Estuarine and Coastal Marine Science最新文献

Periodic surveys have been made of Holm Sand, a Holocene deposit incorporating One Fathom Bank and part of Mackenzie Shoal in the Bristol Channel (British Admiralty Chart, 1182). The deposit is worked for seadredged aggregate, primarily building and concereting sands, although the latter are becoming depleted. The surveys show that the deposit lies on irregular pre-Holocene substrate and is incorporated as two suites of sand waves: large, mainly asymmetrical, outer sand waves and smaller, symmetriclaly-variable, inner sand waves. Sediments are classified into seven types (A-G), outer sand waves being formed in gravelly sands and sandy gravels (types C-F) and inner sand waves in unimodal medium sands (types A and B). It is suggested that sand wave scale is related to transport mode: transport of inner waveform sediments is mainly as suspended load, whereas outer waveform sediments are transported part as bed load, part as suspendes load. A progressive sequence of profiles is evident in outer sand waves and their alignment and mobility indicate that Holm Sand sediments are derived from channels to the northwest and southeast. This sequence, together with a progressive fining in mean sizes towards the deposit axis, suggests that the structure could have evolved during the (Holocene) Sub-Atlantic period.

This paper presents a simple analytical model of tidal motion in a wide estuary. The essential feature of the model is its ability to include both the Coriolis acceleration and, to a limited extent, vertical stratification of density, It is shown that the Coriolis acceleration is not important when considering the depth integrated or barotropic flow, but it is important when considering baroclinic motions. Further, arguments are presented to show that the Stokes' drift is a fair representation of tidally induced redidual flow, and that barotropic Stokes' drift on the kind of length scales appropriate to an estuary are dominated by friction. However, when considering depth dependent flow (the baroclinic mode), and inviscid Stokes' drift is present having a typical magnitude of 2 cm s⁻¹. The flow patterns for this drift in a straight sided estuary shows an equal and opposite flow along each bank, with the flow itself exhibiting a periodic structure (i.e. reversals) at well difined intervals down the estuary. The Stokes' drift along the axis of symmetry of the estuary is zero. Applications of this model to real estuaries are also discussed.

Strong tidal currents in the Sundays rive estuary, South Africa, prompted an investigation into the possibility of endemic populations avoiding or utilizing currents in a vertical and lateral plane as a mechanism of maintaining themselves within the estuary. The copepod, Pseudodiaptomus hessei avoided inflowing and outflowing surface currents, but migrated towards the surface at slack water. Acartia longipatella and A. natalensis remained in greater numbers near the bottom on the ebb tide, moving laterally into areas of slowest current velocity. Spatial distribution patterns of the two species of Acartia were maintained by different behavioural responses on the flood tide. A. longipatella was present in slower currents while. A. natalensis was present in greater numbers in faster flowing currents and so moved higher up the estuary than A. longipatella. The large mysid Rhopalophthalamus terranatalis was always present in greater numbers near the bottom, maintaining position through lateral migration, avoiding faster flowing currents on the ebb, but utilizing these faster currents on the flood tide to move up the estuary. Adults of the mysid, Mesopodopsis slabberi utilized both vertical and lateral migration as a means of maintaining position in the estuary.

Seasonal changes in zooplankton nitrogen biomass, particulate organic nitrogen and dissolved inorganic nitrogen species were measured for 2 years at a station in Buzzards Bay, Massachusetts. The ratio of particulate organic N: dissolved inorganic N: zooplankton N ranged from 64: 32:1 to 5: 2:1. The C: N ratio (by weight) of zooplankton was relatively constant over the 2 year, ranging from 3°6 to 4°7, whereas the C: N ratio of seston (by weight) fluctuated from a minimum of 5°1 in summer to a maximum of 13°6 in winter. The percentages of C and N of the zooplankton average 38% and 10% respectively but decreased to below 5% C and 1% N in August, September and October when the ctenophore Mnemiopsis leidyi was abundant in the Bay.

Zooplankton daily ration was estimated as 25 and 75% of their nitrogen biomass and compared to approximate N assimilation by phytoplankton as well as the total particulate nitrogen pool. Over most of the year in Buzzards Bay the approximate daily N assimilated by phytoplankton was lower than estimated zooplankton daily ration, suggesting that detritus is the dominant particulate nitrogen pool consumed.

A multivariate analysis of 40 years of data on the oyster (Crassostrea virginica) fishery in upper Chesapeake Bay reveals that variations in spat density and seed plantings of past years can explain 56% of the variation in annual harvest. The correlation allows the estimation of oyster harvest 4 years into the future. Spat density, in turn, is found to vary directly as the cumulative high salinity during the spawning season and inversely as the harvest of the previous season.

The Fraser River, the largest river (in terms of both water and sediment discharge) reaching the west coast of Canada, is a sand-dominated river in which most sediment transport occurs during freshet in late spring and early summer. More than half the sediment discharged during this 2–3 month period is sand. Throughout the rest of the year, the river is characterized by lower flow and low suspended sediment concentrations (primarily silt and clay); net offshore transport during these months is slight, and nearbottom transport appears to be landward.

The dominance of sand transport in the Fraser results in an estuarine depositional regime quite different from most mud-dominated rivers and estuaries. Although most sediment in the river is carried in suspension, about 40% of the sand (20% of the total load) settles from suspension in the upper estuary and most of the rest settles prior to reaching the lower estuary.

In a natural situation, much of the river sand probably would continue moving seaward as bed load, as suggested by the prevalence of migrating sand waves in the middle estuary during freshet. Longshore drift of this sand has built tidal flats that now dominate the nearshore environment. Dredging of river channels removes an appreciable part of the total annual sand load. Jetties across intertidal flats and at the river mouth have interrupted longshore transport and increased resuspension of sand in the outer estuary by channelizing flow. All of these factors should combine in shifting tidal flats and adjacent shoreline from their natural state.

Experiments designed to determine removal rate constants and removal mechanisms of various radioactive trace metals (⁵¹Cr, ⁵⁴Mn, ⁵⁸Co, ⁵⁹Fe, ⁶⁵Zn, ⁷⁵Se, ^115mCd, ¹³⁴Cs, ²¹⁰Po, ²¹⁰Pb, ²²⁶Ra, ²²⁸Th) in controlled ecosystems simulating Narragansett Bay conditions in spring and early summer seasons are described. Overall removal could adequately be described with a model assuming first order removal to several reservoirs. Initial removal rates in two identical tanks replicated well during the early summer experiment. The removal behavior of Mn, Cr and Se changed after the first 1–2 weeks of the same experiment. Although adsorption to walls and other tank parts was significant, that fraction seemed to be effectively removed from further interaction and would be accounted for in the model. The major mechanisms for metal uptake that would be characteristic of the natural system were found to be scavenging by particles that settled from the water column (mostly resuspended sediment) and direct adsorption within the bioturbated layer of the sediment. By comparing the relative importance of these sinks and considering the similarities in respective half removal times, the 12 elements studied were grouped according to general behaviour: (1) hydrolysable elements including Fe, Th, Po, Cr (-III), and Se (as SeO²⁻₃), with half removal times ranging from 4 to 40 days; (2) particle-reactive elements Mn and Co with half removal times ranging from 2 to 140 days; (3) Zn and Cd which were removed more slowly, with half removal times ranging from 50 to 400 days and about equally by settling particles and by adsorption within the bioturbated layer of the sediment; (4) Cs and Ra, which were removed most slowly, with half removal times ranging from 600 to 800 days, mostly by adsorption within the bioturbated layer of the sediments. Generally slower removal was observed during the early summer relative to the spring and was ascribed to a combination of trace metal association with low molecular weight organic compounds and increasing rates of return from the sediments.

Bioturbation rates in the top 3 cm of the sediments in the spring experiments were similar to other experimental values for Narragansett Bay and other coastal regions: a mixing coefficient of 2−5×10⁻⁷ cm² s⁻¹ was calculated.

The relationships between the distribution of the polychaete Capitella capitata, sediment type, total organic matter, hydrogen sulphide concentration and heavy metal contamination in an enclosed polyhaline non-tidal dock are reported. Capitella is most abundant in unstable coarse sediments characterized by low levels of organic and sulphide pollution, and is found only in small numbers in stable silt-bearing substrates where high sulphide accumulation, together with large amounts of organic matter, is likely to lead to low oxygen availability. Heavy metal accumulations appear to have no effect on the distribution of the polychaete

The chloroform-methanol extractable compounds (lipids) of organic matter in seawater were measured from February to December 1978 in the Ems-Dollart estuary. The concentration of total lipids (dissolved and particulate) ranged from 0·012 to 0·7 mg carbon 1⁻¹ (0·2-15·2% of total organic carbon). In March 1979 the dissolved lipid concentration in the Ems-Dollart estuary was measured: of the total lipids 63·4–83·8% were dissolved, hence 16·2-36·6% of the lipids are in particulate material. In June and October 1978, two surveys were made in the western part of the Wadden Sea to compare the total lipid concentrations here with the results in the Ems-Dollart. Total lipid concentration in this part of the Western Wadden Sea ranged from 0·018 to 0·154 mg carbon 1⁻¹ (1–4·5% of total organic carbon). The contributions of the ‘living’ and the ‘detrigeneous’ parts in the total lipid content are discussed.