How arsenic contamination influences downslope wetland plant and microbial community structure and function

Vegetation morphology and phytobiology intervene in heavy metal contamination of surface sediments in Yangtze River Estuary

Accumulation of heavy metals in estuaries can represent potential risks to the aquatic environment and public health. Estuarine coastal vegetation's physical form and biological function have important effects on dynamic processes and migration of pollutants in estuaries. Field observations were conducted at sites SJG and LHK in the Yangtze River Estuary (YRE) from September 2021 to February 2022 and September 2022 to December 2022. Site LHK (Liuhekou) represents a typical natural environment, whereas Site SJG (Sanjiagang) is more significantly influenced by anthropogenic activities. At both sites, samples of unvegetated sediments, vegetated sediment, and vegetation were collected and analyzed for six heavy metals (As, Cd, Cr, Pb, Cu, Zn). The sequence of heavy metal concentrations in both sediments and vegetation was as follows: Zn > Cr > As > Pb > Cu > Cd. The results of the contamination assessment indicated that the risk of heavy metal contamination was higher at SJG than at LHK. Cr, As, and Cd were identified as pollutants, with Cd posing the main potential ecological risk. Correlation and principal component analyses indicated that anthropogenic emissions and atmospheric deposition were the main sources of heavy metal contamination, with vegetation exhibiting elemental variability in heavy metal interception. Phytobiological analyses of the pollutant elements Cr, As, and Cd indicated that phytobiology's attenuation of sediment heavy metal contamination was significant based on metabolic processes. However, the hyper-enrichment of Cd was independent of metabolism, with its concentration stabilizing around biotoxic levels. The results in this paper promote a deeper understanding of heavy metal mitigation under the biological effectiveness of vegetation in coastal areas of the Yangtze River Estuary. The proposed analytical method provides ideas for the study of contaminant partitioning under the influence of vegetation in estuaries and coastal water environments.

Impact of drainage on peatland soil environments and greenhouse gas emissions in Northeast China

Peatlands are vital for global carbon storage, but drainage significantly disrupts their natural carbon cycling. Drainage alters peatland soil environments in complex ways, affecting factors such as water table, soil temperature, organic carbon (SOC), pH, and microbial communities. However, how these factors interact to influence GHG emissions remains unclear. In this study, we compared water table, soil temperature, soil properties, microbial community structure, and GHG emissions across three zones of a peatland in Northeast China undergoing drainage: drained, transition, and natural areas. The average water table in the drained area was significantly lower than in the natural area (from 11.45 cm to -13.47 cm), shifting from waterlogged to unsaturated conditions. Deep soil temperatures in the drained area decreased by 1 ~ 3 °C. The pH of the upper soil layer was higher in the drained area (5.05 ~ 5.29 vs. 4.64 ~ 4.71), while SOC was lower (197.31 ~ 374.75 g/kg vs. 437.05 ~ 512.71 g/kg). Aerobic bacteria (mainly Solibacter) were more abundant in the drained area, while methanogens (mainly hydrogenotrophic) declined significantly. Fungal diversity increased from the natural to drained area with increased negative interactions and enhanced network modularity. Drainage reduced CH4 emissions but increased CO2 and N2O emissions, resulting in a significant rise in net GHG emissions (8.86 ~ 10.65 vs. 22.27 ~ 24.26 t CO2-eq·ha⁻¹·season⁻¹), primarily driven by increased CO2. CO2 emissions were positively correlated with soil temperature, aerobic bacteria, facultatively anaerobic bacteria and pH, but negatively correlated with water table, anaerobic bacteria, soil moisture and C/N ratio. CH4 flux was positively correlated with methanogens and water table, but negatively correlated with pH. The effects of drainage were more pronounced near drainage ditches, particularly for CO2 emissions, highlighting the localized impacts of drainage on peatland GHG fluxes.

Synthesis, characterization, and efficacy of alkali-activated materials from mine tailings: A review

Annually, over 5 billion metric tons of tailings are produced worldwide as byproducts of mining processes, posing significant environmental risks due to their potential to pollute and disrupt ecosystems. Concurrently, the production of portland cement (PC), the primary binder in cementitious materials is a major contributor to global anthropogenic carbon dioxide emissions. With the escalating demand for PC, a corresponding surge in carbon emissions is inevitable. Alkali-activated materials (AAMs) present a greener alternative to PC, given their production primarily utilizes industrial wastes. Traditional precursors for AAMs, such as fly ash and slag, however, are not universally available-Canada, for instance, faces a scarcity of fly ash for AAM production. In response to the dual challenges of managing mine tailings and reducing PC's environmental footprint, this review proposes the innovative use of mine tailings as an alternative binder to PC. This paper offers a thorough examination of mine tailings' properties, methodologies to enhance their suitability for AAM synthesis, and an analysis of AAMs produced from diverse tailing sources. Additionally, this paper explores the associated challenges and future prospects, providing a rounded overview of this promising avenue in sustainable construction materials.

Arbuscular Mycorrhizal Fungi Alter Arsenic Translocation Characteristics of Iris tectorum Maxim

Arsenic (As) pollution in wetlands, mainly as As(III) and As(V), has threatened wetland plant growth. It has been well documented that arbuscular mycorrhizal (AM) fungi can alleviate As stress in terrestrial plants. However, whether AM fungi can protect natural wetland plants from As stress remains largely unknown. Therefore, three hydroponic experiments were conducted in which Iris tectorum Maxim. (I. tectorum) plants were exposed to As(III) or As(V) stresses, to investigate the effects of mycorrhizal inoculation on As uptake, efflux, and accumulation. The results suggested that short-term kinetics of As influx in I. tectorum followed the Michaelis-Menten function. Mycorrhizal inoculation decreased the maximum uptake rate (Vmax) and Michaelis constant (Km) of plants for As(III) influx, while yielding no significant difference in As(V) influx. Generally, mycorrhizal plants released more As into environments after 72 h efflux, especially under As(V) exposure. Moreover, mycorrhizal plants exhibited potential higher As accumulation capacity, probably due to more active As reduction, which was one of the mechanisms through which AM fungi mitigate As phytotoxicity. Our study has revealed the role of aerobic microorganism AM fungi in regulating As translocation in wetland plants and supports the involvement of AM fungi in alleviating plant As stress in anaerobic wetlands.

Out of site, out of mind: Changes in feather moss phyllosphere microbiota in mine offsite boreal landscapes

Plant-microbe interactions play a crucial role in maintaining biodiversity and ecological services in boreal forest biomes. Mining for minerals, and especially the emission of heavy metal-enriched dust from mine sites, is a potential threat to biodiversity in offsite landscapes. Understanding the impacts of mining on surrounding phyllosphere microbiota is especially lacking. To investigate this, we characterized bacterial and fungal communities in the phyllosphere of feather moss Pleurozium schreberi (Brid). Mitt in boreal landscapes near six gold mine sites at different stages of the mine lifecycle. We found that (1) both mining stage and ecosystem type are drivers of the phyllosphere microbial community structure in mine offsite landscapes; (2) Bacterial alpha diversity is more sensitive than fungal alpha diversity to mining stage, while beta diversity of both groups is impacted; (3) mixed and deciduous forests have a higher alpha diversity and a distinct microbial community structure when compared to coniferous and open canopy ecosystems; (4) the strongest effects are detectable within 0.2 km from operating mines. These results confirmed the presence of offsite effects of mine sites on the phyllosphere microbiota in boreal forests, as well as identified mining stage and ecosystem type as drivers of these effects. Furthermore, the footprint was quantified at 0.2 km, providing a reference distance within which mining companies and policy makers should pay more attention during ecological assessment and for the development of mitigation strategies. Further studies are needed to assess how these offsite effects of mines affect the functioning of boreal ecosystems.