共查询到20条相似文献，搜索用时 93 毫秒
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J.B. Wilson 《Estuarine, Coastal and Shelf Science》1983,17(5):592-593
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Fourteen proteins and 12 morphometric characters were examined in specimens of blue maomao and sweep to resolve the question: Are they one or two species? Specimens were fixed for the same alleles at 12 protein loci and shared alleles at 4 polymorphic loci. At a further polymorphic locus they differed in allele frequency and at three loci they did not share alleles. A genetic distance of 0.209 was found between blue maomao and sweep suggesting that they diverged about 1 million years ago. One meristic character showed a difference between specimens. On the basis of the electrophoretic data and on gill raker counts it is considered that blue maomao and sweep are two separate species. In view of reported differences from Australian specimens the allocation of scientific names at least to sweep remains uncertain. 相似文献
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M. Alber 《Estuarine, Coastal and Shelf Science》2000,50(6):805
Suspended particle dynamics were investigated in the Ogeechee River Estuary during neap tide in July 1996. Samples were operationally separated into ‘ truly suspended ’ (settling velocity <0·006 cm s−1) and ‘ settleable ’ (settling velocity >0·006 cm s−1) fractions over the course of a tidal cycle to determine whether these two fractions were comprised of particles with differing biological and chemical characteristics. Total suspended sediment, organic carbon and nitrogen, chlorophyll a and phaeopigment concentrations were measured in each fraction, as well as rates of bacterial hydrolytic enzyme activity [β-1,4-glucosidase (βGase) and β-xylosidase (βXase)]. The majority of the suspended sediment (by weight) was in the truly suspended fraction; all measured parameters were largely associated with this fraction as well. When compared to the settleable material, the truly suspended material was significantly higher in % POC (5·7±0·6 vs. 3·9±1·8), % chlorophyll (0·07±0·02 vs. 0·03±0·01), % phaeopigment (0·030±0·006 vs. 0·018±0·012), and weight-specific maximal uptake rates (Vmaxper mg suspended sediment) of both enzymes (1·8±0·4 vs. 0·7± 0·2 nmol mg−1 h−1βGase and 1·1±0·3vs . 0·3±0·2 nmol mg−1 h−1βXase), providing clear evidence for a qualitative distinction between the two fractions. These results are interpreted to mean that the more organic-rich, biologically active material associated with the suspended fraction is likely to have a different fate in this Estuary, as ‘ truly suspended ’ sediments will be readily transported whereas ‘ settleable ’ sediments will settle and be resuspended with each tide. These types of qualitative differences should be incorporated into models of particle dynamics in estuaries. 相似文献
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Stephen P. Letherman 《Progress in Oceanography》1987,18(1-4)
Sea-level is one of the principal determinants of shoreline position. Sea-level rise induces or accelerates on-going shore retreat since deeper water decreases wave refraction, thus increasing littoral drift, and also allowing waves to arrive closer to shore before breaking. Tidal records from the US East and Gulf coasts indicate a relative sea-level rise of approximately 0.3m has occurred during the past century. Concomitantly, erosion has been prevalent almost everywhere along these sandy shorelines. Ocean City, Maryland, was selected as a case study site to determine historical shoreline changes and to project future beach erosion based on accelerated rates of sea-level rise. During the past 130 years (1850–1980), this shore has retreated approximately 75m and many highrise buildings at Ocean City are now threatened during storm conditions. Accelerated sea-level rise is expected to increase the rate of retreat by a factor of 2 to 5 based on analysis of present trends. This significantly reduces the planning time available for mitigating the hazard and increases the vulnerability of this urbanised barrier through time. 相似文献
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《Marine Ecology》1985,6(4):365-366
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Juli Badal Graf 《Marine Geology》1976,22(4):253-270
Comparison of calculated grain sizes with those found in a part of the shoaling zone of south western Lake Michigan reveals that existing quantitative expressions yield sizes which are much larger than those of the natural sediments, but that many aspects of the pattern of size distribution are predictable. An empirical and a theoretical expression were each used to calculate grain sizes in equilibrium with several different wave states for the measured bathymetry. For each wave state, the theoretical equation yields sizes which are closer to those found in the field over most of the shoaling zone, but sizes predicted by each of the two equations approach each other as the shore is approached and natural slopes increase toward the slope used in formulating the empirical expression. Grain-size trends predicted by the calculations include coarsening toward shore and to the south near shore. The calculations with the theoretical expression reveal more detail and predict an anomalously coarse area in the deeper part of the field area and elongate areas of fine sediments close to shore. Some support for the existence of these areas was found in the field. 相似文献
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Hypoxia has occurred in Upper Charlotte Harbor, a shallow (∼3 m) estuary in Southwest Florida, during moderate to high freshwater flows from the Peace and Myakka Rivers and after hurricanes, due to nutrient loading and vertical stratification. This paper studies the annual hypoxia and water quality dynamics in Upper Charlotte Harbor in 2000, using CH3D-IMS, an integrated modeling system which includes coupled models of circulation, wave, sediment transport, and water quality. The CH3D-IMS simulations showed that bottom-water hypoxic conditions occur during periods with relatively steady moderate to high (5–40 m3/s) freshwater inflows and sediment oxygen demand (SOD). During periods of relatively steady moderate to high river discharge, strong vertical salinity stratification results in reduced vertical mixing which prevents surface water from supplying dissolved oxygen (DO) to bottom water where SOD continuously consumes DO. There was significant temporal fluctuation of the hypoxic water volume, as a result of significant temporal variation in vertical turbulent mixing associated with combinations of spring-neap tides and river discharge. The validated modeling system could be used to forecast hypoxia. 相似文献
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L.A. Yarbro P.R. Carlson T.R. Fisher J.P. Chanton W.M. Kemp 《Estuarine, Coastal and Shelf Science》1983,17(5):555-570
A sediment budget for the Choptank River, one of the three largest estuaries on the eastern shore of Chesapeake Bay, was developed from measurements of sediment carried in upland runoff, shore erosion, sedimentation, and levels of suspended sediments in estuarine waters. Shore erosion was the major source of sediment (340 × 106 kg y?1), contributing seven times more sediment than upland runoff. Low relief, the rural character of the Coastal Plain drainage basin, and the susceptibility of poorly consolidated shoreline materials to erosion contributed to the dominance of shore erosion over runoff as a sediment source. Box modelling indicated a net annual flux (14–44 × 106 kg y?1) of sediment from the Choptank River to Chesapeake Bay. A mass balance estimate of sedimentation, calculated as the difference between total inputs and loss at the mouth of the estuary, (350 × 106 kg y?1) agreed well with an estimate based on 210Pb profiles (340 × 106 kg y?1) measured along the longitudinal axis of the estuary. Lead-210 sedimentation rates correspond to accumulation rates of 1·5–7·9 mm y?1. 相似文献