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In order to study the background pollution of Gangnan Reservoir, the paper aim to the various branches of Hutuo river that had been little influenced by human activities, by means of sampling and analyzing the surface water and soil through the period before dry season, the wet season and the period after dry season. Combined with Gangnan Reservoir inflow water quality analysis of cross-section, and the historical water quality material analysis, it obtained the following conclusion:(1)The nitrogen and phosphorus annual average total inflowing of Gangnan reservoir respectively was:total nitrogen 979.1t/a, total phosphorus 41.5 t/a, ammonia nitrogen 53.1 t/a; And the basin background condition nitrogen and phosphorus nonpoint source pollution load contribution quantity respectively were total nitrogen 373.2t/a, total phosphorus 24.6t/a, ammonia nitrogen 18.7t/a.(2) The point source pollution of annual average total inflowing of Gangnan reservoir was respectively:ammonia nitrogen 25.3%,total nitrogen 48.1%,total phosphorus 34.0%. and the nonpoint source respectively was:ammonia nitrogen 74.7%, total nitrogen 51.9%, total phosphorus 66.0%. In the nonpoint source pollution, the contribution from background pollution was:ammonia nitrogen 47.20%, total nitrogen 73.50%, total phosphorus 89.80%; the other nonpoint source load respectively was:Ammonia nitrogen 52.80%, total nitrogen 26.50%, total phosphorus 10.20%.(3)The Hutuo River various branches source area were influenced by the background condition nitrogen and phosphorus nonpoint source pollution, in the surface water the total nitrogen concentration is 0.223～5.631mg/l,the ammonia nitrogen was under detection limite-0.634mg/l, the total phosphorus content was 0.024～0.683mg/l. Under the Hutuo River basin background condition the nitrogen nonpoint source pollution were mainly soluble nitrogen in all hydrological period, and the phosphorus in the form of soluble phosphorus in the dry season, most in the wet period mainly particulate.(4) The different configuration concentration of nitrogen and phosphorus in surface water and in soil has poor certain correlation besides soluble nitrogen.(5)Combined with the 3S technology and traditional USLE model, account USLE model parameters and examine by water quality and quantity practice datas, it established a estimate model of nitrogen and phosphorus nonpoint source pollution load in suitable of Hutuo river characteristics.
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