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UBC Theses and Dissertations

Hydrological processes as function of vegetation type in six vegetation communities in a maritime raised bog Exler, Johannes


Climate change and widespread drainage of peatlands are two main drivers behind shifts in peatland vegetation composition. Peatlands rely on shallow water levels that reduce peat oxidation rates to levels less than carbon accumulation. However, climatic warming and drainage enable non-native vegetation to encroach in areas of lowered groundwater levels where increased water loss due to plant activity cause groundwater levels to drop further. This research aimed at improving the understanding of how drainage and projected climatic change in the Pacific Northwest of North America may affect the hydrology of ombrotrophic raised bogs in the region through associated vegetation community shifts. Research was conducted in a raised bog in southwestern British Columbia, which has a history of drainage that enabled vegetation communities of different structure and species composition to establish. Multi-year energy and water flux and storage observations at an open site near the bog's center identified available energy and atmospheric demand, expressed as vapour pressure deficit (VPD), to be the main drivers of evapotranspiration loss (ET) at a daily time scale, and groundwater level was a secondary control. Interannual variability of growing season ET was driven by differences in VPD. The dominant water loss process shifted from ET in summer to lateral near-surface and surface flow in winter, which was controlled by two groundwater level thresholds. Vertical water exchange fluxes between the peat surface and the atmosphere were a function of vegetation type. A reduction in net precipitation was primarily associated with shrub interception loss, which was higher than interception loss from trees on a per unit ground area basis. At the tree level, transpiration loss was a function of tree size and species; groundwater level was a secondary species-specific control in the short term. Differences in root development between sites that affected stand transpiration were likely a result of historic drainage. Peat surface evaporation was primarily controlled by shading from shrubs and peat moisture content was a strong secondary control. Water loss to the atmosphere was higher at more vegetated sites and relative contribution of fluxes varied according to vegetation type.

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