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UBC Theses and Dissertations

Stream sub-reach differentiation : the influence of land management Richardson, Noelle


Agricultural land-use practices impart unique biophysical signatures on streams at the scale of a farm or ranch. As such, Alderson Creek, a groundwater-fed stream that traverses several small agricultural land holdings, might be segmented into a series of sub-reaches, the boundaries of which align roughly with property divisions. A research project was designed to assess whether land management influences have implications on stream characteristics and aquatic health at the scale of agriculturally segmented landscapes. A series of biophysical and chemical indicators of water quality were monitored regularly at several cross-sections along Alderson Creek. An assessment of the overall water quality was conducted with the use of time-series plots and downstream trends. Discriminant analysis (DA) tests were executed with various combinations of the measured variables. The intent was to identify sub-reach membership based on statistical similarities and differences. The results indicate that there is some evidence for sub-reach differentiation. Clustering of cross-sections was evident in the raw data (i.e., box-plots) as well as in statistical tests (i.e., discriminant analysis), although sub-reaches weren’t delineated exactly as expected. Some sub-reaches were different from one another because land uses were distinctly different (R5 from R4). However, some sub-reaches were not clearly differentiable because land use was not distinctly different and there was some transference of water quality from upstream to downstream (R2 versus R1). Overall, this study determined that sub-reach differentiation is influenced by local influences (at the scale of a cross-section or monitoring site), downstream effects (reach scale), and land use practices (property or sub-reach scale). Research undertaken in this thesis contributes to the literature on the role of human influences on stream health and to the understanding of scales of influence. Researchers as well as land-owners benefit from knowledge about the scale at which agricultural land uses may impact stream health as well as the potential benefits of rehabilitation. The implementation of best-management practices such as riparian rehabilitation along a small segment of a stream bounded by property lines, rather than an entire water course, does lead to overall improvements of water quality and ecosystem health.

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