Study On The Nitrogen And Phosphorus Pollution Load In The Uncontrolled Area Of Poyang Lake Based On The SPARROW Model

As the largest freshwater lake in China,Poyang Lake has always been concerned about the water quality of its basin and there are many related studies.However,there are relatively few studies on the uncontrolled area of Poyang Lake.This paper uses water quality evaluation methods and multivariate statistical analysis methods to evaluate the water quality of the uncontrolled area from 2011 to 2018,analyze the temporal and spatial changes of water quality and the reasons.The study established the SPARROW（SPAtially Referenced Regressions on Watershed attributes）-TN and TP models of the uncontrolled area watershed,fitted the TN and TP inflow load and production rate of each sub-basin and the overall watershed,and identified hot areas with high TN and TP production in the uncontrolled area.Based on this,relevant suggestions are made for the prevention and control of pollution in the uncontrolled area.The main conclusions are as follows:（1）In the single-factor evaluation results,the water quality of the uncontrolled area is mainly classified as Class IV and Class V,with TN as the main pollutant and TP as the secondary pollutant.In the evaluation result of the comprehensive pollution index,the water quality of the uncontrolled area is mainly light pollution and medium pollution.The water quality of the uncontrolled basins during the wet season is better than that in the dry season.DO,NH₃-N,TP,TN and the comprehensive pollution index show a continuous downward trend from January to September of the year.And from September to January of the following year,there was a continuous or volatile upward trend.（2）The cumulative anomaly method combined with the M-K mutation test was used to study the inter-annual changes of water quality in uncontrolled areas from 2011 to 2018.The results showed that the various water quality indicators of the uncontrolled area fluctuated from2011 to 2014,and showed a downward trend from 2014 to 2018.In the study of the spatial distribution law,the Leanhekou section was the most polluted section during the high and low water period,and the Rao River Basin was the most polluted;the Xiuhekou section was the least polluted section during the high and low water period,and the water quality in the Xiushui basin was better.（3）The R² of the SPARROW-TN and TP models in the uncontrolled area reaches 0.82 and0.74,respectively,and the fitting effect is relatively ideal.In the simulation results of the SPARROW model,the sub-basins close to the lake area and the sub-basins within Nanchang City,Fengcheng City,and Leping City have higher TN and TP inflow loads and yields.The main tributary basin of the Ganjiang River,the southern branch basin of the Ganjiang River and the Fuhekou basin contribute higher to the TN and TP pollution load of uncontrolled areas.Cultivated land is the most important source of TN and TP non-point source pollution in the uncontrolled watershed,followed by residential urban land.The above are all regions that should be focused on when formulating pollution control measures in uncontrolled areas.（4）From 2011 to 2017,the average annual load of non-point source TN into the lake in the uncontrolled area was 2.14×10⁷kg/yr,and the load and yield of TN in a rainy year were about 1.5 times that of a dry year.The increase in the proportion of cultivated land and residential urban land,and the increase in rainfall will increase the load of TN into the lake,so the increase in pollution load caused by agricultural expansion and urbanization needs to be vigilant.Based on the simulation results,suggestions are made for pollution prevention and control in uncontrolled areas in terms of industrial transformation,environmental monitoring,agricultural urban and rural planning and management,and water ecological protection measures.