Salinity as a major influence on groundwater microbial communities in agricultural landscapes.

Context. Understanding the impacts of salinity on groundwater microbial communities is imperative, because these communities influence groundwater chemistry, quality, and its suitability for use by humans and the environment. Aim. To assess groundwater salinisation and its influence on groundwater microbial communities within the Murray-Darling Basin (MDB), Australia. Methods. Alluvial aquifers were sampled from 41 bores, within the Lachlan, Murrumbidgee and Murray catchments. Environmental DNA (eDNA), microbial activity and water-quality variables were measured to evaluate microbial communities, which were then correlated with electrical conductivity (EC) and other environmental variables. Results. Our results indicated widespread groundwater salinisation within the MDB, with EC ranging from 63 to 51 257 μS cm^-1. The highest EC values were recorded in the Murray catchment; however, mean EC values did not differ significantly among catchments (P > 0.05). The composition of microbial communities differed significantly between sites with low (<3000 μS cm^-1) and high (>3000 μS cm^-1) EC. Microbial activity, richness and abundances were all greater at low- than high-EC sites. Conclusions. Changes to microbial communities as demonstrated here may have impacts on biogeochemical cycling and ecosystem resilience. Implications. The detrimental ecological impacts of salinity are not limited to groundwater microbes, but present a larger ecological issue affecting all groundwater-dependent ecosystems. [ABSTRACT FROM AUTHOR]