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1.
A new approach to the classification of estuaries is described. The estuary environment classification (EEC) is based on a hierarchical view of the abiotic components that comprise the environments of estuaries. The EEC postulates that climate, oceanic, riverine and catchment factors ‘control’ a hierarchy of processes and broadly determine the physical and biological characteristics of estuaries. The classification differentiates estuaries at four levels of detail. Level 1 differentiates global scale variation based on differences in climatic and oceanic processes, which are discriminated by the factors: latitude, oceanic basins and large landmasses. Level 2 differentiates variation in estuary hydrodynamic processes, which are discriminated by estuary basin morphometry, river and oceanic forcing. Level 3 differentiates variation among estuaries that are due to catchment processes, which are discriminated by catchment geology and catchment land cover. The approach has been applied to all the estuaries in New Zealand using existing data sources. Estuaries were assigned class membership at each level of the classification by applying criteria in the form of decision rules to the database of assignment characteristics. GIS was then used to map the estuaries with classes being defined by colour at any level of the classification. The resulting map provides a multi-scale spatial framework that is suitable for many environmental or conservation management applications.  相似文献   

2.
The annual loads of nutrients (TOxN equal to nitrate+nitrite; ammonium, phosphate, silicate) to all the estuaries on the mainland of the United Kingdom were estimated from data on water flow through gauging stations at the tidal limits of estuaries, and from concentration measurements under the Harmonised Monitoring Scheme of nutrient concentrations in water samples from these stations. The annual loads of nutrients showed distinct regional variations, with estuaries along the west coast of Wales and northern Scotland having much smaller loads than those along the east coast of England. The largest nitrogen loads were of TOxN, and ammonium loads were usually small in comparison. The Severn, Mersey, Humber and Thames had the highest loads, although these were small in relation to the larger continental European estuaries. Loads of TOxN per unit of catchment area were surprisingly constant (about 105 moles N km−2 y−1). The nutrient loads showed that most U.K. catchments were influenced by human activity, the majority being in the ‘ moderately influenced ’ category. Nutrient loads were also normalized for the area of each estuary, as a measure of the relative influence of nutrients on the receiving estuaries. The ratios of N:P, N:Si and P:Si in the annual loads suggested that most estuaries were likely to be, if anything, P limited rather than N or Si limited. However, crude annual loads may conceal significant seasonal variations.The spring maximum chlorophylla concentrations in coastal waters adjacent to each estuary were significantly correlated with the log total annual loads of TOxN, ammonium and phosphate (but not silicate) for each estuary, providing a direct link between a measure of the degree of biological response in coastal waters and the nutrient load through the estuaries. There were no significant correlations between spring maximum chlorophyll a concentrations and either catchment-normalized or estuary-normalized nutrient loads. There was significant correlation between catchment area-normalized loads of phosphate and an urbanization index for the catchments, but not with the catchment area-normalized loads of the other nutrients.  相似文献   

3.
Interactions between ‘oxygen concentration’ (normoxia: >80% oxygen saturation, and hypoxia: 18% oxygen saturation) and ‘water flow velocity’ (low: 0.1 cm s−1, and moderate: 0.5 cm s−1) were studied on growth rates in the brittle star Amphiura filiformis in a flow-through aquaria system. Effects of ‘sublethal predation’ on growth rates were investigated as ‘number of amputated arms’ (1 and 3 arms) and ‘amputation of the disk’. A significant interaction between oxygen concentration and water flow velocity was observed in mean arm regeneration rate, but in both flow velocities higher mean arm regeneration rates were observed in normoxia compared to hypoxia. In hypoxia a positive response in arm regeneration rate was observed in moderate flow compared to low flow velocity. In normoxia, however, no response to flow velocity was observed. The latter observation indicates that Amphiura filiformis is able to maintain the ventilation of the burrow at low flow velocities, but in low oxygen concentrations hydrodynamic forces seem to affect growth. A significant interaction between oxygen concentration and disk amputation was observed in both arm and disk regeneration rates, indicating that the disk is the major organ for gas exchange in this species. The number of arms amputated, however, did not affect mean arm regeneration rate. The results obtained in this study suggest that the secondary production in subtidal infaunal populations could be negatively affected by low oxygen concentrations and that this response is even more negative in combination with low flow velocities in the near-bottom water.  相似文献   

4.
Water samples from the Lena River and stratified Laptev Sea (northeastern Siberia) have been analyzed to determine their stable oxygen isotope composition (18O/16O). Measurements at the Lena River reference station give a δ18O value of −18.9‰ in both surface and bottom waters. In the brackish water surface plume, a nearly perfect correlation is found between δ18O and chlorinity
δO=−18.9+0.7C1−(n=15; r=0.999)
A few values lie distinctly below this correlation; they all correspond to surface samples collected in the semi-enclosed Buorkhaya Gulf, and they most likely reveal the occurrence of ‘old’ water masses. Some of the δ18O values in the deep waters collected in the same zone also fall below the surface-plume correlation line.Dissolved silicate concentrations exhibit a large variability. However, when they are related to the different water masses identified using oxygen isotope data, a more coherent picture is obtained. Concentrations in the surface plume decrease more or less regularly from 50 to 72 μmol in the Lena River, to 7 μmol at the ‘marine’ end-member (Cl− = 14 g l−1). Dissolved silicate results in the Buorkhaya Gulf are quite distinct, with a clear deficiency in the surface waters, and an excess in the deep waters.These δ18O and dissolved silicate variations are discussed in relation to the hydrology and the biological productivity of the investigated area.  相似文献   

5.
The effect of environmental factors (river discharge, water temperature and dissolved oxygen saturation) on the abundance and distribution of Acartia populations and the interactions between their congenerics was evaluated by means of transfer function (TF) models in the estuary of Bilbao during the period 1998–2005. The recorded species were Acartia clausi, Acartia tonsa, Acartia margalefi and Acartia discaudata. Acartia clausi dominated in the entire euhaline region of this estuary until 2003 when it was displaced from the inner part by A. tonsa. This invasive species (A. tonsa) was found for the first time in 2001 and colonized successfully the inner (salinity 30) and intermediate (salinity 33) waters of this estuary since 2003. The TF models revealed an immediate and negative effect of A. tonsa on A. clausi in the intermediate salinity (33) waters, where these species showed the highest spatial overlap. The results indicate that environmental changes from 2003 influenced the abundance of Acartia species, being unfavourable for A. clausi. The decrease of A. clausi abundance in low salinity waters was related to a significant decrease of dissolved oxygen saturation levels, whereas the increase of temperature was linked to a significant increase of A. tonsa. Acartia margalefi and A. discaudata were scarce over the entire period, but they were found to be valuable indicators of hydrological changes, which were associated to climate factors. These two latter species increased in abundance and expanded their seasonal distribution, and in the case of A. margalefi also its spatial distribution, in 2002, coinciding with the period in the time-series when autumn–winter rainfall and summer temperatures were lowest, and dissolved oxygen saturation levels were highest.  相似文献   

6.
Laboratory and in situ experiments were performed to assess the use of bromide as a tracer forin situ studies of benthic solute exchange. Bromide was used in the benthic chamber lander ‘ Elinor ’ for flux measurements in coastal sediments of the German Bight, Kiel Bight and Skagerrak (28–700 m water depth). Tracer and total oxygen uptake were monitored simultaneously in the same chamber incubation. Concurrently, in situ oxygen micro-profiles were recorded at the same locations by the profiling lander ‘ Profilur ’. Deployment in an anoxic silt (Kiel Bight) confirmed that in the absence of bioturbation and advection, tracer transport into the sediment was driven solely by molecular diffusion. This flux could be well described by a simple box model accounting for molecular diffusion only. In oxic sediments (German Bight and Skagerrak) enhanced exchange of bromide tracer due to bioirrigation parallelled enhanced oxygen uptake equivalent to a 4-fold molecular diffusive flux. Our experiments showed that incubations can be short. Depending on irrigation activity of the fauna, however, incubation length should exceed 3 h in order to provide a useful data base for flux calculations. The method demonstrating caveats is discussed and indicate possible improvements. The results show how the bromide tracer addition can be used as a tool for determining solute fluxes exceeding diffusive flux in benthic chamber incubations.  相似文献   

7.
This is a paper from the Swedish research project ‘The coastal zone—scientific criteria for planners’. The goal has been to establish simple, general scientific methods for management of Swedish coastal waters. In this paper the focus is on a set of empirical data from 21 so-called type areas and on the exchange of surface water. The working hypothesis has been that the water retention (or residence) time is regulated by the morphometry. The theory has been verified. It has been shown that the water retention time can be determined from a formula based on only two key morphometric parameters, the exposure and the mean coastal width. It provides an 86% degree of explanation (r2=0·86) of the variation in empirically determined retention times and can be physically linked to the basic mass balance equation. The formula is valid for the bioproductive season (May–Oct.) and for small (1–100 km2) Swedish coastal areas. It cannot be directly applied to areas affected by heavy tides.  相似文献   

8.
High-resolution acoustic and ichtyoplankton sampling with a ‘continuous under-way fish egg sampler (CUFES)’ was performed in two regions of approximately 100 square nautical miles off southern Iberian Peninsula, with the aim of studying the small scale distribution of sardine (Sardina pilchardus) adults and eggs during a spawning event. Very dense patches (246 eggs m− 3) of recently spawned eggs with dimensions (up to 3 nautical miles wide) significantly larger than daytime sardine schools were present in both regions. Egg staging and ageing showed very little intra-sample variation, indicating a synchronous spawning period at dusk. The internal structure of the patches evaluated by variography showed very low internal variability, as if they consisted of a single unit. This hypothesis is confirmed by the acoustic finding of large sardine shoals with similar dimensions to those of the patches after sunset and throughout the night. During that period, adults were found near or in contact with the bottom, suggesting that spawning occurred at depth. A distinct patch of older eggs was found in both areas, but with a few nautical miles of horizontal separation. Their characteristics (a larger area, lower egg densities and a more irregular shape) indicate that these patches were exposed to dispersion and ‘stirring’ by physical forces, reshaping their initial appearance, while mesoscale water circulation could have displaced the core of the patches away by several kilometres within a day.  相似文献   

9.
根据2011年及2013?2018年春、秋两季在海州湾及其邻近海域进行的底拖网调查数据,研究该海域短吻红舌鳎(Cynoglossus joyneri)的资源分布特征及其受环境因子和饵料生物的影响,并比较了两种模型(普通GAM模型和PCA-GAM模型)对其资源分布的预测效果,采用交叉验证的方法对模型的预测能力及拟合效果进行评价。结果显示:PCA-GAM模型的拟合度及预测效果均优于普通GAM模型。春、秋两季海州湾短吻红舌鳎资源丰度均呈现南高北低、近岸浅水区大于深水区的分布特征,因为海州湾南部近岸海域较高的水温利于春、秋季短吻红舌鳎产卵群体性腺发育,较低的盐度利于其鱼卵及仔鱼的生长发育,同时,近岸海域丰富的饵料资源为产卵后的亲体提供大量食物供给。分别应用两种模型预测了2018年春季和秋季短吻红舌鳎在海州湾的资源分布,结果显示,PCA-GAM模型的预测值与实际调查的结果更为吻合,预测效果要优于普通GAM模型。本研究为今后开展渔业生物空间分布的研究提供了一种新的方法。  相似文献   

10.
Understanding the physical and biogeochemical processes that control the exchange of biogenic carbon within and between the arctic shelves, slopes, and deep basins is a key objective of the Western Arctic Shelf-Basin Interaction program (SBI). Here, egg production (EP) of the dominant copepod Calanus glacialis/marshallae was used as an indicator of food limitation for the mesozooplankton community in the Chukchi and Beaufort Seas in spring and summer, 2002. Both C. glacialis and C. marshallae may occur in this region but the two cannot easily be differentiated visually. Four oceanographic regions were objectively identified that roughly corresponded to the different pathways in circulation of nutrient-rich Pacific water. A ‘transition’ region characterized by ‘older’ Pacific water was located at the shelfbreak and separated the nutrient-rich shelf water and the low-nutrient waters of the deep basin. The observed spatial pattern in EP in C. glacialis/marshallae in spring and summer resulted both from the different water mass environments and from the reproductive cycle of the species. EP was greater on the shelf than in the basin, corresponding to differences in body size and nitrogen condition factor (NCF) in females, while the egg viability was generally high throughout the study area. EP showed no relationship with low-chlorophyll a biomass under heavy ice-cover in spring, while a significant relationship was observed in the more open water in summer. Adult female carbon condition factor (CCF) was much higher in summer, reflecting the accumulation of lipids during the growth season. Small animals with a markedly greater NCF dominated on the shelf. The shelfbreak region contained a mixture of females from the shelf and the basin with intermediate sizes, conditions, and EP rates. The occurrence of water typical of the ‘transition’ shelfbreak region and elevated EP in C. glacialis/marshallae offshore on the Barrow Canyon and East Barrow sections indicated offshore transport of productive shelf water and the associated plankton community. The input of nutrient-rich Pacific water and accompanying elevated production to the northern Chukchi Sea and the Chukchi-Beaufort shelfbreak region may contribute to the reproductive success of C. glacialis/marshallae in this region.  相似文献   

11.
The world’s largest mono-specific fishery, the Peruvian anchovy or anchoveta (Engraulis ringens) fishery, has been the subject of many studies since the 1960s. Details of its relationship with other species have mainly focused on alternations with sardine, Sardinops sagax, and little effort has so far been paid to interactions with other species sharing the same ecosystem. This is the case for Pleuroncodes monodon, the crustacean squat lobster or ’munida’, which has become highly abundant along the Peruvian coast since the mid-1990s. Munida is now an important prey for seabirds, mammals and coastal predatory fish. Knowledge of patterns of distribution and ecological niche of munida is scarce however off Peru. Here we describe and compare spatial patterns of distribution of anchoveta and munida and their ecological niches based on data from 26 acoustic surveys performed along the Peruvian coast between 1998 and 2006. The results indicate that munida and anchoveta share ecological niches but that munida is restricted to the coldest part of the productive cold coastal waters whereas anchoveta do not present any temperature preference over a large range (14–23 °C). The recent increase in munida abundance off Peru is concomitant with colder conditions; with their onset munida extended its range from central Chile northwards. Off Peru the very shallow oxycline keeps munida from its usual bottom habitat and has forced it to adopt pelagic behaviour.  相似文献   

12.
It is believed that the ecological balance and productivity of marine coastal environments are directly related to nutrient supplies from various sources including riverine-estuarine-coastal exchange, upwelling, precipitation, nitrogen fixation, and nutrient regeneration. In south Texas coastal waters, where phytoplankton productivity is comparable to other high productive coastal areas, many nutrient sources are suspected, but are not equally important in supplying sufficient nutrients to drive coastal production dynamics. Nitrogen regeneration from the benthos is implicated from a 2.5-y study of the nutrient cycling processes important in contributing to production levels in these waters. Sediments of the south Texas coastal habitat appear to exhibit a sensitive coupling with overlying waters, where a strong negative correlation exists between the random periodicity of external supplies of ‘new’ nitrogen to the coastal system and the rate at which nitrogen is recycled by sediments. This pattern buffers these waters against extended periods of low input of nutrients from external sources. The development of a conceptual scheme for nutrient cycling in this coastal habitat has provided a more holistic framework from which we can derive an objective assessment of the importance of mechanisms in the system. All data collected so far suggest that the primary production of organic matter and passage through the benthic habitat of these coastal waters is an important pattern responsible for the continued maintenance of productivity in the south Texas coastal ecosystem.  相似文献   

13.
Data from three annual surveys, covering inshore and offshore waters of the southeastern North Sea, were analysed to study recruitment variability in dab (Limanda limanda) over the period 1978–1997. Geometric mean abundance of 0- to 5-group dab was estimated using general linear models. Juvenile dab (0- and 1-group) were found over the entire area, from inside the estuaries to 50 m depth offshore. Environmental conditions (water temperature, wind stress, turbidity) affected the catch rates. The potential errors in the estimates of year-class strength, caused by differences in catchability, are discussed. The inter-annual pattern of year-class strength appeared to be established between ages 1 and 2, suggesting that factors determining recruitment are not restricted to the pelagic early life phase only, but also operate during the demersal juvenile phase. Recruitment variability at age 2 was in the order of 50–60% and appears to be equal to, or lower than, recruitment variability in plaice and sole. These results contradict expectations based on the concentration hypothesis, which states that the degree of variation in recruitment is inversely related to the degree of concentration during early life phases.  相似文献   

14.
Multivariate principal components analysis and cluster analysis were performed on data representing presence or absence of 498 species of juvenile and adult fish species in twenty-four coastal marine systems (bays, coastal lagoons, estuaries and coastal zones) distributed from southeast to southern Brazil. Five groups of coastal systems were identified based on fish assemblage similarity: estuaries and bays of the southeast area; an estuary of the southern area; coastal lagoons; rocky coastal zones; and the continental platform. Species assemblages for each zone were identified and used as surrogate habitat indicators to compare and contrast the groups. Stepwise multiple regression of environmental and physical variables as predictors of the number of species indicated that only ‘ area ’ was included in the model as the most important variable explaining the variation of the number of species in these data sets. The total number of fish species increased as surface area increased.  相似文献   

15.
The dynamic processes of bore propagation over a uniform slope are studied numerically using a 2-D Reynolds Averaged Navier–Stokes (RANS) solver, coupled to a non-linear k − ε turbulence closure and a volume of fluid (VOF) method. The dam-break mechanism is used to generate bores in a constant depth region. Present numerical results for the ensemble-averaged flow field are compared with existing experimental data as well as theoretical and numerical results based on non-linear shallow water (NSW) equations. Reasonable agreement between the present numerical solutions and experimental data is observed. Using the numerical results, small-scale bore behaviors and flow features, such as the bore collapse process near the still-water shoreline, the ‘mini-collapse’ during the runup phase and the ‘back-wash bore’ in the down-rush phase, are described. In the case of a strong bore, the evolution of the averaged turbulence kinetic energy (TKE) over the swash zone consists of two phases: in the region near the still-water shoreline, the production and the dissipation of TKE are roughly in balance; in the region farther landwards of the still-water shoreline, the TKE decay rate is very close to that of homogeneous grid turbulence. On the other hand, in the case of a weak bore, the bore collapse generated turbulence is confined near the bottom boundary layer and the TKE decays at a much slower rate.  相似文献   

16.
Saanich Inlet, British Columbia, has long been known for the presence, in most years, of anoxic bottom water. One factor contributing to this anoxia is a high level of primary production, which occurs as a major spring bloom followed by sporadic ‘mini-blooms’ throughout the summer and early fall. The process(es) by which new production is refueled after nutrient exhaustion caused by the spring bloom are not well known, since Saanich is an inverse estuary and vertical mixing driven by winds and tides is low. This study presents new observational evidence that strongly suggests that the dominant mechanism of nutrient resupply during the summer months is intermittent advective exchange, driven by pressure gradients set up by strong tidal mixing in passages outside Saanich Inlet itself. A simple box model is formulated to illustrate this mechanism. When driven by annual freshwater forcing and deepwater renewal functions characteristic of the region and measured tides for 1975, the model predicts resupply of nitrate during most of the periods observed in 1975 observations (Deep-Sea Res. 24 (1977) 775). This ‘action-at-a distance’ nutrient resupply mechanism, involving strong but localized turbulent mixing and subsequent distribution of the products of mixing over large-horizontal distances by pressure-gradient-driven flow, is likely important in other coastal regions where the estuarine circulation is weak.  相似文献   

17.
The main idea of this paper is to identify functional relations between seakeeping characteristics and hull form parameters of Mediterranean fishing vessels. Multiple regression analysis is used for quantitative assessment through a computer software that is based on the SQL Server Database. The seakeeping attributes under investigation are the transfer functions of heave and pitch motions and of absolute vertical acceleration at stern, while the ship parameters influencing motion dynamics have been classified into two groups: displacement (Δ) and main dimensions (L, B, T), coefficients that define the details of the hull form (CWP, CVP, LCB, LCF, etc.).Four multiple regression models having different parameter combinations are here investigated and discussed, giving way to the so-called ‘Simple Model’, ‘Intermediate Model’, ‘Enhanced 1 Model’ and ‘Enhanced 2 Model’. The obtained results are more than satisfactory for seakeeping predictions during the conceptual design stage.  相似文献   

18.
The diversity of small-scale wetlands, high salinity tidal creeks, salt marshes, estuaries, and a wide and shallow shelf with the Gulf Stream close to the break makes the coastal zone of south-eastern North Carolina (U.S.) a natural laboratory for the study of the cycling of nitrogen (N) and phosphorus (P) in coastal and shelf waters. We assessed the summer concentrations, forms, and ratios for each N (total dissolved N, nitrate + nitrite, ammonium and dissolved organic N) and P (total dissolved P, o-phosphate and dissolved organic P) pool as these nutrients travel from tidal creeks, salt marshes and two large estuaries to Long and Onslow Bays. Additionally, we measured ancillary physical (temperature, salinity and turbidity) and chemical (dissolved oxygen, chlorophyll a and pH) water properties. Highest concentrations of all individual N and P compounds were found in the upper parts of each tributary and were attributed to loads from agricultural and urban sources to the coastal watersheds, continuing downstream to receiving estuaries. In all areas, dissolved organic N and P species were predominant constituents of the total dissolved N and P pools (64–97% and 56–93%, respectively). The lower parts of estuaries and surface shelf waters were characterized by oceanic surface values, indicating removal of N and P downstream in all tributaries. The different watershed and hydrological characteristics also determined the different speciation of N and P pools in each estuary. Despite a high level of anthropogenic pressure on the uppermost coastal waters, there is self-regulation in this coastal ecosystem with respect to human perturbations; i.e. significant amounts of the N and P load are retained within estuarine and nearshore waters without reaching the shelf.  相似文献   

19.
A three-dimensional hydrodynamic model has been developed to simulate water mass circulation in estuarine systems. This model is based on the primitive equation in Cartesian coordinates with a terrain-following structure, coupled with a Mellor–Yamada 2.5 turbulence scheme. A fractional-step method is applied and the subset of equations is solved with finite volume and finite element methods. A dry–wet process simulates the presence of the tidal flat at low water. River inputs are introduced using a point-source method. The model was applied to a partially mixed, macrotidal, temperate estuary: Southampton Water, UK. The model is validated by comparisons with sea surface elevation, ADCP measurements and salinity data collected in 2001. The mean spring range 2(M2 + S2) and the mean neap range 2(M2 − S2) are modelled with an error relative to observation of 12 and 16%, respectively. The unique tidal regime of the system with the presence of the ‘young flood stand’ corresponding to the slackening conditions occurring at mid flood and ‘double high water’ corresponding to an extension of the slackening conditions at high tide is accurately reproduced in the model. The dynamics of the modelled mean surface and bottom velocity closely match the ADCP measurements during neap tides (rms of the difference is 0.09 and 0.01 m s−1 at the bottom and at the surface, respectively), whereas at spring the difference is greater (rms of the difference is 0.25 and 0.20 m s−1 at bottom and surface, respectively). The spatial and temporal variation of the degree of stratification as indicated by salinity distributions compares well with observations.  相似文献   

20.
三疣梭子蟹(Portunus trituberculatus)是莱州湾最重要的经济蟹类,其资源丰度受栖息环境影响显著,为了解不同的环境因子对其栖息地分布的影响,根据2010~2020年夏季底拖网调查数据,研究莱州湾三疣梭子蟹栖息地适宜性及其影响因子。利用广义可加模型(generalized additive models,GAM)选取变量因子,通过提升回归树模型(boosting regression tree,BRT)对因子进行权重分析,构建了4种栖息地适宜性指数(habitat suitability index,HSI)模型,并通过实测值和预测值的Pearson检验,对模型比较和验证。结果表明,GAM和BRT优化的HSI模型好于其他3种模型(未优化模型,GAM优化HSI模型,BRT优化HSI模型),以生物量表征资源丰度的模型好于尾数表征资源丰度的模型,算术平均法构建的HSI模型的整体预测准确率和相关系数高于几何平均法,对莱州湾三疣梭子蟹栖息地有较强的预测能力。底层水温、底层盐度和水深对三疣梭子蟹栖息地影响较大,夏季栖息地适宜性较高的海域(HSI>0.7)主要分布在莱州湾南部、东南部和东北部海域,中部和西南部海域分布较少。研究结果为莱州湾三疣梭子蟹增殖放流工作提供了科学依据。  相似文献   

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