Abundance Of Aquatic Invertebrates Research Articles

Globally invasive Potamopyrgus antipodarum (Gray, 1843) – an indicator of the degraded water systems in relation to native aquatic invertebrates

Global changes in climate and human impact favour invasions of aquatic organisms. Along with habitat modification, the abundance of invasive species might increase, leading to their greater impact on ecosystems functioning in disturbed areas. The appearance of species, which are drivers for ecosystem pollution are useful tool for the indication of some environmental changes in the area. We examine the occurrence of P. antipodarum populations, a global invader that established rivers, oxbow lakes, dam reservoirs, sand pits, gravel pits, and subsidence ponds in Poland (Central Europe). The research aims were to determine the extent of invasion in anthropogenically impacted habitats and the relationship between the abundance of aquatic invertebrates and oxygen concentration, pH, N-NO2, N-NO3, chlorides, and ammonia. This investigation helps elucidate the potential of invader to adapt to adverse environmental conditions in aquatic systems in which it was found dominant. The abundance of P. antipodarum showed an unimodal distribution, being higher in disturbed conditions. In snail communities it was a supereudominant or eudominant species in rivers, gravel pits, sand pits and subsidence ponds. Its relative abundance was the highest in gravel pits, in which it constituted more than 50 percent of benthic fauna. We demonstrated that environmental disturbances and pollution increase the vulnerability of water biocoenoses to invasions and the origin of free niches and that P. antipodarum is an indicator of degraded water systems. Results support the management of aquatic systems colonized by invasive species and highlight the need to assess the level of pollution discharged to prevent their dispersion. Management priorities must include the reduction or halt of invader spread because new aquatic environments are and will be created in industrial areas of the world.

Does Microbial and Faunal Pattern Correspond to Dynamics in Hydrogeology and Hydrochemistry? Comparative Study of Two Isolated Groundwater Ecosystems in Münsterland, Germany

The objective of this study was to assess the temporal and spatial variability of aquatic invertebrates and microbial parameters (biomass and activity) with environmental data in springs, and to determine the impact of key parameters on the ecological situation of a groundwater system. Eight springs in the two study areas of Baumberge and Schöppinger Berg (W-NW of Münster, North Rhine Westphalia, Germany) were sampled at three sampling campaigns between 2018 and 2019. Physicochemical parameters of the spring samples and abundances of aquatic invertebrates were determined at each sampling event. Samples for hydro(geo)chemical and microbial analyses were collected during each sampling campaign in the springs. Spearman correlation and principal component analysis were used to identify the key parameters. The abundance of aquatic invertebrates and microbial activity were significantly positively correlated with groundwater table fluctuation. The abundance of stygobite individuals was significantly positively correlated with the Groundwater-Fauna-Index and phosphate in Baumberge, and negatively correlated with chloride in Schöppinger Berg. Most notably, the stable isotopes of water and microbial activity were significantly inversely correlated. The hydro(geo)chemical results showed no significant spatial differences in groundwater in both groundwater systems. Stable isotopes of water indicate a meteoric origin, with an effect of evaporation for two months, even though the downward percolation and groundwater recharge rates are high. The nitrate concentration was higher than 50 mg/L only in SB due to the agricultural activities. Nitrate input into groundwater comes from two sources in Baumberge, while it comes from one source in Schöppinger Berg. There was no evidence of denitrification in both areas. Secondary gypsum is assumed to be the source of sulfate in groundwater in Schöppinger Berg, but anaerobic oxidation of pyrite in the deeper part of the groundwater system as a source of sulfate cannot be excluded.

Neonicotinoid contamination in tropical estuarine waters of Indonesia

Previous studies conducted in other countries showed that neonicotinoid insecticides contaminated environmental waters and reduced aquatic invertebrate abundance. This study analysed neonicotinoid concentrations in estuarine waters of Indramayu Regency, Indonesia, and their potential toxicity to the aquatic environment. Data collection included water sampling and analysis, watershed and paddy field analyses, and literature review. The results showed that the detection frequency of neonicotinoids was 75%, with imidacloprid and thiamethoxam having the highest mean concentrations compared to other compounds. The sample collected in August 2021 from an estuary in the Patrol sub-district contained the highest total neonicotinoid concentration (140.26 ng/L). Five samples (31.25%) contained imidacloprid concentrations that exceeded the chronic benchmark regulated by the Netherlands, thus related regulation and policies are encouraged to be established in Indonesia to prevent potential harmful effect of neonicotinoids to the aquatic environment. There was no significant correlation between the neonicotinoid concentrations and the paddy field and watershed sizes as well as the land use proportion for paddy fields within the watershed. This study is the first to report neonicotinoid contamination in Indonesian estuarine waters.

A melting cryosphere constrains fish growth by synchronizing the seasonal phenology of river food webs.

Mountain watersheds often contain a mosaic of glacier‐, snow‐, and rain‐fed streams that have distinct hydrologic, temperature, and biogeochemical regimes. However, as glaciers diminish and precipitation shifts from snow to rain, the physical and chemical characteristics that make glacial or snowmelt streams distinct from rain‐fed streams will fade. Among the unforeseen consequences of this hydrologic homogenization could be the loss of unique food webs that sustain aquatic consumers. To explore the impacts of a melting cryosphere on stream food webs, we parameterized an aquatic food web model with empirical physicochemical data from glacier‐, snow‐, and rain‐fed streams in southeast Alaska and used the model to simulate the seasonal biomass dynamics of aquatic primary producers and consumers and the growth of juvenile salmon. Model results suggest that glacier‐, snow‐, and rain‐fed streams exhibit seasonal asynchronies in the timing of biofilm and aquatic invertebrate abundance. Although warmer rain‐fed streams were more productive during the summer (June through September), colder glacial and snowmelt streams provided enhanced foraging and growth opportunities throughout the remainder of the year. For juvenile salmon that can track peaks in resource abundance within river networks, the loss of meltwater streams strongly constrained modeled growth opportunities by removing spatially and temporally distinct foraging habitats within a watershed. These findings suggest that climate change induced homogenization of high latitude river networks may result in the loss of unique food web dynamics, which could diminish the capacity of watersheds to sustain mobile consumers.

Farming practice affects rice field animal biota during cultivation but not fallow periods in Taiwan

AbstractRice is one of the most important staple foods in the world, with irrigated rice paddies largely converted from natural wetlands. The effectiveness of rice fields in preserving species depends partially on management practices, including the usage of pesticides. Previous studies have focused predominantly on the cultivation period, leaving the potential effects of soil pesticide residues on organisms during the fallow periods underexplored. Other animals, such as waterbirds, also rely on aquatic invertebrates in flooded fallow fields for their survival. We investigated vertebrates and macroinvertebrates during cultivation and fallow periods in organic and conventional rice fields in Taiwan. The association of environmental factors with terrestrial and aquatic organisms was also analyzed. In total, 32,880 individuals from 144 invertebrate families and 381 individuals from 15 vertebrate families were recorded after nine samplings each in six organic and six conventional rice fields. The family richness and abundance of all invertebrates were higher in organic than in conventional fields during the cultivation period but were similar in fields under either agricultural practice during the fallow period. The differences in richness and abundance of terrestrial invertebrates between the two practices increased with progression of rice cultivation, while there was no difference in abundance of aquatic invertebrates during the fallow period. The richness and abundance of fish, amphibians, reptiles, birds, and migratory waterbirds were not statistically different between the two practices. Our study suggested accumulative effects of pesticides on suppressing terrestrial and aquatic invertebrates during the cultivation period, but no negative effects of soil pesticide residues on aquatic invertebrates during the fallow period. This comprehensive study provided a holistic picture of macroinvertebrate and vertebrate fauna, as well as the potential ramifications of pesticide usage, in a representative Southeast Asian rice paddy ecosystem. Future studies should compare rice fields with natural wetlands to better assess how to capitalize on agroecosystems for biodiversity conservation.

Effects of seasonal hypoxia on macroinvertebrate communities in a small reservoir

AbstractLocalized hypoxia can reduce available habitat, restrict movement and limit the abundance of aquatic invertebrates. Although cultural eutrophication, coupled with the effects of climate change, is likely to increase the frequency and extent of hypoxia in aquatic ecosystems, little is known about how oxygen gradients in small reservoirs influence spatial distribution and abundance of aquatic invertebrates. The present study evaluated the effects of environmental and biological attributes on seasonal and spatial variation of macroinvertebrates and explored how hypoxic conditions influenced littoral, benthic and pelagic macroinvertebrate communities in Lake Alvin, South Dakota. Data on reservoir conditions, in conjunction with macroinvertebrate sampling from May to October 2009–2011, were applied in an information theoretic approach to evaluate factors affecting invertebrate abundance. Hypoxic conditions were present from May to September in the lacustrine zone impacting 10%–39% of the water column. Benthic invertebrates were typically absent from the lacustrine zone during periods of severe hypoxia and were most abundant in the shallow, well‐oxygenated riverine zone. Littoral invertebrates were negatively related to the per cent of the hypoxic water column, suggesting fish, confined to shallow waters by hypoxia, may be consuming a larger portion of littoral invertebrates in their diets. Cladocera and Copepoda densities were influenced primarily by water depth and monthly precipitation. The larger size of Daphnia found in the hypoxic‐prone transitional and lacustrine zones suggested low oxygen concentrations may provide a refuge from fish predation. The results of the present study demonstrated spatial variations in near‐bottom oxygen concentrations were important predictors of macroinvertebrate and zooplankton abundance and size structure in Lake Alvin and that macroinvertebrates, particularly benthic and littoral invertebrates, could benefit from measures taken to reduce summer hypoxia.

Floating along marsh edges: The impact of invasive water hyacinth (Eichornia crassipes) on estuarine species assemblages and predation risk

Estuaries are dynamic environments where the safety of habitat refuges can be altered by a variety of natural and anthropogenic disturbances. After tropical storms or other high water run off events, water hyacinth (Eichhornia crassipes), an invasive floating freshwater plant, can enter estuarine habitats where it can colonize marsh edges and may impact the abundance and distribution of estuarine species. In freshwater environments, hyacinth reduces water quality, increases habitat complexity, and alters freshwater aquatic invertebrate abundance and diversity. Yet, little is known about how this plant impacts estuarine species as it floats from freshwater tributaries to oceanic environments. To examine how water hyacinth impacts estuarine marsh fauna, we examined the effects of water hyacinth on nekton communities and fish predation risk using trapping and tethering techniques along a marsh edge that had been recently colonized by water hyacinth. We placed funnel traps under water hyacinth and in open water habitats to examine how water hyacinth impacted macrofaunal abundance and diversity. We also examined how water hyacinth impacted predation risk by tethering killifish at increasing distances from the marsh edge in open water and water hyacinth habitats. We found that shrimp, blue crabs, and killifish were generally more abundant under water hyacinth, but there was no difference in species richness or diversity between the two habitats. In tethering studies, killifish survival was generally similar between water hyacinth and open water likely due to the increased abundance of blue crabs underneath water hyacinth. This result suggests water hyacinth does not alter predation risk overall, but may alter the distribution of blue crabs and piscivorous fish predators. We did observe short term increases in killifish survival underneath small migrating hyacinth patches indicating patch size may further affect blue crab colonization and predation. Our results indicate that water hyacinth alters the safety of marsh edge habitats by increasing blue crab abundance, ultimately increasing their encounter rates with fish prey. Climate driven increases in tropical storms and coastal restoration efforts that alter salinity gradients will likely increase the abundance of water hyacinth in estuarine marshes offering important post-disturbance habitat structure to fish and invertebrates and increasing predation rates of blue crabs along marsh edges.

Environment-host-microbial interactions shape the Sarracenia purpurea microbiome at the continental scale.

The importance of climate, habitat structure, and higher trophic levels on microbial diversity is only beginning to be understood. Here, we examined the influence of climate variables, plant morphology, and the abundance of aquatic invertebrates on the microbial biodiversity of the northern pitcher plant Sarracenia purpurea. The plant's cup-shaped leaves fill with rainwater and support a miniature, yet full-fledged, ecosystem with a diverse microbiome that decomposes captured prey and a small network of shredding and filter-feeding aquatic invertebrates that feed on microbes. We characterized pitcher microbiomes of 108 plants sampled at 36 sites from Florida to Quebec. Structural equation models revealed that annual precipitation and temperature, plant size, and midge abundance had direct effects on microbiome taxonomic and phylogenetic diversity. Climate variables also exerted indirect effects through plant size and midge abundance. Further, spatial structure and climate influenced taxonomic composition, but not phylogenetic composition. Our results suggest that direct effects of midge abundance and climate and indirect effects of climate through its effect on plant-associated factors lead to greater richness of microbial phylotypes in warmer, wetter sites.

Climatic aridity increases temporal nestedness of invertebrate communities in naturally drying rivers

Climate change is altering the water cycle globally, increasing the frequency and magnitude of floods and droughts. An outstanding question is whether biodiversity responses to hydrological disturbance depend on background climatic context – and if so, which contexts increase vulnerability to disturbance. Answering this question requires comparison of organismal responses across environmental gradients. However, opportunities to track disturbed communities against an undisturbed baseline remain rare. Here we gathered a global dataset capturing responses of aquatic invertebrate communities to river drying, which includes 112 sites spanning a gradient of climatic aridity. We measured the effects of river drying on taxonomic richness and temporal β‐diversity (turnover and nestedness components). We also measured the relative abundance of aquatic invertebrates with strategies that confer resilience (or resistance) to drying. Contrary to our expectations, we found that taxonomic richness recovered from drying similarly across the aridity gradient. The turnover component of β‐diversity (i.e. species replacements over time) largely accounted for differences in community composition before versus after drying. However, increasing aridity was associated with greater nestedness‐driven compositional changes at intermittent sites – that is, after drying communities became subsets of those before drying. These results show that climatic context can explain variation in community responses to the same hydrological disturbance (drying), and suggest that increased aridity will constrain biodiversity responses at regional scales. Further consideration of the climatic context in hydroecological research may help improve predictions of the local impacts of hydrological disturbance by identifying climate regions where communities are more (or less) sensitive to extremes, including river drying events.

Rusty Blackbird (Euphagus carolinus) Foraging Habitat and Prey Availability in New England: Implications for Conservation of a Declining Boreal Bird Species

The Rusty Blackbird (Euphagus carolinus) is an imperiled migratory songbird that breeds in and near the boreal wetlands of North America. Our objective was to investigate factors associated with Rusty Blackbird wetland use, including aquatic invertebrate prey and landscape features, to better understand the birds’ habitat use. Using single-season occupancy modeling, we assessed breeding Rusty Blackbird use of both active and inactive beaver-influenced wetlands in New Hampshire and Maine, USA. We conducted timed, unlimited-radius point counts of Rusty Blackbirds at 60 sites from May to July 2014. Following each point count, we sampled aquatic invertebrates and surveyed habitat characteristics including percent mud cover, puddle presence/absence, and current beaver activity. We calculated wetland size using aerial imagery and calculated percent conifer cover within a 500 m buffer of each site using the National Land Cover Database 2011. Percent mud cover and invertebrate abundance best predicted Rusty Blackbird use of wetlands. Rusty Blackbirds were more likely to be found in sites with lower percent mud cover and higher aquatic invertebrate abundance. Sites with Rusty Blackbird detections had significantly higher abundances of known or likely prey items in the orders Amphipoda, Coleoptera, Diptera, Odonata, and Trichoptera. The probability of Rusty Blackbird detection was 0.589 ± 0.06 SE. This study provides new information that will inform habitat conservation for this imperiled species in a beaver-influenced landscape.

Beta diversity of aquatic invertebrates increases along an altitudinal gradient in a Neotropical mountain

AbstractMountains harbor rich biodiversity and high levels of endemism, particularly due to changes in environmental conditions over short spatial distances, which affects species distribution and composition. Studies on mountain ecosystems are increasingly needed, as mountains are highly threatened despite providing ecosystem services, such as water supply for half of the human population. We aimed to understand the patterns and drivers of alpha and beta diversities of aquatic invertebrates in headwater streams along an altitudinal gradient in the second largest South American mountain range, the Espinhaço mountains. Headwater streams were selected at each 100 m of elevation along an altitudinal gradient ranging from 800 to 1400 m asl, where three substrate types per stream were sampled: leaf litter, gravel, and cobbles. Environmental variables were sampled to represent local riparian canopy cover, instream physical habitat, water quality, climatic data, and land use. Generalized linear models and mixed models were used to test relationships between altitude and the richness and abundance of invertebrates and to assess the influence of environmental variables on the same metrics. Patterns of spatial variation in aquatic invertebrate assemblages along the altitudinal gradient were assessed using multiplicative beta diversity partitioning. The richness and abundance of aquatic invertebrates decreased with increasing altitude, whereas beta diversity increased with increasing altitude. Significant differences in assemblage composition and in relative abundance of invertebrates were observed for both substrates and altitude. We thus show that the high regional beta diversity in aquatic ecosystems in the studied site is due to the high turnover among areas.Abstract in Portuguese is available with online material.

Influence of wildfire and harvesting on aquatic and terrestrial invertebrate drift patterns in boreal headwater streams

Forested headwater streams are strongly connected to their surrounding riparian areas via the transfer of energy subsidies that underpin instream food webs and, therefore, are highly sensitive to riparian disturbances that influence allochthonous inputs. We compared terrestrial and aquatic invertebrates found in drift across headwater streams in boreal forested catchments with wildfire, harvest with minimum 30-m riparian buffers, and reference catchment histories. Fire-disturbed streams contained significantly greater aquatic invertebrate abundance and biomass compared to reference and harvested streams, but no significant trends were seen for terrestrial invertebrate abundance or biomass. Furthermore, fire-disturbed streams supported distinct drifting invertebrate communities compared to reference and harvested sites, driven by high abundances of the mayfly Baetis and caddisfly Dolophilodes. Aquatic invertebrate drift communities were compositionally dissimilar between fire and harvested sites, but not reference sites and no trends were found for terrestrial invertebrate drift samples. Subtle but detectable differences in drifting invertebrate community metrics, structure, and biomass suggest that the effects of wildfire persist well beyond a decade post-fire in boreal headwater streams. Forest management that emulates natural fire disturbance, including streamside disturbance, may be important for promoting the observed patterns detected in our fire-disturbed catchments.

Water regimes and ecosystem in lowland paddy field: a case study in Awlegama, Kurunegala, Sri Lanka

Paddy fields are manmade ecosystems. These fields undergo three water regimes namely, aquatic, semi aquatic and terrestrial within a cultivation season. Accordingly, the ecosystem also changes. In addition, agronomic practices can affect biodiversity and the overall ecology. A study was conducted to assess the water regime and respective ecosystem so that ecosystem can be enhanced as an adaptation for climate variability in paddy cultivation. The study was conducted in a command area of Bayawa minor irrigation system located in Awlegama Agrarian service division in Kurunegala District, Sri Lanka. Six randomly selected locations in the field were used in the fauna survey at different growth stages in Yala season in 2015. A water management index (WMI) was developed to assess the water regime using physical factors of the field and social capacity of farmer. Results revealed that wet condition is expected in more than 69% of farmers since their WMI is more than 0.5. Water regime varied among head, middle and tail sections. Tail end of the command area has more reliability for water than the head and middle sections. The water fluctuation leads to higher biodiversity. The initial water regime and crop growth stages have provided more habitats for the both terrestrial and aquatic invertebrates.The abundance of aquatic invertebrates were significantly (p= 0.01) varied over the five growth stages anddragonflies’ diversity was varied temporarily with respect to the species richness.Alternative wetting and drying have created more favorable habitats for aquatic fauna to increase the biodiversity of the fields. Increase of biodiversity promotes naturally enemies/predators for pests while aquatic fauna improve the nutrient availability in the fields. Therefore, water management in the fields could be used to enhance biodiversity in the rice field to achieve sustainable paddy cultivation.

Can aggregate quarry silt lagoons provide resources for wading birds?

Wading birds have declined across Europe as the intensification of lowland agriculture has resulted in the loss and degradation of wetland areas. Lowland aggregate extraction sites that incorporate areas of fine, waste sediments deposited in silt lagoons have the potential to be restored for wader conservation. We set out to determine the potential value of silt lagoons to wading birds by comparing the water quality, sediment profiles, aquatic invertebrate abundance and diversity (prey availability) and wader site use at five sites representing various stages of active aggregate extraction and restoration for conservation purposes. Wader counts were conducted monthly over a twelve month period using replicated scan samples, and the invertebrate communities studied during the breeding and autumn migration season (June–September). Water quality variables were similar between sites, but sediments from active quarries were dominated by moderately sorted fine sands in comparison to the coarser sediment profiles of restored areas. June and September there was no significant difference in invertebrate diversity between sites, however richness was significantly lower on quarry sites and total abundance a factor of ten higher at restored sites than on silt lagoons, with the dominant taxa similar across all sites. Waders used all sites; albeit at lower abundance and richness on silt lagoons and two species were recorded breeding on active silting sites. We conclude that the fine, uniform sediments of modern silt lagoons limited invertebrate diversity and abundance, diminishing the value of silt lagoons to waders. Simple low-cost intervention measures increasing substrate heterogeneity and creating temporary ponds could increase invertebrate richness and abundance, and enhance the conservation potential of these sites.

Livestock grazing in intermountain depressional wetlands: effects on breeding waterfowl

Livestock grazing is a prevalent land use in western North American intermountain wetlands, and physical and biotic changes related to grazing-related disturbance can potentially limit wetland habitat value for waterfowl. We evaluated breeding waterfowl use in 34 wetlands in relation to water retention, amount of wetlands on the landscape, and livestock grazing intensity. The study was conducted over 2 years in the southern intermountain region of British Columbia, Canada. For a subset of 17 wetlands, we measured aquatic invertebrate abundance over 1 year. Waterfowl breeding pairs and broods were classified into three functional groups: dabbling ducks, and two types of diving ducks, overwater and cavity nesters. We evaluated candidate models with variables considered singly and in combination using the Akaike Information Criterion. When selected, bare ground (an indicator of grazing intensity) and wetland density were negatively associated with breeding use while wetland fullness and invertebrate density were positively associated. Each factor was a significant predictor in at least one of the models, but unexpectedly, grazing intensity was the most consistent predictor of waterfowl wetland use (e.g., it was present in more ‘best models’ than wetland fullness). Grazing was associated with declines in the number of waterfowl pairs and broods, likely mediated through effects on wetland vegetation and aquatic macroinvertebrates. Models with site- and landscape-scale variables generally performed better than simpler models. Waterfowl breeding use of wetlands can be improved by reduced livestock grazing intensity adjacent to wetlands and by grazing later in the season. Wetland water retention is also an important constraint on waterfowl use of wetlands and may become more limiting with a shifting climate.

Uniform carbon fluxes in shallow lakes in alternative stable states

Shallow lakes process large amounts of carbon (C) via gross primary production (GPP) and respiration (R), but C fluxes are highly variable among lakes. We used a two-prong approach to determine whether C fluxes differed between two alternative stable states observed in shallow lakes. First, we used a replicated whole-lake experiment where we manipulated fish densities in four experimental lakes to induce shifts from the phytoplankton-dominated state (turbid state) to a submersed macrophyte-dominated state (clear state), and determined whether whole-lake GPP, R, and net aquatic production (NAP) changed in response to the manipulation. We also compared lake metabolism in the four experimental lakes to four lakes in a turbid state and four lakes in a clear state. Second, we used sediment cores from 68 shallow lakes to test whether modern burial rates of organic C differed between lakes in clear and turbid states. Biomanipulation in the experimental lakes reduced abundance of fish and phytoplankton and increased abundance of aquatic invertebrates and submerged macrophytes. However, there was no significant change in GPP, R, or NAP. Similarly, GPP, R, and NAP did not differ among experimental lakes, turbid-state lakes, or clear-state lakes. Lastly, organic C burial in sediments did not differ between lakes in clear vs. turbid states, though variability among sites was high. High light and nutrient availability facilitate rapid transitions between two alternative groups of competing, rapidly growing primary producers in shallow lakes. These characteristics facilitate relatively uniform C fluxes at the ecosystem scale despite substantial differences in community structure.

The influence of urbanisation on macroinvertebrate biodiversity in constructed stormwater wetlands

The construction of wetlands in urban environments is primarily carried out to assist in the removal of contaminants from wastewaters; however, these wetlands have the added benefit of providing habitat for aquatic invertebrates, fish and waterbirds. Stormwater quantity and quality is directly related to impervious area (roads, sealed areas, roofs) in the catchment. As a consequence, it would be expected that impervious area would be related to contaminant load and biodiversity in receiving waters such as urban wetlands. This study aimed to establish whether the degree of urbanisation and its associated changes to stormwater runoff affected macroinvertebrate richness and abundance within constructed wetlands. Urban wetlands in Melbourne's west and south east were sampled along a gradient of urbanisation. There was a significant negative relationship between total imperviousness (TI) and the abundance of aquatic invertebrates detected for sites in the west, but not in the south east. However macroinvertebrate communities were relatively homogenous both within and between all study wetlands. Chironomidae (non-biting midges) was the most abundant family recorded at the majority of sites. Chironomids are able to tolerate a wide array of environmental conditions, including eutrophic and anoxic conditions. Their prevalence suggests that water quality is impaired in these systems, regardless of degree of urbanisation, although the causal mechanism is unclear. These results show some dependency between receiving wetland condition and the degree of urbanisation of the catchment, but suggest that other factors may be as important in determining the value of urban wetlands as habitat for wildlife.

Can salinity trigger cascade effects on streams? A mesocosm approach

Human activities have greatly increased the salt concentration of the world's rivers, and this might be amplified by water scarcity in the future. While the lethal effects of salinity have been documented for a wide variety of stream invertebrates, the sub-lethal effects (i.e. changes in biological condition without mortality) are not deeply understood yet. One important sub-lethal effect that has yet to be investigated is changes in predation efficiency, which could trigger cascade effects associated to the abundance of herbivorous invertebrates that control algae biomass. In this study we combined the use of biomarkers with community-level data in a stream mesocosm to evaluate the potential cascade effect of increased salinity on the trophic food web. Both predation and salt treatments had an effect on the aquatic invertebrate abundance, richness and community composition. The presence of predators had a clear cascade effect, it reduced herbivorous invertebrate abundance and richness leading to higher chlorophyll a concentrations. The salt treatment significantly reduced taxa richness, but only in the gravel bed. The predators were significantly stressed by salt addition, as shown by the different analyzed biomarkers. Concordantly, in the presence of predators, Tanytarsini registered higher abundances and chlorophyll a showed a lower concentration when salt was added. However, none of these changes was significant. Therefore, although salt addition significantly stressed Dina lineata, our results suggest that a longer exposure time is needed to fully capture cascading effects (e.g. a decrease in chlorophyll a due to a relaxation of predation on herbivorous invertebrates). We suggest that the potential cascade effects of salinization need to be evaluated when addressing the impacts of water scarcity (as caused by climate change and increasing water demand) on river ecosystems, since flow reductions will lead to higher salt concentrations.

Aquatic Invertebrate Abundance and Biomass in Arkansas, Mississippi, and Missouri Bottomland Hardwood Forests During Winter

AbstractThe Mississippi Alluvial Valley once had extensive bottomland hardwood forests, but less than 25% of the original area remains. Impounded bottomland hardwood forests, or greentree reservoirs, and naturally flooded forests are important sources of invertebrate or other prey for waterfowl, but no previous studies of invertebrate abundance and biomass have been at the scale of the Mississippi Alluvial Valley. Additionally, the Lower Mississippi Valley Joint Venture of the North American Waterfowl Management Plan requires precise, contemporary estimates of invertebrate biomass in hardwood bottomlands to determine potential foraging carrying capacity of these habitats for wintering ducks. We used sweep nets to collect aquatic invertebrates from four physiographically disjunct hardwood bottomlands in the Mississippi Alluvial Valley and Mississippi's Interior Flatwoods region during winters 2008–2010. Invertebrate abundance varied inversely with water depth in both early and late winter, with greatest abundances in depths ranging from 10 to 20 cm. The estimate of invertebrate biomass in naturally flooded forests of the Mississippi Alluvial Valley for both years combined was 18.39 kg(dry)/ha (coefficient of variation [CV] = 15%). When we combined data across regions, sites, greentree reservoirs and naturally flooded forests, and years, the estimate of mean invertebrate biomass decreased to 6.6 kg/ha but precision increased to CV = 9%. We recommend the Lower Mississippi Valley Joint Venture adopt 18.39 kg(dry)/ha as a revised estimate for invertebrate biomass for naturally flooded forests, because this estimate is reasonably precise and less than 2% of remaining hardwood bottomland is impounded greentree reservoirs in the Mississippi Alluvial Valley. Additionally, we recommend managing to invoke dynamic flooding regimes in greentree reservoirs to mimic natural flood events and provide maximal coverage of depths less than 30 cm to facilitate foraging ducks' access to nektonic and benthic invertebrates, acorns, and other natural seeds.

The use of benthic macroinvertebrate metrics in the assessment of ecological status of floodplain lakes

Five oxbow lakes of the Łyna River, located in an agricultural area, were studied seasonally in 2005 and 2008. The EPT index (abundance of Ephemeroptera, Plecoptera and Trichoptera larvae), as well as their proportion to Chironomidae indicated that groups sensitive to environmental conditions occurred at low abundance in relation to the different hydrological types of oxbow lakes. The Family Biotic Index, the Biological Monitoring Working Part index adapted to Polish conditions and the Average Score Per Taxon (ASPT) revealed low water quality regardless of the level of hydrological connectivity. In turn, the indices of biodiversity Margalef (d) and probability of interspecific encounters indicated good or satisfactory water quality. The pH correlated positively with the total abundance of aquatic invertebrates, while lower macroinvertebrate abundance was observed in turbid waters of lentic oxbows with a high content of total dissolved solids. Canonical correspondence analysis showed that hydrological connectivity was the main factor responsible for the value of monitoring indices, followed by the physical and chemical parameters of the local environment. Among the indices used, it was ASPT-PL that grouped the studied oxbow lakes according to their hydrological types and seems to be the best index. This study shows that the structure of invertebrate communities inhabiting oxbow lakes reflects physico-chemical conditions of water and can be a valuable source of monitoring data, indispensable to the management and protection of these important aquatic ecosystems.