Factors that control Typha marsh evapotranspiration

Abstract

There is continuing debate about the controls on wetland evapotranspiration (E t ) and whether marshes are profligate water users. We used eddy covariance to measure the CO 2 exchange and E t by a California Tule marsh in 2003. The marsh was dominated by Typha and Scirpus, and there was a large amount of standing litter that acted as a mulch. Canopy development was broadly related to air temperature, with rapid growth in May and senescence in October. E t was a few tenths of a mm d À1 in winter, and 3-4 mm d À1 in summer. The midsummer Bowen ratio was $1, and the annual E t was 49 cm. The peak rate of E t was lower than has been reported for marshes based on lysimeter studies, somewhat lower than has been reported for marshes based on micrometeorological studies, and equivalent to, or somewhat lower than, has been reported for upland grassland. The midsummer water use efficiency was 0.0025 mol CO 2 mol À1 H 2 O, and the d 13 C of foliage was À27.1%, which are both typical for productive C 3 ecosystems. Transpiration accounted for 80% of total E t . Evaporation from water standing beneath the canopy and mulch layer was only a minor component of the marsh's hydrological budget. The low rate of evaporation from standing water was a result of cool water temperatures, which remained within a few degrees of the nocturnal minimum on most days. We believe the mulch layer acted in a way analogous to an electrical diode that allowed the upward loss of heat from the water to the atmosphere at night, and shut off the flux of heat from the atmosphere to the water during daytime, resulting in cool subcanopy water and low rates of evaporation. Our observations are inconsistent with the hypothesis that Tule marshes are inefficient water users, or that their rates of transpiration and CO 2 uptake are unusual compared to upland ecosystems. #

Wetland Evapotranspiration: Eddy Covariance Measurement in the Biebrza Valley, Poland

“…At the same time, due to the high costs of measuring instruments, and also because of various technical factors affecting the quality of the data obtained, a number of studies devoted to the measurement of evapotranspiration present the results of measurement experiments lasting for several weeks or seasons. They mainly present the daily patterns of water vapour flux or the daily totals of evapotranspiration against the background of meteorological conditions (Souch et al 1998;Kurbatova et al 2002;Gasca-Tucker et al 2007), as well as the results of impact assessment of parameters such as foliage surface area or surface resistance on the rate of evapotranspiration (Acreman et al 2003;Gulden et al 2007). …”

Stomatal control of leaf fluxes of carbonyl sulfide and CO<sub>2</sub> in a <i>Typha</i> freshwater marsh

“…The SJFM is located near the campus of the University of California at Irvine, at 3 m above sea level and 8 km northeast of the Pacific Ocean (Goulden et al, 2007). The SJFM is part of the University of California's Natural Reserve System.…”

The hidden hydrology of Groenvlei, a lacustrine wetland on the southern Cape coast of South Africa

“…5, but this pattern was observed in each of the 31 years that were modelled. Further research of the transpiration patterns of vegetation that formed the reed collar around the (Carter, 1996;Holt et al 1998;Goulden et al, 2007 andZhou andZhou, 2009), as well as testing, showed significantly better results were obtained when no evaporation losses were assigned to the reed collar in the winter months (Fig. 6).…”