Nutrient fluxes exhibit significant spatiotemporal heterogeneity due to the interplay of natural processes and anthropogenic factors over the Pearl River Basin (PRB) in southern China. In this study, we combined observational data with Soil and Water Assessment Tool simulations to investigate patterns and controlling mechanisms for each species of nutrients over the PRB. Our results indicate that the strong seasonal variation in nutrient flux is mainly controlled by extensive runoff and fertilizer application. Nitrate is the dominant form of nitrogen, favored by its high mobility in the soil profile as well as its prevalent use in crop cultivation. For phosphorus, inorganic phosphorus dominates during the wet season of high surface flow, while the organic form slightly exceeds its inorganic counterpart during the dry season, attributed to a sufficient source of plant detritus and easy detachment of organic phosphorus from the soil. [JG1] The spatial variability in nutrient intensity across the basin is significant. In the upstream areas, non-point sources of pollutants are prevalent, where inorganic nutrients are notably active in the central northern basin due to high surface flow, while organic nutrients prevail in the agricultural lands of the foothills, exacerbated by considerable soil erosion. In the downstream of urbanized Pearl River Delta, point sources are active, where a markable increase in phosphorus flux is driven by the anthropogenic discharge from the dense population. The combined effects of seasonal surface flow with the non-point upstream and point sources downstream along the stream control the spatiotemporal variability of nutrient species. Our study provides insight into the spatiotemporal variability and dynamics of nutrient fluxes in the streams over the PRB and benefits the understanding of the earth system of land-ocean-atmosphere in the region.
 

ecohydrological processes, fertilizer application, non-point source, point source, runoff, soil and water assessment tool