John Richardson


Research Classification

Research Interests

freshwater biology
food webs

Relevant Thesis-Based Degree Programs

Research Options

I am interested in working with undergraduate students on research projects.

Research Methodology

experimental, hypothesis-driven research
field studies
large-scale experiments


Master's students
Postdoctoral Fellows
Any time / year round
I am open to hosting Visiting International Research Students (non-degree, up to 12 months).

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Graduate Student Supervision

Doctoral Student Supervision

Dissertations completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest dissertations.

Using multiple scales for enhancing predictive capacity in modelling responses to the cumulative effects of disturbance in streams (2020)

Disturbances affect ecosystems in complex ways at multiple spatial and temporal scales. Much research has focused on quantifying multiscale landscape patterns but less has focused on using multiscale information to increase predictive capacity in understanding complex ecosystem processes. Predicting cumulative effects of stressors is important for managing ecologically resilient landscapes. Of particular importance is predicting how changes in land use cumulatively affect aquatic ecosystems, such as streams. Furthermore, despite strong functional linkages showing that headwaters deliver important resources downstream, limited research focuses on understanding landscape-scale variation in headwaters or predicting how many instances of fine-scale headwater alterations cumulatively affects downstream. My dissertation addressed predictive capacity and headwater variability in several ways. First, I used empirical data from headwaters in an urbanizing region to examine multiscale variability in headwater condition and showed that incorporating spatial dependencies can nearly double predictive capacity. Second, I developed and analyzed data from a citizen science protocol designed to examine functional and structural variability of urban headwater streams. Specifically, I examined cotton strip decomposition rates to show that local-scale variation explained nearly 70% of the variability. Third, I developed benthic macroinvertebrate cumulative effects models to examine the effects of environmental context and land cover conditions. I showed that the relative importance of environmental, land cover, spatial, and headwater variables were indicator-dependent suggesting that practitioners should address context dependency when evaluating land cover conclusions. Fourth, I applied a common, multiscale analytical framework (i.e., spatial stream network models) to examine the variability of chemical, decomposition, respiration, and benthic macroinvertebrate indicators to also show that incorporating multiscale dependencies can increase predictive capacity on average, but again this was indicator-dependent. To confront complexity, generate stronger predictions, identify knowledge gaps, and improve understanding of cumulative effects, environmental practitioners stand to benefit from incorporating multiscale dependencies.

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An experimental test of factors limiting leaf litter mass loss and invertebrate assemblages in riparian zones of forested headwater streams (2019)

Riparian zones support a broad diversity of organisms and ecosystem functions, like decomposition, which are integral to both terrestrial and aquatic ecosystems. Riparian zones are globally threatened, and management agencies are increasingly focused on protecting the ecological functions and diversity of these systems. Identifying factors limiting decomposition and invertebrate diversity in riparian zones can improve our understanding of how these ecosystems operate. In this thesis, I identified mechanisms contributing to the diversity of terrestrial invertebrates in riparian zones: flooding and drying cycles, nutrient and water availability, microclimate gradients, vegetation and microhabitat diversity, and unique food resources. I experimentally determined whether water, nutrients, and distance from stream limit (1) early-stage mass loss of leaf litter from red alder (Alnus rubra) and western red cedar (Thuja plicata) trees, and (2) terrestrial invertebrate abundance and diversity in headwater riparian zones in southwestern British Columbia. My experiments revealed that moisture is a limiting factor to red alder leaf litter mass loss during the summer dry period: watered litter lost 4% more mass than un-watered litter in four red alder litterbag trials. Nutrient availability may be limiting to western red cedar mass loss at my sites: leaf litter with nutrient additions lost 5% more mass than litter without nutrients in one of three western red cedar trials, suggesting that nutrients may be limiting to western red cedar mass loss at my sites. The terrestrial invertebrate community appeared sensitive to nutrient additions: pitfall trap abundance and order richness were lower at stations with nutrients. Trap abundance, taxonomic richness, and community composition also differed based on month of capture. I also documented differences in microclimate variables with distance from stream. Temperature and moisture conditions within 1 m of the stream differed from conditions farther away during the summer dry period between July and August, but only temperature differed in winter between December and January. This small difference in microclimate with distance from stream did not appear to influence invertebrate abundance and diversity, or mass loss of either litter species. These results contribute to our understanding of which factors limit decomposition and diversity in headwater riparian zones.

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Assessing and monitoring the stability of stream detrital dynamics under forest disturbances (2019)

Disturbances affect ecosystem stability and the delivery of ecosystem services. Stability responses to disturbances involve multiple components, including changes in the levels (indicating resistance) and recovery time (resilience) of state variables. The stability of stream ecosystems is an active research area, however, empirical studies commonly measure single components of stability, and the basis of its spatio-temporal variability is often unclear. Bivariate and multi-dimensional frameworks were proposed to facilitate stability comparisons within and across ecosystems. I recommended adjusting two bivariate frameworks to better address diverse disturbance-response trajectories, shifting baselines, and broaden their applications for streams and other ecosystems. In my dissertation, I quantified multiple stability components of terrestrial-derived particulate organic matter (POM) availability and breakdown in small, temperate streams under forest harvesting. I focussed on stream POM dynamics, as they underpin the stability of consumer productivity (e.g., fish) and nutrient cycling, which are important aquatic ecosystem services. First, I investigated whether the natural variability of leaf litter breakdown – critical for detecting disturbance impacts – was affected by natural, weather-driven discharge variations across years, and decomposer preference of local versus exotic litter species. I showed that inter-annual hydrologic variations poorly explained litter breakdown, whose natural range of variation exceeded the benchmarks set by a popular bioassessment framework. Accordingly, I recalibrated reference conditions of litter breakdown to allow more robust bioassessments. Decomposer preference did not differ significantly between high-quality native and exotic litter, supporting their standardised use for disturbance studies across geographic regions. Secondly, I demonstrated that the resilience of litter breakdown to forest harvesting was likely greater in streams affected by thinning (with 50% basal area removal of riparian trees; 2-9 years post-harvest) than those affected by clear-cutting with or without riparian buffers (8-15 years). Thirdly, I modelled the resistance of stream POM quantity under variable, realistic harvesting impacts. Logging-induced changes in litterfall were more influential than peak discharge and stream temperature alterations in regulating POM quantity. Management strategies minimising riparian forest disturbances would more likely sustain detrital resource availability and productivity in small streams. My results indicated that riparian vegetation, through litterfall and shading, importantly controlled the stability of stream POM dynamics.

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Cumulative effects of multiple agricultural stressors on freshwater ecosystems (2018)

Agriculture is the primary cause of sedimentation, nutrient enrichment, and insecticide contamination of freshwater ecosystems. Despite the widespread co-occurrence of these ecological stressors, little is known about their potential interactive effects. I conducted three experiments manipulating combinations of these stressors in order to evaluate their cumulative effects on freshwater ecosystems at different scales of biological organization (community, ecosystem, meta-ecosystem). First, I evaluated stream invertebrate community responses to sedimentation, nutrient enrichment, and the insecticide chlorpyrifos using laboratory microcosms with distinct microhabitats. I demonstrated that chlorpyrifos can interact non-additively with fine sediment (reversal) and nutrients (antagonism), with potentially deleterious impacts on small-sized invertebrates. Furthermore, invertebrates in gravel microhabitats were more severely affected than those in leaf packs. Second, I manipulated levels of nutrients, sediment, and the insecticide imidacloprid in experimental pond ecosystems. I demonstrated these stressors had antagonistic effects on pelagic and benthic invertebrate diversity. Moreover, the results suggested imidacloprid increased ecosystem metabolism indirectly, through negative effects on invertebrate consumers. Finally, I explored processes at the scale of the river network meta-ecosystem. Using a network of experimental channels, I investigated how multiple-stressor interactions within tributaries affected downstream ecosystems. My results indicated that complex nutrient-sediment interactions within tributaries could strongly alter the flux of organisms from tributaries to downstream ecosystems. Furthermore, I observed that at small spatial scales, these alterations of within-network migration patterns could be more influential than the transport of the stressors from headwaters to recipient ecosystems. My research contributes novel evidence suggesting that complex interactions among nutrient enrichment, sedimentation, and insecticide contamination are frequent in freshwater ecosystems, and have distinct mechanisms operating at different scales. In particular, these findings underscore the importance of considering multiple-stressor interactions in insecticide environmental risk assessments; even at low concentrations, interactions with other stressors may result in unexpected negative effects for aquatic biota and ecosystem processes.

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Riparian forest management and regeneration: effects on forest structure and stream ecological processes in streams of eastern Amazon, Brazil (2018)

In tropical areas, deforestation and forest degradation are major threats to forests and the surrounding ecosystems, such as riparian forests and streams. These threats to riparian forests and streams in agricultural areas can be reduced by the implementation of riparian buffers. However, disturbances from cleared areas may still impact the forests due to the high edge-to-area ratio of buffers. Selective logging inside the buffers also has the potential to degrade riparian forests and streams. Forest regeneration has the potential to restore ecosystems in degraded lands, but disturbances from ongoing agriculture are expected to arrest or delay the regeneration process in the buffers. I evaluated the efficacy of two riparian buffer management strategies: (1) land abandonment for natural regeneration and (2) the maintenance of mature forest. I also sampled additional sites of different ages to evaluate where buffer treatments fit after riparian forest alterations. I hypothesized that the riparian buffers resulting from land abandonment would have less forest canopy, simpler stand structure, less large wood, higher primary production, and higher decomposition rates than a regenerated riparian forest that was surrounded by mature forest. I expected the same outcomes when comparing the riparian buffers of mature forest versus mature riparian reference sites. I found that forest structure did not differ significantly between riparian buffer management treatments, however, my ordination analysis revealed signs of forest degradation after selective logging in the riparian buffers of mature forest. I found no significant effect of riparian buffer management in any stream variable studied. Large wood was related to channel width and stem density. Stream respiration increased and primary production decreased as the regeneration process advances. Decomposition differed among species, apparently by differences on leaf structural compounds. My results show that both buffer management strategies can be effective for protection of riparian and stream ecosystem in agricultural landscapes. Land abandonment is a viable and inexpensive restoration action where ongoing disturbances are mild and the propagules for regeneration are available. While the implementation of riparian buffers of mature forests is an effective strategy, selective logging should be excluded from these areas as disturbances may intensify in the future.

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The influence of physical habitat structure on invertebrate drift and Pacific salmon production in forest streams (2018)

Untangling the mechanisms linking the physical world to ecological processes is paramount for effectively conserving and restoring habitat for threatened species. Pacific salmon rearing in small streams have been particularly well studied in this regard given that physical habitat features (e.g., velocity) strongly influence their performance and that habitat alteration is a major cause of their decline in many areas. However, despite strong evidence that stream salmonids are food limited, we lack commensurate understanding of how habitat influences their food supply - suspended invertebrates drifting downstream (invertebrate drift). Consequently, the mechanisms linking physical habitat structure to salmonid production remain unclear. My dissertation attempts to address this issue. First, in Chapter 2, I review and synthesize the mechanisms underlying invertebrate drift, discuss potential caveats in methodology, and identify key knowledge gaps. I particularly highlight how the physical and behavioural processes governing drift entry are highly dependent on context-specific abiotic and biotic attributes (e.g., hydraulics, individual condition). In Chapter 3, I use flow manipulation experiments to show that some of this context dependency can be explained by considering behavioural and morphological traits of invertebrate taxa, which underlie their tendencies to drift behaviourally or passively; for instance, body shape predicted the magnitude of responses to increased flows. In Chapter 4, I show that aggregate community-level drift rates vary spatially in streams over scales relevant to individual drift-feeding salmonids. Specifically, I measured spatially explicit rates of drift production, demonstrating that shallow high velocity riffles and deep low velocity pools form distinct sources and sinks of drift within stream networks. In Chapter 5 I build on this result to show that drift generation in riffles coupled with strong preferences for low velocity pools by salmonids leads to maximum fish production occurring in habitats with intermediate ratios of pool-riffle areas; in essence, a trade-off between increasing space but declining food as pool area increases. I extend these results with bioenergetic simulations to show that the shape of this trade-off is sensitive to alternative modes of prey delivery (e.g., aerial inputs of terrestrial invertebrates), which may be decoupled from in-stream habitat conditions.

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Effects of predators on the carbon dioxide dynamics of freshwater ecosystems (2013)

Freshwater ecosystems are important natural emitters of the greenhouse gas CO₂. The magnitude and direction of the exchange of CO₂ between freshwaters and the atmosphere, or flux, is influenced by the concentration of CO₂ in the water. Every organism within a freshwater ecosystem influences the net CO₂ balance of that ecosystem either through respiration, photosynthesis or both. Thus, large changes in populations due to natural or anthropogenic stressors and the underlying food web structure of the ecosystem have the potential to alter CO₂ fluxes of aquatic ecosystems. To evaluate the influences of species loss on food web structure and CO₂ fluxes of aquatic ecosystems, I experimentally manipulated species from different consumer trophic levels (predator, grazer, or detritivore) and tested the effects of these losses on CO₂ fluxes of experimental streams, ponds and bromeliads. In streams, I found that influences on CO₂ emissions were most sensitive to the loss of a predatory insect compared to other trophic levels, including a tadpole grazer and an insect detritivore. Similarly, the removal of a fish predator to ponds or an insect predator to bromeliads resulted in trophic cascades that significantly influenced the CO₂ flux of the ecosystem. Both the identity of the predator and interspecific competition among predatory insects influenced the strengths of cascading effects of predators on CO₂ emissions from bromeliads. However, across all three ecosystems (streams, ponds, and bromeliads) predators, via trophic cascades, had surprisingly consistent effects on the CO₂ flux of the ecosystem. Finally, as alterations to predator abundance often occurs in concert with increasing water temperatures and nutrient loading, I determined the individual and interactive effects of these stressors on pond communities. I found that nutrients often increased top-down control of predators on CO₂ fluxes, but the individual effect of warming and its combined effects with nutrients had negative effects on both consumers and primary producers making predictions about CO₂ fluxes complicated. My results provide novel insights into the influence of predators and food web structure on CO₂ fluxes and the potential for predator loss to markedly alter CO₂ fluxes of freshwaters.

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Can conservation strategies for a single species be used to inform and guide restoration of ecological structure and function in flood plain ponds? (2011)

Freshwater ecosystems worldwide are degraded by habitat loss, fragmentation and conversion. The practice of ecological river restoration has developed to address degradation, but there has been limited monitoring and assessment of river restoration projects that could be used to improve the science of restoration ecology. I used meta-analysis and studied floodplain ponds restored for juvenile coho salmon (Oncorhynchus kisutch) in southwestern British Columbia, Canada to test ecological and conservation science hypotheses about how restoration projects are planned and assessed. I evaluated the efficacy of the umbrella species concept, which suggests that conservation strategies designed for one species may benefit co-occurring species, using meta-analysis. I empirically assessed the potential for coho to be an umbrella species in restored ponds. I studied the relationship between biodiversity and ecosystem function (i.e., standing biomass) and explicitly considered the role of habitat complexity in mediating that relationship. I evaluated the influence of habitat at different scales (watershed, pond and micro-habitat) on the abundance and biomass of juvenile coho and other aquatic vertebrates. I used standard meta-analytic techniques to assess the umbrella species concept and found conservation strategies designed for umbrella species generally benefit co-occurring species. For the empirical studies, I sampled vertebrates in 17 restored ponds in three watersheds three times over a year. I sampled benthic invertebrates and algae once and documented habitat (e.g., depth, cover) at the pond and trap scale. Coho abundance and biomass, as well as that of other aquatic species, varied across ponds indicating a gradient in response to restoration. There was a positive relationship between species diversity and standing biomass, although that relationship was not consistent across taxonomic groups or with respect to habitat complexity. There was a relationship between watershed-scale habitat features (e.g., landcover, elevation) and the relative abundance and biomass of species present, however, different species responded similarly to micro-habitat types suggesting that watershed scale factors acted as a filter for community composition. This study demonstrated that valuable insight into restoration can be gained by studying patterns from a broad study of restored systems and that restoration designed around a single species can benefit other species.

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Master's Student Supervision

Theses completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest theses.

Outcomes of stream invertebrate mesopredator interactions to benthic food webs and ecosystem functions (2022)

Within the predator guild of ecological communities are smaller-bodied mesopredators that have the ability to directly impact community structure and indirectly alter ecosystem processes. Interactions between predators can result in combined predator outcomes to their prey, termed Multiple Predator Effects (MPEs), that can be additive, antagonistic, or synergistic with the strength and direction contingent on predator identity and guild diversity. In streams on the west coast of North America, there are two co-occurring predatory stonefly larvae, Calineuria californica and Hesperoperla pacifica, both of which can cause direct depletion of the prey community which can cascade to indirectly alter leaf litter decomposition and periphyton standing stock. My objective was to quantify the role and outcome of intra- and interspecific interactions of C. californica and H. pacifica on stream food webs. I manipulated stonefly larvae identity and density, as well as richness of the predator guild, then compared larval growth and survival, prey community composition, and measures of basal resources to determine the MPE outcomes. I hypothesized that due to the high degree of niche overlap that competition would lead to antagonistic MPEs. I also hypothesized that increasing density and the presence of the more aggressive H. pacifica would lead to higher competition and stronger antagonistic MPEs. I found that stonefly larvae presence caused a 46% reduction in the prey community, and that increasing biomass of either species significantly caused this decline. For interspecific and intraspecific C. californica pairings there was density-dependent competition resulting in a switch from additive to antagonistic MPEs, while intraspecific H. pacifica pairings had antagonistic MPEs at all densities. I also found that the mechanism of predator impacts varied between the two species, with H. pacifica decreasing the prey community through consumption and C. californica through non-consumptive behavioural modification of prey. However, the effects to the prey community did not cascade to impact the basal resources. My results demonstrate that the type and strength of predator interactions may be contingent on the composition of the predator guild and may result in unexpected, non-linear outcomes to the community.

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Ecological impacts of timber harvest on coastal British Columbia's riparian plant communities through functional trait analysis (2021)

Riparian areas are fundamental for the function of headwater streams, as they provide nutritional and physical inputs and processes essential for ecosystem function. I examined how timber harvest affects the riparian shrub and herb communities of headwater streams to better understand the associated impacts on ecological processes in British Columbia’s coastal small-stream ecosystems. By analyzing effects of environmental gradients at three sites each of three intensities of riparian harvest which were complete tree removal (non-buffered), partial tree retention (buffered) and reference sites, shifts in riparian ecological processes were indicated through plant functional trait responses to conditions such as light and temperature; significant differences were found among species and communities trait values. Buffered sites had intermediate trait values between those of the reference and non-buffered sites. Specific leaf area and leaf nitrogen content values were highest at reference sites, intermediate at buffered sites, and lowest at non-buffered sites; stem specific density and leaf carbon content were highest at non-buffered sites and lowest at reference sites. Directional relations of the six focal traits with the three treatments were consistent for the community-weighted values, and most of the eight focal species’ values. These treatment effects were more evident in the physiological plant traits than chemical traits. Buffers of riparian tree retention showed moderating effects to the environmental changes associated with timber harvest that most strongly influence the plant functional traits studied.

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Growth and survival in the early life history stages of white sturgeon (Acipenser transmontanus) (2021)

Several populations of white sturgeon (Acipenser transmontanus) are experiencing chronic recruitment failure, likely due to low survival in the early life history stages. Despite great conservation interest, knowledge gaps about the basic biology of the early life history stages persists. My first objective was to investigate how periods of starvation after the exhaustion of the yolk sac and the presence of substrate during the yolk sac stage affect growth and survival of the larval stages. I reared newly hatched larvae at 7 levels of starvation after yolk exhaustion (0, 3, 6, 9, 12, 15, and 18 days of starvation). Yolks were exhausted at 11 days post-hatch (dph). After the starvation period, larvae were fed ad libitum to 35 dph. Larvae reared in substrate during the yolk sac stage were 12% heavier in wet mass and 27% heavier in dry mass at the end of the stage (11 dph) than larvae reared without substrate. Masses were not significantly different at 35 dph, after 24 days of feeding. Larval mortality rates were not affected by substrate presence or starvation duration. For starvation resistance, all larvae gained wet mass regardless of starvation duration. However, larvae that faced nine or more days of starvation lost dry mass over the study period, indicating that dry mass may be a better metric of growth for larval sturgeon. My second objective was to examine the effect of fish density and food ration on the growth and survival during the early juvenile stage. I reared 2.5-month-old juveniles at four densities (1, 3, 5, or 7 fish/tank) and two ration levels (50% or 100%) for four weeks. Specific growth rate in the first week was 0.69 ± 1.45 %/day for the fish that survived, and -1.19 ± 0.82 %/day for fish that died. Fish that survived for the duration of the experiment grew at 1.94 ± 0.97 %/day over four 3 weeks, regardless of density or ration treatment. Density significantly and positively influenced the mortality rate, but ration did not. My results indicate that abundant food is critical to the success of white sturgeon in the first year of life.

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The influence of the stream-lake confluence on benthic lake delta communities and the impacts of upstream forest harvest (2021)

The lake delta (LD) is the recipient of nutrient and energy subsidies from upstream habitats. Donor-controlled subsidies can support primary production and consumer densities in recipient LDs. However, LDs may also receive the impacts of upstream disturbance. In coastal British Columbia, small oligotrophic lakes with numerous stream inflows are common, yet forest harvesting (FH) is also pervasive across this region. FH can adversely affect stream biota by altering sediment and nutrient inputs, temperatures, water yields, and food availability. However, downstream contributions, especially to lakes, are rarely measured or considered within FH management. My objectives were to test (1) whether LDs are more productive and/or diverse habitats compared to areas of the lakeshore (LS) not influenced by stream inflows; and (2) whether there are shifts in LD benthic communities in response to upstream FH.I compared LD communities with upstream riparian areas that were harvested (harvested LDs – HLDs) or relatively undisturbed (unharvested – ULDs) within 100 m of the streamside, and LS sites. It was predicted that subsidies would lead to higher periphyton and macroinvertebrate standing stock, and a different community structure in ULDs and HLDs versus LS sites. As nutrient runoff is often higher after FH, higher periphyton measures in HLDs versus ULDs were predicted. Due to adverse effects of FH on aquatic biota, macroinvertebrate abundance and/or diversity and the relative abundance of sensitive versus tolerant taxonomic and functional trait groups were predicted to be higher in ULDs versus HLDs.I found that LDs in British Columbia are hotspots for benthic production; however, upstream FH may reduce periphyton and macroinvertebrate standing stocks by approximately 30 and 50%, respectively. Periphyton and macroinvertebrate standing stocks were 1.5 and 2 times higher on average in ULDs, versus HLDs and LS sites, respectively. The community structure and relative abundance of most taxa and trait groups were similar, and sensitive and tolerant groups showed trends related to food availability. My results suggests that nutrient and energy availability, consumption, and benthic production were likely higher at ULDs. Identifying ULDs as hotspots along the shoreline advances our understanding of FH disturbance in relation to stream-lake connectivity.

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The influence of forest management and spatio-temporal variation on greenhouse gas fluxes from riparian soils along headwater streams (2020)

Riparian zones of headwater streams have valuable ecosystem functions, and are particularly vulnerable to forest harvest in coastal British Columbia. Studies of greenhouse gas (GHG; CO₂, CH₄, N₂O) fluxes from these unique ecosystems, with fluctuating water tables, and high soil organic matter, remain limited. My first objective was to quantify the effects of forestry practices on GHG emissions from riparian forest soils, and determine the dominant driver(s) of emissions over the growing season. I compared sites that were clear-cut without a riparian buffer (“no buffer”) or with a buffer (“buffer”) to relatively undisturbed riparian zones (“reference”). I hypothesized that either a rise in the water table, increased soil temperatures, or disturbance of roots and microbes following forest harvest would have the greatest influence on GHG fluxes. My second objective was to examine the effects of temporal and spatial variation on annual GHG fluxes from relatively undisturbed riparian soils. I hypothesized that groundwater discharge (DIS) areas in the riparian zone would have high soil moisture and nutrients, resulting in greater anaerobically produced CH₄ and N₂O emissions compared to outside of these areas (ND). I further hypothesized that GHG fluxes would peak in the warmest and wettest months. I measured gas fluxes in situ alongside headwater streams using static chambers and gas chromatography. I found that N₂O emissions were 1.71 and 2.12 times lower at buffer and no buffer sites, respectively, than reference sites. Carbon dioxide fluxes were 1.16 and 1.09 times higher at buffer and no buffer sites, respectively, compared to reference sites. Methane fluxes were 1.34 and 2.89 times higher at buffer and no buffer sites, respectively, compared to reference sites. Additionally, CH₄ uptake during the growing season was 2.18 times higher at ND areas than DIS areas. Soil temperature, soil moisture, and depth to the groundwater were significant predictors of GHG emissions, and emission rates were highest in the spring and summer months. The results of my research provide information on the magnitude and drivers of GHG fluxes in riparian zones to help inform GHG budgets and forest management.

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Tributary junction, what's your function? Linking catchment processes to habitat alteration and testing mechanisms for community responses at stream confluences (2019)

Biotic communities are shaped by both regional and local processes. Locally, communities can be influenced by the quality, quantity, and arrangement of habitat structure and resources. At the same time, landscape processes act to arrange structural components and resources in space. In streams, catchment processes can strongly control habitat attributes. This relationship between catchment processes and resulting effects on in-stream communities has been studied extensively in the context of uninterrupted stream reaches. Many processes are influenced by the size of the stream, which has important consequences for river net- works. Streams of differing size and characteristics join to form tributary junctions, which have received relatively little attention in stream ecology. Tributary junctions are hypothesized to be biological hotspots due to high habitat heterogeneity and possibly unique niche space. However, observational studies show mixed support suggesting the need for more of a mechanistic understanding.In this thesis, I link physicochemical processes to habitat attributes and test two mechanisms for community responses at tributary junctions. I conducted an observational study to test whether stream size explains tributary exports of habitat structural components and resources and the resulting effects on mainstem habi- tat attributes. I found that tributaries do alter the habitat attributes in the mainstem, but tributary size was rarely an accurate predictor, except for the concentration of coarse particulate organic matter (CPOM) and nutrient supply from the tributary relative to the mainstem. Additionally, many attributes varied strongly over time. Using a field-based experiment, I tested whether CPOM addition and substrate coarsening were impor- tant mechanisms for macroinvertebrate community responses at tributary junctions. I found that community structure was highly variable with little explanation due to tributary inflow. Experimental treatments and environmental covariates explained little variance, except for effects on taxa-specific abundances with the supply of CPOM. Overall, this thesis shows that tributaries are important agents for altering habitat structure and resources in mainstem channels, but effects on communities are highly site specific and may instead be driven by dispersal processes. The results of this work suggest the need to investigate other specific processes and mechanisms for community responses at tributary junctions.

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Turbidity dynamics as a key component of water quality management (2019)

Given the reliance of many communities on surface water, and the continued degradation of aquatic ecosystems, understanding the limits and uncertainties of water quality assessment is vital. Turbidity is a common measurement of water quality for public health and ecosystem function. It has been frequently studied in larger water bodies but not in small streams. We characterized turbidity dynamics in two sets of small streams over seasonal and spatial scales, by monitoring. We collected continuous turbidity measures every 15 minutes, for one year, with monthly spot turbidity samples, in two regions in British Columbia with varying degrees of land use for over a year. Three streams were in the University of British Columbia’s Malcolm Knapp Research Forest, with forestry as the dominant land use type. Our other study area was the Shawnigan Lake Watershed, located on southern Vancouver Island. We had three sites on each of two creeks, McGee Creek and Van Horne Creek, where Van Horne Creek had higher percentages of industrial and urban land uses determined using a Normalized Difference Vegetation Index. In the Research Forest streams, turbidity maximums were ~16 NTU, whereas McGee Creek reached a maximum of 67 NTU, and Van Horne Creek reached 371 NTU. Using Principle Component Analysis and Linear Mixed Effects Models, we found that both rainfall and discharge were significant drivers of turbidity, particularly during periods of intense precipitation. Turbidity also displayed mostly clockwise hysteresis dynamicss during storm events. Interestingly, turbidity displayed a highly significant seasonal response, where the first-flush response of a few of the highest turbidity events occurred during the spring and summer. Land use was also a significant driver of turbidity, particularly forestry, urban and construction land uses. Our research showed that turbidity was spatially complex, and highly variable over time and space, with individual sites and streams being significantly different from each other. Our results have important implications for turbidity monitoring and assessment, given that current monitoring schemes may be insufficient to determine changes in turbidity due to land uses and to assess water quality accurately over spatial scales.

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Assessing high altitude Andean wetlands using plant community structure: A multivariate analysis and remote sensing approach (2015)

High altitude wetlands of the Central Andes Cordillera in South America are unique ecosystems with valuable ecosystem functions and one of the environments most threatened by climate change. They play a significant role in sustaining endemic biota, in providing the grasslands for herd of alpacas, llamas and vicuñas and by storing water and releasing it during the year to one of the driest regions on the earth, the Atacama Desert. This ecosystem is dependent on groundwater sources, and vegetation regulates the amount of water available during the dry periods. In Chile, the increasing demand for water requires more technical knowledge and research in order to prevent further degradation. The objective of this research is the description of Tarapacá and Atacama regions’ wetlands plant communities, the abiotic factors and human impacts that are more strongly associated with them by multivariate analysis and a remote sensing approach. Chapter 1 is a review of high altitude Andean wetlands and their importance. In Chapter 2, I identified differences in plant communities’ structure. Each region was distinguished by 5 different plant communities according to the vegetation wetland types. Abiotic factors and physical attributes that were more strongly associated with plant communities were the number and width of principal streams found on the wetland and amount of rocks, bare land and percent of organic matter along the vegetation transects. Using field work and remote sensing, in Chapter 3, I performed a spectral discrimination among plant communities using IKONOS-2 and Geoeye-1 high resolution satellites images. They were used to identify which bands and vegetation indices were the most effective for discriminating vegetation classes. Vegetation classes did express different spectral behaviors. The classes with more reflectance variation were mixed grasses with Oxychloe andina, mixed grasses with salt patches and mixed grasses with Zameioscirpus atacamensis, while classes dominated by O. andina, Z. atacamensis and Festuca chrysophylla expressed less variation on the spectral range. General Discriminant Analysis showed that the most important spectral bands and vegetation indices for distinguishing differences between vegetation classes were Band 1-blue, band 4-NIR and the Wide Dynamic Range Vegetation Index.

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Determining the impacts of hydrological drought on endangered Noosack Dace (Rhinichthys cataractae) at the population and individual level: implications for minimum environmental flow requirements (2013)

Understanding the impacts of hydrological drought is crucial to the conservation of freshwater fishes. In British Columbia, Nooksack dace (Cyprinidae: Rhinichthys cataractae) are an endangered riffle specialist and are threatened by extremely low summer flows. The purpose of this thesis was to explore the impacts of drought on Nooksack dace, whether pool habitats may act as refugia to mitigate these impacts, and to define minimum environmental flow requirements. The first two objectives were addressed using a combination of field survey and experimental manipulations. A reduction in Nooksack dace population size with declining summer flow in Bertrand Creek, and a marked decrease in growth at low discharge in experimental riffles, indicated that low discharge has negative impacts on dace at both population and individual levels. Pool habitats were found to play a minor role in mitigating the negative impacts of hydrological drought (e.g., decreased growth rate), save as a refuge from stranding when riffles dewater. The third objective was addressed using the Instream Flow Incremental Methodology (IFIM). Because this study involved an endangered species an emphasis was placed on evaluating two fundamental assumptions of the methodology. Experimental results for Nooksack dace growth at different depths and velocities provided support for the first assumption, that density-based Habitat Suitability Curves (HSCs) accurately reflect habitat quality, but only for the lower limits of the HSCs. Next, a significant positive relationship between Weighted Usable Area (WUA) and dace biomass was found, supporting the assumption that such a relationship exists. However, this relationship was weak indicating a high degree of uncertainty in how Nooksack dace biomass will respond at high discharges. The IFIM model predicted that habitat availability for Nooksack dace begins to decline most rapidly at discharges of 0.12 m³.s-¹. As there is low confidence in upper ranges of the HSCs this low flow threshold may underestimate declines with discharge, and therefore protection of at least 0.12 m³.s-¹ is considered necessary for the persistence of Nooksack dace individuals and populations. Compared to conventional instream flow criteria, 0.12 m³.s-¹ represents ~10% mean annual discharge which is the threshold for severely degraded habitat.

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Ecological implications of flow-mediated scour events for sockeye salmon alevins (Oncorhynchus nerka) (2012)

Pacific salmon (Oncorhynchus spp.) life cycles involve completion of several developmental stages including the alevin stage. As alevins, sockeye salmon are found within freshwater gravel redds where they utilise yolk sacs for nutrition, growth and development. Flow mediated scour events pose a common threat of destruction to both redds and fragile alevins during a several month period of winter incubation. However, to date, there is very little research on the impacts of early forced emergence of alevins. Using sockeye salmon (Oncorhynchus nerka) as a model, simulated elevated discharge event (SEDE) experiments were conducted to examine the relationship between sockeye alevin development, SEDE exposure and alevin survival. Following five weeks of SEDE experiments, survival rates were found to be significantly correlated to both alevin developmental stage and length of elevated discharge exposure. SEDE experiments were followed by experiments designed to investigate the ecological competence level of alevins following forced early dislodgement. Repeated tests during a five week interval immediately following egg hatch indicated that alevins subjected to SEDE exposure took longer than unexposed alevins to rebury in gravel. Alevins exposed to SEDEs took longer to rebury as they developed, but increased their overall ability to rebury. Neither SEDE exposed or unexposed alevins exhibited abilities to initiate exogenous feeding given forced, early emergence. Survival rates of sockeye salmon alevins both during and after SEDE testing increased significantly with advances of developmental stage. Older, larger alevins also exhibited improved performance in responding to ecological challenges presented in laboratory experiments. Knowledge gained from this research has practical implications for water managers and suggests that: (a) the probability of scour induced mortality of both unhatched eggs and alevins is likely similar up to at least 3 weeks after egg hatch, (b) survival rates and ecological competence of alevins has improved significantly by four weeks following egg hatch, and (c) survival of alevins forced into an epibenthic or water column environment as late as one week before volitional emergence is unlikely to differ greatly from that of unforced emergent fry.

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Load sharing shcemes in multiple induction motor drive applications using volts-per-hertz control (2012)

Multi induction-motor (IM) drives are commonly used to share a mechanical load in a wide range of industrial applications. In many existing auxiliary applications, the traditional low-cost Volts-per-Hertz (V/F) drives are typically used in speed control mode to simultaneously operate several IMs. In multi-machine load-sharing applications, it is preferred to have number of identical IMs to share the load equally. Under ideal conditions, the identical IMs would operate with equal loading. However, in practice deviations of the load sharing among the IMs is possible due to many factors including variations in internal or external parameters and operating conditions of each individual IM. Such deviations may result in disproportionate sharing of the mechanical load and even overloading one or several machines while some machines may be under-loaded. The basic low-cost variable frequency drives (VFDs) with traditional open-loop V/F control scheme fail to share the load under such conditions.In this Thesis, two new methods are proposed to address the load sharing problems under an internal disturbances (such as rotor resistance variations) and external disturbances (such as wheel slippage due to snow/water/oil etc.). The new methods are shown to be effective in sharing the load under disturbances. Moreover, the proposed methodologies may be readily extended to an arbitrary number of motors driving a common mechanical load, and are easy to implement with traditional/existing low-cost VFDs, which may be advantageous for many existing or legacy applications.

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Stream invertebrates in northwest British Columbia : an assessment of the relative importance of forest harvesting and environment factors at local and landscape scales (2011)

Streams are strongly linked to their terrestrial environments through processes which influence habitat structure and food availability at several, nested scales. While forest practices can affect the hydrological, sedimentation and disturbance regimes, the relationship between community structure and forest practices across broad scales of natural environments is not well understood. In this study, the relative influence of environment and forest harvest attributes on stream community composition was examined in 143 unique 1st to 6th order streams, across a broad geographic scale in northwest B.C. Environment and forest harvest variables explained unique aspects of the community composition using canonical correspondence analysis (CCA), although landscape level environmental variables representing catchment topography and hydrology were selected first using a stepwise procedure. Using partial CCA, 20% of the variation in community structure between sites was explained by environment variables, 12% by forest harvest variables, and 4% was shared between the two sets of variables. The low proportion of shared variance suggested low redundancy between the two sets of variables. Variables describing recent forest harvest (15 years prior to sampling or less) explained unique aspects of the community composition compared to variables describing older forest harvest (more than 15 years prior to sampling), perhaps suggesting partial recovery of the stream community after 15 years. The 143 stream sites were sorted into three LAND USE groups based on the proportion of forest harvest within the catchment basin. Using catchment area as a covariate, relative abundance and rarified taxa richness increased by 30% and 20% respectively, while the proportion of EPT individuals decreased, in catchments with > 15% harvest compared to undisturbed catchments. Distance-based ordination scores (nonmetric multidimensional scaling) changed significantly between the three LAND USE classes of forest harvest on both axes.The effects of forest harvest on streams were confounded with natural environmental gradients. Generally, the catchment basins with >15% harvest were larger, with less topographic relief, more lakes and wetlands, and less rapid drainage characteristics when compared to undisturbed catchments.

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The influence of stream-derived detritus subsidies on lake benthic community composition and trophic interactions (2011)

Cross-ecosystem subsidies are important for the structure and functioning of communities within many ecosystems. Increases in subsidies have been modeled to increase trophic cascade strength within recipient systems, because of the donor-controlled addition of a resource. Streams receive high inputs of detrital subsidies and what is not processed within the system is transported downstream. Therefore, streams that flow into lakes have the potential to provide large amounts of detritus to lakes compared to the transfer of detritus from forested lake edges. I hypothesized that streams would increase detritus standing stocks around stream mouths in lakes, that streams would affect the benthic invertebrate community composition, and that those effects would change with distance from the lake shore. To test this I conducted a survey of detritus standing stocks and benthic invertebrate communities at six stream/lake interface and six forest/lake interface sites within two lakes. I found that streams and distance into lakes affected detritus standing stocks, but the effect was only seen when individual pairings of stream and forest sites were examined. I also found that headwater streams significantly altered invertebrate community composition in the lake littoral zone, even up to a distance of 27 meters into the lakes, with some taxa only found at stream/lake interfaces. These results suggest that streams alter the amount of basal resources through subsidies and contribute to whole lake biodiversity.My second hypothesis was that increased detritus in lakes would increase trophic cascade strength. To test this hypothesis, I conducted an in-lake cage experiment in which I manipulated detritus standing stocks (5 densities) and presence of a top-predator (trout). I found that increasing subsidies altered strength of trophic cascades. But unexpectedly, low detritus treatments experienced the strongest positive effect on algal biomass. At intermediate detritus levels there was a switch in the indirect effects of predators, and at the highest detritus densities predators had a negative indirect effect on algal biomass. These results provide evidence that along a gradient of detritus subsidies, trophic cascade strength experiences threshold responses in where predators may have strong, but opposite indirect effects on primary production.

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Season-specific survival and growth rates of coastal cutthroat trout across a gradient of stream sizes in southern British Columbia (2010)

To have greater predictive abilities for informed resource management guidelines for freshwater species protection and management, we need to increase our limited knowledge of the many aquatic species that inhabit small coastal streams. Coastal cutthroat trout (Oncorhynchus clarkii clarkii) are common to small streams in the Pacific Northwest and are a species of concern or threatened throughout their native range. To address knowledge needs I (1) examined the seasonal variation in survival rates of coastal cutthroat trout across a size gradient of smaller streams in coastal BC; and (2) contrasted 10th year post-harvest seasonal trout body condition and relative abundances, and thermal and physical habitats with pre-harvest and 4th year post-harvest values in small streams. The survival study used a robust mark-recapture design stratified seasonally to estimate monthly survival rates; and the streamside harvest study used a multi-year, replicated, before-after-control-impact design. Within the size range of smaller streams studied (n = 7), availability of aquatic habitat (i.e., residual depth) at low-flows was the best predictor of monthly survival rates (p = 0.011), supporting my hypothesis that greater availability of habitat confers higher survival in trout. In addition, a fitted curve suggested an asymptotic relation between water depth and survival rates; where beyond 25 cm of water, greater depth did not confer greater benefits to trout survival. Survival estimates also showed that the summer season had the lowest monthly survival rates across all streams in our study area. Post-harvest effects were not detected in trout relative abundances in the 10th year; however body condition had significantly (p
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