Fatty-acid based assessment of benthic food-web responses to multiple stressors in a large river system.

Rivers are often exposed to multiple stressors, such as nutrients and contaminants, whose impacts on the river food webs may not be distinguished by sole assessment of biological community structures. We examined the benthic algal assemblages and the fatty acids (FA) of benthic macroinvertebrates in the lower Athabasca River in Canada, aiming to assess the changes in algal support and nutritional quality of the benthic food web in response to cumulative exposure to natural bitumen, municipal sewage discharge (hereafter, "sewage"), and oil sands mining ("mining"). Data show that the decline in water quality (increases in nutrient concentrations and total suspended solids) was associated with decreases in benthic diatom abundance, and was driven mainly by sewage-induced nutrient enrichment. Responses in nutritional quality of benthic macroinvertebrates, indicated by their polyunsaturated FA (PUFA) concentrations, were taxon- and stressor-specific. Nutritional quality of the larval dragonfly predator, Ophiogomphus, decreased nonlinearly with decreasing benthic diatom abundance and was lowest at the sewage-affected sites, although exposure to natural bitumen also resulted in reduced Ophiogomphus PUFA concentrations. In contrast, the PUFA concentrations of mayfly grazers/collector-gatherers were not affected by natural bitumen exposure, and were higher at the sewage and sewage+mining sites. The PUFA concentrations of the shredder Pteronarcys larvae did not change with cumulative exposure to the stressors. Sediment metal and polycyclic aromatic compound concentrations were not associated with the macroinvertebrate FA changes. Overall, we provide evidence that sewage induced reduction in trophic support by PUFA-rich diatoms, and was the predominant driver of the observed changes in FA composition and nutritional quality of the benthic macroinvertebrates. Fatty-acid metrics are useful to untangle effects of concurrent stressors, but the assessment outcomes depend on the functional feeding guilds used. A food-web perspective using multiple trophic levels and feeding guilds supports a more holistic assessment of the stressor impacts.

Pesticide mixture toxicity to algae in agricultural streams - Field observations and laboratory studies with in situ samples and reconstituted water.

Long-term pesticide water concentrations were investigated in four agricultural streams and their mixture toxicity on algae was assessed, based on realistic (i.e. observed) concentrations in laboratory tests using (i) natural weekly water samples and (ii) reconstituted pesticide-spiked water samples representing mixtures with predicted high mixture. This approach both covered the full complexity of natural water samples and the controlled approach of reconstituted water samples. Long-term monitoring data (time-integrated, weekly samples) revealed more than 11 pesticides (range 11.0 ± 0.25-24.0 ± 0.44) in 75% or more of the almost 1600 samples collected between 2002 and 2018. ∑TUalgae exceeded 0.1 for 29 observations (or 1.8%). Despite the multitude of pesticides in a sample, ∑TUalgae was frequently set by one or a few dominating pesticides that contribute to more than 90% of the mixture's toxicity. Algal growth inhibition tests with in situ stream water showed a high frequency of inhibition, despite the low ∑TU for most of these samples (range 0.000014-0.3858). These "false positive" results were attributed to confounding effects of turbidity, the complexation of nutrients, and toxic effects of metals and/or other unknown contaminants. Algal inhibition tests with spiked reconstituted water showed significant inhibitory effects in the range of 1-10x the ∑TUalgae observed in worst-case field samples. Although these tests disregard the chemical complexity of natural water, they show that inhibitory effects of pesticides on algae may occur at the ∑TUalgae observed in monitoring. Furthermore, considering that the ∑TUalgae of stream water are based on weekly average concentrations and likely underestimate short-term peak concentrations of pesticides, these results strongly suggest that inhibitory effects on algae may occur in the agricultural streams of southern Sweden. We conjecture, however, that the rapid recovery of algae contributes to ameliorate these short-term effects and that pesticide contamination should be seen as one of many stressors in the streams that drain agricultural landscapes.

Inverting nutrient fluxes across the land-water interface - Exploring the potential of zebra mussel (Dreissena polymorpha) farming.

We studied the potential of zebra mussel farming for nutrient retention in a eutrophic lake. Duplicate experimental long-line cultivation units were deployed and mussel growth and nutrient retention were quantified after 28 months. Mussels grew well at shallow water depth (<3 m) and our 625 m2 (lake area) experimental units produced 507 and 730 kg dry biomass, respectively, of which 94% were shells. These yields corresponded to an average retention of 92.7 ± 23.1 kg C, 6.1 ± 0.68 kg N, and 0.43 ± 0.04 kg P retention, or 742 kg C, 49 kg N, and 3.5 kg P for a full-size (0.5 ha) mussel farm. We estimate that concentrating the long-lines to a depth of 2.5 m would probably have doubled these yields, based on the differences in mussel growth among depths. We further estimate that a full-size cultivation unit (0.5 ha) thus could compensate for the annual total-P run-off from 23 ha, or the biologically available P from approximately 49 ha of agricultural soils. As traditional measures have proven insufficient, decision-makers need to facilitate novel approaches to mitigate the negative effects of cultural eutrophication. We envision that zebra mussel farming, within their invaded range, provides a promising approach to invert nutrient losses in lakes and coastal lagoons.

Interactions with freshwater biofilms cause rapid removal of common herbicides through degradation - evidence from microcosm studies.

We investigated the role of periphyton biofilms for the fate of three common herbicides, i.e. bentazone, metazachlor and metribuzin, at low, environmental levels and 100 times higher, during a 16 days laboratory experiment. We found that herbicide water concentrations were stable during the first 8 days, whereas substantial declines (>78%) occurred between days 8-16 for all three herbicides. These rapid declines were explained only to a small extent (<8% of the total herbicide loss) by biofilm sorption. As herbicide concentrations in light and dark treatments without biofilms were similar, and the applied light regimen did not cover the UV-spectrum, herbicide photolysis was ruled out as a possible explanation for the observed declines. Furthermore, based on the compounds' characteristics, also volatilization was judged negligible. Therefore, we conjecture that the observed declines in herbicides were due to biodegradation and subsequent evasion of 14CO2 that was driven by enzymatic action from heterotrophic microbes. We reason that heterotrophic microbes used herbicide molecules as labile organic C-sources during C-limitation. Future studies should identify the microbial communities and genes involved in biodegradation in order to understand better the role of biofilms for the self-purification of surface waters.

Pesticide Mixtures Cause Short-Term, Reversible Effects on the Function of Autotrophic Periphyton Assemblages.

In a laboratory experiment we investigated the effects of pesticide mixtures on the structure and function of freshwater biofilms, with focus on their photoautotrophic component. We identified 6 herbicides and 1 fungicide commonly found in Swedish streams at relatively high concentrations and created 3 ternary mixtures that were tested in concentration series ranging from observed environmental concentrations to up to 100 times higher. Biofilms were exposed to these pesticide mixtures for 8 d and then allowed to recover for another 12 d. Our results show a rapid and consistent inhibition of photosynthesis after just 24-h exposure to the highest test concentration of pesticides, as well as in some treatments with lower concentrations (i.e., 10 times the environmental level), on exposure. Interestingly, the observed effects were reversible because biofilm photosynthesis recovered rapidly and completely in clean media in all but one treatment. In contrast to the functional response, no effects were observed on the algal assemblage structure, as assessed by diagnostic pigments. We conclude that the pesticide mixtures induce a rapid but reversible inhibition of photosynthesis, without short-term effects on biofilm structure. Environ Toxicol Chem 2020;39:1367-1374. © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Limited effects of pesticides on stream macroinvertebrates, biofilm nematodes, and algae in intensive agricultural landscapes in Sweden.

Pesticides are frequently detected in surface waters, sometimes at levels exceeding ecotoxicological guidelines. We screened for almost 100 pesticides in 32 streams from intense agricultural areas in Southern Sweden, in concert with water chemistry parameters. In addition, we investigated the communities of benthic macroinvertebrates, biofilm nematodes and algae and calculated multiple bioassessment metrics. The number of pesticides found in each stream ranged between 2 and 52, but the sum of Toxic Units (ΣTU) for the mixtures was generally low, and exceeded the European Uniform Principles only in a single sample for algae and in 2% of the samples for Daphnia. Only nematode communities were significantly correlated with the ΣTU, potentially due to their higher pesticide exposure in biofilms. Diatom metrics showed that most streams were impacted by eutrophication and macroinvertebrate metrics showed good status in most streams, whereas the SPEARpesticides (SPEcies At Risk) index, specifically designed to indicate pesticide effects, showed that about half of the samples were at risk. Interestingly, SPEARpesticides was not correlated to ΣTUDaphnia, and this discrepancy suggests that redefining the boundaries for quality classes might be necessary for this index. Moreover, SPEARpesticides was positively correlated with the commonly used macroinvertebrate index ASPT, although disparate results were found for several streams. We argue that this questions the scaling of both metrics and the specificity of their responses. We discuss that the overall good/moderate status of the streams, despite the intense agriculture in the catchments, can be due to the fact that i) a sampling strategy with repeated grab samples did not capture peak pesticide concentrations, thus underestimating acute exposure, ii) pesticide run-off indeed was low, due to measures such as buffer strips, and iii) the nutrient-rich conditions and high sediment loads counteracted pesticide toxicity. We conclude that agricultural land use was the overriding stressor in the investigated streams, including strong effects of nutrients, less apparent effects of pesticides and likely impact of hydromorphological alterations (not specifically addressed in this study).

Climate-induced changes in carbon flows across the plant-consumer interface in a small subarctic lake.

Reconstructions of past food web dynamics are necessary for better understanding long-term impacts of climate change on subarctic lakes. We studied elemental and stable isotopic composition of sedimentary organic matter, photosynthetic pigments and carbon stable isotopic composition of Daphnia (Cladocera; Crustacea) resting eggs (δ13CClado) in a sediment record from a small subarctic lake. We examined how regional climate and landscape changes over the last 5800 years affected the relative importance of allochthonous and autochthonous carbon transfer to zooplankton. Overall, δ13CClado values were well in line with the range of theoretical values of aquatic primary producers, confirming that zooplankton consumers in subarctic lakes, even in the long-term perspective, are mainly fuelled by autochthonous primary production. Results also revealed greater incorporations of benthic algae into zooplankton biomass in periods that had a warmer and drier climate and clearer water, whereas a colder and wetter climate and lower water transparency induced higher contributions of planktonic algae to Daphnia biomass. This study thus emphasizes long-term influence of terrestrial-aquatic linkages and in-lake processes on the functioning of subarctic lake food webs.

Assessing microbial contamination and antibiotic resistant bacteria using zebra mussels (Dreissena polymorpha).

Aquatic pollution with faecal bacteria and subsequent consumption of contaminated water or food is a worldwide issue that causes severe health effects (e.g. meningitis, salmonellosis, dysentery). In addition, the excessive use of antibiotics in animal husbandry and human medicine has enhanced the selective pressure on pathogenic bacteria, further increasing human health risks and detrimental effects on natural microbial communities. This urges the need to monitor faecal contamination using a time-integrated approach, as grab water samples can miss pathogen peaks. We tested the ability of zebra mussels (Dreissena polymorpha) to take up and depurate faecal indicator bacteria such as Escherichia coli and intestinal enterococci. Furthermore, we quantified the frequency of antibiotic resistant bacteria in water and mussels both in controlled laboratory tests and under in situ conditions downstream of a sewage treatment plant (STP). Laboratory results show that bacterial indicators in mussels were 132 times higher than their concentration in water, and that mussels retained bacteria up to 2 days after pulse exposure. Field results show decreasing bacterial concentrations in both water and mussels downstream the STP, with maximum E. coli concentrations ranging 173-9 cfu mL-1 in water and 2970-330 cfu g-1 in mussels. Similarly, enterococci ranged 59-4 cfu mL-1 and 1450-240 cfu g-1 in water and mussels, respectively. High proportions of antibiotic resistant E. coli were found in mussels (72%) and water (65%), and slightly lower proportion of resistant enterococci was found in mussels (47%) and in water (34%). Moreover, 33% of the bacteria isolated from mussels were resistant to multiple antibiotics, which emphasizes that resistance is a common feature in surface waters and highlights the need for safe water management. Our results show that zebra mussels provide an efficient, time-integrating tool for quantifying faecal indicators, including resistant and multidrug resistant bacteria.

Assessing the effects of field-relevant pesticide mixtures for their compliance with the concentration addition model - An experimental approach with Daphnia magna.

The environmental risk assessment of pesticides is mainly performed on individual active ingredients. In surface waters within the agricultural landscape, however, contamination is usually characterized by complex pesticide mixtures. To estimate the joint effects caused by these complex mixtures, mathematical models have been proposed. Among these, the model of concentration addition (CA) is suggested as default model for the risk assessment of chemical mixtures as it is considered protective for mixtures composed of similar and dissimilar acting substances. Here we assessed the suitability of CA predictions for seven field relevant pesticide mixtures using acute (immobility) and chronic (reproduction) responses of the standard test species Daphnia magna. Pesticide mixtures indicated largely additive or less than additive effects when using CA model predictions as a reference. Moreover, we revealed that deviations from CA predictions are lower for chronic (up to 3.2-fold) relative to acute (up to 7.2-fold) response variables. Additionally, CA predictions were in general more accurate for complex mixtures relative to those composed of only a few pesticides. Thus, this study suggests CA models as largely protective for the risk assessment of pesticide mixtures justifying its use as default model. At the same time, extrapolating conclusions about the joint effects of pesticides from acute to chronic responses is uncertain, due to partly large discrepancies with regards to the deviation of model prediction and observed effects between exposure scenarios.

History matters: Heterotrophic microbial community structure and function adapt to multiple stressors.

Ecosystem functions in streams (e.g., microbially mediated leaf litter breakdown) are threatened globally by the predicted agricultural intensification and its expansion into pristine areas, which is associated with increasing use of fertilizers and pesticides. However, the ecological consequences may depend on the disturbance history of microbial communities. To test this, we assessed the effects of fungicides and nutrients (four levels each) on the structural and functional resilience of leaf-associated microbial communities with differing disturbance histories (pristine vs. previously disturbed) in a 2 × 4 × 4-factorial design (n = 6) over 21 days. Microbial leaf breakdown was assessed as a functional variable, whereas structural changes were characterized by the fungal community composition, species richness, biomass, and other factors. Leaf breakdown by the pristine microbial community was reduced by up to 30% upon fungicide exposure compared with controls, whereas the previously disturbed microbial community increased leaf breakdown by up to 85%. This significant difference in the functional response increased in magnitude with increasing nutrient concentrations. A pollution-induced community tolerance in the previously disturbed microbial community, which was dominated by a few species with high breakdown efficacies, may explain the maintained function under stress. Hence, the global pressure on pristine ecosystems by agricultural expansion is expected to cause a modification in the structure and function of heterotrophic microbial communities, with microbially mediated leaf litter breakdown likely becoming more stable over time as a consequence of fungal community adaptions.

Interactive effects of an insecticide and a fungicide on different organism groups and ecosystem functioning in a stream detrital food web.

Freshwater ecosystems are often affected by cocktails of multiple pesticides targeting different organism groups. Prediction and evaluation of the ecosystem-level effects of these mixtures is complicated by the potential not only for interactions among the pesticides themselves, but also for the pesticides to alter biotic interactions across trophic levels. In a stream microcosm experiment, we investigated the effects of two pesticides targeting two organism groups (the insecticide lindane and fungicide azoxystrobin) on the functioning of a model stream detrital food web consisting of a detritivore (Ispoda: Asellus aquaticus) and microbes (an assemblage of fungal hyphomycetes) consuming leaf litter. We assessed how these pesticides interacted with the presence and absence of the detritivore to affect three indicators of ecosystem functioning - leaf decomposition, fungal biomass, fungal sporulation - as well as detritivore mortality. Leaf decomposition rates were more strongly impacted by the fungicide than the insecticide, reflecting especially negative effects on leaf processing by detritivores. This result most like reflects reduced fungal biomass and increased detritivore mortality under the fungicide treatment. Fungal sporulation was elevated by exposure to both the insecticide and fungicide, possibly representing a stress-induced increase in investment in propagule dispersal. Stressor interactions were apparent in the impacts of the combined pesticide treatment on fungal sporulation and detritivore mortality, which were reduced and elevated relative to the single stressor treatments, respectively. These results demonstrate the potential of trophic and multiple stressor interactions to modulate the ecosystem-level impacts of chemicals, highlighting important challenges in predicting, understanding and evaluating the impacts of multiple chemical stressors on more complex food webs in situ.

Exposure pathway-dependent effects of the fungicide epoxiconazole on a decomposer-detritivore system.

Shredders play a central role in the breakdown of leaf material in aquatic systems. These organisms and the ecological function they provide may, however, be affected by chemical stressors either as a consequence of direct waterborne exposure or through alterations in food-quality (indirect pathway). To unravel the biological relevance of these effect pathways, we applied a 2×2-factorial test design. Leaf material was microbially colonized for 10days in absence or presence of the fungicide epoxiconazole (15µg/L) and subsequently fed to the shredder Asellus aquaticus under exposure to epoxiconazole (15µg/L) or in fungicide-free medium over a 28-day period (n=40). Both effect pathways caused alterations in asselids' food processing, physiological fitness, and growth, although not always statistically significantly: assimilation either increased or remained at a similar level relative to the control suggesting compensatory behavior of A. aquaticus to cope with the enhanced energy demand for detoxification processes and decreased nutritional quality of the food. The latter was driven by lowered microbial biomasses and the altered composition of fatty acids associated with the leaf material. Even with increased assimilation, direct and indirect effects caused decreases in the growth and lipid (fatty acid) content of A. aquaticus with relative effect sizes between 10 and 40%. Moreover, the concentrations of two essential polyunsaturated fatty acids (i.e., arachidonic acid and eicosapentaenoic acid) were non-significantly reduced (up to ~15%) in asselids. This effect was, however, independent of the exposure pathway. Although waterborne effects were generally stronger than the diet-related effects, results suggest impaired functioning of A. aquaticus via both effect pathways.

The mode of bioturbation triggers pesticide remobilization from aquatic sediments.

After their release into the aquatic environment, contaminants may - depending on the physicochemical properties - adsorb to sediments. From there these contaminants can either be buried or remobilised by abiotic factors (e.g., resuspension) as well as by the bioturbating activity of sediment dwelling invertebrates. Little is, however, know about the effects of bioturbation on the fate of pesticides. Therefore, the present study quantified the impact of the bioturbation mode of benthic invertebrate species (bio-diffusor vs. bio-irrigation), the invertebrate density (i.e. 0-8 individuals per replicate), and the substance-inherent properties (i.e. hydrophobicity, water solubility) on the remobilization of sediment-associated pesticides in a laboratory-based set-up over 13 days. We found that both the bioturbation mode (i.e., species identity) and species density, as well as pesticide properties (i.e., hydrophobicity) affected the direction and magnitude of remobilisation of sediment-bound pesticides. The oligochaeta Lumbriculus variegatus showed a density-dependent effect on the remobilization of lindane to the water phase, whereas those with the amphipod Monoporeia affinis and larvae of the midge Chironomus riparius did not. Although these findings show that sediments not per definition are a sink for pesticides, the rates of pesticide remobilization are limited. This observation, thus, suggests that the risk for aquatic communities posed by the remobilization of pesticides from the sediment due to bioturbation is low.

Phenanthrene bioaccumulation in the nematode Caenorhabditis elegans.

The contribution of food to the bioaccumulation of xenobiotics and hence toxicity is still an ambiguous issue. It is becoming more and more evident that universal statements cannot be made, but that the relative contribution of food-associated xenobiotics in bioaccumulation depends on species, substance, and environmental conditions. Yet, small-sized benthic or soil animals such as nematodes have largely been disregarded so far. Bioaccumulation of the polycyclic aromatic hydrocarbon phenanthrene in the absence and presence of bacterial food was measured in the nematode Caenorhabditis elegans. Elimination of phenanthrene in the nematodes was biphasic, suggesting that there was a slowly exchanging pool within the nematodes or that biotransformation of phenanthrene took place. Even with food present, dissolved phenanthrene was still the major contributor to bioaccumulated compound in nematode tissues, whereas the diet only contributed about 9%. Toxicokinetic parameters in the treatment without food were different from the ones of the treatment with bacteria, possibly because nematodes depleted their lipid reserves during starvation.

Autochthonous resources are the main driver of consumer production in dystrophic boreal lakes.

Dystrophic lakes are widespread in temperate regions and intimately interact with surrounding terrestrial ecosystems in energy and nutrient dynamics, yet the relative importance of autochthonous and allochthonous resources to consumer production in dystrophic lakes remains controversial. We argue that allochthonous organic matter quantitatively dominates over photosynthetic autotrophs in dystrophic lakes, but that autotrophs are higher in diet quality and more important for consumers as they contain essential polyunsaturated fatty acids (PUFA). In a field study, we tested the hypotheses that (1) autochthonous primary production is the main driver for consumer production, despite being limited by light availability and low nutrient supplies, and greater supply of allochthonous carbon, (2) the relative contribution of autotrophs to consumers is directly related to their tissue PUFA concentrations, and (3) methane-oxidizing bacteria (MOB) provide an energy alternative for consumers. Pelagic and benthic consumer taxa representing different trophic levels were sampled from five dystrophic lakes: isopod Asellus aquaticus, megalopteran Sialis lutaria, dipteran Chaoborus flavicans, and perch Perca fluviatilis. Based on carbon and nitrogen stable isotopes, the relative contributions of autochthonous (biofilms and seston) and allochthonous (coarse particulate and dissolved organic matter) resources and MOB to these taxa were 47-79%, 9-44% and 7-12% respectively. Results from fatty acid (FA) analyses show that the relative omega3-FA and PUFA concentrations increased with trophic level (Asellus < Sialis and Chaoborus < Perca). Also, eicosapentaenoic-acid (EPA), omega3-FA and PUFA concentrations increased with the autochthonous contribution in consumers, i.e., a 47-79% biofilm and/or seston diet resulted in tissue EPA of 4.2-18.4, omega3 FAs of 11.6-37.0 and PUFA of 21.6-61.0 mg/g dry mass. The results indicate that consumers in dystrophic lakes predominantly rely on energy from autotrophs and that their PUFA concentrations are dependent on the relative contribution of these autochthonous resources. The limited energy support from MOB suggests they are not negligible and are potentially an integral part of the food webs. Our findings show that autochthonous resources are the main driver of secondary production even in dystrophic lakes and offer new insights into the functioning of these ecosystems.

Evaluation of pesticide monitoring strategies in agricultural streams based on the toxic-unit concept--experiences from long-term measurements.

The European Water Framework Directive requires surface water bodies to have a good chemical and ecological status. Although relatively few pesticides are included in the list of priority pollutants, they pose, due to their intrinsic biological activity, a significant risk for the integrity of aquatic ecosystems. In this context, the pesticide (up to 128 pesticides including some transformation products) exposure pattern in four agricultural streams and two rivers was determined from 2002 to 2011 under the umbrella of the Swedish national monitoring program employing time-proportional and grab sampling strategies, respectively. After transforming the measured pesticide concentrations into toxic units, the European Uniform Principles for algae (chronic), invertebrates and fish (both acute), which are partly employed as benchmark for pesticide regulation, were only occasionally (<2%) exceeded. Moreover, this evaluation showed no long-term trends over the years. However, recent publications suggested that those thresholds are not protective for ecosystem structure and function, indicating a risk of up to 20% and 35% of the samples from the agricultural streams and the rivers, respectively. Moreover, the monitoring data show a continuous but rather low toxic potential of pesticides for all three trophic levels throughout the year, which suggests pesticides as an evolutionary force in agriculturally impacted aquatic ecosystems. However, the flow-triggered sampling, which was implemented as an additional sampling strategy in one of the agricultural streams starting in 2006, displayed an up to 7-fold underestimation of the maximum concentration in terms of toxic units for daphnids and fish during run-off events. The present study thus underpins that the optimal sampling design for pesticide monitoring strongly depends on its overall purpose. If the long-term exposure pattern is of concern a time-proportional composite sampling strategy is recommended, while for an assessment of peak exposures a flow-event-triggered high-resolution sampling strategy is superior.

Distinguishing the effects of habitat degradation and pesticide stress on benthic invertebrates using stressor-specific metrics.

Hydromorphological degradation is a well known stressor for running waters, while the effects of elevated levels of pesticides are widely ignored. Hence, distinguishing between the effects of these two stressors is an urgent task for water managers that aim at appropriate remediation measures. We used a large monitoring data set on benthic invertebrates, habitat descriptors, and physico-chemical variables to develop the SPEAR[%](habitat) metric that indicates the effects of in-stream habitat degradation. SPEAR[%](habitat) correlated significantly with the habitat degradation score (HDS; based on substratum and vegetation coverage), while it did not respond to any physico-chemical variables (r(2)=0.20). This relationship improved for streams with low modeled pesticide inputs (r(2)=0.33), and improved even further for a subset of streams dominated by soft-bottom substrata, i.e. for similar stream-types (r(2)=0.65). These relationships were confirmed for an independent dataset that was not used in the derivation of the HDS (r(2)=0.57 and r(2)=0.65, respectively). These findings show that the SPEAR[%](habitat) had a high degree of specificity for the effects of habitat degradation. Conversely, neither the commonly used EPT and ASPT metrics, nor the German Fauna Index or SPEAR[%](pesticides) showed significant relationships with HDS. These metrics instead correlated significantly with the run-off potential (RP), a proxy of pesticide contamination of streams. Similarly, RP was also the most important explanatory variable for SPEAR[%](pesticides), followed by alkalinity and the number of forested upstream stretches (r(2)=0.61). The latter are expected to alleviate pesticide effects, as indicated by higher SPEAR[%](pesticides) values. These findings show that an integrated analysis of the two stressor-specific SPEAR-metrics in combination with the metrics of general ecological degradation can help water managers to distinguish between the effects of habitat degradation and pesticide stress, two co-occurring stressors in agricultural landscapes.

Interactions with DOM and biofilms affect the fate and bioavailability of insecticides to invertebrate grazers.

We studied the fate and bioavailability of insecticides in short-term experiments (48 h) with different hydrophobicity (3.8 pM carbofuran, 3.0 pM lindane, and 5.3 pM chlorpyrifos) across gradients in dissolved organic matter (low-, medium-, and high-DOM) in freshwater microcosms, mimicking runoff events of pesticides. The effects of biofilms were studied by including treatments with biofilms cultivated under different DOM-concentrations. The presence of biofilms negatively affected chlorpyrifos water concentrations, indicating rapid sorption of this hydrophobic pesticide, while lindane concentrations instead increased and carbofuran concentrations were unaffected. Associations of lindane and chlorpyrifos with biofilms were 1.6-2.0 times higher in low- and high-DOM than in medium-DOM treatments, indicating that sorption was affected not only by the quantity, but also by the quality of DOM. Although the proportion of pesticides recovered in biofilms was consistently less than 1 % of added pesticide, pesticide concentrations in biofilms were on average more than 75- (carbofuran) and 382-times (lindane) higher than those in water. Snail accumulation of all three pesticides was significantly affected by DOM-concentrations and correlated to pesticide hydrophobicity, but the relationships were not straightforward. For example, carbofuran uptake in treatments without biofilms was higher in low-DOM than in medium- and high-DOM treatments, while chlorpyrifos uptake instead increased across the DOM-gradient. Biofilms played a role only for the uptake of chlorpyrifos, which decreased markedly in the presence of biofilms. Bioconcentration factors (BCF) calculated for snails and biofilms differed for the three pesticides and were related to their sorption behaviour (i.e., hydrophobicity). The relative proportion of pesticide uptake through biofilm consumption was consistently less than 2 %, showing that passive uptake was by far the predominant uptake pathway for all three pesticides.

Traits-based approaches in bioassessment and ecological risk assessment: strengths, weaknesses, opportunities and threats.

We discuss the application of traits-based bioassessment approaches in retrospective bioassessment as well as in prospective ecological risk assessments in regulatory frameworks. Both approaches address the interaction between species and stressors and their consequences at different levels of biological organization, but the fact that a specific species may be less abundant in a potentially impacted site compared with a reference site is, regrettably, insufficient to provide diagnostic information. Species traits may, however, overcome the problems associated with taxonomy-based bioassessment. Trait-based approaches could provide signals regarding what environmental factors may be responsible for the impairment and, thereby, provide causal insight into the interaction between species and stressors. For development of traits-based (TBA), traits should correspond to specific types of stressors or suites of stressors. In this paper, a strengths, weaknesses, opportunities, and threats (SWOT) analysis of TBA in both applications was used to identify challenges and potentials. This paper is part of a series describing the output of the TERA (Traits-based ecological risk assessment: Realising the potential of ecoinformatics approaches in ecotoxicology) Workshop held between 7 and 11 September, 2009, in Burlington, Ontario, Canada. The recognized strengths were that traits are transferrable across geographies, add mechanistic and diagnostic knowledge, require no new sampling methodology, have an old tradition, and can supplement taxonomic analysis. Weaknesses include autocorrelation, redundancy, and inability to protect biodiversity directly. Automated image analysis, combined with genetic and biotechnology tools and improved data analysis to solve autocorrelation problems were identified as opportunities, whereas low availability of trait data, their transferability, their quantitative interpretation, the risk of developing nonrelevant traits, low quality of historic databases, and their standardization were listed as threats.

Particle-specific sorption/desorption properties determine test compound fate and bioavailability in toxicity tests with Chironomus riparius--high-resolution studies with lindane.

We studied the sorption (batch equilibrium experiments) and desorption (consecutively harsher supercritical fluid extractions) of lindane to different types of sediment and food particles, as well as larval uptake in standardized peat-based artificial sediment toxicity tests with the midge Chironomus riparius. Lindane sorption to organic particles was fast and efficient, reaching 98+/-0.1 and 97+/-0.1% of added compound in 48 h for peat and Tetraphyll(R), respectively, and 77+/-0.2% in whole sediment. Sorption to inorganic particles, that is, sand and kaolin clay, was much lower, 9.6+/-1.3% and 8.3+/-0.8%, respectively. Supercritical fluid extractions showed that most of the lindane sorbed to organic particles and sediment was loosely bound, as only 9 to 14% remained associated with particles after weak and intermediate extractions strengths. Larval uptake of dissolved lindane was 4.9+/-0.71 and 10.8+/-1.2 microg/g wet weight in 22 and 68 microg/L treatments, respectively, and four to five times higher than that of particle-associated lindane, ranging 1.0+/-0.15 to 2.7+/-0.21 microg/g in the above treatments. Surprisingly, larval uptake of lindane was similar from refractory peat and the more labile Tetraphyll particles. Despite an efficient larval uptake of dissolved lindane, sorption/desorption of lindane to/from Tetraphyll particles will facilitate digestive uptake in toxicity tests, particularly in spiked-water scenarios where food particles may act as vectors. Our results show that the exposure scenario is an important determinant for the behavior and bioavailability of test compounds in standardized toxicity tests.