Arsenic source-sink dynamics under phosphorus competition in sediments from river–lake connected systems†

Abstract

Multiple factors in the river–lake connected system can affect the transport and transformation of arsenic (As) in sediments. In this study, As source and sink characteristics under phosphorus (P) competition in sediments from river (R), lake (L) and lake-centre (LC) of river–lake connected system were analyzed, and the As release regionality and continuity were also discussed. The study showed that the ORP of the sediments at each site was negative with a mean value of −151 mV. The sediments in the R region were weakly acidic and those in the LC region were weakly alkaline. The R region had relatively high EAsC₀ concentrations, while the LC region had the largest EPC₀ value of 0.17 mg L⁻¹. As in the sediments competed very strongly with P for sources and sinks, with the sediments in the R region as a source of strong As and weak P, in the L region as a source of weak As and weak P, and in the LC region as an As sink and P source. Regions of high risk of As release from sediments were the R and L regions. Sediments in the L and LC regions had a high value of DAsS (the degree of As saturation), 8.9–13.1% and 8–13%, respectively, and the P release risk and saturation were inversely proportional to this result. The contribution analysis showed that surface sediments provided the largest contribution of As release, and the release contribution of As(V) was greater than that of As(III). In addition, the microbial community analysis identified Proteobacteria as the most abundant species in the sediments, with a relative abundance ranging from 42.4% to 53.2%. This bacterium, known for its As-metabolizing capabilities, was found to be positively correlated with the risk of As release. The analysis of As content in sediments revealed a gradient of R region < L region < LC region, confirming that rivers are significant contributors of As contamination to the lake.