Evaporation dominates evapotranspiration on Alaska’s Arctic Coastal Plain

ABSTRACT

The dynamics of evapotranspiration (ET), such as the partitioning to evaporation and transpiration, of polygonal ground on the Arctic Coastal Plain are not well understood. We assessed ET dynamics, including evaporation and transpiration partitioning, created by microtopographic features associated with high- and low-centered polygons. Chamber ET and leaf-level transpiration measurements were conducted in one-week field campaigns in two growing seasons with contrasting weather conditions. We found that ET was greater in the drier and warmer sampling period (2013) compared to the colder and wetter one (2014). Evaporation dominated ET, particularly in the wetter and colder sampling period (>90% in 2014 vs. 80% in 2013). In the 2013 sampling period, wetter and warmer conditions increased ET and the contribution of transpiration to ET. If the soils warm with degrading permafrost, ET and the fraction contributed by transpiration may increase to a certain threshold, when moisture must increase with rising temperatures to further increase these fluxes. While the fraction of transpiration may rise with warmer soils, it is unlikely that transpiration will completely dominate ET. This work highlights the complexities of understanding ET in this dynamic environment and the importance of understanding differences across polygonal ground.

KEYWORDS:

• Polygonal ground
• permafrost
• ice wedge
• plant functional type
• evapotranspiration partitioning

Acknowledgments

We thank Lauren Charsley-Groffman and Emma Lathrop (Los Alamos National Lab) for creating the map in Figure 1. We thank Samuel Dempster, Bryan Curtis, Kate Margavichus, and Go Ihwana for field and laboratory assistance.

Additional information

Funding

The Next-Generation Ecosystem Experiments (NGEE Arctic) project is supported by the Office of Biological and Environmental Research in the DOE Office of Science. We thank NSF Hydrology grant #1114457 and NSF Arctic Natural Sciences #1418123, and DOE SciDAC grant #DE-SC0006913 for partially funding J. Young-Robertson.