Carbon Gas Emissions from a Stream Network along Elevation and Vegetation Gradients in a Remote Northern Boreal Watershed (Invited)
Abstract
Gas emissions from inland waters are the product of the gas partial pressure gradient across the water-air interface, gas transfer velocity, and water surface area, all of which vary in space and time for flowing water systems. We combined discrete water sampling of carbon gases, continuous water quality and dissolved carbon dioxide (CO2) monitoring using in situ sensors, stream water discharge monitoring, and water surface area estimates to determine CO2 and methane (CH4) emissions along a 300 km stream reach, originating above tree line and ending in flatlands, in a > 6100 km2 headwaters portion of the Beaver Creek watershed, central interior Alaska. Despite pronounced elevation and vegetation gradients in the watershed, areal stream CO2 yields were relatively constant as streams coursed from headwaters in the White Mountains downstream to the Yukon River. This was largely because stream surface area increases, offsetting the downstream decreases in both pCO2 and gas transfer velocity. In situ sensors tracked seasonal changes in pCO2 versus water discharge from spring ice melt into autumn. We attributed late summer increases in pCO2 and dissolved inorganic carbon to a shift in the proportions of surface runoff versus subsurface water sources to Beaver Creek, coincident with seasonal thaw of the active layer overlying permafrost in the watershed. This was conceptually similar to long-term patterns in aquatic carbon exports thought to be occurring in the Yukon River basin as a whole. Methane emissions to the atmosphere were relatively small, about one percent of CO2 emissions, but were continuous throughout the ice-free season, with aqueous pCH4 exceeding atmospheric pCH4 for all water samples.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFM.H23D1300S
- Keywords:
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- 0428 BIOGEOSCIENCES Carbon cycling;
- 1806 HYDROLOGY Chemistry of fresh water;
- 0315 ATMOSPHERIC COMPOSITION AND STRUCTURE Biosphere/atmosphere interactions;
- 0744 CRYOSPHERE Rivers