Water and Environmental Research Center
Seminars
16 October 2009
Multiple Limitations on Evapotranspiration Rates from an Arctic Coastal Wetland with Implications in a Changing Climate
Anna Liljedahl
Credit: Anna Liljedahl
Barrow, Alaska as seen from a NOAA research plane, mid-June 2006, about 1 a.m.
Abstract
We report on the energy exchange and the underlying physics that exert major controls upon evapotranspiration rates measured by the eddy covariance method over two coastal wetlands in Barrow, Northern Alaska. In summer 1999 - 2003, 41± 13% of the net radiation was partitioned into sensible heat flux at the Central Marsh site (CM) and 35± 13% and 12± 8% into latent and ground heat flux, respectively. At the NSF Biocomplexity site (BE) in 2006-2008 54± 12%, 39± 6% and 8± 4% was partitioned into sensible, latent and ground heat flux, respectively. The sites experience multiple limitations on the water loss to the atmosphere with confined interannual variability. While the net radiation is important in controlling evapotranspiration (ET) rates, there is a potential to evaporate and transpire additional water under the current net radiation regime than occurred (ET<PET). Mean midday ET was below the equilibrium rate at 67% (CM) and 78% (BE) of the time with an overall mean Priestley-Taylor α-value of 0.98± 0.36 (CM) and 0.90± 0.19 (BE). The maritime air mass restricts further loss of water to the atmosphere by maintaining a large temperature gradient (favoring sensible heat) and low vapor pressure deficit (suppressing latent heat). In addition, a seasonal increase in surface resistance infers the importance of the non-vascular mosses' inability to draw from the water table. Despite a rapidly warming climate evapotranspiration rates are unlikely to change mainly due to the dominating influence of on-shore winds supporting the existence of wetlands. The gained mechanistic information is crucial to incorporate into general circulation models.