Detecting the effect of land-use change on streamflow, sediment and nutrient losses by distributed hydrological simulation

Water shortage and water pollution are two major water issues in Northern China. In recent decades, the decrease in inflow and the deterioration of water quality in the Miyun Reservoir have affected the water supply in Beijing. This paper presents a geomorphology-based non-point source pollution (GBNP) model that links the processes of rainfall-runoff, soil erosion, sediment routing, and pollutant transport. On the basis of long-term simulation of the GBNP model, annual runoff presented a decreasing trend from 1980 to 2005. Total nitrogen (TN) and total phosphorus (TP) loads increased from the early 1980s to the mid-1990s, and then decreased after 1999. The decrease in precipitation and increase in air temperature were the dominant factors in runoff decrease. Afforestation, a water-soil conservation practice, positively affected the reduction of non-point source pollution; however, it also caused a reduction of streamflow. A comparison between 1980-1998 and 1999-2005 showed that land-use changes accounted for 39.1% and 23.7% of the decrease in TN and TP, respectively, as well as 6.6% and 9.2% of the decline in streamflow and sediment load, respectively. Although annual sediment, as well as TN and TP loads decreased after 1999, their long-term accumulation in the reservoir continues to diminish water quality. (C) 2011 Elsevier B.V. All rights reserved.