Effects of Land Use Change on Phosphorus Levels in Surface Waters-a Case Study of a Watershed Strongly Influenced by Agriculture

摘要

Phosphorus (P) loss from diffuse sources remains as the main cause of freshwater eutrophication in agricultural regions. The amount of land used for different agricultural practices may be a strong explanatory factor for the P loading to runoff waters. A prerequisite is that the effect of changes in land use on P levels in surface waters needs to be ascertained and quantified. In this study, a comprehensive approach has been developed to explore the environmental consequences of P levels in receiving water with corresponding land use change in a heavily agriculturally influenced watershed. A coupled simulation using Dyna-CLUE model with grey relational analysis (GRA) and grey model GM (1,1) model was employed to stimulate spatial distribution and area demand. Besides, a comprehensive land use index with degree of P saturation (DPS%) as weight coefficient was developed to examine the statistical and spatial relationships of land use and P levels in receiving waters on regional watershed. Moreover, in order to evaluate the practical impact of land use change on water quality, a planned emigration and watershed ecological reconstruction planning were designed into the scenarios. The potential of changes in land use as an abatement action to curb eutrophication was evaluated by modelling the effect of issued emigration and ecological restoration programs in the local watershed of the Yuqiao water reservoir in northeastern China. Kappa indexes above 0.85 for the validation period verify that the coupled land use change model is able to simulate the effect of the abatement actions on land use. Scenario predictions reveals that local emigration and a comprehensive ecological restoration project as abatement actions could significantly decrease contents of P in receiving surface waters: Relative to year 2012, total P and orthophosphate could be reduced by 36 and 45 %, respectively, by the end of year 2018. This modelling approach can, with moderate modifications, also be adapted to other watersheds. The model developed in this study can thus be used by environmental managers as a tool to identify risk for P loss from diffuse sources within a watershed and assist policy makers to assess the effect on P losses by implementing abatement actions that changes land use.