Aquifer Communities - Can they predict changes in Aotearoa's source (ground)water

Louise Weaver, Judith Webber, Philip Abraham, Bronwyn Humphries, Erin McGill, Pierre-Yves Dupont, Murray Close (Institute of Environmental Science and Research)

Groundwater is an extremely valuable resource for municipal, industrial, farm water and domestic supplies. In New Zealand, 40 per cent of drinking water comes from groundwater aquifers (LAWA, 2022). Unfortunately, due to land use activities, human (anthropogenic) influences can contaminate the aquifer system. While the effects of anthropogenic contaminants are well documented on surface water, little is known about their impact on groundwater resources, particularly how they impact bacterial communities. Molecular methods provide an opportunity to examine the bacterial taxa in aquifers and how they respond to contaminants. In this study, we used Miseq sequencing to assess the bacterial taxa in the aquifer systems across four geographic regions (Southland, Canterbury, Nelson, and Hawkes Bay) of New Zealand. Physicochemical parameters were also measured, and the correlations between physiochemical parameters and bacterial taxa were evaluated.

There were significant differences in bacterial diversity between regions (Adonis, p-value = 0.001). Bacterial assemblages in samples from Nelson and Hawkes Bay were similar to and thus clustered among those from Canterbury, while samples from Southland clustered to the left of the ordination and separated into two smaller clusters along the Y axis. 

The presence of Nitrososphaeria across all regions indicates its potential importance in the nitrogen cycle of groundwater ecosystems. The detection of Methanobacteria in the Canterbury and Hawkes Bay regions and its absence in the Southland and Nelson regions points to regional differences in methane-producing bacterial communities. 

Significant correlations (Spearman Rank Correlation) between bacterial phylum and physicochemical parameters indicated environmental factors' influence on the bacterial community composition. There was a strong correlation between Thaumarchaeota abundance with total dissolved nitrogen (rho 0.533, p<0.0001) and nitrate (r=0.539, p<0.0001), suggesting Thaumarchaeota's potential role in nitrogen cycling processes in groundwater.