Stream Invertebrate Assemblages Research Articles

Impact of land use on water quality and invertebrate assemblages in Indonesian streams

Catchment land use of streams can cause deterioration of the stream ecosystems. Studies on the impact of land use on water quality and invertebrate assemblages in tropical streams are currently less common than studies in temperate regions. In the current study, we conducted a field survey on stream invertebrates and habitat characteristics in 23 streams with different land use conditions in Yogyakarta Province, Java Island, Indonesia. Relationships among catchment characteristics, habitat characteristics, and invertebrate assemblages were analyzed to elucidate the importance of land use and water quality in determining invertebrate assemblages. The analyses, using generalized linear models, showed that the relative area of urban land use of the catchment was strongly and positively related to the nutrient concentration of stream water and negatively related to the taxonomic richness of whole invertebrate assemblages and intolerant taxa. Furthermore, the richness metrics were low in streams with high nutrient concentrations, particularly PO4-P. The biplot of nonmetric multidimensional scaling showed that there was a gradient in community structure along the tolerance to water pollution that occurred in urban streams. These results collectively suggest that urban land use, not agricultural use, seemed to be a predominant factor causing nutrient enrichment in stream water and low invertebrate diversity through the exclusion of intolerant taxa in Indonesian streams whose catchments are exposed to rapid urbanization. We suggest that the impact of agricultural wastewater on stream water quality is concealed by the strong impact of urbanization when we consider that farming methods are, in general, not intensive in Indonesia, and that advanced wastewater treatment systems have not been widely introduced. Our results strongly support the development of sewage treatment as an effective solution for restoring tropical stream ecosystems.

Tertiary wastewater treatment combined with high dilution rates fails to eliminate impacts on receiving stream invertebrate assemblages

The amount of wastewater processed in treatment plants is increasing following more strict environmental regulations. Treatment facilities are implementing upgrades to abate the concentrations of nutrients and contaminants and, thus, reduce their effects on receiving systems. Although many studies characterized the chemical composition and ecotoxicological effects of treated wastewater, its environmental effects are still poorly known, as receiving water bodies are often subjected to other stressors. We performed a field manipulative experiment to measure the response of invertebrate assemblages to one year of tertiary-treated wastewater discharges. We poured treated wastewater from an urban wastewater treatment plant into the lower-most 100-m of a previously unpolluted stream (3.6 % daily flow on average) while using another upstream reach as control. The positive correlation between effect sizes of abundance changes and IBMWP scores suggested assemblage modifications were following taxa tolerance to ecological impairment. The treatment increased the temporal variability of SPEARorganic, EPT relative abundance, and invertebrate functional redundancy. Our results show that even in this best-case scenario of tertiary-treated and highly diluted wastewater, the abundance of the most sensitive taxa in the aquatic assemblages is reduced. Further improvements in wastewater treatments seem necessary to ensure these effluents do not modify receiving water ecosystems.

Wildfire and drying legacies and stream invertebrate assemblages

Climate change is engendering droughts and wildfires in many ecosystems, especially those in Mediterranean climates. Yet, there is little information on the long-term responses of stream invertebrates in Mediterranean climates to wildfire, particularly during and after extreme drought. To examine the effects of drought and wildfire on stream invertebrate assemblages, we sampled stream reaches in southern California with surface water in 2016, at the end of a 5-y drought, and stream reaches in 2017, after flows resumed or increased, including sites within (burned), outside (unburned), and downstream of footprints for fires occurring 8 to 10 y ago. Spatial and temporal variation in invertebrate assemblages were attributed to hydrological regimes, including stream drying during the drought, but there were few fire-legacy effects. At the end of the drought, invertebrate assemblages occupying remaining standing water with high solute, temperature, and benthic organic matter levels were dominated by tolerant, lentic taxa. After flows returned in spring 2017, all sites, including those that were dry in 2016, were dominated by quick-colonizing riffle taxa. Invertebrate densities increased into the subsequent summer at the same time that flows declined and temperatures and conductivities increased; however, sensitive cool-water taxa were more abundant at perennial, shaded sites, whereas tolerant, warm-water taxa were more abundant at shallow, open sites that had dried the year before. We observed negative relationships between riparian burning extent vs canopy cover (weak) and coarse particulate organic matter levels (strong); however, invertebrate assemblage structure was similar in basins that did and did not burn. Although invertebrate populations were severely reduced at 1 site whose basin had burned the year before, invertebrate assemblages had largely recovered after 10 post-fire y, and fire-legacy effects were dwarfed by hydrological variation, particularly stream drying during the drought. Our data also suggest the importance of protecting water supplies and riparian vegetation for perennial, shaded headwater reaches, which provide refuges from drought and wildfire for native biodiversity.

Water abstraction reduces taxonomic and functional diversity of stream invertebrate assemblages

AbstractThe structure and function of many rivers and streams worldwide are altered by water abstraction. However, this impact is often coupled with changes in flow regimes, water quality, and sedi...

Land-use impacts on benthic macroinvertebrate assemblages in pampean streams (Argentina)

In recent decades agriculture has intensified in the Argentine Pampa, and pesticide application has also increased. Livestock fields, although being progressively replaced by crops, are still commonly interspersed with crop fields. The objective of the present work is to assess the effects of land use on the benthic invertebrate assemblages of streams in the main Argentine agricultural region. Two areas were sampled during the 2011/12 growing season (November–March): Arrecifes, a homogeneous intensively cultivated area, and La Plata, a heterogeneous area of mixed livestock pasture, cropland and biological reserve.Nutrient concentrations in water were significantly higher in the streams surrounded by cropland. Measured pesticides in stream sediments were those most commonly used in crop production: chlorpyrifos, cypermethrin, lambda-cyhalothrin, endosulfan and its degradation product endosulfan sulfate. Detection frequency and pesticide concentrations were generally higher in streams surrounded by cropland than in streams surrounded by pasture or reserve.Macroinvertebrate assemblages were significantly different in streams with different land uses. Palaemonidae (Decapoda) and Caenidae (Ephemeroptera) were the taxa best represented in the reserve. Hyalellidae (Amphipoda) and Hirudinea were dominant at the streams surrounded by livestock fields. Within the streams surrounded by croplands, Oligochaeta and Hirudinea were best represented in La Plata while Chironomidae, Gastropoda and Oligochaeta were dominant at Arrecifes. Present evidence suggests that agrochemical applications contribute, in combination with other environmental variables, to the observed differences in macroinvertebrate assemblages in streams of different land use.

Horticulture affects macroinvertebrate assemblages in adjacent streams (Buenos Aires, Argentina)

The agrochemicals used on crops can reach watercourses, affecting water quality and biologic communities. The aim of this research was to study the effects of horticulture on the water quality and invertebrate assemblages of adjacent streams in Buenos Aires province, Argentina. Four streams draining horticultural basins were compared with another four considered less disturbed: two of the latter located in a Biosphere Reserve and the other two in extensive livestock-raising basins. Pesticides were detected in the horticulture-related streams, while nutrient concentrations were significantly higher than in the less-disturbed streams. The macroinvertebrate assemblages differed: the less-disturbed streams exhibited a significantly higher taxa richness and density. Hyalella sp. and Simocephalus vetulus were dominant, whereas Entomobryoidea, Dugessidae, and Glossiphoniidae were dominant in the horticulture-associated streams. Ephemeroptera (Caenis and Baetidae) were well represented in the less-disturbed streams and rare or absent in the horticulture-adjacent streams. Multivariate analysis indicated that the horticulture-impacted sites contained high nutrient concentrations and tolerant taxa, while the less-disturbed sites corresponded to lower nutrient concentrations and sensitive taxa. We propose Hyalella sp. and S. vetulus as water-quality indicators in pampean streams and conclude that intensive agrochemical applications in horticulture increase nutrient and pesticide loads affecting the macroinvertebrate assemblages of adjacent streams.

The effect of substrate disturbance on benthic invertebrates in old-growth broad-leaved forest and planted conifer forest basin streams in Japan

ABSTRACTDisturbances such as heavy rainfall impact benthic invertebrate assemblages in streams and other lotic systems. In temperate Japan, the steep topography means that even modest rainfall can result in significant substrate disturbance. Impacts of this disturbance on benthic invertebrates were examined in the following 1 week and compared in streams of an old-growth broad-leaved forest (OBF) and a planted conifer forest (PCF). Disturbance in this study occurred by kicking the stream substrate. The number of individuals and genera in both forest types decreased after disturbance and gradually recovered over time, but no difference in recovery was observed between the OBF and PCF streams. Benthic invertebrate assemblage composition in both forest types changed depending on the days from disturbance, and differences in recovery between the OBF and PCF streams were observed in the composition of benthic invertebrate assemblages. Recovery patterns of individual taxa after disturbance were also different. Complete recovery was not observed 1 week after disturbance in either forest type, suggesting more time was required to reestablish pre-disturbance invertebrate community composition.

Stressor dominance and sensitivity‐dependent antagonism: Disentangling the freshwater effects of an insecticide among co‐occurring agricultural stressors

Abstract Pesticide concentrations are correlated with regional declines in stream invertebrate diversity. Experimental studies have identified that pesticides can have strong and persistent negative effects on aquatic ecosystems. These effects may occur at concentrations orders of magnitude lower than laboratory toxicity studies predict. Synergism among stressors is one explanation for observed laboratory–field differences. However, the true effect of pesticides on stream invertebrates remains uncertain, given interactions between stressors and natural environmental conditions. We experimentally examined multiple‐stressor effects on stream invertebrate assemblages and leaf litter breakdown using 24 independent ~900 L re‐circulating outdoor mesocosms in a semi‐orthogonal design. Two pulses of the pesticide malathion (C10H19O6PS2) were delivered at low and high concentrations (Pulse 1: low at 0.1 and high at 1 µg/L; Pulse 2: at 2.5 and 25 µg/L). These were crossed with a treatment combining stressors commonly associated with agricultural development; nitrogen, phosphorus and sediment (kaolinite). Malathion degradation was rapid (<24 hr half‐life) in all treatments, likely because of photolysis, hydrolysis, the presence of biofilms and sorptive processes. There were significant differences in invertebrate assemblages between treatments, where malathion contributed to 48% and 87% of deviance during Pulse 1 and 2 respectively. Malathion had strong negative effects during Pulse 2, with declines occurring between control and high pesticide treatments in Ephemeroptera, Plecoptera and Trichoptera abundances (Cohen's d = 3.08), invertebrate richness (d = 3.57) and total abundance (d = 3.31). Despite the dominant effects of malathion on invertebrates, agricultural stressors inhibited rates of leaf litter breakdown (p < 0.05), and weakly mitigated malathion toxicity in mesocosms (e.g. PERMANOVA, P ≈ 0.1). Malathion breakdown analysis indicated sediment addition reduced malathion concentrations through alkaline hydrolysis and sorption. Experimental assays on common taxa supported sediment‐malathion interactions resulted in antagonism. Synthesis and applications. Pesticide effects were not synergistic with the stressors tested here. Indeed, sensitivity‐dependent stressor antagonisms were observed, reinforcing a mechanistic understanding of stressor effects and interactions is important. Among aquatic stressors examined, malathion had dominant effects on invertebrate assemblages, despite rapid degradation. Our results suggest that pesticide effects may be underestimated within ecosystems, where pesticides can have severe community‐wide effects, but rapid pesticide breakdown and sorptive processes may conceal causal links.

Invertebrate responses to land use in tropical streams: discrimination of impacts enhanced by analysis of discrete areas

We identified influences of land-use disturbances on invertebrate assemblages in streams draining eight areas of the Great Barrier Reef catchment in tropical Australia (~15.7–22°S), a region of high biodiversity. We used distance-based linear modelling (DistLM) to analyse assemblage data (103 taxa), richness and the SIGNAL2 taxon sensitivity index. DistLM of assemblages explained ~40% of variation across all samples and 7–54% of variation in individual areas. DistLM of richness and SIGNAL2 explained respectively 19–81 and 26–95% of variation. Explanatory variables were land use (especially cropping and grazing v. forest), riparian width, instream habitat, climate (drier south) and water quality (conductivity greater in south). Local impacts of activities such as mining were evident in models of individual areas. A detailed comparison of streams with contrasting riparian management demonstrated a 25% loss of richness, but no change in SIGNAL2 score. Accounting for local environmental gradients and using measures appropriate to the type of disturbance improved identification of impacts, and could form a framework for future regional monitoring of stream ecological condition. The impacts identified may be mitigated by remediation such as riparian rehabilitation, although management at catchment scales is required to be effective.

Modelling outperforms typologies for establishing reference conditions of boreal lake and stream invertebrate assemblages

Continuous modelling and discrete classification (aka typology) are two approaches commonly used to partition natural, spatial variability, and ultimately gauge anthropogenic effects on biodiversity loss and other valued ecosystem services. Using benthic invertebrate assemblages of boreal lakes and streams, we tested the efficacy of continuous modelling and discrete classification for partitioning natural variability of sites judged to be in reference condition. We anticipated that species distributions and assemblage composition would be more accurately predicted by models in general and specifically that models based on suites of predictor variables would outperform models based on a limited number of variables. Furthermore, we predicted that more flexible typologies would perform better than approaches using sets of mandatory categorical variables. Our results showed that models were more accurate at estimating species distributions and assemblage composition than typologies. Furthermore, models calibrated with only a few typology based variables were as accurate as full models, indicating that the main environmental gradients were captured by the classification variables used in our study. Continuous modelling also had lower incidences of false positives (<7%) compared to typological approaches (3.8–56%), i.e. a lower frequency of classifying reference sites as possibly impaired. The findings that continuous modelling outperformed discrete classification and that the latter had substantially higher frequencies of false positives is somewhat disconcerting given the relatively widespread use of typologies in bioassessment and management. Misclassification results in the unnecessary use of resources to re-classify sites, or more seriously implementation of unwarranted measures of rehabilitation.

Response of benthic invertebrate communities to a land use gradient in tropical highland streams in Nigeria

Benthic invertebrate communities have been shown to respond to habitat degradation as a result of land use changes. Although these changes have been well documented in temperate regions, their effects in the tropics have been poorly documented particularly where land use activities differ markedly (e.g., tea, maize and plantations). A survey 55 1st and 2nd order highland tropical streams, across four land use categories, ranging from continuous tropical montane rain forest to intensive crops and pasture. Streams were sampled in the tropical dry season (October–March) for physico-chemical parameters and components of the biological community, (i.e., fine particulate organic matter [FPOM], coarse particulate organic matter [CPOM], algae and benthic invertebrates). Catchment riparian conditions and human water use activities were used to generate a multivariate land use intensity gradient score. Temperatures in pasture streams were warmer than forest streams (up to 25oC) and dissolved oxygen levels frequently low (15–79%). However, physico-chemical conditions did not show any clear patterns across land uses categories. In contrast, benthic invertebrate communities showed strong response with the highest taxonomic diversity in continuous forest streams (mean 20 taxa) and the lowest in streams with intensive crops (e.g., cabbage crops, mean 8 taxa). Marked changes were found in invertebrate communities with several taxa occurring primarily in forested streams (e.g., the mayflies Heptageniidae and Oligoneuriidae and brachyuran crabs). Tropical land use farming (e.g., tea, maize, cabbage) have significant impacts on the benthic invertebrate assemblages of highland streams in Nigeria. However, not all crop and plantation streams had highly impacted communities because some have wider riparian buffer zones. This study further highlight the importance of conservation and management of montane forest fragments in these regionsKeywords: Tropical, Nigeria, highland, benthic invertebrates, land use, degradation

Thermal and hydrologic responses to climate change predict marked alterations in boreal stream invertebrate assemblages.

Air temperature at the northernmost latitudes is predicted to increase steeply and precipitation to become more variable by the end of the 21st century, resulting in altered thermal and hydrological regimes. We applied five climate scenarios to predict the future (2070-2100) benthic macroinvertebrate assemblages at 239 near-pristine sites across Finland (ca. 1200km latitudinal span). We used a multitaxon distribution model with air temperature and modeled daily flow as predictors. As expected, projected air temperature increased the most in northernmost Finland. Predicted taxonomic richness also increased the most in northern Finland, congruent with the predicted northwards shift of many species' distributions. Compositional changes were predicted to be high even without changes in richness, suggesting that species replacement may be the main mechanism causing climate-induced changes in macroinvertebrate assemblages. Northern streams were predicted to lose much of the seasonality of their flow regimes, causing potentially marked changes in stream benthic assemblages. Sites with the highest loss of seasonality were predicted to support future assemblages that deviate most in compositional similarity from the present-day assemblages. Macroinvertebrate assemblages were also predicted to change more in headwaters than in larger streams, as headwaters were particularly sensitive to changes in flow patterns. Our results emphasize the importance of focusing protection and mitigation on headwater streams with high-flow seasonality because of their vulnerability to climate change.

Dissolved-oxygen, current and temperature preferences of stream invertebrates estimated from field distributions: application to assemblage responses to drought

Preferences of stream invertebrate families in south-eastern Australia for dissolved oxygen (‘hydroaerophily’), current velocity (rheophily) and temperature (‘thermophily’) were estimated from occurrences in an extensive multi-year dataset covering New South Wales and the Australian Capital Territory, and tested with another dataset covering the entire Murray–Darling Basin (MDB). As hypothesised, all three traits were strongly associated with long-term climate (annual precipitation and average temperature), whereas taxonomic richness had only weak associations with these climatic variables. Moreover, average hydroaerophily and rheophily of families in samples from the MDB decreased between 2004 and 2010 during the intense ‘Millennium Drought’, while average thermophily rose. These changes were reversed during 2010–2012 after the drought broke. Hydroaerophily, rheophily and thermophily were correlated with one another and with respiration mode, suggesting a trait syndrome related to adaptation to rhithron versus potamon and lentic environments. Hydroaerophily, rheophily and thermophily have the capacity to identify species that are vulnerable to future climatic warming and drying. These traits are also correlated with diet, indicating potential consequences for ecosystem processes of climate-related shifts in the composition of stream invertebrate assemblages.

Aquatic macroinvertebrate assemblages are affected by insecticide applications on the Argentine Pampas

Agriculture intensification in Argentina has increased agrochemicals consumption in the last decades and might represent an environmental risk for adjacent water bodies. The objective of the present work was to assess the effect of land use on water quality and invertebrate assemblages in the Argentine Pampas streams. Eight streams were sampled on 4 occasions during the 2013/14 growing season. Three streams are located within a biosphere reserve, two drain basins with extensive livestock fields, and three run through intensively cultivated plots; one of them contained a 30m wide uncultivated grass-covered strip between the crop and the stream. Macroinvertebrates were sampled from emergent vegetation by means of a D-net with a 500µm pore size, and 30cm diameter.Higher nutrient concentrations were measured in the agricultural streams. Endosulfan was measured in sediments of the agricultural streams, concentrations being significantly lower in the stream with the buffer strip. Invertebrate assemblages in the cropped streams were significantly different from those in the livestock and reserve streams, those in the latter not being different from each other. Ampullaridae (Pomacea canaliculata) and Planorbidae (Biomophalaria peregrina) were the taxa best represented in the agricultural streams. Hyalellidae (Hyalella curvispina), Zygoptera and Planorbidae (B. peregrina) were the taxa best represented in the reserve and livestock streams. Present evidence suggests that the observed differences in the invertebrate composition in the agricultural streams were related with the impact of agrochemicals and that buffer strips represent a useful attenuation practice. Cattle breeding on natural pastures represented a land use with low impact on the invertebrate assemblages.

Arsenic in stream waters is bioaccumulated but neither biomagnified through food webs nor biodispersed to land

Human activities such as mining have contributed substantially to the increase of metals in aquatic environments worldwide. These metals are bioaccumulated by aquatic organisms and can be biomagnified along trophic webs. The dispersal of contaminants from water to land has been little investigated, even though most aquatic invertebrates in streams have aerial stages. We used field and laboratory approaches to investigate the effects of arsenic pollution on stream invertebrate assemblages, and its bioaccumulation, biomagnification and trophic transfer from aquatic to terrestrial environments by emergent insects. We conducted the study in an arsenic-impacted stream (40μgL–1 As at the most polluted site) and a reference stream (0.3μgL–1 As). Invertebrate abundance and richness were lowest at the most impacted site. Arsenic in biofilm and in invertebrates increased with the arsenic content in the water. The highest arsenic accumulators were bryophytes (1760μgg–1), followed by the biofilm (449μgg–1) and shredder invertebrates (313μgg–1); predators had the lowest arsenic concentration. Insects emerging from water and spiders along streambanks sampled from the reference and the impacted stream did not differ in their body arsenic concentrations. In the laboratory, the shredder Sericostoma vittatum had reduced feeding rates when exposed to water from the impacted stream in comparison with the reference stream (15.6 vs. 19.0mg leaves mg body mass–1 day–1; p<0.05), but they grew faster in the polluted water (0.16±0.04% day–1vs. 0.05±0.01% day–1, p<0.05). S. vittatum exposed to contaminated stream water accumulated arsenic from food, not through contact with water. We concluded that although arsenic is bioaccumulated, mainly by food ingestion, it is not biomagnified through food webs and is not transported from the aquatic to terrestrial environment when insects leave the stream water.

Decomposing multiple pressure effects on invertebrate assemblages of boreal streams

Land use often results in multiple pressures affecting the structure and function of aquatic ecosystems. Understanding how pressures interact to affect the biology of aquatic ecosystems is therefore a major challenge for freshwater management. Using a field survey approach, we studied individual and combined effects of impacts arising from agricultural land use and alteration of hydrology and geomorphology (HYMO) on benthic invertebrate assemblages in boreal streams. Variation partitioning of species and trait composition to pressures characterizing agriculture and HYMO revealed significant joint effects on the biota. Changes in species composition were significantly and uniquely related to agricultural pressures, whilst the variance component characterizing HYMO effects was not significant, confounding separation of unique pressure effects. In line with our predictions, the effects of HYMO on species and trait composition were largely negative. However, in contrast to predictions, ranking pressure variables showed that agricultural impacts explained more of the variability in species composition than HYMO impacts. Disturbance of riparian habitats was a strong predictor of shifts in species and trait composition. Interestingly, community responses were less pronounced at sites affected by both loss of riparian integrity and elevated nutrients, suggesting that HYMO effects were mitigated by moderate levels of elevated nutrients. Collectively, our results showed ecologically realistic, impact-specific changes on biodiversity of riverine environments. This knowledge allows managers to rank the importance of individual and combined pressure impacts when designing rehabilitation strategies.

Effect of agrochemicals on macroinvertebrate assemblages in Pampasic streams, Buenos Aires, Argentina

Fil: Solis, Marina. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - La Plata. Instituto de Limnologia Dr. Raul A. Ringuelet. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Limnologia; Argentina

Effects of urbanization on stream benthic invertebrate communities in Central Amazon

Urbanization and its physical and chemical effects on aquatic environments influence invertebrate communities negatively. Yet, it is not clear how urbanization affects inter-annual variation of invertebrate assemblages in streams. We 1) evaluated urbanization effects on the ecological conditions (biotic and abiotic) of streams in Manaus and 2) analyzed invertebrate community variation over time (between 2003 and 2010). Data on abiotic variables and invertebrates from 2003 were obtained from a previous study. In 2010 we sampled abiotic variables and invertebrate communities in the same low-order urban streams sampled in 2003 (n=40). We recorded high values of total nitrogen, total phosphorous, deforestation, total impervious area (TIA), water temperature, pH, and electrical conductivity in the most urbanized streams, as compared to the least-impacted ones. In contrast, the least-impacted streams had high dissolved oxygen concentrations. Water quality was poorer in 2010 than in 2003: oxygen concentration was lower and total nitrogen, total phosphorous, deforestation, and TIA significantly higher in 2010. We recorded higher inter-annual variation of abiotic variables in the most-impacted streams as compared to the least-impacted streams. EPT (%, Ephemeroptera, Plecoptera, and Trichoptera) and richness metrics decreased with urbanization. On the other hand, % OP (percent of Oligochaeta and Psychodidae) increased with urbanization. Observed and EPT richness and% OP increased between 2003 and 2010. On the other hand, rarefied richness decreased between years. Increases of observed and EPT richness between 2003 and 2010 were related to low inter-annual variability in streams conditions; however, differences of% OP and rarefied richness were not related to inter-annual variability in environmental conditions. The degree of urbanization did not explain the magnitude of the within-stream difference of invertebrate communities between 2003 and 2010. The increased effects of urbanization represented by the abiotic variables sampled and the reduction of invertebrate richness and increased dominance of tolerant taxa indicate that public policy is not enough to protect or mitigate human impacts on the urban water systems under study.

Land use effect on invertebrate assemblages in Pampasic streams (Buenos Aires, Argentina).

Agriculture and livestock may contribute to water quality degradation in adjacent waterbodies and produce changes in the resident invertebrate composition. The objective of the present study was to assess land use effects on the stream invertebrate assemblages in rural areas of the Argentine Pampa. The four sampling events were performed at six sites in four streams of the Pampa plain; two streams were sampled inside a biosphere reserve, and another one was surrounded by extensive livestock fields. The fourth stream was sampled at three sites; the upstream site was adjacent to agricultural plots, the following site was adjacent to an intensive livestock plot and the downstream site was adjacent to extensive breeding cattle plots. Higher pesticide concentrations were found at the site adjacent to agricultural plots and higher nutrient concentrations at the sites adjacent to agricultural and intensive breeding cattle plots. The invertebrate fauna were also different at these sites. Multivariate analysis showed a relationship between nutrient concentrations and taxonomic composition. Amphipoda (Hyalella curvispina) was the dominant group in the reserve and extensive breeding cattle sites, but was not present in the agricultural site. Also, Chironomidae were absent from the agricultural site while present at other sites. Gasteropoda (Biomphalaria peregrina), Zygoptera, and Hirudinea were dominant at the most impacted agricultural and intensive breeding cattle sites.

Storm-event-transport of urban-use pesticides to streams likely impairs invertebrate assemblages.

Insecticide use in urban areas results in the detection of these compounds in streams following stormwater runoff at concentrations likely to cause toxicity for stream invertebrates. In this 2013 study, stormwater runoff and streambed sediments were analyzed for 91 pesticides dissolved in water and 118 pesticides on sediment. Detections included 33 pesticides, including insecticides, fungicides, herbicides, degradates, and a synergist. Patterns in pesticide occurrence reveal transport of dissolved and sediment-bound pesticides, including pyrethroids, from upland areas through stormwater outfalls to receiving streams. Nearly all streams contained at least one insecticide at levels exceeding an aquatic-life benchmark, most often for bifenthrin and (or) fipronil. Multiple U.S. EPA benchmark or criterion exceedances occurred in 40 % of urban streams sampled. Bed sediment concentrations of bifenthrin were highly correlated (p < 0.001) with benthic invertebrate assemblages. Non-insects and tolerant invertebrates such as amphipods, flatworms, nematodes, and oligochaetes dominated streams with relatively high concentrations of bifenthrin in bed sediments, whereas insects, sensitive invertebrates, and mayflies were much more abundant at sites with no or low bifenthrin concentrations. The abundance of sensitive invertebrates, % EPT, and select mayfly taxa were strongly negatively correlated with organic-carbon normalized bifenthrin concentrations in streambed sediments. Our findings from western Clackamas County, Oregon (USA), expand upon previous research demonstrating the transport of pesticides from urban landscapes and linking impaired benthic invertebrate assemblages in urban streams with exposure to pyrethroid insecticides.Electronic supplementary materialThe online version of this article (doi:10.1007/s10661-016-5215-5) contains supplementary material, which is available to authorized users.