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991.
For morphological studies in coastal areas the wave-driven currents are often of primary importance. As the computation of the wave-driven current field requires the computation of the driving forces from a wave propagation model, the quality of these forces is basic to the success of the morphological study. It is shown in the paper that, under the common conditions of slowly varying wave fields, the driving force per unit mass is closely proportional to the wave energy dissipation per unit area and that diffraction-related terms give insignificant contributions. This result holds good for wave fields without current refraction. Examples show that formulation of the driving forces in terms of the wave dissipation yields more trustworthy results than those obtained by numerical differentiation of the radiation stress tensor. 相似文献
992.
Marsh vertical accretion via vegetative growth 总被引:1,自引:0,他引:1
John A. Nyman Russel J. Walters Ronald D. Delaune William H. Patrick Jr. 《Estuarine, Coastal and Shelf Science》2006,69(3-4):370
Coastal marshes accrete vertically in response to sea-level rise and subsidence. Inadequate accretion and subsequent conversion of coastal marshes to open water generally is attributed to inadequate mineral sedimentation because mineral sedimentation is widely assumed to control accretion. Using 137Cs dating to determine vertical accretion, mineral sedimentation, and organic matter accumulation, we found that accretion varied with organic accumulation rather than mineral sedimentation across a wide range of conditions in coastal Louisiana, including stable marshes where soil was 80% mineral matter. These results agreed with previous research, but no mechanism had been proposed to explain accretion via vegetative growth. In an exploratory greenhouse experiment, we found that flooding stimulated root growth above the marsh surface. These results indicated the need for additional work to determine if flooding controls accretion in some marshes by stimulating root growth on the marsh surface, rather than by mineral accumulation on the marsh surface. Restoration or management that focus on mineral sedimentation may be ineffective where a relationship between accretion and mineral sedimentation is assumed rather than tested. 相似文献
993.
Global change models predict effects of climate change on hydrological regimes at the continental scale in Europe. The aim of this study was to gain a better understanding of the possible effect of changing external forcing conditions on the functioning of estuarine ecosystems. In densely populated areas, anthropogenic nutrient enrichment and consequent alteration of nutrient biogeochemical cycles have already had a big impact on these ecosystems. The average yearly discharge of the upper Schelde estuary increased nearly threefold over the period 1996–2000, from 28 m3 s−1 in 1996 to 73 m3 s−1 in 2000. The continuously rising discharge conditions over the five-year period were used as a reference situation for possible future effects of climate on ecological functioning through increase of discharge. At high discharges, nutrient (NH4+, NO3−, dissolved silica and PO43−) concentrations in the tidal fresh- and brackish water showed a decrease of up to 50% while total discharged nutrient loadings increased up to 100%. Opposite effects of increasing discharge on NH4+, NO3− and dissolved silica concentrations in summer and winter, resulted in the flattening out of seasonal cycles for these nutrients. Under high discharge conditions, silica uptake by diatom communities was lowered. Dissolved silica loadings to the coastal area increased concurrently with total silica loadings upstream. Salt intrusion to the marine parts of the estuary decreased. This resulted in a downstream shift of the salinity gradient, with lower salinity observed near the mouth. As a result, TDIN, NO3− and dissolved silica concentrations doubled at the mouth of the estuary. 相似文献
994.
Giulio Alessandro De Leo Marco Bartoli Mariachiara Naldi Pierluigi Viaroli 《Marine Ecology》2002,23(S1):92-100
Abstract. In this work we have developed a very simple stochastic mathematical model of Ulva spp. growth to quantitatively evaluate the economic costs of algal harvesting and the related benefits in terms of avoided'economic loss'of clam production due to an effective prevention of algal blooms and the consequent anoxic crises. Algal growth was simulated by means of a discrete time difference equation of Ulva biomass where the finite growth rate depends only upon water temperature. In order to explicitly include environmental variability, a seasonal autoregressive model calibrated on available data was used to simulate water temperature. Different harvesting scenarios were analysed in terms of the number of harvesting vessels employed and the threshold biomass of Ulva at which vessels start to operate. Costs of algal harvesting and disposal, as well as monetary damages resulting from the collapse of clam production as a consequence of algal blooms, were assessed by interviewing the managers of the Clam Fishermen's Union of Goro. A Monte Carlo approach was used to estimate the mean and total statistical distribution of costs and benefits of different harvesting strategies. Our analysis shows that the most cost-effective management policy is attained with 4–6 vessels operating at low algal density able to harvest as much Ulva as possible with intensive and short interventions at the beginning of the seasonal growth. 相似文献
995.
铁锰结核结壳生长过程的一种理论假设 总被引:4,自引:0,他引:4
铁锰结核成矿物质的直接来源是大洋底层水和沉积物孔隙水,结壳只有底层水,因此,底层水和孔隙水的物理化学特征就成为理解铁锰结核(壳)成矿作用特征与过程的关键。铁锰结核(壳)内部构造的两个明显特征是:①韵律性的环状纹层构造,和②树枝状构造,这两种构造是典型的远离平衡的非线性地质作用的产物。正常情况下,海底水—沉积物界面系统的底层水、孔隙水中Mn、Fe是不饱和的。因此,铁锰结核(壳)不可能在平衡状态下连续生长。本文提出铁锰结核(壳)生长的自反馈“振荡式”模型。 相似文献
996.
Koenraad Muylaert Renaat Dasseville Loreto De Brabandere Frank Dehairs Wim Vyverman 《Estuarine, Coastal and Shelf Science》2005,64(4):591-600
To unravel the factors that regulate DOC dynamics in the freshwater tidal reaches of the Schelde estuary, DOC concentration and biodegradability were monitored in the upper Schelde estuary and its major tributaries. Although the Schelde estuary possesses a densely populated and industrialized catchment, our data suggest that the bulk of DOC in the freshwater tidal reaches is not derived from waste water. This was concluded from the low biodegradability of DOC (on average 9%), DOC concentrations that are close to the mean for European rivers (4.61 mg l−1) and the absence of an inverse relationship between DOC and discharge. Most DOC originating from waste water being discharged in tributaries of the estuary appears to be remineralised before these tributaries reach the main estuary. Although dense phytoplankton blooms were observed in the upper estuary during summer (up to 700 μg chl a l−1), these blooms did not appear to produce large quantities of DOC in the freshwater tidal reaches as DOC concentrations were low when phytoplankton biomass was high. The fact that DOC concentrations were high in winter and decreased in summer suggests a predominantly terrestrial source of DOC in the freshwater tidal reaches of the Schelde estuary. 相似文献
997.
多金属结核瞬时生长速率及其意义 总被引:1,自引:0,他引:1
本文用X射线荧光光谱分析,沿结核壳层的生长方向逐点扫描测定铁锰含量,计算结核壳层的瞬时生长速率,划分结核壳层的生长阶段,计算各生长阶段的生长速率,并在结构壳层中建立高分辨率的时间标尺,重建多金属结核生长历史。 相似文献
998.
HUANG Xiaohang LAM Patrick P L LIN Xuezheng LIU Chenlin BIAN Ji GAISANO Herbert 《海洋学报(英文版)》2007,26(1):159-164
1 IntroductionSecretion is a basic function of all living organ-isms. In fish, like in mammals, neurotransmitters,hormones, enzymes and other macromolecules aresecreted in several neuronal, neuroendocrine and ex-ocrine organs and tissues located in brain,… 相似文献
999.
1000.
Pierre Cervenka Christian De Moustier Peter F. Lonsdale 《Marine Geophysical Researches》1994,16(5):365-383
Acoustic backscatter images of the seafloor obtained with sidescan sonar systems are displayed most often using a flat bottom assumption. Whenever this assumption is not valid, pixels are mapped incorrectly in the image frame, yielding distorted representations of the seafloor. Here, such distortions are corrected by using an appropriate representation of the relief, as measured by the sonar that collected the acoustic backscatter information. In addition, all spatial filtering operations required in the pixel relocation process take the sonar geometry into account. Examples of the process are provided by data collected in the Northeastern Pacific over Fieberling Guyot with the SeaMARC II bathymetric sidescan sonar system and the Sea Beam multibeam echo-sounder. The nearly complete (90%) Sea Beam bathymetry coverage of the Guyot serves as a reference to quantify the distortions found in the backscatter images and to evaluate the accuracy of the corrections performed with SeaMARC II bathymetry. As a byproduct, the processed SeaMARC II bathymetry and the Sea Beam bathymetry adapted to the SeaMARC II sonar geometry exhibit a 35m mean-square difference over the entire area surveyed.On leave at the Naval Research Laboratory, Code 7420, Washington D.C. 20375-5350. 相似文献