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Fifth National Climate Assessment - Read the Report

Studying carbon cycle processes in northern aquatic ecosystems

Methane emitted from thawing permafrost below an Arctic thermokarst lake is trapped in bubbles as ice forms in the winter. Credit: Miriam Jones/USGS.

Recent studies are improving the ability to quantify ecosystem carbon dynamics and greenhouse gas exchange in changing Arctic and boreal landscapes.

Northern high latitudes are warming at more than twice the global average, driving permafrost thaw, changes in surface water extent, increased wildfire, and other changes that affect how much carbon is stored in and emitted to the atmosphere by soils, vegetation, and inland waters.1 Measuring the flow of carbon between ecosystems, landscapes, and the atmosphere—known as carbon flux—in the region and the potential impacts on global climate is an active area of research critical to understanding future climate change.

Since 2015, the U.S. Geological Survey (USGS) has conducted large-scale studies of carbon dynamics in stream, rivers, lakes, and wetlands across Alaska (including carbon dioxide and methane exchange with the atmosphere; inorganic carbon weathering and export; and dissolved organic matter amount, chemical composition, export, and storage) in partnership with the U.S. Fish and Wildlife Service, the Bureau of Land Management, NASA, and academic collaborators. A majority of this work is conducted on DOI lands, with funding from NASA’s Arctic-Boreal Vulnerability Experiment (ABoVE) Program, a multiyear experiment that is using satellite, aircraft, and field data to understand the ecological impacts of a rapidly changing climate in Alaska and Northwestern Canada. Recent studies investigated how surface water influences carbon flux in the region and how aquatic ecosystem processes are being altered by climate change.

Wetlands, ponds, and lakes are the largest natural source of methane in the region but are poorly mapped, making estimates of carbon fluxes at the landscape scale a challenge. Researchers integrated airborne data collected by ABoVE aircraft flights, satellite data, and field measurements to identify different classes of landscape, ranging from permanently flooded to dry. Continued field data collection will measure how carbon flux varies across different types of landscapes and lakes, with the goal of upscaling greenhouse gas flux estimates for lakes and wetlands in Arctic-boreal environments.

Changing climate and permafrost are altering the hydrologic connection of lakes and other water bodies with the landscape, affecting how organic carbon moves between ecosystems and the atmosphere. Recent results demonstrate that the reduced delivery of dissolved organic matter from terrestrial to aquatic ecosystems shifts the chemical composition of lake dissolved organic matter, with implications for lake productivity, light penetration, heat transfer, and their biogeochemical function.2 Researchers also developed a novel methodology for estimating gross primary productivity (a measure of carbon uptake by photosynthesis) in lakes by combining satellite data of lake color with field water quality measurements.3 This method can be used to assess change in ecological processes involving carbon cycling in hundreds of thousands of shallow lakes across northern high latitudes. Related investigations integrating field and remote sensing data are ongoing to quantify the effects of climate change on the water resources of boreal and Arctic regions.

1 Schuur, E. A. G., A. D. McGuire, V. Romanovsky, C. Schädel, and M. Mack, 2018: Chapter 11: Arctic and boreal carbon. In Second State of the Carbon Cycle Report (SOCCR2): A Sustained Assessment Report [Cavallaro, N., G. Shrestha, R. Birdsey, M. A. Mayes, R. G. Najjar, S. C. Reed, P. Romero-Lankao, and Z. Zhu (eds.)]. U.S. Global Change Research Program, Washington, DC, USA, pp. 428-468, SOCCR2.2018.Ch11.

2 Johnston, SE, Striegl, RG, Bogard, MJ, Dornblaser, MM, Butman, DE, Kellerman, AM, Wickland, KP, Podgorski, DC, Spencer, RGM, 2020, Hydrologic connectivity determines dissolved organic matter biogeochemistry in northern high-latitude lakes, Limnol. Oceanogr.,

3 Kuhn, CD, Bogard, M, Johnston, SE, John, A., Vermote, EF, Spencer, R, Dornblaser, M, Wickland, KP, Striegl, RG, Butman, D, 2020, Satellite and airborne remote sensing of gross primary productivity in boreal Alaskan lakes, Environ. Res. Lett. 15 105001,