Tuo Zhang

Sand mining activities can significantly impact the microecology of rivers. Scientific studies are needed for the effective protection and restoration of river ecosystems impacted by sand mining activities. In this study, we used high-throughput sequencing technology to analyse the structure and function of sediment bacterial communities in three river habitats of the Jialing River Basin, namely, a natural river channel (no sand mining activities), a channel with continuous large-scale sand mining activities, and a channel in which sand mining had been terminated one year prior, as well as to analyse the main constraints leading to changes in sediment bacterial communities. The results revealed that the dominant bacteria in the different sand mining environments of the Jialing River were Proteobacteria, Chloroflexi, and Acidobacteria, and that total organic carbon (TOC), moisture content (MC) and total nitrogen (TN) were the main limiting factors affecting the structure of the bacterial community. In addition, large-scale sand mining activities caused significant changes (p < 0.05) in major secondary functions, such as energy metabolism, cofactor and vitamin metabolism, and translation. In summary, the persistence of large-scale sand mining activities led to heterogeneous changes in sediment bacterial community structure and function, which had an important impact on the stability of the ecosystem in the Jialing River Basin.

Sepiolite-modified nano-zero-valent iron (S-nZVI) is used as an amendment and incubated to remediate As-Cd-contaminated soil under three different soil‒water management conditions [moderately wet (MW), continuously flooded (CF) and alternately wet and dry (AWD)]. The results showed that soil pH is in the order of CF > AWD > MW. The soil pH increased approximately 0.5 to 1 unit by 3% and 5% doses after 36 d of incubation. Soil pH was negatively correlated with available As-Cd content under the three water regimes (p < 0.01). All doses of S-nZVI significantly reduced soil available As-Cd under the three soil moistures by 45-80% for As and 5-45% for Cd. Moreover, S-nZVI addition also promoted the transformation of As-Cd in the acid-extracted fraction, oxidation fraction, and reduced fraction to a more stable residue fraction. High-throughput sequencing results showed that high doses of S-nZVI had a significant adverse effect on soil bacterial diversity and richness. After 36 d of incubation, the Chao1 index and the Shannon index were significantly decreased in MW, CF, and AWD, respectively. Decreasing the S-nZVI dose and increasing the incubation time simultaneously reduced As-Cd availability and S-nZVI ecotoxicity in the soil, thereby effectively maintaining the survivability of the original dominant bacteria, increasing the soil pH, and promoting the interaction between dominant bacteria and soil factors in As-Cd cocontaminated soil.