Microcosm Design Research Articles

The composition of the arbuscular mycorrhizal fungal bacteriome is species dependent

BackgroundIn addition to their role as endosymbionts for plant roots, arbuscular mycorrhizal fungi (AMF) engage in complex interactions with various soil microorganisms, the rhizosphere, and the root endosphere of host plants. They also host diverse prokaryotic groups within their mycelia, contributing to what is termed multipartite symbiosis. In this study, we examined the impact of three AMF species—Rhizophagus irregularis, R. clarus, and R. cerebriforme—combined with microbial bioaugmentation on the diversity and composition of bacterial communities in the mycelia and hyphosphere. Using a microcosm design to separate the influence of host plant roots from AMF mycelia and Illumina MiSeq amplicon sequencing to analyze the bacterial communities.ResultsOur results revealed that, while AMF identity and microbial bioaugmentation did not affect the structure of bacterial communities in the hyphosphere soil, they significantly altered the communities associated with their mycelia. Although all three AMF species belong to the same genus, with R. irregularis and R. clarus being closely related compared to R. cerebriforme, we observed variations in the bacterial communities associated with their mycelia. Interestingly, the mycelial bacterial community of R. cerebriforme contained 60 bacteriome core taxa exclusive to it, while R. clarus and R. irregularis had 25 and 9 exclusive taxa, respectively.ConclusionThis study suggests that organismal phylogeny influences the bacterial communities associated with AMF mycelia. These findings provide new insights into AMF and bacterial interactions, which are crucial for the successful deployment of AMF inoculants. The taxonomic diversity of AMF inoculants is important for engineering the plant microbiome and enhancing ecosystem services.

Exposure pathways matter: Aquatic phototrophic communities respond differently to agricultural run‐off exposed via sediment or water

Abstract Small shallow ponds are widespread but understudied water bodies in agricultural landscapes. Agricultural run‐off (ARO) transports pesticides and nutrients into adjacent aquatic ecosystems where they occur dissolved in the water column or are bound to sediments. Consequently, aquatic communities are affected by ARO via different exposure pathways. We hypothesize that sediment‐bound ARO mainly affects submerged rooted macrophytes, while phytoplankton and periphyton are more prone to ARO in water. These primary producers compete for resources resulting in a regime shift between alternative stable states of macrophyte or phytoplankton dominance. We hypothesize that warming increases nutrient release from sediments and thereby facilitates the occurrence of phytoplankton dominance. Using a full‐factorial microcosm design, we exposed aquatic primary producers to either sediment or water application of a mixture of common pesticides (terbuthylazine, pirimicarb, tebuconazole and copper) and nitrate at two concentrations and two temperatures (22°C and 26°C) for 4 weeks. Initial and final concentrations of pesticides and nitrate, final biomass of macrophytes, periphyton and phytoplankton, pesticide accumulation in macrophytes and changes in carbon, nitrogen and phosphorus content and selected exoenzyme activities in the sediment were measured. We found lower final macrophyte biomass for both ARO treatments compared to controls, indicating a prevalence of negative effects by herbicides and competition for light with other phototrophs. In contrast, phytoplankton and periphyton biomass increased, but only when exposed to ARO via the water column, indicating a prevalence of positive effects by nutrient supply. Microbial carbon and nutrient cycling in sediments was not affected by ARO. Higher temperature mitigated ARO‐related effects on macrophytes under sediment exposure. Synthesis and application. ARO poses a strong risk of submerged macrophyte loss and establishment of turbid conditions with phytoplankton dominance in aquatic ecosystems. In conclusion, exposure pathways as well as indirect and interacting effects of multiple stressors need to be considered when designing appropriate mitigation measures. Under climate change, we suggest to prioritize local measures as buffer strips a reduced use of pesticides and fertilizers, and sediment removal as appropriate measures to protect these vulnerable but widespread aquatic systems, which are highly relevant for biodiversity in agricultural landscapes.

Aqueous selenium removal and distribution in cattail and duckweed in constructed wetland microcosms

AbstractSelenium (Se)‐affected stormwater runoff raises concerns about potential downstream impact of Se on aquatic ecosystems. Unplanted (UNP) detention ponds augmented with cattail (Typha angustifolia L.; CAT) and duckweed (Lemna minor L.; DWD) may provide a solution for continuous, rapid abatement of Se‐affected runoff. This research was conducted to evaluate the efficacy of CAT or DWD and determining the distribution of Se within a continually flooded detain and drain system. Microcosms containing 3 kg of soil planted to either one CAT, 25 g fresh DWD, or left unplanted (UNP, control) were flooded with a 3‐L solution at 40 μg Se L−1, as sodium selenate (Na2SeO4), or a zero Se control. Over two 10‐d flood–discharge cycles (FDCs), plants in microcosms were evaluated in growth chambers maintained at 30 °C under a 12‐h photoperiod with 400 μmol m−2 s−1 irradiance. Initial and final water, soil, plant, and granular activated charcoal (GAC) were analyzed for total [Se] with inductively coupled plasma–mass spectroscopy (ICP–MS). Data were analyzed with PROC GLM (SAS EG 7.1) at α = .05. Within 10 d after Se application, CAT and DWD decreased aqueous Se from 40 μg Se L−1 to below the 11.8 μg Se L−1 threshold. Selenium recovery ranged between 75 and 100% of the applied Se. In continually flooded systems, the primary elimination pathway appears to be associated with the soil solid phase. Cattail and DWD are suitable species for constructed wetland phytoremediation of Se‐affected runoff. The microcosm design presented may be useful for future evaluations.

In situ microcosms deployed at the coast of British Columbia (Canada) to study dilbit weathering and associated microbial communities under marine conditions.

ABSTRACTDouglas Channel and the adjacent Hecate Strait (British Columbia, Canada) are part of a proposed route to ship diluted bitumen (dilbit). This study presents how two types of dilbit naturally degrade in this environment by using an in situ microcosm design based on dilbit-coated beads. We show that dilbit-associated n-alkanes were microbially biodegraded with estimated half-lives of 57–69 days. n-Alkanes appeared to be primarily degraded using the aerobic alkB, ladA and CYP153 pathways. The loss of dilbit polycyclic aromatic hydrocarbons (PAHs) was slower than of n-alkanes, with half-lives of 89–439 days. A biodegradation of PAHs could not be conclusively determined, although a significant enrichment of the phnAc gene (a marker for aerobic PAH biodegradation) was observed. PAH degradation appeared to be slower in Hecate Strait than in Douglas Channel. Microcosm-associated microbial communities were shaped by the presence of dilbit, deployment location and incubation time but not by dilbit type. Metagenome-assembled genomes of putative dilbit-degraders were obtained and could be divided into populations of early, late and continuous degraders. The majority of the identified MAGs could be assigned to the orders Flavobacteriales, Methylococcales, Pseudomonadales and Rhodobacterales. A high proportion of the MAGs represent currently unknown lineages or lineages with currently no cultured representative.

Food consumption of the cockroach species Blaptica dubia Serville (Blattodea: Blaberidae) using three leaf litter types in a microcosm design

This study investigated the effect of different plant litter types and developmental stages of the cockroach species Blaptica dubia on food consumption, animal growth, and excrement production. Three leaf litter species Alnus glutinosa, Acer platanoides, and Quercus robur were selected as model plants in a microcosm test in which plant litter was consumed by three different cockroach instar groups during five consecutive one-week intervals. At each interval, litter consumption, animal weight, and produced excrements were measured. The results showed slightly higher consumption of A. glutinosa compared to other leaf litter species in all three age/size groups of animals. Animals gained weight with time, especially Group B (medium-sized class animals) feeding on Alnus. The production of excrements was higher in Group C (big class animals) and increased in Alnus among litter species. Foliar litter consumption and excrement production rates were highest in B and C animal groups and in Alnus treatments; however, animal growth rates did not show a clear pattern, except for A. glutinosa. Measured energy contents showed highest values for animals, but slightly higher for leaves compared to excrements. Our results show that using energy budget parameters can help explain the relationship between litter type, cockroach sizes, and their consumption in this microcosm experiment.

Consumption Performance of Five Detritivore Species Feeding on Alnus glutinosa L. Leaf Litter in a Microcosm Experiment

The present study was performed to assess the feeding performance of five detritivore species in a microcosm design. The test animals were four millipede species, Telodeinopus aoutii (Demange), Epibolus pulchripes (Gerstäcker), Cylindroiulus caeruleocinctus (Wood), Glomeris hexasticha (Brandt), and one isopod species, Porcellio scaber (Latreille), all feeding on Alnus glutinosa L. leaf litter for five consecutive weeks. At the end of each one-week interval, litter consumption, animal fresh weight, and excrement production were measured. Then, the feeding activity parameters for each species were calculated. Between big-size animal species, higher leaf consumption rates of 12.3–30.9 mg dry weight day−1 individual−1 were calculated for T. aoutii compared to those of 3.72–8.25 mg dry weight day−1 individual−1 for E. pulchripes. However, there was no difference in the consumption rates among small-size animals ranging from 0.46 to 1.65 mg dry weight day−1 individual−1. Excrement production rates followed a similar trend, as the consumption rates and the animals’ body weight remained constant during the experiment. Time was an important factor influencing the feeding activity of the animals, especially for the big-size group. Overall, the average assimilation efficiency of these species varied from 13.7% to 53.3%. The results of the present work will be the first step for understanding the ecological needs of these decomposer species in soil ecosystems.

Sublethal Effects of Crude Oil on the Community Structure of Estuarine Phytoplankton

While the ecological impacts of crude oil exposure have been widely studied, its sublethal effects on phytoplankton community structure in salt marsh estuaries have not been well documented. The purpose of this study was to simulate oil spill conditions using a microcosm design to examine short-term (2 day) changes in phytoplankton community composition and total biomass following exposure to crude oil obtained from the Deepwater Horizon oil spill and a mixture of Texas crude oils. Microcosm experiments were performed in situ in North Inlet Estuary near Georgetown, SC. A control and six replicated experimental treatments of crude oil additions at final concentrations of 10, 50, or 100 μl l−1 of either Deepwater Horizon spill oil or the Texas crude mixture were incubated under in situ conditions. Photopigments were analyzed using high-performance liquid chromatography and community composition was determined using ChemTax. Total phytoplankton biomass (as chl a) declined with increasing crude oil concentrations. Prasinophytes, the most abundant microalga in both experiments, showed no response to oil exposure in one experiment and a significant negative response in the other. Diatoms euglenophytes and chlorophytes appeared relatively resistant to oil contamination at the exposure levels used in this study, maintaining or increasing their relative abundance with increasing oil concentrations. Chlorophytes and cyanobacteria increased in relative abundance while cryptophyte abundance decreased with increasing oil concentrations. The results of these experiments suggest that low levels of crude oil exposure may reduce total biomass and alter phytoplankton community composition with possible cascade effects at higher trophic levels in salt marsh estuaries.

Bioaccumulation and toxicity of copper in outdoor freshwater microcosms

This study characterizes the effects of copper (Cu) on Florida apple snails ( Pomacea paludosa) and mosquito fish ( Gambusia affinis) using a replicated outdoor microcosm design. Soils used in this study were collected from two Cu-enriched citrus agricultural sites in South Florida (Agler property (AGLR) in St. Lucie County and Sunrise Boys property (SRB) in Palm Beach County) and a reference site (Equus property) in St. Lucie County. The study included a 5-week aging phase, an 11 month exposure phase, and a 3 month post-treatment (exposure) phase. The aging phase was initiated by flooding agricultural soils with rainwater in 4 m 3 fiberglass microcosm tanks. Introducing juvenile apple snails (≤7 d old) and mosquito fish (2–3 cm) into the microcosm tanks initiated the exposure phase. Survival, growth, and reproduction of apple snails and fish, and Cu uptake in apple snails, fish, and periphyton were determined in this study. Water chemistry (e.g., dissolved Cu concentration, dissolved organic carbon and dissolved oxygen concentrations, pH, hardness, alkalinity, etc.) was measured daily or weekly during the study. Initial soil Cu concentrations in Equus, SRB, and AGLR microcosms were 7, 55, and 99 mg/kg dw, respectively. Dissolved Cu concentrations in Equus, SRB and AGLR microcosms at the beginning of the study were 3, 82, and 43 μg/L, respectively and decreased to low saturation levels of about ≤9 μg/L Cu after the first 3 months of the study. The decrease of dissolved Cu concentrations was likely due to the dilution of rainwater. Snail and fish mortality appeared to be higher in SRB microcosms than in Equus and AGLR microcosms. There was no significant difference in growth of the snails between treatments. Snail growth data followed the von Bertalanffy Model. The maximum shell length, shell height, and shell width of the snails calculated by the von Bertalanffy Model ( L ∞) were 2.76, 2.05, and 2.18 cm, respectively. The maximum wet weight was 9.38 g. Growth rate ( k) of the snails increased in order of shell height (0.459), shell length (0.550), and shell weight (0.598). There was no reproduction in the snails in any treatments including the reference during the exposure phase. However, Cu did not affect reproduction of fish during this period. Copper concentrations in periphyton from Equus, SRB, and AGLR microcosms ranged from 2 to 62, 31 to 371, and 13 to 478 mg/kg, respectively. Copper concentrations in fish at the beginning, days 30 and 150 of the study ranged from 3.19 to 7.53 mg/kg and were not significantly different from the different treatments. Average Cu concentrations in the soft tissue of dead snails from SRB and AGLR microcosms were 4602 mg/kg dw (ranged from 2913 to 8370 mg/kg dw) and 2824 mg/kg dw (ranged from 2118 to 3600 mg/kg dw), respectively. The Cu concentrations in the soft tissue of dead snails found in this study were higher than the tissue Cu concentrations in live aquatic organisms reported in the literature. These high Cu concentrations in edible apple snail soft tissue might pose a risk to Florida apple snail predators, including the snail kite. The post-exposure phase, with snails exposed to only water (i.e., no soils) showed depuration of copper from apple snails and reproduction in all treatments.

Heavy Metal Pollution in Lentic Ecosystem of Sub-Tropical Industrial Region and its Phytoremediation

Metals and several physicochemical parameters, from four sampling sites in a tropical lake receiving the discharges from a thermal power plant, a coal mine and a chlor-alkali industry, were studied from 2004–2005. Pertaining to metal pollution, the site most polluted with heavy metals was Belwadah, i.e., waters and sediments had the highest concentration of all the metals examined. The reference site was characterized by the presence of low concentrations of metals in waters and in sediments. Further, several wetland plants were harvested from different sites, and simultaneously, these were assessed for their metal concentration efficiency. Following the water quality monitoring and metal concentration efficiency, two-month field phytoremediation experiments were conducted using large enclosures at the discharge point of different polluted sites of the lake. Eichhornia crassipes, Lemna minor, and Azolla pinnata were frontier metal accumulators hence selected for previously mentioned field phytoremediation experiments. During field phytoremediation experiments using aquatic macrophytes, marked percentage reduction in metals concentrations were recorded. The percentage decrease for different metals was in the range of 25–67.90% at Belwadah (with Eichhornia crassipes and Lemna minor), 25–77.14% at Dongia nala (with Eichhornia crassipes, Lemna minor, and Azolla pinnata) and 25–71.42% at Ash pond site of G.B. Pant Sagar (with Lemna minor and Azolla pinnata). Preliminary studies of polluted sites are therefore useful for improved microcosm design and for the systematic extrapolation of information from experimental ecosystems to natural ecosystems.

Phytoremediation of heavy metals in a tropical impoundment of industrial region

Aquatic pollution poses a serious challenge to the scientific community worldwide, since lakes or reservoirs find multifarious use and most often their water is used for drinking, bathing, irrigation, and aquaculture. Nine metals and several physicochemical parameters, from four sampling sites in a tropical lake receiving the discharges from a thermal power plant, a coal mine, and a chlor-alkali industry, were studied from 2004 to 2005. Pertaining to metal pollution, the site most polluted with heavy metals was Belwadah, i.e., waters and sediments had the highest concentration of all the metals examined. The reference site was characterized by the presence of low concentrations of metals in waters and sediments. Following the water quality monitoring, 2-month field phytoremediation experiments were conducted using large enclosures at the discharge point of different polluted sites of the lake. During field phytoremediation experiments using aquatic macrophytes, marked percentage reduction in metals concentrations were recorded. The percentage decrease for different metals was in the range of 25% to 67.90% at Belwadah (with Eichhornia crassipes and Lemna minor), 25% to 77.14% at Dongia nala (with E. crassipes, L. minor and Azolla pinnata), and 25% to 71.42% at Ash pond site of G.B. Pant Sagar (with L. minor and A. pinnata). Preliminary studies of polluted sites are useful for improved microcosm design and for the systematic extrapolation of information from experimental ecosystems to natural ecosystems.

In situ assays with tropical cladocerans to evaluate edge-of-field pesticide runoff toxicity

Tropical regions' economy is usually based on agriculture, which involves an intensive use, and even frequent overuse, of pesticides. Nevertheless, not much research has been done on the impact of pesticides on tropical aquatic ecosystems, which are often contaminated by runoff-related pesticide inputs due to unpredictable and torrential rainfalls. This study aimed to: (i) adapt and evaluate a short-term sublethal in situ assay using post-exposure feeding as an endpoint, to the tropical cladoceran species Diaphanosoma brachyurum (collected at the Pedra do Cavalo dam in the Paraguaçu River basin, Bahia, Brazil), and, (ii) assess the role of the standard species Daphnia magna as an adequate laboratory surrogate. Lethal and sublethal (post-exposure feeding) responses were assessed for the two species. To evaluate these responses under environmentally realistic exposure conditions, a runoff event was simulated in an agricultural area previously contaminated with different deltamethrin concentrations. The resultant runoff water was used to set up microcosms with different dilutions, simulating the entrance of runoff water in an adjacent lentic system. An in situ assay with D. brachyurum was performed inside the microcosms, allowing to discriminate the effects due to deltamethrin from those due to other potential stressors associated with the experimental design (e.g. organism handling, load of suspended particles, microcosm design). Water samples were collected from microcosms to conduct a laboratory assay with D. magna. The in situ methodologies revealed to be suitable to conduct assays with D. brachyurum under tropical conditions, since all exposed organisms were successfully retrieved from the chambers. Furthermore, none of the potential stressors associated with the experimental design influenced the daphnids' performance. The tropical cladoceran species, exposed under more realistic conditions, revealed to be more sensitive than the laboratory standard species: lethal effects were only observed for D. brachyurum and sublethal effects were noticed at a lower deltamethrin concentration for this species than for D. magna.

Microcosm design and evaluation to study stream microbial biofilms

Biofilms represent the dominant form of microbial life in stream ecosystems. Research of complex environmental biofilms requires appropriate cultivation techniques to address questions central to biofilm structure‐function‐coupling and ecosystem implications. Whereas the cultivation of medical and industrial biofilms has received considerable attention, cultivation devices for environmental biofilms have not. Here we describe and systematically assess the reproducibility of laboratory‐based microcosms that allow the study of the structure and function of stream biofilms under different flow regimes. Microcosms were assembled from 1.3‐m‐long Plexiglas flumes fed with water that recirculated between a header tank and a sink. Each flume was paved with 104 individual unglazed ceramic coupons that served as growth substratum. We operated 3 microcosms designed to simulate laminar, transitional, and turbulent flow. Each microcosm consisted of two duplicate sets of flumes where two flumes shared the same water. We monitored biofilm coverage, bacterial abundance, and chlorophyll a as bulk biomass parameters over a growth period of 28 days and tested for community composition shifts using denaturing gradient gel electrophoresis (DGGE). Based on these variables, we assessed the reproducibility at different levels of microcosm assembly: (1) within individual flumes (i.e., longitudinal gradients), (2) within a shared water body, and (3) within flow regime treatments. Our results revealed good reproducibility at the various levels of the experimental setup and suggest microcosm flumes as highly valuable tools for biofilm studies with multitreatment and multireference designs.

Soil Phosphorus Uptake by Continuously Cropped Lupinus albus: A New Microcosm Design

When grown in soils with sparingly available phosphorus (P), white lupin (Lupinus albus L.) forms special root structures, called cluster roots, which secrete large amounts of organic acids and concomitantly acidify the rhizosphere. Many studies dealing with the understanding of this P acquisition strategy have been performed in short time experiments either in hydroponic cultures or in small microcosm designs with sand or sand:soil mixtures. In the present study, we applied an experimental design which came nearer to the natural field conditions: we performed a one-year experiment on large microcosms containing 7 kg of soil and allowing separation of rhizosphere soil and bulk soil. We planted six successive generations of lupins and analysed P uptake, organic P desorption, phosphatase activities and organic acid concentrations in different soil samples along a spatio-temporal gradient. We compared the rhizosphere soil samples of cluster (RSC) and non-cluster roots (RSNC) as well as the bulk soil (BS) samples. A total shoot biomass of 55.69 ± 1.51 g (d.w.) y−1 was produced and P uptake reached 220.59 ± 5.99 mg y−1. More P was desorbed from RSC than from RSNC or BS (P < 0.05). RSC and RSNC showed a higher activity of acid and alkaline phosphatases than BS samples and a higher acid phosphatase activity was observed in RSC than in RSNC throughout the one-year experiment. Fumarate was the most abundant organic acid in all rhizosphere soil samples. Citrate was only present in detectable amounts in RSC while malate and fumarate were recovered from both RSC and RSNC. Almost no organic acids could be detected in the BS samples. Our results demonstrated that over a one-year cultivation period in the absence of an external P supply, white lupin was able to acquire phosphate from the soil and that the processes leading to this P uptake took place preferentially in the rhizosphere of cluster roots.

Toxicologic and Histopathologic Response of the Terrestrial Salamander Plethodon cinereus to Soil Exposures of 1,3,5-Trinitrohexahydro-1,3,5-Triazine

Red-backed salamanders (Plethodon cinereus) were exposed to four different concentrations of 1,3,5-trinitrohexahydro-1,3,5-triazine (RDX) in soil under controlled laboratory conditions for 28 days. Wild-caught P. cinereus (N = 20/treatment) were exposed to target concentrations of 5,000, 1000, 100, 10, and 0 mg RDX/kg soil (dry wt) using a microcosm design. Animals were fed 5 to 10 uncontaminated mutant Drosophila flies every 3 days and monitored daily. Animals were weighed 1 day before being placed in treatment and weekly thereafter. RDX concentrations in soil were analytically determined after the compound was added and mixed at the beginning, the midpoint, and the end of exposure. RDX soil concentrations were relatively stable throughout the exposure period. Signs of overt toxicity were observed primarily in the highest exposure group. Salamanders exposed to 5,000 mg RDX/kg soil exhibited signs of neuromuscular effects (lethargy, gaping, hypersensitivity, tremors) and exhibited significant weight loss. A single moribund animal from this group lost >20% of its original body weight and was killed. Animals in this exposure group also lost weight relative to animals in other treatments. Histopathologic evaluations, including an evaluation of melanomacrophage parameters, indicated no strong treatment-related findings. This study provided information regarding the effects from subchronic dermal exposure of a terrestrial amphibian species to RDX in soil and provides a microcosm approach to the evaluation of toxicity of contaminants in soil to a terrestrial vertebrate.

Fate and effects of the insecticide–miticide chlorfenapyr in outdoor aquatic microcosms

The concentrations of chlorfenapyr in water and sediment in a lentic pond following early and late applications in a Florida crop treatment program were predicted using PRZM and EXAMS modeling and incorporating 30 years of actual rainfall data. An outdoor microcosm study was also conducted to determine the fate of chlorfenapyr and its effects on zooplankton, macroinvertebrates, phytoplankton, and fish in a freshwater system under exposure conditions representing simulated surface runoff and/or spray drift. The microcosm design used a regression model with five treatments (i.e., 300 μg/L spray, 30 μg/L spray, 15 μg/L spray and 30 μg/L runoff, 1.2 μg/L spray and 2.5 μg/L runoff, 30 μg/L runoff) plus a control. Chlorfenapyr was applied as an aqueous suspension concentrate (36% a.i.) to six microcosm tanks (30.9 m 3). The no-observed-effect-concentration (NOEC) for zooplankton was the water concentration produced from the combination 1.2 μg/L spray and 2.5 μg/L runoff treatment. The NOEC for bluegill sunfish was the water concentration produced from the 30 μg/L runoff, which was significantly higher than the exposure concentrations from the lowest combination treatment. Chlorfenapyr was more toxic via spray to the water than via an exposure simulating surface runoff. The 96-h time weighted average concentrations (TWAs) from the lowest joint treatment and the 30 μg/L runoff treatment in the microcosm study were similar to model-predicted water 96-h TWA concentrations from early and late applications. The toxicity data from laboratory and microcosm studies along with water exposure data indicate low hazard to zooplankton species in the water column. Although chlorfenapyr remained in sediment, TWAs concentrations from the microcosm study along with model-predicted concentrations indicate low hazard to benthic invertebrate species based on acute toxicity to amphipods in the laboratory. Results from this assessment indicate that with appropriate measures to mitigate spray drift to shallow water bodies, applications of chlorfenapyr do not present a hazard to aquatic organisms during labeled uses.

A field method using microcosms to evaluate transfer of Cd, Cu, Ni, Pb and Zn from sewage sludge amended forest soils to Helix aspersa snails

Juvenile Helix aspersa snails exposed in field microcosms were used to assess the transfer of Cd, Cu, Ni, Pb and Zn from forest soils amended with liquid and composted sewage sludge. Zn concentrations and contents were significantly higher in snails exposed to liquid and composted sludge after 5 and 7 weeks of exposure, when compared with control. Trends were less clear for the other metals. Present results show that Zn, among the cocktail of metallic trace elements (MTE) coming from sewage sludge disposal, represents the principal concern for food chain transfer and secondary poisoning risks. The microcosm design used in this experiment was well suited for relatively long-term (about 2 months) active biomonitoring with H. aspersa snails. The snails quickly indicated the variations of MTE concentrations in their immediate environment. Therefore, the present study provides a simple but efficient field tool to evaluate MTE bioavailability and transfer.

USE of outdoor freshwater pond microcosms: I. Microcosm design and fate of pyridaben

AbstractAn outdoor freshwater microcosm study was conducted in which pyridaben, an insecticide‐miticide, was directly applied to water to determine its fate and biological effects on an aquatic community. The following paper describes the design, specific techniques, and fate of pyridaben in microcosms including model prediction of the estimated environmental concentration, whereas the subsequent paper describes the responses of biota. An analysis of variance design was used with four treatments in which pyridaben was applied as an aqueous suspension (75% wettable powder) at three concentrations (0.34, 3.4, 34.0 μg/L) plus an untreated control to 24 microcosm tanks (23 m3). Each treatment was replicated six times. Pyridaben was applied to each microcosm once in April and once in May 1993 to simulate actual crop application. The Exposure Analysis Modeling System predicted that as a result of a drift (5.0%) exposure scenario, the half‐life of pyridaben in water was 30 to 34 h. The model also predicted negligible concentrations of pyridaben in sediment after drift. Surface runoff was not considered an important source of pyridaben to aquatic systems, because the Pesticide Root Zone Model predicted a maximum runoff concentration of 0.1 μg/L. The half‐life in microcosm water for the low, middle, and high treatment concentrations for both applications ranged from 11.8 to 28.5 h. After both applications at 3.4 μg/L, pyridaben was not detected in sediment within 24 h, whereas at 34.0 μg/L the half‐life of pyridaben in sediment was 9.8 d.

Environmental fate of synthetic pyrethroids during spray drift and field runoff treatments in aquatic microcosms

The aquatic fate and persistence of synthetic pyrethroids under spray drift and field runoff treatment regimes were determined in outdoor pond microcosms. In this paper, the experimental design and construction of outdoor microcosms is presented, as well as the aquatic fate of tralomethrin and deltamethrin. Tralomethrin is rapidly degraded to deltamethrin, with a half-life of 12.7 hours under spray drift conditions. Degradation profiles of tralomethrin in water indicated rapid conversion of deltamethrin and to less active isomers and then to decamethrinic acid (BR 2CA). After 24 hours, the percent radioactivity of tralomethrin was 25% of the test material in the water column. In sediment, tralomethrin was immediately converted to deltamethrin. Deltamethrin is rapidly degraded with a half-life of 8 to 48 hours, depending on mechanism of introduction into water. Degradation profiles of deltamethrin in water indicated rapid conversion of deltamethrin to decamethrinic acid (BR 2CA), comprising approximately 90% of the radioactivity in the aqueous phase at 168 hours. Extraction and analysis of fathead minnows ( Pimephales promelas) after 96 hours revealed that tissue residues contained parent compounds and metabolites α-R-deltamethrin, trans-deltamethrin and Br 2CA. Fish residues are directly related to aqueous concentrations, thus bioavailability under field runoff regimes were an order of magnitude lower than tissue residues under spray drift conditions. Plant tissue was found to significantly accumulate pyrethroids.

Development of small outdoor microcosms for studying contaminant transformation rates and mechanisms under various water column conditions

AbstractThree outdoor microcosm treatments were developed to simulate aerobic (aerobic), thermally stratified (stratified), and anaerobic (anaerobic) water columns for assessing contaminant transformation rates under controlled, quasi‐natural conditions. Twelve 3.2‐m‐diameter by 1.4‐m‐deep fiberglass tanks (11.3 m3 water volume) were used in the study, four for each treatment. The tanks were variably manipulated both physically (with internal frames and plastic layers) and chemically (with sediment trays and grass supplements) to facilitate the three environments. The manipulations successfully created three different and reproducible (both between tanks with common treatments and over time) aquatic systems for further study. The aerobic treatment produced a good simulation of a P‐limited, mesotrophic water column. Alternately, both the stratified and anaerobic treatments developed eutrophic to hypereutrophic water conditions and had nutritionally balanced total nitrogen (TN) and total phosphorus (TP) levels (approximately 14:1 mg N/mg P). Mild thermal stratification was achieved in the stratified units and low‐oxygen conditions were established in the anaerobic units. A trial study, using the herbicide alachlor [2‐chloro‐2′,6′‐diethyl‐N‐(methoxymethyl)acetanilide], was performed to test the utility of the three microcosm designs for assessing comparative in situ contaminant transformation rates. This experiment was initiated by adding alachlor to all tanks to a final concentration of 50 μg/L. Alachlor levels and other chemical parameters were then monitored for 36 d. The estimated first‐order alachlor decay coefficients and half‐lives for the aerobic, stratified, and anaerobic treatments were 0.011/d (63 d), 0.024/d (29 d), and 0.020/d (35 d), respectively. Subsequent analyses showed that the highest rates of alachlor decay occurred in units with grass supplements, low DO and pH levels, and comparatively high TP levels. These results suggest that lower nutrient (i.e., low TP levels), photosynthesis‐dominated aquatic systems produce lower alachlor decay rates, whereas higher nutrient, decomposition‐dominated systems produce higher decay rates. This project shows that diverse physical and chemical environments can be created in small outdoor microcosms and that these systems can be used successfully to assess contaminant decay rates in natural systems.

Ryegrass rhizosphere microbial community structure under elevated carbon dioxide concentrations, with observations on wheat rhizosphere

The structure of microbial communities in the rhizospheres of ryegrass and wheat, growing at an elevated atmospheric CO 2 concentration, was investigated using broad-scale DNA techniques. Community DNA hybridisation and %G+C base profiling by thermal denaturation assess changes at the whole microbial community level. DNA analysis of the rhizosphere of ryegrass grown in soil microcosms for 28 or 42 d, showed only minor differences between plants grown at 450 or 720 μl CO 2 l −1. In a second experiment with ryegrass, 5 of 10 replicate microcosms were pulse labelled with 14CO 2 and 5 simultaneously sampled for DNA analysis. Carbon partitioning below ground showed changes due to the elevated CO 2, notably an increased proportion of fixed carbon in non-microbial biomass residue in the rhizosphere. There was again no effect of elevated CO 2 on rhizosphere microbial community structure. Community DNA hybridisation indicated that the rhizosphere communities under ambient and elevated CO 2 were 86% similar (unlikely to be a biologically relevant change), with indistinguishable %G+C profiles. Wheat was grown to maturity (129 d) in a different soil microcosm design, and rhizosphere microbial communities from plants grown at 350 and 700 μl CO 2 l −1 were identical according to the DNA analyses. In these experiments rhizosphere microbial community structure at the broad scale was unaffected by the interactions occurring below ground as a result of elevated concentrations of CO 2.