Deep groundwater irrigation altered microbial community and increased anammox and methane oxidation in paddy wetlands of Sanjiang Plain, China

Biogeochemical mechanisms and biomarkers of groundwater salinization in Jinghuiqu Irrigation District, China

Groundwater salinization poses significant challenges to water resource management, agriculture, and ecosystem sustainability. However, the biogeochemical mechanisms and microbial responses underlying this process in irrigation districts are still poorly understood. This study integrated hydrochemical ratios (Cl--Cl-/Br-, Cl--NO3-/Cl-), stable isotopes (δ2H, δ18O, δ15N-NO3-, δ18O-NO3-), and the MixSIAR model to investigate the dominant factors contributing to salinization in the Jinghuiqu Irrigation District. The results showed that TDS concentrations in groundwater samples ranged from 688 to 5420 mg/L, with 82 % of the samples exceeding WHO drinking water standards. Groundwater salinization was predominantly driven by mineral dissolution and evaporation, compounded by agricultural and domestic inputs. 16S rRNA microbial sequencing identified Candidatus Omnitrophus from the phylum Verrucomicrobiota as a potential biomarker for saline groundwater. PICRUSt2 predictions revealed that the functional traits of microorganisms in saline groundwater tend to enhance adaptability, whereas those in fresh groundwater are more oriented toward growth and metabolism. Spearman correlation analysis showed strong correlations between carbon fixation and nitrification (r = 0.69) and thiosulfate oxidation (r = 0.60). Additionally, as groundwater salinization progressed, the abundance of nitrate- and sulfate-reducing bacteria increased, further impacting nitrogen, sulfur, and carbon cycles. This study deepens knowledge of the biogeochemical processes driving groundwater salinization in irrigation districts and provides new insights for research and management of groundwater salinization in these regions.

Effects of biodiversity on functional stability of freshwater wetlands: a systematic review

Freshwater wetlands are the wetland ecosystems surrounded by freshwater, which are at the interface of terrestrial and freshwater ecosystems, and are rich in ecological composition and function. Biodiversity in freshwater wetlands plays a key role in maintaining the stability of their habitat functions. Due to anthropogenic interference and global change, the biodiversity of freshwater wetlands decreases, which in turn destroys the habitat function of freshwater wetlands and leads to serious degradation of wetlands. An in-depth understanding of the effects of biodiversity on the stability of habitat function and its regulation in freshwater wetlands is crucial for wetland conservation. Therefore, this paper reviews the environmental drivers of habitat function stability in freshwater wetlands, explores the effects of plant diversity and microbial diversity on habitat function stability, reveals the impacts and mechanisms of habitat changes on biodiversity, and further proposes an outlook for freshwater wetland research. This paper provides an important reference for freshwater wetland conservation and its habitat function enhancement.