Nitrogen sources and export in agricultural catchments: A nested catchment comparison

摘要

An experimental agricultural catchment of Wuchuan (area 9.4 km~2), and a nested small catchment (area 1.7 km~2) were selected to investigate nitrogen sources and export in stormflows. Results showed that the mean nitrogen input rate in 2002 was 471.5 kg ha~(-1) over the large catchment, and 421.4 kg ha~(-1) for the smaller. A substantial portion of the nitrogen that entered the catchment was not applied to surface soil of agricultural lands. Nitrogen from animal manure and domestic wastes was deposited partially in the residential lands of the three villages, or volatilized and nitrified. Spatially, a high nitrogen input rate was observed in the residential lands of the villages and the river terraces. The annual export rate was 28.8 kg ha~(-1) from the large catchment in stormflows in 2002, compared to a smaller value of 26.8 kg ha~(-1) for the nested one. The larger nitrogen export rate from the large catchment resulted from both the larger water flows and the higher concentration through the outlets. Understanding the nitrogen sources and export in these catchments could provide a base of knowledge for remediation of diffuse agricultural pollution.