measured by the corresponding upstream first sensor 17a. Since the soil infiltrate has not yet infiltrated the entire resin, but only an upstream sub-layer 6a, a downstream first sensor 17b corresponding to a downstream sub-layer 6b not yet infiltrated does not yet detect significant outward bulging of the detection wall 16. Figure 10 illustrates an embodiment of the device 3 in which the dry compartment 27 is arranged outside the side wall 18 of the housing 15. More specifically, the side wall 18 and the detection wall 16 together define a hollow cylindrical shape encompassing the alkalinity storage layer 6. Upstream of the alkalinity storage layer 6, the hollow cylinder formed by an upstream portion of the side wall 18 encompasses a column, which during operation will be the soil column 9. Although Fig. 10 shows the device 3 itself in a non- operational state and without any soil, the reference numeral 9 for the soil column 9 is nevertheless illustrated in Fig. 10 for reasons of clarity and to aid understanding. In a cross-sectional view, the cross-section of the soil column 9 is essentially identical to and flush with the cross-section of the alkalinity storage layer 6. The hollow cylindrical shape formed by the side wall 18 and the detection wall 16 defines a wet compartment 28 of the device 3, which is configured to be exposed to the soil infiltrate.

[0144] By contrast, a dry compartment 27 housing e.g. the first sensor 17 is arranged outside the hollow cylindrical shape formed by the side wall 18 and the detection wall 16. More specifically, the first sensor 17 is arranged on a second side 162 of the detection wall 16 opposite a first side 161 contacting the alkalinity storage layer 6. Since the dry compartment 27 is arranged outside the housing 15, it further comprises an outer wall itself, including an angled upstream and downstream wall. The inclination angle of the upstream and downstream wall allows the soil infiltrate to be guided in a direction away from the side wall 18 of the housing 15.

[0145] Figure 11 illustrates an embodiment of the system 19 for determining an amount of carbon dioxide taken up by a soil infiltrate over a measurement time period. More specifically, the system 19 includes a device 3 as illustrate in the previous figures. The device 3 further comprises a first communication unit 20, which is configured to transmit measurement data from the sensors to a second communication unit 21 that is arranged aboveground. Furthermore, the system 19 also includes a processing unit 22 that is also installed aboveground and able to process the measurement data to determine the amount of carbon dioxide taken up by the soil infiltrate. Depending on the application, the second communication unit and the processing unit 22 may form a single unit in which they are optionally directly connected to each other, or the system 19 may comprise further communication units. The system 19 may e.g. be used for remote control of the device 3, and / or for remote analysis of the measurement data. The system 3 may also be used to locate a device 3, e.g. for the purposes of maintenance or repair of the device 3.

[0146] LIST OF DESIGNATIONS

[0147] 1 soil infiltrate 162 second side of the detection

[0148] 2 soil 25 wall

[0149] 21 soil surface 17 first sensor

[0150] 3 device 17a, b plurality of first sensors

[0151] 4 solids 18 side wall

[0152] 5 upstream wall 19 system

[0153] 6 alkalinity storage layer 30 20 first communication unit

[0154] 6a, b sub-layers of the alkalinity 21 second communication unit storage layer 22 processing unit configured

[0155] 7 measurement position to be installed aboveground

[0156] 8 downstream wall 23 maintenance door

[0157] 9 soil column 35 24 power supply

[0158] 10 first reference segment of 25 sensor processing unit the soil 26 first infiltration flow guide

[0159] 11 downstream interspacing structure layer 27 dry compartment

[0160] 12 upstream interspacing layer 40 28 wet compartment

[0161] 13 tensiometer 29 second infiltration flow guide

[0162] 14 pump structure

[0163] 15 housing 30 second sensor

[0164] 16 detection wall

[0165] 161 first side of the detection wall

Claims

PATENT CLAIMS1 . Device (3) for determining an amount of carbon dioxide taken up by a soil infiltrate (1 ) over a measurement time period, comprising: a. a housing (15) comprising a water-permeable upstream wall (5) and a water-permeable downstream wall (8) both defining an infiltration flow path; b. an alkalinity storage layer (6) being arranged along the infiltration flow path between the upstream wall (5) and the downstream wall (8), wherein the alkalinity storage layer (6) is formed by a material bearing on its surface a plurality of acidic groups, such that when a soil infiltrate (1 ) comprising aqueous bicarbonate ions and / or aqueous carbonate ions infiltrates through the alkalinity storage layer (6), at least some of the acidic groups are deprotonated.

2. The device (3) according to claim 1 , wherein the material forming the alkalinity storage layer (6) is a material that changes its volumetric expansion upon infiltration of the soil infiltrate (1 ) comprising aqueous bicarbonate ions and / or aqueous carbonate ions through the alkalinity storage layer (6).

3. The device (3) according to claim 2, wherein the alkalinity storage layer (6) contacts a first side (161 ) of a detection wall (16), such that a change in the volumetric expansion of the material forming the alkalinity storage layer (6) leads to a strain on the detection wall (16) and / or to a physical deformation of the detection wall (16).

4. The device (3) according to claim 3, wherein the detection wall (16) is elastically deformable, preferably by elastic outward bulging of the detection wall (16) on a second side (162) opposite the first side (161 ) of the detection wall (16), such that a change in the volumetric expansion of the material forming the alkalinity storage layer (6) leads to a physical deformation of the detection wall (16).

5. The device (3) according to any one of claims 3-4, wherein the detection wall (16) has a lower bending stiffness than a side wall of the housing (15).

6. The device (3) according to any one of claims 2-5, further comprising a first sensor (17) for measuring a change in volumetric expansion of the material forming the alkalinity storage layer (6) over at least a portion of the measurement time period.

7. The device (3) according to claim 6, wherein the first sensor (17) comprises a sensor for measuring a strain on the detection wall (16) and / or a physical deformation of the detection wall (16).

8. The device (3) according to claim 6 or 7, wherein the first sensor (17) comprises a strain gauge interconnected to the detection wall and / or a piezo sensor interconnected to the detection wall (16).

9. The device (3) according to any one of the previous claims, wherein the alkalinity storage layer (6) comprises a plurality of sub-layers (6a, 6b) arranged along the infiltration flow path behind each other.

10. The device (3) according to claim 9, comprising a plurality of first sensors (17a, 17b), wherein each sub-layer (6a, 6b) is interconnected with a respective first sensor (17a, 17b), for measuring a change in volumetric expansion of the material forming the respective sub-layer (6a, 6b) over at least a portion of the measurement time period.1 1 . The device (3) according to any one of the previous claims, wherein the plurality of acidic groups have a pKa of less than 6.35, preferably from 2 to 6, more preferably from 3 to 6.

12. The device (3) according to any one of the previous claims, wherein the plurality of acidic groups are carboxylic acid groups and / or sulfonic acid groups, preferably carboxylic acid groups.

13. The device (3) according to any one of the previous claims, further comprising a second sensor (30) interconnected with the alkalinity storage layer (6) and configured to measure a protonation state of the acidic groups over at least a portion of the measurement time period.

14. The device (3) according to any one of the previous claims, wherein the housing (15) further comprises an essentially water-impermeable side wall (18) circumferentially surrounding the alkalinity storage layer (6).

15. The device (3) according to any one of the previous claims, wherein the alkalinity storage layer (6) has a hydraulic conductivity from 1 to 4000 cm / day, preferably from 100 to 2000 cm / day, more preferably from 1000 to 1500 cm / day.

16. The device (3) according to any one of the previous claims, wherein the alkalinity storage layer (6) comprises a buffer.

17. The device (3) according to any one of the previous claims, further comprising a pH detector configured for measuring a pH and / or a change in pH of the alkalinity storage layer (6) over at least a portion of the measurement time period.

18. The device (3) according to any one of the previous claims, wherein the alkalinity storage layer (6) comprises a resin, preferably an ion-exchange resin, wherein the resin is swellable and / or shrinkable upon contact with an aqueous solution having a pH of higher than 7, preferably upon contact with an aqueous solution having a pH of 8 or higher, more preferably upon contact with aqueous bicarbonate ions and / or aqueous carbonate ions.

19. The device (3) according to any one of the previous claims, further comprising a flow control unit configured for controlling an inside flow rate of the soil infiltrate (1 ) infiltrating through the device (3) such that the inside flow rate has a known or determinable flow rate ratio with respect to an outside flow rate of the soil infiltrate (1 ) infiltrating through a first reference segment (10) of the soil (2) arranged outside the device (3).

20. The device (3) according to any one of the previous claims, further comprising a downstream interspacing layer (1 1 ) arranged along the flow path downstream ofthe alkalinity storage layer (6) and having a higher hydraulic conductivity than the alkalinity storage layer (6), such that backflow of soil infiltrate (1 ) from the downstream interspacing layer (11 ) to the alkalinity storage layer (6) is minimized.21 . System (19) for determining an amount of carbon dioxide taken up by a soil infiltrate (1 ), comprising: a. the device (3) according to any one of the previous claims, wherein the device (3) is configured to be installed underground in a soil (2) and further comprises a first communication unit (20) configured for sending underground measurement data measured over at least a portion of the measurement time period; b. a second communication unit (21 ) configured to be installed aboveground and configured for receiving the underground measurement data; c. a processing unit (22) configured to be installed aboveground and configured for determining a total alkalinity taken up by the alkalinity storage layer (6) over the measurement time period based on the underground measurement data.

22. Use of the device (3) according to any one of claims 1 -20 or of the system (19) according to claim 21 , for determining an amount of carbon dioxide taken up by a soil infiltrate (1 ), preferably in an enhanced weathering process.

23. Method of determining an amount of carbon dioxide taken up by a soil infiltrate (1 ), wherein the method comprises: a. positioning a device (3), preferably a device according to any one of claims 1 -20, in a measurement position (7) in a soil (2) such that an upstream wall (5) of the device (3) is arranged underneath a soil surface (21 ), wherein an alkalinity storage layer (6) of the device (3) is arranged in a vertical direction underneath the upstream wall (5), wherein the alkalinity storage layer (6) is formed by a material bearing on its surface a plurality of acidic groups;b. allowing solids (4) to react during a measurement time period with water and carbon dioxide to form a soil infiltrate (1 ) infiltrating through the soil (2) and through the alkalinity storage layer (6), thereby causing at least some of the acidic groups of the material forming the alkalinity storage layer (6) to be deprotonated over the measurement time period; c. determining a total alkalinity taken up by the alkalinity storage layer (6) over at least a portion of the measurement time period; d. determining based on the determined total alkalinity taken up by the alkalinity storage layer (6) a total amount of carbon dioxide taken up by the soil infiltrate (1 ) during the measurement time period.

24. Method according to claim 23, wherein the step of c) determining the total alkalinity taken up by the alkalinity storage layer (6) over at least a portion of the measurement time period includes: c.i) determining a change in the volumetric expansion of the material forming the alkalinity storage layer (6) over at least the portion of the measurement time period; and c.ii) determining, based on the measured change in the volumetric expansion of the material forming the alkalinity storage layer (6) over at least the portion of the measurement time period, the total alkalinity taken up by the alkalinity storage layer (6) over at least the portion of the measurement time period.

25. Method according to claim 24, wherein the change in the volumetric expansion of the material forming the alkalinity storage layer (6) is a swelling and / or shrinking of the material forming the alkalinity storage layer (6) occurring upon infiltration through the alkalinity storage layer (6) of the soil infiltrate (1 ) formed by reaction of the solids (4) with water and carbon dioxide.

26. Method according to any one of claims 23-25, wherein the method further comprises during the measurement time period controlling an inside flow rate of the soil infiltrate (1 ) infiltrating through the device (3) such that the inside flow rate has a known or determinable flow rate ratio with respect to an outside flow rate of thesoil infiltrate (1 ) infiltrating through a first reference segment (10) of the soil (2) arranged outside the device (3).

27. Method according to claim 26, wherein the step of controlling the inside flow rate comprises controlling a vacuum pressure inside the device (3).

28. Method according to any one of the previous claims, wherein the step of determining the total alkalinity taken up by the alkalinity storage layer (6) over the measurement time period comprises: a. determining for a plurality of intervals within the measurement time period a total interval alkalinity taken up by the alkalinity storage layer (6) during the respective interval; and b. determining the total alkalinity taken up by the alkalinity storage layer (6) over the measurement time period based on the total interval alkalinities determined for the plurality of intervals.

29. Method according to claim 28, wherein the step of determining the total alkalinity taken up by the alkalinity storage layer (6) over the measurement time period is provided by summing up the total interval alkalinities of all intervals for which a positive total interval alkalinity was determined, wherein the total interval alkalinities of all intervals for which a negative total interval alkalinity was determined are optionally discarded.

30. Method according to any one of claims 23-29, wherein the step of determining the total alkalinity taken up by the alkalinity storage layer (6) includes: a. determining for at least some of a plurality of sub-layers (6a, 6b) of the alkalinity storage layer (6) arranged in the vertical direction underneath each other a total alkalinity taken up by the respective sub-layer (6a, 6b); b. determining the total alkalinity taken up by the alkalinity storage layer (6) based on the determined total alkalinities taken up by the respective sublayers (6a, 6b).31 . Method according to 30, whereina. if the determined total alkalinities taken up by the respective sub-layers (6a, 6b) decrease in the vertical direction from each sub-layer (6a, 6b) to each downstream sub-layer (6a, 6b), the total alkalinity taken up by the alkalinity storage layer (6) is provided as a sum of the total alkalinities taken up by all sub-layers (6a, 6b); b. if the total alkalinity of at least one sub-layer is lower than the total alkalinity of a downstream sub-layer arranged in the vertical direction directly underneath said at least one sub-layer, the total alkalinity of said at least one sub-layer is not included in the determination of the total alkalinity taken up by the alkalinity storage layer (6).

32. Method according to any one of claims 23-31 , wherein the device (3) further comprises a downstream interspacing layer (11 ) arranged downstream of the alkalinity storage layer (6) and having a higher hydraulic conductivity than the alkalinity storage layer (6), such that backflow of soil infiltrate (1 ) from the downstream inter- spacing layer (1 1 ) to the alkalinity storage layer (6) is minimized.

33. Method according to any one of claims 23-32, wherein the minerals (4) comprise silicate-containing minerals (4).

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