Ammonia and Nitrite Contamination of Hamilton Harbour, Lake Ontario

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Abstract
The temporal and spatial distribution of total and toxic unionized ammonia, nitrite, nitrate and total dissolved nitrogen concentrations in Hamilton Harbour, Lake Ontario, were investigated during 1987–1988. The concentrations of toxic un-ionized ammonia in vertical and horizontal profiles depended on ammonia loadings from the Hamilton and Burlington municipal sewage treatment plants, the seasonal nitrogen cycle, pH and water temperature. Toxic ammonia levels in the Harbour exceeded the International Joint Commission objective of 20 μg/L at all sampling sites for about half of the year (spring and summer). For extended periods in the late spring and mid-summer, concentrations frequently exceeded the chronic toxicity threshold of 300 μg/L. Toxic un-ionized ammonia concentrations were distributed unevenly over the Harbour with a distinct areal zonation and patchiness. Volatilization of ammonia, estimated at 6.8 tonnes per summer, reduced the toxic effect but was insignificant in the overall NH3-N budget. The nitrite concentrations exceeded the chronic toxicity thresholds of 30 μg/L for most of the summer and frequently surpassed the cold-water fish toxic levels of 250 μg/L. Near the outfall from the Hamilton sewage treatment plant, nitrite levels were 600–1,200 μg/L. The frequency of nitrite toxic episodes was however lower than those of un-ionized ammonia. Nitrite was less abundant than total ammonia and can be considered as a less serious contaminant. Nitrification in Hamilton Harbour appeared to be inhibited by high toxic un-ionized ammonia levels.

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