Water area hydro-fluctuation belt nitrogen release flux prediction method based on remote sensing data

Abstract

The invention provides a water area hydro-fluctuation belt nitrogen release flux prediction method based on remote sensing data. The water area hydro-fluctuation belt nitrogen release flux prediction method comprises the steps of obtaining long-sequence remote sensing image data, water area water level data, water quality monitoring data and land utilization data of a water area hydro-fluctuation belt area of a target water area; based on the long-sequence remote sensing image data, the water area water level data, the water quality monitoring data and the land utilization data, determining a water area hydro-fluctuation belt range, water area submerging characteristics in each period, land utilization type distribution and a concentration gradient of sediment pore water and overlying water; according to the submerging characteristics, the distribution of the different land utilization types and the concentration gradient, establishing a water area hydro-fluctuation belt sediment-water interface nitrogen diffusion flux calculation model; and calculating the total nitrogen exchange flux of the water area hydro-fluctuation zone based on the sediment-water interface nitrogen diffusion flux calculation model. The method provides a scientific basis for water quality management and pollution control of the reservoir water source, and has the advantage of combining macroscopic monitoring and fine analysis.

Description

Technical Field

[0001] This invention belongs to the field of water environment assessment, remote sensing and water quality simulation technology, and specifically relates to a method for predicting nitrogen release flux in the drawdown zone of water bodies based on remote sensing data. Background Technology

[0002] The drawdown zone is the area of ​​a water body that is periodically submerged and exposed due to seasonal water level fluctuations; it is the transition zone between aquatic and terrestrial ecosystems. In water bodies such as reservoirs and lakes, the alternating wet and dry periods of the drawdown zone significantly impact their ecological functions and nutrient cycles. Particularly for reservoir water sources, pollutants such as pesticides and fertilizers remaining from historical land use types (e.g., farmland and residential areas before submersion) in the drawdown zone may be released into the water body when the water level rises and the area is submerged, posing a threat to water quality safety.

[0003] Nitrogen is a key factor in eutrophication, and drawdown zone sediments serve as important nitrogen reservoirs. Understanding the nitrogen exchange flux between drawdown zone sediments and overlying water is crucial for assessing the impact of drawdown zones on water quality, predicting eutrophication risks, and developing effective pollution control measures. However, traditional monitoring methods are typically point- or cross-sectional, making it difficult to comprehensively capture the overall nitrogen exchange in drawdown zones as large areas, and also challenging to quantify the contribution of different land use types to nitrogen exchange.

[0004] While existing research has begun to focus on pollution release from drawdown zones, it lacks an effective method that combines remote sensing macroscopic monitoring capabilities with refined process models to quantitatively predict nitrogen exchange fluxes over long time series in large drawdown zones and differentiate the roles of different land use types. Therefore, there is an urgent need for a method that can utilize spatial information obtained through remote sensing technology, combined with necessary field monitoring data and physicochemical models, to achieve macroscopic and quantitative prediction and assessment of nitrogen exchange fluxes in water drawdown zones. Summary of the Invention

[0005] The purpose of this invention is to provide a method for predicting nitrogen release flux in the water drawdown zone based on remote sensing data. This method can comprehensively utilize remote sensing image information and diffusion flux models to quantitatively predict nitrogen exchange flux between sediments and water bodies of different land use types in the water drawdown zone, thereby providing a scientific basis for water source protection and water quality management.

[0006] The technical solution of the present invention is as follows:

[0007] A method for predicting nitrogen release flux in the water drawdown zone based on remote sensing data, the method comprising:

[0008] Acquire long-sequence remote sensing image data, water level data, water quality monitoring data, and land use data of the water drawdown zone area of ​​the target water area;

[0009] Based on the aforementioned long-sequence remote sensing image data, water level data, water quality monitoring data, and land use data, the range of water level drawdown zone, water inundation characteristics at different periods, distribution of land use types, and concentration gradient of sediment pore water and overlying water were determined.

[0010] Based on the inundation characteristics, the distribution of different land use types, and the concentration gradient, a calculation model for nitrogen diffusion flux at the sediment-water interface in the water drawdown zone is established.

[0011] The total nitrogen exchange flux in the drawdown zone of the water body is calculated based on the nitrogen diffusion flux calculation model at the sediment-water interface.

[0012] Furthermore, the determination of the water level drawdown zone and the characteristics of water inundation in different periods specifically includes:

[0013] Based on the long sequence of remote sensing image data, the water body index method was used to extract the water inundation range at different times.

[0014] Based on the water inundation range at different periods, the range of the water level drawdown zone is determined by overlay analysis.

[0015] Based on the water inundation range at different times, the water inundation frequency of each pixel or region within the water level drawdown zone is calculated, and the duration of different inundation states is statistically analyzed based on the water level data.

[0016] Furthermore, the calculation of the water inundation frequency of each pixel or region within the water level drawdown zone is specifically as follows:

[0017] The water inundation frequency of each pixel or region within the drawdown zone is calculated based on a long sequence of water inundation range layers.

[0018] Furthermore, the specific distribution of land use types is determined as follows:

[0019] Spatial overlay analysis of the water level drawdown zone and the land use data is performed to obtain land use data within the drawdown zone, and the distribution area of ​​various land use types within the drawdown zone is statistically analyzed.

[0020] Furthermore, the concentration gradient between sediment pore water and overlying water was determined as follows:

[0021] Based on the water quality monitoring data, the concentration of pore water in the sediment and the nitrogen concentration in the overlying water are obtained. The concentration difference between the pore water concentration in the sediment and the nitrogen concentration in the overlying water is calculated. The concentration gradient between the pore water in the sediment and the overlying water is determined by dividing the concentration difference by the vertical distance between the sampling points.

[0022] Furthermore, the nitrogen diffusion flux calculation model at the sediment-water interface is based on Fick's law and is used to calculate the nitrogen diffusion flux per unit area and per unit time. The formula is as follows:

[0023]

[0024] In the formula: dC / dx represents the porosity of surface sediments for land use type i; dC / dx represents the concentration gradient between overlying water and sediments; D i,j Let be the nitrogen flux diffusion coefficient from sediments to water bodies for land use type i in period j.

[0025] Furthermore, the total nitrogen exchange flux in the drawdown zone of the water body is calculated specifically based on the sediment-water interface nitrogen diffusion flux calculation model as follows:

[0026] Based on the sediment-water interface nitrogen diffusion flux calculation model, the sediment-water interface nitrogen diffusion flux of different land use types in the water drawdown zone area at different times is calculated.

[0027] Based on the nitrogen diffusion flux at the sediment-water interface for different land use types at different times, and their corresponding land use areas and inundation durations, the total nitrogen exchange flux in the water drawdown zone is calculated.

[0028] Furthermore, the formula for calculating the total nitrogen exchange flux is as follows:

[0029]

[0030] In the formula, W is the nitrogen transport flux in the drawdown zone; F i Let A be the diffusion flux at the sediment-water interface for land use type i; i Δt represents the area of ​​the i-th land use type in the drawdown zone; Δt represents the duration of the inundation or drying period; and n represents the number of land use types used in the calculation.

[0031] Compared with the prior art, the present invention has the following advantages:

[0032] This invention provides a method for predicting nitrogen release flux in the drawdown zone of water bodies based on remote sensing data. This method comprehensively utilizes the spatiotemporal information of remote sensing imagery, water quality monitoring data, and a diffusion flux calculation model based on Fick's law. It can accurately define and analyze the extent, inundation characteristics, and distribution of different land use types within large-area drawdown zones, providing macroscopic spatial information. It quantitatively calculates the diffusion flux of different forms of nitrogen at the sediment-water interface in the drawdown zone, revealing their absorption and release patterns. It distinguishes the contributions of different land use types (such as cultivated land, forest and grassland, and construction land) to nitrogen exchange, helping to identify major pollution source areas. It predicts the total nitrogen exchange flux in the entire drawdown zone during specific periods (such as the flood season and the dry season), providing important parameters for nitrogen budgeting and water quality prediction in reservoir water sources. The method is operable and can be implemented using existing remote sensing and monitoring data, providing a scientific basis and technical support for regional-scale nitrogen management in drawdown zones. Attached Figure Description

[0033] The accompanying drawings illustrate various embodiments generally by way of example rather than limitation, and are used, together with the specification and claims, to explain embodiments of the invention. Where appropriate, the same reference numerals are used in all drawings to refer to the same or similar parts. Such embodiments are illustrative and are not intended to be exhaustive or exclusive embodiments of the apparatus or method.

[0034] Figure 1 A schematic diagram of the method flow of the present invention is shown;

[0035] Figure 2 A schematic diagram of the inundation range of different water level elevations in the water area drawdown zone according to the present invention is shown. Detailed Implementation

[0036] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0037] like Figures 1-2 As shown, this embodiment of the invention provides a method for predicting nitrogen release flux in the water drawdown zone based on remote sensing data, including the following steps:

[0038] Step 100: Acquire long-sequence remote sensing image data of the water level drawdown zone of the target water area, as well as water level data, water quality monitoring data, and land use data of the drawdown zone.

[0039] The remote sensing image data should have sufficient temporal and spatial resolution to capture inundation changes caused by water level fluctuations, such as Landsat TM / ETM+ / OLI series images. The long-sequence data is used to analyze the inundation characteristics of the drawdown zone over multiple years.

[0040] The water level data reflects the actual water level changes of the water body and is used in conjunction with remote sensing imagery to determine the inundation range at a specific water level and to statistically analyze the duration of different water level states.

[0041] The water quality monitoring data includes nitrogen concentration data in sediment pore water and overlying water collected in or near the drawdown zone of the target water area. This data is typically obtained through field sampling and laboratory analysis to determine the concentration gradient at the sediment-water interface.

[0042] The land use data of the drawdown zone reflects the land cover type of the area before it was submerged, such as cultivated land, forest land, grassland, construction land, and unused land. This data can be obtained by interpreting historical remote sensing imagery or using existing land use datasets.

[0043] Step 200: Based on the long sequence of remote sensing image data and water level data, define the range of the water level drawdown zone and determine the inundation range and characteristics of the water level drawdown zone at different times.

[0044] First, select representative remote sensing images from different water level periods. Then, use water body index methods, such as the modified Normalized Water Body Index (MNDWI), to extract the inundation extent for each period. The MNDWI calculation formula is:

[0045]

[0046] In the formula, R Green R MIR These are the reflectance values ​​for the green light band and the mid-infrared band, respectively.

[0047] By setting a threshold (such as 0 to 0.2), the image is divided into water and non-water areas.

[0048] Then, the layers of water inundation extent from different periods were overlaid and analyzed to determine all areas that experienced alternating wet and dry periods during the study period, which constitutes the extent of the water level drawdown zone (see [reference]). Figure 2 ).

[0049] Furthermore, based on a long sequence of water inundation range layers, the water inundation frequency (WIF) of each pixel or region within the drawdown zone is calculated. The WIF calculation formula is:

[0050]

[0051] In the formula, N is the number of water body image layers available within the observation period, and w is a binary variable (w=1 for water body, w=0 for non-water body).

[0052] Step 300: Based on the range of the water level drawdown zone and the land use data, determine the distribution of different land use types within the water level drawdown zone area.

[0053] The obtained drawdown zone extent layer and the drawdown zone land use data layer are spatially overlaid for analysis (see [link]). Figure 2 Land use data within the drawdown zone was extracted, and the distribution area of ​​each land use type within the drawdown zone was statistically analyzed (A). i This area information will be used in subsequent calculations of total nitrogen exchange flux.

[0054] Step 400: Based on the water quality monitoring data, determine the concentration gradient between sediment pore water and overlying water within the drawdown zone of the water body.

[0055] Nitrogen diffusion at the sediment-water interface is driven by a concentration gradient. Using nitrogen concentration monitoring data from sediment pore water (near the interface surface) and overlying water (bottom water immediately adjacent to the interface) collected in-situ, the concentration difference at different locations and time periods was calculated. Dividing the concentration difference by the vertical distance (Δx) between sampling points yields the concentration gradient dC / dx. Specifically, dC / dx = (C... 沉积物 -C 上覆水 ) / Δx, where Csediment is the nitrogen concentration in the sediment pore water, Coverlying water is the nitrogen concentration in the overlying water body, and Δx is the nitrogen concentration measured by Csediment. 沉积物 and C 上覆水 The vertical distance between them. These monitoring efforts should cover different land use types and different hydrological periods (such as flooding and drying periods) to obtain representative concentration gradient data.

[0056] Step 500: Based on the inundation characteristics, the distribution of different land use types, and the concentration gradient, establish and parameterize a calculation model for nitrogen diffusion flux at the sediment-water interface in the water drawdown zone.

[0057] The model is based on Fick's law and is used to calculate the nitrogen diffusion flux F per unit area per unit time. i The basic formula is:

[0058]

[0059] In the formula: F i Nitrogen diffusion flux at the sediment-water interface for land use type i during period j (e.g., a specific flooding or drying period); The porosity of surface sediments for land use type i can be determined through literature review, laboratory measurements, or correlation with soil type; D i,j represents the nitrogen diffusion coefficient from sediment to water for land use type i at time j, which can be determined experimentally or through literature, and its value is related to factors such as temperature, sediment type, and water disturbance; dC / dx is the concentration gradient between overlying water and sediment determined in step 400. Appropriate model parameters need to be determined for different land use types and different hydrological periods (flooding / drying).

[0060] Step 600: Based on the sediment-water interface nitrogen diffusion flux calculation model, calculate the sediment-water interface nitrogen diffusion flux of different land use types in the water drawdown zone at different times.

[0061] The land use type determined in step 300, the inundation characteristics (time period j) determined in step 200, and the corresponding parameters determined in steps 400 and 500 are combined. Input model. For each land use type (i = 1, ..., n) within the drawdown zone, calculate the nitrogen diffusion flux F during different representative periods j (e.g., specific flooding and drying periods). i Flux F i The positive or negative sign indicates the direction of diffusion. A positive value usually indicates that nitrogen is released from sediments into the water, while a negative value indicates that nitrogen is absorbed from the water into sediments. The nitrogen may include different forms such as total nitrogen, ammonia nitrogen, nitrite nitrogen, and nitrate nitrogen, which are calculated separately.

[0062] Step 700: Based on the nitrogen diffusion flux at the sediment-water interface for the different land use types at different times, and their corresponding land use areas and inundation durations, calculate the total nitrogen exchange flux in the water drawdown zone area.

[0063] The diffusion flux F per unit area of ​​different land use types (i) calculated in step 600 within a specific period (j) i Multiply by the area A of that land use type within the drawdown zone. i (Step 300 is determined), then multiply by the duration Δt of that specific period (step 200 is determined), and then sum over all land use types and all periods that need to be considered to obtain the total nitrogen exchange flux W of the entire water drawdown zone during the study period. The formula for calculating the total nitrogen exchange flux W is:

[0064]

[0065] In the formula, F i A represents the nitrogen diffusion flux at the sediment-water interface for the i-th land use type within the water drawdown zone during the corresponding period; iLet be the area of ​​the i-th land use type; Δt be the duration of the corresponding period; and n be the number of land use types used for calculation. The corresponding period can be subdivided into multiple time periods (e.g., by month or by season), and the inundation duration Δt of each time period is determined based on actual water level fluctuations, and then accumulated. Typically, the total flux during the flood season and the dry season are calculated separately, and then the overall trend is analyzed.

[0066] After obtaining the total nitrogen exchange flux, the calculation results can be further analyzed. For example, the contributions of different land use types can be compared, the differences in flux during flooding and drying periods can be analyzed, the overall absorption or release trends can be assessed, and the main nitrogen forms and their migration directions can be determined. These analytical results can be used to identify major pollution source areas, predict future water quality change trends, and provide a scientific basis for developing targeted water environment management and pollution control measures.

[0067] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the technical scope disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for predicting nitrogen release flux in water-level-fluctuating zone based on remote sensing data, characterized in that, The method comprises: obtaining long-sequence remote sensing image data, water level data, water quality monitoring data and land use data of a water area drawdown zone of a target water area; based on the long-sequence remote sensing image data, water level data, water quality monitoring data and land use data, determining the water area drawdown zone range, water area flooding characteristics in each period, land use type distribution and concentration gradient of sediment pore water and overlying water body; according to the flooding characteristics, the distribution of different land use types and the concentration gradient, establishing a sediment-water interface nitrogen diffusion flux calculation model of the water area drawdown zone; based on the sediment-water interface nitrogen diffusion flux calculation model, calculating the total nitrogen exchange flux of the water area drawdown zone.

2. The method of claim 1, wherein, The determination of the water area drawdown zone range, the water area flooding characteristics in each period is specifically: based on the long-sequence remote sensing image data, the water body index method is used to extract the water body flooding range in different periods; based on the water body flooding range in different periods, the water area drawdown zone range is determined through superposition analysis; based on the water body flooding range in different periods, the water body flooding frequency of each pixel or region in the water area drawdown zone is calculated, and the duration of different flooding states is counted according to the water level data.

3. The method of claim 2, wherein, The calculation of the water body flooding frequency of each pixel or region in the water area drawdown zone is specifically: based on the long-sequence water body flooding range layer, the water body flooding frequency of each pixel or region in the drawdown zone is calculated.

4. The method of claim 1, wherein, The determination of the land use type distribution is specifically: spatial superposition analysis is performed on the water area drawdown zone range and the land use data to obtain the land use data in the drawdown zone range, and the distribution area of each type of land use type in the drawdown zone range is counted.

5. The method of claim 1, wherein, The determination of the concentration gradient of sediment pore water and overlying water body is specifically: based on the water quality monitoring data, the concentration of sediment pore water and the nitrogen concentration of overlying water body are obtained, the concentration difference between the concentration of sediment pore water and the nitrogen concentration of overlying water body is calculated, and the concentration gradient of sediment pore water and overlying water body is determined by dividing the concentration difference by the vertical distance between sampling points.

6. The method of claim 1, wherein, The sediment-water interface nitrogen diffusion flux calculation model is based on Fick's law and is used to calculate the nitrogen diffusion flux per unit area per unit time, and the formula is: wherein: is the porosity of the surface sediment of the i-th land use type; dC / dx is the concentration gradient of the overlying water and the sediment; D i,j is the nitrogen flux diffusion coefficient of the sediment to the water body of the i-th land use type at the j-th period.

7. The method of claim 1, wherein, based on the sediment-water interface nitrogen diffusion flux calculation model, the total nitrogen exchange flux of the water area drawdown zone is calculated specifically: based on the sediment-water interface nitrogen diffusion flux calculation model, the sediment-water interface nitrogen diffusion flux of different land use types in the water area drawdown zone in different periods is calculated; based on the sediment-water interface nitrogen diffusion flux of different land use types in different periods, the corresponding land use area and flooding duration, the total nitrogen exchange flux of the water area drawdown zone is calculated.

8. The method of claim 7, wherein, The formula for calculating the total nitrogen exchange flux is: wherein, W is the nitrogen transport flux of the drawdown zone. F i Dif is the diffusion flux of the sediment-water interface for the i-th land use type; A i At is the length of the flood period or the dry period; n is the number of land use types used for the calculation.

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