Acute and Chronic Toxicity of Nitrate to Brook Trout Salvelinus Fontinalis

Background/Need: Nitrates in surface waters of the Little Plover River, a cold, groundwater fed stream located in central Wisconsin, have increased from about 2 mg/L | NO3-N in the 1960s to over 8 mg/L NO3-N by 1997. In groundwater upwelling zones on the Little Plover River, nitrate concentrations can exceed 28 mg/L NO3-N. Nitrate may be a potential problem for the successful recruitment of cold water species such as brook trout, because they prefer to spawn in groundwater upwelling zones in streams and lakes. Water from upwelling zones flush fines from the redd, provide oxygen, and remove metabolic wastes produced by the embryos. Typical incubation times range from 32 to a 165 days depending on temperature. During incubation, the embryo is buried in the substrate, where it may be exposed to high concentrations of nitrate for an extended period, until emergence or swim-up.

Objectives: The purpose of this study was to determine the acute and chronic toxicity of nitrate to feral and domestic brook trout (Salvelinus fontinalis) embryos and larvae, in moderately hard and soft water and to predict the potential for nitrate toxicity to brook trout in Wisconsin streams.