Temperature and annual cycle of nitrification in waters of Narragansett Bay.

Pelagic nitrification, measured over an annual cycle at two sites in Narragansett Bay, Rhode Island, was strongly correlated with temperature. At a nutrient‐poor site, rates ranged from near zero in winter to almost 1 µ mol N liter −1 d −1 in summer, with an apparent Q 10 of 6.8. Rates were always higher at a nutrient‐rich Providence River estuary site, with a summer maximum >11 µ mol N liter −1 d −1 and an apparent Q 10 of 17.6. Laboratory experiments that examined the response of nitrification to temperature alone resulted in a Q 10 of 7.5. The high summer rate of nitrification was balanced by NO 3 − uptake by phytoplankton. Elevated levels of NO 3 − in fall resulted from a marked decline in phytoplankton uptake and a continuing slow rate of nitrification and were not dependent on river inputs. Other N transformations do not respond to temperature as strongly as nitrification did, thus temperature increases may effect the distribution of N.