Modeling the response of river nutrient conditions to land use changes in lowland artificial watersheds (polders)

Abstract

Excess nutrient export from lowland artificial watersheds (polders) led to severe eutrophication and harmful algal blooms of their surrounding rivers and lakes. Taking River Zhong in Lake Taihu basin as the study area, this study attempted to quantify the impacts of polders’ land use changes on river nutrient conditions. A Nitrogen (N) Dynamic Polder model and a Phosphorus (P) Dynamic Polder model was used to estimate N and P export from lowland polders in the context of land use change. The investigation results showed that N and P contribution to River Zhong increased by 7–30% in case that 30% of agricultural lands (paddy lands or dry lands) were changed into residential areas. In case that 30% agricultural lands were changed into water areas, N and P contribution can be decreased by 6% and 35%, respectively. Fertilization period especially during rainy season (from June to August) were the hot moments of nutrient loss, accounted for above 50%. Infiltration was the main pathway of N and P export from polders, accounting for more than 60%. Therefore, from management perspective, we argued controlling urban areas, maintaining water areas and controlling fertilization for polders could be potential strategies for reducing river nutrient concentration in River Zhong.