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UBC Theses and Dissertations

Plant-environment relationships in a disturbed wetland system Downarowicz, Ewa

Abstract

Efforts are increasing to mitigate pressures on wetlands from human disturbance. Conservation of these systems requires expansive knowledge of ecosystem structure and underlying environmental gradients exerting control over plant distribution. A multitude of environmental gradients important in undisturbed wetland systems have been studied extensively. The most important have been shown to be: acidity/base richness, nutrient status, water level fluctuations, and organic matter accumulation (Bridgham et al., 1996). Human modification of wetland hydrology may alter the relationships between species distribution and underlying environmental gradients. It is therefore important to study the plant-environment relations in disturbed systems to collect baseline data and subsequently monitor changes in the system. The primary aim of this thesis was to examine which environmental gradients were important in the distribution of wetland species in a disturbed stream fen/mound bog system. The study area, Blaney bog, is a wetland that has been modified by the construction of a dyke/canal system dividing the area into two separate sections. Aerial photographs and primary survey showed that four plant community types dominate the Blaney bog landscape: Kalmia occidentalis, Phalaris arundinacea, Spiraea douglasii, and Carex spp.. In accordance with the primary aim, a dipwell network was established in the four plant community types. Soil water was sampled from the dipwells for a ten month period, peat cores were collected and the vegetation was surveyed at each site. In addition to the initial 16 dipwell sites, 22 sites were added to the study. At these additional sites the same vegetation and soil data was collected however because the sites lacked dipwells, the water was sampled only once. Data analyses addressed the inter-relations between the water and soil variables and plant community composition. Non-parametric analyses of, variance were used to examine if the differences between plant community groups were significant. Spearman's correlation coefficients were calculated to examine relationships between environmental variables. All variables were also analyzed simultaneously using the Nonmetric Multidimensional Scaling method. Results showed that the Kalmia sites were the most representative of poor fen sites. Sites in the other three plant communities varied in their chemistry compared to the expected range found in undisturbed fens. Water components were much more variable than the soil components. The bog-fen gradient was clearer in the pH values, cation concentrations and nutrient status in the soil compared to unclear patterns in the water data. Although total soil nutrient concentrations may not be reflective of nutrient availability, overall the soil components are much more static and present a clearer picture of site conditions at Blaney bog. The disturbance caused by the dyke/canal system and possibly ongoing influx of drainage waters from neighboring agricultural land, are thought to substantially affect the hydrology of this wetland. Effectively, the water table and chemistry are much more dynamic than in undisturbed wetland systems. This study recommends that future monitoring Blaney bog should focus on the soil component rather than the water component and should further investigate the effect of water table fluctuations on plant distribution.

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