CN112784395B - Method for predicting and simulating total phosphorus concentration of river water body - Google Patents
Method for predicting and simulating total phosphorus concentration of river water body Download PDFInfo
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- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 title claims abstract description 127
- 229910052698 phosphorus Inorganic materials 0.000 title claims abstract description 127
- 239000011574 phosphorus Substances 0.000 title claims abstract description 127
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Abstract
The invention provides a method for predicting and simulating total phosphorus concentration of river water body, which comprises the steps of establishing a river basin hydrological model and constructing a characteristic area basic river basin database; dividing hydrological response units according to different characteristic region basic watershed data; constructing a phosphorus circulation model in a water body; inputting localized model data, and simulating the total phosphorus concentration; establishing scene simulation of future climate change; determining model parameters; and verifying the correctness of the model. Through simulating a series of physical processes such as water circulation, soil erosion, exogenous pollution input and the like, the runoff-producing sand production of each hydrological response unit is calculated, and finally, the migration and transformation process of phosphorus elements in the river is simulated, so that the purposes of predicting the runoff-producing sand produced by human activities in a river basin and the phosphorus concentration of the river water body are achieved.
Description
Technical Field
The invention relates to the technical field of river pollutant concentration simulation, in particular to a method for predicting and simulating total phosphorus concentration of river water.
Background
Rivers are important components of the complete water circulation process of the ground surface and are also important channels for pollutants generated by artificial activities on land to enter rivers and oceans. In a river ecosystem, phosphorus is an essential element of all organisms, is a main factor causing water eutrophication and water bloom, and is one of the important indexes for controlling the total amount of national pollutant emission.
In the management of nutritive salt pollution in a river basin, a total phosphorus prediction model is roughly divided into three types: the system comprises a basin load model, a water quality analysis model and an integrated simulation system. The basin load model can be used for simulating the whole process from generation to entry of pollutants into the receiving water body; the water quality model is mainly used for simulating the transmission and conversion process of pollutants in the water body; integrated simulation systems are generally not limited to a single model, but integrate several models to enhance the simulation function.
Disclosure of Invention
The invention overcomes the defects in the prior art, and provides a method for predicting and simulating the total phosphorus concentration of a river water body.
The purpose of the invention is realized by the following technical scheme.
A method for predicting and simulating the total phosphorus concentration of a river water body is carried out according to the following steps:
step 1, establishing a watershed hydrological model and constructing a characteristic area basic watershed database;
the data in the feature region elementary stream domain database comprises: DEM (Digital Elevation Model) Elevation data, river basin data, meteorological data, soil water shortage data, pollution source discharge data, river hydrological data and monitoring station verification data;
the watershed data comprise sub-watershed areas, the proportion of land utilization types and soil data (soil physicochemical properties); the meteorological data comprise daily rainfall, daily average temperature and hydrologic effective rainfall; the river hydrological data comprise river length, river average width, relation parameters of river water speed/river flow, river base flow index and river upstream and downstream relation; the pollution source data comprises an agricultural source, a livestock and poultry breeding source, an aquaculture source, a rural emission source and an emission source of a town sewage treatment plant; the monitoring station data comprises hydrological observation data (daily average flow) and water quality data (total phosphorus concentration in water);
step 2, dividing hydrological response units according to basic watershed data of different characteristic areas;
after a characteristic area basic river basin database is established, firstly, extracting a river basin and a river network by utilizing DEM elevation data; dividing sub-watersheds according to river network distribution, and determining watershed boundaries and watershed areas of the sub-watersheds; according to different land utilization distribution conditions, further dividing hydrological response units;
step 3, constructing a phosphorus circulation model in the water body;
constructing a phosphorus circulation model in the river water body according to the phosphorus circulation process in the water body, and mainly considering the process of inputting exogenous phosphorus and the change process of phosphorus elements in a soil layer, an underground water layer, the river water body and river bottom sediments;
the specific process is as follows: a. inputting exogenous phosphorus; b. phosphorus fixation-weathering process; c. infiltrating soil phosphorus into underground water phosphorus; d. an aquatic plant absorption process; e. an adsorption and desorption process; f. suspending the bottom mud; g. settling the bottom mud;
the ordinary differential equation of the phosphorus cycle process in the water body is as follows:
in the formula, P TDP,wa The mass of the total dissolved phosphorus in the water body is expressed as kg/day; p TDP,up Represents the mass of total dissolved phosphorus input from an upstream river, kg/day; p TDP,land Represents the mass of total dissolved phosphorus input from land, kg/day; p is eff Shows the concentration of total dissolved phosphorus in the river water body, mg/L, q eff Shows the river inflow, m 3 /s；P up,epi Represents the total dissolved phosphorus absorbed from phytoplankton in kg/day; p is TDP,out Represents the mass of total dissolved phosphorus output to the downstream river, kg/day; p sorbed,wc The mass of phosphorus adsorbed in the suspension, kg/day;
in the formula, P PP,wa The mass of granular phosphorus in the water body is expressed as kg/day; p PP,up The mass of the granular phosphorus input from the upstream river is expressed as kg/day; p PP,land Represents the mass of granular phosphorus imported from land, kg/day; PP (polypropylene) eff Shows the concentration of granular phosphorus in the river water body, mg/L and q eff Indicates the inflow, m 3 /s；P sorbed,wc The mass of phosphorus adsorbed in the suspension; p is PP,ent Represents the mass of particulate phosphorus suspended from the sediment, kg/day; PP (polypropylene) dep Represents the mass of particulate phosphorus settled in the sediment, kg/day; p PP,out The mass, kg/day, of particulate phosphorus output to the downstream river;
in the formula, A sub Denotes the area of the sub-basin, km 2 ；A land Representing the proportion of each land use type in each sub-flow domain;
step 4, inputting localized model data;
after the division of the hydrological response units is completed, inputting meteorological data, soil water shortage data, pollution source data, historical runoff measured values and historical total phosphorus concentration measured values into a basin hydrological model, and then simulating total phosphorus concentration by using the basin hydrological model;
step 5, determining model parameters according to geographical information of the drainage basin unit, and simulating the total phosphorus concentration;
the determination of the model parameters refers to the process of adjusting the values of the model parameters, the initial boundary conditions and the limiting conditions, so that the simulation calculation result of the model is matched with the historical measured data. The determination of the model parameters refers to the process of adjusting the values of the model parameters, the initial boundary conditions and the limiting conditions, so that the simulation calculation result of the model is matched with the historical measured data. The model parameters include C plant Plant absorption factor (m/day), SMD max Maximum water deficiency (mm) of soil, K soil Soil adsorption constant (/ day), n and temperature dependent nonlinear adsorption constant (-), F SD Coefficient of soil erosion by sputtering (s/m), E SD Energy of soil sputteringForce (kg/m) 2 /s)，V eg Vegetation coverage (-), F TC Coefficient of soil transport (kg/m) 2 /km 2 )；n TC Soil transport nonlinear constant (-).
Calculating the total dissolved phosphorus mass (kg/km) absorbed by the vegetation from the soil flow 2 Day), the formula is as follows:
in the formula, C plant Represents a plant uptake factor (m/day); SMD representing soil moisture factor, dimensionless, SMD max Represents the maximum water shortage (mm) of the soil; p is TDP,soil Represents the mass (kg/km) of total dissolved phosphorus in the soil 2 )；V soilwater Indicating the capacity of the soil flow (m) 3 /km 2 ). In the present model, the initial growth period of the plant is at 110 days per year, the growth period is 150 days per year, and P is not in the range of this period in any one year plant Equal to zero.
The mass of phosphorus adsorbed by the soil particles from the soil stream (kg/km) was calculated 2 Day), the formula is as follows:
in the formula, P sorbed,soil Represents the mass (kg/km) of phosphorus adsorbed by the soil particles from the soil stream 2 /day)；K soil Represents the soil adsorption constant (/ day); n represents a temperature-dependent nonlinear adsorption constant, dimensionless; TDP soilwater The concentration (mg/L) of inorganic phosphorus in the soil flow in a dissolved state is shown.
Calculating the soil splash erosion amount (kg/km) 2 Day) and soil delivery (kg/km) 2 Day), the formula is as follows:
in the formula, S SD Shows the amount of soil erosion (kg/km) 2 /day)；F SD The soil splash coefficient is expressed as s/m; r is eff Shows hydrologic effective rainfall (m) 3 /s/km 2 )；E SD Indicating the soil splash erosion capability (kg/m) 2 /s)；V eg The vegetation coverage is expressed and dimensionless. S TC Indicating the soil transport capacity (kg/km) 2 /day)；F TC Expressing the soil transport coefficient (kg/m) 2 /km 2 )；n TC Represents a soil transport non-linear constant, dimensionless.
Step 6, verifying the correctness of the model;
in order to verify the simulated total phosphorus concentration data, the application degree of the model in the simulation is evaluated by adopting 2 commonly used indexes, namely a correlation coefficient (R) 2 ) And the specific calculation formula of the Nash-Sutcliffe efficiency coefficient (N-S coefficient) is as follows:
in the formula Q m Is an observed value; q s Is an analog value; q ma The average value of the observed values; q sa Is the average of the analog values; n is the time length; two correlation coefficient values R 2 The closer to 1, the closer to the measured value, the more the simulation value of the watershed hydrological model is shown; the value of the N-S coefficient value is minus infinity to 1, the N-S value is close to 1, and the simulation value is closer to the observation value, so that the reliability of the basin hydrological model is high; N-S values near 0, representing moduloThe simulation result is close to the average value level of the observed value, namely the overall result is credible, but certain errors exist in the process simulation; if the N-S value is far less than 0, the watershed hydrological model result is deemed to be unreliable.
Step 7, establishing a scene simulation of future climate change;
for the forecast of future rainfall and air temperature change, a set of new scenes characterized by stable Concentration is adopted, namely typical Concentration Pathways (RCPs), three kinds of climate scene data including RCP2.6 (low isothermal chamber gas emission scenes), RCP4.5 (medium greenhouse gas emission scenes) and RCP8.5 (highest greenhouse gas emission scenes), and the scene simulation date is 2020/01/01-2049/12/31.
The invention has the beneficial effects that: compared with the prior art, the method fully utilizes meteorological data and soil data to simulate the phosphorus circulation process of the river ecosystem, can predict and simulate the change characteristics and environmental response of the total phosphorus concentration of the river ecosystem, has high model accuracy, wide application range and high calculation speed, and provides a new method and a new thought for predicting the total phosphorus concentration of the river; meanwhile, the method can scientifically evaluate the phosphorus pollution problem of the river water body by establishing a river phosphorus circulation model, and can predict the potential influence on the total phosphorus concentration of the river water body under the situations of temperature, precipitation change and the like in the future river basin by coupling the future climate change situation mode in the river basin, so that reference is provided for the formulation of the water environment management measures of the future river basin.
Drawings
FIG. 1 is a schematic diagram of the method of the present invention;
FIG. 2 is a plot of different land use types for a study area of an example;
FIG. 3 is a schematic view of the distribution of monitoring sites of the DEM and measured data of total phosphorus concentration in the research area of the embodiment;
FIG. 4 is a calibration and verification plot of a total phosphorus concentration simulation of an example;
FIG. 5 is a graph of the total phosphorus concentration of river water under the climate change situation of the next 30 years.
Detailed Description
The technical solution of the present invention is further illustrated by the following specific examples.
A method for predicting and simulating the total phosphorus concentration of a river water body is carried out according to the following steps:
step 1, establishing a characteristic region basic flow domain database, and dividing hydrological response units;
in this case, the Songhua river basin in northeast China is selected as an example for analysis. Land utilization data of Songhua river basin is shown in FIG. 2, DEM elevation data and total phosphorus concentration monitoring site distribution are shown in FIG. 3.
The watershed data comprise sub-watershed areas, the proportion of land utilization types and soil data (soil physicochemical properties); the meteorological data comprise daily rainfall, daily average temperature and hydrologic effective rainfall; the river hydrological data comprise river length, river average width, relation parameters of river water speed/river flow, river base flow index and upstream and downstream relation of the river; the pollution source data comprises agricultural sources, livestock and poultry breeding sources, aquaculture sources, rural emission sources and discharge sources of urban sewage treatment plants; the monitoring site data includes hydrological observation data (daily average flow) and water quality data (total phosphorus concentration in water).
Step 2, dividing hydrological response units according to basic watershed data of different characteristic areas;
and after the basic flow domain database is established, further dividing hydrological response units. Firstly, generating a river network of a river basin by utilizing DEM elevation data, and defining a total outlet of the river basin; and then dividing the sub-watershed according to the river network distribution, and dividing the research area into three sub-watersheds, wherein the three sub-watersheds are respectively as follows: second Songhua river basin, nenjiang river basin and Songhua river basin (below three-fork), the basic data characteristics of each sub-basin are shown in the following table; on the basis of the sub-watersheds, the watersheds are divided into different hydrological response units according to different land utilization distribution conditions.
TABLE 1 basic data characteristics of sub-watersheds in Songhua river watershed
Step 3, constructing a phosphorus circulation model in the water body;
constructing a phosphorus circulation model in the river water body according to the phosphorus circulation process in the water body, and mainly considering the process of inputting exogenous phosphorus and the change process of phosphorus elements in a soil layer, an underground water layer, the river water body and river bottom sediments;
the specific process is as follows: a. inputting exogenous phosphorus; b. phosphorus fixation-weathering process; c. infiltrating from soil phosphorus to underground water phosphorus; d. an aquatic plant absorption process; e. an adsorption and desorption process; f. suspending the bottom mud; g. settling the bottom mud;
the ordinary differential equation of the phosphorus cycle process in the water body is as follows:
in the formula, P TDP,wa Representing the mass of total dissolved phosphorus in the water body, kg/day; p TDP,up Represents the mass of total dissolved phosphorus input from an upstream river, kg/day; p TDP,land Represents the mass of total dissolved phosphorus input from land, kg/day; p eff Shows the concentration of total dissolved phosphorus in the river water body, mg/L, q eff Indicates the inflow, m 3 /s；P up,epi Represents the total dissolved phosphorus absorbed from phytoplankton in kg/day; p TDP,out Represents the mass of total dissolved phosphorus output into the downstream river, kg/day; p sorbed,wc The mass of phosphorus adsorbed in the suspension, kg/day;
in the formula, P PP,wa Indicating the state of particles in a body of waterMass of phosphorus, kg/day; p is PP,up Represents the mass of granular phosphorus fed from an upstream river, kg/day; p is PP,land The mass of the granular phosphorus input from the land is expressed in kg/day; PP (polypropylene) eff Shows the concentration of granular phosphorus in the river water body, mg/L and q eff Indicates the inflow, m 3 /s；P sorbed,wc The mass of phosphorus adsorbed in the suspension; p PP,ent Represents the mass of particulate phosphorus suspended from the sediment, kg/day; PP (polypropylene) dep Represents the mass of particulate phosphorus settled in the sediment, kg/day; p PP,out Represents the mass of particulate phosphorus output to the downstream river, kg/day;
in the formula, A sub Denotes the area of the sub-basin, km 2 ；A land Indicating the proportion of each land use type in each sub-flow domain.
Step 4, inputting localized model data;
after the division of the hydrological response units is completed, basic data is required to be input into the model, and the model is used for simulating the total phosphorus cycle process. The model input data mainly comprises six types of data including terrain elevation (DEM), land utilization type, soil type and physicochemical properties thereof, rainfall and air temperature, pollution source emission data and total phosphorus concentration monitoring value.
(1) Topographic Data (DEM) spatial distribution data is derived from Radar topographic mapping SRTM (SRTM) data of the U.S. perk space Shuttle;
(2) The land utilization type data is obtained by a remote sensing monitoring data set (CNLUCC) by taking Landsat remote sensing image data of a land satellite of America as a main information source through manual visual interpretation, and 4 types (shown in figure 2) of cultivated land, forest and grass land, water area and other land are selected according to different types of areas and contribution to runoff;
(3) The soil type and the physical and chemical properties in the river basin refer to the second national soil general survey and the Chinese soil basic database;
(4) Selecting actual measurement data of the national weather monitoring station from 2006 to 2017 day by day according to the precipitation and temperature data;
(5) The phosphorus pollution source emission data is according to the phosphorus element industry emission characteristics, the artificial emission sources mainly comprise five types of emission sources including urban domestic sewage emission, rural domestic sewage emission, agricultural planting non-point source emission, livestock and poultry breeding emission and aquaculture emission, the existing statistical data of the country and the place are taken as basic data, firstly, the phosphorus element inflow emission flux of the main emission sources of different provinces in a flow region is estimated, then, on the basis of provincial level statistical data, the artificial emission amount is decomposed into different secondary sub-flow regions by the spatial interpolation method of ArcGIS, and 1km in the region is utilized 2 And (3) interpolating spatial distribution information such as population spatial distribution, livestock and poultry breeding quantity distribution, land utilization type distribution and the like of the grids so as to obtain the discharge amount of the artificial phosphorus element under five discharge units in all secondary sub-flow areas of Songhua river.
(6) Selecting actual measurement data of 46 monitoring sites (figure 3) in 2006-2017 in the river basin day by day from the total phosphorus concentration monitoring data;
step 5, determining model parameters according to geographical information of the drainage basin unit, and simulating the total phosphorus concentration;
the determination of the model parameters refers to the process of adjusting the values of the model parameters, the initial boundary conditions and the limiting conditions, so that the simulation calculation results of the model are matched with the historical measured data. The model parameters include C plant Plant absorption factor (m/day), SMD max Maximum water deficiency (mm) of soil, K soil Soil adsorption constant (/ day), n and temperature dependent nonlinear adsorption constant (-), F SD Coefficient of soil erosion (s/m), E SD Indicating the soil erosion capability (kg/m) 2 /s)，V eg Amount of vegetation coverage (-), F TC Coefficient of soil transport (kg/m) 2 /km 2 )，n TC Soil transport nonlinear constants (-).
Calculating the total dissolved phosphorus mass (kg/km) absorbed by the vegetation from the soil flow 2 Day), the formula is as follows:
in the formula, C plant Represents a plant uptake factor (m/day); SMD representing soil moisture factor, dimensionless, SMD max Represents the maximum water shortage (mm) of the soil; p TDP,soil Represents the mass (kg/km) of total dissolved phosphorus in the soil 2 )；V soilwater Indicating the capacity of the soil flow (m) 3 /km 2 ). In this model, the initial growth period of the plants was at day 110 of each year, the growth period was 150 days/year, and P not in this period ranged for any one year plant Equal to zero.
Preferably, C plant ＝0.01m/day；SMD max ＝150mm。
The mass of phosphorus adsorbed by the soil particles from the soil stream (kg/km) was calculated 2 Day), the formula is as follows:
in the formula, P sorbed,soil Represents the mass (kg/km) of phosphorus adsorbed by the soil particles from the soil stream 2 /day)；K soil Represents the soil adsorption constant (/ day); n represents a temperature-dependent nonlinear adsorption constant, dimensionless; TDP soilwater Represents the concentration (mg/L) of inorganic phosphorus in the soil stream in dissolved form.
Preferably, K soil ＝0.44/day；n＝2。
Calculating the soil splash erosion amount (kg/km) 2 Day) and soil delivery (kg/km) 2 Day), the formula is as follows:
in the formula (I); s SD Shows the amount of soil erosion (kg/km) 2 /day)；F SD Representing the soil erosion coefficient; s/m; r eff Represents the hydrologic effective rainfall flux (m) 3 /s/km 2 )；E SD Indicating the soil splash erosion capability (kg/m) 2 /s)；V eg The vegetation coverage is represented and dimensionless. S TC Indicating the soil transport capacity (kg/km) 2 /day)；F TC Represents the soil transport coefficient (kg/m) 2 /km 2 )；n TC Represents a soil conveying nonlinear constant without dimension; l is reach Represents the river length (m).
Preferably, F SD ＝1s/m，E SD ＝0.04kg/m 2 /s，V eg ＝1；F TC ＝100kg/m 2 /km 2 ，n TC ＝0.1。
Step 6, verifying the correctness of the model;
in the invention, the verification period of 2006-2017 is taken as a simulation result, and R is used 2 And comprehensively evaluating the simulation result by using the N-S two evaluation indexes. The simulation results of the model during the validation period are shown in fig. 4. In general, in the aspect of simulating total phosphorus, the observed value and the analog value are well matched on a monthly scale, the change trend is basically consistent on the whole, the difference between the analog value and the absolute value of the peak value of the measured flood season is small, and the evaluation index R 2 And N-S are within reasonable ranges.
Step 7, establishing a scene simulation of future climate change;
the invention adopts a day-by-day simulation result with the resolution of 256 multiplied by 128 (warp multiplied by weft lattice points) under the driving of a global mode MIROC of a Japanese climate center in a fifth coupling mode international comparison plan CMIP5, comprises three RCPs (RCP 2.6, RCP4.5 and RCP 8.5) climate scene data, and selects 2020/01/01-2049/12/31 as a future prediction time period.
The invention has been described in an illustrative manner, and it is to be understood that any simple variations, modifications or other equivalent changes which can be made by one skilled in the art without departing from the spirit of the invention fall within the scope of the invention.
Claims (2)
1. A method for predicting and simulating the total phosphorus concentration of river water is characterized by comprising the following steps: the method comprises the following steps:
step 1, establishing a watershed hydrological model, and constructing a characteristic area basic watershed database;
the data in the feature region elementary stream domain database comprises: DEM (Digital Elevation Model) Elevation data, watershed data, meteorological data, soil water shortage data, pollution source emission data, river hydrological data and monitoring station verification data;
the watershed data comprise sub-watershed areas, the proportion of land utilization types and soil data; the meteorological data comprise daily rainfall, daily average temperature and hydrologic effective rainfall; the river hydrological data comprise river length, river average width, relation parameters of river water speed/river flow, river base flow index and upstream and downstream relation of the river; the pollution source data comprises an agricultural source, a livestock and poultry breeding source, an aquaculture source, a rural emission source and an emission source of a town sewage treatment plant; the data of the monitoring station comprises hydrological observation data and water quality data;
step 2, dividing hydrological response units according to basic watershed data of different characteristic areas;
after a characteristic area basic river basin database is established, firstly, extracting a river basin and river network by using DEM elevation data; dividing the sub-watersheds according to the river network distribution, and determining the watershed boundaries and the watershed areas of the sub-watersheds; according to different land utilization distribution conditions, further dividing hydrological response units;
step 3, constructing a phosphorus circulation model in the water body;
a phosphorus circulation model in the river water body is constructed according to the process of phosphorus circulation in the water body, and the process of inputting exogenous phosphorus and the change process of phosphorus elements in a soil layer, an underground water layer, the river water body and river bottom sediments are considered, and the specific process is as follows: a. inputting exogenous phosphorus; b. phosphorus fixation-weathering process; c. infiltrating soil phosphorus into underground water phosphorus; d. an aquatic plant absorption process; e. an adsorption and desorption process; f. suspending the bottom mud; g. settling the bottom mud;
the ordinary differential equation of the phosphorus cycle process in the water body is as follows:
in the formula, P TDP,wa Representing the mass of total dissolved phosphorus in the water body, kg/day; p is TDP,up Represents the mass of total dissolved phosphorus input from an upstream river, kg/day; p TDP,land Represents the mass of total dissolved phosphorus input from land, kg/day; p eff Shows the concentration of total dissolved phosphorus in the river water body, mg/L, q eff Indicates the inflow, m 3 /s；P up,epi Represents the total dissolved phosphorus absorbed from phytoplankton in kg/day; p TDP,out Represents the mass of total dissolved phosphorus output to the downstream river, kg/day; p sorbed,wc The mass of phosphorus adsorbed in the suspension, kg/day;
in the formula, P PP,wa The mass of granular phosphorus in the water body is expressed as kg/day; p PP,US Represents the mass of granular phosphorus fed from an upstream river, kg/day; p PP,land The mass of the granular phosphorus input from the land is expressed in kg/day; PP (polypropylene) eff Shows the concentration of granular phosphorus in the river water body, mg/L and q eff Indicates the inflow, m 3 /s；P sorbed,wc The mass of phosphorus adsorbed in the suspension; p PP,ent Represents the mass of particulate phosphorus suspended from the sediment, kg/day; p PP,dep Represents the mass of particulate phosphorus settled in the sediment, kg/day; p PP,out Represents the mass of particulate phosphorus output to the downstream river, kg/day;
in the formula, A sub Denotes the area of the sub-basin, km 2 ；A land Representing the proportion of each land use type in each sub-flow domain;
step 4, inputting localized model data to simulate the total phosphorus concentration;
after the division of the hydrological response units is completed, inputting meteorological data, soil water shortage data, pollution source data, a historical runoff measured value and a historical total phosphorus concentration measured value into a basin hydrological model, and then simulating the total phosphorus concentration by using the basin hydrological model;
step 5, determining model parameters;
the determination of the model parameters refers to the process of adjusting the values of the model parameters, the initial boundary conditions and the limiting conditions, and aims to ensure that the simulation calculation result of the model is matched with the historical measured data;
the model parameters include C plant Plant absorption factor, m/day, SMD max Maximum water shortage of soil, mm, K soil Soil adsorption constant,/day, n and temperature dependent nonlinear adsorption constant, dimensionless, F SD Coefficient of soil erosion, s/m, E SD Indicates the soil erosion capability in kg/m 2 /s，V eg Coverage of vegetation, dimensionless, F TC Soil transport coefficient, kg/m 2 /km 2 ；n TC The soil conveying nonlinear constant is dimensionless;
calculating the total dissolved phosphorus mass, kg/km, absorbed by the vegetation from the soil stream 2 Day, formulaThe following were used:
in the formula, C plant Represents a plant uptake factor, m/day; SMD representing soil moisture factor, dimensionless, SMD max Represents the maximum water shortage of the soil, mm; p is TDP,soil Indicates the mass of total dissolved phosphorus in the soil, kg/km 2 ；V soilwater Denotes the capacity of the soil flow, m 3 /km 2 In the present model, the initial growth period of the plants is at day 110 of each year, the growth period is 150 days/year, and P is not in the range of this period in any given year plant Is equal to zero;
calculating the mass of phosphorus adsorbed by the soil particles from the soil flow, kg/km 2 The formula,/day, is as follows:
in the formula, P sobred,soil Denotes the mass of phosphorus adsorbed by the soil particles from the soil stream, kg/km 2 /day；K soil Represents the soil adsorption constant,/day; n represents a temperature-dependent nonlinear adsorption constant, dimensionless; TDP soilwater Represents the concentration of inorganic phosphorus in a dissolved state in the soil flow, mg/L;
calculating the soil splash erosion amount, kg/km 2 Day and soil delivery, kg/km 2 The formula,/day, is as follows:
in the formula (I); s SD Indicates the amount of soil splash, kg/km 2 /day；F SD Representing the soil splash coefficient; s/m; r is eff Represents the hydrologic effective rainfall flux, m 3 /s/km 2 ；E SD Indicates the soil erosion capability in kg/m 2 /s；V eg Representing the vegetation coverage amount without dimension; s. the TC Expressed in soil transport, kg/km 2 /day；F TC Expressing the soil transport coefficient, kg/m 2 /km 2 ；n TC Expressing a soil transport nonlinear constant without dimension; l is a radical of an alcohol reach Represents the river length, m;
step 6, verifying the correctness of the model;
in order to verify the simulated total phosphorus concentration data, the application degree of the model in the simulation is evaluated by adopting 2 commonly used indexes, namely a correlation coefficient (R) 2 ) And the Nash-Sutcliffe efficiency coefficient (N-S coefficient) is specifically calculated according to the following formula:
in the formula Q m Is an observed value; q s Is an analog value; q ma The average value of the observed values; q sa Is the average of the analog values; n is the time length;
step 7, establishing scene simulation of future climate change;
for the prediction of future rainfall and air temperature change, a set of new scenes characterized by stable Concentration, namely typical Concentration Pathways (RCPs), is adopted, and the three climate scene data comprise RCP2.6 (low isothermal chamber gas emission scene), RCP4.5 (medium greenhouse gas emission scene) and RCP8.5 (highest greenhouse gas emission scene).
2. The method for predicting and simulating the total phosphorus concentration of a river water body according to claim 1, wherein the method comprises the following steps: in step 7, two correlation coefficient values R 2 The closer to 1, the closer to the measured value, the more the simulation value of the watershed hydrological model is shown; the value of the N-S coefficient value is minus infinity to 1, the N-S value is close to 1, and the simulation value is closer to the observation value, so that the reliability of the basin hydrological model is high; the N-S value is close to 0, which indicates that the simulation result is close to the average value level of the observed value, namely the overall result is credible, but certain errors exist in the process simulation; if the N-S value is far less than 0, the watershed hydrological model result is deemed to be unreliable.
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