Michelle D'Aguillo, College of William and Mary

Class Year:

2008

Mentor:

Tom Fisher, Ph.D.

Abstract:

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 SO₄^2-)that were not specifically examined in this study.

Location:

Horn Point Laboratory