Simulation of the spatial and temporal changes of complex non-point source loads in a lake watershed of central China.

In this study, a coupling model of agricultural and urban non-point source (AUNPS) is established in order to estimate complex non-point source (NPS) pollutant loads in the urban-rural fringe. Furthermore, a spatial-temporal change model of non-point source (CA-AUNPS) is established by the coupling of AUNPS and cellular automata (CA) models. The total nitrogen (TN) and total phosphorus (TP) loads in Tangxun watershed were simulated during 1991-2020, and the results show that: (1) the CA-AUNPS model is an effective tool to simulate the spatial-temporal changes of NPS pollutant loads in urban-rural fringe; (2) in terms of the spatial changes, the TN and TP loads generally showed as rural/urban construction land > farmland > forest/green land, and the high-value areas of NPS pollutant loads expanded from north to south with the increase of construction land; with regard to temporal changes, the TN and TP loads generally displayed an increasing tendency during 1991-2020, and by 2020 the TN and TP loads will increase to 370.06 and 33.89 t yr(-1), respectively; (3) the spatial-temporal changes of TN and TP loads in Tangxun watershed correlate strongly with the land-use, slope, and rainfall.