Science Serving Maryland's Coasts

Michelle D'Aguillo, College of William and Mary

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Dissolved CO2 in Groundwater as a Measure of Microbial Respiration in Agriculturally Dominated Areas


An influx of nitrate (NO3-) from agricultural practices has altered the types and amounts of microbial respiratory processes occurring in the sediment downstream of agricultural fields. This study examined dissolved CO2 in groundwater as a measure of microbial respiration, and compared it to dissolved N2, O2, N2O, and CH4. We found unusually high concentrations of CO2 in nearly all groundwater samples, in relation to presently understood rates of aerobic respiration, denitrification, and methanogenesis. We believe that the excess dissolved CO2 can be partially explained by the application of agricultural lime (CaCO3) and the presence of cations in the soil, which stabilize HCO3- ions from air or soil in the groundwater. A large proportion of the excess CO2 found in our samples is most likely a by-product of alternate anaerobic respiratory pathways (reduction of Mn4+, Fe2+, and SO42-)that were not specifically examined in this study.