Effects Of Rainfall And Slope On Nitrogen And Phosphorus Losses From Cultivated And Abandoned Land In The Three Gorges Reservoir Are

Three Gorges Reservoir is an important lake reservoir and water source in China,and its strategic position determines the importance of ecological environment in the reservoir area.The construction and development of Three Gorges Reservoir is always accompanied by agricultural nitrogen and phosphorus pollution,which has become a key issue related to the safe operation of the reservoir,ecological environmental protection and economic development and other efforts.More than 60% of the land in the Three Gorges reservoir area is sloping land,and more than 70% is purple soil with poor erosion resistance,which causes serious loss of nitrogen and phosphorus nutrients due to unreasonable tillage and management measures.In order to clarify the characteristics of nitrogen and phosphorus loss from cropland and abandoned land with different rainfall intensities and slopes,this study used an indoor simulated artificial rainfall experiment to study the flow production,sand production and nitrogen and phosphorus nutrient loss from cropland and abandoned land under different rainfall intensities and slopes,and to construct an empirical formula for nitrogen and phosphorus loss from cropland and abandoned land based on the CREAMS model.The main research results are as follows:(1)Under different rainfall intensities and slopes,the flow and sand production of cultivated land and abandoned land both increased with the increase of rainfall production time,and the flow production of cultivated land was lower than that of abandoned land,and the sand production was higher than that of abandoned land.Under the condition of 15°,the increase of rainfall intensity is more favorable to the sand production of cultivated land and the flow production of abandoned land.Under the condition of 25°,the increase of rainfall intensity is more favorable to the flow production of cultivated land and sand production of abandoned land.Under the low rainfall intensity,the flow production of cultivated land and abandoned land is more influenced by the slope,and there is an obvious interaction between slope and rainfall intensity in soil erosion.Under the same slope,the trends of flow production and sand production with rainfall intensity are 90 mm/h > 60 mm/h > 30 mm/h;under the same rainfall intensity,the trends with slope are 25° > 15°.(2)With increasing rainfall intensity and slope,the runoff total dissolved nitrogen(TDN),nitrate-nitrogen(NN),ammonium-nitrogen(AN)and total dissolved phosphorus(TDP)loss concentrations from cultivated and abandoned land gradually increased.The initial scouring effect of nitrogen and phosphorus loss was obvious.Under different rainfall intensities and slope gradients,runoff and sediment NN were the main forms of nitrogen loss from cultivated and abandoned land,and runoff AN would increase the percentage of loss load with increasing rainfall intensity and slope gradient.Under different rainfall intensities and slopes,nitrogen loss was still dominated by dissolved nitrogen.Under the same slope,the trend of nitrogen and phosphorus loss concentration in both cultivated and abandoned land was 90 mm/h > 60 mm/h > 30 mm/h;under the same rainfall intensity,the trend of nitrogen and phosphorus loss concentration with slope was 25° > 15°.(3)There was a significant positive correlation(p<0.05)between nitrogen and phosphorus nutrient losses and their production of flow and sand in both cultivated and abandoned lands.The relative errors between the predicted nutrient losses and the measured values were within 10%,which indicated that the empirical formulae for nutrient losses were well fitted and could be used for the prediction of nitrogen and phosphorus nutrient losses from cultivated and abandoned land in the reservoir area.