ABSTRACT:The carbon isotope ratio of particulate carbon in an estuary can vary by at least 10 %O throughout the year. In this study. 2 periods of high primary productivity are compared from data collected in both spring and summer of 1987 and 1988 from the Delaware Estuary (USA). In spring. particulate carbon isotopic compositions (6I3C) were the most positive (up to -17 %0), whereas in summer the values were the most negative (to -32 %o). Equations calculating the CO, concentrations within algal cells were used to show that growth of phytoplankton, especially in spring, may be limited by the availability of dissolved carbon dioxide, C02(d)-An alternative hypothesis for the enrichment of I3c in diatoms from spring blooms includes the possibility that a mechanism for active bicarbonate accumulation is induced during high primary productivity. Similarly, a model is developed for phytoplankton growth during summer with C02(d), rather than bicarbonate, being the species of dissolved inorganic carbon (DIC) transported across the membrane. The influence of respired CO2 on the isotopic composition of total DIC in summer is also calculated to explain the differences in isotopic compositions of particulate carbon. The demand for during periods of high primary productivity limits its availability to phytoplankton. This demand could easily be met by the induction of an active transport system for concentrating DIC, which could explain some of the variability in 6'" of partlculate carbon In estuaries and oceans.

ABSTRACT:The relationship between bacteria, phytoplankton and heterotrophlc microflagellates is examined over large spatial and seasonal scales in the Delaware Estuary, USA. The estuary was sampled along the main salinity axis (0 to 30 ppt), from near Philadelphia to the mouth, between February and Auqust 1985. Samples were analysed for bacterial abundance and production, for heterotrophic microflagellate abundance and rate on bacteria, and for phytoplankton production and biomass. Temperature was a major factor that requlated bacteria and microflaqellates. With the exception of cold peridds, bacterla and microflagellates appeared to respond to phytoplankton production During the spring and summer, bacterial production and microflagellate grazing were highest in the lower estuary, where phytoplankton production was also highest. Bacter~al production was on average 23 % of the phytoplankton carbon production. In this area of the estuary grazing on bacteria was h~ghest. Bacterivores grazed 95 % of the bacterial production. Estimates on the carbon flow from phytoplankton to bacteria and subsequently to microflagellates suggest that bacteria and microflagellates do not return lost phytoplankton production to the main phytoplankton-zooplankton food chain in the Delaware Estuary. Instead, it appears that the primary effect of heterotrophic microbes is the mineralization of organic compounds to their inorganic constituents.

Copper, lead, cadmium and zinc have been measured in subsurface and surface-film water samples collected from the Nepean-Hawkesbury river system in New South Wales. Positive correlations were obtained between measured surface-film pressures and the surface excesses of lead, zinc and dissolved organic carbon. Measurements of copper-complexing capacity of the surface samples correlated well with dissolved organic nitrogen data. Enriched zinc was present in the surface film, mainly in bound species, as determined by anodic stripping voltammetry; lead was enriched in both labile and bound forms. Copper was also present in bound species, with many samples being depleted in labile copper. The relative concentrations of these heavy metals in surface films at the different sampling stations could be interpreted on the basis of known inputs.

Dynamic processes in a recirculating seawater aquarium system have been studied in a n attempt to assess nutrient regeneration. Sufficient monitoring has been done over time to construct elemental budgets. Results in nutrient and organic chemistry of this system are compared to published bottle experiments, bell jar experiments, and open system modellng. In regard to chemical specles and regeneration rates, the aquarium system is a better model than bottle or bell jar experiments for assessing natural mixed water-column phenomena. An aquarium provides a useful experimental tool: regeneration can b e measured and the otherwise unquantifiable organic source can b e back calculated. Such a system can give realistic regeneration rates, provide information on chemical species produced, and serve for exploring geochemical behavior. Data on elemental budgets on incoming water and the regeneration products indicate that the dissolved organic phosphorus pool is small and rather labile when compared to the dissolved organic nitrogen pool. From this study and analysis of published coastal water works, it appears that a relatively consistent 54 to 62 % of the total nitrogen (excluding gases) are In the dissolved organic pool.