No abstract

Natural assemblages of marine bacteria were cultured on combinations of C and N sources (amino acids, glucose, and NH,') to span a range of substrate C: N ratios from 1.5 : 1 to 10 : 1.

Continuous cultures of three marine phytoplankton species, Phaeodactylum tricornutum, Dunaliella tertiolecta, and Monochrysis lutheri, were monitored for changes in alkalinity of the culture medium resulting From NO, and NHa+ uptake. Uptake of NO,-caused an increase in alkalinity, whereas uptake of NH,+ produced a decrease. These results are consistent with the type of schematic equation proposed by Redfield, Ketchum, and Richards for photosynthetic assimilation of inorganic nitrogen, in which NO, uptake is balanced by OH-production and NHa+ uptake leads to H+ generation. These reactions suggest active uptake of nitrogen species by microbes. We have been unable to demonstrate the exact stoichiometry of this relationship, and the role of P uptake in the alkalinity change is unclear. An offset in the data, functionally equivalent to the production of some strong acid, may be due to reactions on the walls of the vessel, active uptake of cations, or extrusion of H' ions by the growing cells.

No abstract

A simple model incorporates the combined effects of temperature and nutrient limitation on the growth rate of algae. The temperature function is described by the Arrhenius equation and the nutrient relationship with the Monod model. The Arrhcnius equation is inserted into the Monod model for the maximum growth rate fi, so that the growth rate is described by the product of temperature and nutrient cxprcssions. The utility of the Arrhenius equation in describing the effect of temperature on fi for phytoplankton is tested with data from the literature on continuous culture experiments with freshwater and marinc algae; the Arrhcnius model describes the relationship between fi and temperature extremely well. Several restrictions to widespread use of the model limit its application to laboratory studies, but its general concepts may apply to natural water situations.

Variability in the small-scale temporal and spatial patterns in nitrogenous nutrient supply, coupled with an enhanced uptake capability for nitrogenous nutrients induced by nitrogen limitation, make it possible for phytoplankton to maintain nearly maximum rates of growth at media nutrient concentrations that cannot be quantified with existing analytical techniques.

A fast-growing marine diatom Thalassiosira pseudonana (3H) was grown under NH4+-limited steady state conditions in continuous culture. Growth rate could not be described as a function of external or residual NH

The effect of surface-active organic nmtter generated by seven common species of rnarine phytoplankton on gas ex•e rates under turbulent conditions at the sir-water interface was determined. Reductions in oxygen evasion rates ranging from 5 to 50% were observed relative to clean seawater controls. Relative oxygen exchange coefficients (expressed as R = Kw[sarnple]/Kw[control]) were shown to be sensitive to small changes in total dissolved c•rbohydrate at concentrations <1 mg C (carbon) L -• and to asymptotically decrease to & lower limit (R '-55-70%) at concentrations between 2 and 6 rag C L -1. A corresponding rel&tionship was observed in which R decreased with increasing relative surfactant •mounts derived from surface pressure-area measurements. However, gas exchange reductions were significant for plankton exudate samples displaying surface pressures •<1 mN rn -1. It thus seems that condensed monol•yer films axe not & prerequisite for reduced gas ex•e and that re•atlvely soluble surfactants derived from phytoplankton can strongly •ect the dissipation of near-surface turbulence and lead to changes in the Schmidt number dependency of K•. Based on detailed analyses of carbohydrate-containing surface-active exu•t• isolated by solid phase extraction from one of the species, Phaeodaci•l•n tricor•turn, it appears tkat small g!ucar•s and heteropolysaccharides associated with proteins and possibly lipids were responsible for the observed reductions in R. mN m -• (milliNewtons per meter) even when R was •50%. Since the bulk of r values measured in visible slicks using spreading oils at coastal and open ocean sites are of the order of 1 mN m -• or greater [Hunter and Liss, 1981], we can surmise that the development of coherent surface films is not a prerequisite for the reduction of interfacial gas exchange. Possibly, soluble surfactants, which are known to be effective in reducing gas exchange through rapid readsorption at the surface [Springer and Pigford, 1970], but which do not display concentration-dependent surface pressures, may have played a major role in retarding gas exchange in our experiments. Phytoplankton exudates and degradation products generally are believed to be major sources of marine surfactants [Zutic et al., 1981]. Typical excretion products of many marine phytoplankton species are complex heteropolysaccharides of high molecular weight that often are acidic due to the presence of varying combinations of uronic acids and carboxyl or sulfate ester groups [Allan et al., 1972; Ramus, 1972; Sinestad et al., 1974, 1975; Percival et al., 1980]. Highly soluble fi-glucan-type polysaccharides often are major components of cellular carbohydrate pools in diatoms [M•kelstad, 1974; M•kelstad et al., 1982] and frequently are found in abundance in natural marine waters during phytoplankton blooms [Sakugawa and Hands, 1985a]. While many of these compounds are quite soluble, they are likely to contain sufficient hydrophobic groups to be at least weakly surface-active [oeeenheer, 1985] and thus influence interfacial...