Vulnerability of inland waters and the aquatic carbon cycle
to changing permafrost and climate across boreal
northwestern North America
Collaborative Research by U.S. Geological Survey and Alaska Ecoscience, funded by NASA’s Arctic-Boreal Vulnerability Experiment, 2015-2018
Water is key to all ecosystem functions, including the carbon (C) cycle. Additionally, rates of C biogeochemical processing are commonly much greater in inland waters than terrestrial landscapes, as they collectively store C in sediments, export C to oceans, and emit carbon dioxide (CO2) and methane (CH4) to the atmosphere. Terrestrial ecosystems are a dominant source of C to inland waters through surface and subsurface drainage networks. These networks are changing across boreal and arctic regions, as permafrost thaw, climate warming, and fire create new conduits for water movement, change vegetative water use and evapotranspiration, and alter the distribution of water on the landscape. It is imperative that we understand the dynamics of these changes in the water cycle if we are to understand and accurately project the effects of climate warming and other environmental drivers on circumboreal and arctic ecosystems.
This research effort involves an integrated interdisciplinary research campaign to evaluate the vulnerability of boreal landscapes to change in the “plumbing” that controls water movement and distribution, change in the source and chemical composition of C delivered to inland waters, and change in the rates and processes that control organic and inorganic C processing by inland waters and their emissions of CO2 and CH4 to the atmosphere. Our approach recognizes that permafrost thaw will not only enhance groundwater flow and the development of subsurface connectivity, but that loss of subsurface ice will also change the structure of the land surface, creating thermokarst features in some areas and initiating lake loss or lake creation in others. It also recognizes that terrestrial sources of C to inland waters will change in response to thaw, fire and other drivers of change. These conditions will be evaluated by geophysical and ecosystem surveys with the goal of extrapolation across the boreal ABoVE domain through remote sensing analysis and mapping.
Geophysical subsurface permafrost characterization via new ground and existing airborne surveys will provide the necessary framework for hydrologic field and modeling efforts to evaluate and project the effects of change in lateral connectivity on surface water flow, groundwater flow, and lake distribution. Permafrost thaw enhances groundwater flow, changes the seasonal distribution of streamflow, and alters lake budgets. However, the dynamics that control these changes are not completely understood, and critical baseline information on subsurface permafrost distribution is typically lacking. Using newly developed capabilities for cold regions, our proposed field and modeling approaches will help to fill these gaps in hydrologic understanding and will also inform on the routing of terrestrial C by flow systems to inland waters and the residence time of C in those systems.
Source, routing, and residence time are imperative to understanding C dynamics in inland waters. The study will determine C source and age through analyses of the 14C content of inorganic and organic C species and Cgas emissions. Molecular biomarkers, coupled with measured optical properties of DOC will inform on terrestrial versus autochthonous sources of aquatic C and on its potential for mineralization by biological or photo- degradation. Much of terrestrially-derived aquatic C is degraded before reaching surface waters, so hydrologic modeling of residence times will improve our understanding of where and when inland water C-gas emissions are expected to be greatest. Radiocarbon age of aquatic C will further delineate source and inform on if and where C derived from permafrost or ancient soil sources are delivered to inland waters. Finally, optical properties of water indicative of DOC concentration and chemical composition will be related to remotely sensed lake color and to the potential for C-gas emission, with the goal of extrapolating inland water DOC composition and CO2 and CH4 emissions across the ABoVE domain.
Alaska Ecoscience is collaborating in this research by compiling existing data on permafrost characteristics, conducting new field surveys of permafrost-ecosystem relationships, and using a time-series of historical airphotos and satellite images of quantify rates of permafrost degradation across Alaska.