| As the point source pollution is managed, ecological problems caused by non-point sourcepollution loom large visibly. Nitrogen, phosphorus and other nutrient losses caused by rainfalllead to soil quality degradation and eutrophication, which is the main form of agriculturalnon-point pollution. As the main nutrient of aquatic organisms, phosphorus is one of the keyfactors leading to the water-body eutrophication. Identifying the source andmigration-transformation laws of runoff phosphorus becomes highlight of understanding andcontrolling the process of non-point source pollution.This paper took the YiMeng Mountainous Area, one of the most typical regions of the rockyarea in northern China, as a case study. Based on agricultural production conditions and thecharacteristics of the regional water system of Menglianggu small watershed, the researchadopted runoff field experiments monitoring methods, simultaneously observed rainfall andsurface runoff under natural rainfall conditions, field monitored the phosphorus loss process inthe river section and the different land use types of 2010 and 2011 flood season under differentrainfall conditions, and analyzed its output characteristics. The main conclusions obtained in thisstudy are as follows：1.The organic phosphorus (DOP), dissolved inorganic phosphorus (DIP), total dissolvedphosphorus (DP), total particle phosphorus (PP) and total phosphorus (TP) concentrations in thefirst rainfall were higher than those of the maximum intensity rainfall which was the largestaverage rainfall intensity, but the output of all kinds of phosphorus in first rainfall were all higherthan those in maximum intensity rainfall except dissolved organic phosphorus. The DOP, DIP,DP, PP and TP in two special rainfall events were exported by the ratio of 48%, 81%, 70%, 87%and 81% of the total output of rainy season. DP and TP were mainly composed by DIP and PPrespectively. Both of the two special rainfalls had the first flush effect and the maximumintensity rainfall was stronger than first rainfall, so the analysis on M (V) curve showed thatpriority should be given to the interception of corresponding phosphorus under special events.The regression analysis results showed that linear relation existed between runoff and nutrientoutput, but there were some differences that the slope of the linear equation of the first rainfallwas higher than that of the maximum intensity rainfall.2.The peak of phosphorus concentrations occurred before the peak of water flows, whereas the change processes of the phosphorus fluxes were consistent with that of the water flows andalso the phosphorus flux had a good linear relationship with the water flows. The minimums ofthe phosphorus concentrations in every 10 natural rainfall events had small differences with eachother, but the maximum and EMCs of the phosphorus concentrations differed greatly from eachrainfall event. This was mainly influenced by the precipitation, maximum rainfall intensity andmean rainfall intensity (EMCs) and seldom influenced by rainfall duration. DP and TP weremainly composed of DIP and PP, respectively. There were no significant correlations betweenDIP/DP dynamic changes and rainfall characteristics, whereas significant correlations betweenPP/TP dynamic changes and maximum rainfall intensity were detected. The production of DIP,DP, and TP were mainly influenced by the direct runoff (DR) and base flow (BF). The EMCs ofDIP, DP, TP and the variations of DIP/DP were all found to have significant polynomialrelationships with DR/TR., but the dynamic changes of PP/TP and the EMCS of PP werescarcely influenced by the DR/TR.3. Land use and storm, as important sources of nonpoint pollution, are key factors of soilerosion. Different intensity of storm and land use pattern may greatly impact on losses ofphospheres. The soil erosion was small in the sweet potato and forest land use under differentrainfall conditions, so the sweet potato and forest land use reduce the soil erosion very much.Through analysis of 10 different rainfall total output of phosphorus and sediment characteristicsin different types of land use , the smallest DOP, DIP, DP, PP, TP and sediment output of land usetypes were forest, forest, forest, sweet potato land, forest and sweet potato land, respectively.Through the analysis above, the results would provide a basis for decision making in theimplementation of reasonably and effectively controlling watershed agricultural non-point sourcepollution. Based on the impact of rainfall on agricultural non-point source pollution output, weaimed to provide advice to farmers to reasonably arrange agricultural activities.The phosphorusexports from agro-ecosystem could be significantly cut down by optimizing land use patternsand reducing tillage practices during those sensitive periods. |
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