Pollutants in Lotic Ecosystems II
Presiding: R M Thompson, Biodiversity Research Centre, University of British Columbia; D Olsen, University of Vermont
NB51A-01 08:30h
Effects of Agricultural Pollutants on Competition Between Filter-Feeding Caddis Flies
The effects of agricultural pollutants on competition between lotic macroinvertebrates are largely unstudied. We investigated how agricultural pollution affects competition between larvae of two caddis flies, Hydropsyche spp. and Brachycentrus appalachia. Month-long laboratory experiments were conducted in recirculating stream microcosms at two levels of Hydropsyche abundance: low density (80 Hydropsyche and 40 Brachycentrus per tank) and high density (300 Hydropsyche and 40 Brachycentrus). Experimental factors tested were agricultural pollutant addition (cow manure compost and sand) versus control tanks and taxon combination (Hydropsyche only, Brachycentrus only, and both taxa). In high-density experiments, mortality and drift of Hydropsyche were higher in agricultural tanks than in controls and more Brachycentrus drifted in tanks with Hydropsyche present. In low-density experiments, mortality of Brachycentrus was higher in tanks with Hydropsyche present. In both high and low-density experiments,Brachycentrus had lower mean condition (as measured by body-length residuals) in the presence ofHydropsyche, although these differences were only statistically significant in the high-density experiment. No difference in condition was observed for Hydropsyche at either density. Our results provide evidence of both competition between Hydropsyche and Brachycentrus and direct effects of pollutant addition, but the pollution effects did not alter the competitive interactions between the two species.
NB51A-02 08:45h
Use of Buried Sediment Traps to Estimate Deposition of Fine-Grained Sediment and Organic Contaminants in Salmon Spawning Gravels
Deposition of fine-grained sediments into spawning gravels was estimated in the McKenzie River, OR, in conjunction with reservoir drawdown. Collapsed bags were buried at a depth of 40 cm during August 2003 and retrieved in July 2004. The deployment period included several mid-winter storms when sediment transport was high. Retrieval captured the column of bed sediment overlying the bags, including possible contaminants. Grain size distribution, percent and mass of fine material, chlorinated organic compounds, and organic carbon were measured in the retrieved sediment and pore waters. Deposition of fine materials was least in upstream reference areas, greatest in tributaries downstream of two different reservoirs, and intermediate downstream on the mainstem McKenzie River. Low-levels of organochlorine compounds were detected at two of the five sites, including below one reservoir where historical DDT spraying had occurred, and at the downstream mainstem location. The collapsed bag design, with Teflon lining, was an effective method to estimate time-integrated deposition of fine sediment and contaminants into a streambed.
NB51A-03 09:00h
Feeding Inhibition: the Ups and Downs of Sublethal Effects on Grazers and Detritivores
Sublethal impacts are likely the primary mechanism of exposure for the aquatic community in the case of soluble agricultural pesticides. This study examines the effects of pulsed exposures of the common insecticide, imidacloprid, on the feeding and growth of the mayfly Epeorus longimanus, and the oligochaete, Lumbriculus variegatus. Examining the effects of pulsed exposures of imidacloprid is particularly relevant due to the soluble (0.51g/L) nature of this compound. Recovery experiments were conducted by exposing mayflies and oligochaetes to an environmentally realistic range (0, 0.1, 0.5, 1, 5, 10 ppb) of concentrations for a short period. Effects on feeding were measured by quantifying the foodstuffs consumed by mayflies and egested by oligochaetes. In tandem with the feeding experiments, a series of artificial stream experiments were undertaken that demonstrate the changes in growth and abundance of adult mayflies in response to this common insecticide stressor.
NB51A-04 09:15h
The Widespread use of Methoprene for the Prevention and Control of West Nile Virus in Ontario, Canada: Is it Impairing our Streams?
Catch basins have been identified as a major breeding location for the mosquito Culex pipiens, a primary vector for the spread of West Nile Virus in Ontario. Methoprene, an insect growth regulator, has been applied extensively in catch basins to combat the spread of mosquito populations. Since 2003, an estimated 1 million catch basins located around the Canadian shores of Lake Ontario were treated with 0.7g of 30-day, slow release methoprene pellets (4.25% active ingredient). Although studies have shown that methoprene breaks down quickly in the environment and is relatively non-toxic to mammals and fish, the large quantities being applied across Ontario raise concerns over the effects methoprene and its metabolites may have on non-target aquatic insects. The receiving streams of selected catch basins where methoprene was applied regularly were studied to assess the effects of methoprene application on stream macroinvertebrates. Although methoprene was not detected in the receiving waters, some changes in the community assemblages were observed. Many of the observed changes could be attributed to seasonality, however, percent Ephemeroptera, Plecoptera and Trichoptera (EPT) tended to be lower downstream of the storm sewer discharge compared to upstream and pre-application.
NB51A-05 09:30h
Combined impacts of global warming and pollution: impacts on food web structure and ecosystem function.
Effects of global species loss on ecosystem function have traditionally been extrapolated from studies which investigate the effect of random species loss or addition. Real species loss is highly patterned and clumped according to trophic position, taxonomic relatedness and interconnectedness with the remainder of the food web. Using pond microcosms, I evoked a realistic pattern of species loss using toxins and warming. Species loss was predictably highly patterned. Influences on ecosystem functions ranged from simple and linear in the case of algal productivity, through to complex and step-like in the case of bacterial decomposition. Impacts on algal productivity were mediated by effects on the rate of grazing by invertebrates. There is strong evidence from the bacterial decomposition results of an `insurance effect' whereby the presence of multiple stressors has a strong, non-additive effect on function. These results clearly show that the traditional ecotoxicological practice of studying effects of single toxins on single species may be highly misleading.