Coupling mountain and lowland watershed models to characterize nutrient loading: An eight-year investigation in Lake Chaohu Basin

•A model was proposed for mountain-lowland watershed with a average model fit of R2 = 0.66.•Domestic sewage and crop pollution contribute 56% and 42% of nitrogen (N) and phosphorus (P) loading.•Polders showed a large potential of N and P reduction, with a rate of 61.69% and 64.93%.