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1.
In terms of grain size, surficial sediment distribution patterns in back-barrier tidal basins (e.g., the East Frisian Wadden Sea, Germany) often show a landward fining trend from the sea boundary to the mainland shore. In addition to the cross-shore patterns, there are lateral grain-size trends toward the watersheds of the basins and toward the watersheds of tidal flats bordered by tidal channels on either side. In the present study, interrelationships between morphological evolution and grain-size trends in the back-barrier tidal basins of the East Frisian Wadden Sea were simulated for a period of 60 years by a process-based forward modeling approach using the Delft3D system. The model outputs show that grain size displays a shoreward fining trend within the basin area, which is consistent with in situ observations; such a trend can be interpreted by the shoreward decrease in the cross-shore maximum velocity. Moreover, the model predicts lateral grain-size trends similar to those observed in the tidal basins: coarser sediment remains in the inlets and channels, while finer sediment settles at the tidal watersheds and on the tidal flats between channels. The spatial patterns of tidal flat sediment grain size within the tidal basins are thus related to the distance from the sea boundary and from the tidal channels. The modeling exercise also indicates that the development of the grain-size pattern observed in the East Frisian Wadden Sea is accomplished within a few decades, and that the time periods required to reach equilibrium are much shorter for grain size than for bed elevation. Evidently, spatial grain-size information can be used to assess sediment transport and morphological adaptation processes as, for example, attempted in sediment trend analysis procedures.  相似文献   

2.
《Coastal Engineering》2005,52(2):159-175
The Frisian Inlet is one of the tidal basins of the Dutch Wadden Sea. In 1969, its basin area was reduced by 30%. As documented by bathymetric surveys, this has led to an import of sediment of 30×106 m3 over the first 18 years. The study presented in this paper seeks to establish the mechanisms responsible for the passage of the sediment through the throat cross-section of the inlet channel. Emphasis is on a 14-day period of relative calm when sediment transport can be attributed solely to tidal currents. Use is made of continuous measurements of velocity, sand and silt concentration. The measurement station was located on one side of the throat cross-section in a water depth of approximately 6 m. For both the sand and silt fraction of the sediment, suspended load transport is the dominant transport mode. It is shown that for sand, concentration variations and net transport are determined by the local (in the throat section) velocity. Especially the residual velocity and tidal velocity asymmetry play an important role in the net sand flux. For silt, except for transport associated with locally generated vertical mixing, the net transport is largely determined by sedimentation–erosion processes in the basin and the silt concentration in the North Sea. Comparison with measurements in a station located in the middle of the throat section shows considerable difference in residual velocity and tidal velocity asymmetry. As a result, the sediment fluxes also differ. Accurately determining the net sediment flux in the throat section would require a dense net of measurement stations.  相似文献   

3.
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4.
In the paper two types of numerical models – a lumped-parameter model and a high-resolution two-dimensional hydrodynamic model – are used to analyse the response of a system of partially-connected tidal basins to inhomogeneous open sea forcing. The equations of the lumped-parameter model, suitable for an arbitrary number of basins with sloping walls, are formulated based on one-dimensional continuity and momentum equations. Numerical solutions to the equations are thoroughly examined, showing the influence of inhomogeneous open sea forcing and of geometrical parameters of the basins on the tidal range and the water transport through the system, with particular emphasis given to inter-basin water exchange and cumulative water transport through basins boundaries. The results of the lumped-parameter model simulations for the tidal basins of the German Wadden Sea are successfully compared with the results of calculations with the two-dimensional hydrodynamic model, which is used to investigate in more detail circulation patterns and the influence of specific local features of inlet bathymetry on the hydrodynamic processes in the study area. The influence of wind on the basins response is discussed as well.  相似文献   

5.
Grey seals (Halichoerus grypus) have been extinct in the south-eastern North Sea for centuries. Only in recent decades have they re-established a few colonies, the first of which was located on a group of sand bars off the German island of Amrum. Based on frequent counts from aircraft and boats in 1976–2000, and a photo-identification program in 1997, we investigated seasonal dynamics, trends in abundance, pup production, and pup survival in this population. Numbers of hauled-out seals were highest in spring, with a peak of 70–100 in late March or early April, and usually lower than 40 from late May to late January, including the winter breeding season. Both spring and summer counts indicated an average increase of 4–5% per year. Annual pup production was 3–10 in 1988–1995 and 9–13 in 1996–1999, suggesting a breeding stock of only about half the minimum total population size, i.e. 137 individually recognised seals in 1997. The estimated survival of pups until weaning seemed high enough to support autochthonous increase, and hence suggested a self-sustaining breeding stock at least until the late 1990s. Pup survival declined, however, from 95–100% in 1988–1991 to 60–70% in 1992–1999, probably due to erosion of the sand bars. From (i) the relative excess of hauled-out seals in spring, as compared to the phenology of stocks in the western North Sea, (ii) turnover and net loss of individuals during the spring and summer of 1997, as indicated by photo-ID records, and (iii) the low apparent per capita birth rate, we suggest that grey seals off Amrum split into a resident breeding stock and a similar or higher number of seals immigrating outside the breeding season. The latter may originate from larger colonies in the southern and western North Sea, and return there for breeding. In the future, grey seals currently breeding off Amrum may eventually leave the area because of deteriorating conditions. However, a decline of numbers occurring in spring and summer would not necessarily be expected, because seasonal influx from increasing stocks elsewhere in the North Sea is likely to continue.  相似文献   

6.
Daily observations of the salinity of the Marsdiep tidal inlet, which connects the Dutch western Wadden Sea with the North Sea, already started over 140 years ago, in 1860. Since the year 2000 the sampling frequency has increased because of the use of electronic sensors. Analysis of these salinity data have revealed variations on time scales from tidal (~ 12 hour), seasonal, inter-annual, and multi-decadal, to centennial. The contributions of the salinity variations in the Marsdiep for these different spectral bands or time scales are all of the order of a standard deviation of 0.5 to 1. The centennial variation, which can be expressed as a 140 year long salinity trend, is related to engineering works on the rivers Rhine and IJssel, which already started in the early 18-th century, and more than doubled the magnitude of the freshwater content of the western Wadden Sea since then. In contrast with this anthropogenic salinity trend, the climatic variability of the precipitation over western Europe, and the connected changes in the Rhine discharge, are mainly responsible for the inter-annual variations in the salinity and/or freshwater content of the western Wadden Sea. Since variations in salinity and freshwater content also reflect variations in the terrigeneous and river influence on the Wadden ecosystem, e.g. via the nutrient content, it can be expected that the ecology of the Wadden Sea also experienced changes on centennial time scales.  相似文献   

7.
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   

8.
As a result of aquaculture activities Pacific oysters Crassostrea gigas (Thunberg, 1793) have invaded the European Wadden Sea. Using a variable noncoding mitochondrial marker, we show that the invaded range is the result of two independent invasions. Haplotype frequencies point towards two separate groups, one in the southern and the other in the northern Wadden Sea. We found virtually no genetic differentiation throughout the southern range and the putative source from British Columbia, Canada, suggesting that the Southern region can be considered as a closed population. In the North, mismatch distributions, haplotype ordination and isolation-by-distance analysis suggest a stronger, persistent impact of aquaculture on invasive populations. Due to the ongoing supply of new genetic material from hatchery production the northern invasive populations can therefore be considered as an open population highlighting the importance of aquaculture practice on the genetics of this keystone invader in the Wadden Sea.  相似文献   

9.
The Wadden Sea is a shallow coastal region, with a large area of sedimentary tidal flats that extends from The Netherlands to Denmark and has been declared a site of international importance in the Dutch and German parts (Ramsar status and UNESCO World Heritage Site). Benthic macrofauna are central to the ecosystem functioning of this area, as they recycle nutrients, decompose organic matter and are an important food source for many secondary consumers, like fish and waterbirds. Due to the environmental gradients characteristic of estuarine systems, it is expected that changes in assemblage composition will be observed across the physical and environmental gradients of the Wadden Sea. First, we explored the spatial variation in assemblage composition of benthic macrofauna across the intertidal part of the Dutch Wadden Sea using 3 years of biomass data. Then, we identified the relative importance of six environmental variables for explaining and predicting changes in assemblage composition across the intertidal areas of the Wadden Sea using generalised dissimilarity modelling (GDM). In accordance with the environmental gradients across this system, the biomass contributed by a few common species differed from west to east and were distinct in the Dollard. In the west, bivalves Mya arenaria, Cerastoderma edule and Ensis directus contributed a relatively large and equal share of the total biomass, whereas C. edule contributed the sole largest share of the total biomass towards the east. The polychaete Alitta succinea became a large share of the total biomass in the upper Ems and in the Dollard estuary, but contributed little elsewhere. Similar to the observed differences in species composition, the spatial patterns in assemblage composition, as predicted by the GDM models, identified the Dollard as distinct and that the prevalence of assemblage types in the west differed to the east. Median grain size, followed by microphytobenthic biomass, and exposure time were the most important variables describing differences in assemblage composition. That the Wadden Sea forms a heterogeneous landscape where assemblage composition varies across multiple gradients has repercussions for management and monitoring.  相似文献   

10.
In 1995 the seasonal development of concentrations of both phytoplankton and larvae of the bivalve Macoma balthica was studied in the coastal zone behind the back-barrier island of Spiekeroog (German Wadden Sea). In July/August larvae reached maximum concentrations of about 1000 to 4200 ind. m−3 (depending on the sampling site and tidal period), probably in relation to a phytoplankton bloom in July. This observation of an unusually late maximum of Macoma larvae is discussed in detail in connection with the recent literature available about spawning of M. balthica in the Wadden Sea.  相似文献   

11.
A budget model covering the Baltic Sea was developed for the time period 1980–2000 to estimate water and dissolved silica (DSi) fluxes as well as internal DSi sinks/sources. The Baltic Sea was resolved by eight basins, where the largest basin — the Baltic Proper — was divided laterally into north/west and southern/east parts as well as vertically to take into account the existence of the permanent halocline. The basins demonstrated rather different patterns with regard to silica cycling. The Gulfs of Finland and Riga together with the northernmost basins, Bothnian Bay and Bothnian Sea, are distinguished by substantial specific rates of silica removal accounting for 1.6–4.9 g Si m− 2 yr− 1. Bearing in mind the large total primary production, the basins comprising the Baltic Proper with the specific removal rates 0.2 and 1.2 g Si m− 2 yr− 1, do not appear as regions with a high silica accumulation. The Arkona and the Kattegat mainly behave as regions of rapid through-flows. These results point out the northernmost Gulf of Bothnia, the Gulfs of Riga and Finland as areas with a larger share of biogenic silica accumulation than in the Baltic Proper. It is attributed to hydrographic and hydrochemical features. An estimate of diatom export production was made for the Baltic Proper showing that the diatom contribution accounts for 19–44% of the net export production.  相似文献   

12.
During the period 17–22 December 2001, the onshore distribution and the abundance of Antarctic fur seals Arctocephalus gazella and Subantarctic fur seals A. tropicalis were determined for Prince Edward Island. Two breeding colonies of Antarctic fur seals were located on the south-east coast of the island; the first a mixed (with Subantarctic fur seals) breeding colony with an estimated 24 pups on a vegetated promontory on the northern section of Boggel Beach, and the second, a presumably pure Antarctic fur seal breeding colony with an estimated 380 pups, at Penguin Beach. At a mean intrinsic rate of natural increase of 16.2% per year, Antarctic fur seals appear to be in the rapid recolonization phase of population growth. Breeding colonies of Subantarctic fur seals, largely found on the entire east coast, produced an estimated 15 000 pups, and the population had maintained a mean intrinsic rate of natural increase of some 9.5% per year since 1987/88.  相似文献   

13.
《Journal of Sea Research》2009,61(4):227-234
Daily observations of the sea surface temperature in the Marsdiep tidal inlet, which connects the shallow Dutch western Wadden Sea with the deeper North Sea, already started in the summer of 1860, over 140 years ago. Since the year 2000 the sampling frequency has strongly increased because of the use of electronic sensors and data logging by computer. Analysis of these temperature data has revealed variations with time scales from tidal, daily, seasonal, inter-annual, to centennial. The tidal temperature variations are generated by advection of the seasonally varying temperature gradient between Wadden Sea and North Sea, while the daily variations are mainly caused by the daily variation of solar radiation. The seasonal variation in sea surface temperature only lags a few days behind the coastal surface air temperature, contrary to the sea surface temperature in the deeper nearby North Sea, which is delayed with about 1 month. The North Atlantic Oscillation index has been used as large-scale proxy for the atmospheric forcing of the Wadden Sea temperature. Only for the winter and spring a significant correlation is found between temperature and the winter index. However, this correlation is so strong that also the annual mean temperature is correlated significantly with the North Atlantic Oscillation. At longer time scales, from decadal to centennial, also large temperature variations are observed, of the order of 1.5 °C. However, these are not related to long-term changes of the North Atlantic oscillation. These long-term temperature changes involve a cooling of about 1.5 °C in the first 30 years of the record and a similar warming in the last 25 years. In between, these long-term changes were smaller and more irregular. Similar conclusions can also be applied to individual seasons as well as to the date of the onset of spring.  相似文献   

14.
《Journal of Sea Research》2007,57(4):329-337
Increasing Scandinavian harbour seal populations during the last decades coincide in time with the collapse of the cod fishery. Assumptions of a causal relationship have led to claims favouring re-introduction of seal hunting. Proposals for ‘adaptive management’ often assume that decimating seal populations will automatically favour the fishery. This argument presupposes seal predation to be sufficiently large to have a measurable impact on the fish population. The potential magnitude of the cod-seal interaction was analysed using data on harbour seal abundance, feeding habits and compiled information on cod life history and cod landing statistics. A size-structured life history matrix for the cod population was applied and the size-specific prey preferences of harbour seals were taken into account. Estimated seal predation was small compared to both the landings by the fishery, and to minimum estimates of the total cod population. Furthermore, since the size classes of cod targeted by seals have low reproductive values, the impact of seal predation on cod production will be further reduced. Our analyses suggest harbour seals have a negligible impact on the cod fishery.  相似文献   

15.
Daily observations of the sea surface temperature in the Marsdiep tidal inlet, which connects the shallow Dutch western Wadden Sea with the deeper North Sea, already started in the summer of 1860, over 140 years ago. Since the year 2000 the sampling frequency has strongly increased because of the use of electronic sensors and data logging by computer. Analysis of these temperature data has revealed variations with time scales from tidal, daily, seasonal, inter-annual, to centennial. The tidal temperature variations are generated by advection of the seasonally varying temperature gradient between Wadden Sea and North Sea, while the daily variations are mainly caused by the daily variation of solar radiation. The seasonal variation in sea surface temperature only lags a few days behind the coastal surface air temperature, contrary to the sea surface temperature in the deeper nearby North Sea, which is delayed with about 1 month. The North Atlantic Oscillation index has been used as large-scale proxy for the atmospheric forcing of the Wadden Sea temperature. Only for the winter and spring a significant correlation is found between temperature and the winter index. However, this correlation is so strong that also the annual mean temperature is correlated significantly with the North Atlantic Oscillation. At longer time scales, from decadal to centennial, also large temperature variations are observed, of the order of 1.5 °C. However, these are not related to long-term changes of the North Atlantic oscillation. These long-term temperature changes involve a cooling of about 1.5 °C in the first 30 years of the record and a similar warming in the last 25 years. In between, these long-term changes were smaller and more irregular. Similar conclusions can also be applied to individual seasons as well as to the date of the onset of spring.  相似文献   

16.
The Pacific oyster Crassostrea gigas was introduced in Europe for commercial purposes in the mid 1960s. It was initially thought that low winter temperatures would restrain this species' reproduction and settlement; however, its present distribution in areas where no introduction has taken place suggests that natural invasion and expansion has occurred. Along the European coast, wild populations of Pacific oysters are already found from northern Germany to southern Portugal. Whether C. gigas will continue to further expand through northern waters will depend on its physiological performance. In this study, the performance of wild oyster populations has been studied in terms of growth and reproduction at three stations: La Rochelle (France; 46°N), Yerseke (Oosterschelde estuary, The Netherlands, 51°N), and Texel (Wadden Sea estuary, The Netherlands, 53°N). The French population had the lowest somatic-shell mass ratio and an increase in maximum shell length, somatic and gonadal mass was observed from France to the Netherlands. In addition, mean oocyte diameter decreased significantly from south to north. The combination of increasing gonadal mass and decreasing oocyte volume suggests an increasing reproductive output in terms of egg numbers from France to The Netherlands. Differences in temperature between locations will at least be partly responsible for the observed patterns; however, other environmental factors (such as food availability, predation pressure, sediment type and/or seston concentration) cannot be excluded. Since smaller eggs (oocytes) are thought to have a longer development time, the environmental conditions along the Dutch coast may result in increased larval dispersal and possibly in further population expansion.  相似文献   

17.
Biomarkers of organochlorine exposure, such as the induction of cytochrome P450 1A (CYP1A), can be used to assess the impact of environmental contaminants on the health of free-ranging marine mammal populations. The objective of the present study was to measure CYP1A in skin and liver biopsies obtained from live harbour seals (Phoca vitulina). Twelve harbour seal pups, aged three to five weeks, were captured from the Fraser River estuary, British Columbia, Canada, and temporarily held in captivity. Skin ( approximately 60 mg) and liver ( approximately 40 mg) biopsies, obtained while seals were under general anaesthesia, yielded sufficient tissue for the measurement of CYP1A by immunoblot analysis and ethoxyresorufin O-deethylase activity. A short-term exposure experiment, in which harbour seals (n=3) were treated orally with beta-naphthoflavone (BNF), resulted in increased hepatic and cutaneous CYP1A protein levels, consistent with observations in other mammals. This study is the first to measure CYP1A in skin and liver biopsies from live harbour seals and to report in vivo BNF-associated CYP1A induction in a marine mammal. The results demonstrate that microsamples collected using minimally-invasive techniques can provide toxicologically-relevant information form marine mammals.  相似文献   

18.
More than ten years ago a paper was published in which stochastic population process models were fitted to time series of two marine polychaete species in the western Wadden Sea, The Netherlands (Van der Meer et al., 2000). For the predator species, model fits pointed to a strong effect of average sea surface winter temperature on the population dynamics, and one-year ahead model forecasts correlated well with true observations (r = 0.90). During the last decade a pronounced warming of the area occurred. Average winter temperature increased with 0.9 °C. Here we show that despite the high goodness-of-fit whilst using the original dataset, predictive capability of the models for the recent warm period was poor.  相似文献   

19.
利用ECOM模式模拟南海正压M2、S2、K1、O1分潮, 对南海潮能通量及潮能耗散进行研究.结果显示, M2、S2、K1和O1分潮分别有38.93、5.77、29.73和28.97GW的能通量经吕宋海峡传入南海, 并有2.42、0.36、8.67和7.86GW的能通量由南海经卡里马塔海峡传入爪哇海.由东海及吕宋海峡西北部传入台湾海峡的M2分潮能通量为25.28GW.半日潮进入北部湾和泰国湾的能通量较少(6.52GW), 全日潮则较大(24.74GW).通过民都洛和巴拉巴克海峡断面, 全日潮由南海向苏禄海共输送12.28GW的能通量, 而半日潮则由苏禄海向南海输送1.92GW的能通量.由模式输出结果估计得到的南海各局部海域的底摩擦耗散与净潮能通量存在差异, 为使二者平衡, 可对南海不同海域的底摩擦系数进行调整.依净潮能通量与底摩擦耗散平衡关系计算得到台湾海峡、北部湾、泰国湾及南海深水海域的底摩擦系数分别为0.0023、0.0024、0.0023和0.0021.  相似文献   

20.
In this paper , we present a novel Kalman filter approach to combine a hydrodynamic model-derived lowest astronomical tide (LAT) surface with tide gauge record-derived LAT values. In the approach, tidal water levels are assimilated into the model. As such, the combination is guided by the model physics. When validating the obtained “Kalman-filtered LAT realization” at all tide gauges, we obtained an overall root-mean-square (RMS) difference of 15.1 cm. At the tide gauges not used in the data assimilation, the RMS is 17.9 cm. We found that the assimilation reduces the overall RMS difference by ～ 31% and ～ 22%, respectively. In the Dutch North Sea and Wadden Sea, the RMS differences are 6.6 and 14.8 cm (all tide gauges), respectively. Furthermore, we address the problem of LAT realization in intertidal waters where LAT is not defined. We propose to replace LAT by pseudo-LAT, which we suggest to realize similarly as LAT except that all water level boundary conditions and assimilated tidal water levels have to be enlarged by a constant value that is removed afterward. Using this approach, we obtained a smooth reference surface for the Dutch Wadden Sea that fits LAT at the North Sea boundary within a few centimeters.  相似文献   

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