The Boreal Forest contains about 1/3 of all global terrestrial carbon stored as vegetation and soil organic matter. The fate of this carbon, however, is uncertain because of the widespread degradation of permafrost, which plays a key role in sequestering soil carbon. If the climate warms another 5 to 8 C in Alaska, as predicted by the IPCC (2001), nearly all of the permafrost could be eliminated from this biome, causing dramatic changes in the water and carbon balance of boreal ecosystems.
The effects of permafrost degradation (thermokarst) on surface water and carbon is highly uncertain because of the spatial variability in terrain, topography, vegetation, fire regime, and permafrost characteristics. While field studies have begun to recognize the importance of thermokarst in carbon accumulation and subsequent methane emissions, current modeling approaches still assume a fairly homogenous soil landscape where thawing uniformly lowers the permafrost table and dries the soils. This assumption probably holds up well for permafrost-affected upland areas (23% of boreal landscape in Alaska), but is not valid for lowlands areas (41% of landscape), where thermokarst impounds water. Furthermore, the degradation of permafrost affects the export of carbon very differently in upland and lowland landscapes. In upland landscapes the loss of permafrost increases drainage, which eliminates or alters the seasonality of surface runoff. In contrast, thermokarst in lowland landscapes impounds water into isolated wetlands, thereby disrupting drainage and increasing storage capacity that in turn reduces runoff and increases the residence time of dissolve organic carbon in isolated wetlands. Thus, current modeling approaches neglect the varying ways in which permafrost affects water and carbon on the landscape.
To address these issues, this project will generate a new approach to modeling boreal forest systems by using research tasks designed to (1) assess interactive effects of climate change and fire on permafrost stability; (2) quantify how the varying modes of permafrost degradation initiate various thaw regimes on the landscape by affecting the microtopography, drainage, and soil thermal regimes of boreal systems; (3) determine how various thaw regimes such as drained or ponded systems affect carbon loss or accumulation in biomass and soils, and (4) characterize the export of dissolved organic carbon from watersheds in an effort to fingerprint the various thaw regimes induced by permafrost degradation. Using a replicated design, we will study age sequences of thaw history to capture changes in carbon and water over time since thaw. We will characterize temperature, moisture, water table of each thaw regime to parameterize the physical conditions of each thaw regime and will test model results based on the chemical finger print of thaw-water and on trace gas flux in one unique set of sites.
Broader Impacts: Realistic spatial biogeochemistry models must quantify the redistribution of water and carbon across the landscape that results from permafrost degradation. Process-based biogeochemistry and spatially-explicit permafrost models developed in this project will address interactions among climate, fire, permafrost, carbon and water for the boreal region. This proposal will unite modelers with field scientists. The project will be used to train a new generation of scientists in ecosystem sciences through graduate education at Purdue University and University of Alaska at Fairbanks. Public outreach will be achieved by participating in policy meetings and workshops. Project results will be communicated through scientific meetings and publications and will be distributed through Newsletters and Annual Reports of the Purdue Climate Change Research Center. In addition to the contributions to the global change research community, the knowledge of impact of permafrost degradation on ecosystem carbon and water cycling is critical to the management of fires and habitats on federal lands.
