9632421 Kiene Northern Sphagnum-dominated wetlands are complex, nutrient-poor ecosystems that are major sources of atmospheric methane and store tremendous quantities of organic carbon. These systems can emit unusually large amounts of dimethylsulfide (DMS) into the atmosphere, and this efflux is often greater than emissions from marine habitats that contain much more sulfur. Ongoing studies revealed that rapid fluxes of DMS occur in oligotrophic areas of wetlands rather that in more nutrient-rich sites. This peculiarity may to be due to the fact that the methanogenic demethylation of DMS does not occur in oligotrophic peats, while it does in minerotrophic ones and in neutral lake sediment. The present study will investigate the production, consumption and emission of DMS in wetlands of varying trophic status to elucidate the role of terminal decomposi~ processes in controlling DMS release. Several hypotheses will be tested: 1) DMS emissions are most rapid in oligotrophic (ombrotrophic) regions of wetlands, and this phenomenon is ubiquitous 2) DMS emissions (and accumulation) are faster in oligotrophic regions because DMS is not decomposed by methanogenic bacteria 3) Chemical conditions (i.e., pH, mineral content) are responsible for the lack of DMS consumption in oligotrophic peats 4) Methylotrophic methanogens are sparse in oligotrophic areas 5) Methylated sulfides are produced in all anoxic freshwater systems The project will combine (1) field experiments measuring emissions of reduced gases and distribution of pertinent chemical species along trophic gradients within a wetland, and in separate wetlands of different trophic status; (2) field manipulations in which wetland plots will be amended with selected nutrients and/or trace elements; (3) laboratory experiments to investigate pathways of organic matter transformations and relationships with trace gas production; (4) investigations of the relative distribution and abundance of selected microorganisms using molecular biotechno logy techniques. The results will elucidate important aspects of bacterial metabolic pathways for the production and consumption of methylated S compounds in wetlands, and freshwaters in general. Since DMS transformations are conducted primarily by microorganisms situated at the important terminal end of decomposition, these data will provide insights into what controls decomposition in sites that tend to accumulate large quantities of organic matter, and how methanogenesis, acetogenesis, anaerobic metabolism, and methylation and demethylation activity vary in response to changes in trophic status. The results will have broad applicability to freshwater ecosystems in general.
