Bioavailability of Atmospheric Organic Nitrogen Deposition to Coastal Phytoplankton

Die Stoffwechselintensitat der Riffkorallen und ihre okologische, phylogenetische und soziologische Bedeu-tung. A comparison of monthly rates of linear extension and calcium carbonate accretion measured over a year. Coral Reefs 3: 51-57. 1996. The potential of massive corals for study of high-resolution climate variation in the past millennium, p. 357-373. Zn l? 1994. A non-destructive method for monitoring coral growth affected by anthropogenic and natural long-term changes. Bull. Abstract-Atmospheric dissolved organic nitrogen has recently gained attention as a significant additional source of " new " N loading to the oceans. The effect of atmospheric N on marine productivity depends on the biological availability of both inorganic and organic N forms. Event-based measurements for coastal North Carolina showed that-30% of rain-water N concentration and deposition was organic N. Enrichment bioassay results suggested that-2O-30% of atmospheric organic N is available to primary producers on short (hours to days) time scales, Atmospheric N loading estimates, therefore, should include all available N inputs to properly assess the impact of N deposition on coastal and oceanic primary productivity. Atmospheric nitrogen is a quantitatively important source of external or " new " N loading to geographically diverse marine and freshwater ecosystems (Paerl 1993, 1995; Jassby et al. 1994). Increasing new N inputs are often considered the cause of coastal eutrophication, as indicated by accelerating primary productivity (Paerl 1993; Nixon 1995). In a recent report, Cornell et al. (1995) showed that dissolved organic N (DON) is " a significant component of precipitation " and may double current estimates of atmospheric combined N inputs to oceans. Cornell et al. (1995) contended that the impact of this additional N on oceanic primary productivity and trophodynamics will remain unknown until the bioavailability of atmospheric DON (ADON) is determined. Only a few studies have addressed the question of bioavail-ability directly (e.g. Timperley et al. 1985), and, to the best of our knowledge, none has used marine phytoplankton communities. Comprehensive ADON measurements and results from enrichment bioassays presented here show ADON to be at least partially available as a nutrient for coastal phy-toplankton. Precipitation from rain was collected at a coastal west Atlantic Ocean location (Institute of Marine Sciences, More-head City, North Carolina) using an Aerochem Metrics Model 301 wet/dry collector (wet side). An event was defined as a distinct weather system (e.g. frontal passage, tropical depression) or rain followed by 12-24 h without detectable precipitation. Rainwater was filtered through precombusted (45O " …