HR: 0800h
AN: B11A-0062    [Abstracts]
TI: Seasonal changes in the concentration and chemical quality of dissolved organic matter exported from wetland soils to streams in coastal temperate watersheds
AU: * Fellman, J B
EM: fsjbf6@uaf.edu
AF: University of Alaska Fairbanks, 211 Irving 1, Fairbanks, AK 99775,
AU: Hood, E
EM: eran.hood@uas.alaska.edu
AF: University of Alaska Southeast, 11120 Glacier Highway, Juneau, AK 99801,
AU: D'Amore, D V
EM: ddamore@fs.fed.us
AF: USDA Forest Service Pacific Northwest Research Station, 2770 Sherwood Lane, Juneau, AK 99801,
AU: Edwards, R T
EM: rtedwards@fs.fed.us
AF: USDA Forest Service Pacific Northwest Research Station, 2770 Sherwood Lane, Juneau, AK 99801,
AU: Berkowitz, J
EM: jberkowitz@fs.fed.us
AF: USDA Forest Service Pacific Northwest Research Station, 2770 Sherwood Lane, Juneau, AK 99801,
AB: The concentration and chemical quality of dissolved organic matter (DOM) fluxes from terrestrial to aquatic ecosystems is an important indicator of watershed-scale hydrologic and biogeochemical processes. Understanding the relative magnitude and chemical character of these DOM fluxes is critical because DOM influences an array of biological, chemical, and physical processes. We used PARAFAC modeling of excitation- emission (EEM) fluorescence spectroscopy and biodegradable dissolved organic carbon (BDOC) incubations to investigate changes in the chemical quality of DOM along a soil-stream gradient in two watersheds in coastal Southeastern Alaska. Within each watershed, two sub-catchments (bog and forested wetland) were selected and soil solution from the sub-catchment soils, sub-catchment outlet streams and the watershed outlet streams were sampled weekly from May to October. Throughout the sampling period, concentrations of dissolved organic carbon (DOC) and BDOC were greatest in the soil solution and generally decreased in both the sub-catchment and watershed outlet streams. DOC concentrations at all sites were lowest during the spring runoff, increased during the summer growing season and decreased gradually with the onset of the fall wet season. In contrast, BDOC at all sites was highest during the spring runoff, decreased during the growing season and increased briefly during the fall wet season. The results from PARAFAC modeling indicate a strong seasonal linkage between soil solution and streams during the spring runoff and fall wet season, as demonstrated by the similar contribution of PARAFAC components in soil solution and the sub-catchment and watershed outlet streams. In particular, the relative contribution of two fluorescent amino acids, which have been attributed to tyrosine and tryptophan-like fluorescence, were very similar in both the soil solution and streams during the spring runoff and fall wet season. However, during the summer growing season, the contribution of both amino acids remained high in soil solution but drastically decreased in streams. Moreover, PARAFAC modeling of fluorescence EEMs revealed that the seasonal and longitudinal changes in the fluorescent amino acids were positively correlated with BDOC for all sites. These findings suggest that wetland soils in southeast, Alaska contribute abundant labile DOM to streams in the spring and fall. However, biological uptake of DOM along the soil-stream gradient appears to alter the character of DOM moving from terrestrial to aquatic ecosystems during the summer growing season. Our findings further suggest that DOM characterization and BDOC measurements are useful tools for evaluating seasonal changes in the biogeochemical coupling between terrestrial and aquatic ecosystems and thus, have the potential to be used as a tracer to evaluate the movement of DOM along soil-stream gradients.
DE: 0409 Bioavailability: chemical speciation and complexation
DE: 0428 Carbon cycling (4806)
DE: 0469 Nitrogen cycling
DE: 0470 Nutrients and nutrient cycling (4845, 4850)
DE: 0497 Wetlands (1890)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting