Stream habitat structure influences macroinvertebrate response to pesticides

Macroinvertebrate community and leaf litter breakdown measures lack concordance associated with singular or multiple stressors

Freshwater ecosystems are being degraded by a wide range of stressors resulting from human activities. Various structural and functional metrics or indices are used to assess the 'health' or condition of riverine ecosystems. It is uncertain if structural or functional metrics or indices respond to different stressors and whether some are more responsive to stressors in general. Here we conducted a multi-study synthesis, similar to a meta-analysis, across four independent outdoor mesocosm experiments involving the manipulation of various chemical stressors - two types of salinity (synthetic marine salts (SMS) and sodium bicarbonate), two insecticides (malathion and sulfoxaflor), increased nutrients (N and P), increased sedimentation and two combinations of stressors (1: malathion, nutrients and sedimentation, 2: sulfoxaflor, nutrients and sedimentation). We compare the effects of these singular or multiple stressors on stream macroinvertebrate community structure, and Eucalyptus camaldulensis leaf litter breakdown rates by microbes and total (microbes and invertebrates). Macroinvertebrate communities were adversely affected by the two sets of multiple stressors, SMS, and both insecticides yet, and in contrast to several published studies, both microbial and total leaf litter was unaffected. Nutrients and sodium bicarbonate, increased breakdown rates or had a unimodal 'Ո' shaped response, with maxima at intermediate levels. Sedimentation by fine sand, however, decreased total leaf litter breakdown, while not affecting microbial leaf litter breakdown. Divergent responses between the effects of stressors on leaf litter breakdown rates that we observed and those in the literature may be caused by multiple mechanisms, including differences between communities, functional redundancy and differences in stressor magnitude and interactions with other (unknown) variables.

A study of macroinvertebrate community structure and diversity in response to land use type in the Yiluo River Basin

Land use types have a significant impact on river ecosystems. The Yiluo River is the largest tributary below Xiaolangdi Reservoir in the middle reaches of the Yellow River, and is one of the important water conservation areas in the Yellow River Basin. Studying the ecological status of the Yiluo River under varied land use types in this basin is crucial for both ecological protection and the high-quality development of the Yellow River Basin. This study investigated the impacts of land use types on the macroinvertebrate community and functional structure in the Yiluo River Basin and introduced the concept of the land use health index (LUI). During the survey period, a total of 11,894 macroinvertebrates were collected, and 143 species were identified, belonging to 4 phyla, 7 orders, 22 families, and 75 families. The results showed that LUI had the most significant impact on macroinvertebrate community structure, with substrate type, dry plant weight, total phosphorus, turbidity, and attached algae biomass also playing significant roles in affecting macroinvertebrate communities. The species richness, the Shannon-Wiener index, and the Margalef richness index exhibited a nonlinear positive correlation with LUI of the sampling site, increasing as LUI enhancing and eventually reaching a plateau. Functional richness showed a linear and positive correlation with LUI, increasing with its enhancement, while functional evenness and functional divergence exhibited a nonlinear correlation with LUI. Functional evenness initially increased and then decreased with the enhancement of LUI, while functional divergence decreased with LUI enhancement. This study can provide a scientific reference for river ecological management under various land use scenarios.The Yiluo River is the largest tributary below Xiaolangdi Reservoir in the middle reaches of the Yellow River, and is one of the important water conservation areas in the Yellow River Basin. Studying the ecological status of the Yiluo River under varied land use types in this basin is crucial for both ecological protection and the high-quality development of the Yellow River Basin. This study investigated the impacts of land use types on the macroinvertebrate community and functional structure in the Yiluo River Basin and introduced the concept of the land use health index (LUI). During the survey period, a total of 11,894 macroinvertebrates were collected, and 143 species were identified, belonging to 4 phyla, 7 orders, 22 families, and 75 families. The results showed that LUI had the most significant impact on macroinvertebrate community structure, with substrate type, dry plant weight, total phosphorus, turbidity, and attached algae biomass also playing significant roles in affecting macroinvertebrate communities. The species richness, the Shannon-Wiener index, and the Margalef richness index exhibited a nonlinear positive correlation with LUI of the sampling site, increasing as LUI enhancing and eventually reaching a plateau. Functional richness showed a linear and positive correlation with LUI, increasing with its enhancement, while functional evenness and functional divergence exhibited a nonlinear correlation with LUI. Functional evenness initially increased and then decreased with the enhancement of LUI, while functional divergence decreased with LUI enhancement. This study can provide a scientific reference for river ecological management under various land use scenarios.

Multiple lines of evidence point to pesticides as stressors affecting invertebrate communities in small streams in five United States regions

Multistressor studies were performed in five regions of the United States to assess the role of pesticides as stressors affecting invertebrate communities in wadable streams. Pesticides and other chemical and physical stressors were measured in 75 to 99 streams per region for 4 weeks, after which invertebrate communities were surveyed (435 total sites). Pesticides were sampled weekly in filtered water, and once in bed sediment. The role of pesticides as a stressor to invertebrate communities was assessed by evaluating multiple lines of evidence: toxicity predictions based on measured pesticide concentrations, multivariate models and other statistical analyses, and previously published mesocosm experiments. Toxicity predictions using benchmarks and species sensitivity distributions and statistical correlations suggested that pesticides were present at high enough concentrations to adversely affect invertebrate communities at the regional scale. Two undirected techniques-boosted regression tree models and distance-based linear models-identified which pesticides were predictors of (respectively) invertebrate metrics and community composition. To put insecticides in context with known, influential covariates of invertebrate response, generalized additive models were used to identify which individual pesticide(s) were important predictors of invertebrate community condition in each region, after accounting for natural covariates. Four insecticides were identified as stressors to invertebrate communities at the regional scale: bifenthrin, chlordane, fipronil and its degradates, and imidacloprid. Fipronil was particularly important in the Southeast region, and imidacloprid, bifenthrin, and chlordane were important in multiple regions. For imidacloprid, bifenthrin, and fipronil, toxicity predictions were supported by mesocosm experiments that demonstrated adverse effects on naïve aquatic communities when dosed under controlled conditions. These multiple lines of evidence do not prove causality-which is challenging in the field under multistressor conditions-but they make a strong case for the role of insecticides as stressors adversely affecting invertebrate communities in streams within the five sampled regions.

Microbial community history and leaf species shape bottom-up effects in a freshwater shredding amphipod

Arable land use and the associated application of agrochemicals can affect local freshwater communities with consequences for the entire ecosystem. For instance, the structure and function of leaf-associated microbial communities can be affected by pesticides, such as fungicides. Additionally, the leaf species on which these microbial communities grow reflects another environmental filter for community structure. These factors and their interaction may jointly modify leaves' nutritional quality for higher trophic levels. To test this assumption, we studied the structure of leaf-associated microbial communities with distinct exposure histories (pristine [P] vs vineyard run off [V]) colonising two leaf species (black alder, European beech, and a mixture thereof). By offering these differently colonised leaves as food to males and females of the leaf-shredding amphipod Gammarus fossarum (Crustacea; Amphipoda) we assessed for potential bottom-up effects. The growth rate, feeding rate, faeces production and neutral lipid fatty acid profile of the amphipod served as response variable in a 2 × 3 × 2-factorial test design over 21d. A clear separation of community history (P vs V), leaf species and an interaction between the two factors was observed for the leaf-associated aquatic hyphomycete (i.e., fungal) community. Sensitive fungal species were reduced by up to 70 % in the V- compared to P-community. Gammarus' growth rate, feeding rate and faeces production were affected by the factor leaf species. Growth was negatively affected when Gammarus were fed with beech leaves only, whereas the impact of alder and the mixture of both leaf species was sex-specific. Overall, this study highlights that leaf species identity had a more substantial impact on gammarids relative to the microbial community itself. Furthermore, the sex-specificity of the observed effects (excluding fatty acid profile, which was only measured for male) questions the procedure of earlier studies, that is using either only one sex or not being able to differentiate between males and females. However, these results need additional verification to support a reliable extrapolation.

Identifying the impact of toxicity on stream macroinvertebrate communities in a multi-stressor context based on national ecological and ecotoxicological monitoring databases

In situ bioassays are used to measure the harmful effects induced by mixtures of toxic chemicals in watercourses. In France, national-scale biomonitoring data are available including invertebrate surveys and in-field chemical toxicity measures with caged gammarids to assess environmental toxicity of mixtures of chemicals. The main objective of our study is to present a proof-of-concept approach identifying possible links between in-field chemical toxicity, stressors and the ecological status. We used two active biomonitoring databases comprising lethal toxicity (222 in situ measures of gammarid mortality) and sublethal toxicity (101 in situ measures of feeding inhibition). We measured the ecological status of each active biomonitoring site using the I₂M₂ metric (macroinvertebrate-based multimetric index), accounted for known stressors of nutrients and organic matter, hydromorphology and chemical toxicity. We observed a negative relationship between stressors (hydromorphology, nutrients and organic matter, and chemical toxicity) and the good ecological status. This relationship was aggravated in watercourses where toxicity indicators were degraded. We validated this hypothesis for instance with nutrients and organic matter like nitrates or hydromorphological conditions like percentage of vegetation on banks. Future international assesments concerning the role of in-field toxic pollution on the ecological status in a multi-stressor context are now possible via the current methodology.

Pesticide risk assessment in honeybees: Toward the use of behavioral and reproductive performances as assessment endpoints

The growing gap between new evidence of pesticide toxicity in honeybees and conventional toxicological assays recommended by regulatory test guidelines emphasizes the need to complement current lethal endpoints with sublethal endpoints. In this context, behavioral and reproductive performances have received growing interest since the 2000s, likely due to their ecological relevance and/or the emergence of new technologies. We review the biological interests and methodological measurements of these predominantly studied endpoints and discuss their possible use in the pesticide risk assessment procedure based on their standardization level, simplicity and ecological relevance. It appears that homing flights and reproduction have great potential for pesticide risk assessment, mainly due to their ecological relevance. If exploratory research studies in ecotoxicology have paved the way toward a better understanding of pesticide toxicity in honeybees, the next objective will then be to translate the most relevant behavioral and reproductive endpoints into regulatory test methods. This will require more comparative studies and improving their ecological relevance. This latter goal may be facilitated by the use of population dynamics models for scaling up the consequences of adverse behavioral and reproductive effects from individuals to colonies.

Multiple stressors determine river ecological status at the European scale: Towards an integrated understanding of river status deterioration

The biota of European rivers are affected by a wide range of stressors impairing water quality and hydro-morphology. Only about 40% of Europe's rivers reach 'good ecological status', a target set by the European Water Framework Directive (WFD) and indicated by the biota. It is yet unknown how the different stressors in concert impact ecological status and how the relationship between stressors and status differs between river types. We linked the intensity of seven stressors to recently measured ecological status data for more than 50,000 sub-catchment units (covering almost 80% of Europe's surface area), which were distributed among 12 broad river types. Stressor data were either derived from remote sensing data (extent of urban and agricultural land use in the riparian zone) or modelled (alteration of mean annual flow and of base flow, total phosphorous load, total nitrogen load and mixture toxic pressure, a composite metric for toxic substances), while data on ecological status were taken from national statutory reporting of the second WFD River Basin Management Plans for the years 2010-2015. We used Boosted Regression Trees to link ecological status to stressor intensities. The stressors explained on average 61% of deviance in ecological status for the 12 individual river types, with all seven stressors contributing considerably to this explanation. On average, 39.4% of the deviance was explained by altered hydro-morphology (morphology: 23.2%; hydrology: 16.2%), 34.4% by nutrient enrichment and 26.2% by toxic substances. More than half of the total deviance was explained by stressor interaction, with nutrient enrichment and toxic substances interacting most frequently and strongly. Our results underline that the biota of all European river types are determined by co-occurring and interacting multiple stressors, lending support to the conclusion that fundamental management strategies at the catchment scale are required to reach the ambitious objective of good ecological status of surface waters.

Can SPEcies At Risk of pesticides (SPEAR) indices detect effects of target stressors among multiple interacting stressors?

Pesticides are increasingly recognised as a threat to freshwater biodiversity, but their specific ecological effects remain difficult to distinguish from those of co-occurring stressors and environmental gradients. Using mesocosms we examined the effects of an organophosphate insecticide (malathion) on stream macroinvertebrate communities concurrently exposed to a suite of stressors typical of streams in agricultural catchments. We assessed the specificity of the SPEcies At Risk index designed to determine pesticide effects in mesocosm trials (SPEAR_mesocosm). This index determines the log abundance proportion of taxa that are considered physiologically sensitive to pesticides. Geographic variation in pesticide sensitivity within taxa, coupled with variation between pesticides and the effects of co-occurring stressors may decrease the accuracy of SPEAR_mesocosm. To examine this, we used local pesticide sensitivity assessments based on rapid toxicity tests to develop two new SPEAR versions to compare to the original SPEAR_mesocosms index using mesocosm results. We further compared these results to multivariate analyses and community indices (e.g. richness, abundance, Simpson's diversity) commonly used to assess stressor effects on biota. To assess the implications of misclassifying species sensitivity on SPEAR indices we used a series of simulations using artificial data. The impacts of malathion were detectable using SPEAR_mesocosm, and one of two new SPEAR indices. All three of the SPEAR indices also increased when exposed to other agricultural non-pesticide stressors, and this change increased with greater pesticide concentrations. Our results support that interactions between other non-pesticide stressors with pesticides can affect SPEAR performance. Multivariate analysis and the other indices used here identified a significant effect of malathion especially at high concentrations, with little or no evidence of effects from the other agricultural stressors.

A Review of Biological Monitoring of Aquatic Ecosystems Approaches: with Special Reference to Macroinvertebrates and Pesticide Pollution

Biological monitoring is the evaluating changes in the environment using the biological responses with the intent of using such information in quality control of the ecosystem. Biomarkers and bioindicators are two main components of the hierarchy of biomonitoring process. Bioindicators can be used to monitor changes of ecosystems and to distinguish alteration of human impact from natural variability. There is a wide range of aquatic taxa such as macroinvertebrates, fish and periphyton, planktons which are successfully used in the biomonitoring process. Among them, macroinvertebrates are an important group of aquatic organisms that involves transferring energy and material through the trophic levels of the aquatic food chain and their sensitivity to environmental changes differs among the species. The main approaches of assessing freshwater ecosystems health using macroinvertebrates include measurement of diversity indices, biotic indices, multimetric approaches, multivariate approaches, Indices of Biological Integrity (IBI), and trait-based approaches. Among these, biotic indices and multimetric approaches are commonly used to evaluate the pesticide impacts on aquatic systems. Recently developed trait-based approaches such as SPEcies At Risk of pesticides (SPEAR) index was successfully applied in temperate regions to monitor the events of pesticide pollution of aquatic ecosystems but with limited use in tropics. This paper reviews the literature on different approaches of biomonitoring of the aquatic environment giving special reference to macroinvertebrates. It also reviews the literature on how biomonitoring could be used to monitor pesticide pollution of the aquatic environment. Thus the review aims to instil the importance of current approaches of biomonitoring for the conservation and management of aquatic ecosystems especially in the regions of the world where such knowledge has not been integrated in ecosystem conservation approaches.

Paradise lost? Pesticide pollution in a European region with considerable amount of traditional agriculture

Pesticide contamination of agricultural streams has widely been analysed in regions of high intensity agriculture such as in Western Europe or North America. The situation of streams subject to low intensity agriculture relying on human and animal labour, as in parts of Romania, remains unknown. To close this gap, we determined concentrations of 244 pesticides and metabolites at 19 low-order streams, covering sites from low to high intensity agriculture in a region of Romania. Pesticides were sampled with two passive sampling methods (styrene-divinylbenzene (SDB) disks and polydimethylsiloxane (PDMS) sheets) during three rainfall events and at base flow. Using the toxic unit approach, we assessed the toxicity towards algae and invertebrates. Up to 50 pesticides were detected simultaneously, resulting in sum concentrations between 0.02 and 37 µg L^-1. Both, the sum concentration as well as the toxicities were in a similar range as in high intensity agricultural streams of Western Europe. Different proxies of agricultural intensity did not relate to in-stream pesticide toxicity, contradicting the assumption of previous studies. The toxicity towards invertebrates was positively related to large scale variables such as the catchment size and the agricultural land use in the upstream catchment and small scale variables including riparian plant height, whereas the toxicity to algae showed no relationship to any of the variables. Our results suggest that streams in low intensity agriculture, despite a minor reported use of agrochemicals, exhibit similar levels of pesticide pollution as in regions of high intensity agriculture.

Species occurrence relates to pesticide gradient in streams

Freshwater communities are threatened worldwide, with pesticides being one of the main stressors for vulnerable invertebrates. Whereas the effects of pesticides on communities can be quantified by trait-based bioindicators such as SPEAR_pesticides, single species' responses remain largely unknown. We used the bioindicator SPEAR_pesticides to predict the toxic pressure from pesticides in 6942 macroinvertebrate samples from 4147 sites during the period 2004 to 2013, obtained by environmental authorities in Germany, and classified all samples according to their magnitude of pesticide pressure. Along this gradient of pesticide pressure, we quantified the occurrence of 139 macroinvertebrate species. We identified 71 species characterized by decreasing occurrence with increasing pesticide pressure. These 'decreasing species', mainly insects, occurred at a frequency of 19.7% at sites with reference conditions and decreased to 1.7% at sites with the highest pesticide pressure. We further determined 55 'nonspecific species' with no strong response as well as 13 'increasing species', mainly Gastropoda, Oligochaeta and Diptera, which showed an increase of frequency from 1.8% at sites with reference conditions to 11.4% at sites with the highest pesticide pressure. Based on the change in frequency we determined the pesticide vulnerability of single species, expressed as Pesticide Associated Response (PARe). Furthermore, a trait analysis revealed that species' occurrence may additionally depend on oxygen demand and, to a lesser extent on substrate preference, whereas no significant effect of feeding and respiration type could be found. Our results provide the first extensive pesticide vulnerability ranking for single macroinvertebrate species based on empirical large-scale field data.

Effects of anthropogenic subsidy and glyphosate on macroinvertebrates in streams

Streams and surrounding terrestrial ecosystems are closely linked by numerous resource subsidies including anthropogenic subsidies which are increasingly entering streams due to intensive human activities. Also, streams are threatened by stressors such as glyphosate-the most widely used herbicide worldwide. However, the ecological consequences of anthropogenic subsidies and glyphosate on freshwaters are not fully understood. Here, we deployed leaf litter (Cinnamomum camphora) bags containing neither, either, or both treatments of anthropogenic carrion subsidy (chicken meat) and glyphosate (coated in agar) in four streams, which had different land use (i.e., forest, village, and suburban) in Huangshan, Anhui Province, China. We aimed to investigate the individual and combined effects of anthropogenic carrion subsidy and glyphosate on macroinvertebrates in streams and whether these effects differ with land use change. Macroinvertebrate communities significantly differed among streams: biodiversity index and total taxon richness were highest in village streams and lowest in suburban stream. Overall effects of carrion subsidy and glyphosate on macroinvertebrates were not significant. However, several taxa were affected in one or more streams by the individual or combined effects of carrion subsidy and glyphosate, indicating the importance of local community structure and physical habitats in driving the response of macroinvertebrates to carrion subsidy and glyphosate. Collectively, these results imply that the effects of carrion subsidy and glyphosate on macroinvertebrates are site-specific, and future studies should cover more streams and last longer time to better understand the ecological mechanisms driving such pattern.

Daily stream samples reveal highly complex pesticide occurrence and potential toxicity to aquatic life

Transient, acutely toxic concentrations of pesticides in streams can go undetected by fixed-interval sampling programs. Here we compare temporal patterns in occurrence of current-use pesticides in daily composite samples to those in weekly composite and weekly discrete samples of surface water from 14 small stream sites. Samples were collected over 10-14 weeks at 7 stream sites in each of the Midwestern and Southeastern United States. Samples were analyzed for over 200 pesticides and degradates by direct aqueous injection liquid chromatography with tandem mass spectrometry. Nearly 2 and 3 times as many unique pesticides were detected in daily samples as in weekly composite and weekly discrete samples, respectively. Based on exceedances of acute-invertebrate benchmarks (AIB) and(or) a Pesticide Toxicity Index (PTI) >1, potential acute-invertebrate toxicity was predicted at 11 of 14 sites from the results for daily composite samples, but was predicted for only 3 sites from weekly composites and for no sites from weekly discrete samples. Insecticides were responsible for most of the potential invertebrate toxicity, occurred transiently, and frequently were missed by the weekly discrete and composite samples. The number of days with benthic-invertebrate PTI ≥0.1 in daily composite samples was inversely related to Ephemeroptera, Plecoptera, and Trichoptera (EPT) richness at the sites. The results of the study indicate that short-term, potentially toxic peaks in pesticides frequently are missed by weekly discrete sampling, and that such peaks may contribute to degradation of invertebrate community condition in small streams. Weekly composite samples underestimated maximum concentrations and potential acute-invertebrate toxicity, but to a lesser degree than weekly discrete samples, and provided a reasonable approximation of the 90th percentile total concentrations of herbicides, insecticides, and fungicides, suggesting that weekly composite sampling may be a compromise between assessment needs and cost.

Effects of urban multi-stressors on three stream biotic assemblages

During 2014, the U.S. Geological Survey (USGS) National Water-Quality Assessment (NAWQA) project assessed stream quality in 75 streams across an urban disturbance gradient within the Piedmont ecoregion of southeastern United States. Our objectives were to identify primary instream stressors affecting algal, macroinvertebrate and fish assemblages in wadeable streams. Biotic communities were surveyed once at each site, and various instream stressors were measured during a 4-week index period preceding the ecological sampling. The measured stressors included nutrients; contaminants in water, passive samplers, and sediment; instream habitat; and flow variability. All nine boosted regression tree models - three for each of algae, invertebrates, and fish - had cross-validation R² (CV R²) values of 0.41 or above, and an invertebrate model had the highest CV R² of 0.65. At least one contaminant metric was important in every model, and minimum daytime dissolved oxygen (DO), nutrients, and flow alteration were important explanatory variables in many of the models. Physical habitat metrics such as sediment substrate were only moderately important. Flow alteration metrics were useful factors in eight of the nine models. Total phosphorus, acetanilide herbicides and flow (time since last peak) were important in all three algal models, whereas insecticide metrics (especially those representing fipronil and imidacloprid) were dominant in the invertebrate models. DO values below approximately 7 mg/L corresponded to a strong decrease in sensitive taxa or an increase in tolerant taxa. DO also showed strong interactions with other variables, particularly contaminants and sediment, where the combined effect of low DO and elevated contaminants increased the impact on the biota more than each variable individually. Contaminants and flow alteration were strongly correlated to urbanization, indicating the importance of urbanization to ecological stream condition in the region.

A new method to evaluate the vulnerability of watersheds facing several stressors: A case study in mediterranean Chile

Freshwater systems are subjected to multiple anthropogenic stressors and natural disturbances that act as debilitating agents and modifiers of river systems, causing cumulative and synergistic effects that deteriorate their health and result in watershed vulnerability. This study proposes an easy-to-apply spatial method of watershed vulnerability evaluation using Geographic Information Systems (GIS) in the Andalién River watershed, located in the Chilean mediterranean. A watershed vulnerability index (WVI) based on three sub-indices - anthropogenic stressors, environmental fragility and natural disturbances - was developed. To determine the index grouping weights, expert surveys were carried out using the Delphi method. We subsequently normalized and integrated the factors of each sub-index with relative weights. The ranges of each thematic layer were re-classified to establish vulnerability scores. The watershed was divided into three sections: headwaters zone, transfer zone and depositional zone. The watershed vulnerability index showed that 41% of the watershed had very low vulnerability and 42% had medium vulnerability, while only 1% - in the depositional zone - had high vulnerability. A one-way ANOVA was carried out to analyze the vulnerability differences among the three sections of the watershed; it showed significant differences (F (2, 16) = 8.15: p < 0.05). The a posteriori test showed differences between the headwaters and depositional zones (Tukey test, p = 0.005) and between the transfer and depositional zones (Tukey test, p = 0.014). To validate the WVI, water quality was measured at 16 stations in the watershed; there was a significant correlation between vulnerability level and NO₂^- levels (r = 0.8; p = 0.87; α = 0.05) and pH (r = 0.8; p = 0.80; α = 0.05). The WVI showed the cumulative effects of multiple stressors in the depositional zone of the watershed. This is the first study to evaluate and validate non-regulated watershed vulnerability with GIS using multiple anthropogenic and natural stressors.

The Application of a Macroinvertebrate Indicator in Afrotropical Regions for Pesticide Pollution

Many biotic integrity indices are not able to isolate community effects due to pesticide exposure as the communities also respond to other anthropogenic and natural stressors. A macroinvertebrate trait bioindicator system that is pesticide specific was therefore developed to overcome these challenges. This system, called SPEAR (SPEcies At Risk), was applied in South Africa as an indicator to link known pesticide catchment usage to changes in the macroinvertebrate community, especially when analytical methods are inconclusive. In addition, the SPEAR_salinity index within the SPEAR suite of tools was also evaluated for its effectiveness in South Africa. The results indicated that all of the sites have either been exposed to the same pesticide pressure or not been exposed to pesticides as the SPEAR results were similar when compared to the pesticide intensity. The interaction with other factors like nutrients or salinity was likely a factor that confounded the SPEAR_pesticides indicator.

Exposure Through Runoff and Ground Water Contamination Differentially Impact Behavior and Physiology of Crustaceans in Fluvial Systems

Chemical pollutants enter aquatic systems through numerous pathways (e.g., surface runoff and ground water contamination), thus associating these contaminant sources with varying hydrodynamic environments. The hydrodynamic environment shapes the temporal and spatial distribution of chemical contaminants through turbulent mixing. The differential dispersal of contaminants is not commonly addressed in ecotoxicological studies and may have varying implications for organism health. The purpose of this study is to understand how differing routes of exposure to atrazine alter social behaviors and physiological responses of aquatic organisms. This study used agonistic encounters in crayfish Orconectes virilis as a behavioral assay to investigate impact of sublethal concentrations of atrazine (0, 40, 80, and 160 µg/L) delivered by methods mimicking ground water and surface runoff influx into flow-through exposure arenas for a total of 23 h. Each experimental animal participated in a dyadic fight trial with an unexposed opponent. Fight duration and intensity were analyzed. Experimental crayfish hepatopancreas and abdominal muscle tissue samples were analyzed for cytochrome P450 and acetylcholinesterase levels to discern mechanism of detoxification and mode of action of atrazine. Atrazine delivered via runoff decreased crayfish overall fight intensity and contrastingly ground water delivery increased overall fight intensity. The behavioral differences were mirrored by increases in cytochrome P450 activity, whereas no differences were found in acetylcholinesterase activity. This study demonstrates that method of delivery into fluvial systems has differential effects on both behavior and physiology of organisms and emphasizes the need for the consideration of delivery pathway in ecotoxicological studies and water-impairment standards.

Indication of pesticide effects and recolonization in streams

The agricultural use of pesticides leads to environmentally relevant pesticide concentrations that cause adverse effects on stream ecosystems. These effects on invertebrate community composition can be identified by the bio-indicator SPEAR_pesticides. However, refuge areas have been found to partly confound the indicator. On the basis of three monitoring campaigns of 41 sites in Central Germany, we identified 11 refuge taxa. The refuge taxa, mainly characterized by dispersal-based resilience, were observed only nearby uncontaminated stream sections and independent of the level of pesticide pressure. Through incorporation of this information into the revised SPEAR_pesticides indicator, the community structure specifically identified the toxic pressure and no longer depended on the presence of refuge areas. With regard to ecosystem functions, leaf litter degradation was predicted by the revised SPEAR_pesticides and the median water temperature at a site (R² = 0.38, P = 0.003). Furthermore, we designed the bio-indicator SPEAR_refuge to quantify the magnitude of general recolonization at a given stream site. We conclude that the taxonomic composition of aquatic invertebrate communities enables a specific indication of anthropogenic stressors and resilience of ecosystems.

Pesticides in the rivers and streams of two river basins in northern Greece

The pollution caused by pesticides, and their ecotoxicological implications were investigated in water samples from the Strymonas and Nestos river basins (Northern Greece). Chlorpyrifos was the most frequently detected pesticide in both basins (42 and 37% in the Strymonas and Nestos basins, respectively), followed by fluometuron and terbuthylazine (25 and 12%, Strymonas), and bentazone and boscalid (24 and 10%, Nestos). The Annual Average and the Maximum Allowable Concentration of Environmental Quality Standards set in European Union Directives were exceeded in several cases by alphamethrin and chlorpyrifos. Risk Quotient assessment revealed significant ecological risk towards the aquatic organisms in over 20% of the water samples. Insecticides (mostly pyrethroids and organophosphosphates) contributed more in the ecotoxicological risk than herbicides and fungicides. The three main rivers in the current study (Strymonas, Aggitis, Nestos) exhibited similar sum of RQs indicating that aquatic life in all three of them was at the same risk level. However, the sums of RQs were higher in the various streams monitored than the three rivers.

Pesticides in agricultural headwater streams in southwestern Germany and effects on macroinvertebrate populations

Pesticides are a major burden for stream ecosystems in the central European cultivated landscape. The objective of the present study was to investigate the applicability of ecological indicator methods in relation to toxicity of pesticides under the specific hydro-morphological conditions in small water bodies. Thus, an association of toxicity evaluating methods with different ecological indicators was to be attempted. Based on three random samples taken within the 2016 vegetation period, 23 headwater areas in the Saarland were investigated to test for pesticides and their metabolites. The macroinvertebrate population was also surveyed in 16 of these streams. Evidence was found of 41 substances in total. Most dominant substances include atrazine, isoproturone, quinmerac and tebuconazol as well as metabolites of dimethenamid, chloridazon and metazachlor. At 9 of the 23 sampling points, over 10 plant protection products and metabolites were found. Only 17% of the water bodies investigated contained fewer than 5 substances. Around half of the bodies of water investigated show noticeably high concentrations of metabolites of plant protection products. Maximum concentrations exceeding environmental quality standards or the Health-oriented Guideline Values were measured for 13 substances at individual sampling points. Analysis of the biological data for only 4 of the water bodies investigated resulted in the Ecological Status Class (ESC) "good". All others fell short of the quality target, although they were classified as "good" or "very good" according to the Saprobic index. SPEAR_pesticides as a measurement of the sensitivity of the biocoenosis to pesticides shows their influence in a few water bodies. Likewise, high toxic unit values have also been calculated, indicating the presence of toxic substances at relevant concentrations. However, an actual correlation between SPEAR_pesticides and toxic unit could not be derived. Clearly in these very headwater streams other habitat-determining hydromorphological factors overlay the toxic impact of pesticides.

Towards stressor-specific macroinvertebrate indices: Which traits and taxonomic groups are associated with vulnerable and tolerant taxa?

Monitoring of macroinvertebrate communities is frequently used to define the ecological health status of rivers. Ideally, biomonitoring should also give an indication on the major stressors acting on the macroinvertebrate communities supporting the selection of appropriate management measures. However, most indices are affected by more than one stressor. Biological traits (e.g. size, generation time, reproduction) could potentially lead to more stressor-specific indices. However, such an approach has rarely been tested. In this study we classify 324 macroinvertebrate taxa as vulnerable (decreasing abundances) or tolerant (increasing abundances) along 21 environmental gradients (i.e. nutrients, major ions, oxygen and micropollutants) from 422 monitoring sites in Germany using Threshold Indicator Taxa Analysis (TITAN). Subsequently, we investigate which biological traits and taxonomic groups are associated with taxa classified as vulnerable or tolerant with regard to specific gradients. The response of most taxa towards different gradients was similar and especially high for correlated gradients. Traits associated with vulnerable taxa across most gradients included: larval aquatic life stages, isolated cemented eggs, reproductive cycle per year <1, scrapers, aerial and aquatic active dispersal and plastron respiration. Traits associated with tolerant taxa included: adult aquatic life stages, polyvoltinism, ovoviviparity or egg clutches in vegetation, food preference for dead animals or living microinvertebrates, substrate preference for macrophytes, microphytes, silt or mud and a body size >2-4cm. Our results question whether stressor-specific indices based on macroinvertebrate assemblages can be achieved using single traits, because we observed that similar taxa responded to different gradients and also similar traits were associated with vulnerable and tolerant taxa across a variety of water quality gradients. Future studies should examine whether combinations of traits focusing on specific taxonomic groups achieve higher stressor specificity.

Scaling to the Organism: An Innovative Model of Dynamic Exposure Hotspots in Stream Systems

In flowing systems, fluctuations in the frequency, magnitude, and duration of exposure occurs due to turbulence and geomorphology, causing spatial and temporal variations in chemical exposure at the scale of the organism. Spatial models representing toxicant distribution at the appropriate scales of stream organisms are noticeably missing from the literature. To characterize the fine scale distribution of pollutants in freshwater streams at the scale of a benthic organism, nine artificial stream habitats were created (riffle, pool, run, bend, woody debris) with either sand or gravel substrate. Dopamine was released as a chemical tracer, mimicking a groundwater source, and measurements were recorded with a microelectrode and Epsilon electrochemical recording system. Proxies for the frequency, magnitude, and duration of chemical exposure were extracted. Geographic information systems and an inverse distance weight interpolation technique were used to predict spatially the chemical distribution throughout the habitats. Spatial and temporal variations of exposure were exhibited within and across habitats, indicating that the frequency, magnitude, and duration of exposure is influenced by the organism's location within a habitat and the habitat it resides in. The run and pool with sand substrate contained the greatest frequency, magnitude, and duration of exposure, suggesting a more detrimental exposure compared to other habitats. Differences in peak heights within and across habitats are orders of magnitude in value. Spatial and temporal fluctuations of fine scale exposure need to be considered in both ecotoxicology and water quality modeling to represent and understand the exposure of pollutants impacting benthic organisms.

Chlorpyrifos interacts with other agricultural stressors to alter stream communities in laboratory microcosms

Chlorpyrifos is one of the most widely used agricultural insecticides in the world, but to date there is limited empirical information about its potential to interact with other common agricultural stressors. We conducted a 15-d, community-level, microcosm experiment evaluating individual and combined effects of chlorpyrifos, nutrient enrichment, and sedimentation on stream invertebrate communities (abundance, biomass, richness, size structure, composition) and ecosystem processes (primary productivity and leaf decomposition). We found that sedimentation was the most detrimental stressor, with significant negative impacts on most invertebrate community and ecosystem function variables. Even though chlorpyrifos did not cause significant invertebrate mortality in the microcosms, it still altered ecosystem function by lowering leaf decomposition rates, probably through sublethal inhibition of invertebrate shredders. Furthermore, we observed a significant reversal interaction between chlorpyrifos and sediment for small-sized invertebrates collected in gravel (abundance in sediment × insecticide microcosms was 2.4 times lower than predicted by additivity), as well as an antagonistic interaction with nutrients on invertebrate richness in the same microhabitat (richness in nutrient × insecticide microcosms was 1.6 times higher than predicted by additivity). Our results suggest that chlorpyrifos has the potential to alter freshwater ecosystem function and interact non-additively with other common agricultural stressors. These findings are in keeping with a growing body of research highlighting that multiple stressor interactions and ecosystem processes should be considered when evaluating the impacts of organic toxicants on freshwater ecosystems.

Multiple stress response of lowland stream benthic macroinvertebrates depends on habitat type

Worldwide, lowland stream ecosystems are exposed to multiple anthropogenic stress due to the combination of water scarcity, eutrophication, and fine sedimentation. The understanding of the effects of such multiple stress on stream benthic macroinvertebrates has been growing in recent years. However, the interdependence of multiple stress and stream habitat characteristics has received little attention, although single stressor studies indicate that habitat characteristics may be decisive in shaping the macroinvertebrate response. We conducted an experiment in large outdoor flumes to assess the effects of low flow, fine sedimentation, and nutrient enrichment on the structure of the benthic macroinvertebrate community in riffle and run habitats of lowland streams. For most taxa, we found a negative effect of low flow on macroinvertebrate abundance in the riffle habitat, an effect which was mitigated by fine sedimentation for overall community composition and the dominant shredder species (Gammarus pulex) and by nutrient enrichment for the dominant grazer species (Baetis rhodani). In contrast, fine sediment in combination with low flow rapidly affected macroinvertebrate composition in the run habitat, with decreasing abundances of many species. We conclude that the effects of typical multiple stressor scenarios on lowland stream benthic macroinvertebrates are highly dependent on habitat conditions and that high habitat diversity needs to be given priority by stream managers to maximize the resilience of stream macroinvertebrate communities to multiple stress.

Scale dependency in the hydromorphological control of a stream ecosystem functioning

Physical habitat degradation is prevalent in river ecosystems. Although still little is known about the ecological consequences of altered hydromorphology, understanding the factors at play can contribute to sustainable environmental management. In this study we aimed to identify the hydromorphological features controlling a key ecosystem function and the spatial scales where such linkages operate. As hydromorphological and chemical pressures often occur in parallel, we examined the relative importance of hydromorphological and chemical factors as determinants of leaf breakdown. Leaf breakdown assays were investigated at 82 sites of rivers throughout the French territory. Leaf breakdown data were then crossed with data on water quality and with a multi-scale hydromorphological assessment (i.e. upstream catchment, river segment, reach and habitat) when quantitative data were available. Microbial and total leaf breakdown rates exhibited differential responses to both hydromorphological and chemical alterations. Relationships between the chemical quality of the water and leaf breakdown were weak, while hydromorphological integrity explained independently up to 84.2% of leaf breakdown. Hydrological and morphological parameters were the main predictors of microbial leaf breakdown, whereas hydrological parameters had a major effect on total leaf breakdown, particularly at large scales, while morphological parameters were important at smaller scales. Microbial leaf breakdown were best predicted by hydromorphological features defined at the upstream catchment level whereas total leaf breakdown were best predicted by reach and habitat level geomorphic variables. This study demonstrates the use of leaf breakdown in a biomonitoring context and the importance of hydromorphological integrity for the functioning of running water. It provides new insights for environmental decision-makers to identify the management and restoration actions that have to be undertaken including the hydromorphogical features that should be kept in minimal maintenance to support leaf breakdown.

Response of macroinvertebrate communities to temporal dynamics of pesticide mixtures: A case study from the Sacramento River watershed, California

Pesticide pollution from agricultural field run-off or spray drift has been documented to impact river ecosystems worldwide. However, there is limited data on short- and long-term effects of repeated pulses of pesticide mixtures on biotic assemblages in natural systems. We used reported pesticide application data as input to a hydrological fate and transport model (Soil and Water Assessment Tool) to simulate spatiotemporal dynamics of pesticides mixtures in streams on a daily time-step. We then applied regression models to explore the relationship between macroinvertebrate communities and pesticide dynamics in the Sacramento River watershed of California during 2002-2013. We found that both maximum and average pesticide toxic units were important in determining impacts on macroinvertebrates, and that the compositions of macroinvertebrates trended toward taxa having higher resilience and resistance to pesticide exposure, based on the Species at Risk pesticide (SPEAR_pesticides) index. Results indicate that risk-assessment efforts can be improved by considering both short- and long-term effects of pesticide mixtures on macroinvertebrate community composition.

Multiple exposure routes of a pesticide exacerbate effects on a grazing mayfly

Hydrophobic pesticides such as pyrethroid insecticides tend to occur in their soluble form mainly as transient pulses in streams. In addition, they are regularly detected in significant quantities adsorbed to stream sediments and other organic in-stream structures. Consequently, stream biota is likely subjected to pesticide exposure via multiple routes. In this study we aimed at investigating the influence of exposure routes for the pyrethroid insecticide lambda-cyhalothrin on the grazing mayfly Heptagenia sulphurea. Therefore, H. sulphurea was exposed to lambda-cyhalothrin via single- (water or biofilm) or biphasic exposure (water and biofilm) at environmentally realistic concentrations (0, 0.1, 1μgL(-1)) and exposure duration (2h) in a full factorial design (n=5). Mortality, moulting frequency, and biofilm accrual (proxy for feeding rate) were recorded subsequent to a 7 d post exposure period. Mortality significantly increased and moulting frequency significantly decreased with increasing concentrations of lambda-cyhalothrin in the water phase whereas exposure via biofilm prompted no significant effects on these endpoints (α=0.05). Effect predictions systematically underestimated and overestimated effects for mortality and moulting frequency, respectively. Similarly, mayfly feeding rate was significantly reduced by water phase exposure whereas pre-exposed biofilm did not significantly affect this variable. However, we found a significant but non-systematic interaction between water phase and biofilm exposure on mayfly feeding rate. Our results show that exposure to the same pesticide via multiple exposure routes may increase the magnitude of effects beyond the level predicted from single phase exposures which has clear implications for the aquatic risk assessment of hydrophobic pesticides. However, our results additionally reveal that interactions between pesticide exposure routes may vary between selected dependent variables. We emphasize that unravelling the underlying mechanisms causing these discrepancies in interactive effects between exposure routes is a major aspect that should receive further attention in future research.

Trait Characteristics Determine Pyrethroid Sensitivity in Nonstandard Test Species of Freshwater Macroinvertebrates: A Reality Check

We exposed 34 species of stream macroinvertebrates, representing 29 families, to a 90 min pulse of the pyrethroid λ-cyhalothrin. For 28 of these species, no pyrethroid ecotoxicity data exist. We recorded mortality rates 6 days post-exposure, and the behavioral response to pyrethroid exposure was recorded using automated video tracking. Most arthropod species showed mortality responses to the exposure concentrations (0.01-10 μg L(-1)), whereas nonarthropod species remained unaffected. LC50 varied by at least a factor of 1000 among arthropod species, even within the same family. This variation could not be predicted using ecotoxicity data from closely related species, nor using species-specific indicator values from traditional ecological quality indices. Moreover, LC50 was not significantly correlated to effect thresholds for behavioral responses. Importantly, however, the measured surface area-weight ratio and the preference for coarse substrates significantly influenced the LC50 for arthropod species, with the combination of small individuals and strong preference for coarse substrates indicating higher pyrethroid sensitivity. Our study highlights that existing pesticide ecotoxicity data should be extrapolated to untested species with caution and that actual body size (not maximum potential body size, as is usually available in traits databases) and habitat preference are central parameters determining species sensitivities to pyrethroids.

Environmental context and magnitude of disturbance influence trait-mediated community responses to wastewater in streams

Human land uses and population growth represent major global threats to biodiversity and ecosystem services. Understanding how biological communities respond to multiple drivers of human‐induced environmental change is fundamental for conserving ecosystems and remediating degraded habitats. Here, we used a replicated ‘real‐world experiment’ to study the responses of invertebrate communities to wastewater perturbations across a land‐use intensity gradient in 12 Swiss streams. We used different taxonomy and trait‐based community descriptors to establish the most sensitive indicators detecting impacts and to help elucidate potential causal mechanisms of change. First, we predicted that streams in catchments adversely impacted by human land‐uses would be less impaired by wastewater inputs because their invertebrate communities should be dominated by pollution‐tolerant taxa (‘environmental context’). Second, we predicted that the negative effects of wastewater on stream invertebrate communities should be larger in streams that receive proportionally more wastewater (‘magnitude of disturbance’). In support of the ‘environmental context’ hypothesis, we found that change in the Saprobic Index (a trait‐based indicator of tolerance to organic pollution) was associated with upstream community composition; communities in catchments with intensive agricultural land uses (e.g., arable cropping and pasture) were generally more resistant to eutrophication associated with wastewater inputs. We also found support for the ‘magnitude of disturbance’ hypothesis. The SPEAR Index (a trait‐based indicator of sensitivity to pesticides) was more sensitive to the relative input of effluent, suggesting that toxic influences of wastewater scale with dilution. Whilst freshwater pollution continues to be a major environmental problem, our findings highlight that the same anthropogenic pressure (i.e., inputs of wastewater) may induce different ecological responses depending on the environmental context and community metrics used. Thus, remediation strategies aiming to improve stream ecological status (e.g., rehabilitating degraded reaches) need to consider upstream anthropogenic influences and the most appropriate indicators of restoration success.

Field data reveal low critical chemical concentrations for river benthic invertebrates

River ecosystems are of immense ecological and social importance. Despite the introduction of wastewater treatment plants and advanced chemical authorization procedures in Europe, chemical pollution is still a major threat to freshwater ecosystems. Here, large-scale monitoring data was exploited to identify taxon-specific chemical concentrations beyond which benthic invertebrate taxa are unlikely to occur using Threshold Indicator Taxa Analysis (TITAN). 365 invertebrate taxa and 25 organic chemicals including pesticides, pharmaceuticals, plasticisers, flame retardants, complexing agents, a surfactant and poly- and monocyclic aromatic hydrocarbons from a total of 399 sites were analysed. The number of taxa that responded to each of these chemicals varied between 0% and 21%. These sensitive taxa belonged predominantly to the groups Plecoptera, Coleoptera, Trichoptera, Ephemeroptera, Turbellaria, Megaloptera, Crustacea, and Diptera. Strong effects were observed in response to wastewater-associated compounds, confirming that wastewater is an important cause of biological degradation. The majority of change points identified for each compound were well below predicted no-effect concentrations derived from laboratory toxicity studies. Thus, the results show that chemicals are likely to induce effects in the environment at concentrations much lower than expected based on laboratory experiments. Overall, it is confirmed that chemical pollution is still an important factor shaping the distribution of invertebrate taxa, suggesting the need for continued efforts to reduce chemical loads in rivers.

Influence of rice field agrochemicals on the ecological status of a tropical stream

Many tropical countries contain a high density of protected ecosystems, and these may often be bordered by intensive agricultural systems. We investigated the chemical and ecological status of a stream connecting an area with conventional rice production and a downstream protected nature reserve; Mata Redonda. Three sites were sampled: 1) an upstream control, 2) in the rice production area and 3) a downstream site in Mata Redonda. We sampled benthic macroinvertebrates and pesticides in water and sediments along with supporting physical and chemical data. Pesticide concentrations in water exceeded current safety thresholds at sites 2 and 3, especially during the rainy season, and sediment associated pesticide concentrations exceeded current safety thresholds in three of six samples. Importantly, the highest predicted pesticide toxicity in sediments was observed at site 3 in the Mata Redonda confirming that the nature reserve received critical levels of pesticide pollution from upstream sections. The currently used macroinvertebrate index in Costa Rica (BMWP-CR) and an adjusted version of the SPecies At Risk index (SPEAR) were not significantly correlated to any measure of anthropogenic stress, but the Average Score Per Taxon (ASPT) index was significantly correlated with the predicted pesticide toxicity (sumTUD.magna), oxygen concentrations and substrate composition. Our results suggest that pesticide pollution was likely involved in the impairment of the ecological status of the sampling sites, including site 3 in Mata Redonda. Based on our results, we give guidance to biomonitoring in Costa Rica and call for increased focus on pesticide transport from agricultural regions to protected areas.

Forested headwaters mitigate pesticide effects on macroinvertebrate communities in streams: Mechanisms and quantification

Pesticides impact invertebrate communities in freshwater ecosystems, leading to the loss of biodiversity and ecosystem functions. One approach to reduce such effects is to maintain uncontaminated stream reaches that can foster recovery of the impacted populations. We assessed the potential of uncontaminated forested headwaters to mitigate pesticide impact on the downstream macroinvertebrate communities in 37 streams, using the SPEARpesticides index. Pesticide contamination was measured with runoff-triggered techniques and Chemcatcher® passive samplers. The data originated from 3 field studies conducted between 1998 and 2011. The proportion of vulnerable species decreased significantly after pesticide exposure even at low toxicity levels (-4<TUmax≤-3). This corresponds to pesticide concentrations down to 3-4 orders of magnitude below the LC50 value for standard test organisms. The toxicity of pesticides and the length of the forested reaches together explained 78% of variation in the community composition (SPEARpesticides). The proportion of vulnerable species doubled within the measured length of the forested stream section (0.2-18 km), whereas other characteristics of the forest or abiotic water parameters did not have an effect within the measured gradients. The presence of forested headwaters was not associated with reduced pesticide exposure 3 km downstream and did not reduce the loss of vulnerable taxa after exposure. Nevertheless, forested headwaters were associated with the absence of long-term pesticide effects on the macroinvertebrate community composition. We conclude that although pesticides can cause the loss of vulnerable aquatic invertebrates even at low toxicity levels, forested headwaters enhance the recovery of vulnerable species in agricultural landscapes.

Do predictions from Species Sensitivity Distributions match with field data?

Species Sensitivity Distribution (SSD) is a statistical model that can be used to predict effects of contaminants on biological communities, but only few comparisons of this model with field studies have been conducted so far. In the present study we used measured pesticides concentrations from streams in Germany, France, and Finland, and we used SSD to calculate msPAF (multiple substance potentially affected fraction) values based on maximum toxic stress at localities. We compared these SSD-based predictions with the actual effects on stream invertebrates quantified by the SPEARpesticides bioindicator. The results show that the msPAFs correlated well with the bioindicator, however, the generally accepted SSD threshold msPAF of 0.05 (5% of species are predicted to be affected) severely underestimated the observed effects (msPAF values causing significant effects are 2-1000-times lower). These results demonstrate that validation with field data is required to define the appropriate thresholds for SSD predictions.

Landscape parameters driving aquatic pesticide exposure and effects

Pesticide contamination is considered one of the reasons streams fail to achieve good ecological and chemical status, the main objectives of the Water Framework Directive. However, little is known on the interaction of different pesticide sources and landscape parameters and the resulting impairment of macroinvertebrate communities. We evaluated the potential effects of diffuse and point sources of pesticides using macroinvertebrate monitoring data from 663 sites in central Germany. Additionally, we investigated forested upstream reaches and structural quality as landscape parameters potentially mitigating or amplifying the effects of pesticides. Diffuse pesticide pollution and forested upstream reaches were the most important parameters affecting macroinvertebrate communities (pesticide-specific indicator SPEARpesticides). Our results indicate that forested upstream reaches and riparian buffer strips at least 5 m in width can mitigate the effects and exposure of pesticides. In addition, we developed a screening approach that allows an initial, cost-effective identification of sites of concern.

The contribution of a niche-based approach to ecological risk assessment: using macroinvertebrate species under multiple stressors

We propose that a niche-based experimental approach at population level could be used to solve some uncertainties in traditional approaches in ecotoxicology. We tested this approach in the context of multiple stressors (i.e. chemical and physical) in a selection of six run-of-river reservoirs with different levels of sediment contamination and associated upstream and downstream river sites. A niche-based approach was tested using three functional traits (habitat, food preferences and body size) and discrepancy between the realized and theoretical niches. We first identified three groups of taxa and then recorded differences along the disturbance gradients, such as an increase in competition, a narrowing of spatial and trophic niche breadth (e.g. of Leuctra major and Gammarus pulex), a widening of spatial niche breadth (e.g. of Ephemerella ignita), a greater proportion of small individuals (e.g. of G. pulex) and a decreasing or an increasing (e.g. L. major) discrepancy between realized and theoretical niches.

Culmination of low-dose pesticide effects

Pesticides applied in agriculture can affect the structure and function of nontarget populations at lower doses and for longer timespans than predicted by the current risk assessment frameworks. We identified a mechanism for this observation. The populations of an aquatic invertebrate (Culex pipiens) exposed over several generations to repeated pulses of low concentrations of the neonicotinoid insecticide (thiacloprid) continuously declined and did not recover in the presence of a less sensitive competing species (Daphnia magna). By contrast, in the absence of a competitor, insecticide effects on the more sensitive species were only observed at concentrations 1 order of magnitude higher, and the species recovered more rapidly after a contamination event. The underlying processes are experimentally identified and reconstructed using a simulation model. We conclude that repeated toxicant pulse of populations that are challenged with interspecific competition may result in a multigenerational culmination of low-dose effects.

How to characterize chemical exposure to predict ecologic effects on aquatic communities?

Reliable characterization of exposure is indispensable for ecological risk assessment of chemicals. To deal with mixtures, several approaches have been developed, but their relevance for predicting ecological effects on communities in the field has not been elucidated. In the present study, we compared nine metrics designed for estimating the total toxicity of mixtures regarding their relationship with an effect metric for stream macroinvertebrates. This was done using monitoring data of biota and organic chemicals, mainly pesticides, from five studies comprising 102 streams in several regions of Europe and South-East Australia. Mixtures of less than 10 pesticides per water sample were most common for concurrent exposure. Exposure metrics based on the 5% fraction of a species sensitivity distribution performed best, closely followed by metrics based on the most sensitive species and Daphnia magna as benchmark. Considering only the compound with the highest toxicity and ignoring mixture toxicity was sufficient to estimate toxicity in predominantly agricultural regions with pesticide exposure. The multisubstance Potentially Affected Fraction (msPAF) that combines concentration and response addition was advantageous in the study where further organic toxicants occurred. We give recommendations on exposure metric selection depending on data availability and the involved compounds.

Pesticides reduce regional biodiversity of stream invertebrates

The biodiversity crisis is one of the greatest challenges facing humanity, but our understanding of the drivers remains limited. Thus, after decades of studies and regulation efforts, it remains unknown whether to what degree and at what concentrations modern agricultural pesticides cause regional-scale species losses. We analyzed the effects of pesticides on the regional taxa richness of stream invertebrates in Europe (Germany and France) and Australia (southern Victoria). Pesticides caused statistically significant effects on both the species and family richness in both regions, with losses in taxa up to 42% of the recorded taxonomic pools. Furthermore, the effects in Europe were detected at concentrations that current legislation considers environmentally protective. Thus, the current ecological risk assessment of pesticides falls short of protecting biodiversity, and new approaches linking ecology and ecotoxicology are needed.

Current-use pesticides in stream water and suspended particles following runoff: exposure, effects, and mitigation requirements

The European Union's directive for sustainable use of pesticides requires implementing risk mitigation measures at streams threatened by pesticide entries. The need for mitigation measures was investigated at 10 stream sites within an intensively used arable region in central Germany by characterizing pesticide exposure following edge-of-field runoff and effects on the aquatic macroinvertebrates. Moreover, the influence of riparian buffer strip width (as a mitigation measure) at the sampling sites was considered. Generally, invertebrate fauna was dominated by pesticide-tolerant species, suggesting a high pesticide exposure at almost all sites. This result is also reflected by the elevated levels of suspended particle contamination in terms of toxic units (logTUMax  > -2), corresponding to one-hundredth of the median lethal concentration (LC50) to Daphnia magna. At two sites that received high aqueous-phase entries of the pyrethroid lambda-cyhalothrin (logTUMax  > -0.6), the abundance and number of sensitive species in terms of the species at risk index decreased during the pesticide application period. In contrast, no acute significant negative effects on macroinvertebrates were observed at sites characterised by low water-phase toxicity (logTUMax  < -3.5). An influence of riparian buffer strip width on pesticide exposure was not observed, supposedly because of the presence of erosion rills and ephemeral ditches. In conclusion, results show that mitigation measures (such as the improvement of currently present riparian buffer strips) are needed in the study area.

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.

Integrated assessment of the impact of chemical stressors on surface water ecosystems

The release of chemicals such as chlorinated solvents, pesticides and other xenobiotic organic compounds to streams, either from contaminated sites, accidental or direct application/release, is a significant threat to water resources. In this paper, different methods for evaluating the impacts of chemical stressors on stream ecosystems are evaluated for a stream in Denmark where the effects of major physical habitat degradation can be disregarded. The methods are: (i) the Danish Stream Fauna Index, (ii) Toxic Units (TU), (iii) SPEAR indices, (iv) Hazard Quotient (HQ) index and (v) AQUATOX, an ecological model. The results showed that the hydromorphology, nutrients, biological oxygen demand and contaminants (pesticides and trichloroethylene from a contaminated site) originating from groundwater do not affect the good ecological status in the stream. In contrast, the evaluation by the novel SPEAR(pesticides) index and TU indicated that the site is far from obtaining good ecological status - a direct contradiction to the ecological index currently in use in Denmark today - most likely due to stream sediment-bound pesticides arising from the spring spraying season. In order to generalise the findings of this case study, the HQ index and AQUATOX were extended for additional compounds, not only partly to identify potential compounds of concern, but also to determine thresholds where ecological impacts could be expected to occur. The results demonstrate that some commonly used methods for the assessment of ecological impact are not sufficient for capturing - and ideally separating - the effects of all anthropogenic stressors affecting ecosystems. Predictive modelling techniques can be especially useful in supporting early decisions on prioritising hot spots, serving to identify knowledge gaps and thereby direct future data collection. This case study presents a strong argument for combining bioassessment and modelling techniques to multi-stressor field sites, especially before cost-intensive studies are conducted.

Thresholds for the effects of pesticides on invertebrate communities and leaf breakdown in stream ecosystems

We compiled data from eight field studies conducted between 1998 and 2010 in Europe, Siberia, and Australia to derive thresholds for the effects of pesticides on macroinvertebrate communities and the ecosystem function leaf breakdown. Dose-response models for the relationship of pesticide toxicity with the abundance of sensitive macroinvertebrate taxa showed significant differences to reference sites at 1/1000 to 1/10,000 of the median acute effect concentration (EC50) for Daphnia magna, depending on the model specification and whether forested upstream sections were present. Hence, the analysis revealed effects well below the threshold of 1/100 of the EC50 for D. magna incorporated in the European Union Uniform Principles (UP) for registration of single pesticides. Moreover, the abundances of sensitive macroinvertebrates in the communities were reduced by 27% to 61% at concentrations related to 1/100 of the EC50 for D. magna. The invertebrate leaf breakdown rate was positively linearly related to the abundance of pesticide-sensitive macroinvertebrate species in the communities, though only for two of the three countries examined. We argue that the low effect thresholds observed were not mainly because of an underestimation of field exposure or confounding factors. From the results gathered we derive that the UP threshold for single pesticides based on D. magna is not protective for field communities subject to multiple stressors, pesticide mixtures, and repeated exposures and that risk mitigation measures, such as forested landscape patches, can alleviate effects of pesticides.