Faunal characteristics and sediment accumulation processes in the James River estuary,Virginia

This study was designed to relate fauna characteristics and sediment accumulation processes in the James River, VA and was conducted during June 1981. Physical sedimentary and benthic biological parameters, as well as sediment structure and radionuclide profiles, were evaluated for 11 stations. Faunal distribution patterns reflected species' response to salinity changes along the estuarine gradient, but not to differences in sediment accumulation rates. Levels of bioturbation could not be predicted easily on the basis of faunal characteristics alone. Results suggest that the physical processes of erosion and deposition strongly influence the ability of macrobenthos to bioturbate sediments in this estuary. Areas of rapid deposition (>3 cm y⁻¹) exhibit little evidence of bioturbation, as do areas where erosion, or relatively constant physical reworking of sediments, dominate. Areas with low sediment accumulation rates (0·5-3 cm y⁻¹) exhibit the highest levels of mixing as evidenced in X-radiographs. Estuarine organisms inhabiting soft bottoms are typically ‘opportunistic’, shallow-living and short-lived species, and the composition of their communities is not strongly influenced by rates of deposition. Physical reworking of sediments is most likely to occur near to the sediment-water interface where reworking by shallow-living organisms is most intense. Sediment-mixing processes should be characterized using a range of approaches. The phasing of interactions among erosion, physical transport, deposition and biological mixing must be resolved on the appropriate time scales if the mechanics of processes governing the formation of the sedimentary record are to be elucidated.     

An ecological classification of rocky shores at a regional scale: a predictive tool for management of conservation values

The ecological classification of coastal waters has become an important issue in ecosystem water quality assessment. Previous studies have suggested that abiotic variables seem to be a suitable alternative to biological data for classifying coastal areas at different scales. The study presented here proposes a downscaling methodology for the classification of coastal waters at a regional scale within the NE Atlantic based on standardized data and objective decision rules. Physical variables (temperature, wave exposure, tidal range and radiation) were selected because of their ecological role, availability and statistical decision rules. This information was based on satellite data and mathematical modelling of natural coastal processes. The N and NW Spanish coastline was subdivided into 41 20‐km segments that were classified according to physical variables using the self‐organizing map and k‐means algorithms. To validate the classification with biological data, 21 sites representing the entire range of physical typologies in the study area were simultaneously and consistently sampled. Intertidal macroalgae were identified in each of 10 quadrats of 50 × 50 cm for two to three transects per site, according to a stratified sampling procedure. The coverage of macroalgae was obtained by photographic analysis. The physical classification shows four typologies: Lower Rias, Upper Rias, West Cantabric and East Cantabric. Statistical analyses confirmed the ecological significance of these typologies at the tidal levels where seaweeds were the major structural element (lower and middle intertidal). According to the biological data, the greatest differences were found between the Upper Rias and the rest of the N and NW Iberian Peninsula coast. Thus, the classification methodology has potential application as a management tool.     

Investigating transport pathways in the ocean

The ocean is a very complex medium with scales of motion that range from thousands of kilometers to the dissipation scales. Transport by ocean currents plays an important role in many practical applications ranging from climatic problems to coastal management and accident mitigation at sea. Understanding transport is challenging because of the chaotic nature of particle motion. In the last decade, new methods have been put forth to improve our understanding of transport. Powerful tools are provided by dynamical system theory, that allow the identification of the barriers to transport and their time variability for a given flow. A shortcoming of this approach, though, is that it is based on the assumption that the velocity field is known with good accuracy, which is not always the case in practical applications. Improving model performance in terms of transport can be addressed using another important methodology that has been recently developed, namely the assimilation of Lagrangian data provided by floating buoys. The two methodologies are technically different but in many ways complementary. In this paper, we review examples of applications of both methodologies performed by the authors in the last few years, considering flows at different scales and in various ocean basins. The results are among the very first examples of applications of the methodologies to the real ocean including testing with Lagrangian in-situ data. The results are discussed in the general framework of the extended fields related to these methodologies, pointing out to open questions and potential for improvements, with an outlook toward future strategies.     

Space and time variability of the parameters of ecological economical systems

We propose a procedure for the construction of prognostic models of ecological economical systems based on the combination of dynamical models of natural environments with conceptual models of natural economical complexes. This procedure enables one to study space and time distributions of ecological and economical parameters parallel with the fields of physical, chemical, biological, and other characteristics of the natural environment. With the help of a conceptual model of the “sea-land” natural economical complex in the Sea of Azov used asan example, we show that it is possible to relate the dynamics of the concentrations of pollutants and biological resources of the sea with the economical profitability of fishery and the rates of ecological fines controlling the costs of production. Translated by Peter V. Malyshev and Dmitry V. Malyshev     

Remote sensing of coastal interactions in the Mediterranean region

The coastal regions of the Mediterranean are the site of countless economic and recreational activities, but are threatened by dramatic dangers of misuse and pollution. Adequate tools are needed to study the environmental pressure imposed on these regions by the conflicting needs of protecting their ecological balance and exploiting their natural resources. Coastal ecosystems are very sensitive to the environmental impact of land use in watersheds, along the coast and further inland, of fluvial discharges, and of marine processes. Weathering, erosion, or waste disposal on land, as well as other activities at sea, such as shipping, dumping or oil extraction, are but a few of the factors which would require that the coastal areas be suitably monitored. Modern techniques of environmental assessment call for the use of integrated observation systems. The collection of data with traditional coastal installations remains an important component of such research. However, the large space scales and short time scales of many near-coastal and/or marine processes require the use of (orbital) remote sensors. In particular, optical sensors, operating in the visible/infrared spectral region, have shown their usefulness for providing novel information on physical, geo-chemical and biological processes of the coastal area. Optical remote sensing of the coastal zone finds applications in studies of land use, surface cover, hydrology and coastal ecology at large; of water quality and sediment transport, coastal runoff and circulation, or dynamical processes (looking, e.g., at the evolution of pigment and/or temperature patterns, and their distribution as related to plankton dynamics, currents or river plumes); as well as in those of energy transfer, carbon cycling and climatology in general. Selected applications of optical observation techniques in the Mediterranean region, conducted in the framework of international demonstration programmes (i.e. the Ocean Colour European Archive Network, OCEAN, Project), provide examples of the remote sensing potential in the field of integrated coastal/marine environmental management.     

Threats to sandy beach ecosystems: A review

We provide a brief synopsis of the unique physical and ecological attributes of sandy beach ecosystems and review the main anthropogenic pressures acting on the world's single largest type of open shoreline. Threats to beaches arise from a range of stressors which span a spectrum of impact scales from localised effects (e.g. trampling) to a truly global reach (e.g. sea-level rise). These pressures act at multiple temporal and spatial scales, translating into ecological impacts that are manifested across several dimensions in time and space so that today almost every beach on every coastline is threatened by human activities. Press disturbances (whatever the impact source involved) are becoming increasingly common, operating on time scales of years to decades. However, long-term data sets that describe either the natural dynamics of beach systems or the human impacts on beaches are scarce and fragmentary. A top priority is to implement long-term field experiments and monitoring programmes that quantify the dynamics of key ecological attributes on sandy beaches. Because of the inertia associated with global climate change and human population growth, no realistic management scenario will alleviate these threats in the short term. The immediate priority is to avoid further development of coastal areas likely to be directly impacted by retreating shorelines. There is also scope for improvement in experimental design to better distinguish natural variability from anthropogenic impacts. Sea-level rise and other effects of global warming are expected to intensify other anthropogenic pressures, and could cause unprecedented ecological impacts. The definition of the relevant scales of analysis, which will vary according to the magnitude of the impact and the organisational level under analysis, and the recognition of a physical–biological coupling at different scales, should be included in approaches to quantify impacts. Zoning strategies and marine reserves, which have not been widely implemented in sandy beaches, could be a key tool for biodiversity conservation and should also facilitate spillover effects into adjacent beach habitats. Setback and zoning strategies need to be enforced through legislation, and all relevant stakeholders should be included in the design, implementation and institutionalisation of these initiatives. New perspectives for rational management of sandy beaches require paradigm shifts, by including not only basic ecosystem principles, but also incentives for effective governance and sharing of management roles between government and local stakeholders.     

An aggregate model for the adaptation of the morphology and sand bypassing after basin reduction of the Frisian Inlet

To study the adaptation of the morphology of the Frisian Inlet after basin reduction an aggregate model is developed. In the model, especial attention is given to the sand transport to the down-drift coast. In developing the model the inlet system is divided into three elements, the ebb tidal delta, the Zoutkamperlaag and the tidal flats. Based on observations during the first 18 years after basin reduction the adaptation time scale of the tidal flats is expected to be much larger than that of the ebb tidal delta and the Zoutkamperlaag, essentially reducing the inlet schematization to a two-element system. The dependent variables in the model are the sand volume of the ebb tidal delta and the water volume of the channel. The governing equations are non-linear and for quantitative accurate results are solved numerically. To demonstrate the nature of the solution the equations are linearized assuming the morphological state is close to equilibrium. The linearized equations are solved analytically and the solution is applied to a hypothetical case where the tidal prism of the Frisian Inlet is reduced by 10%. From the analytical solution it follows that the adaptation of the volumes of the two elements, delta and channel, is governed by two system time scales. These system time scales are functions of two local time scales. The local time scales pertain to the adaptation of one element assuming the other element has reached equilibrium. Because there are two system scales the adaptation of the volumes of the delta and channel is not exponential and is not necessarily monotonic. For example, initially the transport of sand to the down-drift coast is larger than the long-shore sand transport entering the inlet system from the up-drift coast, then becomes smaller and after some time increases again to reach the value of the up-drift long-shore sand transport. Comparison of the numerical solution for the actual reduction in tidal prism of 30% with the analytical solution for the 10% reduction in tidal prism shows qualitatively the same results.     

Implications of variability on many time scales for scientific advice on sustainable management of living marine resources

The conceptual basis for understanding and management of living marine resources is built on three basic ecological principles developed in the first half of the past century: the law of the minimum, competitive exclusion, and succession. This paper highlights aspects of these principles that make them insufficient as a sound foundation for understanding and managing marine ecosystems, points out dangers of continuing to use approaches built on them, and presents alternatives which might be more appropriate and of lower risk.To do this, the paper considers variability of marine ecosystems on annual, medium and long-term time scales, highlighting that these scales correspond to less than, approximately equal to, and much greater than, the generation times of dominant predators in the systems. It also considers how each interval of variability may affect directly ecosystems which are controlled from the bottom up, top down, and middle outward, and how position and duration of forcing affect five types of responses: growth, maturation, recruitment, predation, and competition. Generally these five processes have manifestations at the scale of individuals, populations, and ecosystems, attention is drawn to which manifestations are the most significant for each duration and position of forcing.Effects of some combinations of duration of forcing and position of forcing can be explained reasonably well by conventional ecological theory. For other combinations, particularly forcing at time scales of predator generations on top-down or middle-out ecosystems, theory based on contest competition and equilibria are likely to be misleading. In these systems the major dynamics are transients, when many ecosystems are far from their carrying capacities, so scramble competition dominates, and the carrying capacity is not helpful in explaining the system dynamics. This review clarifies the sorts of questions that we should be asking, in order to begin to understand the transient behaviour of these non-equilibrium ecosystems. The answers to the new classes of questions may lead to great improvements in how ecosystems are managed, as well as how their variation is explained.     

Quantitative visualization of geophysical flows using low-cost oblique digital time-lapse imaging

Estuaries and coastal waters are regions where many different important physical processes can be found. Although the physical scale of these processes is often relatively small, their time scales are correspondingly rapid and aliasing is usually a problem in sampling programs. There can be significant spatial variations in mixing and flow patterns, which are usually learned only through long experience in a particular region. Observational and interpretation difficulties might be significantly simplified with a simple remote sensing tool to be used in conjunction with standard techniques. Here, the use of digital time-lapse photography at highly oblique angles as a tool for flow visualization is discussed. The interaction of surface waves with slicks and internal motions can cause apparent changes in the shade and color of water at shallow angles in a way not apparent in downlooking views. The use of time-lapse techniques allows us to isolate time scales of interest and, by "speeding up" low-frequency motions, causes them to become more apparent to the eye. A cheap and portable system based on commercially available equipment is described and various advantages and shortcomings are discussed. Results are shown to illustrate the utility of the observational system.     

Descending surface water at the antarctic marginal ice zone and its contribution to intermediate water: An ice-ocean model

This study concerns the unique physical mechanism of Ekman convergence at the marginal ice zone (ECMIZ) produced by the difference between air-ice drag and air-water drag. A coupled ice-ocean model is used to show the strength and distribution of the ECMIZ with respect to Antarctic Intermediate Water (AAIW) formation, which is important for the uptake of carbon dioxide. Strong ECMIZ occurs in the Atlantic and Pacific sectors from July to October, matched in time and space with ice melting, while it is significantly weaker due to strongly divergent background winds in the Indian sector. Transport analysis by artificial tracer experiments reveals the interannual variability of the ECMIZ correlates well with the Southern Annular Mode (SAM). The downward transport of surface water at the MIZ during a positive SAM (2001) is about 1.4 times as large as that during a negative SAM (2000). In particular the transport in the Atlantic sector is twice that in the Pacific sector in both years. Once the downward flux is analyzed in isolation, the contribution from synoptic scale variability is found to increase the volume transport of surface water in the eastern region of the Pacific. Assuming strong isopycnal mixing, we suggest that ECMIZ is an important mechanism supplying surface water to the formation of AAIW, and its zonal variability is responsible for the interbasin differences in AAIW properties. In particular, the increased ECMIZ and surface melt water input in the Atlantic sector would produce AAIW that is colder and fresher than in the Pacific.     

Lack of significant change in epiphyte biomass with increasing extent of measurement within seagrass meadows

A significant consideration in defining patterns of ecological interest is determining at what spatial scales these patterns are apparent. We performed a mensurative experiment to determine the effect of how changing the extent of sampling, using a fixed grain (panning up), changed our measurements of seagrass epiphyte biomass at a variety of hierarchical spatial scales, ranging from approximately 0.1 m to 2.5 × 10⁵ m. The experiment was performed twice at two sets of nested locations, also capturing an element of seasonality within the spatial extents. While the two regions and their nested locations differed in terms of epiphyte biomass, and values did change over time, mean epiphyte values were invariant at the local scale. This indicates that at the local scale (≤100 m extent), we expect seagrass epiphyte biomass to be relatively homogenous. Contrary to theoretical predictions, we did not detect predictable changes in mean values of epiphyte biomass as sampling extent increased. The results of this study highlight the importance of recognizing the spatial dependence of patterns in heterogeneous environments.     

桶形基础负压沉贯物理模型相似条件建立与比尺初拟

提出了一种确定桶形基础在负压下作准平稳均匀沉贯的物模相似条件和有关相似比尺的简便方法,由这一方法得到的相似比尺可作为尺探讨研究的初设值,通过大小不同尺度的桶基作几次验证性试验对其进行修正,可使之适用。     

A new approach to the local time stepping problem for scalar transport

A new scalar transport method is proposed to reduce computational time when a large number of scalars are transported in coupled hydrodynamic-ecosystem models. The new Local Mass Transport (LMT) method confines subtime transport computations to regions where the local Courant–Freidrichs–Lewy (CFL) number exceeds a given numerical stability criteria for a global (large) time step, but the method does not require either contiguous regions or special boundary algorithms between regions as used in previous Local Time Stepping (LTS) approaches. The new method uses conservative transport of mass rather than dissolved concentration. This approach allows different faces of a single grid cell to use different subtime steps. The new LMT method is further extended to include background filtering (LMTB) so that scalars below a pre-defined background concentration are ignored in transport calculations. This new approach can further reduce computational time where large regions are at or below an irrelevant background concentration. Both LMT and LMTB methods can be more computationally efficient than global subtime stepping.     

Linear evolution of a shoreface nourishment

The morphological evolution of a shoreface nourishment is investigated by interpreting the nourishment as a linear perturbation of the natural system. The nourishment is projected onto the subset of linear eigenmodes with negative growth rates of the morphodynamical system. The evolution of these linear modes then determines the temporal behaviour of the shoreface nourishment. The method is presented, and results are shown for shoreface nourishments of different length scales on a straight coast and subject to normal incidence. Shoreface nourishments are represented by their expansions according to the projection method on a 1:50 plane beach profile. All nourishments are shown primarily to be diffusive features, with long scale nourishments diffusing more slowly than shorter length scale nourishments. Long scale nourishments also exhibit a shoreward movement during their decay. This all indicates that long length scale nourishments may be more beneficial in coastal engineering projects. This study is a first step towards nonlinear projection to study shoreface nourishment behaviour.     

Tuna schools/aggregations in surface longline data 1993–98

Exploratory data analysis of a high‐resolution (hook‐by‐hook), 6‐year time series (1993–98) of observed longline catch data for tunas was used to investigate fine‐scale spatial patterns along individual sets that may be indicative of social behaviour (i.e., schooling) and/or the response of individual fish to favourable extrinsic conditions (i.e., aggregation). Methods of spatial data analysis (i.e., nearest neighbour analysis) that have previously been applied in various other sciences (e.g., forestry and astronomy) were used. Results indicate strong clustering of individual tunas at characteristic scales within the set. Mean Nearest Neighbour Distances (NNDs) were between 100 and 200 m, compared with NNDs of 200–700 m predicted by a heterogeneous Poisson process on the same spatial domain. The results suggest that these adult tunas were either schooling or aggregating at the time of capture; this may therefore be related either to social behaviour or to sub‐mesoscale oceanographic features. An aggregation index was derived from the NNDs, giving a classification method that may be used for similar data and the development of empirical models attempting to relate patterns in fish catch distributions to environmental variables. The success of such models will ultimately depend on elucidating the ecological processes reflected in oceanographic features at biologically meaningful spatial scales.     

Implementation of the European Water Framework Directive: Natural variability associated with the CARLIT method on the rocky shores of the Ligurian Sea (Italy)

The Water Framework Directive (WFD) 2000/60/EC, adopted by the European Community in 2000 with the goal of maintaining and improving the aquatic environments, requires that member states achieve and maintain a good ecological status of all water bodies by 2015. In the marine context, the ecological status has to be quantified applying indexes based on appropriate key biological elements, which allow the categorization of water bodies into five Ecological Status (ES) classes. The CARLIT index is a cartographic monitoring tool enabling the Ecological Quality Ratio (EQR) to be calculated using macroalgae in coastal hard bottoms as a key biological element; at present it is being applied in Spain, France and Italy. To detect actual changes of water quality and, consequently, rely on the application of indexes for the assessment of the ecological status in the marine environment, it is necessary to evaluate their sensitivity to natural variability at different temporal and spatial scales. In this study we present a first quantification of natural (spatial and temporal) variability of EQR‐CARLIT quality assessment in 2006 and 2007 along the Ligurian coast (North‐Western Mediterranean, Italy). The EQR‐CARLIT values recorded along the Ligurian coastline show that natural variability of EQR‐CARLIT is low and that it does not affect the attribution of a given stretch of coast to a particular ES class, in agreement with the major human pressures acting in the area (urbanization, river load, sea‐farming). A small‐scale variability was detected, strengthening the use of cartography of the whole rocky shore, whenever possible, or, alternatively, the assessment of the ecological status for long stretches of coast, to encompass the small‐scale variability due to local factors.     

Cross-shelf exchange in a model of the Ross Sea circulation and biogeochemistry

Transport of warm, nutrient-rich Circumpolar Deep Water (CDW) onto Antarctic continental shelves and coastal seas has important effects on physical and biological processes. The present study investigates the locations of this transport and its dynamics in the Ross Sea with a high-resolution three-dimensional numerical model. The model circulation is forced by daily wind stress along with heat and salt fluxes calculated from atmospheric climatologies by bulk formulae. All surface fluxes are modified by an imposed climatological ice cover. Waters under the Ross Ice Shelf are not included explicitly, but their effect on temperature and salinity is imposed in a buffer zone at the southern end of the model domain. A simple nutrient uptake is calculated based on the climatological chlorophyll distribution and Monod uptake kinetics.Model circulation is strongly affected by bottom topography, due to weak stratification, and agrees with schematics of the general flow and long-term current measurements except near the southern boundary. The sea-surface temperature is similar to satellite estimates except that the warmest simulated temperatures are slightly higher than observations. There is a significant correlation between the curvature of the shelf break and the transport across the shelf break. A momentum term balance shows that momentum advection helps to force flow across the shelf break in specific locations due to the curvature of the bathymetry (that is, the isobaths curve in front of the flow). For the model to create a strong intrusion of CDW onto the shelf, it appears two mechanisms are necessary. First, CDW is driven onto the shelf at least partially due to momentum advection and the curvature of the shelf break; then, the general circulation on the shelf takes the CDW into the interior.