Spreading of river water in Suruga Bay

We have investigated the spreading of river water in Suruga Bay by performing numerical experiments and conducting field surveys with drifting buoys. There are clear seasonal variations in the large river discharges into the bay: increased discharge in the rainy summer season and decreased discharge in the dry winter season. The numerical model reproduces the main feature that has been observed in the actual sea: the river water extends gradually from the northwestern to the southeastern regions in the bay, especially in summer. The river water spreading is greatly influenced by the bottom topography of the bay: the Fuji River water spreads over a deep continental slope as a surface-advected plume and extends well offshore, since a large bulge (anticyclonic eddy at the river mouth) extends well offshore and effectively transports the river water offshore. On the other hand, the Oi River water tends to flow parallel to isobaths (along a coastline) on a shallow continental shelf as a bottomadvected plume. Moreover, the influences of seasonal variations in the stratification and a bay-scale, wind-driven circulation are also investigated. Trajectories of the drifting buoys, which were released around the Fuji River mouth, certainly suggest that the bulge exists there.     

芝罘湾水动力与物质输运现状的数值模拟

为海洋生态保护和海岸工程建设等工作提供参考,基于Mike21模型水动力学（HD）模块,得到最新岸线形态下芝罘湾的潮流场,涨、落潮历时不均,落急潮流流速大于涨急潮流;东北岸流速最大,向西南靠岸渐小;湾北涨、落潮流向相反,湾中、南部流向在涨急时刻为SW向,落急时刻由南呈NW向向北顺时针逐渐转为NE向。计算了15个潮周期的欧拉余流场,余流流向除湾南沿岸局部区域沿岸向南外,整体为中心在湾东北的顺时针余环流,余流流速整体较小,大部分区域不超过0.06 m/s。芝罘湾内等距离释放16个自由粒子,据粒子运移轨迹得知：湾以北外海的物质不易向湾内输运,湾内自由粒子最终均运移出湾外,湾内无聚集,表明芝罘湾的水动力情况利于物质向外输运;担子岛以北的粒子向东输出湾内后,绕开担子岛等岛屿输运至东南外海;担子岛以南的粒子经过在湾内回旋振荡,以“∞”型轨迹最终南下。     

Relationship between Salinity and Nutrients in the Subsurface Layer in the Suruga Bay

We investigated the water structure and nutrient distribution in the Suruga Bay from April 2000 to July 2002, especially the Offshore Water, which occupies a large part of the bay. The maximum salinity in the upper 200 m varied between 34.49 and 34.71, indicating a temporal change in the influence of Kuroshio Water on the Offshore Water. Seasonal variation in nutrient concentrations was largest from surface to 50 m. On the other hand, the variance in nutrient concentrations within each season was largest in the subsurface layer of 100–300 m in spring, summer and fall. In the Offshore Water, the change of nutrients was negatively correlated with that of salinity in each season. This suggests that an increasing intrusion of saline water brings about a lower nutrient concentration in the Offshore Water. Likewise, negative correlations were observed between the change of the maximum salinity and chlorophyll a (Δ [chl.a-int])/nutrients integrated in the upper 200 m. Δ[chl.a-int] was significantly correlated with the changes of nitrate and phosphorus, but there were no significant correlations between Δ[chl.a-int] and the change of silicate. These results suggest that the concentrations of chlorophyll a and nutrients in the Offshore Water were decreased due to the increasing intrusion of Kuroshio Water. The Offshore Water is likely to be related to the regulation of primary production by nitrate.     

狭长海湾象山港三维污染物运移特征的数值模拟

为了探明污染物在狭长海湾象山港内的输运规律,在验证良好的三维潮流模型基础上,计算和分析了不同驱动因素下的余环流结构和污染物的三维运移特征。余流模拟结果表明该海域余流结构区域差异性明显,狭湾内夏季余流垂向分层明显,表、底余流方向相反,分界点约在0.4~0.5倍水深处;口门及以外海域主要以水平环流为主。进一步采用拉格朗日粒子追踪方法,模拟了示踪粒子在湾内的三维运移轨迹。通过对不同位置释放的污染物粒子运移轨迹进行比较分析,最后给出了模拟期间的污染物运移规律。研究结果可为排污口选址和海湾污染治理等提供科学依据。     

Vertical and seasonal differences in biogenic silica dissolution in natural seawater in Suruga Bay, Japan: Effects of temperature and organic matter

Vertical and seasonal characteristics of biogenic silica (BSi) dissolution in seawater were investigated by multiple dissolution experiments using seawater collected from surface and mesopelagic layers in Suruga Bay during the period 2002–2004. The dissolution rate coefficients calculated based on temporal changes of BSi concentration varied with the season of sample collection. They ranged from 0.023–0.057 day^− 1 for surface samples and 0.0018–0.0025 day^− 1 for mesopelagic samples for temperatures approaching in situ conditions. Experiments at various temperatures confirmed that BSi dissolution depends on temperature in natural seawater. Dissolution rate coefficient (day^− 1) of BSi correlated significantly with temperature (°C), and Q₁₀ was 2.6. Addition of bioavailable organic matter to low-bioactivity seawater enhanced the protease activity and abundance of bacteria, and increased BSi dissolution rate by a factor of 1.4–2.0. There is clear evidence that BSi dissolution is accelerated by bacterial activity and potentially limited by bioavailable organic matter in natural seawater. Dissolution rates and total decreases of BSi concentration were lower during experiments using mesopelagic samples than in those using surface samples. This suggests that dissolution of BSi varies with depth and that BSi in the mesopelagic water is more resistant to the dissolution than that in the surface water. This lower dissolution rate was caused by lower temperature and lower bacterial activity due to less bioavailable organic matter in mesopelagic water. Our results provide a mechanistic understanding of variations in silica cycling within the seasonally and vertically differing marine environment.     

人类活动对珠江伶仃洋余环流结构的影响研究：以洪季小潮为例

近20 a来,受高强度人类活动影响,珠江伶仃洋滩槽已发生远超自然过程的异变,其河口动力结构必然发生响应,影响物质输运过程。本研究利用三维水动力数值模型,探讨了伶仃洋河口小潮期余环流结构的变化特征及原因。结果表明：近20 a来伶仃洋底层余流强度提高,沿深槽上溯时向中滩偏转,易引起泥沙汇聚于此。中滩存在表层向西,底层向东的横向余环流结构,主要由非线性对流项和科氏力项驱动。中滩大规模采砂后引起对流项变化,造成余环流结构东移,表、底层余流增强,可加快表底层物质交换。西槽内存在表层向海、底层向陆的纵向余环流结构,主要由正压和斜压梯度力驱动。受浚深影响,向陆斜压梯度力和非线性对流项均增强,引起表层余流减小22%,而底层增大24%,这将削弱小潮期西槽内水体交换能力,即减慢物质输出,易造成西槽淤积、水环境恶化等影响。研究成果对研究人类活动干扰下的河口余环流结构及物质输运响应具有一定借鉴意义。     

Numerical Simulation of Water Exchange Characteristics of the Jiaozhou Bay Based on A Three-Dimensional Lagrangian Model

Based on theory of three-dimensional hydrodynamics,an Euler-Lagrangian particle model is established to study the transport and water exchange capability in the Jiaozhou Bay.The three-dimensional hydrodynamic model,driven by tide and wind,is used to study the effects of wetting and drying of eatuarine intertidal flats by the dry-wet grid technology based on the Estuarine,Coastal and Ocean Model (ECOM).The particle model includes the advection and the diffusion processes,of which the advection process is simulated with a certain method,and the diffusion process is simulated with the random walk method.The effect of the intertidal zone,the turbulent diffusion and the timescales of the water exchange are also discussed.The results show that a moving boundary model can simulate the transport process of the particle in the intertidal zone,where the particles are transported for a longer distance than that of the stationary result.Simulations with and without the turbulent random walk show that the effect of turbulent diffusion is very effective at spreading particles throughout the estuary and speeding up the particle movement.The spatial distribution of residence time is given to quantify the water exchange capability that has very important ramifications to water quality.The effect of wind on the water exchange is also examined and the southeasterly wind in summer tends to block the water exchange near the northeast coast,while the northerly wind in winter speeds up the transport process.These results indicate that the Lagrangian particle model is applicable and has a large potential to help understanding the water exchange capability in estuaries,which can also he useful to simulate the transport process of contaminant.     

Winds and buoyancy-driven circulation in the Tampa Bay

INTROOCCrIOWWiththeimplementationoftimeseriesobservationsspanningseveralsynopticweathersystempassages,theimPOrtanceoftheattnosphericallyforcedpartofestuarinecirculationbecameclearinthe1970s.WeisbetgandSturges(1976)examinedthewindeffectindrivingthenetcirculationintheWestPassageoftheNarragansettBay.Usingvelocitymeasurementsofapproximatelyonemonthduration,theyconcludedthatthelocalwindscoulddominatethegravitationalconvectionindeterminingthenetestuarinecirculationprofileofapartiallymixedestu…     

罗源湾潮流数值计算

研究罗源湾潮汐、潮流及潮波的传播,对罗源湾的开发及海岸工程建设具有一定的实际意义。为系统地了解罗源湾的潮汐、潮流状况,采用不规则三角形网格的分步杂交法,建立罗源湾海域二维变边界潮流数值模型,通过计算得到同潮时线与等振幅线、潮流椭圆、潮致欧拉余流分布及不同时刻潮流场分布。该海湾海流具往复流性质,潮汐、潮流均属正规半日潮,最大流速发生在可门水道。     

湄洲湾潮流数值计算

采用不规则三角形网格的分步杂交法,建立了湄洲湾海域二维变动边界潮流数值模型,通过计算得到最大潮流分布、同潮时线与等振幅线、潮流椭圆、潮致欧拉余流分布及不同时刻潮流场分布。     

罗源湾全日潮汐和潮流数值计算

采用不规则三角形网格的分步杂交法,建立罗源湾海域二维变边界全日潮汐和潮流数值模型。将计算值与实测资料比较,结果表明符合程度良好。给出了同潮时线与等振幅线、潮流椭圆、最大潮流及不同时刻潮流场分布。应用该模型可以较系统地了解罗源湾全日潮的潮汐、潮流状况。     

湄洲湾潮流特性的数值研究

本文运用一个含动边界的二维河口海岸动力模型模拟了湄洲湾潮汐潮流的基本特征,模拟结果与实测数据吻合较好．在此基础上估算了湄洲湾大、小潮过程的纳潮量,并根据湾内保守示踪物的质量（浓度）随涨、落潮流周期性的变化,进一步估算了湄洲湾的水交换周期,其半交换和80％的交换周期分别为5d和15d．同时可以看出,主航道深水区的水交换特性明显强于湾顶浅水区．     

乐清湾悬沙输移机制分析

以乐清湾海区特征测站实测资料为据,运用机制分解法将悬沙净输移通量分解成多个动力项并讨论不同区域悬沙输移的时空分布特征,认为潮泵输沙在湾内贡献均较大,在浅滩附近占明显优势,垂向净环流输沙在小潮期中,内湾作用显著,平流输沙在开阔水域及中湾深槽起主要作用.从余流分布、流速与含沙量的相位关系、垂向余流结构与悬沙浓度垂向梯度变化...     

北部湾潮汐潮流的数值模拟

基于正交曲线坐标的ECOMSED三维水动力模式,对北部湾的潮汐潮流进行数值模拟。选用不同的海底摩擦系数、海底粗糙度系数以及水平湍流摩擦系数进行数值试验。试验结果表明,当海底摩擦系数取2×10-3～3×10-3,海底粗糙度系数取1×10-3～2×10-3m,而水平湍流摩擦系数取1×102～5×103m2/s时,模拟所得潮汐、潮流结果与实测数据吻合较好;并由此对北部湾的潮汐、潮流和潮余流等特征进行了分析。还给出了垂直湍流黏滞系数呈抛物型的分布特征。对该海域的水动力状况有了进一步的了解,为该海域的环境保护规划提供了科学依据。     

象山港余流特征数值研究

基于Delft3D-Flow模块建立了象山港海域的三维斜压潮流数值模型,结合实测水文资料,研究了象山港的潮(余)流特征,对欧拉余流场的时空分布进行了定量的比较和分析,并与潮流测站计算分析得到的欧拉余流分布对比,很好的模拟了象山港的余流特征。结果表明:由湾外至湾顶,余流呈减小的趋势,湾外余流最大为33 cm/s,湾顶最小,余流平均仅5 cm/s。垂向上,表层余流大于底层余流,表层余流指向湾外,而底层余流则指向湾内。对比斜压、正压两种模式下的欧拉余流分布,可以看出湾顶附近主要受径流控制,两种模式得到的结果基本一致,口门至西沪港区域受径流和潮流的共同影响,斜压模式更准确地模拟出了水体层化和垂向余环流结构。     

杭州湾北岸近岸海域N、P 降解系数的围隔实验研究

通过制作生态系围隔实验装置,采用模拟围隔实验的方法,测定N、P营养盐的降解系数.基于夏秋两季杭州湾北岸近岸海域的现场水样采集,测出杭州湾北岸近岸海域无机氮的生物降解系数在0.121~0.269 d-1范围内,均值为0.225 d-1,测得活性磷酸盐的降解系数在0.031~0.179 d-1,均值为0.08 d-1.考虑到实验室静态模拟环境与真实海区状况的差异,采用保守估计法和 Bosko 公式进行处理,最终计算得出的0.21 d-1和0.05 d-1可分别作为杭州湾北岸海域无机氮和活性磷酸盐的实际降解系数.     

渤海湾海域潮流数值计算

采用不规则三角形网格的分步杂交法,建立渤海湾海域二维变边界潮流数值模型,重现该海域潮波及潮流的时空分布,计算得到M2分潮和K1分潮的同潮时线与等振幅线、潮流椭圆及不同时刻潮流场分布。计算结果与实测资料对比验证吻合良好。     

基于FVCOM 的辽东湾水动力特性数值模拟

辽东湾属于半封闭性海湾, 水动力过程具有一定的代表性。本文基于无结构化三角形网格的有限体积海岸海洋模型FVCOM（Finite-Volume Coastal Ocean Model）, 构建了辽东湾及其邻近海域的三维水动力数值模型, 并利用实测数据对6 个潮位验潮站、4 个潮流验潮站的大小潮时刻的潮位、流速、流向进行了对比验证, 该模型能够准确地模拟辽东湾的潮汐、潮流等水动力场情况, 可进一步为研究辽东湾温盐、泥沙、水质、污染物扩散等提供研究基础。     

Numerical study on residual current and its impact on mass transport in the Hangzhou Bay and the Changjiang Estuary Ⅱ. Residual current and its impact on mass transport in winter

I~IOWIn winter, on the impacts Of the Chriolis force and the current along the shore of the EastChina ho, the residual current from the Changjiang River flows south along the shore and enters the ~ Bay in the north, then it moves out of the bay in the south and flows southin the East China Sea (Su and Wang, 1989; Zhu and Shen, 1997). In recent years, scholars have made further analyse on obSerVed date, and have obtained more profound viewson the residual current and mass transport (Pn …     

Determining the age of water and long-term transport timescale of the Chesapeake Bay

The concept of age of water (AW) is applied to the Chesapeake Bay to investigate the long-term transport properties for dissolved substances. A real-time calibrated hydrodynamic Chesapeake Bay model in 3 Dimensions (CH3D), employing a boundary-fitted curvilinear grid, is used for the study. The long-term transport properties, represented by AW, are investigated under the conditions of low river inflow of 1995 and high river inflow of 1996, as well as for constant mean inflows. The influences of freshwater, density-induced circulation, and wind-induced transport on age distribution have been investigated. Model results show that river inflows, wind stress, and density-induced circulation play important roles in controlling the long-term transport in the Bay. The model results shows that it requires 120–300 days for a marked change in the characteristics of the pollutant source discharged into the Bay from the Susquehanna River to affect significantly the conditions near the mouth under different hydrodynamic conditions. An increase of river discharge results in increases of downstream residual current and gravitational circulation, and thus reduces AW. The density-induced circulation contributes to the transport substantially. The dissolved substances discharged into the Bay are transported out of the Bay more rapidly when the estuary becomes more stratified. Southeasterly and southwesterly winds have strong impacts on the transport compared to the northeasterly and northwesterly winds. The former increases lateral and vertical mixing significantly. Consequently, the gravitational circulation is reduced and the transport time is increased by 50%. The model results provide useful information for understanding the long-term transport processes in the Bay.