Aquatic Microcosms Research Articles

Contribution of bacteria to redox potential (E h) measurements in sediments

Increasing evidence suggests that bacteria are capable of creating specific redox conditions which are visible as species-specific continuous redox potential (Eh) measurements. It has been demonstrated that continuous measurements of Eh are valuable for tracking bacterial metabolic activities of bacterial species in liquid cultures. However, it remains uncertain whether this phenomenon is widespread among bacterial species and whether Eh mea- surements reflect similar mechanisms in more complex systems such as soils and sediments. The purpose of this study is therefore to evaluate whether bacteria that natu- rally occur in sediments have the capacity to control Eh and assess the relative partitioning of biological processes involved in Eh in natural sediments. To this end, continu- ous Eh measurements are linked to growth of bacteria in liquid cultures and bacterial metabolic activity in aquatic sediment microcosms containing the bioturbator Tubifex spp., in which we evaluate bacterial partitioning in microcosms treated with the bacteriocide formalin. The tested bacterial species (Micrococcus luteus, Paracoccus pantotrophus and Aminobacter aminovarans) appeared to have specific stable Eh signals during linear-exponential growth phase, suggesting that these species are capable of exerting an extracellular control on Eh measurements, thereby supporting the notion that species-specific Eh signals may be widespread among bacterial species. For- malin treatment reduced temporal variability of Eh in sediment microcosms. This outcome suggests that bacterial metabolism and inherent relative contributions of members of bacterial community principally determine development of Eh in sediment systems and that quantitation of sediment electrochemical properties may offer a potential indicator that characterizes bacterial processes.

Modelling copper bioaccumulation in Gammarus pulex and alterations of digestive metabolism

Bioaccumulation enables to integrate the ability of aquatic organisms to regulate metals and effects of water chemistry on metal bioavailability. Linking this process to biological responses offers thus promising lines of enquiry for protecting aquatic ecosystems. This study aims at characterizing the mechanisms involved in waterborne Cu bioaccumulation and assessing metal impact on digestive metabolism in an ecosystem engineer widely distributed in Europe, Gammarus pulex. The organism was exposed to several Cu concentrations (from 0.5 to 100 μg/L) in aquatic microcosms to establish kinetic parameters for the construction and comparison of two bioaccumulation models, i.e. the biodynamic and saturation models. Cu uptake was recorded in waters exhibiting various concentrations of Na, Mg and Ca at environmental levels to assess the influence of cationic composition on bioaccumulation. Then, the effect of increasing Cu in exposure media on the digestive metabolism of G. pulex was investigated by measuring enzymatic activities (β-glucosidase, N-acetyl-β-glucosaminidase, β-galactosidase). We showed that the saturation model is more suitable than the biodynamic model to describe Cu bioaccumulation in gammarids due to a maximal capacity of animals to accumulate the metal. Cationic composition of water affected insignificantly Cu uptake. All activities of tested enzymes decreased with increasing Cu in exposure media but with different degrees. High correlations were established between the inhibition of enzymatic activities and amounts of Cu bioaccumulated by gammarids. These biological responses could thus provide early-warming of Cu impact on aquatic biota.

Biotic and Abiotic Interactions in Aquatic Microcosms Determine Fate and Toxicity of Ag Nanoparticles. Part 1. Aggregation and Dissolution

To better understand their fate and toxicity in aquatic environments, we compared the aggregation and dissolution behavior of gum arabic (GA) and polyvinylpyrrolidone (PVP) coated Ag nanoparticles (NPs) in aquatic microcosms. There were four microcosm types: surface water; water and sediment; water and aquatic plants; or water, sediment, and aquatic plants. Dissolution and aggregation behavior of AgNPs were examined using ultracentrifugation, ultrafiltration, and asymmetrical flow field flow fractionation coupled to ultraviolet-visible spectroscopy, dynamic and static laser light scattering, and inductively coupled plasma mass spectrometry. Plants released dissolved organic matter (DOM) into the water column either through active or passive processes in response to Ag exposure. This organic matter fraction readily bound Ag ions. The plant-derived DOM had the effect of stabilizing PVP-AgNPs as primary particles, but caused GA-AgNPs to be removed from the water column, likely by dissolution and binding of released Ag ions on sediment and plant surfaces. The destabilization of the GA-AgNPs also corresponded with X-ray absorption near edge spectroscopy results which suggest that 22-28% of the particulate Ag was associated with thiols and 5-14% was present as oxides. The results highlight the potential complexities of nanomaterial behavior in response to biotic and abiotic modifications in ecosystems, and may help to explain differences in toxicity of Ag observed in realistic exposure media compared to simplified laboratory exposures.

Biotic and Abiotic Interactions in Aquatic Microcosms Determine Fate and Toxicity of Ag Nanoparticles: Part 2–Toxicity and Ag Speciation

To study the effects of complex environmental media on silver nanoparticle (AgNP) toxicity, AgNPs were added to microcosms with freshwater sediments and two species of aquatic plants (Potamogeton diversifolius and Egeria densa), followed by toxicity testing with microcosm surface water. Microcosms were designed with four environmental matrices in order to determine the contribution of each environmental compartment to changes in toxicity: water only (W), water + sediment (WS), water + plants (WP), and water + plants + sediment (WPS). Silver treatments included AgNPs with two different coatings, gum arabic (GA-AgNPs) or polyvinylpyrollidone (PVP-AgNPs), as well as AgNO(3). Water samples taken from the microcosms at 24 h postdosing were used in acute toxicity tests with two standard model organisms, early life stage zebrafish (Danio rerio) and Daphnia magna. Speciation of Ag in these samples was analyzed using Ag L3-edge X-ray absorption near edge spectroscopy (XANES). Silver speciation patterns for the nanoparticle treatments varied significantly by coating type. While PVP-AgNPs were quite stable and resisted transformation across all matrices (>92.4% Ag(0)), GA-AgNP speciation patterns suggest significantly higher transformation rates, especially in treatments with plants (<69.2% and <58.8% Ag(0) in WP and WPS, respectively) and moderately increased transformation with sediments (<85.6% Ag(0)). Additionally, the presence of plants in the microcosms (with and without sediments) reduced both the concentration of Ag in the water column and toxicity for all Ag treatments. Reductions in toxicity may have been related to decreased water column concentrations as well as changes in the surface chemistry of the particles induced by organic substances released from the plants.

Role of GbpA protein, an important virulence‐related colonization factor, for Vibrio cholerae's survival in the aquatic environment

Vibrio cholerae N-acetyl glucosamine-binding protein A (GbpA) is a chitin binding protein and a virulence factor involved in the colonization of human intestine. We investigated the distribution and genetic variations of gbpA in 488 V. cholerae strains of environmental and clinical origin, belonging to different serogroups and biotypes. We found that the gene is consistently present and highly conserved including an environmental V. cholerae-related strain of ancestral origin. The gene was also consistently expressed in a number of representative V. cholerae strains cultured in laboratory aquatic microcosms under conditions simulating those found in temperate marine environments. Functional analysis carried out on V. cholerae O1 El Tor N16961 showed that GbpA is not involved in adhesion to inorganic surfaces but promotes interaction with environmental biotic substrates (plankton and bivalve hepatopancreas cells) representing known marine reservoir or host for the bacterium. It is suggested that the ability of GbpA to colonize human intestinal cells most probably originated from its primary function in the aquatic environment.

Phenotypic stress response of Pseudomonas aeruginosa following culture in water microcosms

The purpose of the present study was to explore the potential behavioural changes of Pseudomonas aeruginosa following growth in different aquatic environmental conditions. To achieve this, P. aeruginosa was cultured in various water microcosms for 12 months under fixed (pH, nutrients and temperature) factors. P. aeruginosa responses to these conditions were investigated using colony morphotype, biochemical and enzymatic characterisation, pyocin typing, serotyping, sensitivity to different classes of antibiotics and molecular identification. Results show that starvation in water microcosms lead to unusual phenotypes. Of interest is that the pyocin changed from 24/n in the wild type to 83/a following culture in the water microcosms, and the serotype changed from O6 in the wild type to O1 in microcosm-cultured P. aeruginosa. Furthermore, the starvation period in various aquatic microcosms enhanced the resistance of P. aeruginosa against beta-lactam antibiotics. Compared to the other aquatic environments, the seawater microcosm produced the greatest amount of variations in P. aeruginosa. Overall, data demonstrated a high adaptability of P. aeruginosa to environmental changes. This may explain the unusual antibiotic-resistant phenotypes belonging to P. aeruginosa species, and their capacity for spreading that leads to human infections.

Drowned or Dry: A Cross-Habitat Comparison of Detrital Breakdown Processes

Nutrient cycles in both terrestrial and many freshwater habitats are fueled by terrestrial detritus. However, direct comparisons of decomposition processes in these environments are scarce. Aiming at shedding light on similarities and differences in these processes in different habitats, we studied decomposition of low-quality versus high-quality detritus through the action of shredders versus grazers in aquatic versus terrestrial microcosms under controlled climatic conditions. Decomposition processes were most strongly affected by whether they took place in the terrestrial or the aquatic environment: Leaching resulted in a rapid mass loss of detritus in the aquatic environment, and detritus traits became less pronounced over time. Thus, breakdown was mediated through dissolved organic matter (DOM) in water but through particulate organic matter (POM) on land. Litter mass loss and the promoting effects of detritivores on mass loss also depended on the environment, but shredders always had a greater effect than grazers. Both litter and detritivore diversity were overall of little relevance for litter mass loss, but more so in the aquatic than the terrestrial environment. By contrast, the influence of detritivores on microbes was stronger in water than on land, but effects depended on the litter type. The type of both litter and detritivores, however, was less significant in the aquatic than in the terrestrial environment, possibly due to leaching and abiotic processing of litter during early decomposition, resulting in diminishing differences between litter types. We conclude that the habitat type shapes the dynamics of leaf litter decomposition. Heavy leaching (in the aquatic environment) shortens initial decomposition phases and dislocates the degradation of easily accessible compounds in the form of DOM from the leaves into the water column. Consequently, initial interspecific differences in litter quality diminish, and both functional differences in, and diversity of, both litter and detritivores become less important than in the terrestrial environment.

Effects of Potamogeton crispus L. on the fate of phthalic acid esters in an aquatic microcosm

To study the effects of submerged hydrophytes on the fate of dibutyl phthalate (DBP) and di-2-ethylexyl phthalate (DEHP) in the aquatic environment, a Potamogeton crispus L. (P. crispus) microcosm was constructed. A four-compartment (i.e., water, plant, non-rhizosphere and rhizosphere sediments) level IV fugacity model was established and applied to the simulation experiments in the microcosm. Data obtained from model calculations were in good agreement with those from the experiments. Results of the model calculations showed that the total residues of DBP and DEHP in the microcosm with P. crispus were 39.7% and 19.8% lower than those in the microcosm without P. crispus. The overall biodegradation fluxes of DBP and DEHP in the microcosm with P. crispus increased by 4.7% and 12.3%, respectively, and meanwhile, advective outflow decreased. In the presence of P. crispus, a large fraction of loaded DBP and DEHP (17.7% and 29.0%) transferred to plants, and then to the rhizosphere. 4.8% and 28.0% of loaded DBP and DEHP were removed by biodegradation in P. crispus, and the remaining 12.9% and 1.0% were by biodegradation in rhizosphere sediment which was 3.6% of the total sediment. This finding demonstrates that P. crispus can substantially reduce the accumulation of phthalic acid esters (PAEs) in the experiment system and enhance the removal of PAEs. The enhancement of PAE removal is related to the biodegradation of PAEs in P. crispus, especially for the more hydrophobic DEHP. For the less hydrophobic DBP, biodegradation in the rhizosphere also plays a key role. In addition to nutrient uptake from sediment, transport process between P. crispus and the rhizosphere has also a significant influence on the distribution and fate of PAEs in the aquatic environment.

Synergy between prochloraz and esfenvalerate in Daphnia magna from acute and subchronic exposures in the laboratory and microcosms

Azole fungicides can enhance the toxicity of pyrethroid insecticides on aquatic species. It is, however, unknown to what extend the synergy found under laboratory conditions for strongly sorbing compounds (Azole logKow: 3–4, pyrethroid logKow: 6–7) will also take place in the field. We therefore investigated the synergising potential of the fungicide prochloraz on the pyrethroid esfenvalerate on Daphnia magna in the laboratory and in situ in cages placed in outdoor aquatic microcosms treated with 0.17, 0.33 and 0.83μgL−1 esfenvalerate with and without 90μgL−1 prochloraz. We found that the 8–14 fold synergy observed after 2 and 7days of exposure to mixtures in the microcosms was equivalent to or greater than the 3–7 fold synergy found in 2-day laboratory tests. Incubating new neonates in situ 7 and 14days after pesticide addition gave EC50 values of 0.012±0.001 and <0.005μgesfenvalerateL−1 in the mixture treatments, based on measured water column concentrations. The detection limit is more than ten-fold lower than the lowest esfenvalerate concentration observed to cause ecologically significant effects across seven long term mesocosms studies, hence, even on a longer time scale prochloraz apparently synergises the effect of esfenvalerate under field-like conditions in the microcosms. The results show that synergy found in the laboratory also takes place under field like conditions at quantitatively similar levels, and that it lasts for several weeks. More knowledge on the identification of potential synergists, their true bioavailability and the concentrations and time span within which they can cause synergy needs further study, before an overall evaluation of the occurrence and severity of synergy under field conditions can take place.

Effects of species richness on cadmium removal efficiencies of algal microcosms

Summary1. An important factor limiting the wider application of constructed ecosystems for bioremediation of sites contaminated by toxic chemicals is their relatively low efficiency of contaminant removal. Although there is growing evidence that species‐rich ecosystems may out‐perform species‐poor ecosystems in removing excessive nutrients from water through niche partitioning, it remains unknown whether diverse ecosystems are more efficient in removing toxic chemicals from the environment, and if they are, by what mechanisms diverse ecosystems can lead to enhanced removals.2. In this study, we exposed aquatic algal microcosm ecosystems of varying species richness to a realistic cadmium (Cd) contamination scenario. We explore the mechanisms of Cd removal by assemblages with differing diversity and consider the potential role of diversity on Cd bioremediation.3. Our results suggest that Cd removal efficiencies of the algal microcosms increased with species richness. Furthermore, we found that 45% of all polycultures out‐performed the monocultures of their most efficient component species in removing Cd from the growth substrates (referred as to ‘over Cd removal’). However, the average Cd removal efficiency of the most diverse (eight‐species) polycultures was not higher than that of the most efficient monoculture (i.e. the algal species most tolerant to Cd) in this study. We also showed that the observed over Cd removal could be largely ascribed to the enhanced biomass yields of the polycultures, which were mainly driven by the positive effects of Cd‐tolerant species on Cd‐sensitive species.4. Synthesis and applications. This study demonstrates that some algal polycultures containing both Cd‐tolerant and Cd‐sensitive species may show over Cd removal through facilitation provided by Cd‐tolerant species. These polycultures are likely to be assembled and applied to achieve Cd removals higher than those of their most efficient component species in monoculture. Given that species‐rich ecosystems tend to be more environmentally stable than ones with fewer species, it would be prudent to employ diverse polycultures rather than risk the loss of individual monocultures.

Petroleum coke and soft tailings sediment in constructed wetlands may contribute to the uptake of trace metals by algae and aquatic invertebrates

The fate of trace metals in pore water collected from wetland sediments and organisms exposed to petroleum coke were evaluated within in situ aquatic microcosms. Oil sands operators of Fort McMurray, Alberta, Canada produced 60 million tonnes of petroleum coke by 2008, containing elevated concentrations of sulphur and several trace metals commonly seen in oil sands materials. This material may be included in the construction of reclaimed wetlands. Microcosms were filled with a surface layer of petroleum coke over mine-waste sediments and embedded in a constructed wetland for three years to determine how these materials would affect the metal concentrations in the sediment pore water, colonizing wetland plants and benthic invertebrates. Petroleum coke treatments produced significantly elevated levels of Ni. We also found unexpectedly higher concentrations of metals in “consolidated tailings” waste materials, potentially due to the use of oil sands-produced gypsum, and higher background concentration of elements in the sediment used in the controls. A trend of higher concentrations of V, Ni, La, and Y was present in the tissues of the colonizing macrophytic alga Chara spp. Aeshnid dragonflies may also be accumulating V. These results indicate that the trace metals present in some oil sands waste materials could be taken up by aquatic macro-algae and some wetland invertebrates if these materials are included in reclaimed wetlands.

Trophic and functional cascades in tropical versus temperate aquatic microcosms

Inverse trophic cascades are a well explored and common consequence of the local depletion or extinction of top predators in natural ecosystems. Despite a large body of research, the cascading effects of predator removal on ecosystem functions are not as well understood. Developing microcosm experiments, we explored food web changes in trophic structure and ecosystem functioning following biomass removal of top predators in representative temperate and tropical rock pool communities that contained similar assemblages of zooplankton and benthic invertebrates. We observed changes in species abundances following predator removal in both temperate and tropical communities, in line with expected inverse effects of a trophic cascade, where predation release benefits the predator’s preys and competitors and impacts the preys of the latter. We also observed several changes at the community and ecosystem levels including a decrease in total abundance and mean trophic level of the community, and changes in chlorophyll-a and total dissolved particles. Our results also showed an increase in variability of both community and ecosystem processes following the removal of predators. These results illustrate how predator removal can lead to inverse trophic cascades both in structural and functioning properties, and can increase variability of ecosystem processes. Although observed patterns were consistent between tropical and temperate communities following an inverse cascade pattern, changes were more pronounced in the temperate community. Therefore, aquatic food webs may have inherent traits that condition ecosystem responses to changes in top-down trophic control and render some aquatic ecosystems especially sensitive to the removals of top predators.

The impact of environmental variability and species composition on the stability of experimental microbial populations and communities

Understanding how environmental fluctuations affect the stability of populations and communities is complex, for example, because direct effects of environmental variability on populations may be modified and propagated across communities by species interactions. One way to explore and further understand these complexities is via a factorial manipulation of community composition and environmental conditions. Using laboratory based aquatic microcosms we manipulated environmental fluctuation by creating two environments; one with variable light and one with constant light. Within these environments, community composition was manipulated by constructing communities from all possible combinations of three species that vary in their reliance on light for growth (an autotroph: a diatom completely reliant on light, a heterotroph: a Paramecium species not reliant on light, and a mixotroph: a Paramecium species somewhat reliant on light). Community composition was predicted to affect populations and communities by introducing and altering competitive interactions between species and affecting the degree of niche differentiation between species. We found that population stability was predominantly influenced by an interaction between community composition and environmental variability, whereby the effect of environmental variability synergistically combined with effects of community composition to reduce population stability. Covariance of populations was determined by an interaction between community composition and environmental variability, though this did not result from the effect of niche differentiation between species. Species interactions drove correlations between population biomass and the environment which otherwise did not exist. Our results demonstrate the complex and interrelated effects of abiotic and biotic factors on population and community stability, and suggest the need to consider aspects of community composition when predicting the impact of environmental fluctuations.

Effects of chronic γ-irradiation on the aquatic microbial microcosm: equi-dosimetric comparison with effects of heavy metals

Effects of chronic γ-irradiation were investigated in the aquatic microcosm consisting of flagellate algae Euglena gracilis as producers, ciliate protozoa Tetrahymena thermophila as consumers and bacteria Escherichia coli as decomposers. At 1.1 Gy day −1, no effects were observed. At 5.1 Gy day −1, cell densities of E. coli showed a tendency to be lower than those of controls. At 9.7 and 24.7 Gy day −1, population decrease was observed in E. coli. E. gracilis and T. thermophila died out after temporal population decrease and subsequent population increase in T. thermophila. It is likely that this temporal population increase was an indirect effect due to interspecies interactions. Effect dose rates of γ-rays were compared with effect concentrations of some metals using the radiochemoecological conceptual model and the effect index for microcosm. Comparison of these community-level effects data with environmental exposure data suggests that ionising radiation, gadolinium and dysprosium have low risks to affect aquatic microbial communities while manganese, nickel and copper have considerable risks. Effects of chronic irradiation were smaller than those of acute irradiation, and an acute to chronic ratio was calculated to be 28 by dividing an acute dose by chronic daily dose rate at which the effect index was 10%. This ratio would be useful for community-level extrapolation from acute to chronic radiation effects.

An energetic perspective on the relationship between disturbance and ecosystem productivity

Previous ecological models for disturbance from energetic perspectives have focused on destructive pulses by which storages in a system are quickly drained during disturbance events and recovered thereafter. However, considering the wide range of disturbance intensities, frequencies, and durations in nature, disturbance effects on ecosystem energetics would be better understood by diversifying the disturbance effects on specific system configurations or energy pathways. Based on two hypotheses, we built simulation models of the variable disturbance–productivity relationships observed in a freshwater aquatic microcosm study. First, we hypothesized that disturbances will differentially alter the intrinsic rates of energy pathways in a system. Second, we hypothesized that there is a disturbance threshold where response of the intrinsic rates changes abruptly. Simulation results showed variable patterns of gross primary productivity (GPP) during the disturbance and post-disturbance periods under the diverse scenarios of disturbance effects on the intrinsic rates. Simulation results confirmed that the second hypothesis (i.e., disturbance threshold) was essential to achieve a U-shaped or peaked disturbance–productivity relationship. We evaluated the models by comparing them with the results of the microcosm tests, and suggested possible mechanisms of the variable disturbance–productivity relationships by varying parameters related to the disturbance effects on the intrinsic rates and the disturbance thresholds.

Fluctuating resource availability increases invasibility in microbial microcosms

The fluctuating resource hypothesis (FRH) proposes that fluctuations in resource supply can temporally reduce competitive pressure from resident species, thereby providing ephemeral opportunities for invading species. Although FRH has the potential to integrate many existing hypotheses regarding mechanisms of community invasibility, previous tests and evaluations of FRH were based on single trophic level, did not take the timing effect into account, and had difficulties in distinguishing the effects of resource pulses from other simultaneous processes. Here we test FRH in multi‐trophic aquatic microcosms by creating resource pulses, by controlling resource quantity, propagule supply and pulse recurrence frequency, and by manipulating the timing of pulses relative to the timing of the arrival of new species (i.e. invaders) to local communities. The novelty of our work lies in that we directly manipulate resource pulse timing relative to invader introduction events and thus demonstrate the importance of this timing effect for community invasibility. Our study supports FRH in general: invasion success was positively related to resource pulses, and invaders had strong performance in treatments receiving coincident pulses, although not all invaders gained more benefit when resources were supplied at large‐magnitude than supplied at continuous rates. Since many ecosystems worldwide are experiencing high rates of anthropogenic nutrient input and increasing rates of precipitation, these ecosystems are potentially more fragile and susceptible to invasion. More experiments across multiple ecosystem types are needed to help formulate a general theory of community invasibility.

Understanding self-organization of ecosystems under disturbance using a microcosm study

It is a key to success of ecological engineering to understand self-organization of a target ecosystem. Self-organizing patterns of ecosystems, however, become complicated due to a wide range of disturbance regimes in nature. We investigated how disturbances influence self-organization of ecosystems from energetic perspectives using 14 freshwater aquatic microcosms transplanted from lakes in Florida. We observed five different disturbance–productivity relationships from the microcosm tests and these variable relationships were attributed to the different initial states of the microcosms under the same input sequence of test plans and disturbance regimes. Through processes of self-organization, as the microcosms matured with time, resistance increased and resilience decreased. The microcosm study provided insights regarding restoration and management of ecosystems including the insight that initial seeds for restoration of an ecosystem should be carefully selected in consideration of typical disturbance regimes of the region. It is also suggested that consideration or manipulation of disturbance regimes in each successional stage is sometimes needed for maximum productivity or a designated goal of a restoration project because self-organizing patterns that result under disturbances vary depending on a system's maturity.

Waterborne nickel bioaccumulation in Gammarus pulex: Comparison of mechanistic models and influence of water cationic composition

The biodynamic and saturation models offer promising lines of enquiry to predict the bioaccumulation of metals by aquatic organisms. However, in order to construct these models, the accumulation strategies have to be defined for each metal/organism couple in controlled conditions. This study aims at modelling the waterborne bioaccumulation of Ni and the influence of the water's geochemical properties on this process in a crustacean that is widely distributed in Europe, Gammarus pulex. In the laboratory, G. pulex was exposed to several Ni concentrations (from 0.001 to 100 mg L −1) in aquatic microcosms. Our results show that G. pulex is very tolerant to Ni (LC50 48 h = 477 mg L −1 Ni). Time course experiments enabled the construction of a biodynamic model by determining the uptake ( k u ) and elimination ( k e ) rate constants. When the exposure concentration exceeded 1 mg L −1 Ni, the metal uptake reached a maximum due to a limited number of binding sites for Ni. Therefore, the organism's maximal capacity to accumulate the metal ( B max ) and the half-saturation constant ( K) were determined to establish the saturation model. We showed that the two models are comparable for the lowest exposure concentrations (<1 mg L −1 Ni), with k u / k e = B max / K. Then, the bioaccumulation of Ni was recorded in waters exhibiting various concentrations of three major ions (Na +, Mg 2+ and Ca 2+). Only Ca had an inhibitory effect on the Ni uptake. This study reports for the first time the bioaccumulation of Ni in G. pulex. Because of its high tolerance to Ni and its high capacity to accumulate this metal, this crustacean could be used as an indicator of Ni bioavailability in freshwaters.

Environmental safety to decomposer invertebrates of azadirachtin (neem) as a systemic insecticide in trees to control emerald ash borer

The non-target effects of an azadirachtin-based systemic insecticide used for control of wood-boring insect pests in trees were assessed on litter-dwelling earthworms, leaf-shredding aquatic insects, and microbial communities in terrestrial and aquatic microcosms. The insecticide was injected into the trunks of ash trees at a rate of 0.2 g azadirachtin cm −1 tree diameter in early summer. At the time of senescence, foliar concentrations in most (65%) leaves where at or below detection (<0.01 mg kg −1 total azadirachtin) and the average concentration among leaves overall at senescence was 0.19 mg kg −1. Leaves from the azadirachtin-treated trees at senescence were added to microcosms and responses by test organisms were compared to those in microcosms containing leaves from non-treated ash trees (controls). No significant reductions were detected among earthworm survival, leaf consumption rates, growth rates, or cocoon production, aquatic insect survival and leaf consumption rates, and among terrestrial and aquatic microbial decomposition of leaf material in comparison to controls. In a further set of microcosm tests containing leaves from intentional high-dose trees, the only significant, adverse effect detected was a reduction in microbial decomposition of leaf material, and only at the highest test concentration (∼6 mg kg −1). Results indicated no significant adverse effects on litter-dwelling earthworms or leaf-shredding aquatic insects at concentrations up to at least 30× the expected field concentrations at operational rates, and at 6× expected field concentrations for adverse effects on microbial decomposition. We conclude that when azadirachtin is used as a systemic insecticide in trees for control of insect pests such as the invasive wood-boring beetle, emerald ash borer, resultant foliar concentrations in senescent leaf material are likely to pose little risk of harm to decomposer invertebrates.

Effect of tank bromeliad micro-environment on Aedes aegypti larval mortality

Many species of bromeliads create an aquatic microcosm among their leaves. Besides their native aquatic fauna, these microcosms can be used by larvae of invasive mosquitoes like Aedes aegypti. We compared the mortality among A. aegypti larvae placed inside tanks of Aechmea fasciata bromeliads with larvae placed inside artificial microcosms and with microcosms with low pH (5.4), which simulate the acidic conditions found inside bromeliad tanks. A. aegypti larvae suffered a significantly higher mortality inside bromeliad tanks compared to larvae in control microcosms, but the mortality inside bromeliads did not differ statistically from that found in artificial microcosms simulating bromeliad acidic conditions. We concluded that bromeliad tanks tend to be a less suitable environment for the development of A. aegypti larvae than artificial containers due to the acidification generated by bromeliad physiology.