Responses of Riverine Phosphorus Exports to Land Use and Hydrological Regime in the Jiulong River Watershed

Abstract

In-situ monitoring, geographic information technology (GIS), watershed model, and statistical techniques were coupled in this study to explore the responses of riverine phosphorus exports to land use pattern and hydrological regime in the Jiulong River Watershed (JRW). We analyzed riverine phosphorus concentrations and exports from March 2015 to February 2017 across a land use gradient spanning 14 monitored sampling sites. Results showed that significantly spatial and seasonal variations of phosphorus concentrations and exports were observed in JRW. Mean phosphorus concentrations and exports were the highest in the agricultural watershed, followed by the urban watershed, whereas the West River reach had higher mean phosphorus concentration and export than the North River reach. Mean concentrations of phosphorus were higher in spring and winter, whereas lower concentrations were observed in autumn and summer. Phosphorus exports were higher in spring and summer, consistent with the seasonal trend of runoff. Phosphorus concentrations and exports had negative correlations with percentages of forest and bare land, and were positively correlated with cropland and orchard. The responses of riverine phosphorus to land use types and hydrological regime varied across seasons, whereas the relationships between phosphorus concentrations/exports and land use or runoff were the strongest in summer, suggesting that non-point source pollution associated with agricultural activities would be the critical source of riverine phosphorus and an increase in forest percentage could be useful for improving water quality. Overall, the spatiotemporal patterns of phosphorus exports were affected by land use pattern, as well as the characteristics of the hydrological regime.