Research Of Nitrogen And Phosphorus Loss Character In Watershed Scale Based On Export Coefficient Model

Water quality deterioration caused by non-point source can be defined as non-point pollution.In related research,nitrogen and phosphorus have always been one of the most important role.Export coefficient model is been applied in many research,due to its simple structure and convenient data access.This paper uses simplified runoff plot and watershed monitoring method,analyzed character of nutrient content of runoff of 9 types land use and nutrient load of 8 watersheds in study area.Based on which,by using typical watershed monitoring method,documentary study,equations method of pollutant balance theory,land use export coefficients in study area are calculated.The main conclusions are listed as following:1.High content nitrogen loss happens is winter,nitrogen loss in summer is mainly in particulate form.Rainfall character didn’t show significant influence on runoff nitrogen content.High content phosphorus loss happens in summer,phosphorus content in runoff didn’t show seasonal feature;in land use runoff scale,precipitation show greater influence on phosphorus content than max rain rate and average rain rate.2.Average watershed nutrient export content shows high content nitrogen loss happens in spring,particulate nitrogen contributes main part in nitrogen content in summer and autumn,the ratio of particulate nitrogen falls after summer.Average watershed phosphorus content shows,high content happens in low flow period,low content happens in high flow period;ratio of particulate phosphorus present great fluctuation over a year.3.Flow trend among watersheds shows great similarity,max flow happens in July,low flow period is from November to February.Nitrogen load between watersheds shows significant difference,total phosphorus load and dissolvable phosphorus load show significant difference.4.Export coefficient calculation based on typical watershed monitoring shows,calculating residents’nutrient load by population could reach high accuracy result.Land use export coefficient in study area are:16.72 kg/hm~2?a for nitrogen,7.08 kg/hm~2?a for ammonia nitrogen,0.53 kg/hm~2?a for phosphorus in paddy;24.24 kg/hm~2?a for nitrogen,5.23 kg/hm~2?a for ammonia nitrogen,0.24 kg/hm~2?a for phosphorus in non-irrigated farmland;8.57 kg/hm~2?a for nitrogen,3.53 kg/hm~2?a for ammonia nitrogen,0.48 kg/hm~2?a for phosphorus in forestry;20.47 kg/hm~2?a for nitrogen,2.62 kg/hm~2?a for ammonia nitrogen,0.53 kg/hm~2?a for phosphorus in tea garden;21.39 kg/hm~2?a for nitrogen,3.13 kg/hm~2?a for ammonia nitrogen,0.75 kg/hm~2?a1 for phosphorus in orchard;3.00 kg/hm~2?a for nitrogen,4.85 kg/hm~2?a for ammonia nitrogen,0.45 kg/hm~2?a for phosphorus in grassland.Land use load is calculated based on export coefficient,and result shows,paddy owns highest nutrient load of nitrogen,ammonia nitrogen and phosphorus;main source of nutrient load in study area is agriculture.5.Documentary research based on national survey of pollution sources shows highest nitrogen load land use is paddy;planting load ratio of phosphorus in watershed load is higher than nitrogen;contribution ratio of nitrogen shows little difference.6.Export coefficient result based on equations method of pollutant balance theory shows particularly high accuracy.land use export coefficient in study area are:32.51、31.35 kg/hm~2?a in resident area;29.06 kg/hm~2?a for nitrogen,23.58 kg/hm~2?a for dissolved nitrogen in paddy;31.23 kg/hm~2?a for nitrogen,23.06 kg/hm~2?a for dissolved nitrogen in non-irrigated farmland;71.84 kg/hm~2?a for nitrogen,57.29 kg/hm~2?a for dissolved nitrogen in orchard;55.38 kg/hm~2?a for nitrogen,30.1 kg/hm~2?a 2 for dissolved nitrogen in tea garden;30.00 g/hm~2?a for nitrogen,29.49 kg/hm~2?a for dissolved nitrogen in forestry.Land use load is calculated based on export coefficient above,and result shows paddy owns highest nutrient load of nitrogen,and dissolved nitrogen.