Bacterial Bioclusters Relate to Hydrochemistry in New Zealand Groundwater

Groundwater is a major source of New Zealand's water supply and supports base flows in rivers. Microbial communities in groundwater ecosystems mediate biogeochemical processes, and it is therefore crucial to understand microbial diversity in these ecosystems. We analysed bacterial assemblages from 35 New Zealand groundwater monitoring sites with varying hydrogeochemical conditions across the country. Proteobacteria was the most abundant phylum, and Variovorax represented the most common taxon. Pseudomonas, Burkholderia, Acidovorax, Janthinobacterium, Polaromonas and Caulobacter were the other common taxa. There was no Operational Taxonomic Unit (OTU) that was found in every one of the 35 samples. Here, we introduce a framework that has potential utility for groundwater ecosystem management, where the samples with similar microbial communities are grouped together into 'bioclusters'. Metabolic inferences derived from the taxonomic data were used to predict the oxygen requirements, metabolic potential and bacterial energy sources of each biocluster. Groundwater chemistry explains 59% of the variation in the relative abundance of all OTUs, with NO3-N, pH, DO, NH4-N, Fe, Br and SO4 displaying the strongest relationships to bioclusters. We propose that the biocluster framework, coupled with metabolic inferences derived from the taxonomic data, may have application outside New Zealand for on-going monitoring of the health of groundwater ecosystems.