Effects of repeated application of carbaryl on zooplankton communities in experimental ponds with or without the predator Chaoborus

Zooplankton communities with or without Chaoborus larvae were established in outdoor experimental ponds, to which the insecticide carbaryl was applied repeatedly at 10 or 100 microg litre(-1). In the ponds without Chaoborus, Cladocera dominated, but the species composition differed among the treatments. A large-sized Cladocera Daphnia galeata dominated the controls, the medium-sized cladocerans Diaphanosoma brachyurum and Moina micrura became dominant in the low-dose treatment, and the small-sized Bosmina fatalis increased in the high-dose treatment. These results indicated differential sensitivity to carbaryl among the cladocerans, and that smaller Cladocera were more tolerant of the chemical than the larger one. In the ponds with Chaoborus, rotifers dominated the zooplankton, probably because Chaoborus released rotifers from competition with cladocerans and calanoid copepods, which were eliminated by the Chaoborus predation. No effects of low-dose carbaryl treatment were detected on zooplankton communities in the Chaoborus ponds. The dominance by rotifers, organisms tolerant to carbaryl, minimized the effects. Thus, Chaoborus altered the zooplankton community responses to the chemical application by changing community structure. Repeated application of high-dose carbaryl did affect the rotifer community, decreasing the dominance of Polyarthra trigla and increasing that of Keratella valga. These rotifer species may differ in their sensitivity to carbaryl.     

Effects of a carbamate insecticide, carbaryl, on the summer phyto- and zooplankton communities in ponds

A carbamate insecticide, carbaryl (1-naphthyl-N-methylcarbamate), was applied in concrete ponds and the effects on plankton communities were studied. In a control pond, Cladocera declined following the increase in the density of inedible algae after a cladoceran peak. Once the density of Cladocera became low, Chaoborus larvae suppressed the increase of Cladocera and consequently supported the rotifer dominance in the zooplankton community by their selective predation on cladocerans. In a treated pond, the plankton community and its succession were similar to those in the control pond until the chemical application. 1 ppm of carbaryl killed all zooplankton and Chaoborus larvae. Cladocera reappeared soon and increased rapidly due to the absence of Chaoborus larvae. Consequently, rotifer populations were suppressed. Thus, the chemical application altered the dominance of rotifers to that of cladocerans. The same phenomenon was observed again after the second chemical application 12 days after. Although apparent direct effects of the chemical application on phytoplankton were not found, the phytoplankton community structure changed following the changes in the zooplankton density.     

Effects of the organophosphorus insecticide fenthion on phyto- and zooplankton communities in experimental ponds

The organophosphorus insecticide fenthion was applied to experimental ponds and its effects on phyto- and zooplankton communities were analysed. The sensitivity to fenthion differed among cladoceran and rotiferan species according to the following order: Daphnia galeata > Monia micrura > Bosmina fatalis >/= Polyarthra trigla > Keratella valga. The results suggest that large zooplankton species tend to be more sensitive to fenthion than small ones, large cladocerans more sensitive than small cladocerans, and cladocerans more sensitive than rotifers. The application of fenthion induced an increase in the density of rotifers and phytoplankton. This was a secondary effect of the chemical, which directly depressed cladoceran populations and consequently released rotifers and phytoplankton from competition with, and grazing by cladocerans.     

Effects of carbaryl on the spring zooplankton communities in ponds

A carbamate insecticide, carbaryl, was applied in spring to concrete ponds to study its effects on zooplankton communities. The population density of Cladocera (Daphnia spp.) was nearly constant before application of the chemical. Carbaryl at 1 ppm killed all zooplankton species, including Chaoborus larvae. After treatment, cladocerans never recovered to their previous level. The relatively rapid recovery of a predator, Chaoborus, seemed to interfere with recovery of the cladoceran populations. The lower water temperature occurring in spring was thought to favour the former because of its influence on growth rates.     

Effects of the triazine herbicide, simetryn, on freshwater plankton communities in experimental ponds

The effects of a triazine herbicide, simetryn, on freshwater phyto- and zooplankton communities and water chemistry were investigated using outdoor experimental ponds. Simetryn was applied at a concentration of 0.1 or 1.0 mg l(-1) 18 days after the start of the experiment. Simetryn treatments reduced pH, dissolved oxygen concentration, chlorophyll a concentration and photosynthetic rate in the pond water, whereas they increased the dissolved nutrient concentration. In the phytoplankton community Volvocales and Cryptophyceae were clearly reduced by the herbicide application. In the 0.1 mg l(-1) simetryn-treated ponds, photosynthetic rate of the phytoplankton community recovered slightly about two weeks after the treatment, which coincided with recovery of centric diatoms and Cryptophyceae, whereas it was completely suppressed until the end of the experiment in the 1.0 mg l(-1) simetryn-treated ponds. The decrease in zooplankton density in the treated ponds was not due to the direct toxic effects of simetryn but to indirect effects resulting from reduced algal productivity which in turn reduced the food supply.     

Is Daphnia magna an ecologically representative zooplankton species in toxicity tests?

Daphnia magna is commonly used in aquatic toxicity testing because of many characters that make it easy and economical to culture in the laboratory: it is relatively small, has short life cycle, high fecundity, and parthenogenetic reproduction. On the other hand, D. magna differs from other freshwater zooplankters in size, habitat, life-history, and ability to withstand fish predation. D. magna is a relatively large zooplankton species which makes it so vulnerable to fish predation that it is excluded from fish-inhabiting lakes. It occurs mainly in ephemeral habitats like small ponds and rockpools where vertebrate predators are rare. As a result, D. magna is seldom an indigenous species in lakes which receive pollutants, although representativeness is one important criterion for the standardised toxicity test species. Small ponds are unpredictable habitats with large temporal and spatial variability in abiotic factors. Adaptation to this natural abiotic stress may increase pollution tolerance. The life-history of D. magna also differs from that of lake-inhabiting cladocerans. Large daphnids produce many small neonates, whereas the opposite is true for small cladocerans. The large neonate size allows an earlier maturation of small cladocerans compared to daphnids. In a few comparative studies D. magna tended to be less sensitive to toxic substances than other cladocerans, and this may be due in part to life-history and size differences.     

Effects of temephos on zooplankton communities in enclosures in a shallow eutrophic lake

An organophosphorus insecticide, temephos, was applied to large-volume (105 m3) enclosures set up in a shallow eutrophic lake. Application of the chemical at a target concentration of 500 microg litre(-1) eliminated almost all zooplankters. No recovery of cladocerans was evident at the termination of the experiment (47th day after the treatment). Copepods showed a slight recovery after having been absent for 26 days in one enclosure and 40 days in another. The residual chemical remaining in the water until the final day may have suppressed the recovery of the crustacean zooplankters. The rotifer community was reconstructed 16-20 days after the treatment. However, the species composition of this community differed from that of the rotifer community in the control enclosures. Rotifer species might therefore show differences in susceptibility to temephos.     

An experimental comparison of the effects of two chemical stressors on a freshwater zooplankton assemblage

Mesocosms in an Ohio, USA lake were dosed with ten levels (0-100 microg liter(-1)) of copper (experiment 1) or Carbaryl (experiment 2). Zooplankton responses were determined after 4-day incubations. Species level responses differed for the two chemicals; community level responses were very similar. Across the gradients of increasing Cu or Carbaryl doses, cladocerans were greatly reduced and copepods became dominant. For Carbaryl, the response was consistent with that reported previously. For Cu, different responses were previously observed at other lakes. The taxonomic composition of the zooplankton may largely determine the community level response. In the present experiments, cladoceran declines may have secondarily affected food web function. In the Carbaryl experiment, where the chemical did not directly suppress algae, their biomass increased with dose level. This coincided with the cladoceran decline, suggesting an algal response to reduced top-down control.     

Large-scale utilization of water hyacinth for nutrient removal in Lake Dianchi in China: The effects on the water quality, macrozoobenthos and zooplankton

An ecological engineering project using water hyacinth for nutrient removal was performed in Baishan Bay of a large shallow eutrophic lake, Lake Dianchi in China. In the present study, a systematic survey of water quality, macrozoobenthos and zooplankton inside (IWH), around (AWH) and far away (FWH) water hyacinth mats was conducted in Baishan Bay from August to October 2010. The results showed that the water quality significantly improved at AWH area. Concentrations of nitrogen and phosphorus were lower and transparency was higher at AWH area than those in IWH and FWH areas. Total densities, dominant species densities, and biodiversity indexes of macrozoobenthos and cladocerans as well as copepods did not differ (P > 0.05) among each other in all three areas. It was significantly (P < 0.05) different for those of rotifers at IWH area compared to those in AWH and FWH areas. The results might suggest a tremendous potential for the utilization of water hyacinth in the eutrophic lake like Lake Dianchi for nutrients removal.     

Acid and aluminum effects on freshwater zooplankton: an in situ Mesocosm study

An in situ mesocosm experiment was performed to evaluate the role of aluminum toxicity in determining zooplankton community responses to take acidification. Large plastic enclosures were suspended in East Twin Lake, Ohio, USA, and duplicates were either untreated controls (pH 8.8), acidified to pH 4.5 over a 23 day period, or acidified and also spiked with incremental additions of Al, to produce a final inorganic monomeric Al level of 180 microg/liter at pH 4.5. Zooplankton abundance and species richness declined in both acid treatments, relative to the control, as numerous acid-sensitive species were eliminated. All of the acid-sensitive species were also Al-sensitive, declining in abundance more rapidly in the acid plus Al treatment than in the acid-alone treatment. Only two small cladocerans (Bosmina longirostris and Chydorus sphaericus) were acid tolerant. Both were also tolerant of elevated Al levels.     

Toxicity and hazard of a mixture of SSRIs to zooplankton communities evaluated in aquatic microcosms

The toxicity and hazard of a mixture of selective serotonin reuptake inhibitors (SSRIs), including fluoxetine, fluvoxamine, and sertraline, to zooplankton communities were evaluated using 120,00l outdoor microcosms. Acute (day 4) and chronic (day 35) zooplankton abundance and species richness were assessed for Rotifera, Cladocera, and Copepoda. For acute SSRI exposures, rotifers were the most sensitive zooplankton taxa to changes in abundance (predicted no effect concentration (PNEC)=19 nM); however, no effects in zooplankton species richness were observed for this treatment period. A decrease in Copepoda abundance and species richness was observed following chronic exposures of SSRIs (PNEC=9.1 nM). A 99th-centile predicted environmental concentration (PEC=0.51 nM) yielded HQs at least two orders of magnitude below 1. Therefore, mixtures of SSRIs do not appear to present a hazard to zooplankton communities at environmentally relevant concentrations.     

Zooplankton community responses to chemical stressors: a comparison of results from acidification and pesticide contamination research

The response of freshwater zooplankton communities to two chemical stressors, acidification and pesticide contamination, were investigated in a review of published research results. The objective was to test Odum's predictions (Odum, 1985) that in response to stress, both the average body size of organisms and their efficiency in utilizing resources are reduced. Acidification and pesticide contamination were both found to favor dominance by small cladorecans and rotifers, the smallest zooplankton taxa. This finding was consistent with Odum's predictions, however, there were exceptions to the trend. The dominance of small taxa may be due to rapid reproductive rates, physiological tolerance, development with few transitions through sensitive stages (eg. post-molting), or to the great richness of small species. Regardless of the mechanism, there is evidence that when acidification and pesticide contamination result in small zooplankton dominance, the efficiency of carbon and energy transfer from algae to zooplankton is reduced. This finding is also consistent with Odum's predictions.     

Effects of pollution on dormant-stage banks of cladocerans and rotifers in a large tropical reservoir

Environmental Science and Pollution Research - Here, we describe the abundance and composition of the dormant-stage banks of cladocerans and rotifers at two locations in a tropical reservoir...     

Ammonia effects on microinvertebrates and fish in outdoor experimental streams

Laboratory data on ammonia effects, the US EPA national water quality criteria for ammonia, and ammonia site-specific criteria were evaluated in four outdoor experimental streams (one control and three treatment streams) over a 76-week period. Calculated un-ionised ammonia concentrations varied daily and seasonally according to pH and temperature changes. Populations of four major microinvertebrate taxonomic groups (cladocerans, copepods, rotifers and protozoans) were monitored during a 4-week period early in the study, and six fish species (fathead minnows, bluegills, channel catfish, white suckers, walleyes, and rainbow trout) were tested for various time intervals, from 4 to 26 weeks, throughout the 76-week study period. Copepods and rotifers were unaffected in all three treatment streams, based on comparisons with the control stream. Cladoceran and protozoan populations were reduced in at least two treatment streams, but because of large variability, effects were considered to be inconclusive. However, complete mortality of cladocerans did occur in the high and medium treatments when placed in in situ biomonitor chambers. All six fish species were affected in one or more treatments. Generally, the fish effect values agreed with most laboratory effect values. Of 12 fish groups tested, one channel catfish group and one white sucker group were affected below the recommended protection levels of the national and site-specific criteria. The lowest effect concentrations tested for the other ten groups occurred above the criteria levels.     

Essential versus potentially toxic dietary substances: a seasonal comparison of essential fatty acids and methyl mercury concentrations in the planktonic food web

We investigated seasonal variability of essential fatty acids (EFA) and methyl mercury (MeHg) concentrations in four size categories of planktonic organisms in two coastal lakes. MeHg concentrations increased significantly with increasing plankton size and were independent of plankton taxonomy. However, total EFA increased from seston to mesozooplankton, but decreased in the cladoceran-dominated macrozooplankton size-class. Analysis of EFA patterns revealed that linoleic, alpha-linolenic, arachidonic, and eicosapentaenoic acids increased with increasing zooplankton size, but docosahexaenoic acid (DHA) in the cladoceran-dominated macrozooplankton was generally lower than in seston. This consistent pattern demonstrates that cladocerans, although bioaccumulating MeHg, convey less DHA than similar-sized copepods to their consumers. It is thus evident that fish consuming cladocerans have restricted access to DHA, yet unrestricted dietary access to MeHg. Thus, the structure of planktonic food webs clearly affects the composition of EFA and regulates dietary supply of these essential nutrients, while MeHg bioaccumulates with increasing zooplankton size.     

Littoral zooplankton responses to acid and aluminum stress during short-term laboratory bioassays

During autumn 1990, littoral zooplankton were collected from three alkaline lakes in Ohio, USA. Toxicity tests were performed, in which animals were placed into treatments of pH 4.5, with or without 500 microg litre(-1) Al added. Percentage survival after 24 h was determined for each test species, and compared to survival in controls (pH roughly 8.0). Three distinct responses were observed: (1) Four cladocerans, Simocephalus serrulatus, Diaphanosoma birgii, Acantholeberis curvirostris and Chydorus sphaericus, were tolerant of both acid and Al, with no significant reductions in survival in the treatments. (2) The cladoceran Eurycercus lamellatus and the capepod Acanthocyclops vernalis were sensitive to both acid and Al, and suffered 100% mortality in both treatments. (3) The cladocerans Camptocercus rectirostris, Alona costata and Pleuroxus denticulatus, and the copopod Mesocyclops edax showed decreased survival in the acid treatment, and a significantly greater decrease in the acid plus Al treatment. For nine of the ten test species, the results were consistent with previous survey and paleolimnological studies. The results indicate that direct toxic effects of H+ and Al ions largely determine the responses of these common littoral species to acidification.     

Use of carbon and nitrogen stable isotope ratios to assess the effects of environmental contaminants on aquatic food webs

In this study, the value of carbon (delta13C) and nitrogen (delta15N) stable isotope ratios were determined in nymphs of a top-predator, the common backswimmer (Notonecta glauca L.), collected in 18 m3 outdoor freshwater mesocosms used to assess the fate and ecotoxicological effects of a diphenyl ether herbicide, fomesafen, applied alone or in combination with Agral 90 (mixture of polyethoxylated derivatives of nonylphenol). Both treatments had a negative effect on delta13C values which may reflect changes in carbon fluxes across food webs in the treated ponds associated with a shift in phytoplankton structure. A decrease in delta15N values was observed in the nymphs collected in mixture-treated ponds, which was presumably due to an increase in the abundance of rotifers and Chironominae larvae in these ponds. These preliminary results indicate that stable isotope ratios may be used as shortcuts to detect qualitative or quantitative shifts in the structure of aquatic food webs caused by pollutants.     

Effects of long- and short-term exposure to carbaryl on survival, growth and reproduction of Daphnia ambigua

In laboratory experiments a cladoceran, Daphnia ambigua, was exposed for six instars to the insecticide carbaryl at five different concentrations (1, 2, 3, 4, 5 microg litre(-1)) or received short-term (10-h) exposure to 5 microg carbaryl litre(-1) at different life stages of the animal. In the long-term exposure experiments carbaryl at 1 microg litre(-1) did not have any detectable effects on the animals, whereas 2 microg litre(-1) reduced the survival, growth and reproduction of the animals, and higher concentrations killed all the animals examined before they grew to the fifth instar. These results indicate that the range of sublethal concentrations of carbaryl for D. ambigua is narrow. In the short-term exposure experiments the animals did not suffer any damage when they were exposed to the chemical during the egg stage. However, their growth and egg production were reduced when the short-term exposure was conducted during the life stages from the final embryo stage to the third instar. The effect was most marked when the animals were treated during the first instar, indicating that this is the stage when the animals are most sensitive to the chemical.     

Arsenic contamination in the freshwater fish ponds of Pearl River Delta: bioaccumulation and health risk assessment

This study investigated the extent of arsenic (As) contamination in five common species of freshwater fish (northern snakehead [Channa argus], mandrarin fish [Siniperca chuatsi], largemouth bass [Lepomis macrochirous], bighead carp [Aristichthys nobilis] and grass carp [Ctenopharyngodon idellus]) and their associated fish pond sediments collected from 18 freshwater fish ponds around the Pearl River Delta (PRD). The total As concentrations detected in fish muscle and sediment in freshwater ponds around the PRD were 0.05–3.01 mg?kg^?1 wet weight (w. wt) and 8.41–22.76 mg?kg^?1 dry weight (d. wt), respectively. In addition, the As content was positively correlated (p?<?0.05) to total organic carbon (TOC) contents in sediments. Biota sediment accumulation factor (BSAF) showed that omnivorous fish and zooplankton accumulated higher concentrations of heavy metals from the sediment than carnivorous fish. In addition, feeding habits of fish also influence As accumulation in different fish species. In this study, two typical food chains of the aquaculture ponds were selected for investigation: (1) omnivorous food chain (zooplankton, grass carp and bighead carp) and (2) predatory food chain (zooplankton, mud carp and mandarin fish). Significant linear relationships were obtained between log As and δ ¹⁵N. The slope of the regression (?0.066 and ?0.078) of the log transformed As concentrations and δ ¹⁵N values, as biomagnifications power, indicated there was no magnification or diminution of As from lower trophic levels (zooplankton) to fish in the aquaculture ponds. Consumption of largemouth bass, northern snakehead and bighead carp might impose health risks of Hong Kong residents consuming these fish to the local population, due to the fact that its cancer risk (CR) value exceeded the upper limit of the acceptable risk levels (10^?4) stipulated by the USEPA.     

Combined effects of soil moisture and carbaryl to earthworms and plants: simulation of flood and drought scenarios

Studying tolerance limits in organisms exposed to climatic variations is key to understanding effects on behaviour and physiology. The presence of pollutants may influence these tolerance limits, by altering the toxicity or bioavailability of the chemical. In this work, the plant species Brassica rapa and Triticum aestivum and the earthworm Eisenia andrei were exposed to different levels of soil moisture and carbaryl, as natural and chemical stressors, respectively. Both stress factors were tested individually, as well as in combination. Acute and chronic tests were performed and results were discussed in order to evaluate the responses of organisms to the combination of stressors. When possible, data was fitted to widely employed models for describing chemical mixture responses. Synergistic interactions were observed in earthworms exposed to carbaryl and drought conditions, while antagonistic interactions were more representative for plants, especially in relation to biomass loss under flood-simulation conditions.