Nitrogenous nutrition of the plankton in the Chesapeake Bay. 1. Nutrient availability and phytoplankton preferences

Abstract

Eight stations in the main body of Chesapeake Bay and one on the continental shelf were sampled seven times over a period of 13 months to investigate the nitrogenous nutrition of the phytoplankton.The rates at which the phytoplankton were utilizing NO,, NO,, NHr+, and urea N were determined.The data demonstrate that for a large portion of the year there is inadequate N nutrient available to permit a single doubling of the particulate N. Over temperatures from 4" -28°C and salinities from 2-32&, there was a universally high phytoplankton preference for NH4+ and urea N over NO,-and NO,.A relative preference index indicated that NHa' concentrations in excess of O-5-1.0 pg-atom N liter-l almost totally suppressed NO, utilization.Urea N was used after NH,+ in order of prcfcrence, and when the sum of available NH4+ and urea N was insufficient to meet the phytoplankton N nutrient demand, NO; was used. When the sum of all available N nutrients was less than that required to satiate the phytoplankton demand, NIL', urea N, NO,-, and NO,-were all utilized at rates proportional to their availability. For the midbay region in October 1973, NO, was the dominant N nutrient present both in the water and in the diet of the phytoplankton.

Time course of uptake of inorganic and organic nitrogen by phytoplankton in the Strait of Georgia: comparison of frontal and stratified communities

“…Specifically, regenerated nitrogen (NH: and urea) has been shown to supply most of the phytoplankton nitrogen demand in nitrogen-depleted waters and as the concentration of ambient NO; increases so does the relative importance of NO; for the phytoplankton nitrogen ration (e.g. McCarthy et al 1977, Harrison 1980, Glibert et al 1982a.…”

“…Moreover, most of the nitrogen demands of phytoplankton in nitrogenimpoverished water are supplied by ammonium and urea from regenerative processes, whereas in nitrogen-rich areas nitrogen compounds appear to be utilized at rates proportional to thelr availability (e.g. Dugdale & Goering 1967, McCarthy et al 1977. Experiments using laboratory cultures of phytoplankton have demonstrated that the preconditioning nitrogen substrate affects the response of phytoplankton to the additions of different forms of nitrogen (Horrigan & McCarthy 1981, Dortch & Conway 1984.…”

Nutritive and photosynthetic ecology of subsurface chlorophyll maxima in Canadian Arctic waters

“…It follows that regenerated production possibly fuels a substantial part of total primary production on a daily basis. When abundant, reduced N (i.e., NH + 4 and urea) is generally preferred over NO − 3 , whereas all N forms tend to be used in proportion to their availability when total N is lower than phytoplankton demand (McCarthy et al, 1977;Harrison et al, 1982). Whether SCM communities are predominantly regenerative or efficient vectors of export toward top predators or the deep ocean remains to be assessed.…”

Natural abundance of 15N in particulate nitrogen and zooplankton in the Chesapeake Bay

“…The nitrogen cycle in the Chesapeake Bay, USA, has been studied by a number of workers in recent years, and the gross spatial and temporal patterns of variation in the major reservoirs of nitrogen in the Bay have been described by Carpenter et al (1969), McCarthy et al (1975McCarthy et al ( , 1977, and Taft et al (1978). The high levels of biomass and dissolved inorganic nitrogen which characterize the Bay facilitate experimental studies of the transformation of nitrogen in the water column, and simplify the task of collecting material for isotopic analysis.…”

“…The major sink for NOs-in the Bay is uptake by phytoplankton, and the major source of NH,+ is local remineralization of planktonic biomass (McCarthy et al 1977, Taft et al 1978. In combination with the net movement of surface water toward the south, these 2 processes lead to a southward increase in the extent of biological processing of the nitrogen in the Bay.…”