Abstract Elevated concentrations of the trace element selenium (Se) have resulted in the degradation of several aquatic ecosystems. This study evaluated the comparative toxicity of several aqueous chemical species of selenium to an aquatic cladoceran, Daphnia magna. Responses to mixtures of these selenium forms, varying the sulfate concentration, were also examined. Initial experiments compared the toxicity of aqueous forms of selenate, selenite, seleno‐DL‐methionine, and seleno‐DL‐cystine to neonate Daphnia magna , resulting in 48‐h LC50 values of 2.84, 0.55, 0.31, and 2.01 mg Se per liter, respectively. Immobilization was an acute sublethal response observed during exposure to the organic selenium forms only. The 48‐h IC50 values were 0.045 and 0.52 mg Se per liter for seleno‐DL‐methionine and seleno‐DL‐cystine, respectively. Evaluation of the invertebrate response to various combinations of selenate, selenite, and seleno‐DL‐methionine demonstrated that the toxicities of these forms of selenium are additive. Increasing the concentration of sulfate decreased, varied, and left unaffected the toxicities of selenate, selenite, and seleno‐DL‐methionine, respectively. These results indicate that both the chemical form of selenium and the sulfate concentration can influence the toxicity of selenium.
ABSTRACT Elevated levels of selenium have resulted in the degradation of several ecosystems and have been linked to reproductive impairment in important fish and waterfowl populations in several lakes and reservoirs, indicating the need for a better understanding of the bioaccumulation of selenium by aquatic organisms. Because space limitations prevent an exhaustive review, this paper focuses on the processes and mechanisms of bioconcentration and biomagnification. Comparative uptake and accumulation of selenite, selenate, and selenomethionine are examined, as well as the relative importance of waterborne and foodborne exposure. The observed toxicity of selenium in lakes and reservoirs is briefly discussed. Finally, this information is summarized, pointing out key trends in the uptake and accumulation of selenium. Perhaps the most important information generated by this review involves comparative metabolism of selenite and selenate; selenite is readily reduced and metabolized, while reduction and metabolism of selenate appears to be limited. A knowledge of the processes and factors influencing selenium bioaccumulation in aquatic organisms will be essential in the development of management strategies and treatment methods that can be used to ameliorate selenium contamination problems.
SUMMARY The freshwater dinoflagellate Peridininm penardii (Lemm.) Lemm. fo. californicum Javorn. has a positively phototactic diel migration. The extent of migration seems to vary with population density.
Spatial and temporal distributions of Peridinium penardii were studied during a spring bloom. Blooms developed at the mouths of tributary streams after periods of high runoff and lasted for about 3 weeks. Allochthonous inputs may be necessary for the development of dinoflagellate blooms in this reservoir.
SummaryBlooms of the dinoflagellate, Peridinium penardii (Lemm.) Lemm. fo. californicum Javorn., are shown to have a significant effect on some water quality parameters in a California reservoir. Temperature, dissolved oxygen, and pH are positively correlated with population density while conductivity, nitrates and inorganic carbon are negatively correlated. Possible interactions with other freshwater biota are discussed.
Near simultaneous collection of 34 surface water samples and airborne multispectral scanner data provided input for regression models developed to predict surface concentrations of estuarine chlorophyll a. Two wavelength ratios were employed in model development. The ratios werechosen to capitalize on the spectral characteristics of chlorophyll a, while minimizing atmospheric influences. Models were then applied to data previously acquired over the study area thre years earlier. Results are in the form of color-coded displays of predicted chlorophyll a concentrations and comparisons of the agreement among measured surface samples and predictions basedon coincident remotely sensed data. The influence of large variations in fresh-water inflow to the estuary are clearly apparent in the results. The synoptic view provided by remote sensing is another method of examining important estuarine dynamics difficult to observe from in situ sampling alone.
Abstract Simultaneous acquisition of surface chlorophyll-a concentrations for 39 samples from boats and Daedalus 1260 Multispectral Scanner data from a U-2 aircraft was conducted in the northern reaches of San Francisco Bay on 28 August 1980. These data were used to develop regression models for predicting surface chlorophyll-a concentrations over the study area for ebb-tide (8.40 a.m. P.D.T. (Pacific Daylight Time)) and flood-tide (3.10 p.m. P.D.T.) conditions. After selection of a single 'best fitting' model for both morning and afternoon data sets, the chlorophyll-a concentration was predicted for ebb and flood tide for the entire study area at approximately 40m × 40m resolution. The predicted spatial display of chlorophyll-a revealed a localized area of high phytoplankton biomass that has been inferred from field surveys and appears to be a common summer phenomenon. Knowledge of the distribution of phytoplankton and the location of this zone of high biomass is valuable in establishing management policies for this ecologically important estuary. Furthermore, the techniques used here may provide an alternative cost-effective method for assessing water-quality conditions and they may prove useful for studying spatial variations (patchiness) and seasonal variations in phytoplankton biomass in other estuaries and coastal waters.
ABSTRACT Selenium, an essential trace element, exists in elevated concentrations in several aquatic systems and is apparently responsible for mortality, teratogenesis, reduced reproduction, and decreased populations observed in fish and waterfowl communities. Adverse impacts associated with increasing selenium levels are derived largely from anthropogenic mobilization of selenium in the environment. This paper reviews briefly selenium in aquatic ecosystems, discussing selenium chemistry, cycling, known biological impacts, toxicology, and several potential solutions to the selenium problem. Awareness and understanding of selenium dynamics in aquatic systems is necessary to avoid future problems and manage present ones.
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