Abstract
When compared to surface ecosystems, groundwater sampling has unique constraints, including limited access to ecosystems through wells. In order to monitor groundwater, a detailed understanding of groundwater biota and what biological sampling of wells truly reflects, is paramount. This study aims to address this uncertainty, comparing the composition of biota in groundwater wells prior to and after purging, with samples collected prior to purging reflecting a potentially artificial environment and samples collected after purging representing the surrounding aquifer. This study uses DNA community profiling (metabarcoding) of 16S rDNA and 18S rDNA, combined with traditional stygofauna sampling methods, to characterise groundwater biota from four catchments within eastern Australia. Aquifer waters were dominated by Archaea and bacteria (e.g. Nitrosopumilales) that are often associated with nitrification processes, and contained a greater proportion of bacteria (e.g. Anaerolineales) associated with fermenting processes compared to well waters. In contrast, unpurged wells contained greater proportions of pathogenic bacteria and bacteria often associated with denitrification processes. In terms of eukaryotes, the abundances of copepods, syncarids and oligochaetes and total abundances of stygofauna were greater in wells than aquifers. These findings highlight the need to consider sampling requirements when completing groundwater ecology surveys.
Highlights
There were seven archaea and 88 bacteria orders identified within the samples, with six bacteria and one archaea only being identified to the domain level
Well samples were dominated by bacteria from the orders Burkholderiales, Neisseriales, Actinomycetales, Pseudomondales, Xanthomonadales and Sphingomonadales (Fig. 1)
It is not surprising that wells and aquifers support different biological assemblages, albeit with a great deal of commonality because the well water is derived directly from the surrounding aquifer. The consequence of this difference is that samples collected from wells alone, without accessing groundwater from the surrounding aquifer, may present an incomplete picture of the aquifer community
Summary
Previous studies have shown differences in microbial assemblages between well and aquifer samples using community fingerprinting techniques (e.g. TRFLP)[27] and flow cytometry[28]. Whilst such studies have shown differences in the structure and abundance of microbial communities, the lack of taxonomic resolution in these methods means that the implications of purging (or not) on assessments of biological structure and potential ecosystem function in groundwaters have not yet been adequately explored. The aims of this study are to describe the compositional differences in prokaryotic and eukaryotic communities within aquifer and unpurged well waters using traditional morphological analysis and metagenomics techniques, and to explore the implications of any such differences for sampling and assessments of groundwater ecosystems
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