University of British Columbia, British Columbia, Canada
Abstract: In the era of global climate change and increasing urbanization, anthropogenic disturbances and habitat degradation have become ubiquitous environmental problems. One tool to combat these issues is ecological restoration. As 2020-2030 was declared the UN Decade on Ecological Restoration, there is a global impetus to increase restoration efforts. Restoration of aquatic ecosystems is a key area of study, as streams face a multitude of concurrent sources of degradation, such as loss of riparian vegetation, increases in impervious surfaces and stormwater runoff, and pollutant loading. The cumulative effects of these stressors are having a major impact on these ecosystems. However, there is currently limited knowledge on long-term impacts of ecological restoration on ecosystem functions, particularly in freshwater ecosystems. Therefore, it is important to assess impacts of previous projects now, 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 ecosystem functions. The primary research question of this study was: Do indicators of ecosystem function become more similar to reference ecosystems as age since restoration increases? Eleven 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. A leaf decomposition experiment was conducted, as leaf litter inputs play an important role in stream ecosystem food webs and nutrient dynamics. Leaves were left to incubate in the streams for 3 and 5 weeks, and percent loss per degree day was calculated. There was a significant difference in the decay rates between treatments (ANOVA, p < 0.01). Post-hoc Tukey test determined significant difference between restored and reference sites (p = 0.022) and between reference and degraded sites (p = 0.013). Decay rate was highest in the reference sites (mean = 0.0036 ± 0.0013 [SD]), and lowest in the degraded sites (mean = 0.0014 ± 0.00017). Canopy cover, water temperature, water nutrient concentrations, tree DBH, tree basal area, tree species richness, and algae growth rate were also measured at each site. Tree species richness was significantly higher at restored sites compared to degraded sites (p = 0.039). There was a great deal of variation for all other variables, so there was not a significant difference between restored sites, reference sites, and degraded sites. Evidence thus far suggests that some ecosystem functions do increase through time following restoration.
