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Retrogressive thaw slumps are areas of unstable degraded permafrost that often drain into nearby watersheds, leading to increased sediment loads and changes in water quality. Thaw slumps are prevalent across the Arctic, including western Canada, Alaska, and Russia, and high‐altitude areas of western China. Over the past several decades, increased temperatures and precipitation in the Arctic have led to increases in the size and frequency of thaw slumps. Our study explored the effects of prolonged sedimentation from thaw slumps in the Peel Plateau, NWT, Canada on benthic macroinvertebrate drift, an important biological function of stream ecosystems. Though sedimentation is known to initiate a catastrophic drift response, studies have generally not considered the drift response to ongoing, long‐term perturbation. Drift densities and sediment loads were measured using drift nets and sediment traps at paired sites upstream and downstream of thaw slumps. We compared drift densities and sediment loads between sites and examined how drift differed over a fine‐sediment gradient. The amount of suspended and settling fine sediments increased significantly at downstream sites. Drift densities decreased at downstream sites; however, when drift was corrected for benthic abundance at each site, there was an increase in proportional drift density associated with increased fine sediments. These results indicate that prolonged impacts from thaw slumps result in lower macroinvertebrate abundance and higher proportional drift relative to undisturbed sites. Ultimately, increased sediment loads from thaw slumps represent a chronic stressor that will continue to prevent recovery of macroinvertebrate communities at impacted sites until these features stabilize.

ABSTRACTPlankton community samples from a reservoir were compared to samples from a river downstream of a large hydroelectric generating station on the lower Saint John River, New Brunswick, Canada. The study focused on spatiotemporal variation of the plankton communities and their association with physicochemical parameters in the reservoir–downstream river system after almost 50 years of limnological evolution. The survey revealed 288 phytoplankton and 85 zooplankton taxa, dominated in abundance by rotifers and Cyanobacteria. The taxa richness was significantly greater than reports at the time of the reservoir creation. Spatial variability of the plankton community in the reservoir was statistically homogeneous among sites and the water layers across sites during its stratified period. The river plankton communities followed the same patterns as the reservoir, and river sites were always statistically similar to the reservoir community in terms of richness and abundance. The similarity of the communities across the reservoir and the river was highest during summer. Influential variables explaining seasonal differences in phytoplankton and zooplankton communities included physical, nutrient, and biotic factors. Our study demonstrates how a large, run-of-the-river hydroelectric generating station can regulate the plankton community up to 20 km downstream.

Several letters to the editors are presented in response to the article on actress Sally O'Neil in October 2016 issue, on actor Ray Milland in September 2016 issue and article on actress Faith Domergue.

AbstractWe explored the importance of environmental drivers in structuring benthic macroinvertebrate communities along a spatial hierarchy (local to landscape scale) in Low Arctic stream systems that were previously unstudied. Macroinvertebrate communities from 29 sites in Low Arctic areas of northern Labrador and Québec, Canada, were quantified by taxonomic structure and biological metrics. Environmental variables were quantified at site, reach, and catchment scales using field-collected data and geospatial information. The first three axes of Redundancy Analysis (RDA) ordinations explained 21.0–40.6% of the unconstrained variance in taxonomic structure and biological metrics. Biological data were most highly correlated with site-scale variables, but variables at each spatial scale were highly correlated with community structure. Across all scales, one of the strongest gradients involved environmental drivers that could be associated with habitat structure and instability. Abundance of the chironomid subfamily Diamesinae, a tolerant taxon in high-latitude and high-elevation systems, was highly positively associated with this habitat gradient. This hierarchical framework provides a knowledge base for the development of a sustainable long-term monitoring approach for Low Arctic aquatic ecosystems. By incorporating measures of environmental drivers at multiple spatial scales, future monitoring efforts may more effectively respond to current and future pressures on aquatic biodiversity.

Several letters to the editor are presented including some congratulating "Classic Images" on its 50th anniversary, another urging film lovers to visit The George Eastman House in New York, and another describing his interest for movie memorabilia.

Inputs of nutrients (P and N) to freshwaters can cause excessive aquatic plant growth, depletion of oxygen, and deleterious changes in diversity of aquatic fauna. As part of a “National Agri‐Environmental Standards Initiative,” the Government of Canada committed to developing environmental thresholds for nutrients to protect ecological condition of agricultural streams. Analysis of data from >200 long‐term monitoring stations across Canada and detailed ecological study at ∼70 sites showed that agricultural land cover was associated with increased nutrient concentrations in streams and this, in turn, was associated with increased sestonic and benthic algal abundance, loss of sensitive benthic macroinvertebrate taxa, and an increase in benthic diatom taxa indicative of eutrophication. Chemical thresholds for N and P were defined by applying five approaches, employing either a predetermined percentile to a water chemistry data set or a relationship between water chemistry and land cover, to identify boundaries between minimally disturbed and impaired conditions. Comparison of these chemical thresholds with biological thresholds (derived from stressor–response relationships) produced an approach for rationalizing these two types of thresholds and deriving nutrient criteria. The resulting criteria were 0.01 to 0.03 mg L−1total P and 0.87–1.2 mg L−1total N for the Atlantic Maritime, 0.02 mg L−1total P and 0.21 mg L−1total N for the Montane Cordillera, ∼0.03 mg L−1total P and ∼1.1 mg L−1total N for the Mixedwood Plains, and ∼0.10 mg L−1total P and 0.39–0.98 mg L−1total N for the interior prairies of Canada. Adoption of these criteria should result in greater likelihood of good ecological condition with respect to benthic algal abundance, diatom composition, and macroinvertebrate composition.

Excessive sedimentation in streams and rivers remains a pervasive problem for the protection of aquatic habitat and the sustainability of aquatic communities. Whereas water quality criteria have been determined for suspended sediments in many jurisdictions across North America, comparably little has been done for deposited (also known as bedded) sediments. Through Canada's National Agri‐Environmental Standards Initiative, assessment techniques and analytical tools were developed for estimating environmental thresholds for deposited sediments in agricultural watersheds in New Brunswick (NB) and Prince Edward Island (PEI) in the Atlantic Maritimes of Canada. Physical thresholds were developed through assessment of geomorphic metrics, which were then analyzed using y‐intercept and 25th percentile approaches. For NB, there was strong agreement in physical thresholds for both analytical approaches (e.g., percent fines <2 mm were 7.5 for y‐intercept and 6.9 for 25th percentile approaches). In contrast, physical thresholds for PEI differed considerably between approaches (e.g., percent fines <2 mm were 6.1 for y‐intercept and 19.6 for 25th percentile approaches), likely due to a narrower range in agricultural land cover. Cross‐calibration of our provisional physical thresholds for NB with ecological (i.e., benthic macroinvertebrate) assessments show that ecological thresholds, calculated as change‐points in relationships between Ephemeroptera‐Plecoptera‐Trichoptera relative abundance or Modified Family Biotic Index and geomorphic criteria, were more liberal than physical thresholds. These results suggest that provisional thresholds developed using geomorphic criteria should demarcate change from the least disturbed condition and reduce the risk of sedimentation degrading benthic ecosystems.

Several letters to the editor are presented in response to articles in previous issues including one on actor Victor Jory, another by Jim Foster on actor Bobby Driscoll, and a third on actress Deanna Durbin.

Presents letters to the editor referencing articles and topics discussed in previous issues. Involvement of several actors in activities in Westport, Connecticut; Reaction to an article about actor Robert Mitchum; Response to a memorial article on actress Teresa Wright.

Manipulative field enclosure/exclosure experiments were carried out in Carnation Creek, British Columbia to determine if patch-restricted coho fry (Oncorhynchus kisutch) affected the distribution and abundance of macroinvertebrates in the drift or benthos. Enclosures/exclosures with standardized substrate, detritus, and current velocity were buried in the streambed during the low discharge period, and four treatments used: no fish, ambient fish, double ambient fish, and quadruple ambient fish densities. Density, biomass, and size distribution of macroinvertebrates in the drift were not significantly affected by fish density treatment. Additionally, with the exception of large swimming larvae of Ameletus sp. and Baetis tricaudatus, macroinvertebrate density, size distribution, and biomass in the benthos were also not significantly affected by fish density treatments. Thus, despite fish densities being increased from two to four times above ambient patch levels, patch-restricted coho fry had little measureable effect on macroinvertebrate distribution and abundance in Carnation Creek during the low discharge period of August to September.

A minnow trap that operates in various flow regimes in streams and allows sampling of small fish from stream bed microhabitats was developed. In laboratory and field tests, the most efficient trap design for capturing and retaining various species of fish had one funnel oriented downstream, a plexiglass body, and commercial trout food as bait. These lightweight traps can be set in a wide range of current velocities and depths, and can be useful in investigations that examine the microhabitat use, diel activity patterns or population densities of small lotic fish. Guidelines for the trap's use and for quick verification of capture success in new situations are suggested.

Experimentation using field-based artificial streams provides a promising, complimentary approach to biomonitoring assessments because artificial streams provide control over relevant environmental variables and true replication of treatments. We have used large and small artificial stream systems, based in the field, to examine the effect of treated bleached kraft pulp mill effluent (BKME) on the benthos of three large rivers in western Canada. Under natural regimes of temperature, water chemistry, and insolation, these artificial streams provide current velocities and substrata to food chains or food webs that are representative of those in the study river. With these tools we have shown that BKME stimulated mayfly growth in the Thompson River above that which could be accounted for by fertilization of their algal food supply. In contrast, moulting frequency was inhibited at high BKME concentrations. Results from artificial streams also indicate that increased algal biomass and abundances of benthic communities downstream of BKME outfalls were induced by nutrient enrichment from the effluent. BKME treatments did not change diatom species richness in the Fraser River, or diatom species diversity in either the Athabasca or Fraser Rivers. Artificial streams provide a means of understanding the mechanisms of stressor effects over a continuum ranging from single stressor effects on specific taxa to the effects of multiple stressors on communities and ecosystems. Because riverside deployment provides environmental realism within a replicated experimental design, this approach can (i) address questions that cannot be examined using laboratory tests or field observations, (ii) improve our mechanistic understanding of stressor effects on riverine ecosystems, and (iii) can contribute directly to the development, parameterization, and testing of models for predicting ecosystem-level responses.

Laboratory experiments were performed to test the hypothesis that the trade-off between predator avoidance and food acquisition was affected by forager size. Groups of small and large larvae of the mayfly Baetis tricaudatus were presented simultaneously with foraging patches representing all combinations of two levels of predation risk (predators present or absent) and two levels of food (low, high). We hypothesized that forager body size would affect patch use because field observations in a Rocky Mountain stream suggested that small Baetis experience twice the percapita risk of mortality of large larvae as a result of predation by a nocturnal minnow. Small larvae also spend more time feeding over a diel period than large larvae. Our results showed that relative patch selection was significantly affected by the interaction between predation risk and Baetis size. Although the presence of a predator reduced patch use, the reduction was less pronounced for large Baetis than for small individuals, suggesting that large Baetis accepted more risk when risky patches contained more food. Food intake rates of small Baetis in safe, high-food patches was four times higher than in safe, low-food patches. For large Baetis, the presence of a predator in high-food patches reduced food intake to a greater extent than in low-food patches. Greater use of risky, high-food patches by large Baetis compared with small Baetis was associated with differences in the distance at which larvae responded to predators by initiating a drift response. The mean distance at which large Baetis reacted to predators by drifting out of patches was almost four times lower in risky, high-food patches than in risky, low-food patches. Mean reactive distances of small Baetis to the predatory minnow were similar to those of large Baetis in low-food patches and did not vary with food level.

Mayfly larvae of Paraleptophlebia heteronea (McDunnough) had two antipredator responses to a nocturnal fish predator (Rhinichthys cataractae (Valenciennes)): flight into the drift and retreat into interstitial crevices. Drift rates of Paraleptophlebia abruptly increased by 30 fold when fish were actively foraging in the laboratory streams but, even before fish were removed, drift began returning to control levels because larvae settled to the substrate and moved to areas of low risk beneath stones. This drifting response was used as an immediate escape behavior which likely decreases risk of capture from predators which forage actively at night. Surprisingly, drift most often occurred before contact between predator and prey, and we suggest that in darkness this mayfly may use hydrodynamic pressure waves for predator detection, rather than chemical cues, since fish forage in an upstream direction. Although drifting may represent a cost to mayfly larvae in terms of relocation to a new foraging area with unknown food resources, the immediate mortality risk probably out-weighs the importance of staying within a profitable food patch because larvae can survive starvation for at least 2 d. In addition to drifting, mayflies retreated from upper, exposed substrate surfaces to concealed interstitial crevices immediately after a predator encounter, or subsequent to resettlement on the substrate after predator-induced drift. A latency period was associated with this response and mayflies remained in these concealed locations for at least 3 h after dace foraging ceased. Because this mayfly feeds at night and food levels are significantly lower in field refugia under stones, relative to exposed stone surfaces, predator avoidance activity may limit foraging time and, ultimately, reduce the food intake of this stream mayfly.

Laboratory experiments were performed to identify the mechanisms by which three mayfly grazers, Baetis tricaudatus, Ephemerella aurivilli and Paraleptophlebia heteronea deplete algae from substrates. Field observations indicated these mayflies foraged predominantly (>70% of all individuals) within small (1–2 cm diameter), low biomass areas where algal biomass was significantly lower than the surrounding algal mat. We postulated four models of algal patch depletion based on the combined effects of a type II functional response consumptive model and four possible forms of nonconsumptive loss. These models were tested in laboratory feeding trials by examining the relative importance of consumptive and non-consumptive removal of the diatom, Navicula sp., by the three common mayfly grazers. The trials were conducted in plexiglass streams that contained substrates with one of five biomass levels (0.11, 0.24, 0.43, 0.65, 0.92 mg/cm2 dry weight) of the diatom food. After each 1 h feeding trial, consumption was measured, and the remaining algae scraped from the substrates so non-consumption and total patch depletion could be determined. Consumption by all three species followed a type II functional response; mayflies were capable of grazing diatom layers of extremely low biomass (0.11 mg/cm2) and reached an asymptotic feeding rate when diatom biomass ranged from 0.24–0.43 mg/cm2. Upper asymptotic feeding rates occurred at algal biomasses that were 20 times lower than algal biomass levels within foraging areas in the field and >50 times the overall mean algal biomass on upper stone surfaces in the Bow River. When diatom biomass was low (0.11 mg/cm2), the amount of algae ingested accounted for 27%–75% of total depletion of algal patches. Above this level, nonconsumptive, foraging-related losses increased. Thus, depletion of diatom patches was non-linear and positively related with diatom biomass due to the disproportionate increase in non-consumptive losses combined with the type II functional response consumptive model (Case 4). This disproportionate increase in non-consumptive loss may results from (i) a passive process attributable to mechanical limitations of the feeding apparatus, (ii) an active selection process during foraging or (iii) instability of the diatom material resulting in disproportionately high foraging related dislodgement. Regardless of the mechanism, our experiments indicate the importance of considering algal patch depletion by mayfly grazers as a dual product of consumptive and non-consumptive foraging processes. Furthermore, the non-linear increase in nonconsumptive loss with increased algal biomass suggests this process may be a major mechanism of algal patch depletion by mayflies when algal biomass is high.

Laboratory experiments were performed to quantify the combined effects of food abundance (low, high) and predation threat, imposed using a model fish (safe, risky) on fitness correlates (i.e. growth, time to emergence, adult body mass, fecundity, egg size) of the mayfly Baetis tricaudatus. These effects were determined by rearing larvae under different combinations of food abundance and predator threat. Fitness correlates were significantly affected by food abundance, predation threat or the interaction of these factors. High food abundance and the absence of predation threat significantly increased larval growth rates, adult body mass, fecundity, egg size, and decreased time to emergence. Long-term effects of predator threat and food abundance on fitness correlates of B. tricaudatus were compared to previously conducted short-term patch choice trials to test for concordance between short-term measures of patch choice and their potential longer-term fitness consequences. This comparison indicated that patches that were utilized the most were those that yielded the highest fitness benefits. These results suggest that behavioural costs of balancing mortality risk due to predation against food acquisition by B. tricaudatus can have strong fitness consequences.

Habitat for young-of-the-year rainbow trout Oncorhynchus mykisswas enhanced in a fourth-order stream during August–October 1991 by the addition of wooden structures that simulated accumulations of fine woody debris (FWD). The experiment represented a two-factorial design with the presence or absence of FWD bundles and time since debris introduction as factors. Immediately after FWD placement, fry density, individual biomass, fry condition factor, and total fry biomass were similar in treated and untreated sites. As the experiment progressed, density and total fry biomass significantly increased at treated but not at untreated sites. Individual biomass and condition factor did not differ between treated and untreated areas, and they were affected only by time since FWD placement. Because individuals at treated and untreated sites were the same size, added FWD did not affect an individual's net rate of energy gain. Rather, we hypothesize that the FWD provided structurally complex habitat that acted as a refuge from predators and as sites from which foraging forays were staged. Adding FWD to a stream can increase carrying capacity for trout fry, and adult population density may increase as a result.

The physical and chemical conditions in Hartley Creek, a northeastern Alberta brownwater stream, are described for a two year period and related to the composition of the Trichoptera species present. In 1976 when discharge was high, net-spinners (Hydropsyche species) were dominant in the riffles. However, in 1977 when discharge was substantially lower the Trichoptera fauna in the riffles was dominated by algal piercers (Hydroptilidae spp.). In both years the pool communities were dominated by Hydroptilidae spp.

Since 1997, sediment metal concentrations have been monitored in the Alberta Oil Sands Region (AOSR) of the Lower Athabasca River by the Regional Aquatics Monitoring Program (RAMP; 1997–2002), the Joint Oil Sands Monitoring Program (JOSM; 2012–2014), and the Oil Sands Monitoring Program (OSM; 2015-present). However, it has remained difficult to differentiate industrial sources from natural sources and quantify the extent of pollution due to inadequate knowledge of predevelopment reference conditions. Here, baselines were constructed using predevelopment (i.e., pre-1967) sediment concentrations of US EPA priority pollutants (Be, Cr, Cu, Ni, Pb) and V, an element elevated in bitumen and associated waste materials, normalized to Al concentration in cores from floodplain and upland lakes within the AOSR to characterize the natural range of variability. The Lower Athabasca River sediment metal monitoring data were examined in the context of the predevelopment baselines. Most metals are below the threshold for minimal enrichment (<1.5x baseline) except for chromium (up to 4.8x) in some RAMP samples. The predevelopment baselines for sediment metal concentrations will be of particular importance as the oil sands industry potentially shifts from a no-release policy to the treatment and release of oil sands process waters directly to the Lower Athabasca River.

Several letters to the editor are presented in response to articles in previous issues including "Betsy Ann Hisle; Finding a Lost Player" in the March 2010 issue, an obituary for actress Jennifer Jones, and a reader's question about what happened to actor Brett King.