Quantifying peatland lateral carbon export using a radon mass-balance model
Abstract
Resolving peatland carbon budgets requires to integrate terrestrial and aquatic carbon fluxes. Although the exchange with the atmosphere is a straightforward vertical process, the quantification of lateral export can be affected by the contribution of external water sources. In this presentation, we demonstrate that the naturally occurring 222-radon radioisotope can be used as a tracer of groundwater input as opposed to radon-free peat water and can help quantify the carbon being laterally exported from peat soils. We measured water flow, radon concentrations, dissolved CO2 and CH4 concentrations during a complete growing season (June to October) in the main stream of a 1.5km2 peatland-dominated watershed (51°N; Quebec, Canada). The stream starts within the peatland (i.e. upstream), runs along sandy surficial deposits (i.e. midstream), and continues through the peat (i.e. downstream). Our results show high spatial heterogeneity in radon (120 Bq m-3 upstream; 1600 Bq m-3 midstream; 1000 Bq m-3 downstream) and CH4 concentrations (2000 ppm upstream; 60 ppm midstream; 3200 ppm downstream) but rather stable CO2 concentrations (≈ 6500 ppm) along the stream. We explain this variation by a limited contribution of groundwater input at the upstream site, a direct contribution of groundwater midstream, and a steadily decreasing groundwater input over peat water downstream. High radon concentrations are related to groundwater input while high CH4 concentrations are linked to peat water discharge. The consistent CO2 concentrations are explained by similar concentrations in the groundwater and peat water end-members. The different trends between the 3 variables (i.e. radon, CH4, and CO2) along the stream justifies the need to combine measurements and the use of radon as a groundwater input tracer. The mass balance approach developed in this project has the potential to be applied to other peatland-dominated watersheds and help better constrain the peatland carbon budget.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.B22F..04T
- Keywords:
-
- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCES;
- 0428 Carbon cycling;
- BIOGEOSCIENCES;
- 0475 Permafrost;
- cryosphere;
- and high-latitude processes;
- BIOGEOSCIENCES;
- 4950 Paleoecology;
- PALEOCEANOGRAPHY