Effects of suction-dredging for cockles on non-target fauna in the Wadden Sea     

J. G. Hiddink   《Journal of Sea Research》2003,50(4):315-323

Suction dredging for cockles removes large cockles from tidal flats and may also cause mortality of non-target fauna and make the habitat less suitable for some species. This study examines whether suction dredging for cockles on tidal flats of the Dutch Wadden Sea had affected densities of non-target fauna, directly after fishing and one year later. Densities of non-target fauna in two randomly chosen undredged locations were compared to densities at the surrounding heavily commercially dredged area. A significant negative effect of cockle dredging on densities of 0-group Macoma balthica was observed and this effect persisted one year after dredging. The dredged area appeared to be less suitable for settlement of mussels Mytilus edulis. No significant effects of dredging on the mudsnail Hydrobia ulvae and on 0 and 1-group C. edule were found. For the mobile young Macoma balthica it seems unlikely that the effect found after one year was still due to the mortality caused by dredging and this suggests that the habitat was less suitable as a consequence of dredging. Thus, even in the highly dynamic ecosystem of the Wadden Sea, effects of bottom disturbance by cockle dredging may persist after one year.  相似文献   

Effect of emersion and immersion on the porewater nutrient dynamics of an intertidal sandflat in Tokyo Bay   总被引：2，自引：0，他引：2  

Tomohiro Kuwae  Eiji Kibe  Yoshiyuki Nakamura 《Estuarine, Coastal and Shelf Science》2003,57(5-6):929-940

Porewater nutrient dynamics during emersion and immersion were investigated during different seasons in a eutrophic intertidal sandflat of Tokyo Bay, Japan, to elucidate the role of emersion and immersion in solute transport and microbial processes. The water content in the surface sediment did not change significantly following emersion, suggesting that advective solute transport caused by water table fluctuation was negligible. The rate of change in nitrate concentration in the top 10 mm of sediments ranged from −6.6 to 4.8 μmol N l⁻¹ bulk sed. h⁻¹ during the whole period of emersion. Steep nutrient concentration gradients in the surface sediment generated diffusive flux of nutrients directed downwards into deeper sediments, which greatly contributed to the observed rates of change in porewater nutrient concentration for several cases. Microbial nitrate reduction within the subsurface sediment appeared to be strongly supported by the downward diffusive flux of nitrate from the surface sediment. The stimulation of estimated nitrate production rate in the subsurface layer in proportion to the emersion time indicates that oxygenation due to emersion caused changes in the sediment redox environment and affected the nitrification and/or nitrate reduction rates. The nitrate and soluble reactive phosphorus pools in the top 10 mm of sediment decreased markedly during immersion (up to 68% for nitrate and up to 44% for soluble reactive phosphorus), however, this result could not be solely explained by molecular diffusion.  相似文献   

Short-term and interannual variability of redox-sensitive chemical parameters in hypoxic/anoxic bottom waters of the Chesapeake Bay     

Brent L. Lewis  Brian T. Glazer  Paul J. Montbriand  George W. Luther III  Donald B. Nuzzio  Timothy Deering  Shufen Ma  Stephen Theberge 《Marine Chemistry》2007,105(3-4):296-308

A combination of CTD casts, discrete bottle sampling and in situ voltammetric microelectrode profiling was used to examine changing redox conditions in the water column at a single station south of the Bay Bridge in the upper Chesapeake Bay in late July/early August, 2002–2005. Short-term (2–4 h) fluctuations in the oxic/suboxic/anoxic interface were documented using in situ voltammetric solid-state electrodes. Profiles of dissolved oxygen and sulfide revealed tidally-driven vertical fluctuations of several meters in the depth and thickness of the suboxic zone. Bottom water concentrations of sulfide, Mn²⁺ and Fe²⁺ also varied over the tidal cycle by approximately an order of magnitude. These data indicate that redox species concentrations at this site varied more due to physical processes than biogeochemical processes. Based on analysis of ADCP data, tidal currents at this station were strongly polarized, with the principal axis of tidal currents aligned with the mainstem channel. Together with the chemical data, the ADCP analysis suggests tidal flushing of anoxic bottom waters with suboxic water from north of the site. The present study is thus unique because while most previous studies have focused on processes across relatively stable redox interfaces, our data clearly demonstrate the influence of rapidly changing physical mixing processes on water column redox chemistry.Also noted during the study were interannual differences in maximum bottom water concentrations of sulfide, Mn²⁺ and Fe²⁺. In 2003, for example, heavy spring rains resulted in severe hypoxia/anoxia in June and early July. While reported storm-induced mixing in late July/early August 2003 partially alleviated the low-oxygen conditions, bottom water concentrations of sulfide, Mn²⁺ and Fe²⁺ were still much higher than in the previous year. The latter implies that the response time of the microbial community inhabiting the suboxic/anoxic bottom waters to changing redox conditions is slow compared to the time scale of episodic mixing events. Bottom water concentrations of the redox-sensitive chemical species should thus be useful as a tracer to infer prior hypoxic/anoxic conditions not apparent from ambient oxygen levels at the time of sampling.  相似文献   

The morphodynamic modelling of tidal sand waves on the shoreface     

P.K. Tonnon  L.C. van Rijn  D.J.R. Walstra 《Coastal Engineering》2007

An artificial sand wave on the Dutch shoreface of the North Sea has been studied in conditions with relatively strong tidal currents in the range of 0.5 to 1 m/s and sediments in the medium sand size range of 0.2 to 0.5 mm. The sand wave is perpendicular to the tidal current and has a maximum height and length of the order of 5 m and 1 km, respectively. The sand wave is dynamically active and shows migration rates of the order of a few metres per year. A numerical morphodynamic model (DELFT3D model) has been used to simulate the morphological behaviour of the sand wave in the North Sea. This model approach is based on the numerical solution of the three-dimensional shallow water equations in combination with a surface wave propagation model (wind waves) and the advection–diffusion equation for the sediment particles with online bed updating after each time step. The model results show that the sand wave grows in the case of dominant bed-load transport (weak tidal currents; relatively coarse sediment; small roughness height; low waves) and that the sand wave decays in the case of dominant suspended transport (strong currents, relatively fine sediment, large roughness height; storm waves).  相似文献   

潮滩演变规律在围堤选线中的应用——以江苏辐射沙洲内缘区为例   总被引：2，自引：0，他引：2  

李加林  王艳红  张忍顺  张正龙  齐德利  顾勇 《海洋工程》2006,24(2):100-106

滩涂围垦是沿海地区耕地占补平衡的重要手段。如何进行合理的围堤选线,尽可能减小围堤对潮滩水沙环境的影响,使匡围后的潮滩演变不影响海堤安全,是围海工程设计时必须考虑的问题。以江苏辐射沙洲内缘区仓东垦区匡围工程为例,运用潮滩均衡态概念框架,对条子泥西侧岸滩平均高潮位点变化、师地岛形成及潮沟活动性等潮滩演变特征及趋势进行了分析,并重点探讨了其在围堤选线中的应用。  相似文献   

渤海的环流、潮余流及其对沉积物分布的影响   总被引：16，自引：2，他引：16  

赵保仁  庄国文  曹德明  雷方辉 《海洋与湖沼》1995,26(5):466-473

阐明渤海环流和潮余流的分布特征及其与沉积物输运之间的关系。本文根据８０年代以来的实测海流资料得到：辽东湾的环流是顺时针向的；黄河三角洲外海存在着一支流向东北偏北向流，与辽东湾西部的东北向海流相接；渤海湾内的环流北部为反时针向，南部为顺时针向回转的双环结构。上述环流趋势与渤海沉积物分布相一致。渤海沿岸主要入海河流的特征矿物分布正在上述环流存在的最好佐证。文中进一步讨论了潮余流分布特征及其对渤海环流的  相似文献   

长江口三维潮流数值计算及动力分析   总被引：10，自引：1，他引：10  

于凤香  宋志尧  李瑞杰 《海洋湖沼通报》2003,(3):14-23

采用三维动力学数学模型对长江口潮流场进行了计算，对长江口潮流流态在一个潮周期内逐时进行了分析，并对长江口南支盐水倒灌从动力学角度进行了初步探讨。计算结果表明：文中模型较好地重演长江口潮流场，可以用于大型复杂河口工程实际中的潮流场的计算和分析。  相似文献   

Coastal geomorphic evolution at the Denglou Cape, the Leizhou Peninsula     

Wang Lirong  Zhao Huanting  Song Chaojing  Yuan Jiayi  Yu Hongbing 《海洋学报(英文版)》2002,21(4):597-611

ＩＮＴＲＯＤＵＣＴＩＯＮＴｈｅＤｅｎｇｌｏｕＣａｐｅ ,ｉｎｔｈｅｓｏｕｔｈｗｅｓｔｏｆｔｈｅＬｅｉｚｈｏｕＰｅｎｉｎｓｕｌａ ,ｉｓａｔｔｈｅｎｏｒｔｈｍａｒｇｉｎｏｆｔｒｏｐｉｃａｌｚｏｎｅ .ＳｅｖｅｒａｌｒｅｓｅａｒｃｈｅｓａｎｄｃａｒｔｏｇｒａｐｈｉｅｓｏｆｔｈｅｒｅｇｉｏｎａｌｇｅｏｍｏｒｐｈｏｌｏｇｙａｎｄＱｕａｔｅｒ ｎａｒｙｇｅｏｌｏｇｙ ,ｗｈｉｃｈｗｅｒｅｃａｒｒｉｅｄｏｕｔｉｎｔｈｅｐａｓｔ,ａｌｌｉｎｃｌｕｄｅｔｈｉｓａｒｅａ (ＭＧＬ ,ＳＣＳＩＯ ,ＣＡＳ ,1 978;ＧＰＣＳＧＲＣＺＴ…  相似文献   

Response of a climate model to tidal mixing parameterization under present day and last glacial maximum conditions     

lvaro Montenegro  Michael Eby  Andrew J. Weaver  Steven R. Jayne 《Ocean Modelling》2007,19(3-4):125-137

Experiments with a climate model were conducted under present day and last glacial maximum conditions in order to examine the model’s response to a vertical mixing scheme based on internal tide energy dissipation. The increase in internal tide energy flux caused by a 120 m reduction in sea level had the expected effect on diffusivity values, which were higher under lower sea level conditions. The impact of this vertical diffusivity change on the Atlantic meridional overturning is not straightforward and no clear relationship between diffusivity and overturning is found. There exists a weak positive correlation between overturning and changes to the power consumed by vertical mixing. Most of the climatic response generated by sea level change was not related to alterations in the internal tide energy flux but rather to the direct change in sea level itself.  相似文献   

海州湾淤泥质海滩剖面堆积过程的计算模式     

樊社军  虞志英  金镠 《海洋与湖沼》1997,28(4):411-418

分别于1986年12月和1985年3月1日—1987年3月1日在海州湾进行了波浪和含沙量观测，运用所获资料以及本区长期水文、地形资料，采用流体力学、沉积学和泥沙运动力学相结合的研究方法，建立了海州湾淤泥质海滩剖面堆积过程的二维计算模式。结果表明，在堆积型淤泥质海滩，由于浮泥的经常性存在，使波浪急剧衰减，其对岸滩的作用甚为微弱，潮流成为塑造淤泥质海滩的主要动力，岸滩在淤涨过程中，在平均高潮位厂沿和平均低潮位附近出现两个凸点，上一个凸点外推速率大于下一个凸点，潮下带变化缓慢。  相似文献