Acute and Chronic Toxicity of Nitrate to Brook Trout (Salvelinus fontinalis) Embryos and Larvae
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Date
2002Author
Johnson, Todd
Publisher
University of Wisconsin-Stevens Point, College of Natural Resources
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Show full item recordAbstract
Increasing concentration of nitrate in groundwater is becoming an environmental health
concern. Nitrate levels in pore spaces of groundwater upwelling zones of the Little
Plover River, a cold, groundwater-fed stream located in central Wisconsin, frequently
exceed 20 mg/L NO3-N (nitrate-nitrogen). Because brook trout, Salvelinus fontinalis,
spawn within these zones developing embryos may be exposed to high concentrations of
nitrate for extended periods of time. Therefore, the effect of nitrate exposure was
examined in developing embryos and larvae of two domestic and one feral strain of brook
trout at two levels of water hardness. The lowest observable effect concentration for feral
brook trout was 6.25 mg/L NO3-N for both mortality in developing embryos (96-d test)
and reduced growth of larvae (14-d test) in hard water. For the domestic strain, the
lowest observable effect concentration was 12.50 mg/L NO3-N for embryo mortality (96-
d test) and 100.00 mg/L NO3-N for biomass reduction (14-d test) of larvae. The 96-hour
LC50 values for the domestic and feral brook trout larvae were 2151.4 and 2645.3 mg/L
NO3-N, respectively. Pre-exposure of developing embryos to nitrate slightly decreased
acute toxicity in 96 hour tests indicating the potential for brook trout to develop some
tolerance to subsequent high-level exposures. These results show that under current
conditions in central Wisconsin, increased embryo mortality and reduced growth in brook
trout is possible, especially in areas with high agricultural uses, where groundwater
nitrate levels are elevated.