Significant Increase In Salinity Research Articles

Simulation of hydrodynamic changes and salinity intrusion in the lower Vietnamese Mekong Delta under climate change-induced sea level rise and upstream river discharge

Saltwater intrusion results from a complex interaction of many factors, such as global climate change, extreme climate patterns and overuse of natural resources. Currently, the Vietnamese Mekong Delta (VMD) faces great challenges from saltwater intrusion. This situation is very serious, tends to increase in scope and scale, directly threatens life and property, and negatively impacts the sustainable economic development of this area. The objective of this study is to evaluate and predict changes in the hydrodynamic regime and salinity intrusion in the Lower VMD (from Can Tho and My Thuan to estuaries and coastal regions) caused by anticipated increases in sea level and the decrease in river discharge from upstream, using a two-dimensional numerical model. The research includes many scenarios, such as a baseline scenario in February 2020 and eight sea level rise (SLR) scenarios ranging from 14 cm to 58 cm in 2050 and 2100. The simulation findings indicate that when the sea level rises, there is a significant increase in salinity and saltwater intrusion length, resulting in increased wave height, decreased current speed, and a decline in upstream discharge of the rivers. The work has enhanced our comprehension of the impact of these hydrodynamic alterations on saltwater incursion and riverbank erosion.

From genes to toxins: Profiling Prymnesium parvum during a riverine harmful algal bloom

Blooms of Prymnesium parvum, a unicellular alga globally distributed in marine and brackish environments, frequently result in massive fish kills due to the production of toxins called prymnesins by this haptophyte. In August 2022, a harmful algal bloom (HAB) of this species occurred in the lower Oder River (Poland and Germany), which caused mass mortalities of fish and other organisms. This HAB was linked to low discharge of the Oder and mining activities that caused a significant increase in salinity. In this context, we report on the molecular detection and screening of this haptophyte and its toxins in environmental samples and clonal cultures derived thereof. Both conventional PCR and droplet digital PCR assays reliably detected P. parvum in environmental samples. eDNA metabarcoding using the V4 region of the 18S rRNA gene revealed a single Prymnesium sequence variant, but failed to identify it to species level. Four clonal cultures established from environmental samples were unambiguously identified as P. parvum by molecular phylogenetics (near full-length 18S rRNA gene) and light microscopy. Phylogenetic analysis (ITS1–5.8S-ITS2 marker region) placed the cultured phylotype within a clade containing other P. parvum strains known to produce B-type prymnesins. Toxin-screening of the cultures using liquid chromatography-electrospray ionization - time of flight mass spectrometry identified B-type prymnesins, which were also detected in extracts of filter residues from water samples of the Oder collected during the HAB. Overall, our investigation provides a detailed characterization of P. parvum, including their prymnesins, during this HAB in the Oder River, contributing valuable insights into this ecological disaster. In addition, the droplet digital PCR assay established here will be useful for future monitoring of low levels of P. parvum on the Oder River or any other salt-impacted and brackish water bodies.

Recent changes of the dissolved oxygen distribution in the deep convection cell of the southern Adriatic Sea

The dynamics of dissolved oxygen in the ocean are of crucial importance for understanding marine ecosystems, with influences ranging from exchange with the atmosphere to biological processes and ocean circulation. In this study, we focus on the southern Adriatic Sea, an essential component of the Eastern Mediterranean “conveyor belt”, to investigate long-term oxygen dynamics and its driving factors. We use cross-platform datasets from 2013 to 2020, including remote sensing data, model reanalysis and in-situ observations from Argo floats, ocean gliders and ship-based measurements. Our analysis investigate the interplay of physical, biological and atmospheric forcing that drive oxygen variability. The distribution of dissolved oxygen in the southern Adriatic Sea is influenced by vertical mixing, advection of water masses and ecosystem dynamics. In the surface layer, the variability of dissolved oxygen is triggered by annual primary production and deep convection events. The dynamics in the intermediate and the deep layers are instead primarily influenced by physical processes, such as the vertical mixing and the water masses inflow from the adjacent sub-basins, which is driven by the periodic reversals of northern Ionian Gyre circulation. In particular our study reveals that the water masses advective dynamics driving the increase and decrease of dissolved oxygen have drastically changed in recent years. The highest dissolved oxygen concentrations are currently observed during the northern Ionian Gyre anticyclonic phase, while they have been previously documented during the cyclonic phase. This change appears to be connected with the significant increase in salinity observed in the southern Adriatic Sea in the same period and contributes to a better understanding of the processes that determine oxygen distribution in the Eastern Mediterranean basin.

Recycling of gas-to-liquid sludge as a potential organic amendment: Effect on soil and cotton properties under hyperarid conditions

Gas-to-liquid (GTL) sludge is a specific wastewater treatment by-product, which is generated during the industrial process of natural gas conversion to transportation fuels. This least studied sludge is pathogen-free and rich in organic carbon and plant nutrients. Therefore, it can be reused for soil enhancement as a sustainable management strategy to mitigate landfill gas emissions. In this field study, we compared the performance of soil treatments with GTL sludge to the more conventional chemical fertilizers and cow manure compost for the cultivation of cotton under hyperarid conditions. After a complete growing season, GTL sludge application resulted in the enhancement of soil properties and plant growth compared to conventional inputs. As such, there was a significant dose-dependent increase of soil organic matter (4.01% and 4.54%), phosphorus (534 and 1090 mg kg−1), and cumulative lint yield (4.68 and 5.67 t ha−1) for GTL sludge application rates of 1.5% and 3%, respectively. The produced fiber quality was adequate for an upland cotton variety (Gossypium hirsutum var. MAY 344) and appeared more dependent on the prevailing climate conditions than soil treatments. On the other hand, the adverse effects generally related to industrial sludge reuse were not significant and did not affect the designed agro-environmental system. Accordingly, plants grown on GTL sludge-amended soils showed lower antioxidant activity despite significant salinity increase. In addition, the concentrations of detected heavy metals in soil were within the standards’ limits, which did not pose environmental issues under the described experimental conditions. Leachate analysis revealed no risks for groundwater contamination with phytotoxic metals, which were mostly retained by the soil matrix. Therefore, recycling GTL sludge as an organic amendment can be a sustainable solution to improve soil quality and lower carbon footprint. To reduce any environmental concerns, an application rate of 1.5% could be provisionally recommended since a two-fold increase in sludge dose did not result in a significant yield improvement.

Salinity Variation of Euphrates River between Ashshinnafiyah and Assamawa Cities

AshShinnafiyah and AsSamawa cities suffer from significant increase in salinity of Euphrates River water compared with their counterpart's north AshShinnafiyah city which is reflected adversely on the quality of water within the study area. The study aims to find possible solutions to avoid the deterioration of Euphrates River northern AshShinnafiyah city until AsSamawa city that were presented by total dissolved solid TDS. Twelve main hydrological and fifteen salinity measurement stations were selected to cover 117 km of the river reach within the study area during July-2011. Additional twenty three hydrological and salinity stations were adopted during March-2012, winter season to the river within the study area. After conducting the field and laboratory measurements, mathematical model using HEC-RAS v.4.1 software were implemented, using the available geometric and recorded and measured hydrological data. Eleven scenarios were adopted, by canceled one or more of the drains that cause the deterioration in the river, to find the best scenario using various discharges of Al Ya’uo Regulator (Upstream of study area), where the criteria are the water level at AsSamawa city (downstream boundary) is not less than 6 m.a.m.s.l. and the maximum acceptable salinity for agricultural purposes is 1500 mg/l according to Specification of Iraq No. 417 for maintenance of river pollution, 1967. It was concluded from both models that the problem of salinity in the study area cannot be avoided without diverting one or more of the drains that outfall in the river. The minimum instream flow MIF was found for each scenario. Euphrates River without Eastern Al-Jarah, Al-Khassf, AnNagara, and Al-Haffar Drains, and outfalls Between AshShinnafiyah and Garrb Villages, Scenario 9, is the best one, where it gave the minimum required discharge from Al-Ya’uo Regulator of 82m 3 /s and 165m 3 /s during summer and winter seasons respectively.

Variations of temperature, salinity and oxygen of the Baltic Sea for the period 1950 to 2020

Variations of temperature, salinity and oxygen of the Baltic Sea on interannual to decadal timescales were studied for the period from 1950 to 2020. Both observational data and the output of a numerical circulation model of the Baltic Sea were analyzed. In addition, we investigated the influence of atmospheric parameters and river runoff on the observed hydrographic variations. Variability of sea surface temperature (SST) closely follows that of air temperature in the Baltic on all timescales examined. Interannual variations of SST are significantly correlated with the North Atlantic Oscillation in most parts of the sea in winter. The entire water column of the Baltic Sea has warmed over the period 1950 to 2020. The trend is strongest in the surface layer, which has warmed by 0.3–0.4°C decade−1, noticeably stronger since the mid-1980s. In the remaining water column, characterized by permanent salinity stratification in the Baltic Sea, warming trends are slightly weaker. A decadal variability is striking in surface salinity, which is highly correlated with river runoff into the Baltic Sea. Long-term trends over the period 1950–2020 show a noticeable freshening of the upper layer in the whole Baltic Sea and a significant salinity increase below the halocline in some regions. A decadal variability was also identified in the deep layer of the Baltic Sea. This can be associated with variations in saltwater import from the North Sea, which in turn are influenced by river runoff: fewer strong saltwater inflows were observed in periods of enhanced river runoff. Furthermore, our results suggest that changes in wind speed have an impact on water exchange with the North Sea. Interannual variations of surface oxygen are strongly anti-correlated with those of SST. Likewise, the positive SST trends are accompanied by a decrease in surface oxygen. In greater depths of the Baltic Sea, oxygen decrease is stronger, which is partly related to the observed increase of the vertical salinity gradient.

The Effect of Irrigation with Treated Municipal Wastewater and Agricultural Drainage Water on Soil Chemical Properties

ABSTRACT This study was carried out to investigate the effect of irrigation with treated municipal wastewater and agricultural drainage water on Ahvaz (southwest Iran) soil chemical properties in 24 plots with 1 × 1 (m) area in farm No. 1 of Shahid Chamran University of Ahvaz in 2018–2019. The experiment was carried out as a factorial experiment in a completely randomized block design with three replications. The experiment factors included eight irrigation treatments (A: Irrigation with Karun River water as control), (F: Irrigation with treated municipal wastewater). (Z: Irrigation with agricultural drainage water), (Z1F1: 30% Agricultural drainage water +70% Treated municipal wastewater), (Z2F2: 70% Agricultural drainage water +30% Treated municipal wastewater), (Z3F3: 50% Agricultural drainage water +50% Treated municipal wastewater), (Z4A4:50% Agricultural drainage water +50% Karun River water), (F5A5: 50% Treated municipal wastewater +50% Karun River water), at five time levels (including pre-treatment, first month, second month, fourth month, sixth month were performed at three depths (0–20), (20–40), (40–60) cm. The traits examined in this experiment were pH (Acidity), EC (Electrical Conductivity), Ca2+ (Calcium), Mg2+(Magnesium), Na+(Sodium), K+(Potassium), HCO3-(Bicarbonate), CO3 −2(Carbonate), SAR (Sodium Adsorption Ratio). Experimental factors had different effect on studied traits. Results showed that with increasing soil depth, all treatments except carbonate and acidity decreased. Calcium, magnesium, sodium and bicarbonate showed significant differences over time (P < 0.01). Non-significant difference in potassium was observed during this time (P > 0.01). There was significant increase in salinity over time (P < 0.01). In T1 period Karun River water showed the highest salinity amount irrigation treatment. Also, F5A5 treatment had the lowest concentration of Ca2+, Mg2+, K+ and the highest concentration of SAR. The Z4F4 treatment showed the lowest concentration of SAR and the highest concentration of Mg2+.The Z treatment had the lowest concentration for Mg2+. The A treatment showed the lowest concentration for HCO3-. The F treatment had the highest concentration for Ca2+; the Z3F3 treatment had the highest concentration for K+, the Z1F1 and Z2F2 treatments showed the highest concentration in terms of SAR.

Impact of Al-Ahdeb Oil Field on the Surrounding Environment Using Remote Sensing and GIS Techniques, Wasit Governorate, Iraq

Remote sensing and Geographical Information System (GIS) are used in this study to detect environmental changes in the vicinity of Al-Ahdeb oil field, southwest of Kut City, Wasit Governorate. Different image indices, such as Normalized Differences Vegetation Index (NDVI), Normalized Differences Soil Index (NDSoI), and Normalized Differences Salinity Index (NDSI) are used. Two LANDSAT images with acquired data of September 2007 and 2016 are used to detect the environmental changes and to detect the effect of Al-Ahdeb oil field before and after construction and industrial operation. The results of change detection show there is a high decrease in the vegetation cover during the year 2016 compared with 2007, where the area of vegetation cover has decreased from (165.85 Km 2 ) in 2007 to (119.62 Km 2 ) in 2016. The change detection results from NDSI show that the saline soil in (2016) is higher than those in (2007). The NDSI derived from Landsat TM (2007) image confirms that there is significant increase of salinity in the study area, where the calculated area of the salinity in 2007 is (5.65 Km 2 ) while in 2016 it is (21.951 Km 2 ). Change detection, using NDSoI, show that the land in the study area is going toward desertification and soil degradation. The decrease in the vegetation cover, which in turn led to soil erosion in addition to water shortage and the pollution by the waste of the oil field, could be the main reasons of the desertification in the area. Keywords: Environmental change detection; Image Indices; NDVI; NDSI; NDSoI; Al Ahdeb oil field. DOI: 10.7176/JEES/12-8-03 Publication date: August 31 st 2022

ЗАСОЛЕННЯ РІЧКОВИХ ВОД В УМОВАХ УРБОЛАДШАФТНОЇ ГЕОСИСТЕМИ І ПОТЕПЛІННЯ КЛІМАТУ

Purpose. The growth of surface water salinity in urban landscapes due to both anthropogenic factors and gradual global climate change is studied. The influence of various factors is analyzed, according to the data that have been published in recent years. Methodology. Statistics on the state of surface waters, acidity of precipitation and the quality of drinking water in Ukraine show that in the southern and south-eastern regions the situation is becoming threatening. As Kharkiv region is one of the three leaders in the demands for drinking and technical water among the regions of Ukraine, the analysis of water sources in the Kharkiv region is carried out. Results. The results of measurements of chemical parameters of water samples from different parts of the river system Kharkiv-Lopan-Uda in Kharkiv: at the entrance of each river into the city, at industrial sites, at the mouth and at the exit of the river Uda from the city. It is shown that in recent years there has been a steady increase in the total concentration of salts. The rivers Kharkiv, Lopan and Udy at the entrance to the territory of Kharkiv have a fairly low content of sulfates, chlorides, magnesium and calcium, but after the passage of industrial areas to the city center there is a significant increase in salinity and water hardness. Our own data are in good agreement with the results of water quality tests by other laboratories. Thus, in the context of global climate change, the salt content in the river system Kharkiv-Lopan-Uda increases, which significantly affects the system of groundwater and drinking water. Originality. In the research the detailed data on concentrations of the ions Cl-, SO42-, Са++, Mg++ in 12 locations along the three rivers (Kharkiv, Lopan, Udy) of the complex river sys- tem in different seasons (spring, summer, autumn) have been studied and compared to similar data from open sources. The statistical dependencies of the relative concentrations during the last 40 years have been analyzed. Practical meaning. It is determined that the concentrations of some ions demonstrate the monotones growth during the last years, while others varies non-monotonously. Therefore, the influence of different natural and antropogenic factors on global gradual increase in the river water salinity can be quantified by a complex index weighted over a set of concentrations. Conclusions. The results of the literature and measurement data analysis confirmed that with increasing anthropogenic factors and global climate change, the level of surface and groundwater in the urban area of Kharkiv region will decrease and their quality will deteriorate due to increased salinity, calcification and levels of a number of pollutants, which requires further detailed study of this complex problem, permanent data monitoring and systematization in the open access sources of information, which can be processed both by statistical methods and with the help of new system dynamic approaches for the dynamical systems with the ability to control and stabilize the system.

Eddy Induced Trapping and Homogenization of Freshwater in the Bay of Bengal

AbstractFreshwater from rivers influences Indian summer monsoon rainfall and tropical cyclones by stratifying the upper layer and warming the subsurface ocean in the Bay of Bengal (BoB). Here, we use in situ and satellite data with reanalysis to showcase how river water experiences a significant increase in salinity on sub‐seasonal timescales. This involves the trapping and homogenization of freshwater by a cyclonic eddy in the Bay. Using a specific example from 2015, river water is shown to enter an eddy along its attracting manifolds within a period of 2 weeks. This leads to the formation of a highly stratified subsurface layer within the eddy. When freshest, the eddy has the largest sea‐level anomaly, spins fastest, and supports strong lateral gradients in salinity. Subsequently, observations reveal a progressive increase in salinity inside the eddy within a month. In particular, salty water spirals in, and freshwater is pulled out across the eddy boundary. Lagrangian experiments elucidate this process, whereby horizontal chaotic mixing provides a mechanism for the rapid increase in surface salinity. A salinity budget also suggests that horizontal advection explains much of the change in mixed layer salinity. Further, the adjustment of this freshwater eddy triggers submesoscale dynamics which appear to be an integral part of the process of salinity homogenization. This pathway is distinct from vertical diffusive mixing and is likely to be important for the evolution of salinity in the BoB.

The Effect of Discharge Rejected Brine into the Surface Water on the coast of Port Sudan city

The general aim of this study is to focus on the effects of discharge reject brine into the surface water in Port Sudan city. It considers a baseline study in Port Sudan. Three samples of water were taken from sea land lagoon by using TCD (Temperature, Conductivity and Depth) device, and sample from open sea (Abu Hashish). All samples were collected during summer and winter seasons. The results showed a significant increase in salinity 39.13 – 49.86 , 39.91- 47.45 , 38.62 - 38.87 , 38.48 – 39.27 psu respectively, of the surface water when mixed with the discharge reject brine, this will absolutely affect the marine life. Also, the continuous discharge of rejected brine into water near the intake desalination plants will affect the characteristics of the feed water.

Significant salinity increase in subsurface waters of the South China Sea during 2016–2017

The South China Sea (SCS) is the largest semi-enclosed marginal sea in the North Pacific. Salinity changes in the SCS play an important role in regional and global ocean circulation and the hydrological cycle. However, there are few studies on salinity changes over the SCS due to lack of high-quality and long-term observations. In the past decade, the deployment of floats from the Argo program in the SCS and their accumulated temperature and salinity profiles have made it possible for us to examine salinity changes over the entire basin. In this study, salinity changes were investigated with Argo and underwater glider temperature and salinity observations and gridded temperature-salinity objective analyses (UK Met Office Hadley Centre EN4.2.1 objective analysis and China Argo Real-time Data Center BOA_Argo). The results indicated that the subsurface water in the entire SCS became significantly saltier during 2016–2017. The most significant salinity increase was found during 2016 in the northeastern SCS. The subsurface water in the northeastern SCS exhibited a salinity maximum above 35, which was recorded by three Argo floats during 2015–2016. Such high salinity water was rarely observed and reported prior to the Argo era. Average salinity of 2016–2017 along the 25.5σθ−23.5σθ isopycnal surfaces in the whole SCS is 0.014−0.130 higher than the climatology. Increases in subsurface salinity started from the northeastern SCS and extended southwestward gradually. Moreover, the subsurface salinity changes, especially in the northern SCS, exhibited a semiannual lead behind the subsurface Luzon Strait transport. Further analysis indicated that the predominance of advection, driven by subsurface Luzon Strait transport, led to salinification along the western boundary of the SCS. In other parts of the SCS, negative wind stress curl trends tended to preserve the high salinity characteristics of the subsurface water.

Characterization of the Outfall Area of a Multi-Stage-Flash Desalination Plant in Bahrain

In Bahrain, like the other Gulf Cooperation Council (GCC) countries, desalination is inevitable to meet the escalating municipal water demands. However, desalination is associated with many environmental effects, which need to be minimized to their lowest possible limits. One of the major environmental concerns of desalination in the Arabian Gulf region is the local and regional effects of the outfall areas on the marine environment. In this study, the outfall area of a government-owned MSF desalination plant is characterized in terms of temperature and salinity. The spatial extent of the plume of the desalination plant’s effluent is mapped by a field survey conducted during the winter season around the plant’s outfall area at 25 cm and 1 m below the water surface and at low and high tide. The results of the characterization indicated that the temperature of the brine discharged to the outfall was 37°C, higher than the ambient seawater temperature by 16.5°C at high tide and 17.5°C at low tide, and that the extent of the mixing zone area was found at about 260 m and 1 km from the outfall point at high tide and low tide, respectively. The results also showed that brine thermal discharge is not in compliance with the standard limits (<3°C from ambient within 100 m of shoreline) both at high and low tides with differences reaching more than 10°C. In terms of salinity, the brine discharged salinity was 56.2 parts per trillion (ppt) compared to an ambient seawater salinity of 43.2 ppt. The maximum salinity measured near the outfall point was 56 ppt at low tide and 51 ppt at high tide, both at 1 m below the surface water column. It is found that the current design structure consisting of two jetties to isolate the desalination plant outfall area from its surroundings is not environmentally sound, as the current surface/inter-tidal outfall location is susceptible to significant increases in salinity and temperature around the outfall area due to the limited flushing it experiences. Therefore, the current design of the outfall area needs to be reviewed to ensure meeting brine discharge regulations and mitigate its impact on the surrounding marine area. The spatial extent of the brine plume can be minimized by building a discharge area further offshore at a sub-tidal location where turbulent flow exists to minimize the spatial extent and intensity of the brine plume. It is recommended that this characterization be extended to all desalination plants in Bahrain, and a regular monitoring program, which should also include selected biological communities and organisms of ecological relevance, be established around the desalination plants outfall areas.

Caracterização sazonal das águas do sistema estuarino do Caeté (Bragança-PA)

Investigou-se o efeito das marés de sizí­­gia na qualidade fí­­sica, quí­­mica e biológica da água de canais-de-maré, considerando a sazonalidade regional e a distribuição espacial do furo do Taici e do furo da Estiva no estuário do Caeté. As variáveis abióticas foram determinadas in situ durante o ciclo diurno da maré. Os nutrientes e a clorofilaí a foram determinados por espectrofotometria. Em Taici houve aumento significativo da salinidade (18,57±2,78) e do nitrito (12,93±7,92 µM) no perí­­odo seco, enquanto que no chuvoso foram registradas elevadas turbidez (&gt;900UNT) e clorofila-a (12,09±5,72 µg.L-1). Em Estiva, a salinidade apresentou valores distintos no perí­­odo seco (36,84±1,37) e no chuvoso (21,56±5,54). Na enchente foram registrados valores de pH (7,72±0,18) e oxigênio dissolvido (6,62±0,54 mg.L-1) superiores aos da vazante. Os valores da temperatura (29,26±1,08 °C), fosfato (1,73±1,43 µM) e clorofila-a (33,6±14,74 µg.L-1) foram mais elevados na vazante. O furo da Estiva sofreu influência de águas costeiras, e o do Taici, influência da drenagem do manguezal.

Environmental control on shell size of Middle Triassic bivalve Plagiostoma

Fossil shells of the marine bivalve Plagiostoma striatum Schlotheim sampled from the Middle Triassic (so-called Muschelkalk) of Poland demonstrate that, under unfavourable environmental conditions, this species commonly occurring in Triassic German basins exhibits a dwarfed shell. As a consequence of a marine regression episode resulting in a significant increase of salinity and a partial emersion of seafloor these bivalves vanished. The next transgressive pulse caused a re-emergence of these bivalves. They were initially characterized by half-size shells than in the population living prior to the regression episode and, subsequently, during progressive transgression, their shells returned to normal size. Coincidence between eustatic curve and changes in bivalve shell size and their disappearance may be attributed also to biotic interactions, such as a biotic collapse in primary bioproductivity or/and a competition for space or any other resources due to shelf habitat loss during regressive periods.

Decadal trends of the upper ocean salinity in the tropical Indo-Pacific since mid-1990s.

A contrasting trend pattern of sea surface salinity (SSS) between the western tropical Pacific (WTP) and the southeastern tropical Indian Ocean (SETIO) is observed during 2004–2013, with significant salinity increase in the WTP and freshening in the SETIO. In this study, we show that increased precipitation around the Maritime Continent (MC), decreased precipitation in the western-central tropical Pacific, and ocean advection processes contribute to the salinity trends in the region. From a longer historical record, these salinity trends started in the mid-1990s, a few years before the Global Warming Hiatus from 1998 to present. The salinity trends are associated a strengthening trend of the Walker Circulation over the tropical Indo-Pacific, which have reversed the long-term salinity changes in the tropical Indo-Pacific as a consequence of global warming. Understanding decadal variations of SSS in the tropical Indo-Pacific will better inform on how the tropical hydrological cycle will be affected by the natural variability and a warming climate.

Investigation of the causes of historical changes in the subsurface salinity minimum of the South Atlantic

AbstractIn this study, we investigate the subsurface salinity changes on decadal timescales across the subtropical South Atlantic Ocean using two ocean reanalysis products, the latest version of the Simple Ocean Data Assimilation and the Estimating the Circulation and Climate of the Ocean, Phase II, as well as using additional climate model experiments. Results show that there is a recent significant salinity increase at the core of the salinity minimum at intermediate levels. The main underlying mechanism for this subsurface salinity increase is the lateral advective (gyre) changes due to the Southern Annular Mode variability, which conditions an increased contribution from the Indian Ocean high salinity waters into the Atlantic. The global warming signal has a secondary but complementary contribution. Latitudinal differences at intermediate depth in response to large‐scale forcing are in part caused by local variation of westward propagation features, and by compensating contributions of salinity and temperature to density changes.

Lateral Saltwater Intrusion in the North Channel of the Changjiang Estuary

Saltwater intrusion typically develops in the along-channel direction but exceptions can be found in bifurcated estuaries. Based on the observational data, we found that the saltwater intrusion in the upper reaches of the North Channel (NC) of Changjiang Estuary is dominated by the lateral saltwater intrusion from a small northern outlet (denoted as NONC) of this channel. This phenomenon has severe effects on the freshwater usage in this region. To investigate the underlying mechanisms of this pattern of intrusion, numerical experiments were conducted using a well-validated model. A flux decomposing method was used to decompose the process of saltwater intrusion into several mechanisms. During the neap tide, the saltwater begins to intrude landward into the NONC through shear transport induced by estuarine circulation. During the transition period between the neap tide and the following spring tide, the saltwater that previously reached the NONC further intrudes into the NC via Lagrangian and tidal pumping transports, causing a significant salinity increase in the middle and upper reaches of the NC. During the spring tide and the subsequent middle tide, saltwater intrusion in the NONC retreats. The impacts of the topography of the NONC and the wind stress on this lateral saltwater intrusion were also evaluated in this study.

Gypsum addition to soils contaminated by red mud: implications for aluminium, arsenic, molybdenum and vanadium solubility

Red mud is highly alkaline (pH 13), saline and can contain elevated concentrations of several potentially toxic elements (e.g. Al, As, Mo and V). Release of up to 1 million m(3) of bauxite residue (red mud) suspension from the Ajka repository, western Hungary, caused large-scale contamination of downstream rivers and floodplains. There is now concern about the potential leaching of toxic metal(loid)s from the red mud as some have enhanced solubility at high pH. This study investigated the impact of red mud addition to three different Hungarian soils with respect to trace element solubility and soil geochemistry. The effectiveness of gypsum amendment for the rehabilitation of red mud-contaminated soils was also examined. Red mud addition to soils caused a pH increase, proportional to red mud addition, of up to 4 pH units (e.g. pH 7→11). Increasing red mud addition also led to significant increases in salinity, dissolved organic carbon and aqueous trace element concentrations. However, the response was highly soil specific and one of the soils tested buffered pH to around pH 8.5 even with the highest red mud loading tested (33% w/w); experiments using this soil also had much lower aqueous Al, As and V concentrations. Gypsum addition to soil/red mud mixtures, even at relatively low concentrations (1% w/w), was sufficient to buffer experimental pH to 7.5-8.5. This effect was attributed to the reaction of Ca(2+) supplied by the gypsum with OH(-) and carbonate from the red mud to precipitate calcite. The lowered pH enhanced trace element sorption and largely inhibited the release of Al, As and V. Mo concentrations, however, were largely unaffected by gypsum induced pH buffering due to the greater solubility of Mo (as molybdate) at circumneutral pH. Gypsum addition also leads to significantly higher porewater salinities, and column experiments demonstrated that this increase in total dissolved solids persisted even after 25 pore volume replacements. Gypsum addition could therefore provide a cheaper alternative to recovery (dig and dump) for the treatment of red mud-affected soils. The observed inhibition of trace metal release within red mud-affected soils was relatively insensitive to either the percentage of red mud or gypsum present, making the treatment easy to apply. However, there is risk that over-application of gypsum could lead to detrimental long-term increases in soil salinity.

The Impact of Extreme Low Flows on the Water Quality of the Lower Murray River and Lakes (South Australia)

The impact of extreme low flows on the water quality of the Lower Murray River and Lower Lakes (Alexandrina and Albert) in South Australia was assessed by comparing water quality from five sites during an extreme low flow period (March 2007–November 2009) and a preceding reference period (March 2003–November 2005). Significant increases in salinity, total nitrogen, total phosphorus, chlorophyll a and turbidity were observed in the Lower Lakes during the low flow period. Consequently, water quality guidelines for the protection of aquatic ecosystems were greatly exceeded. Principal Component Analysis, empirical and mass balance model calculations suggested these changes could be attributed primarily to the lack of flushing resulting in concentration of dissolved and suspended material in the lakes, and increased sediment resuspension as the lakes became shallower. The river sites also showed significant but more minor salinity increases during the extreme low flow period, but nutrient and turbidity concentrations decreased. The most plausible reasons for these changes were decreased catchment inputs and increased influence of saline groundwater inputs. The results highlight the vulnerability of arid and semi-arid lake systems to reduced flow conditions as a result of climatic changes and/or water management decisions.