Urban Watershed Comparisons Swan Maltby Pike Lakes
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Urban watershed health and resilience, evaluated through land use history and eco-hydrology in Swan Lake watershed (Saanich, B.C.) by Lise Townsend Bachelor of Science, Royal Roads University, 2004 A Thesis Submitted in Partial Fulfilment of the Requirements for the Degree of MASTER OF SCIENCE in the School of Environmental Studies © Lise Townsend, 2009 University of Victoria All rights reserved. This thesis may not be reproduced in whole or in part, by photocopy or other means, without the permission of the author. ii Supervisory Committee Urban watershed health and resilience, evaluated through land use history and eco- hydrology in Swan Lake watershed (Saanich, B.C.) by Lise Townsend Bachelor of Science, Royal Roads University, 2004 Dr. Valentin Schaefer (School of Environmental Studies) Supervisor Dr. John Volpe (School of Environmental Studies) Co-supervisor Dr. Nancy Turner (School of Environmental Studies) Departmental Member Wm. Patrick Lucey, Aqua-Tex Scientific Consulting Ltd. Industrial Sponsor iii Abstract Dr. Valentin Schaefer (School of Environmental Studies) Supervisor Dr. John Volpe (School of Environmental Studies) Co-supervisor Dr. Nancy Turner (School of Environmental Studies) Departmental Member Wm. Patrick Lucey, Aqua-Tex Scientific Consulting Ltd. Industrial Sponsor Swan Lake watershed, a sub-catchment of the salmonid bearing Colquitz Creek watershed located in the municipality of Saanich, on southern Vancouver Island, British Columbia, Canada, was studied to characterise the linkages between urbanisation and ecological health and resilience. Although rarely applied in watershed ecology, resilience (the ability to absorb disturbances without the loss of ecosystem identity) offers a useful construct in this case study to understand the effects of urban development over the past 150 years, and to outline some principles for integrated, watershed-scale management. Baseline landscape characteristics and processes of historical land-use were determined using paleoecology (pollen analysis) and historical records. Watershed health was assessed using: a Proper Functioning Condition assessment of riparian-wetland and stream channels; vegetation community mapping; vegetation plots; surface flow hydrology; and water quality analyses. Vegetation and lake hydrographs were compared with less disturbed reference ecosystems. Findings are discussed in terms of alternative stable state models and energy dissipation at the site and landscape scale. Analysis of the data revealed that over the past 150 years, forest clearing, agriculture, transportation infrastructure, and non-point source pollution have transformed the landscape and substantially altered the water and energy balance. Impervious surfaces and cleared land (covering 25% and 35% of the watershed, respectively) are inferred to iv have reduced latent heat dissipation of solar energy, an important landscape-scale process affecting resilience to climate change. Degraded stream channels represent reduced ecosystem services and lost social/economic value. The stream/lake hydrographs revealed a typical, urban flashy profile that exacerbates channel erosion and non-point source pollution, while excessive lake stage drawdown is also evident. Water quality is characterized by historic and ongoing excessive nutrient loading and associated cultural eutrophication, heavy metal pollution, and ecosystem “ageing” due to dissolved solids runoff. At the site level, invasive species, particularly reed canarygrass, dominate Swan Lake wetlands, whereas the pollen record shows abundant woody shrubs and associated species (some of which are now extirpated from the site) and an absence of grass; this helps to establish a rationale for vegetation management. Based on the findings of the above studies and according to a proposed conceptual model with assessment criteria in five categories (water, vegetation, energy, soil and nutrients), Swan Lake watershed has impaired ecological health and is not resilient to disturbances such as extreme climate/weather events. Future watershed management should therefore mimic the hydrological function and energy balance of the pre-development conditions. v Table of Contents Supervisory Committee....................................................................................................... ii Abstract...............................................................................................................................iii Table of Contents................................................................................................................. v List of Figures....................................................................................................................vii List of Tables........................................................................................................................x Acknowledgments............................................................................................................. xii Chapter 1. Introduction ....................................................................................................... 1 1.1. Urban Ecology in a Global Context......................................................................... 1 1.2. Study Area ...............................................................................................................3 1.2.1. Overview and Thesis Hypothesis..................................................................... 3 1.2.2. General Landscape Characteristics...................................................................5 1.3. Literature Review: Ecological Health and Resilience ............................................9 1.3.1. Assessing Ecological Health and Resilience.................................................. 13 1.4. Approach and Research Questions.........................................................................17 Chapter 2. History of Landscape Processes and Human Influences in Swan Lake Watershed, ca. 1850 to Present ......................................................................................... 22 2.1. First Peoples of Southern Vancouver Island and Victoria......................................23 2.2. Early European Settlement and Landscape Characteristics...................................25 2.2.1. Terrestrial Ecosystems....................................................................................26 2.2.2. Wetlands, Lakes and Streams......................................................................... 27 2.3. Urbanisation and Watershed Development............................................................ 33 2.4. Airphoto Interpretation ..........................................................................................36 2.5. Discussion.............................................................................................................. 41 2.6. Conclusion..............................................................................................................47 Chapter 3. Proper Functioning Condition of Main Stream Channels in Swan Lake Watershed ..........................................................................................................................49 3.1. Theory and Methods...............................................................................................51 3.2. Assessment Findings ............................................................................................. 54 3.3. Discussion.............................................................................................................. 58 3.4. Conclusions............................................................................................................ 66 Chapter 4. Vegetation of Swan Lake watershed and wetlands..........................................68 4.1. Introduction............................................................................................................ 68 4.2. Methods..................................................................................................................69 4.2.1. GIS and mapping............................................................................................69 4.2.2. Vegetation Field Survey................................................................................. 73 4.3. Results.................................................................................................................... 78 4.3.1. Watershed Scale Vegetation and Land Cover.................................................78 4.3.2. Swan Lake Wetlands - Airphotos................................................................... 79 4.3.3. Swan Lake Wetlands and Reference Sites - Ground Level Study .................81 vi 4.4. Discussion.............................................................................................................. 97 4.5. Conclusions.......................................................................................................... 102 Chapter 5. Present Day Hydrological Patterns and Processes......................................... 104 5.1. Introduction.......................................................................................................... 104 5.2. Methods................................................................................................................107 5.3. Results ................................................................................................................. 111 5.4. Discussion...........................................................................................................