Joseph M. Culp

Acute and Chronic Toxicity of Imidacloprid to the Aquatic Invertebrates Chironomus tentans and Hyalella azteca under Constant- and Pulse-Exposure Conditions

The toxicity of imidacloprid, a nicotinic mimic insecticide, to the aquatic invertebrates Chironomus tentans and Hyalella azteca, was first evaluated in static 96-hour tests using both technical material (99.2% pure) and Admire®, a commercially available formulated product (240 g a.i. L-1). The 96-h lethal concentration (LC)50 values for technical imidacloprid and Admire® were 65.43 and 17.44xa0μg/L, respectively, for H. azteca, and 5.75 and 5.40xa0μg/L, respectively, for C. tentans. Admire® was subsequently used in 28-day chronic tests with both species. Exposure scenarios consisted of a constant- and a pulse-exposure regime. The pulse exposure lasted for four days, after which time the animals were transferred to clean water for the remaining 24 days of the study. Assessments were made on both day 10 and day 28. In the C. tentans under constant exposure, larval growth on day 10 was significantly reduced at 3.57xa0μg/L imidacloprid, the lowest-observed-effect concentration (LOEC). The no-observed-effect concentration (NOEC) and LOEC for the 28-day exposure duration (adult survival and emergence) were 1.14 and greater than 1.14xa0μg/L, respectively; the associated LC50 and LC25 were 0.91 and 0.59xa0μg/L, respectively. The LOEC for the pulse treatment was greater than 3.47xa0μg/L, but the day 10 LC25 was 3.03xa0μg/L. In the H. azteca tests, the day 10 and 28 constant exposure, as well as the day 28 pulse exposure, LOEC (survival) values were similar at 11.95, 11.46, and 11.93xa0μg/L, respectively. The day 10 and 28 constant exposure effective concentration (EC)25s (dry weight) were also similar, at 6.22 and 8.72xa0μg/L, respectively, but were higher than the pulse-exposure day 10 LOEC and EC25 (dry weight) values of 3.53 and 2.22xa0μg/L, respectively. Overall, C. tentans was more sensitive to acute and chronic imidacloprid exposure, but less sensitive to a single pulse, than H. azteca. Chronic, low-level exposure to imidacloprid may therefore reduce invertebrate survival and growth, but organisms are able to recover from short-term pulse exposure to similar imidacloprid concentrations if the stressor is removed after four days.

Development of Environmental Thresholds for Nitrogen and Phosphorus in Streams

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(-1) total P and 0.87-1.2 mg L(-1) total N for the Atlantic Maritime, 0.02 mg L(-1) total P and 0.21 mg L(-1) total N for the Montane Cordillera, ~0.03 mg L(-1) total P and ~1.1 mg L(-1) total N for the Mixedwood Plains, and ~0.10 mg L(-1) total P and 0.39-0.98 mg L(-1) total 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.

Utility of field-based artificial streams for assessing effluent effects on riverine ecosystems

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.

18 – MACKENZIE RIVER BASIN

This chapter discusses the five major rivers of the Mackenzie River system demonstrating the large range of natural diversity and human impacts evident within the basin. These rivers include the Athabasca, Peace, and Slave, which drain the most southern reaches of the watershed, and the Liard River and the main stem of the Mackenzie River, both of which are located north of Great Slave Lake. The chapter also provides a brief overview of physical, chemical, and biological characteristics and human uses of these rivers, and five other rivers of the Mackenzie River basin (Smoky River, Hay River, Yellowknife River, South Nahanni River, and Peel River). Major threats to the rivers are land-use changes, including agriculture, forestry, and mining, hydrologic fragmentation through the creation of reservoirs, and point-source inputs from industry and municipalities. Damming of the Peace River has caused impacts on the Peace–Athabasca Delta approximately 1200km downstream of Williston Reservoir. Commercial fishing is important on basin lakes such as Great Slave Lake and Lake Athabasca, and aboriginal peoples of the basin continue to use wildlife resources for food and furs.

19 – NELSON AND CHURCHILL RIVER BASINS

Two great Canadian rivers, the Nelson and the Churchill, drain waters mainly from the interior of Canada, cut through the Canadian Shield of northern Manitoba, and empty into Hudson Bay. Both the Nelson and Churchill catchments are part of the Hudson Bay complex of the Arctic–Atlantic bioregion and occupy only two major habitat types: temperate headwaters and lakes; and Arctic rivers and lakes. The Nelson and Churchill catchments contain four freshwater ecoregions. The Churchill River mostly occupies the Lower Saskatchewan ecoregion. The Nelson River (main stem) occupies the Lower Saskatchewan ecoregion, the Saskatchewan River mostly occupies the Upper and Lower Saskatchewan ecoregions, and the Red–Assiniboine and Winnipeg rivers mostly occupy the English–Winnipeg Lakes ecoregion. The different physiographic regions heavily influence the hydrology, chemistry, and biology of the rivers. High precipitation and considerable relief in the Rocky Mountains province produce an annual yield of water to rivers in the foothills and the plains beyond. Water quality of rivers arising on the Interior Plains is variable, but water is usually high in dissolved and suspended solids because of erosion. Rivers of the Canadian Shield division, Interior Plains division, and Rocky Mountains province present three different hydrographic scenarios. Rivers in the Canadian Shield are regular in their flow characteristics, rivers of the Interior Plains tend to be erratic, and rivers of the Rocky Mountains are intermediate, although they resemble Canadian Shield rivers more than Interior Plains rivers.

7.1 – INSIGHT INTO POLLUTION EFFECTS IN COMPLEX RIVERINE HABITATS: A ROLE FOR FOOD WEB EXPERIMENTS

This chapter summarizes examples of how food web experiments can improve the understanding of pollution effects from pulp mill and metal mining effluents in complex river environments and how an understanding of the food web aids interpretation of ecological responses to stressor gradients. Assessing pollution impacts in rivers is particularly challenging, because flowing water environments receive multiple, interacting effluent discharges from cities and industries, as well as nonpoint source inputs. Field biomonitoring in rivers is further hindered by uncertainties in estimating exposure to pollutants. River ecologists are faced with the dilemma that large-scale experiments, which incorporate contaminant or nutrient stressors, are not feasible on ethical and practical grounds because they may cause severe acute and chronic effects on riverine communities. In complex environments in situ food experiments can elucidate dose–response relationships between components of the model food web and single or multiple stressors better than standard field observations. The results of ecotoxicological experiments in model food webs can provide a wealth of information on possible species interactions within a community, including knowledge of functional redundancy of species and various indirect effects.

15 – FRASER RIVER BASIN

The Fraser River, with its headwaters in the Rocky Mountains, flows across the dry Fraser Plateau through coastal mountain ranges to the Pacific Ocean. This chapter describes the main-stem Fraser River, as well as eight major tributaries that illustrate the wide range of geologic, climatic, and biological diversity in the basin. The basin is contained within two physiographic provinces. A portion of the Fraser drains from the Rocky Mountains in Canada province in the east and a portion drains from the coast mountains of British Columbia and Southeast Alaska province. The climate of the basin ranges from subarid to arid and mild in southern lower valleys to humid and cold at higher elevations in the northern reaches, reflecting the interaction of the dominant westerly circulation with the mountain ranges. The basin also shows great biological diversity in both flora and fauna. Because the various tributaries across the basin experience a great range of topographic features and precipitation patterns, they are highly variable in their monthly stream flows. The two major activities in the basin are logging and mining. Effects from tree removal and pulp and paper mills have been of most concern.