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UBC Theses and Dissertations

Assessing long-term outcomes of stream and riparian restoration projects in urban and suburban areas Clement, Sarah Elizabeth


In the era of global climate change and increasing urbanization, anthropogenic disturbances and habitat degradation are ubiquitous environmental problems. One tool to combat these issues is ecological restoration. Restoration of aquatic ecosystems is a key area of study, as streams face a multitude of concurrent sources of degradation, such as urbanization, invasive species, pollutants, and increasing temperatures. The cumulative effects of these stressors are having a major impact on these ecosystems. There is currently limited knowledge on long-term impacts of restoration on stream functions. Therefore, it is important to assess impacts of previous projects to ensure the success of future projects. This study used a space-for-time substitution to analyze long-term impacts of riparian and stream restoration on stream ecosystems. The primary research question of this study was: Do structural and functional indicators become more similar to reference ecosystems as years since restoration increases? Twelve restored sites of various ages (2-25 years since restoration) were compared to 2 highly degraded sites and 3 reference sites. All sites are located in Metro Vancouver, BC, Canada. The structural indicators I measured include water temperature, canopy cover, tree diversity and density, water nutrient concentrations, and in-stream flow characteristics. Ecosystem functions included estimates of leaf decomposition and periphyton production. Tree species richness and basal area (cm²/hectare) showed significant responses to restoration. Tree species richness was 3x higher at restored sites compared to degraded sites, and basal area increased with age since restoration in restored sites. For leaf decomposition, there was a significant difference in the decay rates between treatments. Decay rate (g/g/degree day) was highest in the reference sites (mean = 0.0036), and lowest in the degraded sites (mean = 0.0014). For periphyton production, the difference between treatments was not significant but there was a significant increase with years since restoration. There was a great deal of variation for other variables, so there was no significant difference between restored, reference, and degraded sites. Evidence thus far suggests that one ecosystem function, leaf decomposition rate, does increase over time following restoration.

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