Abstract:

Poyang Lake is the largest freshwater lake in China,and the nonpoint source pollution from agriculture is one major cause of water pollution with local intensive industrial and agriculture developing.The systematic analysis of the distribution featur of nitrogen and phosphorus and the source pollution contribution rate will provide necessary basis for the rational allocation of agricultural resource in Poyang Lake.
Pollution loads mainly nitrogen,phosphorus pollutants from agricultural nonpoint pollution sources in 12 counties around the Poyang Lake has been analyzed by Export Coefficient Approach, based on the data from 1997~2007.Meanwhile,Markov model and Gray predication model is used to predict the change of land use and livestock population, and the source pollution during 2011 to 2020.The land use, livestock and poultry,and agricultural population in the research area were considered as major nutrition sources to the loads.The results show that TN/TP take on a steady upward trend,the highly loaded area of nonpoint pollution mainly concentrated in the Nanchang County，Xinjian County  and Nanchang city.In the forecast year,TN/TP have a obvious increasing trend from 2011 to 2020，and the average growth rate of TN/TP will reach 1746% and 1602%.
The pollution load of nitrogen and phosphorus from livestock breeding had got significant increasing trend among three nutrient sources,the contribution rate of land use and agricultural population had a downward trend which reveals livestock pollution will be the main nonpoint source pollution around the Poyang Lake.It is forecasted that the contribution rate of every nutrient source in the Poyang Lake has the same variation tendency in 2011~2020 compared with 1997~2007:the contribution rate of the output load of the beasts and birds has significant increasing trend as time goes on,because the scale of the poultry farming is growing gradually;the contribution rate of the output load of the agricultural population has a downward trend,mainly because the agricultural population gradually reduces with the development of urbanization. The total land area within Poyang Lake is unchanging,but the urban land increases and arable land shrinks,which makes the contribution rate of the TN / TP load of the land output has a decreasing tendency over time.With the help of GIS,the spatial characteristics of TN &TP in the surrounding areas has been represented.Among counties and cities of Poyang Lake,point source pollution load intensity in four counties of Nanchang is higher than that of the whole research area,the main pollution in Nanchang is livestock output,contribution rate has come to 50%.Some key control region of nonpoint source pollution in the research area has been explained and pointed out