Upstream dams and downstream clams: growth rates of bivalve mollusks unveil impact of river management on estuarine ecosystems (Colorado River Delta, Mexico)     

B. R. Schne  K. W. Flessa  D. L. Dettman  D. H. Goodwin 《Estuarine, Coastal and Shelf Science》2003,58(4):715-726

We studied how the extensive diversion of Colorado River water, induced by dams and agricultural activities of the last 70 years, affected the growth rates of two abundant bivalve mollusk species (Chione cortezi and Chione fluctifraga) in the northern Gulf of California. Shells alive on the delta today (‘Post-dam’ shells) grow 5.8–27.9% faster than shells alive prior to the construction of dams (‘Pre-dam’ shells). This increase in annual shell production is linked to the currently sharply reduced freshwater influx to the Colorado River estuary. Before the upstream river management, lower salinity retarded growth rates in these bivalves. Intra-annual growth rates were 50% lower during spring and early summer, when river flow was at its maximum. Growth rates in Chione today are largely controlled by temperature and nutrients; prior to the construction of dams and the diversion of the Colorado River flow, seasonal changes in salinity played an important role in regulating calcification rates.Our study employs sclerochronological (growth increment analysis) and geochemical techniques to assess the impact of reduced freshwater influx on bivalve growth rates in the Colorado River estuary. A combination of both techniques provides an excellent tool to evaluate the impact of river management in areas where no pre-impact studies were made.  相似文献   

酶解条件对条斑紫菜单细胞成活率影响的比较研究     

杨震  唐学玺  戴继勋  沈颂东  宫相忠  贾鹏举 《中国海洋大学学报(自然科学版)》2001,31(3):407-410

该文分别选用不同浓度的海螺酶 ;葡萄糖、蔗糖、甘露醇、山梨醇、氯化钠 5种渗透剂 ;维生素 C和甘露醇 2种抗氧化剂 ;对条斑紫菜酶解单细胞的成活率进行了研究。实验结果表明 :用浓度为 10 %的海螺酶酶解条斑紫菜 ,成活率最高 ;选用 2 mol/ L葡萄糖作渗透剂 ,效果最好 ,成活率达85.2 % ;加入抗氧化剂对细胞成活率没有影响  相似文献   

Estimation of Uplift Capacity of Rapidly Loaded Plate Anchors in Soft Clay     

S. P. Singh  D. P. Tripathy  S. V. Ramaswamy 《Marine Georesources & Geotechnology》2007,25(3):237-249

Plate anchors are extensively used in civil engineering constructions as they provide an economical alternative to gravity and other embedded anchors. The rate of loading is one of the important factors that affects the magnitude of soil resistance as well as soil suction force. This article outlines the effect of pullout rate on uplift behavior of plate anchors (70 mm diameter) buried in soft saturated clay by varying the pullout rate from 1.4 mm/min to 21.0 mm/min. The variation of breakout force and suction force with embedment depth and rate of pull are presented. A correlation between the rate of increase of undrained strength of clay and anchor capacity with rate of strain has been established. Finally an empirical equation has been proposed that includes the rate of pull in the estimation of breakout capacity of anchors.  相似文献   

Discussion: A review on the behaviour of helical piles as a potential offshore foundation system     

Shah Neyamat Ullah  Yuxia Hu 《Marine Georesources & Geotechnology》2020,38(9):1121-1127

Abstract

Helical piles have emerged as an attractive foundation system for offshore applications with renewed interest from the offshore community. Significant research gap currently exists in transferring this technology offshore and this paper discusses how existing and emerging knowledge can be successfully used to bridge some of the gaps. We focus on the Coupled Eulerian Lagrangian (CEL) large deformation finite element (LDFE) modelling technique that is commercially available and can be used to model the three-dimensional installation process with consideration of strain rate and softening effects in soft offshore clays. A helical pile of L?=?7.5?m long is modelled with one or two large-diameter helices (D?=?2?m) attached to a central shaft of d?=?0.5?m in diameter.The net effect of strain rate and softening is to increase the installation torque. The measured torque is within the range of 200–400?kN.m for the offshore clay and the pile geometry studied. Additional helices increase the uplift force but to a lesser degree than that of the measured torque. Remoulding induced strength reduction is found to be within the range of 25–33% of the intact clay strength. Issues of extracting and reusing offshore helical pile foundations are discussed.  相似文献   

Nutrient Limitation in Macroalgae (Ulva and Enteromorpha) from the Rías Baixas (NW Spain)     

Ruben Villares  & Alejo Carballeira 《Marine Ecology》2004,25(3):225-243

Abstract.  Photosynthesis and growth rates in samples of two green seaweeds ( Ulva and Enteromorpha ) were monitored in the laboratory. The macroalgae were collected every 15 days from four coastal embayments in Galicia (NW Spain). Ulva samples were found to be nutritionally limited, particularly in summer. The physiological activity of Enteromorpha did not appear to be as affected by nutrient scarcity, although it may have suffered from phosphorus limitation. The subsistence quotas, critical concentrations and storage capacity for N and P in Ulva were comparable to those obtained by other investigators in similar studies. The trace metals analysed apparently did not negatively affect the macroalgae at the measured concentrations; one explanation is that many of these metals function as essential micronutrients. The complex physiological interactions between metals and nutrients, however, may complicate interpretation of the results.  相似文献   

Spring-spawning herring (Clupea harengus L.) in the southwestern Baltic Sea: do they form genetically distinct spawning waves?     

Hede Jorgensen  Hanne B.; Hansen  Michael Moller; Loeschcke  Volker 《ICES Journal of Marine Science》2005,62(6):1065-1075

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Sediment Transport in Rivers and Coastal Waters     

YANG  Shu-qing 《中国海洋工程》2003,17(4):527-540

Following Bagnold's approach, a relationship between sediment transport and energy dissipation is developed. The major assumption made in the study is that the near bed velocity plays a dominant role in the process of sediment transport. A general relationship between energy dissipation and sediment transport is first proposed. Then the equations for total sediment transport are derived by introducing the appropriate expression of energy dissipation rate under different conditions, such as open channel flows, combination of wave and current, as well as longshore sediment transport. Within the flows investigated, the derived relationships are fairly consistent with the available data over a wide range of conditions.  相似文献   

Accumulation of organic and inorganic carbon in Pliocene–Pleistocene sediments along the SW African margin     

Jacques Giraudeau  Philip A. Meyers  Beth A. Christensen   《Marine Geology》2002,180(1-4):49-69

The Ocean Drilling Program Leg 175 recovered a unique series of stratigraphically continuous sedimentary sections along the SW African margin, an area which is presently affected by active coastal upwelling. The accumulation rates of organic and inorganic carbon are a major component of this record. Four Leg 175 sites (1082, 1084, 1085, 1087) are chosen as part of a latitudinal transect from the present northern to southern boundaries of the Benguela Current upwelling system, to decipher the Pliocene–Pleistocene history of biogenic production and its relationship with global and local changes in oceanic circulation and climate. The pattern of CaCO₃ and C_org mass accumulation rates (MARs) over 0.25-Myr intervals indicates that the evolution of carbon burial is highly variable between the northern and the southern Benguela regions, as well as between sites that have similar hydrological conditions. This, as well as the presence over most locations of high-amplitude, rapid changes of carbon burial, reflect the partitioning of biogenic production and patterns of sedimentation into local compartments over the Benguela margin. The combined mapping of CaCO₃ and C_org MARs at the study locations suggests four distinct evolutionary periods, which are essentially linked with major steps in global climate change: the early Pliocene, the mid-Pliocene warm event, a late Pliocene intensification of northern hemisphere glaciation and the Pleistocene. The early Pliocene spatially heterogeneous patterns of carbon burial are thought to reflect the occurrence of mass-gravitational movements over the Benguela slope which resulted in disruption of the recorded biogenic production. This was followed (3.5–3 Ma) by an episode of peak carbonate accumulation over the whole margin and, subsequently, by the onset of Benguela provincialism into a northern and a southern sedimentary regime near 2 Ma. This mid and late Pliocene evolution is interpreted as a direct response to changes in the ventilation of bottom and intermediate waters, as well as to dynamics of the subtropical gyral circulation and associated wind stress.  相似文献   

The recovery of the Barents Sea capelin (Mallotus villosus) from a larval point of view     

Fossum  P. 《ICES Journal of Marine Science》1992,49(2):237-243

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The intertidal erosion rate of cohesive sediment: a case study from Long Island Sound   总被引：2，自引：0，他引：2  

Y. H. Wang   《Estuarine, Coastal and Shelf Science》2003,56(5-6):891-896

Over the past decades, many attempts have been made to generate useful bottom erosion models for the study of cohesive sediment movement. This study addresses some of the key questions involved in determining the functional relationship between erosion rate and bottom shear stress. Current, wave, and turbidity data were collected from a bottom mounted instrument array in a moderately energetic estuarine environment. The bottom shear stress was calculated from a wave–current interaction model. The erosion rate was derived from the observed sediment concentration using a vertical mixing model. Examination of the relationship between erosion rate and bottom stress showed that the erosion rate varied at intertidal frequency. When averaged over the tidal fluctuation, the erosion rate remained approximately constant at low stress, but increased sharply when the shear stress rose above a critical value. This suggests two-stage erosion. The bed has a layered structure, in which a thin layer of loose, high water content material overlies a more consolidated bed. The top layer of high water content material (fluff) was easily disturbed and re-suspended by tidal currents, but the consolidated bottom layer was eroded only under conditions of high shear stress.  相似文献