Date of Award
Master of Science in Natural Resources Science
Natural Resources Science
Nitrate (NO3-) is the most commonly detected groundwater pollutant in the U.S. Sources of NO3- in the environment include agriculture, septic systems, and atmosphere deposition. Riparian forests have been found to prevent the movement of NO3- from upland areas to ground and surface waters. However, the mechanisms responsible for NO3- attenuation in riparian forests are variable and poorly characterized. There is particular uncertainty about the factors affecting NO3- in groundwater beneath riparian forests. We measured denitrification (the conversion of NO3- to N gas), microbial respiration, and total microbial readily mineralizable and dissolved carbon (C) in aquifer material taken from beneath a riparian forest that had been experimentally dosed with groundwater NO3-. Samples were taken 1 and 5 months after experimental dosing began, from 3 locations between the upland edge and the streamside of the riparian zone. Denitrification and respiration were measured in 5 day laboratory incubations using in situ temperatures and oxygen levels. Amendment studies were done to determine the role of oxygen and C as limiting factors for denitrification. Carbon pools were measured in samples taken from the experimentally dosed areas as well as in “control” sites, immediately adjacent to dosed areas. Denitrification was very low in samples taken 1 month after dosing and was strongly limited by C. Denitrification was much higher after 5 months of dosing. The increase in activity may have been caused by the stimulation of C availability by dosing. Total readily mineralizable and microbial C significantly deceased in the dosed relative to control samples after 5 months of dosing. The highest rates of denitrification that we measured suggest that this process could significantly alter groundwater NO3- concentrations in this riparian zone. However, the effect of dosing on C availability will ultimately control the nature and extent of groundwater denitrification in this riparian forest.
Howard, Galen, "Denitrification and the Effects of Nitrate Dosing on Carbon and Nitrogen Pools in an Aquifer Beneath a Riparian Forest" (1993). Open Access Master's Theses. Paper 2072.