Estuary Environment Research Articles

Flow unit modeling and fine-scale predicted permeability validation in Atokan sandstones: Norcan East field, Kansas

Characterizing the reservoir interval into flow units is an effective way to subdivide the net-pay zone into layers for reservoir simulation. Commonly used flow unit identification techniques require a reliable estimate of permeability in the net pay on a foot-by-foot basis. Most of the wells do not have cores, and the literature is replete with different kinds of correlations, transforms, and prediction methods for profiling permeability in pay. However, for robust flow unit determination, predicted permeability at noncored wells requires validation and, if necessary, refinement. This study outlines the use of a spreadsheet-based permeability validation technique to characterize flow units in wells from the Norcan East field, Clark County, Kansas, that produce from Atokan aged fine- to very fine-grained quartzarenite sandstones interpreted to have been deposited in brackish-water, tidally dominated restricted tidal-flat, tidal-channel, tidal-bar, and estuary bay environments within a small incised-valley-fill system. The methodology outlined enables the identification of fieldwide free-water level and validates and refines predicted permeability at 0.5-ft (0.15-m) intervals by iteratively reconciling differences in water saturation calculated from wire-line log and a capillary-pressure formulation that models fine- to very fine-grained sandstone with diagenetic clay and silt or shale laminae. The effectiveness of this methodology was confirmed by successfully matching primary and secondary production histories using a flow unit-based reservoir model of the Norcan East field without permeability modifications. The methodologies discussed should prove useful for robust flow unit characterization of different kinds of reservoirs.

Regressive and transgressive cycles in a rift-basin: Depositional model and sedimentary partitioning of the Middle Jurassic Hugin Formation, Southern Viking Graben, North Sea

The Jurassic Hugin Formation consists of shallow-marine sandstones that belong to a significant hydrocarbon reservoir in the Sleipner area in the Norwegian North Sea. The formation encompasses coarsening-upward units of mouth bar and shoreface facies, interpreted to record delta outbuilding during regression; and fining-upward units with tidal channel, dune, and tidal flat facies interpreted as part of an estuary environment during transgression. The correlations reveal that the studied part of the Hugin Formation consists of 8 sequences, each with a transgressive and a regressive unit, representing the transgressive systems tract and the highstand systems tract respectively. The sequences are stacked retrogradationally landward as a result of rapid tectonic subsidence and rifting of the Viking Graben. Rifting led to the development of an elongate graben where tidal currents were amplified, wave-action damped and longshore drift (as sediments supply) reduced or absent. Lowstand and forced regressive systems tracts are not identified, and their absence is interpreted to reflect suppression of relative sea level falls in a rapidly subsiding basin where the basin subsidence rate outpaced any potential fall in eustatic sea level. Through facies interpretation and sequence-stratigraphic correlations between wells, these regressive and transgressive units are shown to exhibit characteristic thickness trends in the form of sigmoidal-shaped wedges, stacked in an offset manner in a landward to basinward orientation. These thickness trends illustrate sediment partitioning within the sequences and are explained by the relationship between accommodation versus sediment supply in terms of mass-balance. During regression, the focus of sedimentation was pushed basinward, and during transgression it was pushed landward as sediments were trapped there. The mapping of these sequence-stratigraphic units serves as input to reservoir models and to help increase recovery and identify new exploration targets.

Multi time-scale evolution of a wide estuary linear sandbank, the Longe de Boyard, on the French Atlantic coast

This trans-disciplinary work combines modeling and observational approaches and offers a unique dataset to study the behaviour of a wide estuary linear sandbank over different time-scales. The sandbank studied, the Longe de Boyard, lies in a macrotidal estuary environment off the French Atlantic coast. Side scan sonar data combined with shipek grab samples and numerical modeling of waves and tides revealed its short-term dynamics. Historical (1824) and present-day (2000 and 2003) bathymetric data combined with numerical simulations of waves and tides and tide-related sand transport in 1824, and seismic profiling, were then used to demonstrate the long-term evolution of the sandbank and how this correlates with the short-term dynamics. The geological evolution (centuries to millennia) was finally deduced from seismic stratigraphy combined with an analysis of vibrocore samples. Most of the long-term morphological changes in the ‘Longe de Boyard’ can be explained by the short-term dynamics involving sand transport convergence driven by both tides and waves. Seaward, the changes in the axial part of the bank correspond mainly to erosion and can be explained by wave and tide ravinment. Shoreward, sediment accretion is related to the convergence of tide-related sand transport during ebb and flood due to the dam-effect of the crest of the bank. The changes in the sandbank since 1824 can also be related to a decrease in the tidal channel cross section. The latter was the result of a 10% decrease in tidal currents and tidal prisms subsequent to the rapid sediment infill, and a related 20% reduction in the water volume of the estuary system where the sandbank lies. Seismic stratigraphy and cores showed that the modern sandbank consists of upper clinoforms made of fine sand built up over a core made of coarse sand and gravel related to high-energy environments. Hence, the Longe de Boyard is not only the result of sand convergence driven by both tides and waves but also integrates decreases in the tidal prism subsequent to sediment infilling of the surrounding estuaries on a century and millenia time-scale.

Chronology of the sedimentary processes during the postglacial sea level rise in two estuaries of the Algarve coast, Southern Portugal

Four profiles of estuarine sediments obtained from boreholes drilled in the Algarve, Southern Portugal were studied in order to reconstruct the process of sediment accumulation driven by the postglacial sea level rise. In addition to the sedimentological analysis, the Foraminifera Index of Marine Influence (FIMI) permitted assessment of the nature and organization of sedimentary facies in the Beliche–Guadiana and Gilão–Almargem estuaries. The Beliche–Guadiana CM5 and Almargem G2 profiles accumulated in a sheltered environment, with the former presenting an almost continuous record of the sea level rise since ca 13 000 cal yr BP. The G1 and G3 profiles from the Gilão–Almargem area represent a more discontinuous record of the last 8000 years, which accumulated in the more dynamic environment of an outer estuary. The integration of all radiocarbon ages of dated levels, led to an estimate of sediment accumulation rates. Assuming a constant position of the sediment surface with respect to the tidal range and a negligible compaction of sediment, the sea level rose at the rate of 7 mm yr −1 in the period from 13 000 to 7500 cal yr BP. This process slowed down to ca 0.9 mm yr −1 from 7500 cal yr BP until the present. The marked historical change in the rate of sediment accumulation in these estuaries also occurred with the accumulation of organic matter and is, therefore, important data for global biogeochemical models of carbon. The main obstacle to obtain higher temporal resolution of the sedimentary processes was the intense anaerobic respiration of organic matter via sulphate reduction, which did not allow any accumulation of peat and, furthermore, led to erasure of the palaeontological record by acid formed from the subsequent oxidation of sulphides.

Early Jurassic shell beds from marginal marine environments in southern Mendoza, Argentina

External estuarine facies in Late Sinemurian beds from the base of the Puesto Araya Formation in the Atuel river region, Mendoza Province, Argentina, contain concentrations of a new species of Cardinioides (a shallow burrowing suspension-feeding Pachycardiidae bivalve) and a low diversity benthic fauna. These bivalves appear in tidal inlet facies of a wave-dominated estuary (environment similar to lagoon-barrier island systems), forming bioclastic lags at the channel bases. The taphonomic attributes (such as shell articulation, degree of fragmentation and abrasion, bioclast size, orientation) change from North to South, from monospecific concentrations of nearly complete large Cardinioides shells with low degree of fragmentation and abrasion, through beds with smaller Cardinioides shells associated with a few bivalves from marine environments, to only isolated fragmented specimens associated with a fully marine biota including not only other bivalves but also brachiopods and ammonoids. This, together with different palaeoecologic, sedimentologic and stratigraphic attributes at the studied localities are evidence of southwards changing environmental conditions from marginal marine (brackish) to fully marine on the eastern margin of the Neuquén basin at that time. From detailed analysis of taphonomic features, size distribution of shells, and the associated fauna at the different localities, the new species is regarded as a brackish water endemic, possibly a low salinity euryhaline species, which inhabited well oxygenated waters. Salinity, turbulence levels and food supply were the main limiting factors in the distribution of the species.

Using Environmental Models to Optimize Sensor Placement

Sensors used in protective applications are conventionally placed on perimeters or over areas in an evenly distributed pattern. However, such patterns may actually be suboptimal, since environmental factors may make some forms of attack more or less likely than others. We describe a protective application of sensors for detecting underwater threats in an urban estuary environment. We demonstrate that environmental information, derived from a computational river current model, can be utilized to optimize sensor placement, increasing detection rates and decreasing the number of required sensors. Simulation results show a significant improvement in detection likelihood for a given number of sensors; alternatively, fewer sensors can be used while still maintaining the detection rate of a conventional approach

A controlling factor approach to estuary classification

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.

BROMINATED FLAME RETARDANTS IN AQUATIC ORGANISMS FROM THE NORTH SEA IN COMPARISON WITH BIOTA FROM THE HIGH ARCTIC MARINE ENVIRONMENT

The extent of trophic transfer of brominated flame retardants (BFRs), including hexabromocyclododecane (HBCD) and seven polybrominated diphenyl ethers (PBDEs), were examined in pelagic and benthic aquatic animals (invertebrates and fish) in a near-shore estuary environment of the southeastern North Sea (Norway; 59 degrees N). Whole-body burdens of HBCD and several of the most abundant PBDEs biomagnified with increasing trophic position in the food web. Biomagnification of HBCD was particularly strong, resulting in whole-body burdens of this compound comparable to those of total PBDEs in the higher-trophic-level species. Body burdens of PBDEs were higher in pelagic than in benthic aquatic organisms. This was particularly evident for the lesser-brominated and volatile PBDE congeners. Atmospheric gas-water-phytoplankton exchange of these volatile compounds over the water surface may account for this observation. The PBDE burdens in pelagic zooplankton from the North Sea were more than 60-fold greater than those in corresponding pelagic zooplankton from the colder high Arctic latitudes (>78 degrees N) of Norway (Svalbard). This great difference may relate to reduced chemical gas-water exchange over open waters at the colder Arctic latitudes. However, previously measured whole-body burdens of BFRs in other aquatic marine organisms from the high Arctic were comparable or even exceeded those in the North Sea samples of the present study. These include sympagic (sea ice-associated) invertebrates and fish accumulating high burdens of particle-associated BFRs. The present study provides new insight regarding the distribution of BFRs in ecologically different compartments of marine ecosystems, essential information for understanding the food-web transfer and geographical dispersal of these compounds.

Discriminatory classification of natural and anthropogenic waters in two U.K. estuaries

The ability to distinguish water inputs from both natural and anthropogenic sources was investigated in the complex environment of an urban estuary (Tyne) and a relatively pristine estuary (Tweed). We used a data set from a total of 11 estuarine transects, comprising measurements of bulk dissolved organic matter (dissolved organic carbon and nitrogen), dissolved nitrogen (total dissolved nitrogen, ammonium, nitrate+nitrite and dissolved organic nitrogen), optical absorbance measurements (a350, S290-350) and fluorescence excitation emission matrix measurements (fluorophores A, H, B and T intensity and A and H emission wavelength maxima). In order to investigate trends within the numerous parameters measured, multivariate statistics were employed. Principal components analyses showed 63.4% of the variability in the total data set can be explained by two sets of components and 74.9% of the variability by the spectrophotometric measurements alone. In both analyses the first component correlated to the mixing of terrestrial and marine waters and the second component was correlated to sources of pollution such as domestic sewage. Within the data set, river flow and terrestrially derived DOM were significantly correlated, and situations with high river input showed an increase in terrestrial signature in the estuary. Discriminant analyses were also carried out and indicated that 59.8% (total data set) and 53.3% (solely spectrophotometric data) of the samples can be correctly classified into their respective groups (water categories) assigned on the basis of salinity and sampling location. Overall the results clearly show the potential of spectrophotometric techniques to discriminate distinct water categories with different DOM characteristics. In particular, measurement of the fluorophore H emission maxima, the spectral slope parameter, S290-350, and fluorophores T and B intensity enabled discrimination of DOM from riverine, estuarine, marine, and sewage affected water categories. The results presented here indicate the ability of spectrophotometric data alone to distinguish between marine, anthropogenic and terrestrial DOM and distinguish terrestrial DOM from different catchments (Tyne vs. Tweed). With current advances in the in-situ deployment of absorbance and fluorescence spectroscopy it is anticipated that multivariate statistics will gain importance as a cost effective, powerful and diagnostic approach to assessing the distributions of water types and their associated DOM characteristics and fluxes at the land-ocean interface.

Characterization of sediment dynamics in an estuary environment using acoustic techniques

In recent years, acoustic-based methods have been developed to characterize the dynamical behavior of loose sediments and bed deposits in very shallow water environments. In this paper, we present preliminary results on the estimation of the dynamic changes in an estuarine environment using data from dual-frequency echosounding at high resolution and contemporaneous hydrological measurements including suspended matter concentration, density subbottom profiling, and data assimilation based on a sediment transport model. Those measurements are being conducted in the lower estuary of the Scheldt (Belgium) at the Sint Anna site where strong tide and season-dependent phenomena can be observed. This allows us to construct a ground-truthed, time-dependent geoacoustic model of the environment, i.e., a characterization of sound speed, density, and attenuation in function of time and depth. Synthetic acoustic data generated by that model will then be used to test inversion methods for monitoring sediment dynamics in real time.

Benthic macrofauna of three saline-lake wetlands on the coastal rim of southern Chile

A coastal-lake wetland is a type of inland water ecosystem that does not occur very frequently in Chile, of which lakes Budi, Huillinco and Cucao are examples. Textural differences were found in the various constituent parts of the coastal lake sediments. Gravel was the smallest fraction and showed significant differences among the three coastal lakes (P < 0.05). Significant differences (P < 0.05) were also recorded for the sand and mud fractions. Lakes Cucao and Huillinco are described as muddy sand, in contrast to Lake Budi, which is described as sandy mud, composed primarily of mud with a smaller percentage of sand. There were statistical differences among the lakes with regard to the contributions of organic matter in each fraction. The macrofauna in these bodies of water belongs to the fauna inhabiting estuary environments in southern Chile. Lake Budi had seven taxa, and lakes Huillinco and Cucao ten species of macrofauna each. There were no significant differences in the number of species captured at the three coastal lakes (P > 0.05), but differences did emerge in comparisons made among the sampling stations. Total abundances showed significant differences (P < 0.05) in comparisons made both among the lakes and the stations. Salinity and grain size could be limiting the density and number of species at the lakes.

Geochemical partitioning of lead in sedimetns of the coastal environment, Bay of Bengal

Geochemical partitioning of lead in sediments of the coastal environment of Rushikulya estuary, Gopalpur coast and Bahuda estuary, Bay of Bengal has been carried out over a period of one year. Percentage of dissolved and particular fractions of lead showed significant variations in different seasons because of their involvement in the biochmical cycles. The transport of these fraction of lead into the coastal enviroment have been explained on the basis of adsorption.

A sediment quality triad assessment of the impact of copper mine tailings disposal on the littoral sedimentary environment in the Atacama region of northern Chile

A sediment quality triad (SQT) assessment was made of the impact of copper mine tailings disposal on littoral meiofaunal assemblages in the Atacama region of northern Chile. This situation is unusual in that the disposal is direct into the high-energy coastal system and not via a river estuary or other low-energy environment. This situation also allows for the examination of the impact of copper mine tailings in the absence of confounding effects from other pollutants. The three components of the SQT were: 1. an analysis of the bioavailable metals in both the sedimentary porewater and the adjacent seawater, 2. a microcosm bioassay of both sediments and seawaters using meiofaunal assemblages, and 3. quantitative field samples of the meiofaunal assemblages. Twelve study sites with varying degrees of impact were used, including three reference sites. The study identified that both the meiofaunal assemblage densities and taxa diversities decrease with increasing levels of bioavailable copper, that the Foraminifera and Harpacticoida are sensitive to copper, and that otoplanid Turbellaria are often characteristic of impacted sites; tailings also have both chemical and physical impacts on the environment. In some cases the physical impact of tailings is more important in excluding some organisms e.g. the interstitial polychaete, Saccocirrus sonomacus, from a site than is their chemical impact.

Cost‐benefit analysis and the water framework directive in Scotland

AbstractThe Water Framework Directive seeks to achieve the enhancement of aquatic ecosystem quality for all waters across Europe. However, it recognizes the need to accommodate social and economic considerations, so Heavily Modified Water Bodies may be designated where achievement of the Directive's objectives may result in disproportionate costs. This necessitates the use of cost and benefit data, which may be hard to acquire. Benefits and costs of implementing the Directive also can be tested at the national level. This paper considers the evaluation of costs and benefits at 2 scales in Scotland: microlevel analysis, for case studies on the rivers Tummel and Dee and the Forth Estuary, and macrolevel analysis. In the microlevel analysis, costs of hydroelectric power generation are compared with the marginal benefits of increased fisheries revenues and are argued to be disproportionate. In the estuary environment, the benefits of returning an area to ecologically productive salt marsh and mudflats are compared with the costs of lost agricultural revenue. In the macrolevel analysis, we compare the costs to impacted industries with the estimated national benefits from implementing the Directive. We find that for Scotland as a whole, implementation is predicted to result in positive net social benefits.

Reconstruction of Holocene monsoon history from the Pearl River Estuary, southern China, using diatoms and carbon isotope ratios

This study employs a multiproxy approach in the reconstruction of Holocene monsoon history from sedimentary sequences obtained from the Pearl River Estuary, southern China. A set of modern surface sediment samples were collected within and outside the estuary, and a sediment core was obtained from the mouth of the estuary. A range of modern environmental variables were recorded including water salinity (summer, winter and annual average) and water depth. The diatom results show a good relationship with water salinity, with marine diatoms dominating the more distal samples from outside the main estuary and freshwater diatoms dominating the proximal samples influenced by higher freshwater flux. This pattern is matched by the bulk organic carbon isotopes. The isotope values vary between -21.1 +0.3%0 for samples from the fully marine environment, between -23.2±0.8%. and -23.7±0.8%. for samples from the mid to outer estuary brackish water environment and less than -24.7 + 1.3%. for samples from the inner estuary close to the freshwater sources. Similarly, the C/N ratios vary from below 7+0.6 in the marine end-members to over 14.8 + 3.0 in the freshwater end-members. Both the diatom and carbon data from the sediment core reveal a significant increase in freshwater flux from 8500 cal. yr BP resulting from the enhanced summer monsoon regime in early Holocene. The strength of freshwater flux reached its highest between 7500 and 6000 cal. yr BP. In the last 6000 years, freshwater flux decreased towards present, reflecting a gradual weakening of the summer monsoon.

Cost–Benefit Analysis and the Water Framework Directive in Scotland

The Water Framework Directive seeks to achieve the enhancement of aquatic ecosystem quality for all waters across Europe. However, it recognizes the need to accommodate social and economic considerations, so Heavily Modified Water Bodies may be designated where achievement of the Directive's objectives may result in disproportionate costs. This necessitates the use of cost and benefit data, which may be hard to acquire. Benefits and costs of implementing the Directive also can be tested at the national level. This paper considers the evaluation of costs and benefits at 2 scales in Scotland: microlevel analysis, for case studies on the rivers Tummel and Dee and the Forth Estuary, and macrolevel analysis. In the microlevel analysis, costs of hydroelectric power generation are compared with the marginal benefits of increased fisheries revenues and are argued to be disproportionate. In the estuary environment, the benefits of returning an area to ecologically productive salt marsh and mudflats are compared with the costs of lost agricultural revenue. In the macrolevel analysis, we compare the costs to impacted industries with the estimated national benefits from implementing the Directive. We find that for Scotland as a whole, implementation is predicted to result in positive net social benefits.

Correlation between foraminifera and sedimentary environments in recent estuaries of Southwestern Spain: Applications to holocene reconstructions

A multivariate analysis of the foraminifera collected in three estuaries of southwestern Spain (Guadiana, Piedras, Tinto-Odiel) permits recognition of three main assemblages, with spatial distribution depending on sedimentary environments, grain size classes and salinity variations. Assemblage 1 ( Trochammina inflata, Jadammina macrescens) is typical of salt marsh deposits with high salinity variations and percentages of important silt. Assemblage 2 ( Ammonia beccarii, Ammonia tepida, Astrononion stelligerum, Elphidium williamsoni) includes the most abundant estuarine species, with increasing densities from the channel margin to the subtidal channel. Assemblage 3 ( Quinqueloculina seminulum, Elphidium crispum) is mainly found in the sandy sediments of the subtidal channels located near the mouth, with normal marine conditions. These results and the sedimentological interpretation of seven drill cores collected in the Domingo Rubio Channel (Tinto River) allow reconstruction of the palaeogeographic changes of this small estuary in the last ca. 6500 14C years BP. Seven phases were distinguished, with an evolution from an open marine bay to a very restricted channel limited by broad salt marshes.

Parallel structure among environmental gradients and three trophic levels in a subarctic estuary

We assessed spatial and temporal variability in the physical environment of a subarctic estuary, and examined concurrent patterns of chlorophyll α abundance (fluorescence), and zooplankton and forage fish community structure. Surveys were conducted in lower Cook Inlet, Alaska, during late July and early August from 1997 through 1999. Principle components analysis (PCA) revealed that spatial heterogeneity in the physical oceanographic environment of lower Cook Inlet could be modeled as three marine-estuarine gradients characterized by temperature, salinity, bottom depth, and turbidity. The gradients persisted from 1997 through 1999, and PCA explained 68% to 92% of the variance in physical oceanography for each gradient–year combination. Correlations between chlorophyll α abundance and distribution and the PCA axes were weak. Chlorophyll was reduced by turbidity, and low levels occurred in areas with high levels of suspended sediments. Detrended correspondence analysis (DCA) was used to order the sample sites based on species composition and to order the zooplankton and forage fish taxa based on similarities among sample sites for each gradient–year. Correlations between the structure of the physical environment (PCA axis 1) and zooplankton community structure (DCA axis 1) were strong ( r = 0.43–0.86) in all years for the three marine-estuarine gradients, suggesting that zooplankton community composition was structured by the physical environment. The physical environment (PCA) and forage fish community structure (DCA) were weakly correlated in all years along Gradient 2, defined by halocline intensity and surface temperature and salinity, even though these physical variables were more important for defining zooplankton habitats. However, the physical environment (PCA) and forage fish community structure (DCA) were strongly correlated along the primary marine-estuarine gradient (#1) in 1997 ( r = 0.87) and 1998 ( r = 0.82). The correlation was poor ( r = 0.32) in 1999, when fish community structure changed markedly in lower Cook Inlet. Capelin ( Mallotus villosus), walleye pollock ( Theragra chalcogramma), and arrowtooth flounder ( Atheresthes stomias) were caught farther north than in previous years. Waters were significantly colder and more saline in 1999, a La Niña year, than in other years of the study. Interannual fluctuations in environmental conditions in lower Cook Inlet did not have substantial effects on zooplankton community structure, although abundance of individual taxa varied significantly. The abundance and distribution of chlorophyll α, zooplankton and forage fish were affected much more by spatial variability in physical oceanography than by interannual variability. Our examination of physical-biological linkages in lower Cook Inlet supports the concept of “bottom-up control,” i.e., that variability in the physical environment structures higher trophic-level communities by influencing their distribution and abundance across space.

The food web in the lower part of the Seine estuary: a synthesis of existing knowledge

The Seine estuary illustrates the alterations to estuaries due to human activities heavy releases of pollutants of various origins and significant morphological changes beginning in the middle of the 19th century. The intertidal mudflat surface has been seriously reduced (< 30km2) since the channels of the Seine River came under management. While the role of the Seine estuary in the dynamics of the eastern English Channel ecosystem is recognized as important, the biological characteristics of the estuary remained relatively unknown until the 1990s. Biological diversity was progressively impoverished from the polyhaline zone to the oligohaline zone. In spite of a heavily contaminated environment, the macrobenthic and planktonic fauna of the Seine estuary remains similar to those of other northeastern Atlantic estuaries. The fauna exhibit clear contrasts between areas with very high abundance and others with very low abundance. The pelagic fauna, especially the copepod Eurytemora affinisand the shrimp Palaemon longirostris, are more abundant in the Seine estuary than in other estuaries. Diversified and abundant, Abra alba-Pectinaria koreni and Macoma balthica benthic communities occur, respectively, in the outer and inner parts of the estuary. In subtidal flats, benthic fauna is especially poor in terms of specific richness, abundance and biomass. Paradoxically, considering the high abundance of prey, fish are particularly scarce. Two food webs have been identified. In the oligohaline zone, where turbidity is maximum, the food web is exclusively planktonic, due to dredging that prevented benthic fauna from settling. In the polyhaline zone, fish populations that feed particularly on benthic fauna benefit from low turbidity and high oxygen concentrations. So, in spite of heavy organic and metallic contamination and human activities, the Seine estuary remains a highly productive ecosystem, which provides a nursery for marine fish and feeding grounds for migratory birds. A global management plan appears to be necessary in order to guarantee that the Seine estuary continues to function as it currently does.

World atlas of seagrasses

Seagrasses, a group of about sixty species of underwater marine flowering plants, grow in the shallow marine and estuary environments of all the world's continents except Antarctica. The primary food of animals such as manatees, dugongs, green sea turtles, and critical habitat for thousands of other animal and plant species, seagrasses are also considered one of the most important shallow-marine ecosystems for humans since they play an important role in fishery production. Though they are highly valuable ecologically and economically, many seagrass habitats around the world have been completely destroyed or are now in rapid decline. The World Atlas of Seagrasses is the first authoritative and comprehensive global synthesis of the distribution and status of this critical marine habitat--which, along with mangroves and coral reefs, has been singled out for particular attention by the United Nations Convention on Biodiversity. Illustrated throughout with color maps, photographs, tables, and more, and written by a large team of international collaborators, this unique volume covers seagrass ecology, scientific studies to date, current status, changing distributions, threatened areas, and conservation and management efforts for twenty-four regions of the world. As human populations expand and continue to live disproportionately in coastal areas, bringing new threats to seagrass habitat, a comprehensive overview of coastal resources and critical habitats is more important than ever. The World Atlas of Seagrasses will stimulate new research, conservation, and management efforts, and will help better focus priorities at the international level for these vitally important coastal ecosystems.