The role of groundwater dynamics on carbon export from continuous permafrost watersheds
Abstract
Groundwater flow regimes in the seasonally thawed soils in areas of continuous permafrost are relatively unknown despite their potential role in delivering water, carbon, and nutrients to streams. Using numerical groundwater flow models informed by observations from a headwater catchment in arctic Alaska, we identify several mechanisms that result in substantial surface-subsurface water exchanges across the land surface during downslope transport that are a primary control on dissolved organic carbon (DOC) loading to streams and rivers. Based on these mechanisms, headwater streams have high DOC concentrations, as indicated by field-based measurements showing similar DOC concentrations in the streams and groundwater across large discharge ranges. However, at larger scales, river concentrations of DOC are generally lower and have a different composition than groundwater, suggesting instream processes that remove and alter DOC occur during transit. We found up to ~ 10% of the DOC is converted to CO2, mostly by sunlight and about 30% of the DOC is partially photo-oxidized (and altered in chemical composition) during transport in rivers. The implication is that several mechanisms control the delivery of DOC laden-groundwater into streams and rivers which then facilitate the transformation of this highly labile DOC during transport to the Arctic Ocean. These results demonstrate the importance of integrating the controls on groundwater delivery with controls on in-stream carbon processing in determining eventual export to the Arctic Ocean.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.B42B..08N
- Keywords:
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- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCES;
- 0428 Carbon cycling;
- BIOGEOSCIENCES;
- 0475 Permafrost;
- cryosphere;
- and high-latitude processes;
- BIOGEOSCIENCES;
- 0708 Thermokarst;
- CRYOSPHERE;
- 0793 Biogeochemistry;
- CRYOSPHERE;
- 1823 Frozen ground;
- HYDROLOGY;
- 1865 Soils;
- HYDROLOGY