Estimation of Phosphorus Transport Influenced by Climate Change in a Rice Paddy Catchment Using SWAT

Phosphorus is an essential nutrient for maintaining and increasing crop production. Owing to frequent human activities, phosphorus resources cause serious environmental pollution. Simulating phosphorus transport with a hydrological model could help understand the phosphorus loss processes at catchment scale. However, in previous modeling studies, phosphorus calibration and validation usually run in monthly time steps, it is difficult to correctly simulate the phosphorus transport peak. Additionally, most previous studies have disregarded the form of phosphorus in transported processes and only considered the total phosphorus, which cannot accurately assist in understanding the specific process of phosphorus transport. Rice is an important agricultural product, widely planted in Asia, and the particulate inorganic phosphorus loss in rice paddies is generally high. Previous studies could not fully simulate the transport of different phosphorus forms in rice paddy catchments. We analyzed the impact of climate change on phosphorus transport under different fertilization scenarios using the Soil and Water Assessment Tool. We compared mineral phosphorus flux with the sum of particulate phosphorus and dissolved orthophosphate during the calibration and validation processes. The Nash–Sutcliffe efficiencies of mineral and total phosphorus in both the calibration and validation periods were higher than 0.65. Rice paddies are the major source of phosphorus loss from the catchment, amounting to 5.4 kg/ha, and particulate inorganic phosphorus accounted for 53% of total phosphorus loss. The average annual phosphorus export was 30 tons/yr; the maximum value was nine times higher than the minimum value. Precipitation had a clear impact on phosphorus transport. Graphic Abstract Highlights P-P + dissolved PO4-P as MIN-P is suitable to calibrate SWAT for assessing phosphorus transport in catchments with high PIP flux, such as rice paddy catchments. In the study catchment, rice paddies are the major source of phosphorus loss from the catchment, totaling 5.4 kg/ha, and the main phosphorus loss is attached to the suspended sediment. Climate change is closely related to phosphorus transport; special attention should be paid to phosphorus loss during heavy rainfall events.