Controls on Bioavailability of Phosphorus in the Coastal Ocean: A Coupled Geochemical and Enzymatic Approach

摘要

The primary goal of this study was to determine whether phosphate limitation of phytoplankton occurs in the coastal ocean. Three cruises on the Eel River Shelf, northern California were completed in spring, summer 1996 and winter 1997 from which hydrographic and nutrient inventory data from 3 to 5 shore-perpendicular transects were collected. These geochemical data were coupled with enzymatic assay data for Alkaline Phosphatase (APase), an inducible enzyme indicative of phosphate limitation, to evaluate the importance and spatial distribution of phosphate limitation. Nutrient-nutrient plots (e.g.; DIN versus DIP) indicate a shift from N-limitation in spring to P-limitation in summer. Those stations which exhibit lowest DIP in summer also have high APase activities, suggesting that the algal populations at these sites were phosphate limited. These findings indicate that the prevailing dogma of ubiquitous nitrogen (N) limitation of biological productivity in the coastal ocean is overly simplistic. A high degree of spatial variability in surface-water chl-a, dissolved nutrient concentrations, and APase was observed in spring and summer, illustrating the patchy nature of coastal phytoplankton blooms and the importance of high-density sampling grids to effectively characterize the overall biomass and nutrient limitation conditions of such system.