HR: 09:30h
AN: B21C-07 INVITED     [Abstracts]
TI: Oxidation/Reduction Reactions Involving Dissolved Humics as Electron Shuttlers in Lake Sediments
AU: * McKnight, D M
EM: diane.mcknight@colorado.edu
AF: INSTAAR, 1560 30th St, Boulder, CO 80309 United States
AB: The chemical diversity of dissolved organic material (DOM) increases in aquatic ecosystems as the production of DOM by algae and bacteria contributes to DOM from runoff of soils and vegetation in forested catchments. Recent research has shown that a major DOM fraction, fulvic acid, can be used as electron acceptors by heterotrophic microorganisms in reducing environments and that reduced fulvic acid can in turn be used as an energy source by other microorganisms. The hydrologic transport of reduced DOM from reducing environments, such as lake sediments, to oxidizing environments may influence the mobility of iron and manganese in sediments, along with other trace metals sorbed on oxide phases. The electron shuttling properties of fulvic acids are associated with quinone moieties. One way in which fulvic acid from plant/soil and microbial sources differ is in the chemical characteristics of these quinone moieties. These differences, as well as the oxidation state of the quinones, can be characterized by fluorescence spectroscopy. In a study of an ice-covered lake in the Rocky Mountains, we found that as reduced fulvic acid accumulated in the water column, the concentration of ferrous iron also increased. When the ice-cover broke up in spring, the lake system rapidly oxidized and the iron was removed from solution, potentially deposited on the lake bottom as iron hydroxide. These quinone moieties differ in sensitive to oxidation and photolysis by light. Thus, the chemical diversity and biogeochemical reactivity of DOM in aquatic ecosystems are dynamic, with changes occurring over a day-night cycle being superimposed upon seasonal changes in hydrologic regime.
DE: 1055 Organic and biogenic geochemistry
SC: Biogeosciences [B]
MN: Fall Meeting 2005