Anthropogenically Driven Changes to the Metagenome of a Shallow Groundwater and its Effect on Aquifer Reactivity

Microorganisms are endemic to subsurface environments, and it is accepted that they drive most geochemical reactions within aquifer systems. This is true for basic geochemical reactions that drive redox gradients, nutrient cycling, natural remediation of contaminant plumes, denitrification of excess fertilizer, and mobilization of heavy metals (eg. arsenic). Bacteria are endemic in groundwater systems, but living close to the edge of life viability, which means that these systems are in essence large pools of latent reactivity. Even small amounts of nutrient additions can stimulate this latent reactivity. The overall objective of the proposed study is to ascertain if, and to what extent, the addition of nutrients to a previously pristine aquifer alters the native microbial community. In year 1 we will investigate this question in a well field located near the upper Fox River in Waukesha, Wisconsin. The well field consists of a background well containing unaltered groundwater and two river bank inducement wells that pump water that contains treated wastewater effluent. In year 2 of the project, we will examine experimentally the impact of nutrient additions on the pristine well microbial community composition. Water from the pristine well will be collected and used in replicated bottle incubation experiments with sterile wastewater treatment effluent additions. This is one of the few studies known to the authors that propose to look at how the groundwater metagenome responds to a nutrient input in the field as opposed to in laboratory microcosms. Understanding of not only the physical dynamics, but also the changing chemical dynamics around septic systems, heavily fertilized farm fields, confined animal facility operations (CAFOs) and naturally remediated cleanup sites will be invaluable. This will also be important to understanding the fate and transport of other contaminants, the degradation of which is commonly limited by co-metabolic limits of the native microbiota.