Population‐, community‐, and ecosystem‐level responses to pulsed dosing of a pyrethroid insecticide were studied in experimental aquatic mesocosms. Twelve mesocosms (0.1 ha, 700 m3 volume) were dosed with technical‐grade esfenvalerate dissolved in acetone (subsurface injection of 0‐, 0.25‐, 0.67‐, or 1.71‐μg/L nominal concentrations in triplicated mesocosms) on six dates at two‐week intervals. We monitored dissipation rate of esfenvalerate; survival, growth, and reproduction of bluegill (Lepomis macrochirus); dynamics of benthos and zooplankton; biomass and productivity of phytoplankton; macrophyte biomass; diurnal oxygen pulse; and water quality over a five‐month interval. Esfenvalerate dissipated rapidly from the water column (half‐life, 10 h). Zooplankton and benthic macroinvertebrates decreased at 0.25 μg/L. Changes in invertebrate fauna due to esfenvalerate were partly obscured by indirect effects and seasonal dynamics. Bluegill survival, biomass, adult male survival, and reproductive success were negatively correlated with measured esfenvalerate concentrations. Although direct mortality of fish and invertebrates may be predictable from laboratory single‐species tests, indirect responses of fish, zooplankton, and phytoplankton are predictable only with prior knowledge of factors controlling ecosystem structure and function.
Arid wetlands are being contaminated by subsurface agricultural irrigation drainage throughout the western United States. Historic freshwater inflows have been diverted for agricultural and municipal use, and remaining freshwater supplies are not sufficient to maintain the integrity of these important natural areas once they are degraded by irrigation drainwater. Waterfowl populations are threatened in the Pacific and Central Flyways; migratory birds have been poisoned by drainwater contaminants on at least six national wildlife refuges. Subsurface irrigation drainage is the most widespread and biologically important source of contaminants to wetlands in arid regions of the country. The case history of poisoning at Kesterson National Wildlife Refuge in California and studies at other locations by the U.S. Department of the Interior provide detailed information on the toxicity of drainwater contaminants to fish and wildlife. Biogeochemical conditions favorable for the production of toxic drainage are found throughout the western states. Two actions seem necessary to prevent further drainage‐related degradation of arid wetlands. First is a reduction in the amount of contaminants reaching these wetlands, possibly involving regulatory intervention through the National Pollutant Discharge Elimination System permit process. Second, a better balance must be achieved in the way fresh water is allocated between agriculture and wildlife. Federally subsidized water has supported agriculture at the expense of wetlands for nearly 100 years in the western United States. This trend must be reversed if arid wetlands and their fish and wildlife populations are to survive.
Irrigation drain waters entering Stillwater Wildlife Management Area (SWMA) in south‐western Nevada contain elevated levels of salinity and several inorganic contaminants (As, B, Cu, Li, Mo, and Sr). Mortalities of fish and waterfowl at the management area are believed to be associated with the poor water quality of the drains. The objective of the present study was to use fresh‐water and saltwater animals to distinguish between the toxic effects of salinity and contaminants in effluent samples collected from irrigation drain waters. Static acute effluent tests were conducted with water collected from four sites at SWMA. Animals acclimated or cultured in fresh water (fathead minnows, Pimephales promelas; amphipods, Hyalella azteca; cladocerans, Daphnia magna) and salt water (striped bass, Morone saxatilis; amphipods, Hyalella azteca; and cladocerans, Daphnia magna) were used to separate toxic effects of salinity from the effects of inorganic contaminants in the drain water. One drain water (TJ drain, salinity 19 parts per thousand (grams per liter), osmolality 503 mmol/kg, hardness 3,780 mg/L as CaCO3) was toxic only to freshwater animals and saltwater cultured daphnids; water from a receiving pond (Pintail Bay, salinity 23 g/L, osmolality 542 mmol/kg, hardness 830 mg/L as CaCO3) was toxic to both freshwater and saltwater animals. Acute tests conducted with reconstituted waters representative of the Pintail Bay sample indicated that atypical ion ratios were toxic to striped bass and amphipods, even without the addition of inorganic contaminants. However, the addition of inorganic contaminants representative of the Pintail Bay sample increased the toxicity of this reconstituted water. These findings indicate that the toxicity of the TJ drain sample was related mainly to elevated salinity and that the toxicity of the Pintail Bay sample was a function of inorganic contamination and atypical ion ratios in combination with elevated salinity.
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