Functional distributions of subsurface microbial communities in the Hualalai watershed

We investigated subsurface microbial features (community structure and function) with regard to N (denitrification) and S (sulfoxidizing denitrification and sulfate reduction) cycling in deep, volcanic Hawaiian island aquifers. The Hualalai watershed (Kona, HI) has a semi-arid climate and is acutely vulnerable to stress from urban development due to the complete dependence (100%) upon groundwater for domestic and agricultural water use. The watershed has the potential for large inputs of N due to personal on-site sewage disposal systems (OSDS, e.g. cesspools, septic tanks), as well as S inputs from salt-water intrusion and geothermal activity. In addition, fluctuating rainfall patterns reveal a drying trend, and rising temperatures in the Pacific Islands is predicted to result in decreasing recharge and groundwater storage threatening the future of secure and safe freshwater supplies. This study focuses on samples from the freshest groundwater wells from across the watershed sampled over a two year period (2017-2019). The research questions that framed the study included: 1) How does geochemistry differ spatially and temporally across both aquifers that make up the Hualalai watershed (Kiholo and Keauhou), 2) Does the geochemical structure of the aquifers drive the microbial community structure, and 3) What is the microbial potential (structure and function) with regard to both N and S cycling (denitrification, sulfoxidizing denitrification and sulfate reducing) in these aquifers?