Succession in native groundwater microbial communities in response to effluent wastewater

Aquifer storage and recovery techniques are used globally to mitigate increasing demands for groundwater. Microcosms were used to evaluate the effect of wastewater effluent that may be used for aquifer storage and recovery injection on native aquifer microbial communities. Sulfur Springs water was used as the source of aquifer water. The microcosms were 100% spring water, 100% unchlorinated filtered wastewater effluent, or one of three mixtures of unchlorinated filtered wastewater effluent and spring water. The mixture microcosms were 50%, 30%, and 10% unchlorinated filtered wastewater effluent with the balance as spring water. The effluent water was UV treated prior to assembling the microcosms. Sampling was carried out at 0, 2, 4, and 6 days and 5 replicates were run for each mixture. Water chemistry and 16S microbiome analyses were carried out. In terms of water chemistry, spring water and 10% effluent were nearly indistinguishable, 30% and 50% effluent appeared midway between pure spring water and pure effluent. The microbial communities present in the effluent are distinct from the spring water and it appears a third type of community develops over time when effluent and spring water are mixed together. In mixtures of spring and effluent water, there appeared to be a succession of dominant taxa within the microbial communities. At high effluent concentrations (30% and 50% effluent), the succession was more rapid than at low effluent concentrations (10% effluent) but after six days, all the communities in the mixed microcosms had the same single most dominant taxon, Rheinheimera. There were three other highly abundant taxa found in all three mixtures of effluent and spring water at the end of the mixing experiment. The UV treatment did not completely or permanently inactivate the microbial communities from the effluent, so it is difficult from this study to conclude the relative impact of mixing two different microbial communities from the relative impact of mixing water with two very different nutrient profiles