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PI-Submitted Research Highlights for
Terrestrial Ecosystem Science Program

Microtopography Determines How CO2 and CH4 Exchanges Respond to Temperature and Precipitation at an Arctic Polygonal Tundra Site

William J. Riley
Lawrence Berkeley National Laboratory

Highlight

21 Dec 2017

Microtopography in polygonal tundra affects CO2 and CH4 emissions, but landscape scaling of polygon types accurately represents landscape-scale gas exchanges with the atmosphere

The Science
Scientists from Lawrence Berkeley National Laboratory applied a well-tested three-dimensional land model (ecosys) to the NGEE-Arctic Barrow, Alaska polygonal tundra sites to quantify and scale the effects of microtopography on biogeochemistry, hydrology, and plant processes and thereby CO2 and CH4 exchanges with the atmosphere. Much of the spatial and temporal variations in CO2 and CH4 fluxes were driven from topographic effects on water and snow movement. Although small-scale elevation variation causes large spatial variations, their results demonstrated that representing individual polygon type dynamics allowed for accurate predictions of landscape-scale states and gas exchanges with the atmosphere.

The Impact
They demonstrated excellent agreement between model predictions and NGEE-Arctic observations of CH4 and CO2 fluxes  and the relevant biogeochemical, hydrological, and thermal controlling processes. Interestingly, net primary productivity in higher features and CH4 emissions across the landscape increased from 1981 to 2015, attributed more to precipitation than temperatures increases. Their results highlight needed improvements to the DOE E3SM land model (ELMv1-ECA), which they are actively pursuing.

Summary
Current ESM land model representations of high-latitude biogeochemistry and plant processes in spatially heterogeneous landscapes ignore several important processes and representation. They found a strong control of water and snow movement on biogeochemical dynamics and net primary production that varied by landscape position. The landscape-scale dynamics were also well captured by scaling the various polygon type dynamics. The analysis here demonstrates a viable approach to representing fine-scale processes and links to landscape scales. Together their findings challenge widely held assumptions about controls on landscape-scale energy and water budgets, and are motivating our ongoing improvements to the DOE land model (ELMv1-ECA).

BER PM Contacts
Daniel Stover
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

PI Contact
William J. Riley
Lawrence Berkeley National Laboratory, wjriley@lbl.gov

Funding
This research was supported by the Director, Office of Science, Office of Biological and Environmental Research of the US Department of Energy under Contract No. DE-AC02-05CH11231 as part of the Next-Generation Ecosystem Experiments (NGEE Arctic) project.

Publications
Grant, R. F., Z. A. Mekonnen, W. J. Riley, B. Arora, and M. S. Torn (2017), Mathematical Modelling of Arctic Polygonal Tundra with Ecosys: 2. Microtopography Determines How CO2 and CH4 Exchange Responds to Changes in Temperature and Precipitation, JGR-Biogeosciences, DOI: 10.1002/2017JG004037.

LBNL NGEE-Arctic

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