Arsenic distribution characteristics and release mechanisms in aquaculture lake sediments

Abstract

It is well known that aquaculture can alter the microenvironments of lakes at sediment-water interface (SWI). However, the main mechanisms underlying the effects of aquaculture activities on arsenic (As) transformations are still unclear. In this context, the present study aims to investigate the variations in the sediment As contents in Yangcheng Lake, as well as to assess its chemical transformations, release fluxes, and release mechanisms. The results showed substantial spatial differences in the dissolved As concentrations in the sediment pore water. The As release fluxes at the SWI ranged from 1.32 to 112.09μg/L, with an average value of 33.68μg/L. In addition, the highest As fluxes were observed in the aquaculture areas. The transformation of crystalline hydrous Fe oxide-bound As to adsorbed-As in the aquaculture lake sediments increased the ability of As release. The Partial least squares path modeling results demonstrated the great contributions of organic matter (OM) to the As transformations by influencing the sediment microbial communities and Fe/Mn minerals. The changes in the As fractionation and competing adsorption increased the dissolved As concentrations in the 0-10mm surface sediment. Non-specifically and specifically adsorbed As were the major sources of dissolved As in the sediments. Specifically, microbial reduction of As[V] and dissolution of Fe oxides increased the dissolved As concentrations at the SWI (20 to -20 mm). The results of the current study highlight the positive enhancement effects of aquaculture on As release from sediments. Environmental implicationsUnderstanding the transport and transformation patterns of As in aquaculture lake sediments is crucial for ensuring the protection and safety of aquaculture lakes, as well as for the effective management of water environments. This study showed higher dissolved As concentrations and release fluxes in aquaculture lakes than those in a non-aquaculture lake. Sediments with high total organic carbon (TOC) and P contens promoted the transformation of Fe-bound As to adsorbed-As and dissolved As. In addition, the microbial reduction of As[V] to As[III] played a key role in the As release process. This study highlights the high bioavailability of As in aquaculture lake sediments. Hence, it is crucial to devote great attention to the transformation process of released As from these sediments.