Our primary object is to improve environmental predictability by advancing understanding of how carbon dioxide (CO2) and methane (CH4) flux in permafrost thaw-induced wetlands (thermokarst) will change in the future. Northern latitudes are expected to get warmer and wetter, leading to increased thermokarst thaw both in places already thawing, and in places where the permafrost is currently stable. Understanding the land-atmosphere exchange of these important greenhouse gases will help us understand and predict environmental change.
Data previously collected by the research team showed that CO2 uptake and CH4 emission by a thermokarst bog in Alaska increased in rainy years. The increase in CH4 emission was not associated with wetter soils, as is often assumed. Rather, rain carried heat from the atmosphere into the bog, warming peat to deep depths. Warmer peat temperatures supported plant growth within recently thawed areas of the bog, which increased net CO2 uptake and fueled CH4 production and emission within these areas. Plant growth within older thaw areas minimally responded to the increased temperatures. We hypothesize the difference in plant response between young and old thaw areas was associated with nitrogen availability, a key plant nutrient which is more available in young thaw areas.
These data imply that the formation of thermokarst wetlands will have dynamic effects on the climate system. Net carbon flux and CH4 emissions will change not only as thawed landscapes age, but also as environmental conditions shift. Capturing and correctly accounting for dynamic biosphere–atmosphere interactions and feedbacks, such as those involved with permafrost thaw, requires Earth system modeling. However, current Earth system land models, like the Energy Exascale Earth System Model Land Model (ELM), do not include transport of heat into soil from rain, do not represent sub-grid heterogeneity of land units (e.g., differently aged wetlands), do not fully represent soil nitrogen processing and plant nitrogen uptake, and do not explicitly connect plant productivity with CH4 production. These deficiencies undermine the accuracy and precision of the model and reduce its predictive capability.
We will take a coupled model-experiment-observation approach to advance understanding of thermokarst wetland dynamics and to address these deficiencies in ELM. We have six specific aims:
1. Harness historical data to identify how the amount and timing of rainfall affects peat temperature, nitrogen dynamics, plant productivity, and carbon flux in thermokarst wetlands.
2. Conduct a field manipulation experiment to test our underlying hypothesis that the organic nitrogen content of peat within young and old wetland areas controls the different responses of these areas to rainfall by affecting the production of plant-available nitrogen.
3. Determine how wetland dynamics will change in the future by measuring peat temperatures, vegetation coverage, and carbon flux in differently aged areas of an isolated thawing permafrost bog located in a currently warm and wet climate (i.e., on the Kenai Peninsula).
4. Advance ELM ’s soil thermal-hydrology-biogeochemistry coupling by adding advective heat transport into soil by rain, improving representation of soil nitrogen dynamics, and directly connecting plant productivity with CH4 production.
5. Use field data to parameterize the improved ELM, identify model uncertainty, and use the model to conduct site-level experiments that test hypotheses.
6. Extrapolate the model to northern permafrost region and simulate future CO2 and CH4 fluxes with different climate forcings and wetland-age projections. Enhance understanding of key interactions and feedback mechanisms that affect thermokarst wetland carbon fluxes.
These efforts will improve knowledge and thus representation of coupled thermal-hydrological-biogeochemical processes within ELM, increasing knowledge of climate–carbon feedbacks and progressing environmental predictability.
