Method for calculating energy transmission efficiency of aquatic ecosystem based on aquatic organism fatty acid composition

Abstract

The invention relates to a method for calculating energy transmission efficiency of an aquatic ecosystem based on fatty acid composition of aquatic organisms, and belongs to the technical field of energy evaluation of the aquatic ecosystem. The method comprises the following steps: acquiring biological components of phytoplankton and zooplankton through field sampling, and measuring the unit dry weight fatty acid content, biomass and unit dry weight carbon content; calculating a primary carbon production amount and a primary fatty acid production amount by combining the carbon conversion coefficient and the growth rate, and calculating a secondary carbon production amount and a secondary fatty acid production amount by utilizing a productivity empirical formula; the carbon and fatty acid energy transfer efficiency is obtained from the ratio of the secondary to primary yields. The method is mainly used for quantitative evaluation of energy flow of the aquatic ecosystem and provides support for ecosystem health condition evaluation and response trend prediction. The dependence on historical data and model parameters is reduced, and the result timeliness is improved; the food quality (essential nutrient substance) dimension is introduced, effective energy transfer is reflected more truly, and the defects of a traditional method are overcome.

Description

Technical Field

[0001] This invention belongs to the field of ecological technology, specifically relating to the field of quantitative assessment of energy transfer efficiency in aquatic ecosystems. Background Technology

[0002] Energy transfer efficiency, the proportion of matter and energy transferred from one trophic level to the next, is a key indicator for assessing ecosystem productivity and function. It plays a fundamental role in shaping food chain structure, influencing food chain length and complexity. In ecosystems with high energy transfer efficiency, more energy is transferred upwards along the food chain, providing sufficient energy support for organisms at higher trophic levels and increasing their biomass. As climate change profoundly impacts various ecosystems, research on energy transfer efficiency is becoming increasingly important, providing a basis for assessing ecosystem health and predicting ecosystem response trends.

[0003] Various methods exist for calculating the energy transfer efficiency of aquatic ecosystems. Among them, productivity-based estimation methods quantify energy transfer efficiency as the ratio of productivity between adjacent trophic levels. Implementation requires data on biomass, productivity, diet matrix, and trophic level location for each consumer group. Primary productivity is typically quantified using diurnal dissolved oxygen curves, radiocarbon assimilation, and chlorophyll fluorescence methods. Secondary productivity is estimated using methods such as body length frequency and instantaneous growth rate increment accumulation. Trophic level location is determined through stomach contents analysis or stable isotope analysis. However, in ecosystems with complex trophic relationships, high omnivorousness, or blurred trophic level boundaries, these methods may oversimplify actual trophic interactions, making it difficult to accurately attribute productivity to discrete trophic levels. Furthermore, they may be affected by extreme weather events, leading to biased assessment results.

[0004] Carbon transfer-based methods measure productivity or energy transfer efficiency using total carbon flux. Energy transfer efficiency is estimated by the ratio of total primary productivity to carbon production by primary consumers, requiring both total primary and secondary productivity to be expressed in carbon units. While this method is suitable for estimating energy transfer efficiency between phytoplankton and zooplankton, its application is less common at higher trophic levels because predator-prey relationships are dispersed and diets are mixed, making accurate carbon flux analysis difficult. In autotrophic pathways, net primary productivity is a more appropriate producer term. However, in benthic or detrital systems, energy transfer efficiency should be calculated based on the productivity ratio between adjacent trophic levels, rather than directly on total primary productivity.

[0005] Model-based methods estimate energy transfer efficiency by calculating the transfer of energy or biomass production between different species, functional groups, or trophic levels. For example, the Ecopath model, based on the principle of ecosystem mass conservation, has good repeatability, but the accuracy of the results is highly dependent on the precision of the input parameters. Energy flux models have not yet been widely used in estimating energy transfer efficiency in freshwater ecosystems. Body size profile models track energy flow based on organism body size levels, mainly focusing on energy transfer between consumers, simplifying the ecosystem structure and often ignoring the more complex energy dynamics between bacteria, detritus, and primary producers. Methods based on predator-prey weight ratios originate from ecological metabolic theory, inferring energy transfer efficiency by characterizing the size difference between predators and prey, and identifying predator-prey relationships by combining stable isotope or stomach contents data. They can reflect the biomass relationship between predators and prey, but mainly focus on interactions between consumers, making it difficult to cover herbivorous and detritivorous pathways, thus limiting the representation of the overall food web.

[0006] Overall, existing methods for estimating energy transfer efficiency in aquatic ecosystems have several limitations. First, most rely on existing literature, historical survey data, or the integration of information from different sources, rather than simultaneous field measurements at the same spatiotemporal scale. Significant spatiotemporal differences exist in the biological composition, trophic structure, and environmental conditions of ecosystems, increasing the uncertainty of estimation results and making direct comparisons of energy transfer efficiency across different ecosystems or under different conditions within the same system difficult. Second, estimation methods centered on production or carbon transfer often treat carbon production or total carbon flux as key indicators, assuming that carbon is transferred proportionally upwards along trophic levels, while neglecting the physiological needs and biochemical limitations of organisms for essential nutrients during energy transfer, failing to accurately reflect actual trophic limiting effects. Particularly in phytoplankton-dominant aquatic ecosystems, energy transfer efficiency calculated solely from carbon flux often fails to explain why, despite a high phytoplankton biomass, energy transfer efficiency is significantly low. This contradiction suggests that an increase in the number of primary producers does not necessarily lead to greater upward energy transfer; the core issue lies in the insufficient supply of essential nutrients by primary producers, thus limiting the growth, reproduction, and energy assimilation of consumers.

[0007] Essential nutrients such as ω3 long-chain unsaturated fatty acids are incapable or difficult for aquatic consumers to synthesize, yet they are crucial for maintaining their physiological functions and ensuring population continuity. The efficiency of these substances' transfer between trophic levels directly affects the effectiveness of energy transfer along the food chain. Existing carbon transfer-based methods struggle to identify these nutritional bottlenecks, potentially leading to a systematic overestimation of energy transfer efficiency supported by primary producers with high carbon production capacity but shortages of essential nutrients. To address these issues, this invention incorporates long-chain unsaturated fatty acid-related analytical techniques, directly integrating the acquisition and transfer of essential nutrients into the calculation system of energy transfer efficiency. This approach simultaneously reflects the combined effects of carbon flow and nutrient limitation on energy transfer, mechanistically elucidating the reasons for differences in energy transfer efficiency under different ecosystem states. It provides a new, more physiologically grounded and ecologically explanatory approach for the quantitative assessment of energy transfer efficiency in aquatic ecosystems. Summary of the Invention

[0008] The purpose of this invention is to provide a method for calculating the energy transfer efficiency of aquatic ecosystems based on the fatty acid composition of aquatic organisms. This method addresses the problems of existing methods that rely on historical data and model parameters, leading to high uncertainty in the results, and that neglecting food quality makes it difficult to explain the low energy transfer efficiency of some algae that are abundant. This method improves the accuracy and rationality of the assessment.

[0009] To achieve the above objectives, the present invention provides the following technical solution:

[0010] A method for calculating the energy transfer efficiency of aquatic ecosystems based on the fatty acid composition of aquatic organisms, comprising the following steps:

[0011] Conduct field sampling in the target aquatic ecosystem to obtain biological components;

[0012] The fatty acid content of the biological components was determined to obtain the fatty acid content per unit dry weight.

[0013] The biomass and carbon content of the biological components were determined to obtain biomass data and carbon content per unit dry weight.

[0014] Based on the biomass data and carbon conversion factor, primary carbon production is calculated, and primary fatty acid production is obtained using the primary carbon production, fatty acid content per unit dry weight, and carbon content per unit dry weight.

[0015] Based on the zooplankton biomass data and production parameters in the biomass data, the secondary carbon production is calculated, and the secondary fatty acid production is obtained using the secondary carbon production, fatty acid content per unit dry weight, and carbon content per unit dry weight.

[0016] The energy transfer efficiency of the aquatic ecosystem is obtained by using the ratio of primary carbon production to secondary carbon production and the ratio of primary fatty acid production to secondary fatty acid production.

[0017] In one possible implementation, field sampling includes the following steps:

[0018] Phytoplankton and zooplankton samples for fatty acid analysis were collected using planktonic nets with different pore sizes. The samples were trawled along a preset trajectory and for a set duration, and parallel samples were set up.

[0019] Phytoplankton and zooplankton samples were collected using a glass water sampler for biomass determination, and fixatives were added to the biomass determination samples on-site.

[0020] Fatty acid analysis samples were stored in a low-temperature environment, and biomass determination samples were stored in a refrigerated, light-protected environment and quickly transported to the laboratory for use.

[0021] In one possible implementation, determining the fatty acid content includes the following steps:

[0022] The fatty acid analysis samples of the biological components were freeze-dried, ground and homogenized, and then quantitative samples were taken.

[0023] Lipid extraction and methyl esterification of the quantitative sample were performed under nitrogen protection and low temperature conditions to obtain fatty acid methyl esters.

[0024] The fatty acid methyl esters were analyzed using a gas chromatograph equipped with a flame ionization detector. Qualitative analysis was performed using mixed standards, and quantitative analysis was performed based on a calibration curve to obtain the fatty acid content per unit dry weight.

[0025] In one possible implementation, determining the biomass includes the following steps:

[0026] Phytoplankton samples used for biomass determination were concentrated after standing. A quantitative suspension was placed in a plankton counting frame, and species morphological parameters were counted and measured under a microscope. Cell volume was calculated, and the biomass of each species was obtained by combining the number of individuals per unit volume of water. The total biomass of phytoplankton was obtained by summing the results.

[0027] Zooplankton samples used for biomass determination were identified and counted according to taxonomic groups, and zooplankton biomass data were obtained by using the volume method, body length-weight regression equation, or fixed value conversion.

[0028] In one possible implementation, determining the carbon content includes the following steps:

[0029] The biological components were freeze-dried and ground, and a quantitative sample was weighed and placed in a tin cup. The sample was then burned at high temperature in an elemental analyzer to convert carbon into carbon dioxide.

[0030] The carbon content per unit dry weight is calculated by comparing the peak area of ​​a working standard substance with a known carbon content with the peak area of ​​carbon dioxide produced by the sample.

[0031] In one possible implementation, calculating the primary carbon production includes the steps of:

[0032] The biomass of each type of phytoplankton community is multiplied by the corresponding carbon conversion coefficient, and the sum is obtained to obtain the carbon-based phytoplankton biomass. Then, it is multiplied by the phytoplankton community growth rate to obtain the primary carbon production.

[0033] When calculating the production of primary fatty acids, the production of primary carbon is multiplied by the fatty acid content per unit dry weight, and then divided by the carbon content per unit dry weight to obtain the production of primary fatty acids.

[0034] In one possible implementation, calculating the secondary carbon production includes the steps of:

[0035] The secondary dry weight production was calculated by substituting the average dry weight and abundance of zooplankton into the empirical formula for productivity, and then multiplied by the conversion factor from dry weight to carbon content to obtain the secondary carbon production.

[0036] When calculating the production of secondary fatty acids, the production of secondary carbon is multiplied by the fatty acid content per unit dry weight, and then divided by the carbon content per unit dry weight to obtain the production of secondary fatty acids.

[0037] In one possible implementation, calculating the energy transfer efficiency includes the following steps:

[0038] The carbon energy transfer efficiency is obtained by multiplying the ratio of secondary carbon production to primary carbon production by a percentage.

[0039] The ratio of secondary fatty acid production to primary fatty acid production is multiplied by a percentage to obtain the fatty acid energy transfer efficiency. The energy flow process of the aquatic ecosystem is evaluated by combining the carbon energy transfer efficiency and the fatty acid energy transfer efficiency.

[0040] Compared with the prior art, the advantages of this invention are as follows:

[0041] This invention directly collects biological components from the target aquatic ecosystem, simultaneously measuring fatty acid content, biomass, and carbon content, avoiding the reliance of existing methods on historical literature data or model parameters. The acquired data accurately reflects the actual state of the ecosystem during the study period, reducing uncertainties caused by differences in ecosystems at different times, making the calculation results of energy transfer efficiency more timely and reliable, and improving the comparability of results between different ecosystems.

[0042] In terms of primary productivity estimation, this invention estimates biomass by combining carbon conversion coefficient and growth rate, eliminating the need for complex methods such as radiocarbon tracing or continuous diurnal dissolved oxygen monitoring. This simplifies the experimental procedure, reduces the requirements for specialized instruments and operator skills, decreases time and labor costs, improves the operability of the method, and makes it more suitable for large-scale or long-term ecological monitoring.

[0043] Fatty acids, especially ω3 long-chain unsaturated fatty acids (ω3 LC-PUFAs), are essential nutrients that organisms cannot synthesize or can only synthesize in very small quantities. In aquatic ecosystems, they mainly originate from primary producers and are subsequently transferred upwards along the trophic level. These fatty acids can accumulate and remain relatively stably in the consumer's body in the form of structural lipids or storage lipids. During trophic level transfer, they not only maintain a clear source characteristic but are also preferentially retained and directed to key physiological processes such as growth, reproduction, and cellular function, resulting in a transfer loss rate significantly lower than that of total carbon. Therefore, ω3 LC-PUFAs are not only energy carriers but also directly reflect the effective energy and nutritional value that consumers can actually utilize. Existing methods for assessing carbon transfer efficiency only consider total carbon or carbon flux as core indicators, neglecting differences in nutrient composition. This invention, however, incorporates the nutritional quality of food, represented by essential fatty acids, into the assessment, thus providing a more accurate representation of the effective energy transfer between trophic levels. This method can not only reasonably explain the ecological phenomenon that algal biomass or primary productivity is not low in some water bodies, but secondary production and energy transfer efficiency is low, but it can also clarify the underlying reason why energy seems sufficient but its actual function is limited when the nutritional quality of food is insufficient.

[0044] This invention simultaneously calculates the energy transfer efficiencies of both carbon and fatty acids, constructing a dual-indicator evaluation system. Carbon transfer efficiency reflects the quantitative characteristics of energy transfer, while fatty acid transfer efficiency reflects the qualitative characteristics. These two indicators complement each other, making the assessment of energy transfer efficiency more comprehensive and reasonable. This system corrects the fixed-value assumptions about energy transfer efficiency in traditional ecology, and better reflects the efficiency levels of actual ecological processes. Attached Figure Description

[0045] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0046] Figure 1 This is a flowchart of a method for calculating the energy transfer efficiency of an aquatic ecosystem based on the fatty acid composition of aquatic organisms, according to an embodiment of the present invention.

[0047] Figure 2 This is a schematic diagram showing the distribution of phytoplankton primary production and fatty acid primary production in an embodiment of the present invention.

[0048] Figure 3 This is a schematic diagram showing the distribution of zooplankton secondary production and fatty acid secondary production in an embodiment of the present invention.

[0049] Figure 4 This is a schematic diagram comparing the carbon energy transfer efficiency and fatty acid energy transfer efficiency in an embodiment of the present invention. Detailed Implementation

[0050] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0051] Example:

[0052] It should be noted that the terms "comprising" and "having" and any variations thereof in the embodiments of the present invention are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such processes, methods, products, or devices.

[0053] This embodiment provides a method for calculating the energy transfer efficiency of an aquatic ecosystem based on the fatty acid composition of aquatic organisms, including the following steps:

[0054] Step 101: Conduct field sampling in the target aquatic ecosystem to obtain biological components.

[0055] Specifically, biological components are biological samples collected from aquatic ecosystems for analysis, which can be phytoplankton or zooplankton samples.

[0056] The process of conducting field sampling includes the following steps:

[0057] Phytoplankton and zooplankton samples for fatty acid analysis were collected using planktonic nets with different pore sizes. The samples were trawled along a preset trajectory and for a set duration, and parallel samples were set up.

[0058] Phytoplankton and zooplankton samples were collected using a glass water sampler for biomass determination, and fixatives were added to the biomass determination samples on-site.

[0059] Fatty acid analysis samples were stored in a low-temperature environment, and biomass determination samples were stored in a refrigerated, light-protected environment and quickly transported to the laboratory for use.

[0060] Specifically, the planktonic nets with different pore sizes can be 64μm for collecting phytoplankton and 112μm for collecting zooplankton; the preset trajectory can be in the shape of an "∞"; the preset duration can be 5 minutes; there can be 5 parallel samples at each sampling point; the glass water sampler can be 1L; the fixative can be Lugol reagent; the low temperature environment can be a -20℃ portable freezer; and the refrigerated and light-protected environment can be an insulated refrigerator with ice packs.

[0061] Upon arrival at the sampling points, phytoplankton samples for fatty acid analysis were collected using a 64μm pore size plankton net. The net was placed at a water depth of 0.5m and dragged along a zigzag pattern at a constant speed for 5 minutes. After collection, samples were transferred to 120mL polypropylene sample bottles, with 5 parallel samples taken from each sampling point. Zooplankton samples were collected using a 112μm pore size plankton net in the same manner. For biomass determination samples, phytoplankton and zooplankton samples were collected from the surface water using a 1L glass water sampler. 15mL of Lugol's reagent was added to each sample on-site for fixation. After collection, fatty acid analysis samples were immediately placed in a -20℃ portable freezer, while biomass determination samples were placed in a light-protected, insulated freezer with ice packs. The samples were transported to the laboratory as quickly as possible. The fatty acid analysis samples were subsequently stored at -80℃, while the biomass determination samples were kept refrigerated and protected from light.

[0062] Step 102: Determine the fatty acid content of the biological components to obtain the fatty acid content per unit dry weight.

[0063] Specifically, fatty acid content per unit dry weight is the mass of fatty acids per unit dry weight of biological sample (μg FAME / mgDW).

[0064] The determination of the fatty acid content includes the following steps:

[0065] The fatty acid analysis samples of the biological components were freeze-dried, ground and homogenized, and then quantitative samples were taken.

[0066] Lipid extraction and methyl esterification of the quantitative sample were performed under nitrogen protection and low temperature conditions to obtain fatty acid methyl esters.

[0067] The fatty acid methyl esters were analyzed using a gas chromatograph equipped with a flame ionization detector. Qualitative analysis was performed using mixed standards, and quantitative analysis was performed based on a calibration curve to obtain the fatty acid content per unit dry weight.

[0068] Specifically, the freeze-drying process can be vacuum freeze-drying; homogenization can be thorough grinding with a glass rod; the quantitative sample can be a 25 mg dry weight sample; nitrogen protection is to prevent lipid oxidation; fatty acid methyl esters can be FAMEs; the flame ionization detector can be an FID at 250 °C; the gas chromatograph can be a Thermo Trace 1310; the mixed standard can be a mixed standard of 37 components of FAME and a mixed standard of methyl bacterial phospholipids; the calibration curve can be a seven-point calibration curve; and the fatty acid content per unit dry weight can be μg FAME / mg DW.

[0069] Fatty acid analysis samples were taken out and lyophilized in a vacuum freeze dryer. After lyophilization, the samples were thoroughly homogenized using a glass rod, and 25 mg of dry weight sample was weighed for subsequent processing. Under nitrogen protection and low temperature, lipid extraction and methyl esterification of the quantitative samples were performed according to the method of Guo et al., avoiding air ingress to prevent lipid oxidation, ultimately yielding fatty acid methyl esters. The fatty acid methyl esters were injected into a gas chromatograph equipped with a flame ionization detector. The carrier gas was helium at a flow rate of 1 mL / min, and the detector gases were hydrogen at 35 mL / min, nitrogen at 30 mL / min, and air at 350 mL / min. The temperature program was as follows: initial temperature 100℃ held for 3 min, increased to 200℃ at 3℃ / min held for 3 min, then increased to 240℃ at 3℃ / min held for 6 min. Qualitative analysis was performed using a mixed standard of 37 FAME components and a mixed standard of methyl bacterial phospholipids. Quantification was performed using a seven-point calibration curve established based on known concentration standards, ultimately obtaining the fatty acid content per unit dry weight.

[0070] Step 103: Determine the biomass and carbon content of the biological components to obtain biomass data and carbon content per unit dry weight.

[0071] Specifically, biomass data is the mass of organisms in a unit volume of water (mg / L); carbon content per unit dry weight is the percentage of carbon in a unit dry weight biological sample (C%).

[0072] The determination of the biomass includes the following steps:

[0073] Phytoplankton samples used for biomass determination were concentrated after standing. A quantitative suspension was placed in a plankton counting frame, and species morphological parameters were counted and measured under a microscope. Cell volume was calculated, and the biomass of each species was obtained by combining the number of individuals per unit volume of water. The total biomass of phytoplankton was obtained by summing the results.

[0074] Zooplankton samples used for biomass determination were identified and counted according to taxonomic groups, and zooplankton biomass data were obtained by using the volume method, body length-weight regression equation, or fixed value conversion.

[0075] Specifically, the settling time can be 48 hours; the concentration volume can be 30 or 50 mL; the quantitative suspension can be 0.1 mL; the plankton counting frame can be a special frame adapted for microscope observation; the morphological parameters can be length, width, and diameter; the cell volume can be calculated using a geometric formula; the taxonomic group can be protozoa, rotifers, cladocerans, or copepods; the volume method is applicable to protozoa and rotifers; the body length-weight regression equation is applicable to crustaceans; the fixed value can be 0.003 mg / individual, used for copepod nauplius larvae that are extremely small, have undifferentiated body segments, and whose body length is difficult to measure accurately.

[0076] When processing phytoplankton samples, the fixed samples were allowed to stand for 48 hours. The supernatant was then siphoned off, and the solution was concentrated to 30 or 50 mL depending on the lake's nutrient level. After thorough mixing, 0.1 mL of the algal suspension was added to a plankton counting frame, and the samples were counted under a microscope. Each sample was counted twice. For each species, at least 50 individuals were randomly selected, and the parameters corresponding to the geometric shape closest to the morphology were measured. The cell volume was calculated using a geometric formula. The average cell volume was multiplied by the number of individuals of that species per unit volume of water to obtain the biomass of that species. The biomass of all species was added together to obtain the total phytoplankton biomass. When processing zooplankton samples, they were identified and counted according to taxonomic groups such as protozoa, rotifers, cladocerans, and copepods: 0.1 mL of protozoa was counted at 200× magnification; 1 mL of rotifers was counted at 100× magnification; cladocerans and copepods were diluted and counted in a 5 mL counting frame. When converting biomass, protozoa and rotifers were calculated using the volume method, assuming a specific gravity of 1; crustaceans were calculated using a body length-weight regression equation for wet weight; nauplii were converted at 0.003 mg / individual, and the final zooplankton biomass data were obtained.

[0077] The determination of the carbon content includes the following steps:

[0078] The biological components were freeze-dried and ground, and a quantitative sample was weighed and placed in a tin cup. The sample was then burned at high temperature in an elemental analyzer to convert carbon into carbon dioxide.

[0079] The carbon content per unit dry weight is calculated by comparing the peak area of ​​a working standard substance with a known carbon content with the peak area of ​​carbon dioxide produced by the sample.

[0080] Specifically, freeze-drying and grinding can be glass rod grinding after vacuum freeze-drying; quantitative sample can be an appropriate amount of dry weight sample; tin cup is a container used for sample combustion; elemental analyzer is a device for realizing high-temperature combustion and carbon detection; high-temperature combustion temperature can be a temperature sufficient to completely convert carbon into carbon dioxide; working standard substance can be an organic compound with known carbon content; carbon content per unit dry weight is the percentage of carbon in a unit dry weight sample, which can be C.

[0081] Phytoplankton and zooplankton samples from the biological components were freeze-dried separately in a vacuum freeze dryer, and then thoroughly ground into a uniform powder using a glass rod. An appropriate amount of the ground sample was weighed and placed in a tin cup, ensuring the sample was evenly distributed at the bottom. The tin cup was placed in an elemental analyzer, and the instrument was started for high-temperature combustion to completely convert the carbon in the sample into carbon dioxide. During the detection process, 2-3 working standard substances with known carbon contents were simultaneously added, and the instrument recorded the peak areas of carbon dioxide produced by the combustion of the standard substances and the sample. By comparing the peak area of ​​the carbon dioxide in the sample with that in the working standard substances, and considering the known carbon content of the standard substances, the carbon content per unit dry weight of the sample was calculated.

[0082] Step 104: Calculate the primary carbon production based on the biomass data and carbon conversion coefficient, and obtain the primary fatty acid production using the primary carbon production, fatty acid content per unit dry weight, and carbon content per unit dry weight.

[0083] Specifically, primary carbon production is the carbon production capacity of phytoplankton per unit time and per unit volume, which can be mg CL⁻¹・day⁻¹; primary fatty acid production is the fatty acid production capacity of phytoplankton per unit time and per unit volume, which can be μg FAME L⁻¹・day⁻¹.

[0084] The calculation of the primary carbon production includes the following steps:

[0085] The biomass of each type of phytoplankton community is multiplied by the corresponding carbon conversion coefficient, and the sum is obtained to obtain the carbon-based phytoplankton biomass. Then, it is multiplied by the phytoplankton community growth rate to obtain the primary carbon production.

[0086] When calculating the production of primary fatty acids, the production of primary carbon is multiplied by the fatty acid content per unit dry weight, and then divided by the carbon content per unit dry weight to obtain the production of primary fatty acids.

[0087] Specifically, the various phytoplankton groups can be cyanobacteria, dinoflagellates, diatoms, or green algae; the carbon conversion coefficient can be 0.22 for cyanobacteria, 0.13 for dinoflagellates, 0.11 for diatoms, and 0.16 for green algae; the carbon-based phytoplankton biomass can be mgC L⁻¹; the phytoplankton community growth rate can be 1.0 day⁻¹; the primary carbon production can be mg CL⁻¹・day⁻¹; and the primary fatty acid production can be μg FAME L⁻¹・day⁻¹.

[0088] Biomass data for various phytoplankton species were compiled and categorized by taxa. Cyanobacteria, dinoflagellates, diatoms, green algae, and other taxa corresponded to carbon conversion coefficients of 0.22, 0.13, 0.11, 0.16, and 0.11, respectively. The biomass of each taxa was multiplied by its corresponding carbon conversion coefficient, and the sum was obtained to obtain carbon-based phytoplankton biomass. The phytoplankton community growth rate was determined by consulting literature. In a warm, eutrophic, shallow lake, a timeframe of 1.0 day⁻¹ was used. Primary carbon production was calculated using the formula: Primary carbon production = Carbon-based phytoplankton biomass × Growth rate. Subsequently, primary fatty acid production was calculated using the formula: Primary fatty acid production = Primary carbon production × Fatty acid content per unit dry weight ÷ Carbon content per unit dry weight. Substituting the previously measured fatty acid and carbon content per unit dry weight data, the primary fatty acid production was obtained.

[0089] Step 105: Calculate the secondary carbon production based on the zooplankton biomass data and production parameters in the biomass data, and obtain the secondary fatty acid production using the secondary carbon production, fatty acid content per unit dry weight, and carbon content per unit dry weight.

[0090] Specifically, secondary carbon production is the carbon production capacity of zooplankton per unit time and per unit volume, which can be mg CL⁻¹・day⁻¹; secondary fatty acid production is the fatty acid production capacity of zooplankton per unit time and per unit volume, which can be μg FAME L⁻¹・day⁻¹.

[0091] The calculation of the secondary carbon production includes the following steps:

[0092] The secondary dry weight production was calculated by substituting the average dry weight and abundance of zooplankton into the empirical formula for productivity, and then multiplied by the conversion factor from dry weight to carbon content to obtain the secondary carbon production.

[0093] When calculating the production of secondary fatty acids, the production of secondary carbon is multiplied by the fatty acid content per unit dry weight, and then divided by the carbon content per unit dry weight to obtain the production of secondary fatty acids.

[0094] Specifically, the empirical formula for productivity can be SP = 10^(-0.23log(M)-0.73)×1.12MN; the average dry weight per individual can be mg; the abundance can be individuals L⁻¹; the secondary dry weight production can be mg L⁻¹・day⁻¹; the conversion factor can be 1 / 2.3; the secondary carbon production can be mg CL⁻¹・day⁻¹; and the secondary fatty acid production can be μgFAME L⁻¹・day⁻¹.

[0095] The average dry weight per individual (M) and abundance (N) were extracted from zooplankton biomass data and substituted into the empirical productivity formula SP=10. (−0.23log(M)−0.73)The secondary dry weight production is calculated by multiplying the secondary dry weight production by 1.12MN. Since secondary carbon production must be expressed in carbon units, the secondary dry weight production is multiplied by the conversion factor from dry weight to carbon content, 1 / 2.3, to obtain the secondary carbon production. Following the calculation logic for primary fatty acid production, the secondary fatty acid production is calculated using the formula: Secondary fatty acid production = Secondary carbon production × Fatty acid content per unit dry weight ÷ Carbon content per unit dry weight. Substituting the relevant data, the secondary fatty acid production is then obtained.

[0096] Step 106: Obtain the energy transfer efficiency of the aquatic ecosystem by using the ratio of primary carbon production to secondary carbon production and the ratio of primary fatty acid production to secondary fatty acid production.

[0097] Specifically, energy transfer efficiency is the ratio of productivity between adjacent trophic levels.

[0098] The calculation of the energy transfer efficiency includes the following steps:

[0099] The carbon energy transfer efficiency is obtained by multiplying the ratio of secondary carbon production to primary carbon production by a percentage.

[0100] Multiplying the ratio of secondary fatty acid production to primary fatty acid production by a percentage yields the fatty acid energy transfer efficiency. Combining the carbon energy transfer efficiency and the fatty acid energy transfer efficiency yields the energy flow process of the aquatic ecosystem.

[0101] Specifically, the carbon energy transfer efficiency can be 11.80% for the water body with the dominant group of essential fatty acids in Taihu Lake; the fatty acid energy transfer efficiency can be 20.38% for the water body with the dominant group of essential fatty acids in Taihu Lake; the comprehensive energy transfer efficiency is an integrated assessment of the two types of efficiency, reflecting the quantity (carbon) and quality (essential fatty acids) dimensions of energy transfer.

[0102] The calculated data on primary carbon production, secondary carbon production, primary fatty acid production, and secondary fatty acid production were compiled. The carbon energy transfer efficiency was calculated using the formula: Carbon Energy Transfer Efficiency = (Secondary Carbon Production ÷ Primary Carbon Production) × 100%. This efficiency reflects the proportion of energy transferred in quantity. Similarly, the fatty acid energy transfer efficiency was calculated using the formula: Fatty Acid Energy Transfer Efficiency = (Secondary Fatty Acid Production ÷ Primary Fatty Acid Production) × 100%. This efficiency reflects the proportion of energy transferred in quality. By combining the results of these two types of efficiencies with the actual conditions of the ecosystem, such as trophic level and species composition, the energy transfer efficiency of the aquatic ecosystem was obtained, comprehensively characterizing the effect of energy transfer between trophic levels.

[0103] Taking the carbon and fatty acid transport efficiency between phytoplankton and zooplankton in Taihu Lake as an example, a method for calculating the energy transport efficiency of an aquatic ecosystem based on the fatty acid composition of aquatic organisms includes the following steps:

[0104] Step 201: Field sampling and acquisition of biological components.

[0105] Field sampling was conducted in the target aquatic ecosystem. Phytoplankton samples for fatty acid analysis were collected using a 64 µm pore size plankton net. During sampling, the plankton net was placed at a water depth of 0.5 m and dragged along a zigzag pattern at a constant speed for 5 min. Collected samples were immediately transferred to 120 mL polypropylene sample vials, with five replicates at each sampling point. Zooplankton samples for fatty acid analysis were collected using a 112 µm pore size plankton net, with the same dragging method and number of replicates as the phytoplankton samples.

[0106] All samples used for fatty acid analysis were immediately placed in a portable freezer (−20°C) after collection and then transferred to the laboratory at −80°C as quickly as possible. Phytoplankton samples used for biomass determination were collected from surface water using a 1 L glass sampler, fixed on-site with 15 mL of Lugol's reagent, and stored in a light-protected, temperature-controlled freezer. Zooplankton samples used for biomass determination were collected in two categories: protozoan and rotifer samples were collected from 1 L of mixed surface water and fixed with 15 mL of Lugol's reagent; cladocerans and copepod samples were collected from 20 L of water, filtered through a 64 µm plankton net, and the retained material was stored in 100 mL sample vials. All samples used for biomass determination were stored in a light-protected, temperature-controlled freezer with ice packs and transferred to the laboratory for subsequent analysis as quickly as possible.

[0107] Step 202: Determination of fatty acid content.

[0108] All planktonic samples used for fatty acid analysis were lyophilized using a vacuum freeze dryer. After lyophilization, the samples were thoroughly homogenized using a glass rod. The dry weight of the samples used for lipid extraction was 25 mg. The lipid extraction and methyl esterification processes were described in [reference needed]. The extraction and methyl esterification processes were carried out under nitrogen protection and low temperature conditions.

[0109] Fatty acid methyl esters (FAMEs) were analyzed using a gas chromatograph (GC; Thermo Trace 1310) equipped with a flame ionization detector (FID, 250 °C). Helium was used as the carrier gas at a flow rate of 1 mL / min; the detector gases included hydrogen (35 mL / min), nitrogen (30 mL / min), and air (350 mL / min). The GC temperature program was as follows: initial temperature 100 °C, hold for 3 min; increase to 200 °C at 3 °C / min, hold for 3 min; then increase to 240 °C at 3 °C / min, hold for 6 min. The instrument was equipped with a programmable temperature injector and an autosampler. The separation of FAMEs was performed using a Supelco™ SP-2560 capillary chromatograph. Qualitative analysis of FAMEs was performed using a mixed standard of 37 FAME components (Supelco 47885-U) and a mixed standard of methyl bacillus phospholipids (Supelco 47080-U) as external standards. Quantitative analysis of FAMEs was conducted using a seven-point calibration curve based on standards of known concentrations. Fatty acid composition was expressed as fatty acid mass fraction (µg FAME / mgDW).

[0110] Step 203: Biomass and carbon content determination.

[0111] Phytoplankton samples used for biomass determination were allowed to stand for 48 h. The supernatant was carefully aspirated using a siphon, and the remaining sample was concentrated to 30 or 50 mL depending on the lake's nutrient level. After thorough mixing, 0.1 mL of the algal suspension was added to a plankton counting frame, and the samples were observed and counted under a microscope. Each sample was counted twice. Since the density of phytoplankton is approximately equal to that of water, its cell volume can be directly used for biomass estimation. Cell volume was calculated based on the morphological characteristics of each species by measuring the morphological parameters (such as length, width, height, or diameter) corresponding to the closest geometric shape. At least 50 individuals of each species were randomly selected for measurement, and the average value was taken. The cell volume was then calculated using the corresponding geometric formula. The average cell volume was multiplied by the number of individuals of that species per unit volume of water to obtain the biomass (mg / L) of that species. The total phytoplankton biomass was obtained by summing the biomass of all species.

[0112] Zooplankton were identified and counted according to taxa. For protozoa, 0.1 mL samples were placed in a counting frame, and the entire frame was counted at 200× magnification; for rotifers, 1 mL samples were placed in a counting frame, and the entire frame was counted at 100× magnification. Cladocera and copepods were diluted and placed in 5 mL counting frames, and counted in multiple fields of view. For unsegmented larvae, the entire sample was counted when the number of individuals was small; when the abundance was high, the sample was diluted, and the average was calculated from 3–5 replicates. All samples were thoroughly shaken before counting to avoid air bubbles and sample loss. For biomass estimation, protozoa and rotifers were converted using the volume method, assuming a specific gravity of 1; crustacean biomass was calculated based on the body length-body weight regression equation; and nauplius biomass was converted to a fixed value of 0.003 mg / individual.

[0113] Phytoplankton and zooplankton samples were freeze-dried using a vacuum freeze dryer, and then thoroughly ground until homogeneous using a glass rod. An appropriate amount of sample was weighed and placed in a tin cup, where it was subjected to high-temperature combustion in an elemental analyzer to convert the carbon in the sample into CO2. The carbon content (C%, i.e., the percentage of carbon per unit dry weight) of the sample was calculated by comparing the peak area of ​​the CO2 produced by the sample with the peak areas of 2–3 working standards with known carbon contents.

[0114] Step 204: Calculation of primary production volume.

[0115] The carbon production of phytoplankton is calculated by multiplying the biomass of each phytoplankton group by its corresponding carbon conversion factor. Specifically, the carbon conversion factors used are: 0.22 for cyanobacteria, 0.13 for dinoflagellates, 0.11 for diatoms, 0.16 for green algae, and 0.11 for all other phytoplankton groups. Subsequently, the carbon content of all taxa was summed at each sampling point to obtain carbon-based phytoplankton biomass.

[0116] Since primary productivity can be simply defined as the product of phytoplankton biomass and its growth rate, this invention uses this formula to estimate phytoplankton primary productivity. Previous studies have shown that in warm, eutrophic shallow lakes, the specific growth rate of phytoplankton is typically between 0.2 and 2 day⁻¹, with field measurements of approximately 1.0 ± 0.2 day⁻¹. .

[0117] The formula is as follows:

[0118] Where PP represents the estimated primary phytoplankton production (mg CL⁻¹·day⁻¹), B is the carbon-based phytoplankton biomass (mg CL⁻¹), and μ is the growth rate of the phytoplankton community, which is taken as μ=1 in this implementation case.

[0119] Phytoplankton fatty acid production (μg FAME L⁻¹·day⁻¹) is obtained by multiplying zooplankton carbon production (mg CL⁻¹·day⁻¹) by the fatty acid content per unit dry weight (μg FAME / mg DW) and dividing by the carbon content per unit dry weight (mg C / mg DW).

[0120] See Figure 2 In this case, the calculated primary production of phytoplankton was 0.22-1.38 mg L⁻¹·day⁻¹; the primary production of fatty acids from phytoplankton was 0.001-0.033 μg L⁻¹·day⁻¹.

[0121] Step 205: Calculation of secondary production volume.

[0122] Based on zooplankton biomass data and production parameters, their carbon production (SP) is calculated. Zooplankton carbon production is calculated using an empirical formula for productivity: SP=10 (−0.23log(M)−0.73) ×1.12MN

[0123] Where SP represents secondary production (mg L⁻¹·day⁻¹), M is the average dry weight per individual (mg), and N is abundance (individuals L⁻¹). To convert secondary production from dry weight units to carbon content, SP is further multiplied by 1 / 2.3, which represents an empirical factor for converting dry weight to carbon content.

[0124] Zooplankton fatty acid production (μg FAME L⁻¹·day⁻¹) is obtained by multiplying zooplankton carbon production (mg CL⁻¹·day⁻¹) by the fatty acid content per unit dry weight (μg FAME / mg DW) and dividing by the carbon content per unit dry weight (mg C / mg DW).

[0125] See Figure 3 In this case, the calculated zooplankton secondary production was 0.01-0.14 mg L⁻¹·day⁻¹; the zooplankton fatty acid secondary production was 0.0001-0.0036 μg L⁻¹·day⁻¹.

[0126] Step 206: Calculation of energy transfer efficiency.

[0127] Energy transfer efficiency (TTE) of aquatic ecosystems is calculated based on primary and secondary production. TTE is defined as the ratio of secondary consumer production to primary producer production, and its calculation formula is as follows: TTE C =Secondary production volume / Primary production volume × 100%

[0128] Energy transfer efficiency of aquatic ecosystems is calculated based on primary and secondary fatty acid production. (TTE) ω3 Defined as the ratio of fatty acid production by secondary consumers to fatty acid production by primary producers, its calculation formula is as follows: TTE ω3 =Secondary fatty acid production / Primary fatty acid production × 100%

[0129] The TTE obtained in this way can comprehensively reflect the efficiency of energy quantity and food quality transfer between trophic levels.

[0130] See Figure 4 In this case, the carbon energy transfer efficiency (TTE) in Taihu Lake is... C The average value is 11.80%; the energy transfer efficiency (TTE) of ω3 LC-PUFA is... ω3 The average value was 20.38%; TTE ω3 Significantly higher than TTE C (20.38% vs 11.80%).

[0131] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0132] The above embodiments are merely illustrative of the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made based on the essence of the content of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for calculating the energy transfer efficiency of aquatic ecosystems based on the fatty acid composition of aquatic organisms, characterized in that, Including the following steps: Conduct field sampling in the target aquatic ecosystem to obtain biological components; The fatty acid content of the biological components was determined to obtain the fatty acid content per unit dry weight. The biomass and carbon content of the biological components were determined to obtain biomass data and carbon content per unit dry weight. Based on the biomass data and carbon conversion factor, primary carbon production is calculated, and primary fatty acid production is obtained using the primary carbon production, fatty acid content per unit dry weight, and carbon content per unit dry weight. Based on the zooplankton biomass data and production parameters in the biomass data, the secondary carbon production is calculated, and the secondary fatty acid production is obtained using the secondary carbon production, fatty acid content per unit dry weight, and carbon content per unit dry weight. The energy transfer efficiency of the aquatic ecosystem is obtained by using the ratio of primary carbon production to secondary carbon production and the ratio of primary fatty acid production to secondary fatty acid production.

2. The method according to claim 1, characterized in that, The steps involved in conducting field sampling are as follows: Phytoplankton and zooplankton samples for fatty acid analysis were collected using planktonic nets with different pore sizes. The samples were trawled along a preset trajectory and for a set duration, and parallel samples were set up. Phytoplankton and zooplankton samples were collected using a glass water sampler for biomass determination, and fixatives were added to the biomass determination samples on-site. Fatty acid analysis samples were stored in a low-temperature environment, and biomass determination samples were stored in a refrigerated, light-protected environment and quickly transported to the laboratory for use.

3. The method according to claim 1, characterized in that, The determination of the fatty acid content includes the following steps: The fatty acid analysis samples of the biological components were freeze-dried, ground and homogenized, and then quantitative samples were taken. Lipid extraction and methyl esterification of the quantitative sample were performed under nitrogen protection and low temperature conditions to obtain fatty acid methyl esters. The fatty acid methyl esters were analyzed using a gas chromatograph equipped with a flame ionization detector. Qualitative analysis was performed using mixed standards, and quantitative analysis was performed based on a calibration curve to obtain the fatty acid content per unit dry weight.

4. The method according to claim 1, characterized in that, The determination of the biomass includes the following steps: Phytoplankton samples used for biomass determination were concentrated after standing. A quantitative suspension was placed in a plankton counting frame, and species morphological parameters were counted and measured under a microscope. Cell volume was calculated, and the biomass of each species was obtained by combining the number of individuals per unit volume of water. The total biomass of phytoplankton was obtained by summing the results. Zooplankton samples used for biomass determination were identified and counted according to taxonomic groups, and zooplankton biomass data were obtained by using the volume method, body length-weight regression equation, or fixed value conversion.

5. The method according to claim 1, characterized in that, The determination of the carbon content includes the following steps: The biological components were freeze-dried and ground, and a quantitative sample was weighed and placed in a tin cup. The sample was then burned at high temperature in an elemental analyzer to convert carbon into carbon dioxide. The carbon content per unit dry weight is calculated by comparing the peak area of ​​a working standard substance with a known carbon content with the peak area of ​​carbon dioxide produced by the sample.

6. The method according to claim 1, characterized in that, Calculating the primary carbon production includes the following steps: The biomass of each type of phytoplankton community is multiplied by the corresponding carbon conversion coefficient, and the sum is obtained to obtain the carbon-based phytoplankton biomass. Then, it is multiplied by the phytoplankton community growth rate to obtain the primary carbon production. When calculating the production of primary fatty acids, the production of primary carbon is multiplied by the fatty acid content per unit dry weight, and then divided by the carbon content per unit dry weight to obtain the production of primary fatty acids.

7. The method according to claim 1, characterized in that, Calculating the secondary carbon production includes the following steps: The secondary dry weight production was calculated by substituting the average dry weight and abundance of zooplankton into the empirical formula for productivity, and then multiplied by the conversion factor from dry weight to carbon content to obtain the secondary carbon production. When calculating the production of secondary fatty acids, the production of secondary carbon is multiplied by the fatty acid content per unit dry weight, and then divided by the carbon content per unit dry weight to obtain the production of secondary fatty acids.

8. The method according to claim 1, characterized in that, Calculating the energy transfer efficiency includes the following steps: The carbon energy transfer efficiency is obtained by multiplying the ratio of secondary carbon production to primary carbon production by a percentage. The ratio of secondary fatty acid production to primary fatty acid production is multiplied by a percentage to obtain the fatty acid energy transfer efficiency. The energy flow process of the aquatic ecosystem is evaluated by combining the carbon energy transfer efficiency and the fatty acid energy transfer efficiency.

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