Effects of Land Use on Nitrogen Export in Xitiaoxi Watershed
西苕溪流域土地利用对氮素输出影响研究

The hydrological modeling and spatial analysis extensions of Arcview3.2 was used to delineate and select 11 representative sub-watersheds of Xitiaoxi River,a branch of Taihu Lake in China.Land use data derived from TM/ETM satellite images in 2000.Total nitrogen(TN) concentrations were measured 3 times in Jul.,Sep.and Dec.of 2004 within these sub-watersheds,to analyses temporalspatial characteristics of nitrogen concentrations and the effects of land use on nitrogen export.Results show TN concentration increase from upriver to downriver sub-watersheds and generally rising from Jul.to Sep.to Dec.,except upriver sub-watersheds have a contrary trend.It is due to TN concentrations vary greatly depending upon seasonal precipitation conditions and land use type and management across a watershed.Land use composition is a principal factor in controlling the amount of nitrogen exported from a watershed.Nitrogen export decrease with a higher percentage of forest land area,and the percentage of human-induced land use type such as arable land and residential area enlarge can increase the nitrogen export,whereas no relation was found between the size of sub-watersheds and TN concentrations.