Baker, M. A.. Centre d'Écologie des Systèmes Aquatiques Continentaux,
Dahm, C. A.. University of New Mexico,
Valett, H. Virginia Polytechnic Institute and State University,

Microbial metabolism in the groundwater-surface water (GW/SW) interface of lotic ecosystems is often limited by labile dissolved organic carbon (DOC) availability. Because of atmospheric isolation, the GW/SW interface can contain zones of hypoxia or anoxia. Acetate and similar organic acids are components of DOC that may be of particular importance to metabolism in this environment. Acetate accounts for 20-70% of total DOC at Rio Calaveras, NM during baseflow. We performed an experimental injection of acetate to the GW/SW interface to test the hypothesis that microbial metabolism is limited by DOC availability and to determine the importance of aerobic vs. anaerobic processes. Acetate addition stimulated subsurface respiration as evidenced by CO2 production along monitored flowpaths. Changes in solutes associated with microbial terminal electron accepting processes also suggested increased metabolism. Dissolved oxygen, nitrate, and sulfate significantly decreased, while ferrous iron and methane significantly increased compared to background concentrations in most wells. Aerobic respiration accounted for a maximum of 30% of acetate metabolism during the experiment. Our results show that both aerobic and anaerobic metabolism are limited by DOC availability. We propose that low molecular weight organic acids like acetate represent an important metabolic substrate in hypoxic stream sediments.
Day: Thursday, Feb. 4
Time: 12:00 - 12:15pm
Location: Sweeney Center
Code: SS33TH1200S