Groundwater Ecosystem Monitoring: Microbial diversity and function, report 2

GNS Science’s Groundwater Ecosystem Monitoring workstream (Strategic Science Infrastructure Fund) aims to investigate groundwater-ecosystem health and identify relationships between microbial diversity and groundwater chemistry. This programme complements the National Groundwater Monitoring Programme (NGMP) and was initiated in 2020. This report is the second in a series of annual reports summarising the results of this monitoring. Conclusions are preliminary and may be adjusted following further sampling and analysis of Aotearoa New Zealand groundwaters in future years. The accompanying datasets include data on microbial taxonomy and functional capability, groundwater chemistry and sample details. This information can be used, for example, by regional authorities to inform groundwater-ecosystem management and protection. Groundwater samples (n = 178) from 44 aquifers across the country were collected at monitoring wells or private wells either by council or GNS Science staff. Each sample was analysed for a chemical suite, including major ions and heavy metals, although the range of parameters varied across samples. Duplicate samples were collected for DNA extraction and sequencing. DNA sequences were classified using either metagenomic analysis (n = 28), or 16S rRNA gene sequencing (n = 145). DNA extraction for sequencing was unsuccessful in five samples.Chemical composition varied across the samples, for example, electrical conductivity 59–2120 µS/cm and redox -486–303 mV. Chloride concentrations ranged between 0.6 and 552.0 mg/L, while bicarbonate (as HCO3) was measured between 16.7 and 849.3 mg/L. Concentrations of potentially toxic elements were elevated in some samples. Variations within chemistry, particularly salinity, have been previously shown to drive microbial diversity in a wide range of environments. This was shown in the corresponding microbial diversity dataset, where microbial communities comprised a wide range of taxa, with 2159 genera identified, although most of these were at low abundance. In total, 88 genera were detected in >90% of samples and 12 genera were ubiquitous across all samples.Sequencing or prediction of functional genes identified potential metabolic capabilities within the microbial communities. The following metabolic functions were investigated: nitrogen cycling, degradation of toxic substances and resistance to heavy metals or antibiotics. Of the 173 samples, 168 were predicted to have the capability for complete denitrification (nitrate to nitrogen). The potential for removing contaminants such as arsenate and mercury was prevalent across all groundwater samples, while resistance to heavy metals and antibiotics was more geographically clustered. Ongoing sampling and monitoring and more consistency in which hydrochemical parameters are measured are necessary to further develop the database. The next Groundwater Ecosystem Monitoring report will focus on identifying correlations between microbial diversity, locations and aquifer lithology (auth)