Intellectual merit: Groundwater holds a large reserve of DIN (dissolved inorganic nitrogen) with extended residence times. Current analysis suggests that 20% of global DIN conversion to N2 (via denitrification) occurs in aquifers. The PIs will focus their efforts on a newly discovered DIN reaction pathway, anaerobic ammonium oxidation (anammox) that combines NH4+ with NO2- to produce N2. Although anammox has proven to be an important route of DIN loss in many marine systems, it is almost completely uncharacterized in groundwater environments despite geochemical conditions that should promote its activity. The preliminary evidence suggests that anammox may exceed denitrification in N-rich aquifers. The PIs propose to investigate anammox, and its connection(s) to denitrification and nitrification at the geochemical and microbial levels through a series of laboratory and newly developed in situ molecular and isotopic investigations. The overall goal of this study is to address the following questions: 1) Does anammox occur at sufficient in situ rates to warrant its consideration as an important mechanism of N loss during groundwater transport? 2) Are there indicative chemical or isotopic signatures for anammox in groundwater that can aid in its detection and quantification? The proposed work will yield the first reported in situ anammox rates for groundwater and define how microbial nitrogen cycling communities (anammox, denitrification, nitrification) interact in a mutualistic or competitive fashion to regulate nitrogen fate in aquifers.
Broader impacts: The project provides internship opportunities through the UCONN Center for Environmental Science and Engineering (CESE). Graduate student support is provided to UNCW and UCONN. Tobias is in a unique position as Coordinator for the UCONN Coastal Studies undergraduate major to incorporate this work into undergraduate education. The project leverages the UNCW Center for Undergraduate Research and Fellowship and will help support two departmental honors degrees. Research experience for high school students will be achieved within the UNCW "Summer Ocean Ventures" program where participants will help with DNA analysis and graduate students act as mentors. The project will support a public lecture on connecting groundwater DIN contamination to coastal eutrophication as part of UCONN's "Coastal Perspectives" and UNCW's "Planet Ocean" public lecture series. Successful efforts to augment groundwater anammox may result in remediation recommendations that can be transferred to regional managers through the Massachusetts USGS district office.
