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|Title:||Surface Cover and Air Mass Controls on Evaporation from a Subarctic Marsh|
|Authors:||Lafleur, Marcel Peter|
|Abstract:||<p>Measurements of radiation and energy balance components and leaf stomatal resistance and leaf area were conducted in a coastal marsh on James Bay during the snow-free period of 1985. Measurements were taken at three sites; a sedge covered backshore zone, a wet sedge marsh, and a wooded (deciduous shrub) beach ridge. The objective of the study was to examine atmosphere-biosphere interactions for the three surfaces, with regard to implications for changes in climate and/or surface cover. The scientific contributions to the literature made by this thesis and it's important results can be summarized into three categories; contributions to wetland microclimate Iiterature, contributions to ecological and bioclimate studies, and contributions to evaporation modelling.</p> <p>In the field of wetland microclimate, the results of this thesis directly increase our understanding of the physical microclimate of subarctic marshes. Specifically, the thesis outlines the importance of the annual vegetation growth on energy partitioning and the evaporation regimes of the subarctic marsh. The results also address the controversial topic of evaporation from open water surfaces versus evaporation from vegetated surfaces. This thesis supports the view that the presence of vegetation reduces open water evaporation.</p> <p>Within the field of plant ecological studies, the collection and presentation of the leaf resistance data set in this thesis can be considered to be a significant accomplishment in itself. Of particular importance are the analysis of leaf resistance of four previously untested wetland species, the comparison of resistance for wetIand woody versus herbaceous species, and the confirmation of the vapour pressure deficit response by these species.</p> <p>These contributions can also be extended to the surface resistance data set, particularly the surface response to changing meteorological conditions. The Bowen ratio analysis presented here represents the first attempt to provide a physically based explanation of the relative importance of surface and meteorological controls on evaporation under variable meteorological conditions at the subarctic coast. It is concluded that while the influence of surface resistance was significant, its overaII effect on β was overwhelmed by the meteorological controls exhibited by changes in airmass.</p> <p>The contribution of the thesis to evaporation modelling resides in the evaluation of the Shuttleworth and Wallace (1986) combination formula. The work presented here is quite Iikely the first field application of this theoretical approach. The model appears to be valid for aII ranges of Ieaf area and the discussion of some important model parameters is given.</p> <p>Result from the study suggest that climate change (such as globaI warming from CO₂) wouId have a significant impact on the evaporation regime and, hence, the regional water balance of these wetlands. This might also result in a vegetation feed back responses. The lack of experimentation on coniferous open woodland species is cited as an important area for further study.</p>|
|Appears in Collections:||Open Access Dissertations and Theses|
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