Ammonia and Nitrate Uptake in the Lower Great Lakes

Abstract

Uptake of NH₄⁺ is consistent with Michaelis–Menten kinetics in the Lower Great Lakes only if one assumes that the indophenol method of measuring NH₄⁺ overestimates the in situ concentration. Short-term incubations were found necessary to avoid induction of nitrate uptake or changes in the rates of NH₄⁺ uptake that occurred in long-term incubations. Uptake rates of nitrate are slow most of the summer. Since the nitrate is also present in low concentrations, most of the summer regeneration of nitrate must be very slow. The slow turnover of particulate N, low nutrient concentrations, slow rate of uptake relative to their ability to take up nitrogen, and the high affinity for ammonia (low K_t) suggest that in summer the primary productivity of the Lower Great Lakes is restricted by nitrogen deficiency.Key words: ammonia, nitrate, Lower Great Lakes