Houghton, K.M.; Fournier, M.; Tschritter, C. 2022 Effects of saltwater intrusion on groundwater microbial community diversity. Lower Hutt, N.Z.: GNS Science. GNS Science report 2021/39. 45 p.; doi: 10.21420/HDB3-FJ35
Abstract:
Microbial communities in groundwater carry out biochemical processes that are essential ecosystem functions, such as nutrient cycling and removal of contaminants. These processes play an important role in the quality of groundwater used for drinking and irrigation as well as interconnected surface water. The effects of climate change on these communities, e.g. from increasing salt levels from rising sea levels, or from global temperature increases, are unknown. This study used a combination of culture-dependent (growth curves, isolation of bacteria) and culture-independent (marker gene sequencing, functional gene quantification) methods to identify the potential effects of saltwater intrusion on groundwater microbes and their functions. Groundwater samples were collected from sites in two regions, Waikato and Canterbury, and exposed to a range of concentrations of chloride. Each groundwater sample responded differently to chloride, depending on the microbial community present within that sample. Some groundwater microbial communities were negatively impacted by increasing chloride concentrations, including declines in bacteria responsible for nitrate and ammonia removal. These ecosystems should be prioritised for future protection from sea level rise or increased pumping of groundwater for agriculture. Other samples were stimulated in the presence of chloride, often caused by an increase in abundance of salt-tolerant heterotrophic bacteria using sugars, peptides, or organic acids for energy. Identification of keystone species affected by saltwater in these ecosystems will enable management decisions to be made about future abstraction limits or if defences against sea level rise are needed. (auth)
