Mixing and flushing of tidal embayments in the western Dutch Wadden Sea part I: Distribution of salinity and calculation of mixing time scales

The distribution of salinity in the western Dutch Wadden Sea is described, mainly on the basis of surveys carried out during 1970 to 1974. Relations are discussed between the salinity distribution and relevant environmental factors such as: fresh water discharge, salinity of the North Sea, the tide, the windfield and the morphology of the area. Flushing time scales of 15 and 31 tidal periods were obtained for fresh water originating from the main sluicing gates near Den Oever and Kornwerderzand, respectively Stationary salinity distributions were used for the calculation of exchange coefficients between compartments of a box model of the area. By means of the box model a series of time scale relevant to the flushing of the area has been calculated and their areal distribution is shown. Distinction has been made between ages and transit times of water originating either from one of the two tidal inlets (sea water) or from one of the two sluicing gates (fresh water). Of the former, the ages in the basin (11.3 and 12.3 T) exceed the transit times (2.7 and 3.0 T) whereas the opposite is found for fresh water (ages 10.6 and 19.8 T, transit times 14.5 and 29.1 T). Turn-over times of the main tidal basins were also calculated, the result being 13.7 T for the Marsdiep basin and 9.0 T for the Vlie basin.     

Temporal and lateral fluctuations in production and biomass of bacterioplankton in the western Dutch Wadden Sea

To contribute to the validation of a recently developed ecosystem model of the western Wadden Sea (EON, 1988), data on bacterial biomass and production were acquired. Seven field stations, spread over the two main basins of the estuarine system, were sampled monthly in 1986. Between these basins significant differences were found in counts, biovolume, biomass and production of bacteria (measured by the ³H-thymidine method) with consistently higher mean values of bacterial variables in the Vlie basin. Bacterial production rates of 2 to 175 mg C· m⁻³· d⁻¹ were obtained for the Vlie basin, with an annual production of 10 to 11 g C· m⁻³, while the production in the Marsdiep basin did not exceed 45 mg C·m⁻³ ·d⁻¹, with an annual production of g C·m⁻³. Bacterial biomass varied over the year from 2 to 140 mg C·m⁻³ in the study area, with a mean biomass of 39 mg C·m⁻³ in the Vlie basin and 23 mg C·m⁻³ in the Marsdiep basin. Blooms of bacteria occurred in May and July–August. Spatial and temporal fluctuations in bacterial variables are discussed, taking into account different environmental factors and the availability of food for bacteria in relation to transport and exchange of water masses between the two basins and the North Sea. Results are compared with the results as simulated by the ecosystem model.     

The measurement of hydro-geomorphological discontinuities on a uniform forested slope

On a uniform forested slope in a small drainage basin in the Keuper region of Luxembourg, an experiment has been set up to establish the degree of discontinuity in hillsope runoff. This paper describes the objectives of the experiments, the experimental design and the instrumentation being used.The investigated slope is located in a series of nested drainage basins, for which the input, flowpaths and outputs of water and sediments have been or are being measured. At three locations on the slope, water-table elevations are being measured with capacitative water-level recorders, connected to data-loggers. These instruments allow a very precise continuous registration to be made.     

On selective tidal transport in the migration of North Sea Plaice (pleuronectes platessa) and other flatfish species

Evidence is given for selective tidal transport in North Sea plaice and other flatfish species. Data collected during midwater plankton surveys in two Dutch Wadden Sea inlets in early spring in the years 1970 to 1977 show that plaice, sole, flounder and dab demonstrate pelagic swimming behaviour in that period. Plaice, sole and flounder show a clear selective tidal transport mechanism to re-enter the Wadden Sea after staying in the open sea in winter whereas dab tends to leave the Wadden Sea. Data on by-catches of semi-pelagic pair trawl fishery for gadoids in the Dutch coastal area show that small quantities of plaice may be caught off the bottom throughout the whole year whereas sole moves to higher levels in two distinct periods only. The first period lower left diagram) demonstrate a strong preference for northgoing currents. This is also the direction towards the areas from which the plaice used had been transported to the laboratory and therefore this preference for northgoing tides might be interpreted as a clear case of homing to the Silverpits and Borkum areas.Also the rate of dispersion of the cluster of displaced tagged plaice in general (Fig. 18, lower right diagram) is much faster in the first months after release than that of the local plaice. Thus displaced plaice are more strongly motivated to migrate than non-displaced fish. This may well have been the case too in the plaice equiped with the transponding acoustic tags. This together with the release in an area with strong currents and narrow tidal ellipses means that the plaice should be considered to have been in an exceptional situation, extremely suited for travelling at great speeds in a fixed direction. Fig. 18 also shows the average surface tidal current velocities, derived from the 13 maps with hourly data on water circulation in the Stroomatlas Nederland (1963). It is obvious that the Lowestoft plaice, mostly released nearer to the coast within the release area, encountered the highest average current velocities observed in the North Sea. It cannot be proven that these circumstances explain completely the vast speed of the Lowestoft plaice but it certainly demonstrates that there is a bias in these experiments which could easily affect the results. When drawing conclusions in respect to the “normal” picture of plaice migration this bias should not be ignored.In the common sole selective tidal transport is observed in juveniles when entering the Wadden Sea in spring. In adult soles this mechanism is a common feature in March to May during the spawning migration but no evidence for the use of this mechanism is available during other periods of the year. The sole thus is an example of a flatfish species using selective tidal transport in a restricted period and for special purposes only.In plaice the use of selective tidal transport in the Wadden Sea inlets has been shown for juveniles. In adult plaice the need for using the mechanism might be much less although plaice have been seen swimming at the surface in spring (van den Ende, 1849) during day time quite in contrast with their normal behaviour. In spring nights, among soles swimming at the surface, plaice too have been observed (together with some dabs and turbots) but in much lower numbers than the sole (de Veen, 1967).On the whole there is not much evidence for a strong continuous use of selective tidal migration in plaice. No serious drops in the catch rates during specific tidal phases in the bottom trawl fisheries have been recorded by the results of the UK 81 otter trawl fishery. The coincides with the re-entering of soles in the Wadden Sea and with the well-known phenomenon of soles swimming at the surface. During this period the soles use selective tidal transport to reach the spawning grounds near the continental coasts.Data on catch per unit effort of a Dutch ottertrawler in 1958 to 1960, constantly fishing in one restricted area near Terschellingerbank lightvessel, reveal significant differences between day and night catch rates and a change from a preference for flood tide in the first half of the year to a preference for ebb tide in the second half.The available evidence for selective tidal transport in plaice is discussed in relation to the patterns of migration in 4 plaice sub-stocks studied by means of tagging experiments, and in relation to results of displacement experiments with mature and immature plaice. The tagging and displacement experiments present a picture of migration in which the directional swimming is a weak component superimposed on largely random movements and the speeds of travelling are low. The plaice react to displacement by trying to return to their original grounds and this tendency to home lasts for a full year.This picture about selective tidal transport contrasts with results obtained by the Lowestoft Laboratory. Plaice equiped with transponding acoustic tags did show largely directed and fast tidal migration before and after spawning. Arguments are given that these plaice were, however, in an exceptional position and may have shown homing behaviour. Notwithstanding this reservation to the Lowestoft experiments, these results and the present ones are explained if it is assumed that apparently only a fraction of the population uses the mechanism of selective tidal migration, thus saving energy and achieving quick transport when necessary. It is likely that in plaice as in sole the mechanism will be used in special cases only, probably for short periods, in certain areas.     

Radon anomaly as a possible precursor of a submarine earthquake

In the framework of investigating the ventilation of deep-sea basins in the Indonesian archipelago, ²²²Rn was determined in near bottom water samples. In one of these basins, the Halmahera Basin, excess ²²²Rn concentration and the related standing crop was unexpectedly high. At this station excess Radon has an almost uniform concentration of about 2 dpm·kg⁻¹ up to 120 meters above the bottom. In this paper the possibility is discussed that the high standing crop in this basin is connected with three submarine earthquakes with a magnitude of resp. 4.4, 5.4 and 5.9 mb that took place four days after we took the samples, possibly in combination with submarine faults, which are typical for the Indonesian archipelago. The epicentres were within 100 km from the station. All over the world variations in ²²²Rn concentrations have been observed prior to earthquakes (up to 500 km from the epicentre). This can be regarded as an important non-seismic precursor to earthquakes, but it has to our knowledge never been observed in deep-sea basins.     

Tidal asymmetry and estuarine morphology

Estuarine morphology is to a large extent determined by the residual sediment transport pattern. However, the inverse statement is also true. Residual sediment transport depends on differences in magnitude and duration between ebb and flood tidal currents. Such differences (“tidal asymmetry”) are produced by the distortion of the tidal wave propagating on the coastal shelf and entering bays and estuaries. In this study the relationship between tidal asymmetry and estuarine morphology is investigated. Based on theoretical considerations some general principles are derived and compared with field observations.     

汛期辽宁各流域的降水量变化及预测研究

为了准确预测汛期辽宁省的洪涝灾害趋势,满足日益增长的服务需求,建立汛期辽宁省各流域的洪涝灾害趋势客观化预报方法,以便为实际气候预测服务工作提供有价值的参考依据。以辽宁省53个测站的1961～2011年6-8月平均的降水量资料开展研究。结果表明：辽宁省内流域都属于面积较小的流域,可以用算术平均法作为汛期各流域的降水量的计算方法。除浑河流域汛期降水量略有增加趋势外,其他流域都是下降趋势。各流域在60年代中期前后发生了突变。1月500hPa位势高度场西太平洋副高系统、1月太平洋海温场Nino3-4区、2月海平面气压场西伯利亚高压系统、 2月东南太平洋区域海温场与辽宁省各流域汛期降水相关显著。所建立的各流域汛期总降水量多元回归预报方程都通过了0.01信度的显著性检验,说明这些回归方程有显著意义。     

Carbon dioxide and oxygen disequilibrium in a tidal basin (Dutch wadden sea)

Measurements of total CO₂, alkalinity and dissolved oxygen were conducted in a tidal basin with estuarine properties during three cruises. In winter CO₂ and oxygen were close to equilibrium with the atmosphere. In May the basin was a large source for CO₂, where the fractional gain with respect to the freshwater CO₂ was as high as 42%. Also in September high pCO₂ indicated a release to the atmosphere; both in May and September there was accompanying low oxygen. Water originating from the tidal flats was shown to affect the water in the adjacent tidal channel significantly. Tidal-flat water was characterized by high TCO₂ and alkalinity and low oxygen as compared with the surrounding water. It develops through biological processes on the tidal flats (only in the vegetative season), as well as through the local discharge of a small freshwater source with very high alkalinity (and TCO₂). Using alkalinity as a tracer it was calculated that in March 12% of the fresh water in an adjacent tidal channel might originate from this source, although it constituted only 1.5% of the total freshwater discharge.     

A Study on the Model of Surface Storm-Water Runoff at Urban Gully

On the assumption that the runoff on the catchment of each gully flows into the gully itself, in this paper, a model of surface storm-water runoff at urban gully is presented, which includes runoff sub-model and concentration sub-model.The runoff sub-model describes the rainfall event with instantaneous rainfall intensity, the runoff-generated event with runoff coefficient of integrative area and the runoff converged event with the principle of equal time of flowage.The concentration sub-model shows that the pollutant concentration event only changes with the runoff event at the gully.In this paper, the concrete form of the model for two gully inlets in Shapingba District of Chongqing is given.The model is calibrated with the data from the synchronized measurements of water quantity and quality at the two gully inlets obtained from July to September 2000.The relative error is calculated by comparing the model predictions with the field-measured results.     

Experimental determination of salt intrusion mechanisms in the Volkerak estuary

Salt transport mechanisms in the Volkerak estuary, The Netherlands, are analysed by use of the results of simultaneous measurements of current and salt concentrations in 32 verticals distributed over six cross-sections.Longitudinal salt fluxes in each cross-section are evaluated by interpolating measured values of current speed and salt concentration over the cross-section and in time.Salt fluxes are decomposed in an advective flux, a local salt flux (covariance of the deviations of velocity and salt concentration from the cross-sectional mean) and a non-local salt flux (covariance of the tidal variation in current speed and salt concentration). From a theoretical analysis it follows that the non-local flux in a cross-section equals the difference between the local salt flux in that cross-section and the local salt flux in a cross-section moving with the tidal velocity. Because of the relatively large tidal amplitude to depth ratio the existing decomposition techniques are expanded to include cross-sections with time-varying water levels.The field data and subsequent analysis reveal that in the seaward part of the estuary the advective salt flux is balanced by the non-local dispersive flux. Salt intrusion in this region is caused by large scale exchanges of water bodies between the Volkerak estuary and Eastern Scheldt estuary, between different tidal channels at channel junctions and between tidal channels and tidal flats. In the landward part of the estuary gravitational circulation is the dominant salt intrusion process, reflected most strongly in the local salt flux component associated with steady vertical variations in velocity and salt concentration.     

On the timing of foraging flights by oystercatchers,haematopus ostralegus,on tidal mudflats

The tidal movements of flocks of oystercatchers foraging on mudflats at low tide and roosting inland behind a dike at high tide were studied and the effects of day-to-day variations in the time of mudflat exposure by ebb analysed.High mean water levels and short low tides led to reduced intake during low water due to increased bird densities in addition to temporal constraints (Fig. 4). Increased feeding around the roost apparently compensated for some of the reduced intake (Figs 6 ad 7) although accurate intake measurements could be made for foraging on the tidal flats only. It is argued that optimal timing of foraging flights to coincide with exposure of the mussel banks would contribute to exploitation of this tidal food source.The median departure time from the roosts relative to the time of mudflat exposure was early on days when the tide went out late and late when the tide was early (Figs 8 and 9). Daily variations in departure time were predicted by the daily variations in tabulated high water times, but not by variations in mudflat exposure or coverage (Fig. 10). The conclusion is drawn that the birds employ a timing mechanism not directly associated with the tidal water movements.In some pilot experiments in caged oystercatchers, feeding schedules elicitated feeling attempts in anticipation of expected food. The anticipatory patterns were different for fixed and tidally shifting daily food schedules, and moreover differed between the two feeding times per day (Figs 12 and 13).Five possible mechanisms for tidal anticipation are discussed, making use either of unknown exogenous cues, or of—likewise unknown—endogenous timers of hourglass type of rhythmic with circatidal, circalunadian or circadian period. Experimental tests for these possibilities are outlined.     

江厦潮汐电站库区滩涂水产养殖现状及对策

以江厦潮汐电站库区滩涂水产养殖现状为例,分析2011年江厦潮汐电站滩涂水产养殖的发展现状,包括水产养殖成鱼的成本构成情况及收益水平,并探析其养殖经济效益的主要影响因素,阐述电站库区滩涂水产养殖存在的问题,并提出相应的对策。研究结果显示：虽然库区滩涂进行水产养殖的养殖主体平均收入水平高于温岭市农村居民人均纯收入水平,但其收入有“被增长”现象;养殖水域污染及富营养化的现象有待解决;依然是以传统的养殖产业模式为主,可尝试开发生态渔业。     

Physical aspects of the flushing of the east Indonesian basins

The flushing of the deep basins in the east Indonesian archipelago is studied by means of water mass analysis, current observations and simple theoretical models. The Banda Sea and its secondary basins appear to be flushed from the Pacific Ocean with a typical flushing time of the order of 40 years. This fast flushing is made possible due to the high vertical diffusivity which is estimated to be of the order of 10⁻³ m²·s⁻¹. Theoretical models to descrive the vertical distribution of tracers due to mixing and basin wide upwelling turn out to fit the data very well. The observations cannot be used to confirm the horizontal structure of the deep circulation which results from a simple β-plane model. The vertical structure of the Aru Basin and the Timor Trench is more complicated due to the presence of water from the Indian Ocean, the Pacific Ocean and the Banda Sea. But also here simple models can be applied.     

The heat balance of a tidal flat area

The results of a heat balance investigation of tidal flats in the western part of the Dutch Wadden Sea are presented. It is shown that heat balance studies of tidal flat areas, which are very complicated due to the tidal cycle, can be carried out with success.It turned out, that bottom properties could be derived from the temperature measurements at different depths; the thermal diffusivity α was established at 1.06 x 10⁻⁶·m²·s⁻¹. The albedo of the dry tidal flat was found as a = 0.14, while for water a = 0.06 can be used. For mean daily heat balance calculations an average value of α = 0.10 should be taken. The net radiation can be estimated with reasonable accuracy from simple weather data from nearby coastal station. Then it is shown that the daily heat balance interacts with the tidal cycle, resulting in a 15-day periodicity in the water temperature as well in the bottom temperature. Further it is demonstrated that with a simple model and some measured “bulk”-parameters, it is possible to predict daily mean water temperatures during the whole measuring period from simple weather data measured at a nearby coastal station.     

槽式太阳能集热器传热模型及性能分析

槽式太阳能集热器一维和二维传热数学模型是一组非线性代数方程,为改进求解的稳定性和计算精度,将槽式太阳能集热器一维和二维传热模型的求解看作有约束优化问题,建立了集热器传热过程求解的有约束优化数学模型,应用MATLAB软件优化函数fmincon进行求解。分析了传热流体入口温度及太阳能辐射热流密度变化对集热器性能的影响。采用fmincon函数求解集热器传热过程,计算速度快,计算过程稳定。分析表明,传热流体温度变化对集热器效率的影响大于太阳能辐射热流密度对集热器效率的影响。     

A GIS-Based Study of the Pollution Load of Adsorbed Nitrogen and Phosphorus in Jialing River Basin, P. R. China

Some reasonable and suitable methods for factor calculation of the equation were chosen based on the American Universal Soil Loss equation,the characteristics of the Jialing River basin in P.R.China,and related research results.The soil erosion and loss in each hydrological unit of the basin were estimated using GIS.Employing the non-point source adsorbed nutrition load model,the loads of adsorbed nitrogen and phosphorus pollution were calculated and analyzed.The results show that the average sediment transportation module in the Jialing River Basin in recent years is 161.94 t/(km2a),and the loads of adsorbed nitrogen and phosphorus pollution are 29 620.8 t/a and 1 391.96 t/a,respectively,at the watershed outlet(Beibei hydrologic station).Adsorbed nitrogen and phosphorus pollution are serious in the Bailong River and Xihanshui basins.The descending order of land type with adsorbed nitrogen and phosphorus loss modulus is as follows: wild land,bush,turf,field,city and forest.     

Combining input uncertainty and residual error in crop model predictions: A case study on vineyards

As crop modelling has matured and been proposed as a tool for many practical applications, there is increased need to evaluate the uncertainty in model predictions. A particular case of interest that has not been treated before is that where one takes into account both uncertainty in the model explanatory variables and model residual error (the uncertainty in model predictions even when the explanatory variables are perfectly known). The specific case we consider is that of a model for predicting water stress of a vineyard. For many of the model explanatory variables, the vine grower (or the farmer advisor) has a choice between approximate values which are easily obtainable and more precise values that are more difficult (and more expensive) to obtain. We specifically discuss the explanatory variable “initial water stress” which is directly based on the initial soil water content and can be estimated or measured (precise but expensive). The vine grower is interested in the decrease in uncertainty that would result from measuring initial water stress, but it is the decrease in total uncertainty, including model residual error, that is of importance.We propose using accurate measurements of water stress over time in multiple vineyards, to estimate model residual error. The uncertainty in initial water stress can be estimated if one has approximate and precise values of initial water stress in several vineyards. We then combine the two sources of error by simulation thanks to an independence hypothesis; the model is run multiple times with a distribution of values for initial water stress, and on each day a distribution of model residual errors is added to the result.The results show that the resulting uncertainty is quite different in different fields. In some cases, uncertainty in initial water stress becomes negligible a short time after the start of simulations, in other cases that uncertainty remains important, compared to model residual error, throughout the growing season. In all cases, residual error is a substantial percentage of overall error and thus should be taken into account.     

Three-dimensional current structure in the Dutch coastal zone

As part of a more comprehensive programme on the hydrography in the Netherlands coastal zone its complex current structure is investigated. One of the aims is to identify the various dominant factors that control the patterns of the coastal flow. To that end field observations covering a one year period were taken at strategic locations in the Dutch coastal area.One of the main results reported here concerns the long term (i.e. one year) average residual currents. Near the bottom these appear to have a significant onshore directed component, with values of the order 2.5 to 3.5 cm/s. In the upper layer typical average values are between 7 and 11 cm/s. The near surface residual flow is mostly in longshore direction with an onshore component increasing with distance from shore, due to the prevailing southwesterly winds (i.e. close to longshore) over the area.The observed large variability of the three-dimensional current structure on different time-scales is largely induced by variations in wind conditions. If strong winds are accompanied by a high river discharge, a distinct two layer system results with very high residual current speeds in the upper-layer, up to 40 cm/s. The observations also produce evidence for the outflow of Rhine river water to be at least partly responsible for the significant onshore component of residual currents near the bottom, as it determines the density structure in this area.Tidal current ellipses show a marked vertical structure both with respect to shape and sense of rotation. For the region considered the spatial distribution of these parameters clearly illustrates the large influence of bottom friction and coastal boundaries, in combination with earth's rotation. Furthermore the data show that variations due to the spring-neap tidal cycle are substantial.     

3-D Simulation of Methanol-steam Reforming for Hydrogen Production in Microreactor

In order to investigate the effects of inlet temperature,velocity and water methanol molar ratio on methanol- steam reforming for hydrogen production in microreactor, we carry out 3-D simulation of methanol-steam reforming for hydrogen production in self-designed plate microreactor with the application of general finite reaction rate model in CFD software of FLUENT, The kinetics used are DE and SR model, The results show that, At the conditions of inlet velocity, temperature and water methanol molar ratio are 2.88 m/s, 493 K and 1.3 respectively, methanol conversion at the reactor outlet reaches 79.8%. Through the simulation, we can see that in microreactor it can be maintain higher hydrogen molar fraction and methanol conversion at high reactant flow rate.     

Regional Marginal Costs and Cost Savings from Economies of Scale in Municipal Waste Treatment: An Application to the Chesapeake Bay Region

Marginal costs of removing effluent from waste treatment facilities are defined under different assumptions about regulatory policies. Marginal costs are different under a policy of uniform treatment for all plants compared to a least-cost policy, where different plants treat at different levels. The cost savings under these alternative policies are compared for river basins of the Chesapeake Bay when there are economies of scale in treatment costs. Current regulations for treatment plants in the Bay, which are not entirely uniform, are also compared to both the uniform and least-cost solutions. The potential savings from a least-cost policy are substantial for some basins.