Spatiotemporal Variations of Adsorbed Nonpoint Source Nitrogen Pollution in a Highly Erodible Loess Plateau Watershed

摘要

Soil erosion is the main pathway of nutrients to fresh water in highly erodible regions. In this study, a dynamic erosion-type nonpoint source (NPS) pollution model was proposed to investigate spatiotem-poral characteristics of adsorbed NPS total nitrogen (TN) load before and after returning farmland. Results indicate that: 1) the erosion-type NPS TN load showed a significant decreasing trend since the implementation of a returning farmland project from 1997, where the average TN load in 2009-12 was 2719.7 t/a, which decreased by about 80.7% compared with the initial period of governance (1995-98); 2) Spatial distributions of erosion-type NPS TN load are closely related to sediment yield, the high risk values of TN load mainly occur along the main river banks of the Yanhe River watershed from northwest to southeast; 3) Before returning farmland, the adsorbed NPS TN load in the Yanhe River upstream was relatively large, while after that it had a decreasing trend in the upper reaches of the Yanhe River watershed. Dry land is still a critical source area of NPS pollution load in the loess hilly and gully region. Therefore, it is essential to strengthen water conservation measures in highly erodible regions for the amelioration of regional water environment quality.