HR: 1340h
AN: U53A-0716    [Abstracts]
TI: The hydrologic and biogeochemical response of undisturbed mountain ecosystems in the Western United States to multiple stressors: Interactions between climate variability and atmospheric deposition of contaminants
AU: * Campbell, D H
EM: Donald.Campbell@usgs.gov
AF: USGS, Mailstop 415, Federal Center, Lakewood, CO 80225 United States
AU: Mast, M A
EM: mamast@usgs.gov
AF: USGS, Mailstop 415, Federal Center, Lakewood, CO 80225 United States
AU: Clow, D W
EM: dwclow@usgs.gov
AF: USGS, Mailstop 415, Federal Center, Lakewood, CO 80225 United States
AU: Ingersoll, G P
EM: gpingers@usgs.gov
AF: USGS, Mailstop 415, Federal Center, Lakewood, CO 80225 United States
AU: Nanus, L
EM: lnanus@usgs.gov
AF: USGS, Mailstop 415, Federal Center, Lakewood, CO 80225 United States
AB: Wilderness areas and national parks of the West are largely protected from acute changes in land use such as urbanization and natural resource development. However, the ecosystems in these areas are sensitive to both climate variability and atmospheric deposition of acids, nitrogen (N), and toxic contaminants, and these stressors interact in ways that we are just beginning to understand. Here we examine some examples of the interactions between climate variability and nitrogen and mercury cycling in high elevation watersheds. During the recent drought, which began in 2000, streamwater nitrate concentrations nearly doubled in the Loch Vale watershed in Rocky Mountain National Park, exceeding 60 $\mu$M during early snowmelt. Much of the elevated nitrate resulted from an increased percentage contribution to streamwater of nitrate-rich shallow groundwater. In a nearby pond used for breeding by a threatened amphibian species, nitrate concentrations were negligible but ammonium concentrations were extremely high (850 $\mu$M) during the drought. In this case, organic N in pond sediments was likely mineralized and released during cycles of drying and rewetting of pond sediments. Even after 2 years of near-average precipitation, water levels remained below normal and ammonium concentrations remained elevated, indicating that the hydrologic response of this small system has a timescale of many years. Mercury (Hg) deposition at high elevations of the Rocky Mountains is comparable to that of the Midwest and Northeast, but the processes that control Hg cycling in alpine/subalpine ecosystems are not well understood. Methylation and bioaccumulation of Hg must occur before Hg reaches levels harmful to the ecosystem or human health, and both climate and nutrient cycling affect these processes. Fluctuating water levels caused by climate variability can mobilize Hg from lake and pond sediments, increasing reactivity and bioavailability of Hg in the ecosystem. Increased nutrient release from the terrestrial ecosystem (eg. from N saturation) may increase productivity and accumulation of organic matter, altering Hg cycling in the aquatic system. Long durations of ice cover and thick snowpacks are likely to cause elevated methyl Hg in aquatic ecosystems. Snow and ice cover on lakes promotes hypoxia in lake water, favoring production and accumulation of methyl Hg- the percentage of methyl-Hg in lake water under snow and ice was as much as 6 times greater than the percentage measured during late summer in a northwestern Colorado lake. Analysis of long-term trends indicates that climate variability is increasing in the Mountain West. Climatic extremes appear to exacerbate adverse impacts of atmospheric deposition, as well as stressing ecosystems directly. A better understanding of these interactions is needed in order to predict the response of mountain ecosystems to future changes in climate and atmospheric deposition.
DE: 1803 Anthropogenic effects
DE: 1806 Chemistry of fresh water
DE: 1854 Precipitation (3354)
DE: 1615 Biogeochemical processes (4805)
SC: Union [U]
MN: 2004 AGU Fall Meeting