Effects Of Different Rainfall Types And Land Use Patterns On The Loss Of Nitrogen And Phosphorus In Fengyu River Watershed

At present,non-point source pollution has become the main reason for water eutrophication in China.It is the comprehensive response of different planting types or land use and its spatial pattern to rainfall and runoff.Different land use types lead to different processes of producing and sinking,and eventually produce different nitrogen.Phosphorus output characteristics.In plateau mountainous agricultural areas,the mechanism of nitrogen and phosphorus loss is more complicated due to mountain precipitation and fragmented land use.Therefore,in this study,the Fengyu River watershed,which is a typical plateau agricultural area,was selected as the research area.The field measurement method and simulated rainfall method were used to analyze the impact of rainfall conditions and land use on nitrogen and phosphorus loss,revealing the nitrogen The natural and artificial driving mechanism of phosphorus loss.The main conclusions of this study are as follows:?1?During the monitoring period,the rainfall in the Fengyu River Basin during the flood season accounted for 77%to 90%of the annual rainfall.Affected by the monsoon climate,the runoff in the flood season of the basin accounted for 48%to 68%of the year.Field observations revealed that the flood season?May-September?was the main loss period of nitrogen and phosphorus in this small watershed.Due to the dilution effect,the nitrogen and phosphorus concentrations in the flood season were 1.86 mg·L^-1and 0.08 mg·L^-1,respectively.It is lower than 1.97 mg·L^-1and 0.09 mg·L^-1in non-flood season.Therefore,rainfall is an important driving factor affecting the loss of nitrogen and phosphorus.?2?Subsequently,the correlation analysis of the rainfall and water quality data for many years in the basin was found,and it was found that different rainfall intensities had different effects on different forms of nitrogen and phosphorus concentrations.The average concentrations of TN and TP are the largest under heavy rain conditions,which are 1.89 mg·L^-1and 0.82 mg·L^-1,respectively,and lower in light rain are 1.08 mg·L^-1and 0.19 mg·L^-1,but in Under heavy rain,the nitrogen and phosphorus concentrations are between moderate and heavy rain.The proportion of different forms of nitrogen and phosphorus also has an influence.The proportion of NH₄⁺-N in TN is greater than that of PN,and the proportion decreases with the increase of rainfall intensity from 76.85%to 57.14%,and then increases to 66.84%during heavy rain;The proportion of TDP in TP is less than PP,and with the increase of rainfall intensity,the proportion increases from 26.32%to 28.00%,and then decreases to 24.39%during heavy rain.?3?Simulated rainfall experiments were conducted on soil type,fertilization intensity and slope,and it was found that fertilization intensity had different effects on the loss of different forms of nitrogen under different soil types and different slopes.Under paddy soil conditions,the concentration of NH₄⁺-N is highest when the fertilizer concentration is 300 kg N·hm^-2,NO₃^--N is highest when it is 60 kg N·hm^-2,and TN is highest when it is 180 kg N·hm^-2;Red soil Under the conditions,the concentrations of NH₄⁺-N and TN are the highest when the fertilizer concentration is 300 kg N·hm^-2,and the NO₃^--N is the highest when the fertilizer concentration is 180 kg N·hm^-2.At the same time,the concentrations of NH₄⁺-N,NO₃^--N and TDN in the paddy soil under different slopes increased rapidly with time and then fell sharply and then tended to be gentle.The nitrogen concentration was compared to 0°>5°;NH₄⁺-N and TDN in red soil the order of concentration is 5°>15°>0°.?4?The Fengyu River watershed in Erhai Basin is mainly dominated by woodland grassland,of which the grassland area is the largest,accounting for 44.44%of the basin area,and the water area is the smallest,accounting for 0.45%of the basin area.Through sampling along the main channel,it is found that the water quality at the source of the basin is good.The nitrogen and phosphorus concentrations are0.54 mg·L^-1and 0.01 mg·L^-1,respectively,which can meet the surface water quality standard of Class II,and is affected by farmland and rural life.Afterwards,the water quality at the sampling site deteriorated,and the average concentration of nitrogen and phosphorus in various forms increased to 5.35 mg·L^-1and0.20 mg·L^-1,which was inferior to category?water quality.Among the different land use types,the main factors affecting water quality are dry land,grassland and water.Among them,the larger the proportion of dry land area,the worse the water quality;the larger the proportion of grassland area,the better the water quality;and the TOC showed a trend of increasing first and then decreasing with the increase of water area.