Dissolved Organic Matter as an Indicator of Changing Watersheds in Northern Rivers

George Aiken, US Geological Survey, graiken@usgs.gov (Presenter)

Responses of frozen soils to climate warming are particularly significant to understanding long term climate effects on global carbon cycling and carbon export by high latitude rivers. Monitoring climate effects on carbon cycling, however, is complicated by logistical and analytical challenges associated with spatially heterogeneous processes occurring over large watershed areas. Dissolved organic matter (DOM) chemistry and flux are potentially useful, albeit underutilized, indicators of watershed change. As the large reserves of organic carbon associated with frozen soils in the northern permafrost regions are mobilized by changes in soil microbial processes and hydrologic flow paths, it is anticipated that the composition and flux of DOM will change in waters draining these soils. Results are presented here that demonstrate the utility of assessing DOM composition and flux for gaining insight into processes controlling DOM in the Yukon River and its tributaries. We used DOM data in two ways to define carbon cycling and transport processes throughout the basin. First, analyses of chemical composition using DOM optical properties (UV-Vis absorbance, fluorescence), isotopic composition (14C), lignin phenol content and chromatographic fractionation indicate that DOM currently exported from watersheds dominated by peat soils and underlain by permafrost has undergone little degradation and is of recent origin, suggesting that large scale degradation of peat is not occurring at this time. In the second approach, DOM concentration and river discharge data were used to determine DOM flux, a parameter that is useful to assess DOM yields from watersheds. This approach provided evidence that DOM export by the Yukon River significantly decreased during the growing season from 1978-80 to 2001-03, indicating a major shift in terrestrial to aquatic DOM transfer. This observation challenges the generally held assumption that rising temperatures in northern latitudes will result in significant increases in DOM flux from northern rivers to the marine system. Continued assessment of DOM composition and export from northern watersheds will be important for the long term evaluation of climate effects on carbon cycling in these watersheds and will provide a basis for understanding the accompanying concomitant changes in biogeochemical processes resulting from these changes.

Presentation Type:  Poster

Session:  Coupled Processes at Land-Atmosphere-Ocean Interfaces   (Mon 4:00 PM)

Associated Project(s): 

• Related Activity

Poster Location ID: 8