Emergent Aquatic Insects Research Articles

Influences of the antidepressant fluoxetine on stream ecosystem function and aquatic insect emergence at environmentally realistic concentrations

Fluoxetine, a selective serotonin reuptake inhibitor (SSRI), is frequently detected in surface waters globally, yet the effects of SSRIs on ecological processes at environmentally realistic concentrations are not currently known. We used a controlled, replicated artificial stream experiment to expose biofilm, algal and stream insect communities to two different concentrations of fluoxetine: 20 ng/L (typical concentration detected in surface waters) and 20 µg/L (concentration shown to influence insect emergence and algal productivity). We quantified a range of community and ecosystem response metrics over the course of the 21d experiment including; algal biomass (chl-a), net ecosystem production (NEP), gross primary production (GPP), ecosystem respiration (ER) and invertebrate emergence. At 20 ng/L, fluoxetine significantly suppressed algal colonization on rocks, and reduced GPP after 13 days, but by day 21 chl-a, NEP and GPP did not differ between treatments and control. Fluoxetine increased ER on leaves where invertebrates were excluded, but had no effect on leaves accessible to invertebrates. Streams receiving 20 ng/L of fluoxetine had adult insects from the order Diptera emerge sooner and at a greater rate than control streams. Our results suggest that ecosystem function, including primary production and respiration, and invertebrate population dynamics are sensitive to SSRIs and that fluoxetine may alter these key processes concentrations found in the environment.

Artificial lighting at night alters aquatic-riparian invertebrate food webs.

Artificial lighting at night (ALAN) is a global phenomenon that can be detrimental to organisms at individual and population levels, yet potential consequences for communities and ecosystem functions are less resolved. Riparian systems may be particularly vulnerable to ALAN. We investigated the impacts of ALAN on invertebrate community composition and food web characteristics for linked aquatic-terrestrial ecosystems. We focused on food chain length (FCL), a central property of ecological communities that can influence their structure, function, and stability; and the contribution of aquatically derived energy (i.e., nutritional subsidies originating from stream periphyton). We collected terrestrial arthropods and emergent aquatic insects from a suite of stream and wetland sites in Columbus, Ohio, USA. Stable isotopes of carbon (13 C) and nitrogen (15 N) were used to infer FCL and contribution of aquatically derived energy. We found that moderate-to-high levels of ALAN altered invertebrate community composition, favoring primarily predators and detritivores. Impacts of ALAN, however, were very taxon specific as illustrated, for example, by the negative impact of ALAN on the abundance of orb-web spiders belonging to the families Tetragnathidae and Araneidae: key invertebrate riparian predators. Most notably, we observed decreases in both invertebrate FCL and reliance on aquatically derived energy under ALAN (although aquatic energetic contributions appeared to increase again at higher levels of ALAN), in addition to shifts in the timing of reciprocal nutritional subsidies. Our study demonstrates that ALAN can alter the flows of energy between aquatic and terrestrial systems, thereby representing an environmental perturbation that can cross ecosystem boundaries. Given projections for global increases in ALAN, both in terms of coverage and intensity, these results have broad implications for stream ecosystem structure and function.

Adverse effects of mosquito control using Bacillus thuringiensis var. israelensis: Reduced chironomid abundances in mesocosm, semi-field and field studies

The ecological consequences of mosquito control using the larvicide Bacillus thuringiensis israelensis (Bti) are still a matter of debate especially when it comes to adverse effects on non-target but susceptible non-biting midges (Chironomidae). Our work aimed to assess the effects of Bti applied in operational mosquito control rates on chironomid abundances in seasonal flooded freshwater wetlands. We assessed the invertebrate community alongside with aquatic insect emergence rates in studies with increasing ecotoxicological complexity, ranging from artificial mesocosms, over a semi-field approach using enclosures to natural conditions in field studies. Study sites represented different habitats (forest, meadow, floodplain) with regularly Bti treated and untreated temporal wetlands that are located in the Upper Rhine Valley, Germany. Larval chironomids were the most affected group of organism in the altered aquatic invertebrate communities of the Bti treated pond mesocosms. The larvae of the chironomid subfamilies Chironominae and Orthocladiinae were affected by Bti field concentrations while emergence rates of Tanypodinae did not change. The Bti treatment significantly reduced the targeted mosquitoes in the mesocosm and in the field studies. At the same time, however, the application of operational Bti field rates reduced overall chironomid emergence rates to about half of the control rates. The observed abundance reductions occurred independently of the ecological complexity in the study design in artificial mesocosms as well as realistic field conditions. The considerable reduction of the abundant non-target chironomids along with mosquitoes may subsequently lead to unwanted indirect negative effects for birds, bats and other aquatic organisms feeding on midges. Hence, large-scale applications of Bti for mosquito control in seasonal wetlands should be considered more carefully. This is of special importance when these wetlands are parts of national parks, nature reserves or Natura 2000 sites that were created for the protection of nature and environmental health.

Spatial and seasonal variability of emergent aquatic insects and nearshore spiders in a subtropical estuary

Variability in the density and distribution of adult aquatic insects is an important factor mediating aquatic-to-terrestrial nutritional subsidies in freshwater ecosystems, yet less is understood about insect-facilitated subsidy dynamics in estuaries. We surveyed emergent (i.e. adult) aquatic insects and nearshore orb-weaving spiders of the families Tetragnathidae and Araneidae in a subtropical estuary of Florida (USA). Emergent insect community composition varied seasonally and spatially; densities were lower at high- than low-salinity sites. At high-salinity sites, emergent insects exhibited lower dispersal ability and a higher prevalence of univoltinism than low- and mid-salinity assemblages. Orb-weaving spider density most strongly tracked emergent insect density rates at low- and mid-salinity sites. Tetragnatha body condition was 96% higher at high-salinity sites than at low-salinity sites. Our findings contribute to our understanding of aquatic insect communities in estuarine ecosystems and indicate that aquatic insects may provide important nutritional subsidies to riparian consumers despite their depressed abundance and diversity compared with freshwater ecosystems.

Wildfire and debris flows affect prey subsidies with implications for riparian and riverine predators

Ecosystems are connected through fluxes of nutrients, organic matter, and organisms. Disturbances that alter structure and function of one ecosystem may have consequences for other linked ecosystems. We investigated how wildfire and subsequent debris flows altered fluxes of invertebrates from tributaries in the Salmon River Basin, Idaho, USA. We compared fluxes of invertebrates downstream through drift and laterally via insect emergence from streams with varying disturbance histories (unburned, burned, and burned + debris flow) during two summers (3–4 years post fire and 2–3 years post debris flow). We observed that the combination of wildfire and debris flow increased the biomass export of invertebrates from tributaries to main-stem ecosystems 2–3 × compared to other streams. In contrast, aquatic insect emergence did not differ in magnitude among streams of different disturbance histories, but instead diverged in timing. Underwater surveys indicated trout in the main-stem river selected confluence habitats, with a tendency for stronger selection of confluences with burned streams. In a behavioral comparison between confluence and non-confluence habitats, rates of agonistic behavior were 4–6 × higher in confluence areas, indicating that confluences may be worth defending. Abundances of web-spinning spiders that depend on emerging insects did not vary with disturbance history in early-mid summer, but tended to be highest in riparian areas along burned streams by August. Because wildfire and debris flows are predicted to increase, our results elucidate potential pathways by which altered disturbance regimes may affect coupled aquatic-terrestrial ecosystems.

Community-level and phenological responses of emerging aquatic insects exposed to 3 neonicotinoid insecticides: An in situ wetland limnocorral approach.

Seasonal aquatic insect emergence represents a critical subsidy link between aquatic and terrestrial ecosystems. Early and late instar larvae developing in wetlands near neonicotinoid-treated cropland can be at risk of chronic insecticide exposure. In the present study, an in situ wetland limnocorral experiment compared emergent insect community responses to imidacloprid, clothianidin, and thiamethoxam. Twenty-one limnocorrals were dosed weekly for 9 wk to target peak nominal doses of 0.0, 0.05, or 0.5 μg/L, followed by a 6-wk recovery period. Thirty-nine aquatic insect taxa were recorded but 11 taxa groups made up 97% of the community composition. Principal response curves (PRCs) indicated that during the dosing period, community composition among the treatments resembled the controls. During the 6-wk recovery period, significant deviance was observed in the high imidacloprid treatment with similar trends in the clothianidin treatment, suggesting that community effects from neonicotinoid exposure can be delayed. Non-biting midges (Diptera: Chironomidae) and damselflies (Odonata: Zygoptera) emerged 18 to 25 d earlier than controls in the imidacloprid and clothianidin neonicotinoid treatments, with no effects from thiamethoxam treatments. These data suggest that phenology and subtle community effects can occur at measured neonicotinoid concentrations of 0.045 (imidacloprid) and 0.038 μg/L (clothianidin) under chronic repeated exposure conditions. Synchronization and community dynamics are critical to aquatic insects and consumers; thus, neonicotinoids may have broad implications for wetland ecosystem function. Environ Toxicol Chem 2018;37:2401-2412. © 2018 SETAC.

Seasonal and spatial variations of stream insect emergence in an intensive agricultural landscape

A growing amount of literature exists on reciprocal fluxes of matter and energy between ecosystems. Aquatic subsidies of winged aquatic insects can affect terrestrial ecosystems significantly, but this issue is rarely addressed in agroecosystems. By altering the production of benthic macroinvertebrates, agricultural practices could increase or decrease the strength of aquatic subsidies and subsequently the provision of several ecosystem services to agriculture. Effects of seasons and environmental variables on aquatic insect emergence were investigated in third-order agricultural streams in northwestern France. Most emerging dry mass (DM) of caught insects belonged to Trichoptera (56%), Chironomidae (25%) and Ephemeroptera (19%). We estimated that annual emerging dry mass of aquatic insects ranged between 1445 and 7374 mg/m2/y depending on the stream. Seasonal variations were taxon-specific, with Ephemeroptera emerging only in spring, Trichoptera emerging in spring and early summer, and Chironomidae emerging throughout the year. The percentage of watershed area covered by agriculture, ammonium concentration and hypoxia positively influenced emerging DM of Chironomidae but negatively influenced Ephemeroptera. Emerging DM of Trichoptera and Ephemeroptera increased significantly as water conductivity and temperature increased. Channel openness increased the emerging DM of all taxonomic groups, but Chironomidae were more abundant in narrow, incised streams. Assuming that the biomass of aquatic invertebrates ultimately disperse toward terrestrial habitats, nutrient accumulations on land near streams were estimated to reach 0.5–2.3 kg C ha−1 y−1, 0.1–0.5 kg N ha−1 y−1 and 0.005–0.03 kg P ha−1 y−1, depending on the stream. This suggests a significant flux of aquatic nutrients to agroecosystems and the need for future studies of its potential influence on the ecosystem services provided to agriculture.

Trophic transfer from aquatic to terrestrial ecosystems: a test of the biogeochemical niche hypothesis

AbstractMatter and energy flow across ecosystem boundaries. Transfers from terrestrial to aquatic ecosystems are frequent and have been widely studied, but the flow of matter from aquatic to terrestrial ecosystems is less known. Large numbers of midges emerge from some lakes in northern Iceland and fly to land. These lakes differ in their levels of eutrophication due to different intensities of geothermal warming and nutrient inputs. In the context of this material transfer from an aquatic to a terrestrial ecosystem, we investigated the relationships between the deposition of midges and the elemental composition and stoichiometry of organisms in low‐productivity terrestrial ecosystems. We analyzed several terrestrial food webs in northeastern Iceland with similar food web compositions of terrestrial arthropods but different inputs of midges and analyzed the stoichiometric composition of the different trophic groups. Elemental composition differed among trophic groups and taxa much more than within each trophic group or taxa across the midge deposition gradient. Specifically, the change in N concentration was significant in plants (up to 70% increase in the site with maximum input) but not in predators, which had a more homeostatic elemental composition. These results thus show (1) a significant movement of matter and nutrients from an aquatic to a terrestrial habitat via the emergence of aquatic insects and the deposition of insect carcasses, (2) a larger impact on the elemental composition of plants than arthropods, and (3) support for the biogeochemical niche hypothesis, which predicts that different species should have a specific elemental composition, stoichiometry, and allocation as a consequence of their particular metabolism, physiology, and structure.

Seasonality of dipteran-mediated methylmercury flux from ponds.

Methylmercury (MeHg) is an aquatic contaminant that can be transferred to terrestrial predators by emergent aquatic insects. We assessed the effects of month and pond permanence on dipteran-mediated MeHg flux (calculated as emergent dipteran biomass × dipteran MeHg concentration) in 10 experimental ponds. Emergent dipterans were collected weekly from permanent ponds with bluegill (Lepomis macrochirus; n = 5) and semipermanent ponds without fish (n = 5) over a 7-mo period (February-August, 2015). We detected a significant effect of month on MeHg flux from 6 dipteran taxa and aggregate MeHg flux, with the highest MeHg flux from herbivorous/detritivorous chironomid midges and predatory midges in March; biting midges, phantom midges and herbivorous/detritivorous orthoclad midges in April; and mosquitoes in August. Aggregate dipteran-mediated MeHg flux peaked in April and then declined throughout the remainder of the summer. We did not detect a significant main effect of pond permanence or a significant month × pond permanence interaction effect on MeHg flux for any of the taxa examined in the present study or for aggregate MeHg flux. Given their ubiquity in aquatic systems and their importance in food webs at the land-water interface, dipterans are important taxa that should not be overlooked as a part of the Hg cycle. Environ Toxicol Chem 2018;37:1846-1851. © 2018 SETAC.

DNA metabarcoding of nestling feces reveals provisioning of aquatic prey and resource partitioning among Neotropical migratory songbirds in a riparian habitat.

Riparian habitats are characterized by substantial flows of emergent aquatic insects that cross the stream-forest interface and provide an important source of prey for insectivorous birds. The increased availability of prey arising from aquatic subsidies attracts high densities of Neotropical migratory songbirds that are thought to exploit emergent aquatic insects as a nestling food resource; however, the prey preferences and diets of birds in these communities are only broadly understood. In this study, we utilized DNA metabarcoding to investigate the extent to which three syntopic species of migratory songbirds-Acadian Flycatcher, Louisiana Waterthrush, and Wood Thrush-breeding in Appalachian riparian habitats (Pennsylvania, USA) exploit and partition aquatic prey subsidies as a nestling food resource. Despite substantial differences in adult foraging strategies, nearly every nestling in this study consumed aquatic taxa, suggesting that aquatic subsidies are an important prey resource for Neotropical migrants nesting in riparian habitats. While our results revealed significant interspecific dietary niche divergence, the diets of Acadian Flycatcher and Wood Thrush nestlings were strikingly similar and exhibited significantly more overlap than expected. These results suggest that the dietary niches of Neotropical migrants with divergent foraging strategies may converge due to the opportunistic provisioning of non-limiting prey resources in riparian habitats. In addition to providing the first application of DNA metabarcoding to investigate diet in a community of Neotropical migrants, this study emphasizes the importance of aquatic subsidies in supporting breeding songbirds and improves our understanding of how anthropogenic disturbances to riparian habitats may negatively impact long-term avian conservation.

Seasonal bat activity related to insect emergence at three temperate lakes.

Knowledge of aquatic food resources entering terrestrial systems is important for food web studies and conservation planning. Bats, among other terrestrial consumers, often profit from aquatic insect emergence and their activity might be closely related to such events. However, there is a lack of studies which monitor bat activity simultaneously with aquatic insect emergence, especially from lakes. Thus, our aim was to understand the relationship between insect emergence and bat activity, and investigate whether there is a general spatial or seasonal pattern at lakeshores. We assessed whole‐night bat activity using acoustic monitoring and caught emerging and aerial flying insects at three different lakes through three seasons. We predicted that insect availability and seasonality explain the variation in bat activity, independent of the lake size and characteristics. Spatial (between lakes) differences of bat activity were stronger than temporal (seasonal) differences. Bat activity did not always correlate to insect emergence, probably because other factors, such as habitat characteristics, or bats’ energy requirements, play an important role as well. Aerial flying insects explained bat activity better than the emerged aquatic insects in the lake with lowest insect emergence. Bats were active throughout the night with some activity peaks, and the pattern of their activity also differed among lakes and seasons. Lakes are important habitats for bats, as they support diverse bat communities and activity throughout the night and the year when bats are active. Our study highlights that there are spatial and temporal differences in bat activity and its hourly nocturnal pattern, that should be considered when investigating aquatic–terrestrial interactions or designing conservation and monitoring plans.

Artificial Light at Night Affects Organism Flux across Ecosystem Boundaries and Drives Community Structure in the Recipient Ecosystem

Artificial light at night (ALAN) is a widespread alteration of the natural environment that can affect the functioning of ecosystems. ALAN can change the movement patterns of freshwater animals that move into the adjacent riparian and terrestrial ecosystems, but the implications for local riparian consumers that rely on these subsidies are still unexplored. We conducted a two-year field experiment to quantify changes of freshwater-terrestrial linkages by installing streetlights in a previously light-naive riparian area adjacent to an agricultural drainage ditch. We compared the abundance and community composition of emerging aquatic insects, flying insects, and ground-dwelling arthropods with an unlit control site. Comparisons were made within and between years using generalized least squares and a BACI design (Before-After Control-Impact). Aquatic insect emergence, the proportion of flying insects that were aquatic in origin, and the total abundance of flying insects all increased in the ALAN-illuminated area. The abundance of several night-active ground-dwelling predators (Pachygnatha clercki, Trochosa sp., Opiliones) increased under ALAN and their activity was extended into the day. Conversely, the abundance of nocturnal ground beetles (Carabidae) decreased under ALAN. The changes in composition of riparian predator and scavenger communities suggest that the increase in aquatic-to-terrestrial subsidy flux may cascade through the riparian food web. The work is among the first studies to experimentally manipulate ALAN using a large-scale field experiment, and provides evidence that ALAN can affect processes that link adjacent ecosystems. Given the large number of streetlights that are installed along shorelines of freshwater bodies throughout the globe, the effects could be widespread and represent an underestimated source of impairment for both aquatic and riparian systems.

Mercury bioaccumulation in bats reflects dietary connectivity to aquatic food webs

Mercury (Hg) is a persistent and widespread heavy metal with neurotoxic effects in wildlife. While bioaccumulation of Hg has historically been studied in aquatic food webs, terrestrial consumers can become contaminated with Hg when they feed on aquatic organisms (e.g., emergent aquatic insects, fish, and amphibians). However, the extent to which dietary connectivity to aquatic ecosystems can explain patterns of Hg bioaccumulation in terrestrial consumers has not been well studied. Bats (Order: Chiroptera) can serve as a model system for illuminating the trophic transfer of Hg given their high dietary diversity and foraging links to both aquatic and terrestrial food webs. Here we quantitatively characterize the dietary correlates of long-term exposure to Hg across a diverse local assemblage of bats in Belize and more globally across bat species from around the world with a comparative analysis of hair samples. Our data demonstrate considerable interspecific variation in hair total Hg concentrations in bats that span three orders of magnitude across species, ranging from 0.04mg/kg in frugivorous bats (Artibeus spp.) to 145.27mg/kg in the piscivorous Noctilio leporinus. Hg concentrations showed strong phylogenetic signal and were best explained by dietary connectivity of bat species to aquatic food webs. Our results highlight that phylogeny can be predictive of Hg concentrations through similarity in diet and how interspecific variation in feeding strategies influences chronic exposure to Hg and enables movement of contaminants from aquatic to terrestrial ecosystems.

Seasonality of odonate-mediated methylmercury flux from permanent and semipermanent ponds and potential risk to red-winged blackbirds (Agelaius phoeniceus).

Methylmercury (MeHg) is an aquatic contaminant that can be transferred to terrestrial predators by emergent aquatic insects such as odonates (damselflies and dragonflies). We assessed the effects of month and pond permanence on odonate-mediated MeHg flux (calculated as emergent odonate biomass × MeHg concentration) in 10 experimental ponds and the potential risk to nestling red-winged blackbirds (Agelaius phoeniceus) posed by consuming MeHg-contaminated odonates. Emergent odonates were collected weekly from permanent ponds with bluegill (Lepomis macrochirus; n = 5) and semipermanent ponds without fish (n = 5) over an 8-mo period (January-August 2015). The MeHg flux from damselflies, aeshnid dragonflies, and libellulid dragonflies began in March and peaked in April, May, and June, respectively, and then declined throughout the rest of the summer. Odonate-mediated MeHg flux from semipermanent ponds without fish was greater than that from permanent ponds with fish. Nesting of red-winged blackbirds overlapped with peak odonate emergence and odonate-mediated MeHg flux. Because their diet can be dominated by damselflies and dragonflies, we tested the hypothesis that MeHg-contaminated odonates may pose a health risk to nestling red-winged blackbirds. Concentrations of MeHg in odonates exceeded wildlife values (the minimum odonate MeHg concentrations causing physiologically significant doses in consumers) for nestlings, suggesting that MeHg-contaminated odonates can pose a health risk to nestling red-winged blackbirds. Environ Toxicol Chem 2017;36:2833-2837. © 2017 SETAC.

Investigating Aquatic Insect Emergence: A Demonstration of the 5E Learning Cycle

Traditionally, exploration of ecosystems in the context of undergraduate education has been restricted to connections within conventionally defined habitats (i.e., within a stream, within a forest). Further, instruction regarding the aquatic-terrestrial interface has emphasized directional inputs from land to water. However, a relatively new body of research has characterized reciprocal interactions and draws attention to fluxes from water to land, including the emergence of aquatic insects that serve as prey for terrestrial predators. We present a guide to an inquiry-based lesson for undergraduate biology that explores interactions and connections across aquatic and terrestrial habitat boundaries. The focus is on cross-habitat linkages within ecosystems, specifically addressing the question, What is the role of insect emergence in connecting the web of life linking aquatic and terrestrial habitats and organisms? Students (1) engage with a documentary film, (2) explore insect emergence and make observations of riparian insectivores, (3) explain the collected data, (4) elaborate on alternative study designs and a measure of ecosystem health, and (5) evaluate their new understanding. This lesson addresses core concepts and competencies for undergraduate biology education, as identified in the Vision and Change report.

Low-cost floating emergence net and bottle trap: comparison of two designs

ABSTRACTSampling emergent aquatic insects is of interest to many freshwater ecologists. Many quantitative emergence traps require the use of aspiration for collection. However, aspiration is infeasible in studies with large amounts of replication that is often required in large biomonitoring projects. We designed an economic, collapsible pyramid-shaped floating emergence trap with an external collection bottle that avoids the need for aspiration. This design was compared experimentally to a design of similar dimensions that relied on aspiration to ensure comparable results. The pyramid-shaped design captured twice as many total emerging insects. When a preservative was used in bottle collectors, >95% of the emergent abundance was collected in the bottle. When no preservative was used, >81% of the total insects were collected from the bottle. In addition to capturing fewer emergent insects, the traps that required aspiration took significantly longer to sample. Large studies and studies sampling remote locations could benefit from the economical construction, speed of sampling, and capture efficiency.

Plant genotype influences aquatic‐terrestrial ecosystem linkages through timing and composition of insect emergence

AbstractTerrestrial leaf litter provides aquatic insects with an energy source and habitat structure, and species differences in litter can influence aquatic insect emergence. Emerging insects also provide energy to riparian predators. We hypothesized that plant genetics would influence the composition and timing of emerging insect communities among individual genotypes of Populus angustifolia varying in litter traits. We also compared the composition and timing of emerging insect communities on litter from mixed genotypes of three cross types of a hybridizing cottonwood complex: P. angustifolia, P. fremontii, and their F1 hybrids. Using litter harvested from an experimental common garden, we measured emerging insect community composition, abundance, and production for 12 weeks in large litter packs affixed with emergence traps. Five major findings emerged. (1) In support of the genetic similarity hypothesis, we found that, among P. angustifolia tree genotypes, litter from more closely related genotypes had more similar litter thickness, nitrogen concentrations, decomposition rates, and emerging insect communities. (2) Genetic similarity was not correlated with other litter traits, although the litter fungal community was a strong predictor of emerging insect communities. (3) Litter decomposition rate, which was the strongest predictor of emerging aquatic insect communities, was influenced by litter thickness, litter N, and the litter fungal community. (4) In contrast to strong community composition differences among P. angustifolia genotypes, differences in community composition between P. fremontii and P. angustifolia were only marginally significant, and communities on F1 hybrids were indistinguishable from P. angustifolia despite genetic and litter trait differences. (5) Mixed litter packs muted the genetic effects observed in litter packs consisting of single genotypes. These results demonstrate that the genetic structure of riparian forests can affect the composition and timing of aquatic insect emergence. Because many riparian trees are clonal, including P. angustifolia, large clone size is likely to result in patches of genetically structured leaf litter that may influence the timing and composition of insect emergence within watersheds. Riparian restoration efforts incorporating different tree genotypes could also influence the biodiversity of emerging aquatic insects. Our work illustrates the importance of plant genes for community and ecosystem processes in riparian corridors.

Fluvial geomorphology and aquatic‐to‐terrestrial Hg export are weakly coupled in small urban streams of Columbus, Ohio

AbstractAlthough mercury (Hg) contamination is common in stream ecosystems, mechanisms governing bioavailability and bioaccumulation in fluvial systems remain poorly resolved as compared to lentic systems. In particular, streams in urbanized catchments are subject to fluvial geomorphic alterations that may contribute to Hg distribution, bioaccumulation, and export across the aquatic‐to‐terrestrial boundary. In 12 streams of urban Columbus, Ohio, we investigated the influence of fluvial geomorphic characteristics related to channel geometry, streamflow, and sediment size and distribution on (1) Hg concentrations in sediment and body burdens in benthic larval and adult emergent aquatic insects and (2) aquatic‐to‐terrestrial contaminant transfer to common riparian spiders of the families Pisauridae and Tetragnathidae via changes in aquatic insect Hg body burdens as well as in aquatic insect density and community composition. Hydrogeomorphic characteristics were weakly related to Hg body burdens in emergent insects (channel geometry) and tetragnathid spiders (streamflow), but not to Hg concentrations in sediment or benthic insects. Streamflow characteristics were also related to emergent insect density, while wider channels were associated with benthic insect community shifts toward smaller‐bodied and more tolerant taxa (e.g., Chironomidae). Thus, our results provide initial evidence that fluvial geomorphology may influence aquatic‐to‐terrestrial contaminant Hg transfer through the collective effects on emergent insect body burdens as well as on aquatic insect community composition and abundance.

Aerial insect responses to non-native Chinook salmon spawning in a Great Lakes tributary

Abstract We investigated whether spawning by non-native Chinook salmon influenced aerial insect abundance in the riparian zone of Thompson Creek, a tributary of Lake Michigan, located in Michigan, USA. Specifically, we evaluated whether decades of salmon disturbance affected patterns of aquatic insect emergence, and how both live salmon and salmon carcasses influenced the abundance of terrestrial carrion flies. Retaining wall timbers from a low-head dam on Thompson Creek were removed, providing a unique opportunity to compare stream reaches that were exposed to the immediate ecological impacts of salmon (i.e., disturbance, subsidy effects) with reaches experiencing decades of spawning activity. Using sticky traps to collect aerial insects, we observed fewer adult aquatic insects in downstream reaches conditioned to decades of salmon disturbance in comparison to naive upstream reaches. Reduced abundance in downstream reaches was primarily driven by taxa more susceptible to disturbance in the larval life stage (e.g., Diptera: Simuliidae, Ephemeroptera). A greater abundance of adult Chironomidae midges were detected in upstream reaches with higher numbers of spawning salmon and carcasses. Though abundance of adults differed between upstream and downstream reaches, we observed no evidence of early emergence. In addition, carrion fly abundance was greatest at reaches with more live and dead salmon. Evidence from our study suggests that non-native salmon have the potential to influence patterns of aerial insect abundance in riparian zones. Our findings suggest that non-native Chinook salmon can affect aerial insect assemblages; however, the propagating effects of these changes through riparian food webs warrant further investigation.

LIFE CYCLES AND SECONDARY PRODUCTION OF EPHEMEROPTERA, PLECOPTERA, AND TRICHOPTERA (INSECTA) UNDER AN EXTREME CONTINENTAL CLIMATE (RIVER KHARAA, MONGOLIA)

There are still knowledge gaps and uncertainties concerning the research of macroinvertebrates, in particular, a life cycle study of representative species are one such section of information missing in Mongolia. Therefore, this study was conducted within the framework of the biomonitoring program in the Kharaa River Basin under the research aims of the project entitled ‘Integrated Water Resources Management (IWRM) in Central Asia: Model Region Mongolia (MoMo)’. This study provided the first quantitative results on the life cycle, production, growth rate and emergence of aquatic insects from Mongolia, to allow comparisons with studies in other regions using the same methods. The 3-year study (2007-2009) of the life cycles of eighteen selected species according to the larval body size distribution and emergence period showed that the life cycle strategies in Ephemeroptera, Plecoptera, and Trichoptera and their production in the Kharaa River Basin clearly indicated adaptations to the harsh environmental conditions with strict univoltinism and low secondary production. In conclusion, it is essential to obtain knowledge especially about life cycle strategies of macroinvertebrates to predict re-colonisation potential of disturbed habitats and to evaluate the efficiency of management measures.