Impacts of climate and land-use changes on the migration of non-point source nitrogen and phosphorus during rainfall-runoff in the Jialing River Watershed, China

Abstract

Summary The loss of nitrogen and phosphorus via non-point source (NPS) pollution in the Jialing River Watershed has become the main pollution sources of river waters in the Three Gorges reservoir area in the past decades, while climatic conditions and human activities directly affect changes of rainfall-runoff and land use types which are closely related to NPS pollution. This study is to assess the impact of climate change on hydrological behavior considering future land-use types and rural residential area and their propagation to NPS pollution loads. An integrated pollution load model composed of regional climate, the Semi-distributed Land Use based Runoff Processes (SLURPs) hydrological model and the improved export coefficient approach within a single framework was explored and developed to assess impacts of climate and land-use changes on NPS pollution load. Climate data for the Special Report on Emissions Scenarios (SRESs) future scenario B2 from Met Office Hadley center were generated and used as the input data for the runoff and NPS load evaluation of the Jialing River Watershed and the Markov process was used to forecast changes of land use types, respectively. Simulations of present and future regional NPS pollution from land use, livestock and poultry breeding, and agricultural population over the Jialing River Watershed were performed to investigate the potential impacts of global climate change on river water quality using the established model. Results demonstrate that: (1) Annual pollution load would obviously change due to variations of runoff and livestock and poultry breeding, the largest growth months in one year for total nitrogen (TN) and total phosphorus (TP) load are both in June, which is in accordance with changes of rainfall amount. (2) The impacts of global climate change on pollution load are relatively greater when compared to the impacts of future livestock and poultry breeding increase or agricultural population reduction; the effects from runoff increment leads to approximately 28.6% and 22.5% increases of TN and TP pollution load, respectively. And (3) the impacts of land-use change have shown insignificant effect due to soil conservation measures, whereas the impacts of rural residential area account for great proportion changes, of which about 5% of its increases are contributed to the increase of livestock and poultry breeding; but the biggest contribution rate is still from the output of different land use types. These data will be useful and valuable in evaluating potential NPS pollution load for the control of watershed pollution in the future and understanding its migration and transformation in a large-scale watershed where meteorological and underlying surface data are mutative.