A comparative assessment of groundwater ecosystems under irrigated agriculture and pasture

The impacts of intensive agriculture on underlying groundwater ecosystems are not yet fully understood, although agricultural practices are firmly implicated in the modification of stygofauna (invertebrate) and microbial populations in aquifers, primarily through changes in water quality associated with irrigated agriculture. The aim of this study was to determine how biological communities in groundwater vary with agricultural land use, and along environmental gradients. Biological and environmental samples were collected from groundwater under irrigated agricultural landscapes and pasture in the Condamine Catchment (QLD), and Gwydir Catchment (NSW). Bacterial populations were evaluated through the analysis of high-throughput 16S rDNA sequence data. The findings of this study did not support the hypothesis that stygofauna distributions vary with agricultural land-use. Molecular data did not support a relationship between microbial distributions and agricultural land-use. Microbial assemblages became more dissimilar with increasing geographic distance. Microbial and stygofauna distributions were poorly correlated with groundwater chemistry gradients. In summary, the influence of agriculture on stygofauna community structure is likey to be limited, since their distributions in the landscape are largely defined by physical limitations of the alluvial aquifer environment. In contrast, the influence of agricultural land-use on groundwater quality is likely to have a quantifiable bearing on microbial distributions, although evidence to support this hypothesis was not forthcoming from the environmental and molecular analysis here. To assess the hypothesis that microbial communities differ with agricultural land-use, further studies should use a metagenomic sequencing approach to estimate the relative abundance of microbes between sites.