Seasonal Variations In Salinity Research Articles

Picophytoplankton Seasonal Dynamics and Interactions with Environmental Variables in Three Mediterranean Coastal Lagoons

Picophytoplankton (Pico) seasonal dynamics and ecology were investigated in three eutrophic coastal lagoons (Calich, Santa Giusta, and Corru S’Ittiri) located in the same geographic region (Sardinia, Mediterranean Sea). Pico dynamics were examined to determine a relationship with variability in environmental conditions characterizing the three sites, and identify which parameters affected observed Pico dynamics. Results showed Pico density reached 108 cells L−1 and biomass values did not exceed 72.8 μg C L−1. Statistical analyses detected significant differences in hydrographic and nutrient conditions among lagoons, which were also characterized by variable Pico seasonal dynamics and composition. Calich and Santa Giusta were dominated all year around by picocyanobacteria. Maximum picocyanobacteria abundance was observed during summer in both lagoons, associated with the highest temperatures recorded. Picocyanobacteria abundance and nutrient concentrations showed a significant negative and positive correlation in Calich and Santa Giusta, respectively. In contrast, picoeukaryotes dominated Pico assemblages in Corru S’Ittiri, where the highest transparency and salinity and the lowest seasonal variation in salinity were recorded. In Corru S’Ittiri, the maximum Pico abundance was observed in autumn, when lower temperature and the highest nutrient concentrations were observed. Our study provides information on Pico assemblage ecology, which remains scarce in coastal and transitional environments, particularly in Mediterranean climate regimes.

Fingerprinting environmental conditions and related stress using stable isotopic composition of rice (Oryza sativa L.) grain organic matter

Sea level rise (SLR) is a primary factor responsible for inundation of low-lying coastal regions across the world, which in turn governs the agricultural productivity. In this study, rice (Oryza sativa L.) cultivated seasonally in the Kuttanad Wetland, a SLR prone region on the southwest coast of India, were analysed for oxygen, hydrogen and carbon isotopic ratios (δ18O, δ2H and δ13C) to distinguish the seasonal environmental conditions prevalent during rice cultivation. The region receives high rainfall during the wet season which promotes large supply of fresh water to the local water bodies via the rivers. In contrast, during the dry season reduced river discharge favours sea water incursion which adversely affects the rice cultivation. The water for rice cultivation is derived from regional water bodies that are characterised by seasonal salinity variation which co-varies with the δ18O and δ2H values. Rice cultivated during the wet and the dry season bears the isotopic imprints of this water. We explored the utility of a mechanistic model to quantify the contribution of two prominent factors, namely relative humidity and source water composition in governing the seasonal variation in oxygen isotopic composition of rice grain OM. δ13C values of rice grain OM were used to deduce the stress level by estimating the intrinsic water use efficiency (WUEi) of the crop during the two seasons. 1.3 times higher WUEi was exhibited by the same genotype during the dry season. The approach can be extended to other low lying coastal agro-ecosystems to infer the growth conditions of cultivated crops and can further be utilised for retrieving paleo-environmental information from well preserved archaeological plant remains.

BENTHIC FORAMINIFERA AS BIOINDICATORS OF SALINITY VARIATION IN LAKE SHIHWA, SOUTH KOREA

Lake Shihwa suffers from trace-metal pollution discharged from the Banweol stream and the Shihwa Industrial Complex. Installation of floodgates in 2001 increased water exchange and decreased trace-metal content, thereby improving the benthic environment within the lake. We analyzed surface sediments (including grain size, pH, trace-metal concentrations), water-quality data, and the assemblages of, and prevalence of deformities in, the benthic foraminifera, to understand the effects of recent changes in salinity variability. Since spatial and temporal distributions of benthic foraminifera are known to vary in response to both biotic and abiotic environmental variables, they are useful indicators of environmental change. Since the installation of floodgates, surface-sediment composition coarsened from silt to sandy mud/muddy sand in response to increased water flow. Trace-metal contaminants (Ni, Cu and Zn) have decreased and are close to the Effect Range-Low (ER-L) designation. We identified 15 species of benthic foraminifera (3 agglutinated, 10 calcareous-hyaline, and 2 calcareous-porcelaneous). Buccella frigida and Elphidium albiumbilicatum were dominant, but seven sampling localities formed a nearly abiotic zone. Although trace contaminants have decreased, a high prevalence of test deformities (up to 65%) was observed, mostly in E. albiumbilicatum . Our findings suggest these abnormalities may be strongly related to the effects of seasonal variation of salinity in Lake Shihwa.

On the seasonal variations of salinity of the tropical Atlantic mixed layer

AbstractThe physical processes controlling the mixed layer salinity (MLS) seasonal budget in the tropical Atlantic Ocean are investigated using a regional configuration of an ocean general circulation model. The analysis reveals that the MLS cycle is generally weak in comparison of individual physical processes entering in the budget because of strong compensation. In evaporative regions, around the surface salinity maxima, the ocean acts to freshen the mixed layer against the action of evaporation. Poleward of the southern SSS maxima, the freshening is ensured by geostrophic advection, the vertical salinity diffusion and, during winter, a dominant contribution of the convective entrainment. On the equatorward flanks of the SSS maxima, Ekman transport mainly contributes to supply freshwater from ITCZ regions while vertical salinity diffusion adds on the effect of evaporation. All these terms are phase locked through the effect of the wind. Under the seasonal march of the ITCZ and in coastal areas affected by river (7°S:15°N), the upper ocean freshening by precipitations and/or runoff is attenuated by vertical salinity diffusion. In the eastern equatorial regions, seasonal cycle of wind forced surface currents advect freshwaters, which are mixed with subsurface saline water because of the strong vertical turbulent diffusion. In all these regions, the vertical diffusion presents an important contribution to the MLS budget by providing, in general, an upwelling flux of salinity. It is generally due to vertical salinity gradient and mixing due to winds. Furthermore, in the equator where the vertical shear, associated to surface horizontal currents, is developed, the diffusion depends also on the sheared flow stability.

Impacts of extreme weather events on highly eutrophic marine ecosystem (Rogoznica Lake, Adriatic coast)

Rogoznica Lake is highly eutrophic marine system located on the Eastern Adriatic coast (43°32′N, 15°58′E). Because of the relatively small size (10,276m2) and depth (15m) it experiences strong natural and indirect anthropogenic influences.Dynamics within the lake is characterized by the extreme and highly variable environmental conditions (seasonal variations in salinity and temperature, water stratification and mixing, redox and euxinic conditions, concentrations of nutrients) which significantly influence the biology inside the lake.Due to the high phytoplankton activity, the upper part of the water column is well oxygenated, while hypoxia/anoxia usually occurs in the bottom layers. Anoxic part of the water column is characterized with high concentrations of sulfide (up to 5mM) and nutrients (NH4+ up to 315μM; PO43− up to 53μM; SiO44− up to 680μM) indicating the pronounced remineralization of the allochthonous organic matter, produced in the surface waters. The mixolimnion varies significantly within a season feeling effects of the Adriatic atmospheric and ocean dynamics (temperature, wind, heat fluxes, rainfall) which all affect the vertical stability and possibly induce vertical mixing and/or turnover. Seasonal vertical mixing usually occurs during the autumn/winter upon the breakdown of the stratification, injecting oxygen-rich water from the surface into the deeper layers. Depending on the intensity and duration of the vertical dynamics (slower diffusion and/or faster turnover of the water layers) anoxic conditions could developed within the whole water column.Extreme weather events such as abrupt change in the air temperature accompanied with a strong wind and consequently heat flux are found to be a key triggering mechanism for the fast turnover, introducing a large amount of nutrients and sulfur species from deeper parts to the surface. Increased concentration of nutrients, especially ammonium, phosphate, and silicates persisting for several months after the mixing event, together with anoxic stress conditions, additionally influence already stressed ecosystem, hence shifting the community structure and food/web interactions in this marine system.

Effects of osmotic stress on predation behaviour of Asterias rubens L.

Environmental stress plays an important role in determining ecosystem functioning and structure. In estuarine areas both tidal and seasonal salinity changes may cause osmotic stress on predators, affecting their behaviour and survival. The interaction between these predators and their prey may affect performance, thus influencing predator impact on prey populations. The common starfish, Asterias rubens, inhabits estuarine areas, such as the Dutch Wadden Sea, that exhibit large seasonal variation in salinity (10–32PSU). In those areas A. rubens exerts top down control on its prey, thus representing an important shellfish predator. This predation may impact on cultured and natural shellfish populations. However, the effects of osmotic stress on A. rubens performance may influence its effect on prey. Although the effect of salinity in A. rubens survival has been extensively studied, the impact on its predation behaviour and acclimation capacity remains unclear. In this study, we analyse the performance of A. rubens preying on mussels (Mytilus edulis) after a salinity decrease and monitor its acclimation capacity over a period of 22days. Our experiments demonstrated that salinity affected performance by reducing feeding activity and altering size prey selection. Moreover, as acclimation occurred, A. rubens predation performance improved in all sub-lethal treatments. We conclude that osmotic stress caused by decreasing salinity potentially influences A. rubens distribution, abundance, and potential impact on prey populations. However the magnitude of the change in salinity (from 31 to a minimum of 10PSU) and its timescale (3weeks) mediate this effect.

VERTICAL ZONATION OF FORAMINIFERA ASSEMBLAGES IN GALPINS SALT MARSH, SOUTH AFRICA

ABSTRACT Salt-marsh foraminifera are used as precise sea-levelchange indicators as surface assemblages vary in relation totheir position in the tidal frame. Surface-sediment sampleswere collected across an elevation gradient at Galpins saltmarsh, South Africa, to study the vertical distribution offoraminifera and their potential use for sea-level studies. Themarsh is divided into three vertical zones (high marsh, middlemarsh, and mud flats) represented by three assemblagegroups, with agglutinated species restricted to the upperreaches of the marsh and calcareous species more dominanttowards the intertidal channel. The high marsh area isdominated by Jadammina macrescens with a presence ofTrochammina inflata. The middle marsh is characterised byboth T. inflata and Miliammina fusca. Calcareous speciesfound in the mud flats consist of Haynesina germanica,Ammonia batava, and Quinqueloculina sp. This paperdescribes how marsh foraminifera can be used to definesmall-scale vertical zones along modern marsh surfaces andhow these zones correspond to floral zones. We demonstratethat marsh foraminifera have potential to be used as preciseindicators for sea-level reconstructions in South Africa.INTRODUCTIONModern foraminiferal assemblages form discrete verticalzones in salt marshes, strongly correlated with tidal levels(Scott et al., 2001; Gehrels & Newman, 2004). Therelationship between modern foraminiferal distributionand a range of environmental variables, including elevation,vegetation cover, pH, and salinity, can be preciselyquantified (e.g., using multivariate statistics), representinga modern analogue against which to compare fossilassemblages. Salt marshes experience daily and seasonalvariations in salinity and frequency of flooding linked totidal overflow. Several authors suggest that verticalzonation of foraminifera is strongly related to elevation,especially in temperate environments (Scott & Medioli,1980; Scott & Leckie, 1990; Horton & Edwards, 2003, 2006;Leorri et al., 2010).It is well known that a variety of ecological controls exertan influence on the distribution of surface foraminifera(e.g., Murray, 1971; Scott et al., 1998; Horton, 1999),although assemblages are consistently shown to be verti-cally zoned in accordance with tidal frames, either directlyor indirectly (Berkeley et al., 2007). A study conducted inthe Great Marshes of Massachusetts by De Rijk T Horton & Edwards, 2006).Modern analogues of marsh foraminifera are traditionallycollected at the location where a sediment core is extractedfor palaeontological analysis (Gehrels, 1994; Kemp et al.,2009). Where assemblages are identified solely at a singlesite, some fossil samples may lack a modern analogue,thereby compromising the accuracy of the reconstruction(Murray, 2006). This lack of modern analogues could beaddressed by sampling a broader range of contemporaryenvironments (Hayward et al., 2004; Horton & Edwards,2006; Kemp et al., 2009).Researchers have debated the best assemblage make-upfor foraminiferal population studies. Some advocate totalassemblage use, indicating environmental conditions forboth seasonal and temporal fluctuations (Scott et al., 2001;Horton et al., 2005). According to Murray (1971), livingpopulations best represent the modern environment as theuse of dead assemblages alone fails to account for post-mortem changes. However, it can be argued that thedistribution of living assemblages will be dependent on theconditions at time of sampling and not an average overtime. In temperate environments some suggest it isimportant to exclusively use dead assemblages as they arenot susceptible to seasonal variations, thus accuratelyreflecting subsurface assemblages (Murray, 1979; Hortonet al., 2005; Horton & Murray, 2007). On occasion, trainingsets comprised of total assemblages (live + dead) are stillused based on the assumption that live assemblages in timewill contribute to the fossil record (Booth et al., 2010). Astudy conducted on foraminiferal assemblages in surfacesediments from a marsh in Nova Scotia concluded thattotal foraminiferal assemblages provide a good basis forpalaeoenvironmental studies (Scott & Medioli, 1980).Previous studies have described the distribution of salt-marsh foraminifera in temperate environments (e.g. Leorriet al., 2010). The highest intertidal zones are oftendominated by Jadammina macrescens and Trochamminainflata, which are replaced by species such as Haplophrag-moides sp. and Miliammina fusca as elevation decreases(Hawkes et al., 2010). Agglutinated species are prevalent inthe upper and middle marsh while calcareous species arescarce. This relationship depends on the accessibility of

Evaluating the effects of temperature, salinity, starvation and autotomy on molting success, molting interval and expression of ecdysone receptor in early juvenile mud crabs, Scylla paramamosain

Newly molted first stage juvenile mud crabs (C1), Scylla paramamosain, were subjected to different temperatures (14, 20, 26, 32 and 39°C), salinity (5, 10, 20, 30 and 40), starvation conditions and autotomy (for the autotomy experiment, the second stage crabs (C2) were used) to assess their effects on molting success, molting interval and corresponding expressions of the crab's ecdysone receptor (EcR). The results showed that at a low temperature of 14°C no molt occurred with a subdued EcR mRNA level detected. In contrast, a higher temperature of 32°C induced a significant increase in the expression of EcR gene and dramatically reduced the C1 molting interval as compared to other treatments. As the temperature further increased to 39°C and after a period of 6 or more hours the expression of EcR gene dropped abruptly and all C1 crabs died without molt. On the other hand, a low salinity of 5 increased EcR mRNA levels at 72h and shortened the molting interval significantly whilst high salinity of 40 resulted in the opposite. No significant difference in percentage molting success was detected among salinity from 10 to 40. When C1 crabs were subjected to starvation for longer than 48h, the expression of EcR was found to be significantly repressed as compared to the feeding control, in which none of the starved crabs successfully molted. Meanwhile, although the molting success of C2 crabs was not significantly affected by autotomy, the molting interval significantly increased from 5.8days for intact crabs to 6.2days for the autotomized crabs. Interestingly, when compared to intact crabs, the expression level of EcR gene in autotomized crabs was at first repressed (i.e. during the first 120h) but increased sharply to a level significantly higher than the control at 134h (i.e. during premolt stage of the autotomized crabs). Our results showed that temperature, salinity, starvation and autotomy all affected molting of early juvenile mud crabs and changes in their EcR mRNA levels appeared to play an important role in regulating the molting process. The current experiment also showed that S. paramamosain early juveniles could withstand a broad range of temperatures and salinity, therefore highlighting their adaptability to the seasonal variation in salinity and temperature of natural habitat.

Salinity and turbidity distributions in the Brisbane River estuary, Australia

Summary The Brisbane River estuary (BRE) in Australia not only plays a vital role in ecosystem health, but is also of importance for people who live nearby. Comprehensive investigations, both in the short- and long-term, into the salinity and turbidity distributions in the BRE were conducted. Firstly, the analysis of numerical results revealed that the longitudinal salinity varied at approximately 0.45 and 0.61 psu/h during neap and spring tides, respectively. The turbidity stayed at a higher level and was less impacted by tide in the upper estuary, however, the water cleared up while the tide changed from flood to ebb in the mid and lower estuary. The second investigation into the seasonal variations of salinity and turbidity in the BRE was conducted, using ten-year field measurement data. A fourth-order polynomial equation was proposed, describing the longitudinal variation in salinity dilution changes as the upstream distance in the BRE during the wet and dry seasons. From the observation, the mid and upper estuaries were vertically well-mixed during both seasons, but the lower BRE was stratified, particularly during the wet season. The estuary turbidity maximum (ETM) zone was about 10 km longer during the wet season than the dry season. Particular emphasis was given to the third investigation into the use of satellite remote sensing techniques for estimation of the turbidity level in the BRE. A linear relationship between satellite observed water reflectance and surface turbidity level in the BRE was validated with an R 2 of 0.75. The application of satellite-observed water reflectance therefore provided a practical solution for estimating surface turbidity levels of estuarine rivers not only under normal weather conditions, but also during flood events. The results acquired from this study are valuable for further hydrological research in the BRE and particularly prominent for immediate assessment of flood impacts.

Increasing fluctuations of soil salinity affect seedling growth performances and physiology in three Neotropical mangrove species

Micro-tidal wetlands are subject to strong seasonal variations of soil salinity that are likely to increase in amplitude according to climate model predictions for the Caribbean. Whereas the effects of constant salinity levels on the physiology of mangrove species have been widely tested, little is known about acclimation to fluctuations in salinity. Aims and methods The aim of this experiment was to characterize the consequences of the rate of increase in salinity (slow versus fast) and salinity fluctuations over time versus constant salt level. Seedling mortality, growth, and leaf gas exchange of three mangrove species, Avicennia germinans, Laguncularia racemosa, and Rhizophora mangle were investigated in semicontrolled conditions at different salt levels (0, 685, 1025, and 1370 mM NaCl). Results Slow salinity increase up to 685 mM induced acclimation, improving the salt tolerance of A. germinans and L. racemosa, but had no effect on R. mangle. During fluctuations between 0 and 685 mM, A. germinans and R. mangle were not affected by a salinity drop to zero, whereas L. racemosa took advantage of the brief freshwater episode as shown by the durable improvement of photosynthesis and biomass production. Conclusions This study provides new insights into physiological resistance and acclimation to salt stress. We show that seasonal variations of salinity may affect mangrove seedlings’ morphology and physiology as much as annual mean salinity. Moreover, more severe dry seasons due to climate change may impact tree stature and species composition in mangroves through higher mortality rates and physiological disturbance at the seedling stage.

Influence of Seasonal Variations in Sea Level on the Salinity Regime of a Coastal Groundwater–Fed Wetland

Seasonal variations in sea level are often neglected in studies of coastal aquifers; however, they may have important controls on processes such as submarine groundwater discharge, sea water intrusion, and groundwater discharge to coastal springs and wetlands. We investigated seasonal variations in salinity in a groundwater-fed coastal wetland (the RAMSAR listed Piccaninnie Ponds in South Australia) and found that salinity peaked during winter, coincident with seasonal sea level peaks. Closer examination of salinity variations revealed a relationship between changes in sea level and changes in salinity, indicating that sea level-driven movement of the fresh water-sea water interface influences the salinity of discharging groundwater in the wetland. Moreover, the seasonal control of sea level on wetland salinity seems to override the influence of seasonal recharge. A two-dimensional variable density model helped validate this conceptual model of coastal groundwater discharge by showing that fluctuations in groundwater salinity in a coastal aquifer can be driven by a seasonal coastal boundary condition in spite of seasonal recharge/discharge dynamics. Because seasonal variations in sea level and coastal wetlands are ubiquitous throughout the world, these findings have important implications for monitoring and management of coastal groundwater-dependent ecosystems.

Sources of Salinity Variation in a Coastal Lagoon in a Karst Landscape

Bahia de la Ascension (BA) is a shallow, mangrove-fringed coastal bay connected to the Caribbean through two inlets, outlined by the Mesoamerican Barrier Reef System. This work represents an initial investigation of the relative contribution of hydrometeorological and hydrodynamic forcing on salinity variation in this lagoon. Our objective is to assess the sensitivity of the salinity in BA to fluctuations in freshwater inflow and coastal oceanography. Two field trips were undertaken during rainy and dry seasons in 2007. Surface salinity was mapped across the system and CTD deployments carried out within BA and in the sea end-member to characterize temperature, conductivity, and water level. Also, cross-sectional CTD profiles were implemented to examine vertical stratification. The water balance indicated that 16 % of rainfall over the drainage basin (DB) becomes groundwater discharge plus surface runoff into BA during dry season, while 68 % of the precipitation input to the DB is supplied through groundwater–surface runoff to the bay during rainfalls. This combined inflow showed larger fluctuations than direct rainfall and, thus, has a greater potential to alter the seasonal salinity variations within BA. The tidal signal is selectively attenuated within BA, as diurnal frequencies are more readily filtered out than semidiurnal frequencies. Mesohaline conditions in the southwest bay are associated with freshwater sources, while saline water masses in the inlet are influenced by prevalent SE winds in the region and tidal phase, establishing a strong horizontal SW-NE estuarine salinity gradient.

Seasonal variability of salinity and circulation in a silled estuarine fjord: A numerical model study

A three-dimensional hydrodynamic model is used to study seasonal variability of circulation and hydrography in Hood Canal, Washington, United States, an estuarine fjord that develops seasonally hypoxic conditions. The model is validated with data from year 2006, and is shown to be capable of quantitatively realistic simulation of hydrographic variability. Sensitivity experiments show the largest cause of seasonal variability to be that of salinity at the mouth of the fjord, which drives an annual deep water renewal in late summer–early autumn. Variability of fresh water input from the watershed also causes significant but secondary changes, especially in winter. Local wind stress has little effect over the seasonal timescale. Further experiments, in which one forcing parameter is abruptly altered while others are kept constant, show that outside salinity change induces an immediate response in the exchange circulation that, however, decays as a transient as the system equilibrates. In contrast, a change in the river input initiates gradual adjustment towards a new equilibrium value for the exchange transport. It is hypothesized that the spectral character of the system response to river variability will be redder than to salinity variability. This is demonstrated with a stochastically forced, semi-analytical model of fjord exchange circulation. While the exchange circulation in Hood Canal appears less sensitive to the river variability than to the outside hydrography at seasonal timescales, at decadal and longer timescales both could become significant factors in affecting the exchange circulation.

Seasonal variations of the salinity and turbidity in the Brisbane River estuary, Queensland, Australia

ABSTRACT Yu, Y., Zhang, H. and Lemckert, C., 2013. Seasonal variations of the salinity and turbidity in the Brisbane River estuary, Queensland, Australia. In: Conley, D.C., Masselink, G., Russell, P.E. and O'Hare, T.J. (eds.) The Brisbane River estuary, Queensland, Australia, is a vital ecological region and of importance for people who live nearby. The estuarine health status has been influenced by both marine and riverine conditions. The estuary experiences high turbidity and salinity throughout most of the year, however, little is known about the actual turbidity and salinity structures within it. This study examined ten-years of field data to investigate the seasonal variations in salinity and turbidity. The results revealed that the salinity at the Brisbane River mouth was estimated to be 31.7 and 32.8 ppt during wet and dry seasons, respectively. The surface longitudinal salinity then decreased along the estuary, with the highest decreasing rates of 0.7 and 0.6 ppt/km occurring within the mid-estuar...

Structure and dynamics of distinct fish assemblages in three reaches (upper, middle and lower) of an open tropical estuary in Brazil

AbstractWe collected fishes and environmental variables in three zones (upper, middle and lower) of a small open tropical estuary during flood tide. The aim was to test for differences in fish assemblages along a gradient from freshwater to marine waters and to detect any seasonal variation in fishes and environmental variables across these zones. A total of 111 species (18 in the upper, 50 in the middle and 66 in the lower estuary) were recorded, forming three distinct fish assemblages, with the family Eleotridae dominating in the upper, Gerreidae in the middle, and Sciaenidae in the lower estuary. Only two species (Geophagus brasiliensis in the upper and the middle zones, and Eucinostomus argenteus in the middle and the lower zones) composed more than 1% of the total number of individuals in more than a single zone. Short‐term (tidal) changes in salinity in the middle estuary were associated with different assemblages in the three estuarine zones, even in winter, when the differences in salinity are lowest between the middle and the lower zones. Seasonal variation in salinity was irrelevant, except in a protected sidewater lagoon in the middle estuary. Low salinity seasonal change may be related to the lack of seasonal variation in the structure of fish assemblages in all estuarine zones.

Water Quality and Soil Natural Salinity in the Southern Imera Basin (Sicily, Italy)

The Southern Imera river crosses one of the most arid part of Sicily. The geochemical composition of the river water is due to the solubilization processes of gypsum rocks, which accounts for the particularly low quality of resources in the areas in which the presence of evaporitics deposits is highest. The geochemical composition and hydraulic parameters of river was monitored with the aim of reaching a better understanding of the relationships between litology and water quality. The Imera river is a potential local hydric resource, but seasonal variability of salinity does not allow farmers to use its water. A geochemical monitoring of the Imera river water has been carried out in selected localities integrating a GIS analysis of the river hydrography basin and of the distribution of the evaporitic formation. During 2003 and 2005 we performed four monitoring surveys of water chemicophysical parameters (temperature, pH and electrical conductivity) and of the main ionic concentrations (Ca2+, Mg2+, K+, Na+, Cl-, SO4 2- ). We also installed a multiparameter probe next to the hydrometrical station of Drasi, about 15 km from the river mouth. Such multiparameter probe was used to determine, continuously and simultaneously, temperature, electrical conductivity, pH, dissolved oxygen, redox potenzial, water level. The geochemical composition of the water allowed to confirm the results of Roda (1971) and Favara (2000), who pointed out that the main cause of degrade of the Southern Imera river are the salt-rich waters of some tributaries flowing over gypsum rocks and halite deposits. We have been able to identify which specific areas are the main contributors to the degradation of the Imera river.

A 6.5-year continuous record of sea surface salinity and seawater isotopic composition at Harbour of Ishigaki Island, southwest Japan†

We produced continuous records of sea surface salinity and isotopic composition from 1998 to 2004 at Ishigaki Island, southwest Japan, and found clear seasonal variations in salinity and oxygen isotopic composition and increasing trends of them after 1999. These increasing trends could be principally due to the decreasing difference between local precipitation (P) and evaporation (E), as a result of the reduction of horizontal vapour transport from adjacent oceans. When samples collected in heavy rainfall events were excluded, the average Δδ18O/Δ salinity slope was obtained as 0.31, 0.35 in summer and 0.28 in winter. Estimated E/P ratios based on the isotopic box model are in good agreement with the ratios of independently estimated E to observed P. †Updated paper: originally presented on the IAEA International Symposium “Quality Assurance for Analytical Methods in Isotope Hydrology” (August 2004, Vienna).

Short and long-term temporal variation of the zooplankton in a tropical estuary (Amazon region, Brazil)

Nyctemeral and seasonal distribution of the zooplankton of the Taperaçu estuary and the effect of the hydrological parameters on the dynamics of these organisms were studied in March (rainy season) and September 2005 (dry season). Zooplankton samplings were carried out during spring tides at 2-hours intervals during a 24 h period. Samples were collected with a plankton net of 120 μm mesh size. Simultaneous temperature, salinity, pH and dissolved oxygen concentration measurements were accomplished at subsurface. The estuary presented a high seasonal variation in salinity (9.1-40.0) with regimes oscillating from mesohaline to polihaline/marine during the rainy and dry season, respectively. Temperature, pH and salinity were significantly higher during the dry season. A total of 50 taxa were identified, belonging to the following groups: Arthropoda, Sarcomastigophora, Cnidaria, Mollusca, Nematoda, Platyhelminthes, Bryozoa, Chordata, Annelida and Chaetognatha. Copepods dominated quantitatively the local zooplankton with 50% of the total organisms. Total zooplankton densities oscillated from 16,491 to 397,476 ind.m-3 during the dry and rainy season, respectively. Rainfall was the principal responsible for the hydrological parameters oscillations, mainly salinity, which influenced directly the population dynamics of the zooplankton of the Taperaçu estuary.

Environmental factors governing the distribution of the bottlenose (Tursiops truncatus) and the spotted dolphin (Stenella attenuata) in Golfo Dulce, South Pacific, off Costa Rica

This study, conducted from June 1996 to July 1997, was directed at determining the abiotic environmental factors governing the distribution of the bottlenose dolphin (Tursiops truncatus) and the pan-tropical spotted dolphin (Stenella attenuata) in Golfo Dulce. The spotted dolphin was associated with significantly deeper zones (t-test = -9.761; p < 0.001, n = 202) and with higher salinity (t-test = -3.538; p = 0.001; n = 202) than the bottlenose dolphin. The combi- nation of environmental variables in the distribution areas of each species in Golfo Dulce was different, both spatially (F = 9.724, df = 12; p < 0.001) and seasonally (F = 9.735; df = 12; p < 0.001). Of all the environmental variables considered, Multiple Discriminant Analysis showed depth to be the main factor differenciating the distribution areas of the two species. The relationship between group size in each species, depth, and the location of their distribution areas in relation to the shore were analyzed and evidence regarding these aspects and variations in foraging strategies and prey composition was proposed to explain the differences found in their spatial distributions. Seasonal variations in salinity in the distribution areas and their inverse relationship with the time of the year were analyzed in relation to their possible combined effects on prey composition during different seasons in order to explain the seasonal variations in distribution patterns.

Constraining modern and historical recharge from bore hydrographs, 3H, 14C, and chloride concentrations: Applications to dual-porosity aquifers in dryland salinity areas, Murray Basin, Australia

Water table fluctuations and renewal rates based on 3H and 14C concentrations in bores screened within 5 m of the water table were used to estimate recharge rates in five dryland salinity areas in northern Victoria, Australia. Given the resolution of each technique both methods yield broadly similar results of 4–90 mm/yr (up to 14% of modern rainfall) that reflect the recharge rates following land clearing over the last 200 years. Deeper bores show mixing of modern recharge with older water flowing laterally through the aquifers. Recharge estimates based on Cl concentrations are up to two orders of magnitude lower (<1 mm/yr), implying that they largely reflect pre-land clearing recharge rates, as is the case elsewhere in the Murray Basin. Recharge rates are similar across the areas from upper slopes to plains, indicating that recharge occurs across substantial areas of each catchment. This is also implied by bore hydrographs in all parts of the flow systems being in phase, the presence of 3H in groundwater from across the area, and seasonal variations in salinity and δ18O values in groundwater from water table bores. Since recharge occurs across broad areas, any attempts to slow the rate of water table rise requires management of the landscape as a whole, not just the uplands. That the increased recharge since land clearing has not lowered groundwater salinity is due to the system having dual porosity, where older saline water trapped in clays within the unsaturated zone is slowly incorporated into the groundwater as the water table rises.