TEMPERATURE AND THE 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-mu-mol N liter-1 d-1 in summer, with an apparent Q10 of 6.8. Rates were always higher at a nutrient-rich Providence River estuary site, with a summer maximum > 11-mu-mol N liter-1 d-1 and an apparent Q10 of 17.6. Laboratory experiments that examined the response of nitrification to temperature alone resulted in a Q10 of 7.5. The high summer rate of nitrification was balanced by NO3- uptake by phytoplankton. Elevated levels of NO3- 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.