A method for determining the hydrological path and source contribution of agricultural non-point source pollution in a watershed

Abstract

The present invention relates to a method for determining the hydrological path and source contribution of agricultural non-point source pollution in a watershed, and relates to the field of water pollution. The method comprises: determining water quality indicators and isotope indicators of a watershed to be tested; the water quality indicators include nitrate nitrogen; the isotope indicators are hydrogen and oxygen isotopes of water samples and nitrogen and oxygen isotopes of nitrate nitrogen; qualitatively identifying the hydraulic connectivity between groundwater and river runoff in the watershed to be tested, and determining the contribution of surface runoff and base flow to river runoff in different hydrological paths in the watershed to be tested based on hydrogen and oxygen isotope indicators; determining the contribution of nitrate nitrogen to the nitrate nitrogen load at the outlet of the watershed to be tested under different hydrological paths in the watershed to be tested; and determining the nitrate nitrogen load corresponding to each agricultural pollution source under different hydrological paths in the watershed to be tested based on a Bayesian mixed model and nitrogen and oxygen isotope flavors of nitrate nitrogen. The present invention determines the contribution of each agricultural pollution source to nitrate nitrogen in river runoff under different hydrological paths, and provides a more accurate basis for the prevention and control of agricultural non-point source pollution in the watershed.

Description

Technical Field

[0001] The present invention relates to the technical field of water pollution, and in particular to a method for determining the hydrological path and source contribution of agricultural non-point source pollution in a river basin. Background Art

[0002] Agricultural non-point source pollution is one of the sources of nitrogen in the water bodies of the basin. It has many sources, complex migration paths and is difficult to control. Therefore, identifying the hydrological paths of agricultural non-point source pollution in the basin entering the target water bodies of the basin and the contribution of various agricultural sources (such as livestock and poultry manure, fertilizers, etc.) under different hydrological paths has always been the focus of attention in the field of agricultural non-point source pollution prevention and control in the basin, and is also the basis for achieving precise prevention and control of agricultural non-point source pollution. Agricultural non-point source pollutants in the basin enter the surface water bodies through hydrological paths such as base flow and surface runoff. How to determine the characteristics of the main hydrological processes in the basin through the hydraulic connectivity of precipitation, surface water and groundwater, and on this basis calculate the contribution ratio of different hydrological paths to the nitrogen output of the basin, as well as the contribution ratio of agricultural sources under different hydrological paths, is a key technology that urgently needs to be broken through in the efficient prevention and control of agricultural non-point source pollution in the basin. Summary of the invention

[0003] The purpose of the present invention is to provide a method for determining the hydrological path and source contribution of agricultural non-point source pollution in a watershed, determine the contribution of nitrate nitrogen in the target water body corresponding to each agricultural pollution source under different hydrological paths, and provide a more accurate basis for the prevention and control of agricultural non-point source pollution in the watershed.

[0004] To achieve the above object, the present invention provides the following solutions:

[0005] A method for determining the hydrological path and source contribution of agricultural non-point source pollution in a watershed, comprising:

[0006] Determine the water quality index and isotope index of the watershed to be tested; the water quality index includes nitrate nitrogen; the isotope index is the hydrogen and oxygen isotopes and nitrate nitrogen and oxygen isotopes of the water sample;

[0007] Identify the hydraulic connectivity between groundwater and river runoff in the measured basin, and determine the contribution of surface runoff and base flow of different hydrological paths in the measured basin to river runoff based on the hydrogen and oxygen isotopes and digital filtering technology;

[0008] Determining the contribution of nitrate nitrogen under different hydrological paths in the measured watershed to the nitrate nitrogen load at the outlet of the measured watershed;

[0009] Based on the Bayesian mixed model and nitrate nitrogen and oxygen isotopes, the contribution of various agricultural pollution sources to the nitrate nitrogen load of river runoff under different hydrological paths in the measured basin was determined.

[0010] Optionally, the identifying the hydraulic connectivity between groundwater and river runoff in the measured watershed specifically includes:

[0011] Determine the atmospheric precipitation line of the basin to be measured based on the spatial precipitation, river runoff and hydrogen and oxygen isotope indicators of groundwater in the basin to be measured;

[0012] If the degree of overlap between the hydrogen and oxygen isotope scatter diagram of the river runoff in the measured basin and the hydrogen and oxygen isotope scatter diagram of the groundwater in the measured basin is greater than the set overlap value, and the overlapping position of the hydrogen and oxygen isotope scatter diagram of the river runoff in the measured basin and the hydrogen and oxygen isotope scatter diagram of the groundwater in the measured basin is on the atmospheric precipitation line, then the groundwater and the river runoff are strongly hydraulically connected; otherwise, the groundwater and the river runoff are weakly hydraulically connected.

[0013] Optionally, based on the hydrogen and oxygen isotopes and digital filtering technology, determining the contribution of surface runoff and base flow of different hydrological paths in the measured basin to river runoff specifically includes:

[0014] From the perspective of the outlet of the measured basin, the contribution rate of surface runoff to river runoff and the contribution rate of base flow to river runoff are determined by digital filtering technology, which are recorded as the first surface runoff contribution rate and the first base flow contribution rate respectively;

[0015] From the spatial perspective of the watershed to be measured, the double-endmember mixing model of hydrogen and oxygen isotopes is used to determine the contribution rate of surface runoff to river runoff and the contribution rate of base flow to river runoff, which are recorded as the second surface runoff contribution rate and the second base flow contribution rate respectively;

[0016] When the difference between the second surface runoff contribution rate and the first surface runoff contribution rate is less than the set first difference, and the difference between the second base flow contribution rate and the first base flow contribution rate is less than the set second difference, the first surface runoff contribution rate is used as the contribution rate of surface runoff to river runoff, and the first base flow contribution rate is used as the contribution rate of base flow to river runoff.

[0017] Optionally, the determining the contribution of nitrate nitrogen under different hydrological paths in the measured watershed to the nitrate nitrogen load at the outlet of the measured watershed specifically includes:

[0018] From the perspective of the outlet of the watershed to be measured, the water quality index and the hydrological index are used to determine the nitrate nitrogen load at the outlet of the watershed to be measured; the hydrological index is flow rate;

[0019] From the perspective of the outlet of the measured basin, the baseflow nitrate nitrogen load at the outlet of the measured basin and the contribution of the baseflow nitrate nitrogen load to the nitrate nitrogen load in the river runoff at the outlet of the measured basin are determined according to the nitrate nitrogen load at the outlet of the measured basin.

[0020] Optionally, the agricultural pollution sources include fertilizers, soil organic nitrogen, manure and sewage.

[0021] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0022] The present invention discloses a method for determining the hydrological path and source contribution of agricultural non-point source pollution in a watershed. The method determines different hydrological paths in the watershed to be tested by qualitatively identifying the hydraulic connectivity between groundwater and river runoff in the watershed to be tested. The method determines the nitrate nitrogen load corresponding to each agricultural pollution source under different hydrological paths in the watershed to be tested based on a Bayesian mixed model and nitrate nitrogen and nitrogen oxygen isotopes, thereby providing a more accurate basis for the prevention and control of agricultural non-point source pollution in the watershed. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0024] Figure 1 A schematic flow chart of a method for determining the hydrological path and source contribution of agricultural non-point source pollution in a watershed according to the present invention;

[0025] Figure 2 This is a schematic diagram of the structure of a system for determining the hydrological path and source contribution of watershed agricultural non-point source pollution according to the present invention. DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] The purpose of the present invention is to provide a method for determining the hydrological path and source contribution of agricultural non-point source pollution in a watershed, determine the contribution of various agricultural pollution sources to nitrate nitrogen in river runoff under different hydrological paths, and provide a more accurate basis for the prevention and control of agricultural non-point source pollution in the watershed.

[0028] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0029] Figure 1 The figure is a flow chart of a method for determining the hydrological path and source contribution of agricultural non-point source pollution in a watershed according to the present invention. Figure 1 As shown, a method for determining the hydrological path and source contribution of agricultural non-point source pollution in a watershed includes:

[0030] Step 101: Determine the water quality index and isotope index of the watershed to be tested; the water quality index includes nitrate nitrogen; the isotope index is the hydrogen and oxygen isotopes of the water sample and the nitrate nitrogen and oxygen isotopes (NO3 - -N nitrogen and oxygen isotopes).

[0031] Wherein, step 101 specifically includes:

[0032] First, flow and water quality are monitored simultaneously at the outlet of the watershed to be tested, where runoff flow is obtained from the local hydrological department. Secondly, river water and groundwater samples are collected along the river direction to test their water quality indicators and isotope indicators; then, rainwater from precipitation events throughout the year is collected for the basin precipitation to test its isotope indicators; finally, in order to reduce the uncertainty of nitrogen and oxygen isotope traceability technology, potential agricultural nitrogen sources and non-agricultural nitrogen sources in the basin are sampled and their isotope indicators are measured. Among them, non-agricultural nitrogen sources refer to atmospheric precipitation (AP); agricultural nitrogen sources include chemical fertilizers (CF), soil organic nitrogen (SON), feces and sewage (M&S). When laying out specific sampling points, factors such as land use type, river confluence, and human activity impact should be considered. The sampling frequency is once a month (except for rainwater sample collection), and the sampling time is at least one complete hydrological year. Water quality indicators include nitrate nitrogen (NO3 - -N); isotope indicators include NO3 - -N nitrogen and oxygen isotopes (δ 15 N-NO3 and δ 18 O-NO3) values ​​and water sample hydrogen and oxygen isotopes (δD-H2O and δ 18 O-H2O) value.

[0033] Step 102: Qualitatively identify the hydraulic connectivity between groundwater and river runoff in the measured basin, and determine the contribution of surface runoff and base flow in different hydrological paths to river runoff in the measured basin based on the hydrogen and oxygen isotopes of the water samples and digital filtering technology, where the contribution includes contribution rate (percentage) and contribution amount.

[0034] Wherein, step 102 specifically includes:

[0035] The atmospheric precipitation line of the basin to be measured is determined based on the spatial precipitation, river runoff and hydrogen and oxygen isotope indicators of groundwater in the basin to be measured.

[0036] If the degree of overlap between the hydrogen and oxygen isotope scatter diagram of the river runoff in the measured basin and the hydrogen and oxygen isotope scatter diagram of the groundwater in the measured basin is greater than the set overlap value, and the overlapping position of the hydrogen and oxygen isotope scatter diagram of the river runoff in the measured basin and the hydrogen and oxygen isotope scatter diagram of the groundwater in the measured basin is on the atmospheric precipitation line, then the groundwater and the river runoff are strongly hydraulically connected; otherwise, the groundwater and the river runoff are weakly hydraulically connected.

[0037] From the perspective of the outlet of the measured basin, the contribution rate of surface runoff to river runoff and the contribution rate of base flow to river runoff are determined by digital filtering technology, which are recorded as the first surface runoff contribution rate and the first base flow contribution rate respectively;

[0038] From the spatial perspective of the watershed to be measured, the double-endmember mixing model of hydrogen and oxygen isotopes is used to determine the contribution rate of surface runoff to river runoff and the contribution rate of base flow to river runoff, which are recorded as the second surface runoff contribution rate and the second base flow contribution rate respectively;

[0039] When the difference between the second surface runoff contribution rate and the first surface runoff contribution rate is less than the set first difference, and the difference between the second base flow contribution rate and the first base flow contribution rate is less than the set second difference, the first surface runoff contribution rate is used as the contribution rate of surface runoff to river runoff, and the first base flow contribution rate is used as the contribution rate of base flow to river runoff.

[0040] As a specific embodiment, the hydrological path analysis process in the watershed to be tested includes:

[0041] 1) Qualitative identification of hydraulic connectivity of different water bodies within a basin

[0042] Based on the hydrogen and oxygen isotopes (δD and δ 18 O) composition characteristics, and determine the atmospheric precipitation line in the basin. Then, based on the river runoff and groundwater hydrogen and oxygen isotopes (δD and δ 18 O) The overlap of the scatter plot and its relative position to the atmospheric precipitation line can qualitatively identify the hydraulic connectivity between groundwater and river runoff.

[0043] 2) Quantitative analysis of the contribution of different hydrological paths in the basin to river runoff

[0044] The results of the river runoff segmentation in the basin are verified from the perspectives of basin space and basin outlet. The digital filtering technology has the advantage of repeatability in estimating the base flow of the river, but it is also subjective. Therefore, the δ 18 The double-end member mixing model of O isotopes is used as auxiliary verification. The specific steps are as follows:

[0045] ① At the outlet of the basin, based on the daily runoff monitoring data, the baseflow digital filtering technology is used to divide the river runoff (Q) into surface runoff (Q S ) and base flow (groundwater, Q G ), see Equation 1. If the hydraulic connectivity between groundwater and rivers is high, it means that groundwater is the main path for the transport of pollutants in river runoff and the main source of pollutants in rivers.

[0046] Q=Q S +Q G (Formula 1)

[0047] In formula 1, Q represents the runoff flow at the river outlet (m 3 / s); Q S Indicates the runoff component of the river at the outlet of the basin - surface runoff flow (m 3 / s); Q G Indicates the runoff component at the outlet of the basin - base flow (m 3 / s).

[0048] For digital filtering technology, the dual-channel digital filter technology developed by Arnold et al. was selected, see formula 2;

[0049]

[0050] In formula 2: q t represents the direct runoff in time step t, Q t represents the river runoff in time step t, Q t-1 represents the river runoff within time step t-1, and β is the filtering parameter.

[0051] Base flow t Calculate using formula (3):

[0052] b t =Q t -q t (Formula 3)

[0053] ② In the basin space, based on the δ 18 O isotope value, using δ 18 O isotope double-endmember mixing model to quantify groundwater (Q G ) to the river runoff (Q), see Formula 4-Formula 6.

[0054] δ s =f p δ p +f g δ g (Formula 4)

[0055] fp +f g =1 (Formula 5)

[0056] f g =(δ S -δ p ) / (δ g -δ p ) (Formula 6)

[0057] In formula 4-6: f p and f g They represent the contribution ratio of rainfall and groundwater to river runoff in the basin; δ s ,δ p and δ g represent the δ of river runoff, rainfall and groundwater in the basin respectively. 18 O value.

[0058] ③ If digital filtering technology and different water bodies δ 18 The baseflow contribution ratios obtained by the two methods of the double-endmember mixing model of O isotopes are close, which proves that the runoff division method is reasonable from the perspective of basin outlet and basin space, and the monthly average baseflow flow estimation is accurate.

[0059] Step 103: Determine the contribution of nitrate nitrogen under different hydrological paths in the measured watershed to the nitrate nitrogen load at the outlet of the measured watershed, where the contribution includes contribution rate and contribution amount.

[0060] Wherein, step 103 specifically includes:

[0061] From the perspective of the outlet of the measured basin, water quality indicators and hydrological indicators are used to estimate the nitrate nitrogen load at the basin outlet.

[0062] From the perspective of the outlet of the measured basin, the baseflow nitrate nitrogen calculation method is used to estimate the baseflow nitrate nitrogen load at the basin outlet and its contribution to the nitrate nitrogen load in the river runoff at the basin outlet.

[0063] As a specific example, NO3 - -N load on the basin outlet NO3 - -N load contribution identification, the specific steps include:

[0064] (1) Under the premise of ignoring the attenuation process of the river channel, NO3 - -N Total load (P T ) According to the hydrological path process, it can be divided into surface runoff NO3 - -N load (P S ) and base flow NO3 - -N load (P G ), see formula 7. According to the basin outlet flow Q and NO3 --N concentration monitoring data, calculation of NO3 at the basin outlet - -N load (P T ). If the water quality monitoring data is on a daily time scale, directly estimate P according to Formula 8 T Otherwise, based on the measured data of flow and water quality, the LOADEST (Load ESTimator, Loadest) model is used to establish the statistical relationship between water quality and flow to estimate the load value.

[0065] P T =P S +P G =f S ×P T +f G ×P T (Formula 7)

[0066] P T =∑C i ×Q i ×100 (Formula 8)

[0067] In formulas 7 and 8: P T Indicates NO3 at the outlet of the basin - -N load (kg), f S and f G Indicates the NO3 that enters river runoff through surface runoff and baseflow - -N load accounts for NO3 at the outlet of the basin - -N load ratio (%), Q i Indicates the runoff at the basin outlet (m 3 / s), C i Indicates NO3 at the outlet of the basin - -N concentration (mg / L).

[0068] (2) Using the monthly average baseflow flow weighted concentration (C G ) and the monthly average base flow (Q G ) Calculate the monthly base flow NO3 at the basin outlet - -N Load P G , the formula is as follows:

[0069]

[0070] In formula 9: P G Indicates the NO3 at the basin outlet through the base flow path - -N Monthly output load (kg); Q G represents the monthly average base flow at the basin outlet (m 3 / s), C G Indicates NO3 at the outlet of the basin - -The monthly average concentration of N.

[0071] Monthly mean base flow NO3 - -N flow weighted concentration (C G ) is determined according to the method proposed by Schilling and Zhang (2004) and is given by the following formula:

[0072]

[0073] Formula 10: Q base-i It indicates the base flow when the base flow accounts for more than 90% of the river runoff (m 3 / s); C base-i Indicates that Q base-i The corresponding nitrate nitrogen concentration (mg / L); n represents the number of days in a month when the base flow accounts for more than 90%.

[0074] Step 104: Based on the Bayesian mixed model and nitrate nitrogen and oxygen isotopes, determine the contribution of various agricultural pollution sources to the nitrate nitrogen load of river runoff under different hydrological paths in the measured watershed, where the contribution includes contribution rate and contribution amount.

[0075] Basin NO3 - -N sources are mainly divided into two categories: non-agricultural sources and agricultural sources. Among them, agricultural nitrogen sources include chemical fertilizers (CF), soil organic nitrogen (SON), manure and sewage (M&S).

[0076] (1) NO3 under different hydrological paths - -N Agricultural Source Quantitative Source Analysis

[0077] NO3 under different hydrological paths - -N The specific steps of quantitative source analysis of agricultural sources are as follows:

[0078] ① Groundwater NO3 based on Bayesian mixture model - -N Agricultural Source Analysis:

[0079] Groundwater NO3 - -N traceability result calculation is shown in formula 11.

[0080]

[0081] In formula 11: f G Indicates the NO3 that enters river runoff through groundwater - -N load accounts for NO3 at the outlet of the basin - -N load ratio (%); f G,i Indicates the i-th NO3 in the basin - -N source to NO3 in groundwater --N contribution ratio (%). Where n = 4, 1 ≤ i ≤ 4, when i = 4, it represents the four sources of atmospheric precipitation (AP), chemical fertilizer (CF), soil organic nitrogen (SON), manure and sewage (M&S).

[0082] The calculation formula of the Bayesian mixed model is shown in formula (12-15).

[0083]

[0084]

[0085]

[0086]

[0087] In formula 12-15: X ij represents the ratio of isotope j in sample i (i=1,2,3,…,N; j=1,2,3,…,J); S jk represents the ratio of isotope j of source K, which has a mean value of u jk , with variance ω jk The standard normal distribution of C jk represents the fractionation coefficient of isotope j in source K, which has a mean value of λ jk , with a standard deviation of τ jk The standard normal distribution of jk Represents the residual of the isotope j ratio in sample i, which is used to describe the error between observations not included in the model. This parameter has a mean of 0 and a standard deviation of σ j The standard normal distribution of k Represents the proportion of source K, estimated by the Bayesian mixture model.

[0088] ② NO3 in river runoff based on Bayesian mixed model - -N source parsing job

[0089] According to the results of the basin hydrological path identification, NO3 - -N as independent NO3 - -N sources, that is, pollution sources in rivers can be expanded to five sources, namely atmospheric precipitation (AP), chemical fertilizers (CF), soil organic nitrogen (SON), groundwater (GW), feces and sewage (M&S). - -N source parsing work, see formula 16.

[0090]

[0091] In formula 16, f TIt represents the NO3 under the hydrological path of surface runoff and base flow at the outlet of the basin - -N load on the basin outlet NO3 - -N is the sum of the load contribution ratios, which is equal to 1; f S and f G The NO3 - -N load ratio (%); f S,i and f G,i Respectively represent the i-th NO3 - -N sources to NO3 in surface runoff and groundwater - -N contribution ratio (%), where n=4, 1≤i≤4, when i=4, it represents the four sources of atmospheric precipitation (AP), chemical fertilizer (CF), soil organic nitrogen (SON), and manure and sewage (M&S).

[0092] (2) NO3 at the watershed outlet under different hydrological paths - -N Load estimation

[0093] At the outlet of the basin, the river runoff NO3 - -N load is equal to the NO3 of each pollution source at the outlet of the basin - The sum of the NO-N load is also equal to the NO of each pollution source under the hydrological path of surface runoff and base flow. 3- -Sum of N loads, see formula 17-18.

[0094]

[0095]

[0096] In formula 17-18, P S,i and P G,i represents the NO3 of the ith source under the hydrological path of surface runoff and base flow - -N load (kg). Where 1≤i≤4. When i=4, they represent atmospheric precipitation (AP), chemical fertilizer (CF), soil organic nitrogen (SON), manure and sewage (M&S).

[0097] Based on river runoff and base flow NO3 - -N load estimation and source analysis results, estimation of NO3 in different hydrological pathways in the basin - -N load, see formula 19-20.

[0098] P G,i =f G,i ×P G (Formula 19)

[0099] P S,i =(f T,i-f G ×f G,i )×P T (Formula 20)

[0100] In formula 19-20, P S,i and P G,i It refers to the NO3 at the outlet of the basin under the hydrological path of surface runoff and base flow respectively. - -N pollution source load (kg), i = 1, 2, 3, 4, representing atmospheric precipitation (AP), chemical fertilizer (CF), soil organic nitrogen (SON), manure and sewage (M&S), respectively; f G,i represents the i-th NO3 entering the river runoff through the base flow hydrological path - - Contribution ratio of N pollution sources (%), f T,i represents the i-th NO3 in the river runoff - -Contribution ratio of N pollution sources (%).

[0101] The present invention discloses a method for determining the hydrological path and source contribution of agricultural non-point source pollution in a watershed, specifically a method for analyzing the hydrological path and source contribution of agricultural sources of agricultural non-point source pollution entering a water body in a watershed, providing technical support for achieving accurate and efficient prevention and control of agricultural non-point source pollution at a watershed scale.

[0102] The present invention is based on the identification of basin hydrological processes and the tracing of nitrate nitrogen isotopes, and realizes the analysis of agricultural sources of nitrate nitrogen in the basin under different hydrological paths. The method of the present invention not only scientifically explains the nitrate nitrogen load and the contribution ratio of different agricultural sources under different paths, but also provides targeted suggestions for the selection of subsequent basin water environment governance measures, thereby reducing the cost of basin non-point source pollution and improving the comprehensive governance effect.

[0103] Figure 2 The schematic diagram of the structure of a system for determining the hydrological path and source contribution of watershed agricultural non-point source pollution according to the present invention is as follows: Figure 2 As shown, a system for determining the hydrological path and source contribution of agricultural non-point source pollution in a watershed includes:

[0104] The water quality index and isotope index determination module 201 of the watershed to be tested is used to determine the water quality index and isotope index of the watershed to be tested; the water quality index includes nitrate nitrogen; the isotope index is the hydrogen and oxygen isotopes of the water sample and the nitrate nitrogen and oxygen isotopes.

[0105] A hydrological path determination module 202 is used to identify the hydraulic connectivity between groundwater and river runoff in the measured basin, and determine the contribution of surface runoff and base flow of different hydrological paths in the measured basin to river runoff based on the hydrogen and oxygen isotopes and digital filtering technology;

[0106] The module 203 for determining the contribution of nitrate nitrogen load at the outlet of the watershed is used to determine the contribution of nitrate nitrogen under different hydrological paths in the watershed to the nitrate nitrogen load at the outlet of the watershed to be measured.

[0107] The nitrate nitrogen load determination module 204 corresponding to each agricultural pollution source is used to determine the contribution of each agricultural pollution source to the nitrate nitrogen load of river runoff under different hydrological paths in the measured watershed based on the Bayesian mixed model and nitrate nitrogen and oxygen isotopes.

[0108] The hydrological path determination module 202 specifically includes:

[0109] The atmospheric precipitation line determination unit is used to determine the atmospheric precipitation line of the basin to be measured based on the spatial precipitation, river runoff and hydrogen and oxygen isotope indicators of groundwater in the basin to be measured.

[0110] A hydraulic connectivity determination unit is used to determine that if the degree of overlap between the hydrogen and oxygen isotope scatter diagram of the river flow in the measured basin and the hydrogen and oxygen isotope scatter diagram of the groundwater in the measured basin is greater than a set overlap value, and the overlapping position of the hydrogen and oxygen isotope scatter diagram of the river flow in the measured basin and the hydrogen and oxygen isotope scatter diagram of the groundwater in the measured basin is on the atmospheric precipitation line, then the groundwater and the river flow have strong hydraulic connectivity; otherwise, the groundwater and the river flow have weak hydraulic connectivity.

[0111] The digital filtering technology is used to determine the contribution units of surface runoff and base flow. From the perspective of the outlet of the measured basin, the digital filtering technology is used to determine the contribution rate of surface runoff to river runoff and the contribution rate of base flow to river runoff, which are recorded as the first surface runoff contribution rate and the first base flow contribution rate, respectively.

[0112] The double-endmember mixing model is used to determine the contribution units of surface runoff and baseflow. From the spatial perspective of the measured basin, the double-endmember mixing model of hydrogen and oxygen isotopes is used to determine the contribution rate of surface runoff to river runoff and the contribution rate of baseflow to river runoff, which are recorded as the second surface runoff contribution rate and the second baseflow contribution rate, respectively.

[0113] The river runoff division result verification unit is used to use the first surface runoff contribution rate as the contribution rate of surface runoff to river runoff, and the first base flow contribution rate as the contribution rate of base flow to river runoff when the difference between the second surface runoff contribution rate and the first surface runoff contribution rate is less than a set first difference, and the difference between the second base flow contribution rate and the first base flow contribution rate is less than a set second difference.

[0114] The module 204 for determining the contribution of nitrate nitrogen load at the watershed outlet specifically includes:

[0115] From the perspective of the outlet of the measured basin, water quality indicators and hydrological indicators are used to estimate the nitrate nitrogen load at the outlet of the basin;

[0116] From the perspective of the outlet of the measured basin, the baseflow nitrate nitrogen calculation method is used to estimate the baseflow nitrate nitrogen load at the basin outlet and its contribution to the nitrate nitrogen load in the river runoff at the basin outlet.

[0117] The agricultural pollution sources include fertilizers, soil organic nitrogen, manure and sewage.

[0118] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the system disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0119] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A method for determining the hydrological path and source contribution of agricultural non-point source pollution in a river basin, characterized in that: include: Determine water quality indicators and isotope indicators of the watershed to be tested; the water quality indicators include nitrate nitrogen; The isotope indicators are hydrogen and oxygen isotopes and nitrate nitrogen and oxygen isotopes of the water sample; Identify the hydraulic connectivity between groundwater and river runoff in the measured basin, and determine the contribution of surface runoff and base flow of different hydrological paths in the measured basin to river runoff based on the hydrogen and oxygen isotopes and digital filtering technology; Determining the contribution of nitrate nitrogen under different hydrological paths in the measured watershed to the nitrate nitrogen load at the outlet of the measured watershed; Based on the Bayesian mixture model and nitrate nitrogen and oxygen isotopes, the contribution of various agricultural pollution sources to the nitrate nitrogen load of river runoff under different hydrological paths in the measured watershed is determined; The contribution of surface runoff and base flow of different hydrological paths in the measured basin to river runoff based on the hydrogen and oxygen isotopes and digital filtering technology specifically includes: From the perspective of the outlet of the measured basin, the contribution rate of surface runoff to river runoff and the contribution rate of base flow to river runoff are determined by digital filtering technology, which are recorded as the first surface runoff contribution rate and the first base flow contribution rate respectively; From the spatial perspective of the watershed to be measured, the double-endmember mixing model of hydrogen and oxygen isotopes is used to determine the contribution rate of surface runoff to river runoff and the contribution rate of base flow to river runoff, which are recorded as the second surface runoff contribution rate and the second base flow contribution rate respectively; When the difference between the second surface runoff contribution rate and the first surface runoff contribution rate is less than the set first difference, and the difference between the second base flow contribution rate and the first base flow contribution rate is less than the set second difference, the first surface runoff contribution rate is used as the contribution rate of surface runoff to river runoff, and the first base flow contribution rate is used as the contribution rate of base flow to river runoff; The formula for estimating the nitrate nitrogen load in different hydrological pathways in the basin is: P G,i =f G,i ×P G P S,i =(f T,i -f G ×f G,i )×P T Among them, P S,i and P G,i It refers to the NO3 at the outlet of the basin under the hydrological path of surface runoff and base flow respectively. - -N pollution source load, i = 1, 2, 3, 4, representing atmospheric precipitation, fertilizer, soil organic nitrogen, feces and sewage respectively; f G,i represents the i-th NO3 entering the river runoff through the base flow hydrological path - -N pollution source contribution ratio, f T,i represents the i-th NO3 in the river runoff - -Contribution ratio of N pollution sources, P G is the monthly base flow NO3 at the basin outlet - -N load, P T NO3 at the outlet of the basin - -N Load amount.

2. The method for determining the hydrological path and source contribution of watershed agricultural non-point source pollution according to claim 1 is characterized in that: The identifying of the hydraulic connectivity between groundwater and river runoff in the watershed to be measured specifically includes: Determine the atmospheric precipitation line of the basin to be measured based on the spatial precipitation, river runoff and hydrogen and oxygen isotope indicators of groundwater in the basin to be measured; If the degree of overlap between the hydrogen and oxygen isotope scatter diagram of the river runoff in the measured basin and the hydrogen and oxygen isotope scatter diagram of the groundwater in the measured basin is greater than the set overlap value, and the overlapping position of the hydrogen and oxygen isotope scatter diagram of the river runoff in the measured basin and the hydrogen and oxygen isotope scatter diagram of the groundwater in the measured basin is on the atmospheric precipitation line, then the groundwater and the river runoff are strongly hydraulically connected; otherwise, the groundwater and the river runoff are weakly hydraulically connected.

3. The method for determining the hydrological path and source contribution of watershed agricultural non-point source pollution according to claim 1 is characterized in that: Determining the contribution of nitrate nitrogen under different hydrological paths in the measured watershed to the nitrate nitrogen load at the outlet of the measured watershed specifically includes: From the perspective of the outlet of the watershed to be measured, the water quality index and the hydrological index are used to determine the nitrate nitrogen load at the outlet of the watershed to be measured; the hydrological index is flow rate; From the perspective of the outlet of the measured basin, the baseflow nitrate nitrogen load at the outlet of the measured basin and the contribution of the baseflow nitrate nitrogen load to the nitrate nitrogen load in the river runoff at the outlet of the measured basin are determined according to the nitrate nitrogen load at the outlet of the measured basin.

4. The method for determining the hydrological path and source contribution of watershed agricultural non-point source pollution according to claim 1, characterized in that: The agricultural pollution sources include fertilizers, soil organic nitrogen, manure and sewage.

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