Effects of atmospheric reactive phosphorus deposition on phosphorus transport in a subtropical watershed: A Chinese...

Atmospheric phosphorus (P) deposition is not only an important external macronutrient source for aquatic ecosystems but also a major cause of high export coefficient (EC) values. However, there are limited numbers of studies in the literature that focus on estimating the deposition flux of reactive P (P_r). The aim of this study is to estimate the P_r deposition on the Xiangxi River watershed, and therefore, provide a comprehensive understanding about the P_r deposition on subtropical watersheds in China. Results have shown that maximal P_r deposition fluxes reached 12 kg km^-2 in our selected subtropical watershed. Furthermore, we found out the particulate phosphorus (PP) were dominating the total P_r deposition in the Xiangxi River watershed. According to our experiments, certain forms of P_r deposition were associated with high correlation coefficients with respect to the variation of rainfall intensity. Results also demonstrated that the dissolved organic phosphorus (DOP) and soluble reactive phosphorus (SRP) via wet deposition had large influences on the DOP and SRP concentrations in runoff, while the PO₄-P and PP via wet deposition only affected PO₄-P and PP loads through runoff discharge. Our experiments also shown that most parts of the P_r in runoff water was derived from rainfall and its magnitudes varied with land types. Results suggested that during the dry season, the P_r wet deposition not only was an important source for the P_r transport driven by runoff, but also was one of the most important influencing factors that dominated the P_r transport in subtropical watersheds.