Low Salinity Values Research Articles

THE INVASIVE RAPA WHELK RAPANA VENOSA (VALENCIENNES 1846): STATUS AND POTENTIAL ECOLOGICAL IMPACTS IN THE RIO DE LA PLATA ESTUARY, ARGENTINA-URUGUAY

Recent range extensions of the invasive rapa whelk Rapana venosa, biological data of the population and possible ecological impacts on the food webs of the Río de la Plata estuary are presented. A total of 41 rapa whelks and 21 egg capsules were collected between February 2004 and March 2006. Specimens were found all over the mixohaline waters of the estuary, with records off Montevideo, Samborombón Bay and off Punta Rasa. Specimens ranged between 28 and 120 mm shell length. Almost all R. venosa presented epibionts all over the shell, suggesting an exposed lifestyle. Egg-masses were attached to specimens of R. venosa, debris and plastic garbage. The spatial distribution of R. venosa within the estuary was coupled with the spatial distribution of Mactra isabelleana, a typical subtidal bivalve of mixohaline waters. The implications for the food webs of the estuary, including possible predators, are discussed. The presence of R. venosa in muddy sediments together with the finding of egg-capsules over the specimens, and the low salinity values at which it is found in the Río de la Plata estuary, confirmed the high plasticity of R. venosa and the potential capability of successfully invading novel environments.

Effects of two hurricanes onSyringodium filiforme, manatee grass, within the Loxahatchee River estuary, Southeast Florida

In September 2004, the Loxahatchee River Estuary was affected by Hurricanes Frances and Jeanne, which resulted in a monthly rainfall record of 610 mm and abnormally high freshwater discharges to the system. The occurrence, density, and biomass ofSyringodium filiforme in the Loxahatchee River Estuary declined significantly following the September 2004 storms based on 15 mo of pre-hurricane monitoring and 12 mo of post-hurricane monitoring. Throughout posthurricane monitoring,S. filiforme showed no sign of recovery, thoughHalophila johnsonii increased considerably during the post-hurricane period. Freshwater discharges resulting from the September 2004 hurricanes lowered minimum daily salinity values to near zero and increased standard deviation of daily salinity values to 11‰. Extremely low minimum daily salinity values and high daily salinity fluctuations likely resulted in the observed decline ofS. filiforme. We advise the use of minimum daily salinity values when assessing seagrass habitat suitability or when modeling the effects of alternative water management scenarios.

Biological Adverse Effects on Bivalves Associated with Trace Metals Under Estuarine Environments

Toxic effects of pollutants on marine organisms can be studied both by performing field measurements, and by undertaking laboratory simulation experiments. Here is described the effect of trace metals Zn, Cd, Pb and Cu on the clam Scrobicularia plana along a salinity gradient simulated in a hypothetical estuary using simulation experiments. The simulator produces a continuous entry of trace metals into the estuary through injection in the lower salinity tank of the system. The clams were exposed during two weeks to different concentration of trace metals to assess the bioaccumulation process along a salinity gradient. Bivalves were analysed for body tissue residue to determine the bioaccumulation factors related to each metal and the salinity influence was addressed. Differences among tanks were observed as a result of the salinity gradient. In the achieved assays, the mechanism of bioaccumulation of Zn and Cd in organisms was more efficient at high salinity values. Bioaccumulation factors for both metals showed a linear increase with the increase of salinity values. It seems that the mechanism of bioaccumulation of Pb and Cu in organisms was dependent on two simultaneous processes: the proximity to the input point of metals and the low salinity values.

Variation of a sandy beach macrobenthic community along a human-induced environmental gradient

Among the diverse sources of impact on sandy coasts, man-made freshwater flows and discharges of sewage effluents strongly modify environmental quality by changing salinity and nutrient regimes. However, sandy beaches, which occupy three-quarters of the world's shoreline, have received relatively little attention concerning consequences of this human-induced disturbance on the structure and dynamics of resident fauna. This paper reports the spatial effects of a freshwater canal discharge (Canal Andreoni) on the habitat and resident macrobenthos of an exposed sandy beach through a combined analysis of communities, populations and the surrounding habitat in three sites defined by previous studies as undisturbed (Barra), moderately disturbed (Coronilla) and grossly disturbed (Andreoni). Andreoni showed significant lower values of salinity, beach width, swash width and slope. Abundance, biomass, species richness, diversity and evenness significantly decreased towards the source of disturbance and were significantly and positively correlated with spatial variations in salinity. Multiple regressions explained up to 36% of the variability, often resulting in models composed by only one significant predictor, salinity, which can be considered as an aggregate variable that carries itself with different simultaneous effects in the nearshore-surf zone environment. The cirolanid isopod Excirolana armata generally dominated all sites in abundance, but at significantly lower values in the grossly disturbed site. The suspension feeders Donax hanleyanus and Emerita brasiliensis, which were well represented at Barra and Coronilla, did not occur in Andreoni, where insects were the most commonly represented after E. armata. In addition, the number of species and abundance of polychaetes tended to decrease towards the canal mouth, with the exception of punctual pulses of abundance of Scolelepis gaucha at Coronilla. In terms of biomass, the isopod E. armata dominated at Andreoni and Coronilla, whereas the suspension feeders D. hanleyanus and E. brasiliensis dominated at Barra. It is concluded that artificial freshwater discharges could significantly influence the distribution, abundance and community attributes of the biota of sandy beaches, and that further study of these ecosystems should include human activities as important factors affecting spatial and temporal trends. The combination of natural experiments together with macrocosm field and microcosm laboratory experiments is also suggested as a rich research vein for detecting the extent of disturbances in sandy beaches.

Biogeochemistry of the Bay of Bengal: physical, chemical and primary productivity characteristics of the central and western Bay of Bengal during summer monsoon 2001

Reliable data on biological characteristics from the Bay of Bengal are elusive. In this paper, we present results on physics, chemistry and biology simultaneously measured during the summer monsoon, 2001 from open ocean and coastal areas of the region. It was characterised by cold core eddies and thermocline oscillations. However, these were capped by prevalent low saline upper regime and prevented surfacing of nutrients. The river plume effects were evident from the low salinity values observed in the surface layers of the upper bay, but this did not bring-in significant amount of nutrients. The chlorophyll a concentrations (10-20 mg m -2 ) and primary productivity values (40-502 mg C m -2 d -1 ) were low and not up to Arabian Sea values for the same season. Diatoms dominated the phytoplankton community and consisted of more number of genera compared to the Arabian Sea. Large colonies of the tunicate, Pyrosoma, which occurred at the surface as well as mid-depths could have consumed a part of the phytoplankton population. These results, albeit limited, have implications on the biogeochemistry of the region.

Diatom-Based Paleoenvironmental Reconstruction of Lake Telmen for the Last 6230 Years

The preserved diatom flora in a 14C dated (0-6230 yBP), 343 cm long core sequence from Lake Telmen, Mongolia, was investigated to determine the nature of the lake-ecosystem and watershed response to Late Holocene climate change. Modern Lake Telmen is a slightly saline (presently 4 g L-1) closedbasin lake located along a N-S and E-W aridity ecotone in north-central Mongolia, making it sensitive to climate-driven changes in effective moisture balance. Diatoms were not preserved regularly in two areas of the Lake Telmen sediment record (5380-41 50 yBP and 1050-425 yBP) possibly due to high carbonate preservation; however, diatom preservation between these areas was good to excellent. Diatom-based paleosalinity reconstruction using species-specific salinity optima from the Northern Great Plains of North America and community analysis suggests the following climate-lake response model during the Late Holocene. From 6230 to 5520 radiocarbon years ago, warm-dry climate resulted in a small salty (20 g L-1) lake in the Telmen basin that was dominated by high salinity indicator species (e.g. Cyclotella caspia, Navicellapusilla, Brachysira aponina). From 3 860 to 1200 radiocarbon yBP, Lake Telmen recorded a period of a modulating climate that resulted in regular fluctuations in paleosalinity from 2 to 4 g L-1 in conjunction with lake level changes. Dominance in the diatom flora fluctuated between the freshwater planktonic form Cyclotella bodanica var. affinis and the salinity-tolerant benthic taxon Anomoeoneis sphaerophora f. costata during this period characterized by generally more humid climatic periods interspersed with dry-as-present conditions. The most modern samples (0-250 yBP) preserve floristic assemblages similar to those found between 3860 to 1200 radiocarbon yBP and indicate that as recently as 250 years ago Lake Telmen had lower salinity values than modern day.

The behaviour of heavy metals from the Guadalquivir estuary after the Aznalcóllar mining spill: field and laboratory surveys.

The spill at 'Los Frailes' caused a large input of metals into the riverine, estuarine and coastal ecosystems. Metal behaviour in natural waters can be studied both by performing field measurements, and by undertaking laboratory simulation experiments. Here is described the behaviour of the heavy metals Zn, Cd, Pb and Cu in the Guadalquivir estuary using incubation experiments and the results compared to those obtained during field assessments. If the toxic waste water had been discharged untreated into the environment, it could have raised the heavy metal concentrations in the estuary water to high values, such as 20.65 microM for Zn and 40 x 10(-3) microM for Cd. These values are several times higher than those obtained in samples collected in the area during the monitoring of the early impact. The metals present a non-conservative behaviour, with a high loss to waters of low salinity values.

NON-MARINE OCCURRENCE OF THE FORAMINIFER CRIBROELPHIDIUM GUNTERI IN NORTHERN LAKE WINNIPEGOSIS, MANITOBA, CANADA

Analysis of sediment samples from the sediment-water interface of Point River Bay, northern Lake Winnipegosis, a very large lake in central Manitoba, indicates that Cribroelphidium gunteri, a coastal marine foraminifer, is living and has adapted to this northern lake environment in salinities as low as 1–2‰. In Point River Bay, summer water temperatures reach 15.6°C, marginally above the minimum 14.5°C required for reproduction by C. gunteri. This benthic foraminifer colonized saline parts of the lake during the warm Holocene Hypsithermal (6000–3500 years BP), probably by avian transport. Previous analysis of stratigraphic data suggested that C. gunteri had died out in this area as conditions became cooler. This hypothesis had been corroborated by the post-Hypsithermal retreat of the marine range of C. gunteri from the Maritimes of Atlantic Canada to the south of Cape Cod, MA. Although recent colonization of the lake cannot be precluded, marine source populations of C. gunteri are now quite distant, making the only viable colonization mode, avian transport, very difficult. The adaptation of the mid-Holocene populations of this species to the progressively colder post Hypsithermal climate and often to extremely low salinity values in Lake Winnipegosis is remarkable. The great abundance of C. gunteri in sediments of Lake Winnipegosis, in some areas making up most of the sediment, also raises potential concerns about the interpretation of supposed marine sections based exclusively on the presence of foraminifera.

Preferential settling of smectite on the Amazon continental shelf

Seventy-five surface and subsurface sediment samples collected on the Amazon continental shelf were analyzed by X-ray diffraction (XRD) in the grain-size fractions smaller than 2 μm. The groups of clay minerals thus identified were smectite, kaolinite, illite, and mixed-layer illite/smectite. Calculation of relative abundance shows a predominance of smectite (37%) in the whole area, followed by kaolinite (27%), illite (23%), and a small percentage of mixed-layer illite/smectite (12%). The distal, northwest region of the continental shelf is characterized by a high abundance of smectite (41%), high salinity values, and high sediment accumulation rates (10 cm year−1), whereas the proximal region is characterized by a comparatively low abundance of smectite (30%), low salinity values, and low sediment accumulation rates (<1 cm year−1). This trend of increasing abundance northwestwards documents a preferential settling of smectite in the distal and more saline regions of this estuarine system.

Influence of net freshwater supply on salinity in Florida Bay

An annual water budget for Florida Bay, the large, seasonally hypersaline estuary in the Everglades National Park, was constructed using physically based models and long‐term (31 years) data on salinity, hydrology, and climate. Effects of seasonal and interannual variations of the net freshwater supply (runoff plus rainfall minus evaporation) on salinity variation within the bay were also examined. Particular attention was paid to the effects of runoff, which are the focus of ambitious plans to restore and conserve the Florida Bay ecosystem. From 1965 to 1995 the annual runoff from the Everglades into the bay was less than one tenth of the annual direct rainfall onto the bay, while estimated annual evaporation slightly exceeded annual rainfall. The average net freshwater supply to the bay over a year was thus approximately zero, and interannual variations in salinity appeared to be affected primarily by interannual fluctuations in rainfall. At the annual scale, runoff apparently had little effect on the bay as a whole during this period. On a seasonal basis, variations in rainfall, evaporation, and runoff were not in phase, and the net freshwater supply to the bay varied between positive and negative values, contributing to a strong seasonal pattern in salinity, especially in regions of the bay relatively isolated from exchanges with the Gulf of Mexico and Atlantic Ocean. Changes in runoff could have a greater effect on salinity in the bay if the seasonal patterns of rainfall and evaporation and the timing of the runoff are considered. One model was also used to simulate spatial and temporal patterns of salinity responses expected to result from changes in net freshwater supply. Simulations in which runoff was increased by a factor of 2 (but with no change in spatial pattern) indicated that increased runoff will lower salinity values in eastern Florida Bay, increase the variability of salinity in the South Region, but have little effect on salinity in the Central and West Regions.

Tectonic and Karstic Effects on the Western Taurus Region, Southwestern Turkey: Relations to the Present Temperature Gradients and Total Organic Carbon Content

The western Taurus region is one of the promising hydrocarbon provinces and the largest karstic terrain of Turkey. The Mesozoic Beydaglari units deposited in the study area are composed mainly of a carbonate succession which has potential hydrocarbon source rocks of various ages. To confirm the tectonic and karstic influence on the regional temperature gradient and total organic carbon content, subsurface data obtained from four drillholes, and the results of the surface samples and water samples analyses, were used. The low salinity values (less than 2500 mg/liter) of the formation water, and the measured hole temperatures, indicate the presence of the meteoric water circulation in the geologic section. Since the Late Miocene, intensive tectonic deformations and karstification have provided the development of the aquifer characteristics of the Beydaglari units. Water circulation in the aquifer system has influenced the total organic carbon content and karstic conduits within carbonates.

Persistence of colonizing plant species along an inferred successional sequence on a subarctic coastal dune (Québec, Canada)

Coastal dune systems have been extensively studied in various parts of the world, but few investigations have been made in the Subarctic where temperatures remain relatively low during the short growing season. Here, we report the results of a study performed on a subarctic coastal dune system on the east coast of Hudson Bay, Canada. We determined the spatiotemporal dynamics of some important substrate characteristics, described the spatial dynamics of the vascular plant community, and followed temporal changes in the populations of the two major plant species, Leymus mollis (Poaceae) and Lathyrus japonicus (Fabaceae), along a toposequence, from the embryo dunes to the stabilized dune. The observed spatial changes in substrate characteristics were consistent with those reported in studies of lower-latitude dune systems, but they were generally of lesser magnitude. The subarctic climate appears to have unusual effects on the spatial gradient of substrate salinity and water content. For instance, salinity did not vary along the toposequence early in the season while the bay was still partly frozen, but it showed a significant gradient during the summer, with lower salinity values on the stabilized dune. Life-form turnover, from the upper beach to the stabilized dune, was lower than what has been reported for lower-latitude dune systems because of the rarity of annual plant species. Although the density and biomass of Leymus and Lathyrus ramets decreased along the toposequence, both species persisted onto the stabilized dune where they were the most frequent vascular plants. Such persistence appears to be related to the ability of both species to physiologically adjust to local conditions. Because of the climatic context, subarctic coastal dunes constitute unique systems, with characteristics quite different from those of lower-latitude coastal dune systems.

The effect of salinity on the growth rate of the macroalgae Enteromorpha intestinalis (Chlorophyta) in the Mondego estuary (west Portugal)

Abstract The excessive growth of opportunistic macroalgae in estuaries and other coastal areas, characterised by enormous values of vegetal biomass in the form of dense mats, is a common and widespread picture nowadays. In such conditions, macroalgae completely dominate the nutrient dynamics in the ecosystem and function as high quality food for the microbial, meio- and macrofaunal communities. Due to their important role in the nutrient pathways of the ecosystems, it becomes essential to obtain new information on variables and processes that regulate the bloom formation of these primary producers. The Mondego estuary (west Portugal) is a eutrophic estuary, where usually macroalgae of the genera Enteromorpha seasonally bloom. Nevertheless, in years with high precipitation characterised by a significant increase of the freshwater runoff to the system, no Enteromorpha blooms are observed. Possible explanations for this are related to the reduction of light in the water column, high water speed, high sediment turbulence and low salinity values. Thus, because the decrease in salinity seemed an important feature during such periods, a set of experiments were conducted, to evaluate to what extent the growth of Enteromorpha intestinalis (the most abundant species in the Mondego estuary) is affected by fluctuations in salinity and, particularly, by low salinity values. In the laboratory, the growth rate of E. intestinalis was tested against a range of salinity, from 0 to 32 psu. E. intestinalis showed the lowest growth rates at extreme low salinity values (≤ 3 psu) and for salinity ≤ 1 psu, the algae died. Growth rates at salinity lower than 5 psu and higher than 25 psu were also low, when compared with growth between salinity of 15 and 20 psu, where E. intestinalis showed the highest growth rates. These results agree with the field observations and suggest that, in the Mondego estuary, salinity is an important external parameter to control the growth of E. intestinalis, which has important ecological implications for the system.

Tracing dissolved organic substances and nutrients from the Lena River through Laptev Sea (Arctic)

Abstract Dissolved organic substances and inorganic nutrients were determined in the central and northern Laptev Sea north of the Lena delta region in August 1995. These results are discussed with data from the Lena River from July 1994. Enhanced concentrations of dissolved organic matter (DOM) and silicate in the Lena River generate a concentration gradient extending towards the oceanic regions of the Laptev Sea. Several parameters show higher concentrations in a plume of low salinity water ( a concentrations. While inorganic nutrients increased with depth, all components of DOM decreased. Of these, carbohydrates decreased most rapidly. The distribution of DOC is largely controlled by conservative mixing. A correlation between salinity and silicate indicates its riverine input. Most of the silicate values are below the theoretical dilution line between river and ocean reflecting biological uptake. The distributions of carbohydrates and amino acids were quite variable, with the higher concentrations generally associated to low salinity and high chlorophyll values. Lignin phenols, which are unequivocal tracers for terrestrially derived organic matter, were about 23 nM in the Lena delta region, 7 nM in the lower salinity water and about 2 nM in areas less influenced by river runoff. From these values we estimate that the contribution of riverine derived freshwater to the water budget in the Laptev Sea is about 30 to 10%, decreasing towards the Eurasian Basin. Calculation based on this proportion and on the concentrations of DOC in the Lena River and the Laptev Sea indicate that about 60% of the DOC in the surface layer of the Laptev Sea is of terrigenous origin.

The importance of open-boundary estimation for an Indian Ocean GCM-data synthesis

The Indian Ocean general circulation is estimated by fitting the MIT Ocean General Circulation Model to the annual mean climatological hydrography and surface forcing, using the model and its computer-generated adjoint. Open boundary conditions are implemented to the west of the Indonesian Archipelago and near 30S. The approach simultaneously optimizes the initial conditions of the hydrographic fields, surface fluxes, and the open boundary conditions (temperature, salinity, and horizontal velocities). Compared to previous results obtained in a closed domain, the estimated velocity field shows a marked improvement near the southern boundary, with a reasonably strong Agulhas Current leaving the model domain. The Indonesian throughflow (ITF) is estimated as 2.7 Sv (1 Sv is 10^6 m^3/s) westward, which is on the low end of the range of previous estimates. The model is able to sharpen fronts in surface salinity, compared to climatology, and suggests that the low surface salinity values in the eastern equatorial region arise from advection out of the Bay of Bengal rather than from the ITF. Consistent with the closed-domain results, the meridional overturning is dominated by a shallow (above 500 m), wind-driven cell of 16 Sv maximum, which carries the bulk of the southward heat transport. We have defined generalizations of meridional heat and freshwater transports appropriate in the presence of a throughflow. The estimated meridional heat transport has a maximum of 0.8 PW at 12S, maximum freshwater transport is 0.29 Sv southward at 9S. The meridional transport divergences are well balanced by the surface heat and freshwater fluxes, indicating near-steady state and small influence of the ITF.

Implications of groundwater weathered profile interactions to the mobilization of radionuclides

This study reports the nature and extent of open-system interaction between groundwater and a weathered profile developed in the high grade thorium and REE ore body in Morro do Ferro, Poços de Caldas plateau. The radioelement mobility in the shallow oxidizing environment was considered by using chemical data in conjunction with 234U/ 238U, 226Ra/ 230Th, 230Th/ 234U, 228Th/ 232Th, 228Ra/ 232Th and 230Th/ 228Ra activity ratios (AR’s) for borehole spoil and groundwater samples. Recharging groundwater from the studied borehole has low salinity values, with total dissolved solids content of 14.7 mg/l and total ionic strength of 0.00018. The ratio of the weight of dissolved radioelement per unit volume of solution to the weight of radioelement in solid phase per unit weight of solid phase showed that the radioelement solubility in the studied waters varied according to the following order: radium>uranium>thorium. 234U/ 238U AR’s less than 1 were measured in solid phase and can justify the enhancement of 234U in solution. 226Ra/ 230Th AR’s greater than 1 and 230Th/ 234U AR’s less than 1 were evaluated between 20 and 27 m in depth, where a 2.1-m thick magnetite dike was intersected. These ratios could be justified by deposition of U and Ra associated with Fe-Mn oxides and kaolinite, where mineral saturation indices evaluated from the available data confirm this possibility. Covariations among disequilibria involving 228Th/ 228 Ra and 228Ra/ 232Th AR’s showed the preferential removal of 228Ra relative to Th isotopes, 228Th and 232Th. The recent deposition of radium within the timescale of at least the last 35 years also is suggested.

Seasonal and inter-annual variability in properties of surface water off Santander, Bay of Biscay, 1991–1995

The annual cycle of temperature, salinity and nutrients of surface waters (up to 100 m depth) was studied from June 1991 to December 1995 in a cross-shelf section over the continental shelf waters off Santander (southern Bay of Biscay). The time series showed that the temperature followed the expected seasonal warming and cooling pattern, which determines a seasonal process of stratification and mixing of the water column. The stratification period occurs annually between May and October in a layer of about 50 m depth from the neritic station beyond to the shelf-break. In the period between November and April the water column remained mixed. During spring and summer low salinity values were found in the surface due to continental runoff and advection from oceanic waters. In late autumn and winter, the salinity pattern was governed by an influx of salty water associated with the poleward current. As in other temperate latitudes, nitrates showed the highest values in winter throughout the water column and the lowest values at the surface during the stratified period. Wind-induced upwelling events were observed mainly in summer, which are characterised by low temperatures (< 12°C), high salinity and nutrient concentrations. The inter-annual variability of temperature showed a warming trend in the upper layers but this sign was not found at 100 m depth. In salinity a decreasing trend was observed throughout the water column, and this feature corresponds to the relaxing of the high salinity anomaly detected in the North Atlantic at the beginning of the 1990s. Both trends were coherent in the cross-shelf section from the coast to the slope.

Salt marsh foraminifera from the Great Marshes, Massachusetts: environmental controls

By using sites in the Great Marshes at Barnstable (Massachusetts, USA) this study examines the effects of a set of environmental parameters on the foraminiferal distribution. The studied parameters are: elevation above mean high water; salinity of the porewater; various sediment characteristics; vegetation; and food source. Relations between the environmental parameters and foraminiferal properties (frequencies, densities and diversities) are quantified with correlation coefficients. For the first time Siphotrochammina lobata and Balticammina pseudomacrescens are documented in the New England region. The following species show a significant correlation with one or more of the studied parameters and are designated as key-species: Haplophragmoides manilaensis, Jadammina macrescens, Balticammina pseudomacrescens, Miliammina fusca and Tiphotrocha comprimata . Based on cluster analysis and the presence, absence or dominance of the key-species characteristic associations are distinguished. The distribution of three associations is indicative of specific marsh environments: the marsh fringe, the middle marsh and the marsh edge. These three marsh units are separated by their own salinity regime, flooding and sediment characteristics. The marsh fringe is typified by the H. manilaensis Association and experiences freshwater input (seepage, surface runoff and rainwater) and only slight marine influence, resulting in low salinity values (2.5–20‰). The width of the marsh fringe is variable, dependent on the amount of seepage which in turn is controlled by the permeability of the basement and the peat. The J. macrescens Association characterizes the middle marsh where salinities are controlled by infiltration of sea- and rainwater and by evaporation. Salinity values are higher than 20‰, while temporarily salinity can reach extreme high values during periods without flooding and high evaporation rates (e.g., 44‰). The fully marine M. fusca Association occupies the daily flooded marsh edge where the salinities have the same values as Cape Cod bay water (ca. 28‰). Unlike many other salt marshes the distribution of foraminiferal assemblages in the Great Marshes does not show a vertical zonation with respect to mean high water. This shows that a worldwide applicable model for paleoenvironmental studies in salt marshes based on foraminifera is not feasible. Each salt marsh has its own characteristics. Regional factors such as climate play an important role in the salinity regime, while the local upland characteristics determine if seepage takes place. Thus each marsh has its own foraminiferal fingerprint showing the opportunistic behaviour of the salt marsh agglutinants. A surface study is an indispensable first step in assessing the value of foraminifera as paleo-ecological indicators.

Partitioning of hydrochlorinated pesticides to chitin in seawater: Use of a radial-diffusion model to describe apparent desorption hysteresis

Desorption hysteresis has been reported frequently in the literature, with several theories advanced to explain the cause of this phenomenon. Batch experiments were performed to observe sorption-desorption behaviour of endrin and heptachlor epoxide onto chitin in seawater as a function of chitin concentration, temperature and salinity. For full range of solids concentrations, sorption was described by a single linear partition coefficient. Desorption hysteresis was found at low chitin concentrations for endrin, increasing both at low temperatures and high salinity values. Results of these experiments were interpreted with a radial-diffusion sorption rate model. Model predictions of the desorption experiments showed that slow desorption rates explained most of the apparent hysteresis. The “salting effect” in marine systems makes partition coefficients ∼ 0.2 log unit higher than comparable partition coefficents measured in freshwater.

La présence de fossiles marins dans le Crétacé terminal des Andes centrales et ses conséquences paléogéographiques

The Maastrichtian deposits (late Campanian? to early Danian?) of the central Andes comprise three transgressive-regressive sequences. In Bolivia (El Molino Formation) they have yielded diverse terrestrial, brackish-water or marine fossils, which make it possible to define the depositional environments at their exact stratigraphic position. Marine-influenced transgressive facies are by far the best developed in the first sequence. Among the vertebrates, five groups of fishes are restricted, with some rare exceptions, to marine environmentsl. Some other fish families, genera or species, are known to occur both in freshwater, brackish and marine environments and therefore provide no precise environmental indications. Among the invertebrates, echinoids, serpulids, foraminifera and some pelecypods and gastropods attest to a marine-influenced environment, which may however have experienced periodic salinity variations. The other pelecypods and gastropods generally indicate freshwater environments. The ostracods, often ubiquitous, only provide paleoecologic indications when they constitute oligospecific shell beds, suggesting abnormally low salinity values. Calcispheres and dinoflagellates indicate a stronger marine influence. Charophytes, especially when abundant, suggest a lacustrine environment. Because of their stratigraphic and paleogeographic positions, stromatolites may indicate intertidal to supratidal environments. The fossils most likely of marine generally occur in the transgressive lower parts of the three sequences, where marine oolites and glauconite are also observed. The often endemic nature of the marine assemblages, the common occurrence of dwarfism and the lack of true nektonic forms suggest that most part of the basin was permanently rather shallow and subjected to important, frequent and/or local, salinity variations. The freshwater fishes appear to be reworked and dissociated in the marine levels, but are better preserved in the mainly continental upper parts of the sequences. Marine fossils are rare in the upper sequence. These data contradict with interpretations which suggest that the central Andean Senonian deposits are exclusively terrestrial. Given other paleogeographic constraints, we propose that Maastrichtian sedimentation took place in a wide, elongated, subsident basin, forming the eastern foreland of the paleo-Andes and showing a “cul-de-sac” shape in the south. This restricted basin was periodically connected with the open sea through present-day Venezuela. The salinity of its southern part, situated far from the basin mouth, was shallow and affected by fresh water from inflowing rivers.