Pollutants in Lotic Ecosystems I Posters
Presiding: E Marti, Centre d'Estudis Avancats de Blanes (CSIC); C Hoagstrom, South Dakota State University
NB33J-01 1330h
Multiple Contaminant and Predatory Stressors in Experimental Pond Communities
Anthropogenic contaminants, such as agricultural pesticides found in aquatic systems, have the potential to negatively impact organisms via direct and indirect pathways. The magnitude of these indirect effects depends on the strength of the interactions through which they are propagated. We sought to determine how environmentally realistic levels of the insecticides endosulfan and malathion and the herbicide atrazine impact pond communities. We investigated the effects of these pesticides in mesocosm communities containing larval dragonflies (Anax junius), adult water bugs (Belostoma flumineum), and snails (Planorbella trivolvis). Dragonflies presented a moderate predatory threat to snails, as they affected snail behavior but not survival. Direct effects of pesticides on snails were limited, and pesticides only induced modest changes in snail behavior. All pesticides negatively influenced dragonfly survival and this was most pronounced in treatments with endosulfan. However, the reduction in dragonfly survival did not transmit benefits to snails that were detectable as changes in behavior or survival, as would be expected if dragonflies represented a stronger predatory threat. These results show that individuals in communities can be differentially impacted by contaminants, and indicate that strong indirect effects depend on the strength of underlying trophic interactions.
NB33J-02 1330h
Effects of Room-Temperature Ionic Liquids on Zebra Mussels (Dreissena polymorpha)
Zebra mussels (Dreissena polymorpha) are exotic bivalves that are widely distributed in eastern North America. We propose that this nuisance organism could serve as a model species for studies of aquatic toxicology. We tested zebra mussels response to room-temperature ionic liquids (ILs), which are being synthesized as environmentally friendly alternatives to volatile organic solvents. Volatile organic solvents contribute to atmospheric pollution and ozone depletion, whereas ILs are non-volatile and less harmful to the atmosphere. Although ILs would contribute significantly less to air pollution, little is known about their potential effects on aquatic ecosystems. In 72-hour toxicity tests, we determined the acute effects of three imidazolium-based ILs (1-butyl-3-methylimidazolium bromide (bmimBr), 1-hexyl-3-methylimidazolium bromide (hmimBr), and 1-octyl-3-methylimidazolium bromide (omimBr)) on the survival of zebra mussels. As alkyl chain length decreased, median lethal concentration (LC50) decreased from 1291 mg L-1 for bmimBr, to 105 mg L-1 for hmimBr, and 21.2 mg L-1 for omimBr. For bivalve mussels, the toxicities of these ILs are comparable to the toxicities of commonly used industrial solvents (e.g., toluene, benzene). This study presents a foundation for using zebra mussels in toxicity studies as well as possible models for less common Unionid mussels.
NB33J-03 1330h
Effects of Room-Temperature Ionic Liquids on Freshwater Primary Producers
Room-temperature ionic liquids (ILs) are non-volatile chemicals, which are presumed to be environmentally friendly because they pose no significant threat to air quality. However, the potential toxic effects of ILs on aquatic environments have not been studied, despite the likelihood of unintentional releases into streams and lakes during industrial applications. We studied the effects of ILs on the growth rates of the freshwater green algae Scenedesmus quadricauda and Chlamydomonas reinhardtii in 96-h bioassays. ILs with increasing alkyl chain lengths (from 1-butyl- to 1-hexyl- to 1-octyl-3-methylimidazolium bromide) were increasingly toxic to S. quadricauda (EC-50 values of 0.28 mg*L-1, 0.04 mg*L-1, and <0.005 mg*L-1 respectively). S. quadricauda growth rates decreased with increasing IL concentration across all treatments. Compared to controls, C. reinhardtii growth rates were higher at 200-800 mg*L-1 1-butyl-3-methylimidazolium bromide (bmimBr) treatments, but declined at 1600 mg*L-1 bmimBr. These results illustrate that different algal taxa can respond quite differently to potential chemical pollutants. Furthermore, by studying the effects of ILs on primary producers in concert with organisms from other trophic levels, we can develop hypotheses about how these effects may be felt throughout aquatic ecosystems.
NB33J-04 1330h
Hydroponic Uptake of Atrazine and Lambda-cyhalothrin in Aquatic Macrophytes
Phytoremediation encompasses an array of plant-associated processes known to mitigate contaminants from soil, sediment, and water. Modification of pesticides associated with agricultural runoff includes processes directly associated with aquatic macrophytes in addition to soil geochemical modifications and associated rhizospheric degradation. Remediation attributes of two vegetative species common to agricultural drainages in the Mississippi Delta, USA, were assessed using atrazine and lambda-cyhalothrin. Concentrations used in 8-d hydroponic exposures were calculated using recommended field applications and a 5% runoff model from a 0.65-cm rainfall event on a 2.02-ha field. While greater atrazine uptake was measured in Juncus effusus, greater lambda-cyhalothrin uptake occurred in Ludwigia peploides. Maximum pesticide uptake was reached within 48 h for each exposure and subsequent translocation of pesticides to upper plant biomass occurred in macrophytes exposed to atrazine. Sequestration of 98.2% of lambda-cyhalothrin in roots of L. peploides was measured after 8 d. Translocation of lambda-cyhalothrin in J. effusus resulted in 25.4% of pesticide uptake partitioned to upper plant biomass. These individual macrophyte remediation studies measured species- and pesticide-specific uptake rates, indicating that the seasonality of pesticide applications and macrophyte emergence might interact strongly to enhance mitigation capabilities in edge-of-field conveyance structures.
NB33J-05 1330h
Sublethal Ionic Liquid Concentrations Alter Grazer-Periphyton Interactions
Ionic liquids (ILs) are non-volatile organic salts that are considered environmentally-friendly replacements for volatile organic compounds. While ILs will not pollute the atmosphere, they could enter aquatic ecosystems and negatively affect communities and ecosystem processes. To determine if the IL, 1-methyl-3-butylimidazolium bromide (bmimBr), affected grazer-periphyton interactions, we factorially crossed 4 levels of bmimBr (0, 1, 10, and 100 mg/L1) with the presence or absence of the snail, Physa acuta, in laboratory experiments. After 14 days, all bmimBr concentrations reduced chlorophyll a (chl a) abundance by 35-49% relative to controls lacking bmimBr. Algal biovolume also declined by 65-85% at 10 and 100 mg/L1 bmimBr relative to controls. When both bmimBr and snails were present, chl a abundance and algal biovolume were higher than expected if both factors acted additively, suggesting that snails were less efficient grazers in the presence of bmimBr. Furthermore, snail growth rates declined by 41-101% at 10 and 100 mg/L1 bmimBr relative to controls. At the ecosystem level, snails stimulated periphyton primary production in the absence of bmimBr, suggesting that bmimBr can indirectly alter ecosystem processes. Our research shows that sublethal levels of an IL can negatively impact aquatic communites and ecosystem processes via complex trophic interactions.
NB33J-06 1330h
Effects of Fungicides on Aquatic Fungi and Bacteria
Aquatic microorganisms play an important role in conditioning leaf litter that enters streams and serves as an important base of production for consumers. Contamination of streams by fungicides may adversely affect microorganisms and alter leaf litter processing rates. Unfortunately, microorganisms are rarely used in acute toxicity tests for fungicide evaluation and registration. We adapted the resazurin reduction assay, which is used in medical microbiology, to assess the acute toxicity of four fungicides (azoxystrobin, trifloxystrobin, kresoxim-methyl and chlorothalonil) to aquatic fungi (Articulospora tetracladia) and bacteria (Cytophaga spp.), and investigated the ability of the toxicants to inhibit leaf breakdown in microcosms. Fungi were more sensitive to fungicides than many standard test organisms (cladocerans, green algae, trout), while bacteria were often the least sensitive. All of the fungicides except kresoxim-methyl, when added to microcosms at concentrations that inhibited the fungi by 90 percent in acute tests, reduced leaf breakdown rates by an average of 14.7 percent. Thus, aquatic fungi and their associated functions in streams may be relatively sensitive to fungicides applied terrestrially that enter streams through non-point sources. These data highlight the importance of including aquatic fungi in safety assessments of pesticides for protection of microbial function.
NB33J-07 1330h
Effects of Insecticides on Benthic Communities Under Pulse and Press Exposures.
Benthic macroinvertebrates are often exposed to short-term pulses of pesticides following runoff events as well as through low background exposure. Pulse events may be important exposure routes for highly soluble insecticides such as imidacloprid. We examined the effects of imidacloprid on the benthos through press and pulse exposures, beginning with a press, range-finding field experiment (0, 5, 15 ppb) designed to estimate thresholds for effects on the invertebrate community. This experiment demonstrated a dose response with higher insecticide treatments reducing abundance, richness and evenness relative to the control. A subsequent experiment aimed at lower concentrations, more consistent with natural levels, contained both pulse (0, 0.1, 0.5, 1.0, 5, 10 ppb) and press (0, 0.1, 0.5, 1.0 ppb) concentrations to detect which exposure caused effects in the benthic community, or affected emerging insect abundance and size. No significant differences in abundance or richness were found with concentrations up to 1 ppb regardless of treatment or design. However, sublethal effects were observed as Baetis adults were generally longer (total length) in pulse versus press exposures and had larger abdomens at higher insecticide concentrations. Current studies are measuring insecticide concentrations during the flood hydrograph to better understand the consequences of these sublethal effects.
NB33J-08 1330h
Predation Risk versus Pesticide Exposure: Consequences of Fear and Loathing in the Life of Stream Shredders
Stream invertebrates are exposed to complex stressor regimes including both biotic and abiotic factors. Species living in streams in agricultural landscapes are often subjected to episodic or continuous exposures to low levels of agrochemicals, which may approach or exceed specific substance guidelines. Sublethal effects of pesticides may result in direct effects on organisms (e.g. reduced physiological performance), which may in turn contribute to indirect effects relating to survival (e.g. increased predation risk). Here, we investigate the possibility that predator-release kairomones can act additively with low-level pesticide exposure to reduce physiological performance and survival of stream invertebrates in previously unforeseen ways. Feeding, metabolic and behavioural responses of two shredder insects, the North American stonefly Pteronarcys comstockii and the European caddisfly Sericostoma vittatum were measured under exposure to the insecticide imidacloprid at different levels of indirect predation stress using predator-release kairomones from Brown Trout (Salmo trutta). Pteronarcys feeding was measured in terms of mass of naturally conditioned alder leaf discs consumed over a 6-day and 10 -day period in animals held in cages in stream mesocosms. Pteronarcys feeding was impaired at 1 ppb in the 6-day trial and at 0,5 ppb in the 10-day trial relatively to unexposed controls. Metabolic rate was measured in the lab in terms of oxygen consumption of Pteronarcys. Animals exposed to 0.5 and 1 ppb imidacloprid showed elevated respiratory rates compared to controls. Laboratory experiments with Sericostoma, currently in progress, are examining the separate and combined effects of imidacloprid and predator kairomone on similar endpoints. These preliminary results are discussed in relation to the development of the Mechanistic Unifying Stressor Effects (MUSE) model which can be used to predict combined ecological effects of multiple stressors at the population level.
NB33J-09 1330h
Biological And Ecological Responses Of Macrobenthic Assemblages To Sediment Contamination In French Streams
In order to fit the requirements of the European Water Framework Directive, member states have to quantify the relationships between the biological status and physical and chemical properties of surface waters and to develop validated tools to assess the ecological quality of freshwater ecosystems. With the objectives 1) to describe toxic impact on in situ macrobenthic communities and 2) to identify key biological metrics for describing toxic pressures, the relationships between stream sediment toxicity (concentration of trace elements, PAHs, organochlorine compounds and pesticides) and the functional structure of macrobenthic communities were analysed. Faunal and chemical data were obtained from the French water data network and analysed by multivariate and regression approaches. Combinations of biological and ecological traits were related to faunal changes and compared to sediment contamination. Moreover, the possibility of using these results for predicting the stream ecological status as a function of chemical contamination were examined. The relevance of observed tendencies and pressure/impact relationships will be discussed.