Estuarine and Coastal Marine Science最新文献

Three different sampling designs, based upon the manner in which the total cross-sectional area is decomposed into sub-areas, are explored for their applicability to assessing the transverse and vertical variations of properties in an estuary cross-section. Three hypotheses on the nature of the distribution are used to test the designs.

The procedures are applied to Southampton Water where it is found that although both the salinity and velocity have important transverse and vertical variations, the longitudinal advective salt flux is almost totally due to their vertical deviations. This results, which contrasts with previous analyses, follows from the effect of gravity in vertically stratifying both the salinity and velocity distributions.

Cold bottom water is found during the summer months in a region extending from the shelf break to the nearshore zone in the area of the New York Bight. This cold bottom water, some of which is in the temperature range of the cold cell (8 °C or less), is observed to move onshore in response to upwelling events initiated by a strong wind stress from the south. Surf temperatures, nearshore temperature sections off Monterey Beach, N.J., wind velocities and offshore temperature sections are combined to document the cold cell's formation during 1974 and to demonstrate that the shoreward boundary of the cold bottom water and possibly cold cell water can move into the surf zone causing rapid decreases in surf temperature. In addition, under upwelling conditions, such onshore movements may have significant biological impacts, such as were observed during the summer of 1976 when anoxic conditions prevailed in much of this region.

The annual cycle of metazooplankton biomass has been compared with that of particulate organic detritus in the 20m water column of Kiel Bight. Zooplankton biomass was high from April through September and small neritic copepods were the dominant organisms. The particulate detritus levels fluctuated with greater frequency than zooplankton stocks during this period and no quantitative relationship between the two could be discerned.

The contribution of whole calanoid copepod faecal pellets to the detritus pool in terms of carbon was below 10% on an average from April to September and well below 5% during the rest of the year. The ratio by numbers of copepod faecal pellets to copepods showed a marked seasonal variation with low values in spring and summer when copepods were most abundant and high values during autumn and winter. Calculated residence times of pellets in the water column were a few hours in summer and two orders of magnitude longer in winter. The latter residence times indicate that in situ sinking rates of pellets must be considerably lower than the high values given in the literature derived from in vitro studies. Zooplankton feeding and microbial breakdown in the water column rather than sedimentation to the sea-bed appear to be the important mechanisms determining removal rate of faecal pellets from the water column in Kiel Bight, particularly in summer. Results from sediment traps support this conclusion, as the annual minimum in sedimentation occurs in late spring and summer and coincides with the season of largest zooplankton stocks. Grazing by small neritic zooplankton will thus tend to conserve essential nutrients in the surface layer.

Seasonal variations of size-frequency distribution, sex ratio, and percentage of egg-carrying females and juveniles in a population of Jassa falcata Leach inhabiting jetties at Helgoland Harbour (North Sea) are described. Reproduction occurs all the year round, but two maxima and thus, two main generations per year can be observed: a weaker one in winter, and a more pronounced one in late spring/early summer. Maximum body length is about 12 mm in females, and about 13 mm in males. Reproduction of females occurs soonest at 5 to 6 mm and ceases the latest at about 10 mm body length. Biochemical composition and energy contents of J. falcata show only in part a seasonal cycle. There is an inverse relationship between the protein and lipid fractions, whereas the former is negatively, the latter positively correlated with the amount of suspended food in the water. Protein, carbohydrote, lipid and the weight-specific energy equivalent show a decreasing trend with increasing size of the amphipods, while chitin significantly reveals an opposite trend.

Variation of chromium concentrations with grain size in estuarine sediments comples use of a sediment textural indicator in examination of pollutant chromium distribution. Sediment specific surface area is shown to be superior to measurements of the proportion of fine-grained sediment in defining regional variations of chromium concentration with sediment texture in three relatively unpolluted estuaries. Mineralogy is the prime control on chromium levels in these estuaries. The application of a textural normalization technique using specific surface areas in an estuary receiving a chromium-rich effluent allows differentiation of polluted from nonpolluted sediments. Accumulation of effluent chromium occurs within the estuary, not in adjacent coastal sediments, and concentration occurs in intertidal rather than subtidal zones.

In the brackish tropical water of the Ebrié lagoon (Ivory Coast), the influence of the incident light upon the PO₄ uptake is variable, and depends on the depletion of dissolved inorganic phosphate; this uptake also seems related to the ATP concentration in the seston. So luxury uptake may be observed, which causes imbalance in the elementary composition of the phytoplankton and in the uptake ratios. In P-depleted zones, the photosynthetic C uptake is much more active than the P uptake, giving C/P ratios higher than 300/I.

Sholkovitz (1980) states that the observations of Eaton (1979) on freshwater removal of soluble Fe in the Potomac River actually represent cation coagulation at very low salinities. It is shown here that the salinity does not change over the region of Fe removal and thus the original hypotheses of Eaton (1979) are a better explanation in this case.

The use of microfungi as an indicator of mass water movement in the Thames River Estuary of Eastern Long Island Sound was shown from a study over a two year period. The fungi, of terrestrial origin, were obtained from surface and bottom water samples taken in the river and from surface water samples in the sound. Seasonal variation in colony forming units revealed that the greatest number of fungi at any station occurred during the interval November–May and the lowest number during the interval June–September for both 1974–1975 and 1975–1976. The seasonal variation occurred in both surface and bottom water samples of stations in the river, although fewer colonies were produced from bottom samples than from surface samples. Correlations between salinity and colony forming units in the Thames River and near shore stations and lack of correlations at the off-shore stations in Long Island Sound indicate movement and dispersion of microfungi during the mixing of the water from the Thames River and Long Island Sound. Analysis of temperature, precipitation, salinity and river discharge data indicate that fluctuations in river discharge and mixing processes are the major factors that affect the dispersion of microfungi in this estuary.

The influences of biological and physical factors on dissolved oxygen (DO) dynamics are examined for an estuarine ecosystem near Calvert Cliffs, Chesapeake Bay. In several areas of the Chesapeake Bay community photosynthesis (P) and respiration (R) were estimated by observing time-course changes in DO in the open water and in bottles and benthic chambers. In shallow waters (3 m depth) diel changes of DO appeared to be generally dominated by biological metabolism, as has been observed in many other aquatic environments; however, unusual patterns of DO over 24-h periods at deeper stations (10 m) suggested strong influences of physical processes. Diel oxygen budgets were developed for the 10 m stations to investigate possible reasons for these anomalous DO patterns. These DO balances were constructed using explicit measurements for diffusion, D_a (across the air/water interface) and D_z (in the vertical plane of the water column), as well as for P and R. Horizontal net dispersion (H_n) was then calculated by difference. In general, biological and physical process each contributed about half to the total oxygen flux at the deeper stations. On the basis of four budgets, mean values of P contributed about 50% of the total inputs to DO stocks, while R accounted for about 43% of the outflows. Gas transfer with the atmosphere, D_a, represented only about 8% of the inputs and 3% of the outputs, and D_z accounted for about 5% of both inputs and outputs. Horizontal dispersion, H_n, contributed the remainder, about 40–50% of DO flux in either direction. Measurements of P and R in closed systems (bottles and chambers) differed from measurements in the open water on 11 of 16 occasions by a factor of about 1.5–4. Evidence is provided to suggest that the open-water estimates are more realistic, and that the difference may be due to artificial decoupling of the experimental systems from major pathways of nutrient flux. Some tentative generalizations are also provided concerning which aquatic environments are likely to be amenable to use of open-water techniques.