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1.
The influence of an extreme drought event in the fish community of a southern Europe temperate estuary 总被引：2，自引：2，他引：2
F. Martinho R. Leito I. Viegas M. Dolbeth J.M. Neto H.N. Cabral M.A. Pardal 《Estuarine, Coastal and Shelf Science》2007,75(4):537-546
Between 2003 and 2006, a severe drought occurred throughout the Mondego River catchment's area, inducing lower freshwater flows into the estuary. As a consequence, both 2004 and 2005 were considered as extreme drought events. From June 2003 to June 2006, the fish assemblage of the Mondego Estuary was sampled monthly in five stations during the night, using a 2 m beam trawl. Fish abundance was standardized as the number of individuals per 1000 m2 per season and the assemblage was analyzed based on ecological guilds: estuarine residents, marine juveniles, marine adventitious, freshwater, catadromous and marine species that use the estuary as a nursery area. A total of 42 species belonging to 23 families were identified, with estuarine residents and nursery species dominating the fish community. Variations in the fish community were assessed using non-metric MDS, being defined as three distinct periods: summer and autumn 2003, 2004/2005 and winter and summer 2006. The main drought-induced effects detected were the depletion of freshwater species and an increase in marine adventitious in 2004/2005, due to an extended intrusion of seawater inside the estuary and a significant reduction in abundance during the driest period of estuarine resident species. Nevertheless, from the management point of view, it could be stated that although some variations occurred due to environmental stress, the main core of the Mondego Estuary fish community remained relatively unchanged. 相似文献
2.
《Marine Chemistry》1991,32(2-4)
The occurrence of hypoxia in October 1988 in the Krka estuary is described, with special reference to the Prokljan Lake. Hypoxia develops near the bottom in autumn in response to the temperature maximum that appears this time of the year. The decomposition rate of naturally present organic matter increases, creating higher biological oxygen demand. As the water column is stratified by salinity and temperature, mixing of seawater near the bottom with oxygen-supersaturated water which resides closer to the surface is very slow. When an extensive marine phytoplankton bloom appears below the halocline in the Prokljan Lake, then, because of the sinking and degradation of phytoplankton near the bottom, the dissolved oxygen concentration decreases further. The hypoxia becomes so severe that it causes massive mortality of benthic macrofauna. The decomposition of the macrofauna further decreases the dissolved oxygen concentration. The hypoxia may persist until an increase in the freshwater inflow occurs, which forces the arrival of colder marine water near the bottom via a compensating flow. In the absence of autumn rains, the hypoxia may be recorded throughout winter. 相似文献
3.
《Marine Chemistry》1992,39(4)
Surface active substances have been studied in the Krka River Estuary using an a.c. polarography method and various fractionation procedures. Total surface substances (SAT) were separated into (particulate) heterodispersed and dissolved fractions by filtration. The dissolved fraction was separated into hydrophobic basic and neutral components, hydrophobic acid and hydrophilic components by sorption on to XAD-8 resin.The content and the composition of SAT varied seasonally, depending on the biological activities taking place in the Krka River Estuary. The accumulation of SAT, with hydrophobic properties, occurred at the fresh/saline water interface along the vertical profile. Daily changes in the form of the surface active substances along the vertical profile were observed. The formation of the heterodispersed fraction, especially observable in the upper freshwater layer and at the halocline, resulted in the change of physico-chemical properties of surface active substances. Organic matter appeared mainly in a dissolved form in the deeper saline water layer, showing negligible oscillations.The electrochemical characterization of the fractionated SAT indicated that strong hydrophobicity of the surface active substances under natural pH conditions could be attributed to the significant contribution of the heterodispersed fraction of the organic material, which is the most reactive part of the surface active substances in the Krka River Estuary.The dissolved fraction of the surface active substances, prevailing in the deeper saline water layer, exhibited either hydrophilic or conditionally hydrophobic properties, depending on pH and ionic strength of the medium. 相似文献
4.
Two physicochemical parameters: specific surface area (SSA) and heat-of-wetting (ΔwH) were measured in order to characterize the surface of sediments from river and marine environments. The data for the sediment samples of the Krka River Estuary were compared with polluted river and shelf marine sediment samples. It was found that organic free samples from the polluted river sediments show two to three times larger SSA compared to native samples. At the same time, ΔwH was two to three times higher for native samples. The inverse of this trend was found for marine sediment samples. In the Krka River Estuary a narrow transition zone is evident, where such an inversion occurs. This inversion is attributed to significant compositional changes of organic matter within the estuary. 相似文献
5.
《Marine Chemistry》1991,32(2-4)
Before the onset of wind in the Krka Estuary, a sharp halocline extends from 2.5 to 4 m below the surface, separating the upper brackish water layer from the lower marine layer. Strong wind (20 m s−1) induces a tilt of the halocline surface so that downwind (5-km wind fetch) the halocline is pushed to 4.6 m below the surface. Wind-driven surface currents induce a vertical gyre within the upper layer and a gyre in the opposite direction in the lower marine layer. As a consequence, the halocline close to the coast on the downwind side is not only deeper but is also steepened. The entrainment of marine water into the upper brackish water layer is intensified on the windward side. The possible role of wind in oxygenating the bottom layer is discussed. 相似文献
6.
《Journal of Sea Research》2007,57(1):1-18
Dissolved and particulate Mn concentrations were investigated on a seasonal scale in surface waters of the NW German Wadden Sea (Spiekeroog Island) in 2002 and 2003. As the Wadden Sea forms the transition zone between the terrestrial and marine realms, Mn was analysed in coastal freshwater tributaries and in the adjoining German Bight as well. Additionally, sediments and porewaters of the tidal flat sediments were analysed for Mn partitioning and microbial activity.Dissolved Mn concentrations show strong tidal and seasonal variation with elevated concentrations during summer at low tide. Summer values in the Wadden Sea (av. 0.7 μM) are distinctly higher than in the central areas of the German Bight (av. 0.02 μM), suggesting a possible impact of the Wadden Sea environment on the Mn budget of the North Sea. Seasonality is also observed for particulate Mn in the Wadden Sea (winter av. 800 mg kg− 1; summer av. 1360 mg kg− 1). Although particles are relatively Mn-poor during winter, the high SPM load during this season causes elevated excess concentrations of particulate Mn, which in part exceed those of the dissolved phase. Therefore, winter values cannot be ignored in balance calculations for the Wadden Sea system.Porewater Mn concentrations differ depending on sediment type and season. Maximum concentrations are found in surface sediments at a mixed flat site (190 μM) during summer, while winter values are distinctly lower. This indicates that enhanced microbial activity owing to higher temperature during summer leads to increased reduction of Mn-oxides in surface sediments and enhances the corresponding diffusive and advective Mn flux across the sediment-water interface. Draining of Mn-rich porewaters from sediments is also documented by analyses of tidal creek waters, which are highly enriched in Mn during summer.Furthermore, an important Mn source is freshwater discharged into the Wadden Sea via a flood-gate. The concentration of dissolved Mn in freshwater was highly variable during the sampling campaigns in 2002 and 2003, averaging 4 μM. In contrast, particulate Mn displayed a seasonal behaviour with increasing contents during summer. On the basis of salinity variations in the Wadden Sea, the total amount of Mn contributed to the Wadden Sea via freshwater was estimated. This balance shows the importance of the freshwater environment for the Mn inventory of the Wadden Sea. During winter the total Mn inventory of the Wadden Sea water column may be explained almost completely by freshwater discharge, whereas in summer the porewater system forms the dominating source. 相似文献
7.
利用水龄理论的新方法,借助环境水动力学模型定量讨论了多年平均径流条件下长江河口径流和潮汐作用对河口水流输运时间的影响。研究给出了长江河口水流输运时间的时空格局:多年平均流量条件下,水流从徐六泾输出至河口(122.5°E)大约需要24d,南、北槽分流口以上河段水流输运时间主要由径流控制,水流输运时间为8d,向下至拦门沙滩顶水域由径流和潮汐共同控制,水龄为16d,说明最大浑浊带区域的水流输运速度较上下游为慢,从一个侧面阐述了最大浑浊带区域水动力的特征;长江河口水流输运时间存在明显的层化现象,表底层相差最大值可达6d。数值模拟试验结果表明长江河口的潮汐作用是影响河口水流输运时间的关键要素,河口巨大的进潮量增强河口水流交换能力并减小水流输运时间,从而显著影响随水体运动的物质输运格局。水流输运时间研究,不仅可以成功应用于河口水动力环境的量化研究,而且可以为泥沙输运及污染物输运等环境变化研究提供动力的基础。 相似文献
8.
为了揭示长江口外海域海流的特征及其季节和垂向变化规律,于2006年8月1日-2007年7月31日在长江口外海域（平均水深约46.0m）利用大型浮标进行了1年的分层海流流速流向观测。结果表明：（1）该海域海流为顺时针方向的旋转流,在垂向上流向较一致,季节变化不显著。（2）长江口外海域水平流速总体较大,夏季表层最大流速为128.5cm/s,冬季最大表层流速为105.5cm/s;垂线平均流速相近（差异<8.0 cm/s）,夏季流速最大为47.0cm/s,冬季为40.8cm/s。小潮的平均流速为26.5cm/s,大潮平均流速为小潮的2倍。（3）剖面各层流速垂向差异明显,最大流速出现在表层（春季和冬季）或次表层（夏季和秋季）,最小流速均出现在底层;各层的最大平均流速为57.9cm/s,出现在夏季的18m层。（4）垂线平均余流为7.5~11.3 cm/s,春季最强冬季最弱;春季和冬季各层余流均为东向,夏季和秋季基本为东北向或北向。（5）观测海域海流受长江冲淡水、台湾暖流、季风、潮汐等动力作用的共同制约。 相似文献
9.
河口只是河流与海洋之间的一小部分水域,但对人类社会的发展和生物的进化起着重要的作用。它不仅是生物种群繁殖、育幼和栖息的场所,而且是溯河和降海鱼类洄游的必经之路,因此,河口对生物种群的繁衍延续和资源补充,以及保持生态平衡具有十分重要的意义。
然而,河口又是生态环境十分脆弱和敏感的水域,同时也是受人类干扰最为严重的区域。因此,河口的生态环境问题愈来愈引起人们的关注,其中包括长江三峡水库的兴建对长江口及其附近海域生态、环境的影响,特别是对位于河口两侧的我国著名两大渔场——舟山渔场和吕四渔场的影响问题。影响渔业资源的因子是多方面而且错综复杂的。本文主要通过长江径流的变化与环境因子变量的相关分析,并根据三峡水库不同蓄水方案,对河口近海渔业的影响问题进行初步探讨。 相似文献
10.
Z.A. Kuzyk R.W. Macdonald M.A. Granskog R.K. Scharien R.J. Galley C. Michel D. Barber G. Stern 《Estuarine, Coastal and Shelf Science》2008
A conceptual scheme for the transition from winter to spring is developed for a small Arctic estuary (Churchill River, Hudson Bay) using hydrological, meteorological and oceanographic data together with models of the landfast ice. Observations within the Churchill River estuary and away from the direct influence of the river plume (Button Bay), between March and May 2005, show that both sea ice (production and melt) and river water influence the region's freshwater budget. In Button Bay, ice production in the flaw lead or polynya of NW Hudson Bay result in salinization through winter until the end of March, followed by a gradual freshening of the water column through April–May. In the Churchill Estuary, conditions varied abruptly throughout winter–spring depending on the physical interaction among river discharge, the seasonal landfast ice, and the rubble zone along the seaward margin of the landfast ice. Until late May, the rubble zone partially impounded river discharge, influencing the surface salinity, stratification, flushing time, and distribution and abundance of nutrients in the estuary. The river discharge, in turn, advanced and enhanced sea ice ablation in the estuary by delivering sensible heat. Weak stratification, the supply of riverine nitrogen and silicate, and a relatively long flushing time (∼ 6 days) in the period preceding melt may have briefly favoured phytoplankton production in the estuary when conditions were still poor in the surrounding coastal environment. However, in late May, the peak flow and breakdown of the ice-rubble zone around the estuary brought abrupt changes, including increased stratification and turbidity, reduced marine and freshwater nutrient supply, a shorter flushing time, and the release of the freshwater pool into the interior ocean. These conditions suppressed phytoplankton productivity while enhancing the inventory of particulate organic matter delivered by the river. The physical and biological changes observed in this study highlight the variability and instability of small frozen estuaries during winter–spring transition, which implies sensitivity to climate change. 相似文献
11.
12.
闽江口及其附近海域棘头梅童鱼资源的研究 总被引：5，自引：0，他引：5
利用2006～2007年4个季节的底拖网捕捞渔获调查数据,对闽江口及附近海域底拖网鱼类中的棘头梅童鱼的资源状况进行了分析.结果表明：棘头梅童鱼在春季和冬季的渔获质量所占比例较高,分别为3.2%和4.8%;而夏季和秋季的渔获质量所占比例较低,分别为1.8%和1.5%.优势体长组为110～120mm;4个季节的资源密度波动于1.44～38.61kg/km2之间,其平均值为16.14kg/km2.4个季节的平均资源现存量约为58.09t,其中冬季资源量最大（138.99t）;资源密度在春、冬季明显高于夏、秋季;资源分布与水温、水深及盐度等环境因子关系密切.其喜栖息于低温、低盐和浅水海域,秋、冬季分布较广,部分出现离岸及南移现象.文中还应用ELEFAN技术分析了棘头梅童鱼的Von Bertalanffy生长参数（K）、极限体长（L∞）、总死亡系数（Z）、自然死亡系数（M）和开发率（E）,各指标值分别为0.60、183.75mm、2.42、0.69和0.71.这说明其生长较为迅速,但捕捞死亡率过高,已出现过度捕捞现象,应该加强保护以实现资源可持续再生与利用. 相似文献
13.
A modelling study of residence time in a macro-tidal estuary 总被引：2，自引：0，他引：2
This paper outlines a numerical modelling study to predict the average residence time of a conservative tracer in a macro-tidal estuary, namely the Mersey Estuary, UK. An integrated hydrodynamic-dispersion model was used to predict the average residence time in the estuary for various tidal level and freshwater discharge conditions. The numerical model was verified against six sets of field measured hydrodynamic data, with the model-predicted water elevations and salinity levels generally agreeing well with the field measurements. The numerical model results show that in the Mersey Estuary both the tidal level and river discharge affect significantly the predicted average residence time. The value of the average residence time is also shown to be closely linked to the intensity of the residual tidal current. This is due to the fact that a large proportion of the Upper and Inner Estuary dries out during low tides, thus a significant amount of the tracer material is transported through the deep channels. An increase in the freshwater discharge causes a considerable increase in the intensity of the residual current along the main channels and thus a reduction in the average residence time. The predicted overall tracer residence time for the whole estuary is relatively short for a relatively large estuary, ranging from less than 1 day to 4 days for various tidal level and freshwater flow combinations. When the tidal range and freshwater discharge are both small, then the local tracer residence time in the upper part of the estuary can be significantly longer than the values predicted for the middle and lower reaches of the estuary. 相似文献
14.
琼州海峡东部水进入北部湾对广西沿海环流的影响 总被引：1，自引：0，他引：1
本文通过对琼州海峡东部水域温盐资料和沿岸海洋站同步观测资料的对比发现：夏季，广西涠洲岛盐度变化规律和琼州海峡东部、中部变化规律一致，广西北海略受影响，而远离琼州海峡的龙门和白龙尾两站，则更多反映夏季陆地水文规律。同时，采用琼州海峡多年海流资料和涠洲岛定点站及近期测流站的海流观测资料对比看出，琼州海峡冬夏季余流方向仍然是自东向西。结合数值模拟计算结果，同样得出琼州海峡东部水自东向西进入北部湾的事实。这些温盐分布特征和余流观测结果进一步证实：粤西沿岸流是琼州海峡水向西输运的主要来源，形成粤西沿岸流这种现象的根源在于珠江冲淡水的西向流，它们通过琼州海峡进入北部湾，加强了北部湾北部气旋式环流的形成。夏季，在强的西南风作用下，产生较强北部湾西岸北向沿岸流，促使低盐冲淡水向外海输运，然后在东部涠洲岛附近形成更大范围内气旋式环流。琼州海峡东部水进入北部湾对广西沿海环流影响的研究，直接向琼州海峡冬夏季水体输运方向的传统结论提出了新的挑战。 相似文献
15.
磨刀门口夏冬季沿岸流特征及成因分析 总被引：1，自引：0，他引：1
根据2011—2012年磨刀门口的夏、冬季大、中、小潮定点观测资料,对欧拉余流、斯托克斯余流以及拉格朗日余流进行分析。结果表明:（1）外海测点的欧拉余流和拉格朗日余流,冬季在各潮型下均为一致的西南沿岸方向,夏季除东、西汊道点在强径流下表现为顺汊道指向外海方向,其余外海各点仍以西南沿岸方向为主;（2）斯托克斯余流远小于欧拉余流,夏季明显大于冬季,方向基本与欧拉余流相反;（3）冬季磨刀门口海域具有稳定西南向沿岸流特征,南海东北季风的驱动作用是其形成的主要原因;夏季磨刀门口各潮型下沿岸流特征各异,其影响的主要因素为径流和风,同时地形的影响不可忽略,特别是拦门沙形成的汊道分流作用,对强径流作用下水沙输移影响十分显著。 相似文献
16.
利用2006～2007年春、夏、冬季3个航次的CTD资料分析闽江冲淡水扩展范围季节变化特征.通过分析闽江口及邻近海域温度、盐度的平面、垂直分布特征,结果表明:闽江冲淡水的扩展范围具有明显的季节变化.春季由于闽江口附近受到闽浙沿岸流的影响,冲淡水的扩展范围难以确定,但从盐度分布情况不难看到闽江口表层被盐度低于25的具有明显冲淡水特征的水体覆盖.夏季闽江口被温度高于27℃、盐度低于25的冲淡水覆盖,冲淡水前沿向东北扩展至罗源湾、三沙湾.冬季闽江径流减弱,闽江口主要受到闽浙沿岸水的影响,基本看不到闽江冲淡水的痕迹.春季、夏季闽江冲淡水明显的影响闽江口时,闽江口附近海域被25盐度等值线包围,25盐度等值线可作为闽江口明显受冲淡水影响的指征. 相似文献
17.
根据珠江口外沿岸海域2006年夏季(7-8月)及冬季(2006年12月-2007年1月)航次的CTD调查资料,分析了调查海域夏季与冬季的温度、盐度分布,温度、盐度、密度跃层特征及其与上升流、中尺度涡旋和海流的关系.结果表明:1)夏季调查海域冲淡水扩展、上升流、中尺度涡等现象在温度、盐度分布中都有很明显的表征,并对跃层分布有显著的影响,形成了复杂的跃层类型;在冲淡水扩展的影响下,还形成了双跃层与障碍层现象.2)冬季海水混合剧烈,沿岸浅水区域跃层现象不明显,在陆坡深水区存在跃层现象. 相似文献
18.
Residence times of the three main channel systems of Manukau Harbour were calculated by methods based on the salinity measured in 10 tidal excursion segments: the freshwater replacement technique and a volume exchange model. The amount of freshwater present in the segments at high water was low (< 11% throughout the year), so salinities were high, with minimum values (winter) in each segment being in the range 30.1–34.0 (compared with a median value of 34.5 in the nearby coastal waters). The proportion of each segments’ volume which was exchanged with an adjacent segment during a tidal cycle varied markedly across the harbour, from ≤ 5 % in several shallow inner harbour segments to 65% in a deep segment adjacent to the entrance channel. For annual average conditions the freshwater replacement times of the channels were 11–18 days. Slightly longer residence times—12–26 days—were obtained from the volume exchange model. Calculated replacement times for two non‐conservative tracers— inorganic phosphorus and nitrogen—were approximately half those for freshwater, as 5–12% of these species disappeared from the water column each day. 相似文献
19.
冬季大风影响下的渤黄海水交换特征 总被引：1，自引：0，他引：1
利用ROMS海洋数值模式对2006年冬季渤黄海的海洋动力环境进行模拟,基于温度、盐度模拟结果,使用谱混合模型进行水团分析,定义了渤海海峡地区的水交换区。并进一步讨论了冬季大风事件对水交换区的影响,给出了冬季大风影响下的渤黄海水交换特征。研究得出,冬季的黄海水团以“舌”形分布于渤海海峡地区,水交换区则表现为沿“舌”形边缘呈带状分布,具有西北——东南的走向趋势,并且在“舌”尖处的水交换面积最大。通过缩小研究范围,发现位于黄海最北部的沿岸海域并不参与渤黄海之间的水体交换。最后研究发现,冬季大风事件对渤海水交换具有促进作用,具体表现为：大风过程使黄海暖流对渤海的入侵更加深入,水交换区向渤海方向伸展,南部的水交换带变宽,河流径流进入渤海后与渤海水的混合区加大,并发生北移。 相似文献
20.
P. M. Sagar 《新西兰海洋与淡水研究杂志》2013,47(4):377-386
Recolonisation of previously dry channels by stream invertebrates was studied in the Rakaia River during winter 1981 and summer 1982. The winter experiment continued for 42 days, with stable low flows, whereas the summer experiment was characterised by fluctuating large flows which caused it to be abandoned after 27 days. The fauna was dominated numerically by Chironomidae, a leptophlebiid mayfly (Deleatidium), and oligochaetes during the winter, and by Deleatidium alone during the summer. Recolonisation was considered complete after 33 days in winter and 15 days in summer. Flow fluctuations were the main factor affecting colonisation rates, and it was assumed that drift was the main source of colonising animals. Small freshes during low‐flow periods in winter resulted in a rapid increase in total density of invertebrates and number of taxa present and also affected the population structure of Deleatidium larvae in colonisation baskets. Before these freshes numbers had increased steadily over a 27 day period. In summer large floods during high flow periods initially decreased benthic invertebrate numbers in samples but numbers increased rapidly once the flood had passed. This appears to be the first study of its kind on a large unstable river system. 相似文献