Effects of the spatial and temporal variability of land use and precipitation on stream quality of Xitiaoxi watershed in eastern China

摘要

This paper presents the findings of a study which has investigated the effects of land use and precipitation space-time variability upon the stream quality in Xitiaoxi watershed, located in the southwest of Taihu basin, China. A variety of hydrological variables and water quality parameters were monitored at some gauging stations and other selected control sections in the past several decades. Significant changes have taken place in the underlying surface since 2002 as a result of intensive human activities. The precipitation data of 2002 and 2008 represent two entirely different monthly distribution patterns. The land use and precipitation data of 2002 and 2008 are used to explore the variability of stream quality. Based on this, the effects of the spatial distribution of land use and precipitation on the stream quality are discussed by geospatial analysis in the ArcGIS and ArcSWAT model. The spatial variability of the data used in this study includes six land use types (Arable land, orchard, forest, build-up land, water body and bare land) and precipitation data from 17 rainfall gauging stations. With the 20 sections as outlets, the watershed was divided into 20 subwatersheds in ArcSWAT. The contaminant concentrations including COD, BOD, DO, NH_4-N, TN and TP of the 12 times sampling at each of the 20 monitoring sections were analysed by comparison. The land use structure and change of each subwatershed, together with the spatial variability and monthly precipitation distribution, is considered. The results show that: (1) the land use structure and spatial variability of precipitation in each subwatershed are the main causes of the spatial variation of stream quality; (2) the monthly precipitation distribution pattern is the main cause of temporal variation of stream quality. This paper probes into the comprehensive effects of the spatial and temporal variability of land use and precipitation by quantitative methodology. The results obtained from this study provide support for water resources management and water environment protection under the rapid urbanization background. They also provide insights on the relevance of water resources sustainability and harmonious coexistence between man and nature.