HR: 15:10h
AN: H53F-07    [Abstracts]
TI: Ecohydrological Linkage Between Surface-Derived Dissolved Organic Matter and Subsurface Carrying Capacity for Unattached Subsurface Bacterial Populations: Implications for Biodegradation in Contaminated Groundwater Environments
AU: * Harvey, R W
EM: rwharvey@usgs.gov
AF: USGS, 3215 Marine Street, Ste. E-127, Boulder, CO 80303 United States
AU: Gruden, C L
EM: cyndee.gruden@eng.utoledo.edu
AF: University of Toledo, Dept. of Civil Engineering, Toledo, OH 43606 United States
AU: Aiken, G R
EM: graiken@usgs.gov
AF: USGS, 3215 Marine Street, Ste. E-127, Boulder, CO 80303 United States
AU: Metge, D W
EM: dwmetge@usgs.gov
AF: USGS, 3215 Marine Street, Ste. E-127, Boulder, CO 80303 United States
AU: Kinner, N E
EM: nancy.kinner@unh.edu
AF: University of New Hampshire, Dept. of Civil Engineering, Durham, NH 03824 United States
AB: Degradation by aquifer microbial populations of dissolved organic matter (DOM) transported from the surface environment exerts strong controls on the concentration, composition, and reactivity of DOM as it is transported in ground water. In turn, the quantity of readily degradable DOM may be a major control of the carrying capacity for bacteria in groundwater and, consequently, would affect the fate of lower levels of organic contaminants being advected through the same sediments. For a 5-km long plume of groundwater organic contaminants in a sandy aquifer at Cape Cod, Massachusetts, the partitioning of bacteria between solution and grain surfaces increased with decreasing distance downgradient from the source. In general, the unattached bacterial populations were particularly sensitive to the level of DOM present. Approximately 2/3 of the spatial variability for unattached bacteria within the upgradient 3 km of the contaminant plume can be explained statistically simply by the abundance of the more degradable (non alkyl benzene surfactant [ABS]) DOM, even though predation by groundwater nanoflagellates (protists) and sorptive-filtration of unattached bacteria both vary spatially. However, distance downgradient from the contaminant source, which directly correlates with both the age and abundance of the DOM, could explain ~98% of the variability of unattached bacteria along the longitudinal axis of the plume. Down-well incubations (USGS well site F513) were performed using membrane (100K Dalton cutoff) chambers (initially seeded with undifferentiated, laboratory-grown aquifer bacteria at abundances of 1 x 10$^{5}$ or of 1 x 10$^{7}$ bacteria/mL) that come to chemical equilibrium with surrounding groundwater within ~1 day. Following a 7-day down-well incubation, numbers of unattached bacteria within the chambers converged on a final abundance value of 2.0 $\pm$ 0.6 x 10$^{6}$ bacteria per mL, consistent with the in-situ bacterial abundance within that part of the plume (typically between 1.0 x 10$^{6}$ and 2.0 x 10$^{6}$/mL). Incubation for a longer (21 day) period resulted in final bacterial abundances that were not statistically different than those observed for the shorter (7-day) incubations. Results from the Cape Cod study suggests the carrying capacity of the system for unattached groundwater bacteria that are advecting downgradient with specific organic contaminants may be determined by the more degradable fraction of the DOM.
DE: 1829 Groundwater hydrology
DE: 1831 Groundwater quality
DE: 1832 Groundwater transport
DE: 0400 Biogeosciences
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting