NITROGEN-UTILIZATION IN ICE ALGAL COMMUNITIES OF BARROW STRAIT, NORTHWEST-TERRITORIES, CANADA

Identified a significant temporal shift from NO3- dominated metabolism during the early stages of algal biomass accumulated under the ice to NH+4-dominated metabolism later on when biomass was in decline. Volume-based uptake rates of both nitrogen compounds were 2-3 orders of magnitude higher (1-80 μmol N l-1h-1) than rates typical for coastal plankton populations but so were biomass levels (4-18 mg chlorophyll a l-1) and interstitial nitrogen concentrations (NO-3:4-123 μmol N l-1, NH+4:4-40 μmol N l-1). Ammonium was utilized preferentially. Despite high concentrations, however, NH+4 apparently had little inhibitory effect on the activity of the NO-3 assimilatory enzyme, nitrate reductase, at least during the early stages of ice-algal growth. Results support the contention that these sea-ice communities are not nitrogen-limited. -from Authors