Seasonal variation characteristics and release potential of phosphorus in sediments: a case study of the Qiuxi River, a typical diffuse source pollution river in southwestern China

摘要

Purpose To better control and manage phosphorus (P) in the aquatic environment of the Qiuxi River, a typical river severely influenced by anthropogenic activities in southwest China, the morphological characteristics and the release potential of P in sediments during different water seasons were determined. Materials and methods The overlying water and sediment samples were collected from the Qiuxi River in the normal-water season (NWS), low-water season (LWS), and high-water season (HWS), and physicochemical properties were quantified. Total phosphorus (TP) in sediment and the inorganic phosphorus (P-i) fraction were analyzed using the standard measures technology (SMT) procedure, and organic phosphorus (P-o) was further determined to be labile P-o (LOP), moderately labile P-o (MLOP), or non-labile P-o (NLOP). The release potential of P from the sediments was studied by experiments under simulated conditions. Results and discussion The results showed that P pollution in the Qiuxi River was the most serious during the LWS, with mean TP concentrations in the sediment of 854.6 mg kg(-1), and the release risk of the sediment P was also highest during this water season. The variation in P concentration was significantly influenced by the discharge of domestic sewage, agricultural diffusion, flow rate, and OM. The concentrations of P fractions varied with water season, but P-i was constantly higher than P-o. HCl-extractable P-i (HCl-P-i) accounted for most of the P in the sediments, which was related to its characteristics and the geographical location of the Qiuxi River. The maximum P release (R-max) was 25.9 mg kg(-1) in the LWS and 15.3 mg kg(-1) in the HWS, which were positively correlated with the TP (r(2) = 0.848, p 0.01) and OM (r(2) = 0.847, p 0.01) concentrations in the sediments and explained why the release risk of the sediment P in the LWS was higher than that in the HWS. Conclusions Phosphorus pollution and the P release potential in the sediments of the Qiuxi River were most severe in the LWS, so more effective measures to restrain the release of P should be taken during the LWS. Moreover, OM in sediments should be given more attention owing to its significantly positive correlation with the risk of P release.