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1.
Hydrodynamic modeling of flushing time in a small estuary of North Bay, Florida, USA 总被引：1，自引：0，他引：1
Freshwater fraction method is popular for cost-effective estimations of estuarine flushing time in response to freshwater inputs. However, due to the spatial variations of salinity, it is usually expensive to directly estimate the long-term freshwater fraction in the estuary from field observations. This paper presents the application of the 3D hydrodynamic model to estimate the distributions of salinity and thus the freshwater fractions for flushing time estimation. For a case study in a small estuary of the North Bay in Florida, USA, the hydrodynamic model was calibrated and verified using available field observations. Freshwater fractions in the estuary were determined by integrating freshwater fractions in model grids for the calculation of flushing time. The flushing time in the North Bay is calculated by the volume of freshwater fraction divided by the freshwater inflow, which is about 2.2 days under averaged flow conditions. Based on model simulations for a time series of freshwater inputs over a 2-year period, a power regression equation has been derived from model simulations to correlate estuarine flushing time to freshwater inputs. For freshwater input varying from 12 m3/s to 50 m3/s, flushing time in this small estuary of North Bay changes from 3.7 days to 1.8 days. In supporting estuarine management, the model can be used to examine the effects of upstream freshwater withdraw on estuarine salinity and flushing time. 相似文献
2.
W.R. Geyer 《Estuarine, Coastal and Shelf Science》1997,44(6):713-722
Observations of two small estuaries in Cape Cod, U.S.A. indicate large variations in salinity structure that are forced by variations in along-estuary wind stress. During onshore winds, the estuarine circulation is reduced, and the along-estuary salinity gradient increases as freshwater accumulates. During offshore winds, the surface outflow is enhanced, freshwater is flushed out of the estuary, and the along-estuary salinity gradient becomes weak. Constrictions block the wind-induced flushing, resulting in strong salinity fronts across the constrictions. The residence time of one of the estuaries varies by more than a factor of three in response to variations in wind-induced flushing. The other estuary has little variation of flushing associated with winds, due to a constriction at the mouth that inhibits the wind-induced exchange. The strong influence of winds on the flushing of these estuaries is due in part to their shallow depths, which accentuates the influence of wind stress relative to the effects of the horizontal density gradient. In addition, the residence times of the estuaries are comparable to the time scale of wind forcing, allowing large changes in water properties during wind events. 相似文献
3.
不同初始场对台风Khanun模拟效果的影响及其暴雨过程的螺旋度分析 总被引：3，自引：0，他引：3
利用中尺度非静力MM5模式,在NCEP和JMA两种初始场方案下,对2005年严重影响我国的15号台风Khanun的登陆过程进行了数值模拟,模拟结果的对比分析及其与观测的比较表明:台风对初始场十分敏感,JMA初始场方案在台风路径、强度和暴雨预报上较NCEP初始场方案都有显著改善。利用JMA方案高分辨模拟结果,对台风暴雨过程的螺旋度特征进行了诊断分析,结果表明:暴雨区上空螺旋度呈高层负值区,低层正中心分布,低层700hPa和850hPa螺旋度高值中心位置和强度演变对未来6h暴雨落区与强度有一定指示意义。 相似文献
4.
Inter-annual variability in phytoplankton summer blooms in the freshwater tidal reaches of the Schelde estuary (Belgium) 总被引：1，自引：1，他引：0
Marie Lionard Koenraad Muylaert Abdel Hanoutti Tom Maris Michle Tackx Wim Vyverman 《Estuarine, Coastal and Shelf Science》2008,79(4):694-700
The inter-annual variability in phytoplankton summer blooms in the upper reaches of the Schelde estuary was investigated between 1996 and 2005 by monthly sampling at 10 stations. The large inter-annual variations of the chlorophyll a concentration in the freshwater tidal reaches were independent from variations in chlorophyll a in the tributary river Schelde. Summer mean chlorophyll a concentrations were significantly negatively correlated with flushing rate (Spearman correlation: r = −0.67, p = 0.05, n = 9) but not with temperature, irradiance and suspended particulate matter or dissolved silica (DSi) concentrations. During dry summers, low flushing rates permitted the development of dense phytoplankton populations in the upper part of the estuary, while during wet summers high flushing rates prevented the development of dense phytoplankton blooms. Flushing rate was also found to be important for the phytoplankton community composition. At low flushing rates, the community was dominated by diatoms that developed within the upper estuary. At high flushing rates, chlorophytes imported from the tributary river Schelde became more important in the phytoplankton community. The position of the chlorophyll a maximum shifted from the head of the estuary when flushing rates were low, to more downstream when flushing rates were high. Although DSi concentrations tended to be lower during years of high phytoplankton (mainly diatom) biomass, the relation with flushing rate was not significant. 相似文献
5.
以地面影响系统为主要依据 ,使用天气动力学和统计学相结合的方法 ,将1 983～ 2 0 0 0年 6～ 8月青岛地区的 4 0次暴雨分为气旋、台风和冷锋 3种类型。根据预报经验 ,选取相应的预报因子 ,建立 0 -1权重回归方程 ,用于预报青岛地区未来 2 4 h的暴雨。对于台风暴雨 ,认为来自低纬度洋面的东南 (或西南 )低空急流是水汽、涡度的输送通道 ,它向台风提供了形成暴雨所需的水汽和能量 ,因此把它列为起始场条件。因子选取了代表水汽、位势不稳定、能量及冷空气活动的物理因子。统计得出 :台风类暴雨方程的预报准确率为 96%。用该方程对1 975年 6～ 8月进行试报 ,没有出现空漏报现象 ,效果较好 相似文献
6.
Thomas M. Church 《Marine Chemistry》1986,18(2-4)
Generally the large tidal estuaries of the eastern United States, such as Delaware Bay, are characterized by rather high suspended particle concentrations at the landward end and high biological activity at the seaward end. As such, these estuaries can be conceptualized as geochemical and biochemical “reactors” for those processes controlling the transmission of trace elements from fresh to the coastal shelf waters. The efficiency of these reaction processes relative to estuarine flushing will control the residence times of microconstituents in such estuaries.Evidence is drawn from the Delaware estuary to illustrate biogeochemical estuarine reaction processes using salinity distribution data and mass balance calculations. The Delaware retains some of its estuarine trace elements as sedimented estuarine particles, while others are more conservative and largely exported. Those retained by sedimenting processes include trace elements in primarily geochemical (particle reactive) chemistries, while those exported appear recycled by biochemical (nutrient reactive) chemistries. Often, the behavior of trace elements (e.g., Fe, Cd) and nutrients (e.g., PO4) appear biogeochemically linked. Other examples are drawn from mixing studies to illustrate particle interaction, and benthic flux measurements to illustrate limited diagenetic reflux.The residence time of estuarine microconstituents should depend seasonally on the relative turbidity, flushing rate, and primary production of tidally dominated estuaries such as the Delaware. Thus, residence times of the more biogeochemically reactive microconstituents must be substantially shorter (days to weeks) than the average flushing times of these larger estuaries, while the residence times of the less reactive ones should approach such flushing times (weeks to months). True estuarine residence times of microconstituents can only be modeled after using large data sets averaged over time (season, tides) and space (salinity). 相似文献
7.
The response of a long flexible cylinder excited by random waves in a large model basin was investigated. The linear and non-linear physical mechanisms associated with the wave–cylinder interaction were analysed using system identification and modelling techniques. A third-order frequency domain Volterra model and its orthogonalized counterpart were used to analyse the relationships between wave elevations at various locations in the vicinity of the cylinder and cylinder acceleration data at various cylinder longitudinal locations. It was found that linear mechanisms dominate, particularly at the frequency band where the majority of the wave energy is located. At higher frequencies, the cubic component of the Volterra model is the main contributor to the total model coherence, i.e. the fraction of the measured output power that can be approximated by the model output, whereas the quadratic component's contribution to the total model coherence was in general quite small. This process of identification and quantification of the non-linear mechanisms of the unknown physical system can lead to the design of improved parametric models for the cylinder response, which should by design simulate non-linearities such as the ones identified by the Volterra model. The estimated linear and non-linear Volterra transfer functions were also used to predict the cylinder acceleration under excitation inputs not used in the estimation of the model transfer functions. The good match between predicted and measured output auto-power spectra suggests that the estimated transfer functions are indeed true models of the underlying physical mechanisms of the interaction. However, the latter can only be achieved if a minimum number of data segments, as determined by an error analysis involving modelling and prediction errors, is used in the estimation of the Volterra transfer functions. 相似文献
8.
9.
《Marine Chemistry》2007,103(1-2):172-184
Here we report on temporal changes in the concentration and composition of lignin phenols in high molecular weight (< 0.2 μm, > 1 kDa) dissolved organic matter (HMW DOM) collected from the lower Mississippi and Pearl Rivers (MR and PR) (USA). Monthly water samples were collected at a station in the lower reach in each river from August 2001 to August 2003. Significantly higher concentrations of lignin and Λ8 values (mg lignin phenols in 100 mg organic carbon) in the Pearl River than in the Mississippi River, reflected sporadic inputs of terrestrial DOM during rainstorm events from wetlands and forest soils. Larger seasonal variations in lignin concentration and composition in the Pearl River, compared to the Mississippi River, were attributed to shifts in organic matter sources from topsoil inputs during rainstorm events to groundwater inputs and in situ production during base flow in this small river. Conversely, lower Λ8 and vanillic acid to vanillin ratios [(Ad/Al)v] in the HMW DOM of the lower Mississippi River may be a result of a lower export rate of lignin from agricultural soils due to lower carbon storage in the expansive agricultural systems of the Mississippi River watershed, as well as dilution of phytoplankton DOM inputs. Large seasonal changes in lignin concentration and Λ8 (linked at times with river discharge), and minimal variability in the composition of lignin phenols, likely represented an integrated signal of soil-derived vascular inputs from the upstream drainage basin. If we are to better understand the controls of organic matter delivery to the coastal zone from both small and large rivers, sampling strategies need to be adjusted to account for the different scales of hydrologic response time and in situ processing associated with different residence times. 相似文献
10.
A theoretical and digital simulation on waves generated by an impulsive bed upthrust of a rectangular block with various ratios of length/width is presented. The two-dimensional fast Fourier transform (FFT) algorithm is used to obtain the water surface profile near the generation region. The three-dimensional pictures were constructed from an array of 256 × 256 pixel by using image processing. Comparison of the present three-dimensional results, with previously published two-dimensional results, indicates that for large length/width ratios, the water surface profile is quite similar at certain locations for a small time after the impulsive bed motion is completed. Generally, the water surface profiles deviate significantly from the two-dimensional results. 相似文献
11.
0418号"艾利"台风暴雨过程的数值模拟 总被引：5，自引：1，他引：5
本文利用中尺度MM5模式模拟了0418号“艾利”台风造成闽东北强降水的一次物理过程．模拟结果表明：充沛的水汽和强烈的上升运动是造成台风暴雨的直接原因，降水与850hPa涡度场、散度场有较好的对应关系．基本流场存在二次切变时，横渡型扰动会激发产生并且发生不稳定，从而导致暴雨天气的产生．台风附近相当位温密集陡峭和CAPE值的突增表明台风有加强的可能，CISK和涡旋Rossby波的传播是可能的机制．水汽的敏感性试验结果表明：水汽变化会影响台风的强度和降水的强度，水汽的微小变化可造成降水极大的变化，但对台风的位置影响不大． 相似文献
12.
Fine sediment resuspension dynamics in a large semi-enclosed bay 总被引：3，自引：0，他引：3
A field study was conducted to investigate fine sediment resuspension dynamics in Moreton Bay, a large semi-enclosed bay situated in South East Queensland, Australia. One S4ADW current meter and three OBS sensors were used to collect the field data on tides, mean currents, waves and suspended sediment concentrations in a mean water depth of 6.1 m for about 3 weeks. Two small cleaning units were specially designed to automatically clean the OBS sensors several times every hour to avoid biological growth on the OBS sensors. Based on the collected field data, the main driving force for fine sediment resuspension is found to be the storm wind-waves generated locally in the Bay, not the tidal current or penetrated ocean swell. The critical wind-wave orbital velocity for sediment resuspension was determined to be Urms=7 cm/s and the critical bed shear stress τcr=0.083–0.095 Pa at this study site. 相似文献
13.
本文用MM5模式模拟了0307号台风“伊布都”影响广西的暴雨过程．其结果表明：副高西侧偏南风急流的加强为广西大范围的暴雨天气创造了有利条件，台风环境风场的不对称结构导致其暴雨的不对称分布．盂加拉湾至中南半岛一带维持强盛的西南风急流，为台风南部维持强的涡度中心提供了大尺度的背景场．涡度空间分布的不对称是造成台风南部暴雨的主要原因．本次桂南暴雨的水汽源来自盂加拉湾，中南半岛水汽输送通道明显；过程前期螺旋度高低空负、正垂直螺旋度配置十分有利于系统自身的发展及暴雨的维持；对流不稳定度的增强和湿斜压涡度的发展，导致中低层湿位涡的增强，有利于降水加剧． 相似文献
14.
《Deep Sea Research Part I: Oceanographic Research Papers》2006,53(6):1044-1060
Zooplankton and nekton at 2000 m depth in the axial valley of Endeavour Segment, Juan de Fuca Ridge, show marked variability in abundances in a plane at 20 m above bottom. A remotely operated vehicle flew a gridded rectangle 3.2×0.5 km that included two large high-temperature and two small low-temperature vent fields. Numbers of zooplankton, jellyfish, shrimp and fish were recorded with a video camera, and the abundance patterns were examined with the program SADIE©. Each organism group displayed a distinctive distribution pattern. Abundance gaps over the high-temperature fields were significant and, for the more abundant copepods, were related to the locations of individual smokers. Pelagic shrimp and macrourid fish abundances were correlated and concentrated around the northern high temperature field. Distinct aggregations of zooplankton and nekton were correlated with the fluid indicators from both the low temperature diffuse effluent and the focused high temperature vents. Patterns were likely established by organism choice that forms aggregations and gaps, and by physical processes that entrain passive particles near vigorous smoker plumes. While enhanced plankton and nekton numbers were not observed over the vent fields, overall abundances in the axial valley may be sustained by production transported from the vent fields on the seafloor. 相似文献
15.
Three stations located in the Laurentian Trough were investigated three times during the summer production maximum (in June-July 1990; COUPPB90-1 cruise). A range of multivariate analyses was carried out to extract major physical-biological features in a large data set covering the whole cruise. This study presents the advantages of combining conventional principal component analysis (PCA) with a three-way data analysis. PCA provides the centre of gravity of the different locations for each variable and each sample during the cruise without temporal information. Three-way data analysis produces the trajectory of the different site/time locations for each variable and each sample, and clarifies spatial and temporal relationships between variables. The results reproduce the main patterns of the lower St Lawrence Estuary during the summer plankton bloom and indicate an upstream movement of warm and less saline waters associated with surface production. Apparently these large changes at the surface are not reflected in the deeper layers. Cluster analysis suggests that autotrophic and heterotrophic activities are decoupled when production is low and are correlated only when production increases. 相似文献
16.
Jean-Pascal Torrton Emma Rochelle-Newall Aymeric Jouon Vincent Faure Sverine Jacquet Pascal Douillet 《Estuarine, Coastal and Shelf Science》2007,74(4):766
Hydrodynamic modeling can be used to spatially characterize water renewal rates in coastal ecosystems. Using a hydrodynamic model implemented over the semi-enclosed Southwest coral lagoon of New Caledonia, a recent study computed the flushing lag as the minimum time required for a particle coming from outside the lagoon (open ocean) to reach a specific station [Jouon, A., Douillet, P., Ouillon, S., Fraunié, P., 2006. Calculations of hydrodynamic time parameters in a semi-opened coastal zone using a 3D hydrodynamic model. Continental Shelf Research 26, 1395–1415]. Local e-flushing time was calculated as the time requested to reach a local grid mesh concentration of 1/e from the precedent step. Here we present an attempt to connect physical forcing to biogeochemical functioning of this coastal ecosystem. An array of stations, located in the lagoonal channel as well as in several bays under anthropogenic influence, was sampled during three cruises. We then tested the statistical relationships between the distribution of flushing indices and those of biological and chemical variables. Among the variables tested, silicate, chlorophyll a and bacterial biomass production present the highest correlations with flushing indices. Correlations are higher with local e-flushing times than with flushing lags or the sum of these two indices. In the bays, these variables often deviate from the relationships determined in the main lagoon channel. In the three bays receiving significant riverine inputs, silicate is well above the regression line, whereas data from the bay receiving almost insignificant freshwater inputs generally fit the lagoon channel regressions. Moreover, in the three bays receiving important urban and industrial effluents, chlorophyll a and bacterial production of biomass generally display values exceeding the lagoon channel regression trends whereas in the bay under moderate anthropogenic influence values follow the regressions obtained in the lagoon channel. The South West lagoon of New Caledonia can hence be viewed as a coastal mesotrophic ecosystem that is flushed by oligotrophic oceanic waters which subsequently replace the lagoonal waters with water considerably impoverished in resources for microbial growth. This flushing was high enough during the periods of study to influence the distribution of phytoplankton biomass, bacterial production of biomass and silicate concentrations in the lagoon channel as well as in some of the bay areas. 相似文献
17.
The effect of human trampling on the abundance of small invertebrates inhabiting rocky shallow bottoms was studied at Asinara Island MPA. To this aim we have conducted two experiments. The first was a quantitative study and tested the hypothesis that small invertebrates are more abundant at no-entry locations than at the location visited by tourists through time (before, during and after tourist season). The second was a manipulative experiment and tested the hypothesis that the abundance of small invertebrates is indirectly related to experimental trampling intensities. The effect due to tourist visitation was not highlighted on overall assemblages, suggesting that present seasonal tourist load at the MPA does not cause a significantly negative effect on the zoobenthic community studied. Although tourists exhibited trampling activity at the visited location, none of taxa examined showed a significant lower abundance during and strictly after the end of seasonal tourism peak in the visited location, rather than at control locations. However, results obtained with the second experiment suggested that the effects of different experimental trampling intensities on small invertebrates were variable among taxa. The experimental trampling caused immediate declines in the density of tanaids, nematodes, acari, bivalves, gammarids, echinoderms, isopods, and harpacticoids. For some of these taxa a recovery in abundance was observed within one month. This kind of data may offer important information to estimate the number of visitors compatible with the sensitivity of zoobenthic assemblages, and may substantially contribute to appropriate MPA management. 相似文献
18.
《Estuarine, Coastal and Shelf Science》2005,62(1-2):339-351
A simplified protocol has been developed to meet the need for modeling hydrodynamics and transport in large numbers of embayments quickly and reliably. The procedure is illustrated with 42 embayments in southern New England, USA, giving special attention to Greenwich Bay, RI. The methodology uses simplifying assumptions. It efficiently uses available information wherever possible, and invokes experience where data are unavailable. It uses two-dimensional hydrodynamic and transport models to simulate tidal and subtidal circulation, flushing times, local residence times, and the distributions of conservative constituents over individual embayments. Preliminary results for a subset of the systems compare favorably with published values. The full set of results reveals relationships between flushing times and physical properties of the embayments. A set of relationships to estimate flushing and maximum residence times from the length and surface area of embayments in southern New England is also presented. 相似文献
19.
We sampled zooplankton and fecal pellets in the upper 200 m of Monterey Bay and nearby coastal regions in California, USA. On several occasions, we observed high concentrations of large pellets that appeared to be produced during night-time by dielly migrating euphausiids. High concentrations of pellets were found in near-surface waters only when euphausiids co-occurred with high concentrations of large (>10 μm) phytoplankton. Peak concentrations of pellets at mid-depth (100 or 150 m) during the day were consistent with the calculated sinking speeds of pellets produced near the surface at night. At these high flux locations (HI group), pellet concentrations declined below mid-depth. In contrast, at locations where the phytoplankton assemblage was dominated by small phytoplankton cells (<10 μm), pellet production and flux were low (LO group) whether or not euphausiid populations were high. Protozooplankton concentrations did not affect this pattern. We concluded that the day and night differences in pellet concentration and flux in the HI profiles were mostly due to sinking of dielly-pulsed inputs in the surface layer, and that small zooplankton (Oithona, Oncaea), heterotrophic dinoflagellates, and bacterial activity probably caused some pellet degradation or consumption below 100 m. We estimated that consumption of sinking pellets by large copepods was insignificant. High fluxes of pellets were episodic because they required both high concentrations of large phytoplankton and large stocks of euphausiids. Under these conditions, flux events overwhelmed retention mechanisms, resulting in large exports of organic matter from the upper 200 m. 相似文献
20.
2002年8月闽东一次暴雨天气过程的可能物理成因和数值试验 总被引：2，自引：0，他引：2
利用MM5模式对2002年8月10～11日发生在闽东的一次暴雨过程进行了数 值模拟和诊断分析．结果表明:暴雨中心位于低层正螺旋度中心附近。而且雨强的变 化与正螺旋度的变化近于一致．在MM5模式能较好地模拟本次过程的基础上,对地 形和风场做了对比试验．试验结果表明:地形对暴雨有较强的增幅作用;风速垂直廓 线的线性和非线性分布激发产生的中尺度重力惯性波和涡旋Rossby波,在切变基流 中有可能发生不稳定而导致暴雨天气过程的产生． 相似文献