Black blooms-induced adaptive responses of sulfate reduction bacteria in a shallow freshwater lake

Decomposition of waterside plants greatly affects the transformation and mobility of sedimentary antimony in water-sediment systems after emergency treatment: A microcosm study

Polyferric sulfate (PFS) coagulation has proven to be effective in addressing antimony (Sb) water pollution accidents; however, the impact of waterside plant decomposition on its effectiveness has not been adequately elucidated. This study investigated the effects of Alternanthera philoxeroides (AP) and Digitaria sanguinalis (DS) decomposition on Sb cycling after PFS treatment. Without plant decomposition, the Fe(OH)3 hydrolysate-associated Sb remained stable, and the sediment continued to exhibit Sb sink properties. Plant residue decomposition facilitated sedimentary Sb release, and DS decomposition had a greater impact than AP decomposition. The strong decomposition phases triggered abiotic/biotic reduction processes, leading to Fe(OH)3 dissolution and subsequent Sb(V) release. Concurrently, sulfate reduction and dissolved organic matter (DOM) release regulated Sb mobility. In addition, Sb(V) reduction occurred, and Sb(III) was elevated in the overlying water. The Sb(III) levels gradually decreased during the later aerobic stages, however, did not completely disappear within a short timeframe. Furthermore, the role of the sediment as an Sb sink was significantly hindered, maintaining relatively high levels of dissolved Sb. Sedimentary Sb speciation analysis revealed that plant decomposition induced a shift in Fe-oxyhydroxide-bound Sb to more bioavailable and stable fractions. Our results indicate that plant residue decomposition easily deteriorates PFS efficiency and increases the risk of secondary Sb pollution in water-sediment systems.

The decomposition of algae has a greater impact on heavy metal transformation in freshwater lake sediments than that of macrophytes

Heavy metal (HM) pollution is a major concern in freshwater ecosystem management. The different types of endogenous organic matter and the way their decomposition affects HM transformation in freshwater lakes is not well understood. An ex situ mesocosm study was conducted to compare HM transformation in sediments during anaerobic decomposition of cyanobacterial bloom biomass (CBB) and submerged cyanobacterial vegetation in Lake Taihu, known as Potamogeton malaianus (PM). Microbial community structures were examined through Illumina sequencing of 16S rDNA. Results indicate that Zn had a remarkably higher amount of potential mobile fraction than other heavy metals (Cr, Pb, Cu, Ni, and Cd) detected in sediments, especially in sediments collected from CBB-dominated areas (approximately 150 mg kg-1). CBB decomposition has caused a significant increase in exchangeable Zn content in sediments and a decrease in reducible Zn that was three times greater than PM decomposition. Additionally, oxidizable Zn content declined during CBB decomposition but increased during PM decomposition. Furthermore, the relative abundance of the main fermentative bacteria and some sulfate-reducing bacteria genera (e.g., Desulfomicrobium) were significantly associated with the HM content of exchangeable and reducible fractions during CBB decomposition. Overall, the findings indicate that Zn is more susceptible to endogenous organic matter decomposition than other metals in freshwater lakes, and the impacts of CBB decomposition on the transformation of heavy metals in sediment are greater than that of submerged macrophyte decomposition.

Immobilization of phosphorus in water-sediment system by iron-modified attapulgite, calcite, bentonite and dolomite under feed input condition: Efficiency, mechanism, application mode effect and response of microbial communities and iron mobilization

Four kinds of iron-based materials, i.e., iron-modified attapulgite, calcite, bentonite and dolomite (abbreviated as Fe-ATP, Fe-CA, Fe-BT and Fe-DOL, respectively) were prepared and used to immobilize the phosphorus in the system of overlying water (O-water) and sediment under the feed input condition, and their immobilization efficiencies and mechanisms were investigated. The influence of application mode on the immobilization of phosphorus in the water-sediment system by Fe-ATP, Fe-CA, Fe-BT and Fe-DOL was researched. The effects of Fe-ATP, Fe-CA, Fe-BT and Fe-DOL on the concentration of labile iron in the water-sediment system and the microbial communities in sediment were also studied. The results showed that the Fe-ATP, Fe-CA, Fe-BT and Fe-DOL addition all can effectively immobilize the soluble reactive phosphorus (SRP), dissolved total phosphorus (DTP) and diffusive gradients in thin-films (DGT)-labile phosphorus in O-water under the feed input condition, and also had the ability to inactivate the DGT-labile phosphorus in the top sediment. Although the change in the application mode from the one-time addition to the multiple addition reduced the inactivation efficiencies of SRP and DTP in O-water in the early period of application, it increased the immobilization efficiencies in the later period of application. Although Fe-ATP, Fe-CA, Fe-BT and Fe-DOL had a certain releasing risk of iron into the pore water, they had negligible risk of iron release into O-water. The addition of Fe-ATP, Fe-CA, Fe-BT or Fe-DOL reshaped the sediment bacterial community structure and can affect the microorganism-driven phosphorus cycle in the sediment. Results of this work suggest that Fe-ATP, Fe-CA, Fe-BT and Fe-DOL are promising phosphorus-inactivation materials to immobilize the phosphorus in the water-sediment system under the feed input condition.

Distribution heterogeneity of sediment bacterial community in the river-lake system impacted by nonferrous metal mines: Diversity, composition and co-occurrence patterns

Metal(loid) pollution caused by mining activities can affect microbial communities. However, knowledge of the diversity, composition, and co-occurrence patterns of bacterial communities in aquatic systems impacted by nonferrous metal mines. Here, the metal(loid) contents and bacterial communities in sediments from the Zijiang River (tributary to mainstream) to Dongting Lake were investigated by geochemical and molecular biology methods. The results indicated that the river sediments had lower pH and higher ecological risk of metal(loid)s than the lake sediment. The diversity and composition of bacterial communities in river sediments significantly (p < 0.05) differed from those in lake sediments, showing distributional heterogeneity. The biomarkers of tributary, mainstream, and lake sediments were mainly members of Deltaproteobacteria, Firmicutes, and Nitrospirae, respectively, reflecting species sorting in different habitats. Multivariate statistical analysis demonstrated that total and bioavailable Sb, As, and Zn were positively correlated with bacterial community richness. pH, TOC, TN, and Zn were crucial factors in shaping the distribution difference of bacterial communities. Environment-bacteria network analysis indicated that pH, SO42-, and total and bioavailable As and Sb greatly influenced the bacterial composition at the genus level. Bacteria-bacteria network analysis manifested that the co-occurrence network in mainstream sediments with a higher risk of metal(loid) pollution exhibited higher modularity and connectivity, which might be the survival mechanism for bacterial communities adapted to metal(loid) pollution. This study can provide a theoretical basis for understanding the ecological status of aquatic systems.

Effect of remediation reagents on bacterial composition and ecological function in black-odorous water sediments

Black-odorous urban water bodies and sediments pose a serious environmental problem. In this study, we conducted microcosm batch experiments to investigate the effect of remediation reagents (magnesium hydroxide and calcium nitrate) on native bacterial communities and their ecological functions in the black-odorous sediment of urban water. The dominant phyla (Proteobacteria, Actinobacteria, Chloroflexi, and Planctomycetes) and classes (Alphaproteobacteria, Betaproteobacteria, and Gammaproteobacteria, Actinobacteria, Anaerolineae, and Planctomycetia) were determined under calcium nitrate and magnesium hydroxide treatments. Functional groups related to aerobic metabolism, including aerobic chemoheterotrophy, dark sulfide oxidation, and correlated dominant genera (Thiobacillus, Lysobacter, Gp16, and Gaiella) became more abundant under calcium nitrate treatment, whereas functional genes potentially involved in dissimilatory sulfate reduction became less abundant. The relative abundance of chloroplasts, fermentation, and correlated genera (Desulfomonile and unclassified Cyanobacteria) decreased under magnesium hydroxide treatment. Overall, these results indicated that calcium nitrate addition improved hypoxia-related reducing conditions in the sediment and promoted aerobic chemoheterotrophy.