Responses Of Benthic Invertebrates Research Articles

Benthic macroinvertebrate response to estuarine emergent marsh restoration across a delta-wide environmental gradient

Benthic invertebrates play vital roles in estuarine ecosystems, but like other taxa they have been excluded from former marshlands by diking and land use conversion. Dike removal is one way of restoring marsh, but the response of benthic invertebrates has been little studied. Also understudied is variation in benthic invertebrate communities across entire deltas, particularly in the Pacific Northwest of North America where deltas receive high flows and sediment loads for their size. Our goals were to evaluate invertebrate response to large-scale dike removal on the Nisqually River Delta in Puget Sound, Washington, U.S.A., characterize delta-wide invertebrate community variation, and relate invertebrate response and spatial variation to environmental conditions. We sampled invertebrates annually from one year before to three years after dike removal in restoring marsh, previously restored marsh, undisturbed reference marsh, and adjacent tidal flats. Marine taxa immediately colonized the area recently restored to tidal inundation and population size grew exponentially thereafter for several of them. Community composition and diversity recovered completely, and density and biomass were approaching recovery three years later. Invertebrate communities converged between restoring and pre-existing marsh (previously restored and reference), suggesting an influence of reestablished connectivity. Just offshore from the dike line, invertebrates declined one year after dike removal but then rebounded indicating resilience to short-term disturbance. Dike removal effects were not detected farther offshore. Near the offshore edge of the delta, invertebrate biomass and body size were greater than elsewhere and a diverse assemblage of crustaceans, polychaetes, and bivalves was present. Farther inshore, tidal flats were dominated by a few species of small-bodied polychaetes and had higher density but lower biomass and diversity. Facultative detritivores, which can also filter feed, were the dominant feeding guild everywhere on the tidal flats. Density, biomass, diversity, and community composition on the marsh were more similar to the inner than outer tidal flats. Environmental variables most associated with invertebrate community variation were elevation, salinity, and sediment grain size and organic content. Our results are relevant to assessing performance and setting expectations for future restorations and have broad implications for the role of benthic invertebrates in estuarine ecosystems.

Impact of Fine Sediment on Benthic Macroinvertebrates Communities of Freshwater Ecosystem: A Review

The freshwater environment in Ethiopia is exposed to severe human influence because of fast population growth and other factors. Anthropogenic activities in developing countries such as river regulation and pollution have a potentially negative cumulative impact on water quantity and quality of the rivers and wetlands, hence negatively impacting benthic invertebrates and fishes. This review aims to identify the impacts of fine sediment on the community of benthic macroinvertebrates, and freshwater food webs, and to assess the response of benthic invertebrates to fine sediment pollution. Literature review was used as a methodology. Fine segment load on the freshwater ecosystem from both point and nonpoint sources may directly/indirectly alter the macroinvertebrate communities. Organic and inorganic contaminants as well as other sediment variables (sediment grain size, total organic carbon, nutrients, etc.) were affecting the community composition of benthic invertebrates. However, habitat features like the number of supplements or the silt grain measure clarify the variation in macroinvertebrate indices and metrics. The impact of metals and, to a lesser extent, organic contaminants may also be significant. Benthic macroinvertebrates are commonly used indicators of river ecological conditions that can be adversely affected by fine sediment loads. Sedimentation can change the suitability of the substrate for some taxa, increase macroinvertebrate drift, and affect respiration and feeding. To conclude, excessive fine sediment severely alters the structure and function of macroinvertebrates. At the regional and national levels, different governmental and non-governmental organizations, research institutions, and policy makers are recommended to take responsibility for reducing sediment discharge to the freshwater ecosystem by applying different conservation measures of benthic macroinvertebrates.

Effects of sediment and water column acidification on growth, survival, burrowing behaviour, and GABAA receptor function of benthic invertebrates

In coastal regions, sediment-dwelling animals are exposed to a high degree of variability in seawater and sediment pH and pH is expected to decline due to anthropogenic effects. The impacts of 6-week exposure to reduced-pH seawater on length, weight, and survival of two species of molluscs that inhabit mudflats, juvenile soft-shell clams (Mya arenaria) and adult mud snails (Tritia obsoleta), were examined in two laboratory trials (2017 and 2018). The interactive effects of this prior exposure to water column acidification and subsequent sediment acidification on burrowing behaviour were then investigated for these mollusc species and adults of the amphipod Corophium volutator. In a separate experiment, the potential involvement of GABAA receptors in changes in burrowing behaviour in reduced-pH conditions was tested by exposing three species: C. volutator, T. obsoleta, and the Baltic clam Limecola balthica to sediment acidification and the neuroinhibitor gabazine. Reduced-pH water conditions only decreased the shell length of T. obsoleta in 2017 while all other morphometric metrics were not significantly impacted for this species in either year or for M. arenaria. The burrowing of T. obsoleta was reduced by 13% in acidified sediments in one of the two years but not by prior exposure to water column acidification. The burrowing of M. arenaria was not affected by either factor. The burrowing of C. volutator was impacted by the interaction of water column exposure and sediment acidification in 2017 with the acidified water, control sediment treatment having 14% higher burrowing then the remaining treatment combinations. In 2018, C. volutator burrowing was reduced in acidified sediment by 30%. The presence of gabazine only had an interactive effect on the burrowing of one species, C. volutator. The presence of gabazine increased the proportion of C. volutator individuals burrowed in the acidified water treatment by almost 30%, suggesting that GABAA neuroreceptors are involved in the mechanism for the impact of sediment acidification on burrowing in this species. The results of our experiments indicate that there is taxonomic variation in species' responses of benthic invertebrates to ocean and sediment acidification with respect to growth, survival, and burrowing behaviour.

Effects of semidiurnal water column acidification and sediment presence on growth and survival of the bivalve Mya arenaria

In coastal environments, water column pH is affected by a variety of factors that result in lower and more variable pH in comparison to the open ocean. Consequently, it is critical to integrate variability in pH into laboratory experiments to better predict the response of coastal organisms to ocean acidification. For infaunal organisms, sediment can provide refuge from the water column conditions especially in coastal environments. As such, understanding how both water column conditions and the potential buffering abilities of sediment interact can provide insight into how infaunal organisms may respond to future oceanic conditions. Effects of pH variability on juvenile soft-shell clams (Mya arenaria; 2–11 mm in shell length), an ecologically and economically important species in the Bay of Fundy, Canada, were examined in a laboratory experiment. We manipulated pH through the addition of CO2 to seawater and exposed M. arenaria to three water treatments, no CO2 addition (mean ± sd; pH = 7.95 ± 0.06), semidiurnal intermittent CO2 addition (“on” pH =7.70 ± 0.13, “off” pH = 7.90 ± 0.11), and constant CO2 addition (pH = 7.73 ± 0.13). We found that M. arenaria final shell length, three mass metrics, and survival were negatively impacted by the constant CO2 addition treatment. Growth of juvenile M. arenaria only occurred in the presence of sediment, indicating the importance of sediment to M. arenaria, although sediment did not buffer the effects of constant CO2 addition. In the presence of sediment, the semidiurnal intermittent CO2 addition treatment did not negatively impact the growth of M. arenaria, indicating that it provided the clams with a recovery period. The similar growth rates of juvenile M. arenaria burrowed in sediment in the intermittent CO2 addition and control treatments suggests that M. arenaria may not be as negatively affected by future oceanic conditions as anticipated. This study demonstrated that pH variability can alter the response of benthic invertebrates to CO2 addition and thus this type of approach should be used to study other species of invertebrates.

Drainage‐induced browning causes both loss and change of benthic biodiversity in headwater streams

AbstractConcentrations of dissolved organic carbon (DOC) have increased over the past few decades, causing freshwater browning. Impacts of browning on biodiversity have been little studied, despite many of the individual stressors associated with browning being known to control freshwater communities. We explored the responses of benthic invertebrates along a wide gradient of DOC concentrations (3.6–27 mg L−1) in 63 boreal streams variously impacted by peatland drainage or peat production. DOC was a prime determinant of macroinvertebrate diversity and abundance, with the strongest negative response in algal scrapers. Threshold indicator taxa analysis indicated an abrupt community change at 12–13 mg DOC L−1, with only four taxa increasing, while 13 taxa decreased along the gradient. Our findings of both a gradual loss and abrupt change of biodiversity along a browning gradient provide a benchmark against which changes to stream biodiversity relative to the predicted browning trend can be gauged.

Long‐term responses of benthic invertebrates to rotenone treatment

AbstractBiological invasions are regarded as one of the largest threats to native biodiversity. The eradication of alien invasive fish or parasites by culling of hosts is a controversial conservation strategy, particularly when using indiscriminate methods involving whole ecosystem collateral damage. While short‐term effects are abundantly documented, long‐term surveys needed to detect potential wider ecosystem effects are scarce. Here, we report a five‐year study on effects of the piscicide rotenone on invertebrate communities from a Norwegian watercourse using a Before‐After‐Control‐Impact design. Kick‐net samples of benthic invertebrates were collected from three lentic sampling stations and two lotic stations two to four times per year in both a treated and nearby control catchment. In general, only relatively minor short‐term effects, measured as temporal beta‐diversity of benthic invertebrates, were observed in lentic and lotic locations following rotenone treatment. However, the lotic fauna was severely negatively affected following a period of long‐term rotenone exposure from a late autumn treated upstream lake where rotenone degradation was slow, likely due to low temperatures. Species turnover co‐varied markedly between control and treatment locations, indicating that natural environmental variation override effects of rotenone treatment. Likewise, the abundance of invertebrate taxa varied considerably both over time and between control and treatment locations. Our study indicates minor short‐term (i.e., <1 month) or long‐term (i.e., 4 years) effects of rotenone treatment on benthic invertebrates, but severe effects on the lotic fauna 8 months after treatment following long‐term low‐dose exposure. This suggests that exposure time is of high importance. The findings from the current study therefore highlight both the importance of long‐term monitoring including control sites for the study of rotenone treatment effects on benthic invertebrates as well as the importance of minimizing exposure time.

Methods of sampling benthic invertebrates in lotic habitats: a spatial and temporal evaluation

Abstract Aim We compared the effectiveness of two sampling devices, the Surber sampler and the D-frame net, commonly used in the analysis of invertebrate fauna structure in biomonitoring programs. These programs use the response of benthic invertebrates to assess changes in aquatic ecosystems because they respond quickly to spatial and temporal variations. However, the lack of consensus on the best method of sampling the fauna may reduce the quality of these studies. Methods We evaluated both devices in four structurally different reaches of streams, two in places with preserved riparian vegetation and two occurring in places with many anthropic disturbances. We repeated the analysis at the dry season of two consecutive years. Results The two samplers were equally effective in analyzing the benthic fauna and sensitive enough to identify spatial and temporal variation in the structure of this fauna, influenced by the presence or absence of riparian vegetation, by the position of the reach with this vegetation (upstream or downstream of the reach without vegetation) and the characteristics of the substrate. Conclusions The analyzed fauna structure was similar for the two samplers, but we consider the use of Surber more advantageous and effective because it collects a smaller number of individuals, reducing the time of processing and identifying in the laboratory, and allows a better definition of the area sampled.

Can coir increase native biodiversity and reduce colonisation of non-indigenous species in eco-engineered rock pools?

The expansion of built infrastructure in the marine environment threatens natural ecological communities at local and regional scales. An increasing interest in incorporating heterogeneity that is reflective of natural rocky shores into artificial structures through ecological engineering seeks to mitigate negative impacts. The addition of complex surfaces and novel habitats, such as water-retaining features, has been particularly successful at increasing biodiversity of marine infrastructures to date. Importantly, key habitat-forming groups, such as the complex turfing algae Corallina officinalis found on natural shores and their associated assemblages are still lacking from these eco-engineered features. Furthermore, whether observed biodiversity increases from eco-engineering are due to native or non-indigenous species remains largely unknown. Here, we investigated whether adding small-scale complexity (artificial turf) to artificial rock-pools (‘flowerpots’) on urban seawalls enhanced their effectiveness to increase native biodiversity. Responses of benthic invertebrates, algae, epifauna and fish in flowerpots with and without artificial turf (coir) were quantified. Contrary to existing literature, which reports an increase in biodiversity with an increase in complexity, no consistent effect of coir was seen on benthic, epifaunal or fish assemblages. Native species consistently occupied more than 95% of space in flowerpots while the proportion of non-indigenous species in flowerpots was small (<75% of the assemblage) regardless of treatment, and decreased over time. This result is promising, but warrants further investigation to determine if these trends reflect seasonal patterns or if non-indigenous species colonise early, but are replaced over time by native species. These are important considerations when planning large-scale deployments of eco-engineering features on seawalls to ensure that native species are targeted without increasing opportunities for non-indigenous species.

Responses of benthic invertebrates to repeated hydropeaking in semi‐natural flume simulations

AbstractWe assessed the effects of repeated hydropeaking over five consecutive days on the zoobenthic community by manipulating discharge in five experimental flumes directly fed by an Alpine stream. Treatment consisted of two different hydropeaking intensities which increased discharge two‐ and threefold from baseflow and lasted for 5 h each day. The resulting sudden changes in flow directly affected benthic invertebrates through the induction of catastrophic drift as a direct response to high (hydropeaking) flow conditions, and of behavioural drift in the low, baseflow conditions (at the conclusion of each hydropeaking event) for some taxa. We observed: an initial strong peak in catastrophic drift within the first 3 min of increased discharge, followed by a decreased drift rate throughout the following hours of the experiment; a strong response in the first day of the simulation, with successive days having substantially decreased drift; taxa‐specific responses over the short and long‐time scales: least‐resistant taxa (i.e. Baetis spp.) were removed via the initial catastrophic drift, while more resistant taxa began to behaviourally drift later in each hydropeak (i.e. Simuliidae). Peaks in drift rates corresponded to the initial removal of CPOM which, during low flows, provided habitat and food resource for a high number of individuals and taxa. Quantification of drift responses over time scales larger than the single hydropeaking event underlines the relevance of the typical intermittency and repetition frequency as a stress factor for benthic communities, and that the response to hydropeaking is closely related to the time elapsed since the last perturbation. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Colonization of formulated substrates of different composition by benthic macroinvertebrate community in an estuarine ecosystem: a case study of response of benthic invertebrates to substrate alteration

Colonization of formulated artificial substrate was investigated in a tropical estuarine ecosystem for six months to determine possible response of benthic macroinvertebrates to disturbance arising from substrate alteration. Five different formulated substrates which served as content for ten cages were used for this experiment. A total of 406 individuals comprising 18 macroinvertebrate species colonized the cages. In overall, cage 1 which is the control recorded the highest number of individuals and average number (8) of colonizing species at a time, while the least number (4) was observed in cage 3. Cages 2, 4, and 5 recorded average of five species each. In terms of number of individuals, cage 1 which is the control, had the highest number (153), followed by cage 2 which recorded 122 individuals. Cages 3, 4 and 5, recorded 41, 61 and 80 individuals respectively. Analysis of temporal variability in the number of species observed in the experimental cages shows that there was a progressive decrease in the number of colonizing species after the second month. Colonizing macroinvertebrate groups were not different from the known resident species in the estuarine lagoon. However, pattern of variation in the number of individuals of colonizing species were remarkably different. The assemblage recorded in this experiment was defined by the populations of two bivalve mollusc; Macoma cumana and Tellina nymphalis , two gastropod mollusc; Pachymelina aurita and Tympanotonus fuscatus and two crustacean arthropods; Clibanarius africanus and Penaeus notialis . Among the FFGs recorded, collector-filterers dominated in number of individuals and species. Nutrient concentrations of formulated substrate had strong effects on number of colonizing individuals and species.

Benthic Communities of Low-Order Streams Affected by Acid Mine Drainages: A Case Study from Central Europe

Only little attention has been paid to the impact of acid mine drainages (AMD) on aquatic ecosystems in Central Europe. In this study, we investigate the physico-chemical properties of low-order streams and the response of benthic invertebrates to AMD pollution in the Banská Štiavnica mining region (Slovakia). The studied streams showed typical signs of mine drainage pollution: higher conductivity, elevated iron, aluminum, zinc and copper loads and accumulations of ferric precipitates. Electric conductivity correlated strongly with most of the investigated elements (weighted mean absolute correlation = 0.95) and, therefore, can be recommended as a good proxy indicator for rapid AMD pollution assessments. The diversity and composition of invertebrate assemblages was related to water chemistry. Taxa richness decreased significantly along an AMD-intensity gradient. While moderately affected sites supported relatively rich assemblages, the harshest environmental conditions (pH &lt; 2.5) were typical for the presence of a limited number of very tolerant taxa, such as Oligochaeta and some Diptera (Limnophyes, Forcipomyiinae). The trophic guild structure correlated significantly with AMD chemistry, whereby predators completely disappeared under the most severe AMD conditions. We also provide a brief review of the AMD literature and outline the needs for future detailed studies involving functional descriptors of the impact of AMD on aquatic ecosystems.

Multiple drift responses of benthic invertebrates to interacting hydropeaking and thermopeaking waves

ABSTRACTSudden instream releases of hypolimnetic water from hydropower plants [i.e. hydropeaking (HP)] can cause abrupt temperature variations [i.e. thermopeaking (TP)], typically on a daily basis. The propagation of discharge and thermal waves is asynchronous, causing the benthic community to undergo two different but consecutive impacts. Invertebrates respond to sudden increases in discharge with catastrophic drift, and respond to sudden changes of temperature with behavioural drift. Owing to the time lag separating discharge and thermal wave peaks, catastrophic and behavioural drift can occur as distinct events. We conducted simulations in a set of open air flumes directly fed by an Alpine stream, and analysed drift induction in benthic invertebrates caused by a HP wave followed by a cold TP wave, and compared it with drift induced only by a cold TP wave. Drift propensity increased during HP and TP simulations, with a synergic effect: drift was higher when the TP wave followed the HP one. We also recorded a selective effect: some taxa did not respond to the alterations, some taxa responded to the discharge variations and to the thermal variations, or to the thermal variations alone. The most abundant taxa in benthos were Chironomidae and Baetidae, followed by Simuliidae. Simuliidae and Chironomidae were the most abundant drifting taxa. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Development of a new index for the assessment of hydromorphological alterations of the Mediterranean rocky shore

The assessment of the status of coastal waters is required by the European Water Framework Directive. The aim of the present study was to test the response of benthic invertebrates to hydromorphological (HM) alterations and to develop a new index for the assessment of HM alterations of the rocky shore, based on benthic invertebrates. Fifty samples were collected, 10 from pre-classified HM classes 1, 3, 5; 15 from class 2, and 5 from class 4. Seven HM variables describing habitat conditions were used to test the benthic invertebrate response and to develop the HM stressor gradient: material, texture, structure, belt length, sedimentation, water retention and artificially induced mobility. Abundance, some diversity (Shannon–Wiener, Simpson's and Evenness) and richness (number of taxa) metrics showed low correlation values ( r < 0.5) against HM variables and HM stressor gradient, indicating that tested metrics have limited value in assessment of the HM degradation impact on coastal benthic invertebrates. On the other hand, significant differences in the structure of benthic invertebrate assemblages among HM classes were observed (One-way ANOSIM global test r = 0.53, P < 0.0001). In the partial canonical correspondence analyses each of seven HM variables statistically significantly ( P < 0.05) explained individual portion of the benthic invertebrate taxa variability. HM indicative values ranging from 1 to 9 were defined for each of 229 taxa, according to its distribution along the five HM classes. HM indicative weights ( WHM) between 1 and 5 were defined according to the valences distribution among HM classes. HM indicative values, WHM and log 5 abundance classes were combined in a new Benthic Index for Rocky Shore (BIRS), using the weighted average approach. The combination of all three parameters in the BIRS showed a statistically significant ( P < 0.05) response of the new developed index to HM stressor gradient, with a high Pearson correlation coefficient ( r = 0.97). Further work has to be done in order to develop a WFD compliant method with five classes’ boundary values. Nevertheless, the new developed index has a good potential to contribute to existing coastal assessment systems. Especially, as impact of hydromorphological alterations on coastal communities was almost neglected so far, despite being one of the main threats to coastal water integrity.

Subsidy-stress and multiple-stressor effects along gradients of deposited fine sediment and dissolved nutrients in a regional set of streams and rivers

Summary 1. Stream managers need to understand relationships between multiple stressors and ecological responses. We examined responses of benthic invertebrates and algae along two land-use-related stressor gradients of concern in running waters. Our correlative study of the consequences of augmented deposited fine sediment and nutrient concentrations was conducted in a regional set of streams and rivers monitored by a water management authority in New Zealand and incorporated a wide range of catchment geologies and stream orders. 2. We used multiple linear regression analysis and an information-theoretic approach to select the best predictive models for our biological response variables by testing multiple competing hypotheses that include nonlinear subsidy-stress relationships and interactive effects between the two stressors. 3. Patterns consistent with a subsidy-stress response to increasing dissolved inorganic nitrogen concentration were found for the relative abundances of the common invertebrate genera Pycnocentrodes and Deleatidium and for the relative abundance of total individuals in the EPT orders (Ephemeroptera, Plecoptera, Trichoptera). 4. Fine sediment seemed the more pervasive stressor, apparently counteracting and overwhelming any initial subsidy effect of increased nutrients, and accounting for more of the variance in biological response variables. Relationships with high nutrient concentrations were weaker and modelled with less certainty, probably reflecting the indirect modes of action of nutrients compared to those underlying sediment effects. Nevertheless, in several cases, the models indicated that nutrients interacted synergistically with fine sediment, lending further weight to the conclusion that managers need to address both stressors to achieve the best outcomes.

Structural and functional responses of benthic invertebrates to imidacloprid in outdoor stream mesocosms

Structural and functional responses of a benthic macroinvertebrate assemblage to pulses of the insecticide imidacloprid were assessed in outdoor stream mesocosms. Imidacloprid pulses reduced invertebrate abundance and community diversity in imidacloprid-dosed streams compared to control streams. These results correlated well with effects of imidacloprid on leaf litter decomposition and feeding rates of Pteronarcys comstocki, a stonefly, in artificial streams. Reductions in oxygen consumption of stoneflies exposed to imidacloprid were also observed in laboratory experiments. Our findings suggest that leaf litter degradation and single species responses can be sensitive ecotoxicological endpoints that can be used as early warning indicators and biomonitoring tools for pesticide contamination. The data generated illustrates the value of mesocosm experiments in environmental assessment and how the consideration of functional and structural endpoints of natural communities together with in situ single species bioassays can improve the evaluation and prediction of pesticide effects on stream ecosystems.

Effects of re‐braiding measures on hydromorphology, floodplain vegetation, ground beetles and benthic invertebrates in mountain rivers

1 Medium-sized and large mountain rivers are among the most degraded river types in Europe and numerous river restoration projects are currently carried out to achieve ‘good ecological status’. Surprisingly little is known about the effects of river restoration measures on aquatic and terrestrial organisms. We investigated the effects of restoration on hydromorphology, floodplain vegetation, ground beetles and benthic invertebrates of Central European mountain rivers by comparing seven restored, multiple-channel sections with seven nearby non-restored, straight sections. 2 Floodplain mesohabitats and aquatic microhabitats were recorded along 20 transects per river section (200 m long). Samples of floodplain vegetation (444 samples), ground beetles (153) and benthic invertebrates (134) were taken per habitat type and section. Two hydromorphological metrics and 13 biotic metrics were calculated. 3 The number of floodplain mesohabitats was significantly higher in restored sections, but there was no significant effect on the number of aquatic microhabitats. Floodplain vegetation reacted most strongly to restoration, with more vegetation assemblages and higher number of species in restored sections. The number of ground beetle species also increased, but there was no effect on number of species or diversity of benthic invertebrates. 4 Habitat composition and assemblages were compared by cluster analysis. When using mesohabitat data, restored vs. non-restored sections clustered to separate groups, while the use of aquatic microhabitat data produced mixed groups. Floodplain vegetation data clustered in restored and non-restored sections. For benthic invertebrates, the restored and non-restored sections of each individual river were always clustered together. Ground beetle assemblages responded more strongly to restoration than benthic invertebrates but less than floodplain vegetation. 5 Synthesis and applications. River restoration measures which re-created multiple-channel patterns differ in their effect on floodplain vegetation, ground beetles and benthic invertebrates. The strong increase in the number of floodplain vegetation species is due to the creation of additional habitats, while riparian ground beetles react mainly to the increased availability of gravel bars. The lack of response of benthic invertebrates to restoration measures is due to the comparatively small changes in aquatic microhabitat composition. Our results indicate that floodplain habitats react more strongly to re-braiding as a restoration measure compared to in-stream habitats and that floodplain communities might be best suited to judge the immediate effects of restoration.

Assessing urban stormwater toxicity: methodology evolution from point observations to longitudinal profiling

The quality of aquatic habitat in a stormwater management facility located in Toronto, Ontario, was assessed by examining ecotoxicological responses of benthic invertebrates exposed to sediment and water from this system. Besides residential stormwater, the facility receives highway runoff contaminated with trace metals, polycyclic aromatic hydrocarbons (PAHs), and road salt. The combined flow passes through two extended detention ponds (in series) and a vegetated outlet channel. Toxicity of surficial sediment collected from 14 longitudinally arrayed locations was assessed based on 10 acute and chronic endpoints from laboratory tests with four benthic organisms. Greatest overall toxicity was observed in sediment from sites in the upstream pond, where mortality to amphipods and mayflies reached up to 100%. Downstream pond sediment was less toxic on average than the upstream pond sediment, but not the outlet channel sediment where untreated stormwater discharges provided additional sources of contamination. Macroinvertebrate communities in sediment cores were depauperate and dominated by oligochaetes and chironomids, with minimum densities and diversity at the deeper central pond sites. While sediment toxicity was associated with high concentrations of trace metals and high-molecular weight PAHs, benthic community impoverishment appeared related to high water column salinity.

Responses of benthic invertebrates in an experimental channel to artificial flushes

A large experimental channel was used to examine the responses of benthic invertebrate communities to artificial flushes. Two artificial flushes were done at a 20-day interval with a 2-fold difference in peak discharge and duration between them. The effects of the flushes on macroinvertebrates were monitored by comparing the abundance of individual taxa, taxon richness, diversity measures, and similarity indices. Taxon richness and abundances of invertebrates were drastically reduced by every flush. However, the diversity of invertebrates was not significantly reduced by the flushes, and the composition was similar before and after each flush. The fast recruitment of some taxa, having short life cycles, reduced the diversity of invertebrates in the interval between the two flushes. The flushes caused significant reductions in the abundance of epiphytes and fauna living in the streambed. The fauna more resistant to flushes were invertebrates that fasten their cases or retreats by silk threads to substrata. Taxa living in sediment under stones and having a sucking apparatus were also resistant to flushes.

Stream invertebrate community functional responses to deposited sediment

We investigated functional responses of benthic invertebrates to deposited sediment in four Missouri USA streams. In each stream, invertebrates were sampled along continuums of deposited sediment (particles <2 mm in size) from 0 to 100% surface cover in reaches of fairly homogeneous substrate composition, current velocity, and water depths. Correlations, graphical representations, and the cumulative response curves of feeding and habit groups provided strong empirical support for distinct community functional changes due to deposited sediment. Feeding groups were more sensitive to deposited sediment than habit groups. Densities of all the feeding groups decreased significantly with increasing deposited sediment, while relative densities of gatherers increased significantly. Taxa richness also decreased significantly for all the feeding groups except for the shredders. Increases in deposited sediment were related to significant density decreases for only the clingers and sprawlers in the habit group, resulting in significant increases in the relative densities of both burrowers and climbers. Clingers, sprawlers, and swimmers also showed significant decreases in taxa richness.

Influence of sediment quality on the responses of benthic invertebrates after treatment with the fungicide triphenyltin acetate

After decades of pollution, benthic communities in floodplain lake ecosystems are likely to be exposed to a diverse assortment of sediment-bound historical toxicants and nutrients as well as pulses of newly discharged or deposited toxicants. The aim of this study was therefore to analyze the effects of background sediment pollution on the responses of benthic invertebrates to an experimental toxic shock in a laboratory setting. Sediment from a relatively clean and a historically polluted floodplain lake located along the River Waal, a branch of the River Rhine, The Netherlands, was selected, and the fungicide triphenyltin acetate (TPT) was used as the acute stressor. Juvenile stages of the mayfly Ephoron virgo and the midge Chironomus riparius were chosen as test organisms because of their different response to sediment-bound toxicants and food quantity and quality. Our results demonstrated that the type of sediment had no effect on survival and growth of C. riparius when exposed to sediment-associated TPT and that E. virgo was more affected by sediment-associated TPT on clean sediment than on polluted sediment. For the mayfly, no cumulative response of the historical pollution and the recent toxic shock was observed. This observation is discussed in view of the variable content of organic matter, acting both as food and as sorbent, and leads to the hypothesis that a very strong sequestering of TPT in historically polluted sediment prevents expression of toxic effects.