BACTERIAL COMMUNITY ANALYSIS AS A METHOD TO TRACK SURFACE WATER PERTURBATION TO GROUNDWATER

Disease outbreaks from drinking untreated groundwater remain a serious public health concern. More research is needed to properly assess threats from contaminant sources, including surface waters containing elevated pathogen loads, to groundwater wells serving as sources of drinking water. In this study, bacterial community analysis was used to assess bacterial contamination of groundwater downgradient from one oligotrophic, two mesotrophic and two eutrophic lakes in Cape Cod, MA. Groundwater and surface water was easily distinguishable based on bacterial community composition. All groundwater samples had a higher abundance of Acidobacteria, Firmicutes and Nitrospirae, whereas lake water samples contained a higher abundance of Actinobacteria and Cyanobacteria. Within Actinobacteria, multiple unidentified genera from the ACK-M1 family were abundant in the lakes and were also detected in groundwater collected immediately downgradient of the lakes. Mycrocystis spp. and Dolichospermum spp., known to produce cyanotoxins, were observed in the eutrophic lakes, but were not observed in the mesotrophic or oligotrophic or any groundwater samples. Synechococcus spp., a cyanobacterium often associated with harmful algal blooms (HABs), was observed in the groundwater samples collected 7 and 23 m downgradient from the eutrophic lakes. Legionella spp., commonly associated with waterborne disease outbreaks was observed in low abundance but not specific to any lake or groundwater source. Mycobacterium spp., another waterborne pathogen from the phylum Actinobacteria, was observed in all lake water samples; most groundwater samples in the ”lake shadow”, but rarely observed (0 – 0.3%) in groundwater samples collected immediately upgradient from the lakes. ACK-M1 could be a useful indicator for the presence of pathogens from surface water sources in groundwater due to its abundance and specificity to lake water impacted groundwater in this study.