High Salinity Zones Research Articles

Deciphering the genetic diversity of Avicennia officinalis L. across the salinity gradient in the Sundarbans mangrove forest of Bangladesh

Mangroves adaptive plasticity in the changing environmental conditions is of vital importance for conservation management. Genetic diversity of mangrove brings about adaptive plasticity, enabling a species to cope with different habitat conditions. The Sundarbans of Bangladesh is the largest coastal wetland and mangrove forest with diversified habitat conditions that support a wide diversity of flora and fauna. Avicennia officinalis L. is the pioneer species in mangrove succession in the low-salinity, medium-salinity and high-salinity zones of the Sundarbans. Adopting RAPD-PCR analysis, the genetic diversity of A. officinalis was studied to explore the ecotypes of this species in the Sundarbans. The genetic distances of A. officinalis between the low-salinity and medium-salinity zones (0.50) and between the low-salinity and high-salinity zones (0.52) are significantly (p < 0.05) higher than that between the medium-salinity and high-salinity zones (0.09). The expected heterozygosity of A. officinalis of medium-salinity (0.54 ± 0.14) and high-salinity zones (0.55 ± 0.10) are higher than that of low-salinity zone (0.37 ± 0.12). The genetic diversity of A. officinalis of medium-salinity (0.5417 ± 0.3167) and high-salinity (0.5458 ± 0.3189) zones is significantly (p < 0.05) higher than that of low-salinity zone (0.3750 ± 0.2313). This genetic diversity of A. officinalis bears significant ecological consequences. A. officinalis growing in the low-salinity zone is the low salt-adapted ecotype while that growing in the medium-salinity and high-salinity zones is the high salt-adapted ecotype in the Sundarbans. These two ecotypes of A. officinalis are of both in-situ and ex-situ conservation importance for the Sundarbans and coastal plantations of Bangladesh to face the climate change induced salinity regime changes in the future.

Asymmetric responses of spatial variation of different communities to a salinity gradient in coastal wetlands

Various ecological communities are susceptible to the salinity gradients in coastal wetlands. Remane diagram has well described the macrozoobenthos diversity pattern along salinity gradients. Yet, further research is still needed, that is, the changes in diversity and biomass of other communities (e.g. plants, fish) along salinity gradients, and whether these changes are consistent or different among different communities. In this study, using China's Yellow River Delta wetland as a case study, we analyzed the variation of the community composition, species richness, and biomass of plant, macrozoobenthos, and fish communities along a salinity gradient from <0.5 to 30 ppt. We found that plant community composition exhibited more distinct variation along the salinity gradient than macrozoobenthos, with the least distinction for fish. Plant species richness decreased greatly along the gradient, whereas macrozoobenthos richness first decreased and then increased with increasing salinity, with the low richness occurring at a salinity of 0.9–12.3 ppt. Fish had the highest richness at a salinity of 14.8–16.0 ppt. The sum of plant, macrozoobenthos, and fish species and macrozoobenthos richness were both similar to the Remane diagram. Plants had higher biomass in low-salinity zones than in high-salinity zones, except for high biomass at a salinity of 14.8–16.0 ppt, whereas macrozoobenthos and fish showed the opposite trend. Principal-coordinate analysis showed an obvious dissimilarity map based on the composition, richness, and biomass of the plant, macrozoobenthos, and fish communities. Overall, the effects of salinity gradient differed among different communities. These findings demonstrate the asymmetric responses of different communities to salinity gradients, and have practical implications for maintaining a salinity gradient in coastal wetlands.

Identification of subsurface fluid flow using the 2D geoelectric method in Marunda, North Jakarta

Jakarta is the most densely populated province in Indonesia and it will grow over time. This overwhelming population causes a decrease in the quality and supply of groundwater. Brines has been discovered in several areas in Jakarta. Several studies conducted by earth science researchers conclude that brine in Jakarta appears from either seawater intrusion or trapped connate water. This study focuses on the use of the geoelectric method to evaluate the groundwater quality problem in Kelurahan Marunda. Methods used in this study are resistivity, self-potential, and groundwater sampling. Conductivity, Salinity, pH and water table elevation are the parameters used in this study. These methods are done to observe subsurface groundwater quality, fluid flow and how far the seawater infiltrated. Based on the result of groundwater data of 40 wells, high conductivity and high salinity zones are found. High conductivity in this area affected mostly by the saline factor indicated by high salinity and neutral pH. The subsoil has low resistivity values showed by 2D resistivity data. Also, self-potential data displays a North-South groundwater subsurface fluid flow 1, 20 km from the coastline. Altogether, these data indicate seawater intrusion in Kelurahan Marunda, North Jakarta.

Possible factors for increasing water salinity in an embanked coastal island in the southwest Bengal Delta of Bangladesh

Increasing water salinity in coastal areas is a concern for the coastal environment. Increased salinity is affecting water quality, freshwater availability, and water-related ecosystems in the southwest coastal region of the Bengal Delta. The study used a synergies and robust approach to assess the possible factors for increasing water salinity in an embanked coastal island in the southwest Bengal Delta. The hydrochemical analysis revealed that surface and groundwater are enriching with Na+ and Cl− concentration, also controlling by seawater through the ion exchange mechanism (Ca2+ and Mg2+ replacing by Na+, and Cl−), mixing stage of water solution (freshwater-saltwater), and anthropogenic salt contamination by human activities (e.g., saltwater shrimp cultivation and excessive irrigation). Piper diagram showed that river water is occupying at the mixing stage of solution, where pond and groundwater are occupying at seawater (saline) zone. The water quality index showed that surface water is not fresh anymore and unsuitable for drinking purposes. The isotope analyses exposed the presence of strong precipitation variance in the study area. Cluster observation analysis showed a strong correlation between Na+, Cl−, and TDS (similarity is 97% to 99%). The remote sensing application illustrated that high salinity zones are in the northern part, and groundwater salinity is higher (7.5 to 8 ppt) in the northern part of polder 32. The salinity of both groundwater and surface water showed a positive correlation with land surface temperature and potential evapotranspiration. The study exposed four responding factors for increasing groundwater salinity in this region, which are - regional surface geological settings, hydrological settings, hydraulic head gradient, and human activities. A conceptual model illustrated the presence of lateral recharge of saltwater from the surrounding tidal rivers to the groundwater.

Spatial Characteristics Reveal the Reactive Transport of Radium Isotopes (224Ra, 223Ra, and 228Ra) in an Intertidal Aquifer

AbstractThis study presents high‐resolution two‐dimensional distributions of radium isotopes in the shallow intertidal aquifer of Tolo Harbor, Hong Kong, illustrating the importance of salinity, groundwater residence time, and tidal flushing and mixing in controlling radium behavior in the system. The activities of radium isotopes are low in the fresh groundwater zone with activities increasing in the transition zone (1 &lt; salinity &lt; 25) due to desorption of radium from sediment surface coatings. In the high salinity zone (salinity &gt; 25), the activities of radium isotopes increase with depth due to tidal flushing and mixing of the recirculating seawater in the shallow aquifer as well as increasing residence time with depth. The dissolved radium isotopes are identified to be in disequilibrium in shallow intertidal aquifer based on radium isotopic ratios and observed depletion of dissolved radium isotopes compared to the theoretical mixing line between the equilibrium activity and fresh groundwater. The influence of continuous tidal flushing of the shallow intertidal aquifer on radium is revealed, and shallow sediments are observed to have less total exchangeable radium isotopes than deeper in the aquifer. A new one‐dimensional reactive transport model that considers a depth‐dependent production rate is applied to simulate the vertical distribution of radium isotopes in the intertidal aquifer as seawater infiltrates the beach. Using least squares fitting of the model to field data, the vertical infiltration seepage velocity is estimated to be ~0.5 m/day, and the dimensionless adsorption partition coefficient of radium isotopes (K) is 350. This agrees well with K values (202–365) calculated using an adsorption/desorption model as well as measured values (266 in February and 205 in April). Based on the spatial distribution of radium isotopes and flow patterns in the intertidal aquifer, groundwater in Ra disequilibrium zone is recommended as the endmember for tide‐ or wave‐driven submarine groundwater discharge (SGD) that has shallow flow paths, and groundwater in Ra equilibrium zone is recommended as endmember for seasonally driven or density‐driven SGD that has deep flow paths.

The Effect of Hurricane Irma Storm Surge on the Freshwater Lens in Big Pine Key, Florida using Electrical Resistivity Tomography

Animals and plants on low elevation oceanic islands often rely on a thin lens of fresh groundwater and this lens is vulnerable to seawater contamination from storm surge. Documentation of the impact of the storm surge on the freshwater lens and its subsequent recovery is limited. In September 2017, Hurricane Irma made landfall in the Florida Keys as a category 4 storm with storm surge heights in excess of 2 m. This study used Electrical Resistivity Tomography (ERT) to investigate the effect of the storm surge on the freshwater lens of Big Pine Key, FL. The study compared ERT images along three profiles ranging between 220 and 280 m length collected in 2011 with post storm data collected about 3 to 4 months (November 2017/January 2018) and eight (May 2018) months after Irma. The post storm data documented that the storm surge impacted the freshwater lens on all three profiles with low resistivity (i.e., high salinity) zones in the upper 2 m of the groundwater. The increase in salinity was most pronounced in the lower elevations of the profiles. The May 2018 data were collected immediately after 2 weeks of intense precipitation. These data showed 40% recovery of the freshwater lens, most pronounced in the lower elevation of the profiles. This suggests that both the impact of storm surge and the freshwater recovery due to precipitation are most pronounced in low elevation regions where both saline and freshwater can collect at the surface.

Classification and 3-D distribution of upper layer water masses in the northern South China Sea

Using the fuzzy cluster analysis and the temperature-salinity (T-S) similarity number analysis of cruise conductivity-temperature-depth (CTD) data in the upper layer (0–300 m) of the northern South China Sea (NSCS), we classify the upper layer water of the NSCS into six water masses: diluted water (D), surface water (SS), the SCS subsurface water mass (US), the Pacific Ocean subsurface water mass (UP), surface-subsurface mixed water (SU) and subsurface-intermediate mixed water (UI). A new stacked stereogram is used to illustrate the water mass distribution, and to examine the source and the distribution of UP, combining with the sea surface height data and geostrophic current field. The results show that water mass UP exists in all four seasons with the maximum range in spring and the minimum range in summer. In spring and winter, the UP intrudes into the Luzon Strait and the southwest of Taiwan Island via the northern Luzon Strait in the form of nonlinear Rossby eddies, and forms a high temperature and high salinity zone east of the Dongsha Islands. In summer, the UP is sporadically distributed in the study area. In autumn, the UP is located in the upper 200 m layer east of Hainan Island.

Physiologically adaptive plasticity in nutrient resorption efficiency of Avicennia officinalis L. under fluctuating saline environments in the Sundarbans of Bangladesh

Nutrient resorption efficiency is an important nutrient conservation and ecophysiological mechanism of mangroves growing in saline environments. This study investigated the nitrogen, phosphorus, and potassium resorption efficiency of Avicennia officinalis L. growing across a salinity gradient with seasonal variations in the Sundarbans of Bangladesh. Due to decreasing salinity during the monsoon and postmonsoon seasons, the nutrient availability in soil and nutrient resorption efficiency did not vary significantly among the low-salinity, medium-salinity, and high-salinity zones. However, the nutrient availability in the medium-salinity and high-salinity zones was significantly lower than that in the low-salinity zone during the premonsoon season due to increased salinity. Consequently, nutrient resorption efficiency in the medium-salinity and high-salinity zones was significantly higher than that in the low-salinity zone during the premonsoon. Further, leaf vein density of A. officinalis in the medium-salinity and high-salinity zones was significantly higher than that in the low-salinity zone. This modification in vein density was the mechanism for the higher nutrient resorption efficiency of A. officinalis in the medium-salinity and high-salinity zones than that in the low-salinity zone. This plasticity in nutrient resorption efficiency is a physiologically adaptive mechanism that enables A. officinalis to persist in increasingly saline environments due to climate change.

Photosynthetic tolerance to non-resource stress influences competition importance and intensity in an invaded estuary.

In an attempt to clarify the role of environmental and biotic interactions on plant growth, there has been a long-running ecological debate over whether the intensity and importance of competition stabilizes, increases or decreases across environmental gradients. We conducted an experiment in a Chinese estuary to investigate the effects of a non-resource stress gradient, soil salinity (from 1.4‰ to 19.0‰ salinity), on the competitive interactions between native Phragmites australis and invasive Spartina alterniflora. We linked these effects to measurements of photosynthetic activities to further elucidate the underlying physiological mechanism behind the competitive interactions and the driver of invasion. The experiments revealed that while biomass of both species decreased in the presence of the other, competition did not alter photosynthetic activity of either species over time. P.australis exhibited high photosynthetic activity, including low chlorophyllase activity, high chlorophyll content, high stomatal conductance and high net photosynthetic rate, at low salinity. Under these conditions, P.australis experienced low competitive intensity, leading to high biomass production and competitive exclusion of S.alterniflora. The opposite was observed for S.alterniflora: while competitive intensity experienced by P.australis increased with increasing salinity, and photosynthetic activity, biomass, competitive dominance and the importance of competition for P.australis growth decreased, those of S.alterniflora were stable. These findings demonstrate that S.alterniflora invasion driven by competitive exclusion are likely to occur and expand in high salinity zones. The change in the nature of competition along a non-resource stress gradient differs between competitors likely due to differences in photosynthetic tolerance to salinity. The driver of growth of the less-tolerant species changes from competition to non-resource stress factors with increasing stress levels, whereas competition is constantly important for growth of the more-tolerant species. Incorporating metrics of both competition intensity and importance, as well as linking these competitive outcomes with physiological mechanisms, is crucial to understanding, predicting, and mediating the effects of invasive species in the future.

Variability in phytolith spectra of some Panicoid grasses from different soil salinity zones of the deltaic West Bengal, India: implications in understanding depositional environments

Phytoliths are microscopic silica bodies deposited in and between plant cells. They are known to be important environment indicators and thus hold significant prospect for present and past ecological and environmental interpretations. We present here results of morphometric and assemblage analyses of phytoliths from five Panicoid grasses, i.e. Chrysopogon aciculatus, Imperata cylindrica, Oplismenus burmannii, Paspalum distichum, and Echinochloa crus-galli. Each was collected separately from mesophyte-dominated low saline and halophyte-rich high saline phytoecological zones of the lower Gangetic delta of West Bengal, India. Bilobate phytoliths with relatively longer shanks, and rondel and tower morphotypes were recovered in significantly higher frequencies from samples of high salinity zones, whereas cross, polylobate, and trapeziform morphotypes were found predominantly in grasses from mesophyte-dominated low salinity zones. The above-mentioned morphotypes were found to be strongly correlated with soil salinity. Phytolith data of the grasses from two different ecophysiological zones were further subjected to principal component analysis (PCA), which successfully distinguished the two salinity zones. The present investigation may serve as a basis to identify distinct phytoecological zones resulting from differences in salinity by using grass phytoliths. This study further explores the possibility of identifying different depositional environments when used during regional palaeovegetational and palaeoenvironmental reconstructions.

The Effects of Local Environmental Conditions and the Emergence of Young of the Year on the Regional Distribution, Prevalence, and Intensity of Ergasilus labracis (Copepoda) Parasitic on Three-Spined Stickleback (Gasterosteus aculeatus) from the Bay d'Espoir/Hermitage Bay Region of Newfoundland, Canada

The effects of local environmental conditions on the regional distribution, prevalence, and infection intensity of Ergasilus labracis (Copepoda) parasitic on 3-spined stickleback (Gasterosteus aculeatus) was investigated in the Bay d'Espoir region of Newfoundland during May to September of 2015. Environmental conditions (e.g., temperature, salinity, and oxygen) were measured monthly at 7 beach sites distributed through the region. Analysis of environmental characteristics indicated that the area could be divided into 3 zones based on salinity (low-salinity zone: 13.56 ± 0.32 practical salinity units [psu]; medium-salinity zone: 21.11 ± 0.04 psu; high-salinity zone: 29.91 ± 0.32 psu). Ergasilus labracis was found to be the most prevalent parasitic copepod sampled from fish in upper Bay d'Espoir (low-salinity and medium-salinity zones: greater than 75%), but rarely on fish from Hermitage Bay/Connaigre Bay (high-salinity zone: less than 15%). Parasite intensities were highest in the low-salinity zone within Bay d'Espoir at 18–22°C, but decreased significantly in Hermitage Bay/Connaigre Bay (salinity > 20 psu; temperature 3 cm total body length (September). Our data suggest that G. aculeatus could act as a key amplification source for these parasites and thus may impact adjacent aquaculture sites in the bay.

Electromagnetic exploration in high-salinity groundwater zones: case studies from volcanic and soft sedimentary sites in coastal Japan

Estimating the spatial distribution of groundwater salinity in coastal plain regions is becoming increasingly important for site characterisation and the prediction of hydrogeological environmental conditions resulting from radioactive waste disposal and underground CO2 storage. In previous studies of the freshwater–saltwater interface, electromagnetic methods were used for sites characterised by unconsolidated deposits or Neocene soft sedimentary rocks. However, investigating the freshwater–saltwater interface in hard rock sites (e.g. igneous areas) is more complex, with the permeability of the rocks greatly influenced by fractures. In this study, we investigated the distribution of high-salinity groundwater at two volcanic rock sites and one sedimentary rock site, each characterised by different hydrogeological features. Our investigations included (1) applying the controlled source audio-frequency magnetotelluric (CSAMT) method and (2) conducting laboratory tests to measure the electrical properties of rock core samples. We interpreted the 2D resistivity sections by referring to previous data on geology and geochemistry of groundwater. At the Tokusa site, an area of inland volcanic rocks, low resistivity zones were detected along a fault running through volcanic rocks and shallow sediments. The results suggest that fluids rise through the Tokusa-Jifuku Fault to penetrate shallow sediments in a direction parallel to the river, and some fluids are diluted by rainwater. At the Oki site, a volcanic island on a continental shelf, four resistivity zones (in upward succession: low, high, low and high) were detected. The results suggest that these four zones were formed during a transgression–regression cycle caused by the last glacial period. At the Saijo site, located on a coastal plain composed of thick sediments, we observed a deep low resistivity zone, indicative of fossil seawater remnant from a transgression after the last glacial period. The current coastal plain formed in historical times, following which fresh water penetrated the upper parts of the fossil seawater zone to form a freshwater aquifer ~200 m in thickness.

Carbonate system biogeochemistry in a subterranean estuary – Waquoit Bay, USA

Quantifying carbon fluxes associated with submarine groundwater discharge (SGD) remains challenging due to the complex biogeochemistry of the carbonate system in the subterranean estuary (STE). Here we conducted time series measurements of total alkalinity (TAlk) and dissolved inorganic carbon (DIC) in a well-studied coastal aquifer (Waquoit Bay, Massachusetts, USA). Groundwater samples were collected monthly from May 2009 to June 2010 across the freshwater-saltwater mixing zone of the Waquoit Bay (WB) STE. The concentrations of both TAlk and DIC in zero-salinity groundwater were variable, but were lower than those in the bay water (S∼28). DIC underwent slightly non-conservative mixing between low and intermediate salinities while there was an apparent additional DIC source at high salinity (>20) in all seasons. TAlk concentrations exhibited even stronger variations, with evidence of both production and consumption in high salinity zones, and consistent TAlk consumption at intermediate salinity in summer and fall (June–December, 2009). The increases in DIC and TAlk at high salinity were attributed to aerobic respiration and denitrification in WB sediments during bay water recharge of the STE. We infer that the loss of TAlk at intermediate salinity reflects H+ production as reduced compounds (e.g. Fe2+) are oxidized within the STE. In terms of impacts on surface water inorganic carbon budgets, the SGD-derived DIC flux was mainly controlled by seasonal changes in SGD while a combination of TAlk concentration variability and SGD drove the TAlk flux. SGD-derived DIC, aqueous CO2, and H+ fluxes to the bay were ∼40–50% higher in summer vs. in winter, a result of enhanced marine groundwater flux and significant TAlk removal (proton addition) during periods of high seawater intrusion. Furthermore, the SGD-derived DIC flux was consistently greater than TAlk flux regardless of season, indicating that SGD serves to reduce the CO2 buffering capacity of surface water. Our results highlight the importance of seasonality and subsurface biogeochemical processes on the subterranean estuary carbonate system and the resulting impact on SGD-derived TAlk, DIC, aqueous CO2, and H+ fluxes to the coastal ocean.

Distribution and fractionation of rare earth elements and Yttrium in suspended and bottom sediments of the Kali estuary, western India

Concentrations of rare earth elements (REE) and yttrium (Y), and major metals (Al, Fe and Mn) were measured in suspended particulate matter (SPM) and bottom sediments of the Kali estuary, western India, for their distribution and fractionation. The contents of SPM and metals in it were more uniform along the longitudinal transect during the monsoon. During the post- and pre-monsoons, low SPM in the upper/middle estuary coincided with high Fe and Mn and total REE (∑REE). But in the lower estuary SPM and its ∑REE content increased seaward, while Fe and Mn decreased. The Y/Ho ratios decreased seaward during the monsoon but increased during the post-monsoon. Sm/Nd ratios were more uniform along the transect during monsoon but decreased marginally seaward in other seasons. The Post-Archean Average Australian Shale (PAAS)-normalized REE patterns exhibited middle REE and heavy REE enrichment with positive Ce ($${\text{Ce}}/{\text{Ce}}^{*}$$ ), Eu ($${\text{Eu}}/{\text{Eu}}^{*}$$ ) and Y anomalies. The $${\text{Ce}}/{\text{Ce}}^{*}$$ increased but $${\text{Eu}}/{\text{Eu}}^{*}$$ decreased marginally seaward. The fine-grained sediments showed higher ∑REE and lower Y/Ho ratios than in coarse-grained sediments. The PAAS-normalized REE patterns of sediment were similar to that of SPM. The results revealed two processes, colloidal flocculation and coagulation of metals in the low-salinity zone and an estuarine turbidity maximum in the high salinity zone. Rare earths and yttrium (REY) in SPM and sediments primarily reflected the source rock composition than that of chemical weathering. Apart from physico-chemical processes, the mineralogy and grain size of sediments controlled the distribution and fractionation of REY in the estuary.

Distribution and Source Identification of Heavy Metal Concentration in Chilika Lake, Odisha India:An Assessment Over Salinity Gradient

Extent of heavy metal contamination in Chilika Lake was assessed to conserve the eco-dynamics of the lake. Distribution of heavy metals, cations and total organic carbon were analysed in the sediment samples collected from three sites that represent a salinity gradient. Analysis of environmental indices, viz. enrichment and contamination factors, geo-accumulation (I geo ) and pollution load indices showed that the concentrations of Cd and Hg were significantly high with geoaccumulation index being greater than one in all three stations. Levels of Pb and Co were also found to be elevated with I geo value of 0.025 and 0.048 respectively. Among the three sampling stations, Kaluparaghat witnessed the highest pollution load index followed by Balugaon and Rambhartia. Principal component analysis revealed that the high-salinity zone was associated with high concentration of Hg and decreased concentration of other toxic metals, indicating that source of pollution of Hg is different from that of other metals.

An innovative systematic approach to internalize external costs of salinization in major irrigated systems

Agricultural production has external costs embedded in different forms. These externalities have not yet been internalized in the market's prices. The study applied a basin-wide systematic approach to manage river salinity, which is one of the most vexatious of these externalities, and needs urgent remediation. The application of the approach is exemplarily demonstrated for the Murray Darling Basin (MDB) in Australia. An in-depth economic analysis indicates that in the upper areas, plant-based options are suitable and economically viable, while in middle and downstream parts of the MDB, more options are suitable such as irrigation management, subsurface drainage and effluent reuse, and salt interception systems and Sequential Biological Concentration (SBC). The SBC differs from most other options since it provides direct economic benefits to the operators and is profitable. We adopt Pigouvian recommendations as polluters pay principle to internalize externality. Charging salinity credits in terms of polluters pay principle (e.g. in this case of about A$53 t–1) would result in attractive economic returns even at higher level of salinity, thus offering sufficient incentives to invest in relevant salinity management strategy. We recommended that potential salinity mitigation technique should consider regional characteristics and that it should be focused on high impact salinity zones to increase the effectiveness of the effort.

Application of macrobenthic diversity to estimate ecological health of artificial oyster reef in Yangtze Estuary, China

In this study, several macrobenthic diversity investigations were performed in Yangtze Estuary Oyster Reef, the largest artificial oyster reef in China, from 2012 to 2014. The sampling sites of the south branch showed considerably higher diversity than those of the north branch. The richness measures exhibited a significant increasing trend from low- to high-salinity zone; however, the evenness measures were typically high in the middle-salinity zone. During the past decade, the results were combined with historical data to detect the changes in macrobenthos. The variation in substrate organisms and macrobenthic diversity followed a steady trend after a major fluctuation. Redundancy analysis indicated that the water salinity and substrate factors were the main indicators that influence macrobenthic distribution. All sampling sites in the south branch were protected by a nature reserve. However, the N2 and N6 sites in the north branch were subjected to severe and mild human interventions, respectively.

Assessment of groundwater suitability for irrigation in Madinah City, Saudi Arabia

In this study, the suitability of groundwater for irrigation purposes in Madinah city, Saudi Arabia was assessed. Of the 23 wells that were drilled in different locations of the city, 20 wells were sampled for water quality analyses. The United States Department of Agriculture (USDA) classification of irrigation water that is based on sodium hazard (SAR) and salinity hazard was used for irrigation suitability assessment. In addition, the residual sodium carbonate (RSC) and soluble sodium percentage (%Na) were calculated for all samples and also used for irrigation suitability assessment. Results showed that all groundwater samples are in the acceptable quality range for irrigation based on RSC values, and the majority of the samples had %Na in the acceptable range for irrigation. When SAR and salinity hazard were assessed, results showed that while almost all groundwater samples fell in the acceptable range of SAR, they were either in the high or very high salinity zones, indicating that the water can be used for irrigation after adopting some management practices. Comparing total dissolved solids (TDS) concentration obtained 35 years ago for the study area with the current TDS values indicates that the recent accelerated urban development in the study area did not significantly impact groundwater quality with regard to irrigation suitability.

A conectividade hidrogeológica de uma nascente salina de baixa vazão em turfeiras topotróficas na região de areias betuminosas de Athabasca, Canadá

Saline springs can provide clues as to the nature of groundwater flow, including how it relates to subsurface wastewater storage and the distribution of solutes in the landscape. A saline-spring peatland neighboring a proposed in-situ oil facility was examined near Fort McMurray, Alberta (Canada). The study area is situated just north of a saline groundwater discharge zone, which coincides with the erosional edge of the Cretaceous Grand Rapids Formation. Na+ (mean 6,949 mg L−1) and Cl− (mean 13,776 mg L−1) were the dominant salts within the peatland, which increased by an order of magnitude in the opposite direction to that of the local groundwater flow. Rivers and freshwater wetlands within the study area had anomalously high salinities, in some cases exceeding 10,000 mg L−1 total dissolved solids within deeper sediments. Saline-spring features were observed as far as 5 km from the study area. A low-permeability mineral layer underlying the peatland restricted vertical groundwater exchange (estimated to be less than several mm over the 4-month study period). Sand and gravel lenses underlying the fen’s high-salinity zone may function as areas of enhanced discharge. High Cl/Br ratios point to halite as a potential source of salinity, while δ18O and δ2H signatures in groundwater were lower than modern-day precipitation or Quaternary aquifers. The complex connectivity of saline-spring wetlands within the landscape has implications for industry and land-use managers, and justifies incorporating them into monitoring networks to better gauge the magnitude and flow history of natural saline discharge in the oil sands region.

Dissolved inorganic carbon (DIC) and its δ13C in the Ganga (Hooghly) River estuary, India: Evidence of DIC generation via organic carbon degradation and carbonate dissolution

In this study, we present comprehensive data on dissolved Ca, dissolved inorganic carbon (DIC) and its carbon isotope composition (δ13CDIC) of (i) the Ganga (Hooghly) River estuary water sampled during six seasons of contrasting water discharge over 2years (2012 and 2013), (ii) shallow groundwater from areas adjacent to the estuary and (iii) industrial effluent water and urban wastewater draining into the estuary. Mass balance calculations indicate that processes other than the conservative mixing of seawater and river water are needed to explain the measured DIC and δ13CDIC. Results of mixing calculations in conjunction with the estimated undersaturated levels of dissolved O2 suggest that biological respiration and organic carbon degradation dominate over biological production in the estuary. An important outcome of this study is that a significant amount of DIC and dissolved Ca is produced within the estuary at salinity ⩾10, particularly during the monsoon period. Based on consideration of mass balance and a strong positive correlation observed between the “excess” DIC and “excess” Ca, we contend that the dominant source of DIC generated within the estuary is carbonate dissolution that is inferred to be operating in conjunction with degradation of organic carbon. Calculations show that groundwater cannot account for the observed “excess” Ca in the high salinity zone. Estimated DIC contributions from anthropogenic activity are minor, and they constitute ca. 2–3% of the river water DIC concentrations.The estimated annual DIC flux from the estuary to the Bay of Bengal is ca. (3–4)×1012g, of which ca. 40–50% is generated within the estuary. The monsoon periods account for the majority (ca. 70%) of the annual DIC generation in the estuary. The annual DIC flux from the Hooghly estuary accounts for ca. 1% of the global river DIC flux to the oceans. This is disproportionately higher than the water contribution from the Hooghly River to the oceans, which accounts for ca. 0.2% of the global river water flux. The results of this study suggest that estuaries in regions affected by tropical monsoon can be important in terms of their production of significant amounts of DIC and its delivery to the world’s oceans.