川中紫色土地区不同集水区暴雨氮流失特征分析

Analysis on nitrogen loss characteristics of different catchments in purple soil area of Central Sichuan Basin

农业区域非点源污染排放引起的水体污染是我国水体污染控制与流域治理的重要内容。迄今为止,丘陵区农业小流域内不同土地利用方式下氮素污染机理的径流驱动过程仍不明晰。选择川中紫色土丘陵区3种典型集水区(集镇、农林复合区、林地区),对暴雨过程中非点源氮素迁移特征进行了实地观测和分析,探讨了不同土地利用方式下非点源氮迁移机制及负荷变化特征。分析结果表明:(1)集镇集水区径流对暴雨事件反应最迅速;农林复合区响应较慢,波动幅度较缓;林地集水区植被覆盖度较高,由于植被截留等原因,其响应最慢。(2)集镇集水区总氮(TN)、可溶性氮(DN)及硝态氮(NN)含量最高,且呈多峰值特点;农林复合集水区TN含量相对稳定;林地集水区TN,DN,NN及颗粒态氮(PN)波动最小,且浓度最低。(3)集镇和农林复合区PN和铵态氮(AN)迁移过程呈现一定"初期冲刷效应";而林地TN,DN,NN迁移呈现一定的"初期冲刷效应",且PN迁移"末期冲刷效应"显著。研究成果可为丘陵区复杂小流域污染源识别、污染负荷估算与预测提供科学基础。

The pollution of agricultural nonpoint source to water body is an important content in water body pollution control and basin management in China. However,the runoff-driving mechanism of nitrogen losses in hilly area under different land uses remains poorly understood. 3 typical catchments with different land use types（ township,agroforestry,woodland） in the purple soil hilly area in the central Sichuan Province were selected to research non-point Nitrogen migration mechanism in rainstorm and nitrogen loads variation characteristics. The results showed that（ 1） township runoff response to rainstorm was the most rapid;agroforestry was the second rapid with a gentle fluctuation; forest catchment response was the slowest due to the rainfall interception by denser forest;（ 2） total nitrogen（ TN）,total dissolved nitrogen（ DN） and nitrate nitrogen（ NN） were the highest in township area with multi-peaks,TN content in agroforestry catchment area was relatively stable,TN,DN,NN and particulate nitrogen（ PN） in woodland catchment area had the least fluctuation and the lowest concentration;（ 3） in township and agroforestry area,the transport process of PN and ammonium nitrogen（ AN） showed a certain ＂ initial flushing effect＂,while in woodland area,that of TN,DN and NN also showed a certain ＂ initial flushing effect＂ and PN showed an obvious ＂ late flushing effect＂. This study could provide scientific basis for pollution source identification and pollution load prediction in complex small hilly watershed.