Hydrological dynamics and associated greenhouse gas fluxes in a mountain peatland under different climate scenarios

Authors: Millar, David; COOPER, DAVID - Colorado State University; DWIRE, KATHLEEN - Forest Service (FS); HUBBARD, ROBERT - Forest Service (FS); RONAYNE, MICHAEL - Colorado State University; VON FISCHER, JOSEPH - Colorado State University

Submitted to: Ecohydrology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/6/2023
Publication Date: 2/15/2023
Citation: Millar, D.J., Cooper, D.J., Dwire, K.A., Hubbard, R.M., Ronayne, M.J., Von Fischer, J. 2023. Hydrological dynamics and associated greenhouse gas fluxes in a mountain peatland under different climate scenarios. Ecohydrology. 16(5):e2536. https://doi.org/10.1002/eco.2536
DOI: https://doi.org/10.1002/eco.2536

Interpretive Summary: Mountain peatlands have sequestered atmospheric carbon for millennia, but their source/sink role for ecosystem-atmosphere C exchange is dependent on temperature and a shallow water table, which are likely to change under a future climate. We used an empirical modeling approach to estimate ecosystem-atmosphere carbon exchange in a mountain peatland under current and potential future climate scenarios. We found that net uptake of carbon dioxide may decrease, along with CH4 emissions, for mountain peatlands under a warmer climate, particularly for those found at elevations where winter precipitation may increasingly fall as rain, rather than snow, and snow melt has the potential to occur earlier.

Technical Abstract: Peatlands have sequestered atmospheric carbon dioxide (CO2) for millennia, and can also act as significant sources of atmospheric methane (CH4). Hydrological processes that control water table dynamics, and climatic conditions such as air temperature, play important roles in mediating peatland-atmosphere exchange of these greenhouse gases. These controls are likely to be impacted by climate change, particularly for those found in cold environments, including mountain regions. In this study, we developed empirical models to simulate hydrological dynamics and ecosystem-atmosphere C exchange in a mountain peatland under three climate scenarios (2012 air temperatures, + 2°C, and + 4°C). Observed water table dynamics and air temperature were used to model ecosystem-atmosphere C exchange during the 2012 growing season. Modeled snow melt dynamics were used to predict water table position at the beginning of the growing season for warming scenarios, and the subsequent water table dynamics and increased air temperature were used to drive the same C exchange models during the growing seasons. Increased air temperatures led to earlier snow melt and water table decline, causing water tables to drop by 10 cm and 19 cm for the + 2°C and + 4°C scenarios, respectively. This led to roughly a two-fold decrease in growing season net ecosystem production (NEP) in both warming scenarios, as a result of increased ecosystem respiration relative to gross primary production. Methane efflux was positively correlated with NEP, and therefore decreased under the warming scenarios, albeit to a lesser degree. These results indicate reductions in NEP and CH4 efflux are likely in mountain peatlands that are dependent on snowpack-derived hydrologic inputs and found at elevations where future winter precipitation will increasingly fall as rain rather than snow and melting of snowpack will occur earlier under warmer conditions.