Estuarine and Coastal Marine Science最新文献

Concentrations and utilization rates of alanine, aspartate, lysine, glucose, glycollic, acetic and lactic acids have been determined on six occasions at least, during a full seasonal cycle in the water column of three stations (Scheldt estuary, coastal North Sea and English Channel) with greatly differing biological characteristics.

No significant differences in substrate concentration could be detected between the three stations, although the rate of utilization of all substrates differed greatly, decreasing in the order estuarine〉coastal〉open sea environment.

This apparent paradox is explained by aid of a simple model showing that the steady state concentration of a particular substrate is independent of its rate of production (and thus of consumption) and depends only on purely physiological characteristics of the bacteria. Using published data for the pertinent physiological parameters of marine bacteria, the model accounts for at least the order of magnitude of substrate concentrations observed, and the absence of important seasonal variations.

A numerical model of a partially mixed estuary is postulated, in which temporal changes in density current and vertical salinity stratification at a given point depend only on the longstream gradient of cross-sectional average salinity, S̄, and the tidal speed, ‖U‖, averaged over a tidal period. The salt conservation requirement leads to a partial differential equation on S̄: under steady state conditions this becomes an ordinary differential equation, that can easily be solved analytically for an estuary bed of any shape. The qualitative features of the solution are similar to those of real and laboratory model partially-mixed estuaries.

The time-dependent equation on S̄ is soved numerically, for the James River, U.S.A., in the 2-month period following Hurricane Agnes (June 1972). Agreement with observation is good, considering the extreme simplicity of the model. In particular, it is found in both observation and model, (i) that salt penetration up the James River appears to respond strongly and rapidly to changes in salinity at the mouth, overshadowing the responses to changing river flow and the spring neap cycle; (ii) that stratification depends primarily on the spring-neap tidal cycle, and very little on river flow.

A common configuration in fjords is a basin embraced by sills. This paper addresses the dynamics of a large fjord basin lying between comparatively deep sills where tidal mixing is vigorous: Puget Sound's Main Basin (∼ 10 km × 90 km × 0·3 km) between 44 m (landward) and 66 m (seaward) depth sills. Tidal action over the sills causes a vigorous two-layer circulation in the basin where no net motion occurs near the average depth of the embracing sills. On the flood tide lower-layer water is upwelled at the landward sill and upper-layer water is downwelled at the seaward sill. The resultant circulation in the basin is quite active at all depths throughout the year.

Currents computed from differences in dissolved oxygen between hydrographic stations compare favorably with measured currents. Based on differences between the ends of the basin, the bulk residence time in the lower layer is about three weeks—a short time for a large fjord basin.

Experiments in a hydraulic model demonstrate the marked sensitivity of basin circulation to tidal action in the sill zones: transport in the upper layer is directly proportional to the tidal prism inland of the landward sill zone, and there is an exponential type of response to abrupt changes in fresh-water flowing into the seaward sill zone (approximately 60% of equilibrium attained in 2 months). The rapid response causes the basin's lower-layer water properties to follow closely both the primary and secondary features of the seasonal cycles of local air temperature and runoff.

A new genus and a new species of a psammobiotic, sphaeromatid isopod, Tholozodium ocellatum, is described from the west coast of India (Goa). It is found on fine sediment beaches (Mdo = 2·72-2·47) located in the vicinity of estuaries which receive large inputs of organic matter.

The species is mainly distributed at the upper reaches of the beach and occurs in densities ranging from a few individuals to over 4700 m⁻². The existing evidence indicates that this herbivorous/omnivorous species has a fossorial existence without the occurrence of a free-swimming phase and with little interaction with the rest of the fauna. Moreover T. ocellatum in common with some other platybranch genera does not fit into any of the sub-divisions of this group as proposed by Hansen (1905). This suggests that with more information becoming available an extensive revision of this group of sphaeromatids is needed.

Three species of marine algae representing major taxonomic groups of phytoplankton, Isochrysis galbana (Chrysophyceae), Carteria sp. (Chlorophyceae), and Thalassiosira pseudonana (Bacillariophyceae), were utilized to investigate the potential of naturally occurring chlorophyll a of living algae to produce trihalomethanes during the chlorination of saline waters. Chlorination of filtered natural estuarine water (salinity=23 p.p.t.) from the North Edisto River, South Carolina, results in rapid formation of 201–221 μg 1⁻¹ trihalomethanes comprised mainly of bromoform (CHBr₃) and chlorodibromomethane (CHBr₂Cl). In the presence of 10⁶ cells ml⁻¹ Isochrysis galbana, chlorination of filtered estuarine water with sodium hypochlorite (NaOCl) to a nominal 10 mg 1⁻¹ chlorine increased the total trihalomethane concentration by an average of 41% (N = 6). The presence of Thalassiosira pseudonana resulted in an average 24% decrease (N = 6) while Carteria sp. did not produce a statistically significant effect upon the total trihalomethane concentration formed.

The absence of any significant statistical correlations between the chlorophyll a content of algal cultures and trihalomethane concentrations causes us to discount chlorine-chlorophyll a interactions as a source of these compounds. However, trihalomethane concentrations produced from the chlorination of algal culture media, after removal of algal populations, suggests instead that the observed trends in trihalomethane production are mainly due to chlorines reaction with the by-products of algal metabolism.

A description is given of the assembly, calibration and performance of an irradiance meter intended for underwater measurements in a single wave-band. The meter features high sensitivity by utilizing CdS photoconductors and a FET-type ohm meter, giving a linear response from 10⁻¹–10⁻⁶ W m⁻². Instrument performance is discussed in relation to angular light response, immersion effect, response time, temperature dependence and filter bandwidth error.

The introduction and growth of the calcareous reef-forming polychaete, Mercierella enigmatica Fauvel, during the past 50 years has greatly aggravated the eutrophication processes in Lac de Tunis, a broad, shallow lagoon on the North African coast. To quantify the polychaete's importance in the lagoon's oxygen and nutrient dynamics, portions of a reef were isolated by large in situ plexiglas enclosures (open to the atmosphere) during six experiments between December 1976 and April 1977. The concentrations of oxygen, ammonia, nitrite, nitrate, and phosphate were measured every 2 h for 24 h in a reef enclosure, in a control enclosure, and in the open water to allow calculation of exchange rates. Fourier series are used as explicit functions describing net productivity and net nutrient exchange rates in each enclosure. Reef respiration represented a large oxygen sink averaging 5·8 g O₂ m⁻² day⁻¹. The polychaetes fed on organic particulates and excreted large amounts of inorganic nutrients during specific periods of activity. This rapid nutrient recycling mechanism contributes to a state of active producer metabolism in the lagoon.

The energy requirements and energy consumption of curlew sandpipers Calidris ferruginea at Langebaan Lagoon, South Africa, are described. The paper also includes estimates of the net annual production of the benthic invertebrates potentially available to the birds, and of the birds' impact on this.

Mean estimated energy requirement of a free-living curlew sandpiper was 125 kJ day⁻¹. Mean energy intake was 180 kJ day⁻¹, with 144 kJ assimilated at an assumed assimilation efficiency of 80%. Overwintering immature birds had a negative energy balance. A substantial positive balance existed in late summer and autumn, when adult birds moult and lay in fat reserves for migration. The estimated mean net annual production of benthic invertebrates potentially available to curlew sandpipers was 705±444 kJ m⁻² yr⁻¹. The birds took 12·3% of this or 86·7 kJ m⁻² yr⁻¹. It appears that the carrying capacity of Langebaan Lagoon for curlew sandpipers has not been reached with respect to food, but food is unlikely to be the only limiting factor.

PCB uptake by adult copepods of the genus Acartia exposed to ¹⁴C-labeled PCB-contaminated water, inorganic suspended sediments, and phytoplankton was determined. PCB uptake from water and inorganic particles followed an asymptotic function, with apparent equilibrium values reached after about 36 h. Copepods fed PCB-contaminated phytoplankton showed a substantial increase in PCB accumulation relative to unfed copepods, despite similar PCB concentrations in the water. Significantly greater mortality was observed among copepods fed contaminated phytoplankton than among copepods without phytoplankton. These experiments indicate that phytoplankton provide an important vehicle for PCB uptake at the herbivore trophic level.

The flounder Platichthys flesus was studied between October 1970 and August 1973 in the Ythan estuary, Aberdeenshire, Scotland. A general survey of its diet indicated that Corophium volutator was the main prey item on the mudflats of the upper estuary, whereas small polychaetes and oligochaetes were taken on the softer mudflats in the middle region. Nereis diversicolor and Carcinus maenas were eaten on the mussel beds, and shoals of clupeids were preyed upon by older fish at the mouth of the estuary. A detailed analysis of the diet was carried out on one mudflat (Sleek of Tarty) where it was found that variations in diet between day and night were relatively small, as were variations between age groups. Numerically, Cor. volutator was important for most of the year with Hydrobia ulvae secondarily important. In terms of calorific equivalents N. diversicolor was important in autumn and winter whilst Cor. volutator was most important in spring and summer.

Sampling of flounders throughout 24-h periods showed that their stomachs were filled during the high-tide period on the intertidal mudflats, irrespective of whether high tide occurred by day or night. Most fish had empty stomachs at low tide. Flounders remaining in the sublittoral river channel at high tide during the day had little food in their stomachs. From a combination of observations in aquaria and the interpretation of fin marks and feeding holes left on the intertidal mudflats it was found that flounders fed by arching the body above the substratum in order to obtain and angled bite of the sediment. The mouthful of mud and sand was sifted through the gill rakers to obtain the infauna, primarily Cor. volutator, the mud being expelled through both branchial apertures. This technique was used by day and night. Flounders also fed on organisms (including clupeids) in the water column where visual cues may have been important in detecting and securing prey.