Nitrogen transformations in Lake Ontario / by D.R.S. Lean and R. Knowles.: En13-5/86-146E-PDF

"The increasing nitrate concentration in Lake Ontario has caused the phytoplankton in 1982 to be phosphorus deficient, whereas, 10 years previously, nitrogen was most likely limiting the summer biomass. Seasonal changes in the concentration of the various nitrogen fractions are documented and related to nitrogen flux rates from one form to another. Specifically, although 15N- tracer methodology shows rapid ammonium uptake, much of this is by chemoautotrophic nitrifying bacteria rather than phytoplankton. Nitrate, rather than ammonium, is the principal form of nitrogen used for algal growth. Quantities of nitrate used for protein synthesis (see Cuhel and Lean) were related to seasonal nitrate declines and provide an upper limit for protein available to support the food chain. Seasonal increases in ammonium and nitrite were shown to be related to rates of zooplankton excretion. In view of the high concentrations of oxygen and low concentrations of nitrous oxide, denitrification is robably not a significant process. Consequently, at present ates of N loading nitrate concentrations will likely continue to increase"--Management perspective.

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