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

Abstract

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.