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| Titel |
Nonlinear controls on evapotranspiration in arctic coastal wetlands |
| VerfasserIn |
A. K. Liljedahl, L. D. Hinzman, Y. Harazono, D. Zona, C. E. Tweedie, R. D. Hollister, R. Engstrom, W. C. Oechel |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 8, no. 11 ; Nr. 8, no. 11 (2011-11-18), S.3375-3389 |
| Datensatznummer |
250006206
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| Publikation (Nr.) |
 copernicus.org/bg-8-3375-2011.pdf |
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| Zusammenfassung |
| Projected increases in air temperature and precipitation due to climate
change in Arctic wetlands could dramatically affect ecosystem function. As a
consequence, it is important to define controls on evapotranspiration, the
major pathway of water loss from these systems. We quantified the
multi-year controls on midday Arctic coastal wetland evapotranspiration,
measured with the eddy covariance method at two vegetated, drained thaw lake
basins near Barrow, Alaska. Variations in near-surface soil moisture and
atmospheric vapor pressure deficits were found to have nonlinear effects on
midday evapotranspiration rates. Vapor pressure deficits (VPD) near
0.3 kPa appeared to be an important hydrological threshold, allowing
latent heat flux to persistently exceed sensible heat flux. Dry (compared to
wet) soils increased bulk surface resistance (water-limited). Wet soils
favored ground heat flux and therefore limited the energy available to
sensible and latent heat flux (energy-limited). Thus, midday
evapotranspiration was suppressed from both dry and wet soils but through
different mechanisms. We also found that wet soils (ponding excluded)
combined with large VPD, resulted in an increased bulk surface resistance
and therefore suppressing evapotranspiration below its potential rate
(Priestley-Taylor α < 1.26). This was likely caused by the
limited ability of mosses to transfer moisture during large atmospheric
demands. Ultimately, in addition to net radiation, the various controlling
factors on midday evapotranspiration (i.e., near-surface soil moisture,
atmospheric vapor pressure, and the limited ability of saturated mosses to
transfer water during high VPD) resulted in an average evapotranspiration
rate of up to 75% of the potential evapotranspiration rate. These
multiple limitations on midday evapotranspiration rates have the potential
to moderate interannual variation of total evapotranspiration and reduce
excessive water loss in a warmer climate. Combined with the prevailing
maritime winds and projected increases in precipitation, these curbing
mechanisms will likely prevent extensive future soil drying and hence
maintain the presence of coastal wetlands. |
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