Responses of benthic fish exposed to contaminants in outdoor microcosms--examining the ecological relevance of previous laboratory toxicity tests.

Previous laboratory studies indicate that coal combustion wastes (a mixture composed of fly ash and other lower volume wastes such as bottom ash; hereafter collectively referred to as ash) adversely affect the health of benthic fish (Erimyzon sucetta; lake chubsucker), but fish in these studies were provided with ample uncontaminated food resources. Because aquatic disposal of ash can also adversely affect food resources for benthic fish, we hypothesized that changes in resources might exacerbate the effects of ash on fish observed in laboratory studies. We exposed juvenile E. sucetta in outdoor microcosms to water, sediment, and benthic resources from an ash-contaminated site or a reference site for 45 days and compared our findings to previous laboratory studies. Benthic invertebrate biomass was nearly three times greater in controls compared to ash microcosms. Total organic content of control sediment (41%) was also greater than in ash sediments (17%), suggesting that additional benthic resources may have also been limited in ash microcosms. Benthic invertebrates isolated from the ash microcosms had trace element concentrations (As, Cd, Co, Cr, Cs, Se, Sr, and V) up to 18 times higher than in weathered ash used in laboratory studies. The concentrations of trace elements accumulated by fish reflected the high dietary concentrations encountered in the ash microcosms and were associated with reduced growth (final mass = 0.07 g) and survival (25%) compared to controls (0.37 g and 67%, respectively). Accumulation of trace elements, as well as reductions in growth and survival, were more pronounced than in previous laboratory studies, suggesting that resource conditions may be important in mediating ash toxicity. Taken together, our studies suggest that ash discharge into aquatic systems is a more serious threat to the health of benthic fish than previously predicted based upon laboratory toxicity tests.

Relative nutritional value of ciliate protozoa and algae as food forDaphnia.

The relative importance of autotrophic flagellates, desmids, cyanobacteria, and ciliates as food forDaphnia magna was examined using cohort life tables. Each cohort was fed a single food type at a given concentration, and comparisons among each type were made. Algal feeding treatments included three levels of young (7 to 14 days old)Chlamydomonas reinhardi (Chlorophyta, Chlamydomonadacae), two levels of senescent (> 14 days old)C. reinhardi, two levels ofCryptomonas sp. (Chlorophyta, Cryptomonadacae), two levels ofStaurastrum sp. (Chlorophyta, Desmidacae), four levels of young (7 to 15 days old) or senescent (> 15 days old)Microcystis aeruginosa (Cyanophyta, Chlorococcacae), and a no-food treatment. The ciliatesCyclidium sp. andParamecium caudatum were also presented at concentrations of 1 or 10(2) cells/ml, as well as mixtures ofC. reinhardi (10(3)/ml) andCyclidium (1/ml) orP. caudatum (1/ml).Daphnia growth, reproduction, and survivorship were highest whenC. reinhardi orCryptomonas were the food source, while those starved or fedM. aeruginosa had shorter survivorship and lower growth and reproduction.Daphnia grew and had high survivorship when fedP. caudatum, but even though eggs were produced, most were aborted after 2 or 3 days.Staurastrum andCyclidium produced intermediate growth and survivorship, but reproduction was seen only in the 10(3) Staurastrum/ml treatment. Carbon and nitrogen content were general indicators of nutritional value. However, growth, reproduction, and survivorship were higher in some cohorts fed treatments containing relatively low levels of carbon and nitrogen. Other cohorts were short-lived and did not reproduce, despite being fed much higher levels of carbon and nitrogen. The results also suggest that green algae are nutritionally valuable forDaphnia, whereas cyanobacteria are not. As measured by life-table parameters, the nutritional value of ciliates was variable, with some being poor food sources. Thus, the potential of ciliates as a trophic link between microbial production and higher trophic levels may vary with the ciliate community structure. Our results suggest that ciliates alone were insufficient as a food source to supportDaphnia population growth.