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

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 (Pr). The aim of this study is to estimate the Pr deposition on the Xiangxi River watershed, and therefore, provide a comprehensive understanding about the Pr deposition on subtropical watersheds in China. Results have shown that maximal Pr deposition fluxes reached 12 kg km-2 in our selected subtropical watershed. Furthermore, we found out the particulate phosphorus (PP) were dominating the total Pr deposition in the Xiangxi River watershed. According to our experiments, certain forms of Pr 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 Pr in runoff water was derived from rainfall and its magnitudes varied with land types. Results suggested that during the dry season, the Pr wet deposition not only was an important source for the Pr transport driven by runoff, but also was one of the most important influencing factors that dominated the Pr transport in subtropical watersheds.