| Compared with point source pollution, the feature of non-point source is complexity, uncertainty, hysteresis of damage, widespread temporal and spatial distribution. All of those increase the difficulties of formulating countermeasures and management system. Now, the use of PLOAD model in our country is relatively rare, and most of those are focused on south area and the index in a researching area is not all-inclusive. In this study, the equations of PLOAD model was used for calculating the load of non-point source pollution of total nitrogen, ammonia, nitrate, nitrite, total phosphorus and COD in Liu River catchment, combined with the data of land use, DEM and so on. We can identify the high incidence area of non-point source pollution, through making diagrams with ArcGIS. The influence of non-point source pollution to water quality was investigated in Liu River, Meanwhile, combined with environmental quality assessment on single factor index method and comprehensive index method and the load of non-point source pollution. Through this study, we hope that we can provide some basis for the controlling of non-point source pollution in Liu River catchment and support for research in other area. The main results are as follow:(1) The single factor index of pollution parameters almost has the same trend in three sections which is named Hong Shi La, Xiao Dong Qu and Li Ying. That is to say, all of total nitrogen index greatly exceed the standard limit; most of total phosphorus exceed the standard limit; ammonia and COD exceed the standard limit occasionally; almost no nitrate exceeds the limit. Comprehensive index analyses show that the Hong Shi La section belongs to heavy pollution grade, and Xiao Dong Qu and Li Ying belong to serious pollution grade. Among of those, Xiao Dong Qu is the most polluted, which Comprehensive index goes up to3.5.(2) In2012, the load capacity of point source pollution of total nitrogen, ammonia, nitrate, nitrite, total phosphorus and COD in Liu River are355.872t/a,83.430t/a,163.640t/a,7.162t/a,701.288t/a and5797.512t/a, respectively. The load capacity of non-point source pollution of total nitrogen, ammonia, nitrate, nitrite, total phosphorus and COD in Liu River are1798.884t/a,193.612t/a,358.381t/a,18.750t/a,171.718t/a and5468.452t/a, respectively.(3) In2012, the load capacity of non-point source pollution in unit area of total nitrogen, ammonia, nitrate, nitrite, total phosphorus and COD in Liu River are16.103 kg/ha·a,1.733kg/ha·a,3.208kg/ha·a,0.168kg/ha·a,1.537kg/ha-a,48.952kg/ha-a. All of the sub basins in Liu River catchment which can produce relatively large load of total nitrogen, ammonia, nitrate, nitrite, total phosphorus and COD in unit area, numbered sub basins11,12,14,16; sub basins11,12; sub basins9,11,12,14; sub basins9,11,12,14; sub basins11,14,16and sub basins11,12.(4) Combined with the distribution of land use in different sub basins, the distribution of towns and villages are focused on the sub basins9,11,12,14,16. So we can get the results that towns and villages are the most sources of non-point sources pollution. Especially in the villages, the controlling is very difficult, as its distribution is relatively scattered. So we should priority control the four sub basins whose ID is9,11,12,14and16, for reducing the produce of non-point source pollution.(5) Comparing the non-point source pollution load with the total pollution load, the fractions of the non-point load in total nitrogen, ammonia, nitrate, nitrite, total phosphorus and COD among the corresponding total load are43.3%,69.9%,68.7%,72.4%,19.7%,48.5%, respectively. The results show that the non-point source pollution of different forms of nitrogen and organics has the most ratio of the total pollution, so that we should increase management of non-point source pollution of total nitrogen and organics. However, the pollution of phosphorus is mostly from point source, so that we should enhance management of point source pollution. |
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