紫色丘陵区小流域典型降雨径流氮磷流失特征

Characteristics of Nitrogen and Phosphorus Losses in Typical Rainfall-runoff Events in a Small Watershed in Hilly Area of Purple Soil

对2007年盐亭小流域两场典型降雨(施肥后首场大雨和大暴雨)的径流过程进行了连续监测,同步测定了径流量、氮磷浓度,旨在阐明农业小流域典型降雨氮磷流失随降雨径流的变异规律。结果表明,流量曲线与浓度过程线变化趋势一致。整个径流过程中的氨态氮(AN)与磷酸盐(PO34--P)浓度较低且波动较小。初期径流颗粒态氮(PN)、颗粒态磷(PP)与总磷(TP)的浓度高于后期径流,初期冲刷效应明显。颗粒态氮(PN)是氮素在径流初期迁移的主要形态,而后期以硝态氮(NN)为主;但PP是整个径流过程中的主要迁移形态。初期径流中AN、PN、TP、PP及泥沙(SS)负荷分布较大,而硝态氮(NN)、总氮(TN)和PO34--P则主要分布在径流后期。污染物初期冲刷和NN后期淋溶是暴雨径流氮素流失的主要原因,而施肥后首场降雨氮素流失的主要原因是NN淋溶。暴雨径流产生氮磷负荷巨大,TN与TP分别为167.04kg和20.75kg;而施肥后首场大雨径流氮磷流失负荷较小,分别为12.07kg(TN)、1.04kg(TP),其中60%的TN以NN流失。

First heavy rainfall after fertilization and heavy storm were typical rainfall events in hilly area of purple soil, which affected nitrogen and phosphorus losses from agricultural watershed. Rainfall-runoff discharge, pollutant concentrations and loads combined with those two typical rainfall-runoff events were monitored at a small watershed in the central Sichuan Province, China in 2007. The objects of study were to investigate： （ 1 ）changes of nitrogen and phosphorus losses with rainfall-runoff; and（2 ）the effects of rainfall conditions on nitrogen and phosphorous losses. The results showed that changes of the concentrations for nitrogen and phosphorus with time were same to that for rainfall-runoff discharge. The concentrations of ammonium（ AN ）and phosphate （PO4^3--P）in the runoff kept low with small variations during the rainfall process. The concentrations of particulate nitrogen （PN）, particulate phosphorus （PP）, and total phosphorous （TP）were much higher in the early stage of the rainfall-runoff than those in the later stage, indicating that significant initial wash-out effects of occurred to PN, PP and TP. In initial rainfall-runoff, PN was the main transport form of nitrogen, while nitrate-nitrogen （NN）dominated in the later portion. PP was the main transport form of phosphorus during the whole rainfall-runoff process. The loads of AN, PN, TP, PP, and sediment （SS）were mostly transported by the early portion of rainfall-runoff, and NN, TN and PO4^3--P were in the later portion. Transport forms and loads of pollutants were affected by rainfall conditions. Nitrogen losses from storm runoff were influenced by two transport processes with initial wash-out effect and followed by NN leaching, while only by the NN leaching process in heavy rainfall-runoff after fertilization. Nitrogen and phosphorus losses from first heavy rainfall-runoff after fertilization were lower with the loads of 12.07 kg for TN and 1.04 kg for TP, and 60% of TN load was lost as NN from heavy rainfall-runoff;while that from storm-runoff were larger with the loads of 167.04 kg for TN and 20.75 kg for TP, which could pose great threats to Yangtse downstream water environment.