December 21, 2017

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

Microtopography in polygonal tundra affects CO2 and CH4 emissions; landscape scaling of polygon types represents landscape-scale gas exchanges.

The Science

Scientists from Lawrence Berkeley National Laboratory applied a well-tested three-dimensional land model (ecosys) to the Next-Generation Ecosystem Experiments (NGEE)–Arctic Barrow, Alaska, polygonal tundra sites to quantify and scale the effects of microtopography on biogeochemistry, hydrology, and plant processes and thereby carbon dioxide (CO2) and methane (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, project results demonstrated that representing individual polygon type dynamics allowed for accurate predictions of landscape-scale states and gas exchanges with the atmosphere.

The Impact

The scientists 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 temperature increases. Their results highlight needed improvements to the U.S. Department of Energy (DOE) Energy Exascale Earth System (E3SM) land model (ELMv1-ECA), which they are actively pursuing.

Summary

Current Earth system model (ESM, a land model) representations of high-latitude biogeochemistry and plant processes in spatially heterogeneous landscapes ignore several important processes and representation. Scientists 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 the ongoing improvements to the DOE land model (ELMv1-ECA).

Principal Investigator

William Riley
Lawrence Berkeley National Laboratory
wjriley@lbl.gov

Program Manager

Daniel Stover
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
daniel.stover@science.doe.gov

Funding

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

References

Grant, R. F., Z. A. Mekonnen, W. J. Riley, and B. Arora, et al. "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 122 (12), 3174–3187  (2017). https://doi.org/10.1002/2017JG004037.