Study On The Characteristics Of Nitrogen, Phosphorus And Ion Migration In A Small Agricultural Watershed In The Purple Soil Hilly Area

There are obvious temporal and spatial variation characteristics of Sediment,nitrogen and phosphorus export in agricultural watershed.Change regulation of them are analyzed,that has important implications for control agricultural non-point source pollution.In this study,the characteristics of runoff,sediment and phosphorus?TP,DP,PP?were monitored and sampled during typical heavy rainfalls in four nested agricultural watersheds?3-1236 hm²?in hilly region with purple soil.The results showed that:Su Rong and Jie Liu watersheds had synchronized runoff,sediment concentration curves,While sediment peak did not respond well to runoff peak in larger watersheds?Daxing and Wanan?.There was a consistent significant relationship between sediment-TP?R>0.6,P<0.01?.The load of sediment and TP was highest in headwater catchment and lowest at the outlet?Wanan?,indicating that larger watershed area was,the smaller load of sediment and phosphorus loss.PP accounted for more than 50%of total phosphorus loss.Various forms of nitrogen concentration curve and flow curve trend about the same,After reaching peak value total nitrogen?TN?concentration slow decline,Later rise again,The concentration of nitrate nitrogen?NO₃-N?line rise as a whole,particulate nitrogen?PN?concentration in runoff process rapidly declined precipitously after peak,Ammonia nitrogen?NH₄-N?content is low and less volatile.PN transported by the surface flow was dominated in the early periods of storm runoff,while NH4-N dominant in the late period,suggesting the importance of subsurface flow transporting of nitrate.The loss loads of N in storm runoff were high,with mean loads of TN was 4.5g/m^-3,Baced on a?MV?curve,the loads of PN mostly distributed in the early portion of storm run-off,showing first flush effects was important and particulate N were transported with overland flow.By contrast,NH₄-N loads mainly were in the later portion of rainfall,implying NH₄-N was transported with subsurface flow.This study investigated the NO₃-N concentrations of groundwater in hilly area of purple soil during 2016.The range of groundwater NO₃-N mean value between8.15mg/L.of 10mg/L,NO₃-N concentration were over the recommendations?US EPA?for drinking water in medium?5?NO₃-N<10mg/L?were approaching the standard.The results of multivariate regression analysis showed that runoff and sediment content could be used to predict phosphorus flux.The difference of phosphorus losses between the scales is mainly due to the difference of land use pattern and their spatial organization in small watershed.A combination of sloping cropland,woodland and paddy field has obvious effect on reducing sediment and phosphorus loss.This study systematically revealed the dynamics of phosphorus transport and its influencing factors by multi-scale monitoring,which made the calculation and prediction of phosphorus transport load in small watershed more reliable.Groundwater nitrate affected by rainfall and fertilizer factors control in time-shifted;Spatial variation is affected by the way of land use and topography conditions.The large surpluses of nitrogen in the soil,Unreasonable agricultural management practices,The root cause of groundwater nitrate content is higher in the region.And rich soil grains is the main channel migration from soil to groundwater.