Nutrient limitation of phytoplankton in Chesapeake Bay

Abstract

This paper presents evidence of a seasonal shift from P to N as the nutrient limiting the accumulation of algal biomass in Chesapeake Bay. Following the winter/spring maximum in freshwater runoff, (1) the ratio of dissolved inorganic nitrogen to soluble reactive phosphorus (DIN/PO,) was greater than the N/P of algal biomass; (2) alkaline phosphatase activity was high; (3) phosphate turnover times were short; (4) ammonium turnover times were long; and (5) growth rates of phytoplankton were stimulated by additions of phosphate but not by additions of ammonium or silicate. During the period of low runoff in summer, all indicators reversed, and N limited algal growth rates. Silicate concentrations also showed evidence of biological depletion in spring, which may have limited diatom abundance. Due to the concordance of all indicators at large and small scales, we argue that phytoplankton growth rates exert primary control over biomass accumulation. We conclude that P and Si limit the accumulation of algal biomass along the major axis of Chesapeake Bay in spring, whereas N limits algal accumulation in summer, similar to the conclusions of D'Elia et al. (1986; Can. J. Fish. Aquat. Sci. 43: 397-406) for the Patuxent subestuary. Controlling eutrophication of the Bay and its subestuaries will require basin-specific management practices for both N and P reductions in influent waters. Such management efforts will provlde ecosystem tests of nutrient hmitation on a scale similar to those successfully conducted in lakes.

Pelagic metabolism of the Douro estuary (Portugal) – Factors controlling primary production

“…In estuaries, where seasonal and spatial variations of freshwater and seawater mixtures occur, this concept is not so clear (Bernhard and Peele, 1997). Seasonal alternation of nitrogen and phosphorus limitation has been reported (Fisher et al, 1992;Mallin et al, 1999) as well as a spatial shift from phosphorus to nitrogen limitation in some estuaries (Yin et al, 2001). In the present study, N:P ratio was usually high and always above the Redfield ratio except for the bottom and middle depth samples collected at the lower and middle stations during the September flood tide survey.…”

Algal blooms on coral reefs: What are the causes?

“…The enzyme APA is presented as ''useful as a means to gauge the degree of P-limited productivity of coral reef macroalgae,'' but no evidence is provided to support this assertion for any of the nine species examined. High levels of APA have been shown to be induced by low levels of PO 4 and to be an indicator of P limitation (e.g., Healey and Hendzel 1979;Jansson et al 1988;Fisher et al 1992;Hernandez 1996) but not of N enrichment, nor of organic P availability (Atkinson 1987;Jansson et al 1988). It would have been useful to sample the algae in high and low nutrient environments (e.g., along the steep nutrient gradient away from the groundwater springs), but this was not done.…”

Joint effect of freshwater plume and coastal upwelling on phytoplankton growth off the Changjiang River

“…For example, Fisher et al (1992) reported that during high runoff periods in spring and autumn, the Chesapeake Bay was limited by phosphate with the observation of high N / P ratios, high APA, and short P turnover time. Phytoplankton growth in the surface water of the Mediterranean Sea during the stratified summer season was also limited by P availability (Vaulot et al, 1996).…”