Pore Water Salinity Research Articles

Phenotypic Variation Among Invasive Phragmites australis Populations Does Not Influence Salinity Tolerance

Phenotypic variation within species can have community- and ecosystem-level effects. Such variation may be particularly important in ecosystem engineers, including many invasive species, because of the strong influence of these species on their surrounding communities and environment. We combined field surveys and glasshouse experiments to investigate phenotypic variation within the invasive common reed, Phragmites australis, among four estuarine source sites along the east coast of North America. Field surveys revealed variation in P. australis height and stem density among source sites. In a glasshouse environment, percent germination of P. australis seeds also varied across source sites. To test the degree to which phenotypic variation in P. australis reflected genetic or environmental differences, we conducted a glasshouse common garden experiment assessing the performance of P. australis seedlings from the four source sites across a salinity gradient. Populations maintained differences in morphology and growth in a common glasshouse environment, indicating a genetic component to the observed phenotypic variation. Despite this variation, experimentally increased porewater salinity consistently reduced P. australis stem density, height, and biomass. Differences in these morphological metrics are important because they are correlated with the impacts of invasive P. australis on the ecological communities it invades. Our results indicate that both colonization and spread of invasive P. australis will be dependent on the environmental and genetic context. Additional research on intraspecific variation in invasive species, particularly ecosystem engineers, will improve assessments of invasion impacts and guide management decisions in estuarine ecosystems.

Submarine groundwater discharge driven nitrogen fluxes to Long Island Sound, NY: Terrestrial vs. marine sources

Bottom-waters in Smithtown Bay (Long Island Sound, NY) are subject to hypoxic conditions every summer despite limited nutrient inputs from waste-water and riverine sources, while modeling estimates of groundwater inputs are thought to be insignificant. Terrestrial and marine fluxes of submarine groundwater discharge (SGD) were quantified to Smithtown Bay using mass balances of 222Rn, 224Ra, 226Ra and 228Ra during the spring and summer of 2014/2015, in order to track this seasonal transition period. Intertidal pore waters from a coastal bluff (terrestrial SGD) and from a barrier beach (marine SGD) displayed substantial differences in N concentrations and sources, traced using a multi-isotope approach (222Rn, Ra, δ15N-NO3−, δ18O-NO3−). NO3− in terrestrial SGD did not display any seasonality and was derived from residential septic systems and fertilizer. Marine SGD N concentrations varied month-to-month because of mixing between oxic seawater and hypoxic saline pore waters; N concentrations were greatest during the summer, when NO3− was derived from the remineralization of organic matter. Short-lived 222Rn and 224Ra SGD fluxes were used to determine remineralized N loads along tidal recirculation flow paths, while long-lived 228Ra was used to trace inputs of anthropogenic N in terrestrial SGD. 228Ra-derived terrestrial N load estimates were between 20 and 55% lower than 224Ra-derived estimates (excluding spring 2014); 228Ra may be a more appropriate tracer of terrestrial SGD N loads. Terrestrial SGD NO3− (derived from 228Ra) to Smithtown Bay varied from (1.40–12.8)∗106 molN y−1, with comparable marine SGD NO3− fluxes of (1.70–6.79)∗106 molN y−1 derived from 222Rn and 224Ra. Remineralized N loads were greater during the summer compared with spring, and these may be an important driver toward the onset of seasonal hypoxic conditions in Smithtown Bay and western Long Island Sound. Seawater recirculation through the coastal aquifer can rival the N load from terrestrial SGD from a heavily polluted aquifer.

Effects of Small-Scale Armoring and Residential Development on the Salt Marsh-Upland Ecotone

Small-scale armoring placed near the marsh-upland interface to protect single-family homes is widespread but understudied. Using a nested, spatially blocked sampling design on the coast of Georgia, USA, we compared the biota and environmental characteristics of 60 marshes adjacent to either a bulkhead, a residential backyard with no armoring, or an intact forest. We found that marshes adjacent to bulkheads were at lower tidal elevations and had features typical of lower elevation marsh habitats: high coverage of the marsh grass Spartina alterniflora, high density of crab burrows, and muddy sediments. Marshes adjacent to unarmored residential sites had higher soil water content and lower porewater salinities than the armored or forested sites, suggesting that there may be increased freshwater input to the marsh at these sites. Deposition of Spartina wrack on the marsh-upland ecotone was negatively related to elevation at armored sites and positively related at unarmored residential and forested sites. Armored and unarmored residential sites had reduced densities of the high marsh crab Armases cinereum, a species that moves readily across the ecotone at forested sites, using both upland and high marsh habitats. Distance from the upland to the nearest creek was longest at forested sites. The effects observed here were subtle, perhaps because of the small-scale, scattered nature of development. Continued installation of bulkheads in the southeast could lead to greater impacts such as those reported in more densely armored areas like the northeastern USA. Moreover, bulkheads provide a barrier to inland marsh migration in the face of sea level rise. Retaining some forest vegetation at the marsh-upland interface and discouraging armoring except in cases of demonstrated need could minimize these impacts.

Metagenomes from deep Baltic Sea sediments reveal how past and present environmental conditions determine microbial community composition

Microbial communities that lived near the sediment surface in the past become slowly buried and are the source of deep subsurface communities thousands of years later. We used metagenomes to analyse how the composition of buried microbial communities may change to conform to altered environmental conditions at depth. Sediment samples were collected from down to 85m below sea floor during the Integrated Ocean Drilling Program Expedition 347, “Baltic Sea Paleoenvironment”. The sediments vary in age, organic carbon content, porewater salinity, and other parameters that reflect the changing Baltic environment from the last ice age and throughout the Holocene. We found microorganisms capable of energy conservation by fermentation, acetogenesis, methanogenesis, anaerobic oxidation of methane, and reductive dehalogenation. Glacial sediments showed a greater relative abundance of genes encoding enzymes in the Wood-Ljungdahl pathway and pyruvate:ferredoxin oxidoreductase than Holocene sediments. Relative abundance of genes conferring salinity tolerance was found to correlate with the present salinity, even in deep late-glacial sediment layers where salinity has increased since the sediment was deposited in a freshwater lake >9000years ago. This suggests that deeply buried and isolated sediment communities can slowly change in composition in response to geochemical changes that happen long after deposition.

Physicochemical and Geotechnical Alterations to MX-80 Bentonite at the Waste Canister Interface in an Engineered Barrier System

The study investigated the basic geomechanical and mineralogical evolution of the bentonite barrier under various experimental boundary conditions which replicated the near-field Thermo-Hydro-Chemico (THC) conditions in a repository. The relationships between the physicochemical alterations and changes in the geotechnical properties have seldom been studied, especially on a consistent dataset. This paper attempts to link the physicochemical properties of Na-bentonite (MX-80) to the macro-scale engineering functionality of the bentonite post THC exposure. Experiments investigated the impact of THC variables on the engineering and physicochemical functionality of the bentonite with respect to its application within a High-Level Waste (HLW) engineered barrier system. Intrinsic alterations to the MX-80 bentonite under relatively short-term exposure to hydrothermal and chemical conditions were measured. Additionally, two long-term tests were conducted under ambient conditions to consider the impact of exposure duration. The intrinsic measurements were then related to the overall performance of the bentonite as a candidate barrier material for application in a UK geological disposal facility. Findings indicate that exposure to thermo-saline-corrosion conditions (i.e., corrosion products derived from structural grade 275 carbon steel) inhibits the free swell capacity and plasticity of the bentonite. However, the measured values remained above the design limits set out for the Swedish multi-barrier concept, from which the UK concept may take a lead. Corrosion alone does not appear to significantly affect the geotechnical measurements compared with the influence of thermal loading and high saline pore water after relatively short-term exposure. Thermal and corrosion exposure displayed no impact on the intrinsic swelling of the smectite component, indicating that no significant structural alteration had occurred. However, when exploring more complex saline solutions i.e., mixed Na, K and Ca, rather than the reference NaCl, divalent cation replacement was observed within the interlayer exchange site. This was accelerated in higher thermal loading conditions.

Neptunium sorption and redox speciation at the illite surface under highly saline conditions

Neptunium (Np) uptake on illite is investigated in 1 and 3.2 molal (m) NaCl solutions under inert (Ar) atmosphere for 4<pHm<10 (pHm=−log mH+) and 5×10−8<[Np(V)]tot<3×10−4M. In agreement with a previous study in 0.1m NaCl solutions (Marsac et al., 2015a), Np(V) is the prevailing oxidation state in the aqueous solution, but Np uptake by illite is affected by surface induced reduction. The extent of Np(V) reduction to Np(IV) follows the measured redox potential (or the pe=−log ae−), which is influenced by the introduced Np(V) amount, because of the low redox capacity of the illite. The presence of Np(IV) on the solid phase is verified by X-ray Absorption Near Edge Spectroscopy (XANES). We can conclude that Np uptake by illite is not significantly affected by the variation of mNaCl from 0.1 to 3.2m and thus is in agreement with reports on tetravalent actinide and Np(V) sorption to clays at high ionic strength. The combination of (i) the two site protolysis non-electrostatic surface complexation and cation exchange model, (ii) the specific ion interaction theory to calculate activity coefficients for dissolved species and (iii) by accounting for redox equilibria and the stability of surface Np species, the overall Np uptake by illite can be simulated as a function of pHm, pe and mNaCl using a single set of parameters. The present experimental and modeling results are particularly important in the context of deep geological nuclear waste disposal since many sedimentary rocks or clay formations that are deemed suitable for this purpose exhibit highly saline porewaters.

Effect of Pore Water Salinity on Mechanical Properties of Clay Soil

Effect of Pore Water Salinity on Mechanical Properties of Clay Soil

High porewater exchange in a mangrove-dominated estuary revealed from short-lived radium isotopes

We hypothesise that mangroves play an important role in groundwater exchange processes in sub-tropical and tropical estuarine waters. To investigate this, multiple high resolution time series measurements of radium across a tidal estuary (Coffs Creek, NSW, Australia) were performed as well as a spatial survey in both bottom and surface layers. Results from the spatial survey revealed increasing radium concentrations in parts of the estuary surrounded by mangroves. The average radium concentration in estuary areas lined with mangroves was 2.5 times higher than the average concentration at the mouth of the estuary and 6.5-fold higher than upstream freshwater areas. Additionally, the area enriched in radium coincided with low dissolved oxygen concentrations, implying that porewater exchange may drive anoxia. A radium mass balance model based on 223Ra and 224Ra isotopes at different sections of the estuary confirmed higher porewater exchange rates from areas fringed with mangrove vegetation. Estimated porewater exchange rates were 27.8±5.3 and 13.6±2.1cmd−1 (0.8±0.1 and 0.4±0.1m3s−1) based on 223Ra and 224Ra isotopes, respectively. The average saline porewater exchange was∼10-fold larger than the upstream surface freshwater inputs to the estuary. We suggest that mangrove environments within subtropical estuaries are hotspots for porewater exchange due to the complex belowground structure of crab burrows and the effect of tidal pumping. Because porewater exchange releases carbon and nitrogen from coastal sediments, development and modification of mangrove areas in subtropical estuaries have a significant effect on coastal biogeochemical cycles.

Density-dependent shift from facilitation to competition in a dwarf Avicennia germinans forest

The global effort to rehabilitate and restore destroyed mangrove forests is unable to keep up with the high mangrove deforestation rates, which exceed the average pace of global deforestation. Although facilitation theory presents new possibilities for the restoration of heavily degraded mangrove sites, knowledge of tree–tree interactions in stressed mangrove forest ecosystems is too limited to utilize facilitation appropriately. The aim was to determine the mode of local interaction among stressed mangrove trees by investigating the effect of clustering on tree size and crown morphology under contrasting stand densities. The study was conducted in a dwarf Avicennia germinans forest in Northern Brazil, in which tree growth is limited by infrequent inundation and high pore-water salinity. Autoregressive regression, Voronoi tessellation and spatial point pattern statistics were used to address the spatial processes underlying tree interaction. Under low stand density (1.2 trees m−2) dwarf trees which grew in clustered cohorts of A. germinans had a less stunted crown morphology revealing the dominance of a positive neighborhood influence among plants. In contrast, dwarf trees in the denser forest stand (2.7 trees m−2) were interacting competitively as indicated by the more negative effect of neighbors on crown morphology and size. The shift from facilitative to competitive interactions is an important feature of mangrove forest regeneration under harsh environmental conditions. If mangrove trees are unable to regenerate naturally on severely degraded sites, intraspecific facilitation could be used to assist regeneration by planting seedlings in clusters and not evenly spaced.

Salinization of porewater in a multiple aquitard-aquifer system in Jiangsu coastal plain, China

Chemical and isotopic compositions were analyzed in porewater squeezed from a clayey aquitard in Jiangsu coastal plain, eastern China, to interpret the salinity origin, chemical evolution and water-mass mixing process. A strong geochemical fingerprint was obtained with an aligned Cl/Br ratio of 154 in the salinized aquitard porewater over a wide Cl− concentration range (396–9,720 mg/L), indicating that porewater salinity is likely derived from a mixing with old brine with a proportion of less than 20%. Very small contributions of brine exerted limited effects on water stable isotopes. The relationships between porewater δ18O and δD indicate that shallow and intermediate porewaters could be original seawater and were subsequently diluted with modern meteoric water, whereas deep porewaters with depleted stable isotopic values were probably recharged during a cooler period and modified by evaporation and seawater infiltration. The cation–Cl relationship and mineralogy of associated strata indicate that porewater has been chemically modified by silicate weathering and ion-exchange reactions. 87Sr/86Sr ratios of 0.7094–0.7112 further confirm the input source of silicate minerals. Numerical simulations were used to evaluate the long-term salinity evolution of the deep porewater. The alternations of boundary conditions (i.e., the third aquifer mixed with brine at approximately 70 ka BP, followed by recharge of glacial meltwater at 20–25 ka BP, and then mixing with Holocene seawater at 7–10 ka BP) are responsible for the shift in porewater salinity. These timeframes correspond with the results of previous studies on ancient marine transgression-regression in Jiangsu coastal plain.

Characterization and Origin of Brines from the Bakken-Three Forks Petroleum System in the Williston Basin, USA

Brine (also referred to as ‘produced water’) samples were collected from 28 wells producing oil from the Late Devonian-Early Mississippian Bakken and Three Forks Formations in the Williston Basin of eastern Montana and western North Dakota. The samples were analyzed for major ions, trace metals, stable isotopes, and strontium isotopes. The brines in these formations are highly saline with total dissolved solids averaging 308 g/L, almost ten times the salinity of modern seawater. Relative to modern seawater, the brines are enriched approximately 10 to 20 times in [Na], [K], [Cl], and [Br]. Greater enrichments of 100 to 400 times in [Li], [B], [Sr] and [Rb], and 2,000 to 10,000 times in [Cs] and [Ba] are probably due to water-rock interaction (WRI). WRI is further indicated by 87Sr/86Sr values typically between 0.710 and 0.711—considerably larger than marine values of 0.7081 to 0.7083 during this depositional interval. Bakken Formation sediments were deposited in a stratified water column with salinity increasing with depth. The deeper water may have been saturated in calcium carbonate and possibly gypsum, but there is no evidence that halite saturation had been attained. Therefore, brines may have been introduced into the Bakken Formation from the underlying Devonian Prairie Formation or from the overlying Charles Formation before these brines were diluted or replaced by meteoric water. Alternatively, salinity of the native pore water was increased by membrane filtration driven by overpressuring within the Bakken Formation.

The influence of evaporation and rainfall on supratidal groundwater dynamics and salinity structure in a sandy beach

AbstractEvaporation has been recognized as a major driving force affecting coastal aquifer systems. However, its effects on subsurface flow and salinity structure have not been investigated in sufficient detail. This paper presents field measurements and numerical simulations of pore water flow and subsurface salinity structure in the supratidal zone of a sandy beach subjected to evaporation as well as rainfall. It was found that evaporation significantly increased pore water salinity, up to 85 g/L, within a shallow layer, approximately 10 cm below the beach surface. The induced density gradient generated salt fingers near the beach surface, which caused local groundwater circulation (i.e., fingering flow). However, unlike inland aquifers, the salt fingering was significantly diminished by tidal action that prompted the horizontal mixing of salt in the beach. The subsequent precipitation (e.g., rainfall) diluted the evaporation‐induced high saline plume near the beach surface and drove the plume to migrate downward; the plume gradually dispersed and was diluted along the groundwater pathways. The simulation results indicated that evaporation as well as precipitation at the beach surface induced complex driving mechanisms for supratidal groundwater flow. Depending on the intensity at the beach surface, evaporation and rainfall significantly altered the pore water flow and associate solute transport processes in the supratidal zone of the beach.

Microphytobenthos as an indicator of environmental quality status in intertidal flats: Case study of coastal ecosystem in Pertuis Charentais, France

Microphytobenthos communities of different sediment types were investigated in intertidal flats of the coastal area around La Rochelle (Pertuis Charentais, France) in July 2014 and January 2015. Biotic variables of biomass, abundance and species composition of microphytobenthos were evaluated together with environmental variables, including irradiance, sediment temperature, grains size, pore water salinity, pH, nutrients, organic matter, water content and heavy metal concentrations in the sediment. The relationships between biotic and environmental parameters showed that: (1) the microphytobenthos biomass and community structures showed significant differences among different sediment types; (2) variation in the microphytobenthos communities were significantly correlated with environmental variables, especially with the heavy metals, grain size, irradiance, pore water salinity, organic matter and concentration of PO43+ and Si(OH)4; (3) the species number and richness were both significantly correlated with organic matter, and (4) the species Entomoneis corrugate, Navicula aitchelbee and Gyrosigma cf.limosum were positively correlated to heavy metals, and so were N. phylleptosoma, Surirella brebissonii to Si(OH)4 and NH4+ concentrations, and G. acuminatum and S. brebissonii to PO43+ and NH4+. It is suggested that the spatial variation in biodiversity of microphytobenthos may reflect environmental quality status in coastal intertidal ecosystems.

Succession of bacterial community structure and potential significance along a sediment core from site U1433 of IODP expedition 349, South China Sea

To evaluate the potential impact of geological processes and depositional history on shaping the subsurface biosphere, the bacterial community structures in a sediment core of the South China Sea was investigated by molecular approaches that target 16S rRNA gene fragments. Samples were obtained from different lithologic intervals at site U1433 during the International Ocean Discovery Program (IODP) Expedition 349. Bacterial abundance decreased rapidly with depth, with nearly three orders of magnitude decline within the first 100m below seafloor (mbsf). Community diversity displayed a similar decreasing pattern, yet, a slight increase in diversity emerged in the early to middle Miocene. Such excursion might reflect enhanced cell activity in response to increasing temperature due to a steep geothermal gradient. Non-metric multidimensional scaling ordination revealed that the bacterial communities along the sediment core represent four clusters based on depth and geological time. There were distinct bacterial community shifts among clusters at 4.50–98.93mbsf (Pleistocene), 108.15–273.20mbsf (Pleistocene), 296.09–709.13mbsf (Pliocene and late Miocene), and 732.10–789.91mbsf (early to middle Miocene). Classification analysis revealed a striking pattern: the relative abundance of microorganisms affiliated with Gammaproteobacteria, Actinobacteria, and Cyanobacteria overall consistently decreased with depth, whereas those affiliated with Chloroflexi, candidate division OP9, candidate phylum BHI80-139, and Nitrospirae increased; these findings correspond to different clusters. Total organic carbon content and ratio of total organic carbon: total nitrogen, along with pore water phosphate concentration and salinity, were the statistically most significant variables that explained the bacterial community cluster pattern, which indicates potential linkages of bacterial communities to changes in quality and quantity of buried organic matter over geological time scales. Geographic isolation across depth was more important than environmental condition and geological age for the development of unique community structure in marine deep biosphere, although environmental variables partially shaped bacterial community composition.

Effects of beach slope breaks on nearshore groundwater dynamics

AbstractInteractions between fresh groundwater and seawater affect significantly the nearshore pore water flow, which in turn influences the fate of nutrients and contaminants in coastal aquifers prior to discharge to the marine environment. Field investigations and numerical simulations were carried out to examine the groundwater dynamics in the intertidal zone of a carbonate sandy aquifer on the tropical island of Rarotonga, Cook Islands. The study site was featured by distinct cross‐shore slope breaks on the beach surface. Measured pore water salinities revealed different distributions under the influences of different beach profiles, inland heads, and tidal oscillations. Fresh groundwater was found to discharge around a beach slope break located in the middle area of the intertidal zone. The results indicate a strong interplay between the slope break beach morphology and tidal force in controlling the nearshore groundwater flow and solute transport. The fresh groundwater discharge location was largely determined by the beach morphology in combination with the tidal force. The nearshore groundwater flow can be very sensitive to beach slope breaks, which induce local circulation and flow instabilities. As slope breaks are a common feature of beaches around the world, these results have important, general implications for future studies of nutrients transport and transformations in nearshore aquifers and associated fluxes via submarine groundwater discharge.

Rediscovery of Ellobium scheepmakeri (Petit De La Saussaye, 1850) (Mollusca: Gastropoda: Ellobiidae), a rare ellobiid in Bukit Belimbing mangrove forest, Peninsular Malaysia

ABSTRACTThe ellobiid Ellobium scheepmakeri (Petit de la Saussaye, 1850) is reported from the banks of the Selangor River estuary, 57 years after it was first collected in Peninsular Malaysia. It was found in abundance under logs in the dryland mangrove forest of a dominantly Nypa swamp at the upper reaches of the Kuala Selangor estuary where sediment pore water salinity was recorded at 6–7 ppt.

Carbonate and silicate cementation of siliciclastic sediments of the New Jersey shelf (IODP Expedition 313): relation with organic matter diagenesis and submarine groundwater discharge

The New Jersey continental shelf extends 150 km off the shoreline. During IODP Expedition 313, siliciclastic deposits of late Eocene to late Pleistocene age were drilled down to 631, 669 and 755 m below seafloor at sites 27A, 28A and 29A respectively in very shallow waters (33.5 to 36 m depth). Pore water salinities display multilayered brackish-salty-brine units 10 to 170 m thick, where low-salinity water is preferentially stored in fine-grained sediments. The sharp boundaries of these buried aquifers are often marked by cemented layers a few centimetres thick. The mineralogy and scanning electron microscope observations of these layers show two phases of cementation by authigenic minerals: (1) the early carbonate cement is frequently associated with pyrite, and (2) the late silicate cement infills the residual porosity. The isotopic compositions of the carbonate cements vary widely: −2.4 < δ18O ‰ VPDB < +2.8; −15.1 < δ13C ‰ VPDB < +15.6. The δ18O values indicate that the carbonate cements precipitated with pore waters comprising variable mixtures of seawater and 18O-depleted fresh water originating from submarine groundwater discharge. The δ13C values of the carbonate cements are related to organic matter diagenesis, providing 13C-depleted dissolved inorganic carbon during bacterial sulphate reduction and anaerobic oxidation of methane, and 13C-rich dissolved inorganic carbon during methanogenesis. The diagenetic cementation processes included chemical weathering of reactive silicate minerals by the CO2-rich pore waters issued from organic matter diagenesis that released bicarbonate, cations and dissolved silica, which were further precipitated as carbonate and silicate cements. The estimated range of temperature (18±4 °C) during carbonate precipitation is consistent with carbonate cementation at moderate burial depths; however, silicate cementation occurred later during diagenesis at deeper burial depths.

Effects of soil abiotic factors on the plant morphology in an intertidal salt marsh, Yellow River Delta, China

Plant morphology plays important role in studying biogeography in many ecosystems. Suadea salsa, as a native plant community of northern China and an important habitat for diversity of waterbirds and macrobenthos, has often been overlooked. Nowadays, S. salsa community is facing great loss due to coastal reclamation activities and natural disturbances. To maintain and restore S. salsa community, it's important to address the plant morphology across marsh zones, as well as its relationships with local soil abiotic conditions. In our studied intertidal salt marsh, we found that less flood disturbance frequency, softer soil conditions, rich soil organic matter, total carbon and total nitrogen, lower water depth and water content, less species competition will benefit S. salsa plant in the morphology of high coverage, above-ground biomass, shoot height and leaf length. Lower soil porewater salinity will benefit the below-ground biomass of S. salsa. Thus, we recommend managers help alleviate soil abiotic stresses in the intertidal salt marshes, making the soil conditions more suitable for S. salsa growth and succession.

Porewater salinity reveals past lake-level changes in Lake Van, the Earth\u2019s largest soda lake

In closed-basin lakes, sediment porewater salinity can potentially be used as a conservative tracer to reconstruct past fluctuations in lake level. However, until now, porewater salinity profiles did not allow quantitative estimates of past lake-level changes because, in contrast to the oceans, significant salinity changes (e.g., local concentration minima and maxima) had never been observed in lacustrine sediments. Here we show that the salinity measured in the sediment pore water of Lake Van (Turkey) allows straightforward reconstruction of two major transgressions and a major regression that occurred during the last 250 ka. We observed strong changes in the vertical salinity profiles of the pore water of the uppermost 100 m of the sediments in Lake Van. As the salinity balance of Lake Van is almost at steady-state, these salinity changes indicate major lake-level changes in the past. In line with previous studies on lake terraces and with seismic and sedimentological surveys, we identify two major transgressions of up to +105 m with respect to the current lake level at about 135 ka BP and 248 ka BP starting at the onset of the two previous interglacials (MIS5e and MIS7), and a major regression of about −200 m at about 30 ka BP during the last ice age.

Persistent benthic communities in the extreme dynamic intertidal mudflats of the Amazonian coast: an overview of the Tanaidacea (Crustacea, Peracarida)

The extreme dynamics of the Amazonian coast and associated mudbanks raises questions about their unknown resistant infauna. In order to fill the gap, we investigated the seasonal variations of species composition, abundance and population structure of Tanaidacea in two dynamic mudbanks near the coast of French Guiana. Despite the low species richness recorded for this taxon, the very high densities and biomass of tanaids constituted a potential plentiful trophic resource for many coastal species, such as shorebirds, fish, shrimps, and crabs. The estuarine habitat at Sinnamary presented more tanaid species than the bare marine mudflat at Awala-Yalimapo. All species showed strong female-biased sex ratios and differed in range of total length and stage of maturity. The species with smaller body size with sexual maturity occurring at an earlier stage were dominant and widely distributed. Pore water salinity and predator pressure may be considered key factors driving seasonal variations of tanaid abundance and population structure. This study gives a novel insight into the macrobenthos communities along the highly dynamic Amazonian coast.