Main Cations Research Articles

Chemosensory modulation of neural circuits for sodium appetite.

Sodium is the main cation in the extracellular fluid that regulates various physiological functions. Sodium-depletion in the body elevates the hedonic value of sodium taste, which drives animals toward sodium consumption 1,2. Conversely, oral sodium detection rapidly promotes satiation of sodium appetite 3,4, suggesting that chemosensory signals have a central role in sodium appetite and its satiety. Nevertheless, the neural basis of chemosensory-based appetite regulation remains poorly understood. Here, we dissect genetically-defined neural circuits in mice that control sodium intake by integrating sodium taste and internal depletion signals. We show that a subset of excitatory neurons in the pre-locus coeruleus (pre-LC) that express prodynorphin (PDYN) serve as a critical neural substrate for sodium intake behavior. Acute stimulation of this population triggered robust sodium ingestion even from rock salt by transmitting negative valence signals. Inhibition of the same neurons selectively reduced sodium consumption. We further demonstrate that peripheral chemosensory signals rapidly suppressed these sodium appetite neurons. Simultaneous in vivo optical recording and gastric infusion revealed that sensory detection of sodium, but not sodium ingestion per se, is required for the acute modulation of pre-LC PDYN neurons and satiety of sodium appetite. Moreover, retrograde virus tracing showed that sensory modulation is partly mediated by specific GABAergic neurons in the bed nucleus of the stria terminalis. This inhibitory neural population is activated upon sodium ingestion, and sends rapid inhibitory signals to sodium appetite neurons. Together, this study reveals a dynamic circuit diagram that integrates chemosensory signals and the internal need to maintain sodium balance.

THE USE OF THE ISOTOPIC METHOD IN THE ASSESSMENT OF THE URBANIZATION OF ATMOSPHERIC PRECIPITATION IN MOSCOW

The study was carried out on the basis of all the individual samples (101 cases) of precipitation for 2014, sampled at the Meteorological Observatory of Moscow State University. The concentrations of the main anions and cations, the total mineralization and δ18O values were determined. 12 cases of relatively high mineralization of precipitation were recorded. Average weighted mineralization values ranged from 12.0 to 67.7 mg/L, specific values of mineralization varied from 3.2 to 229.0 mg/L. Chlorine prevails among anions, calcium prevails among cations. The used isotope data analysis and backward trajectories of air masses showed the hydro-chemical composition of precipitation in Moscow not to be linked to the origin of air masses. This indicates to the predominantly urban origin of pollutants in precipitation. In general, in 2014 precipitation were significantly more mineralized than in previous years of observations, due to the climatic conditions of a particular year - small amount of precipitation and number of days with precipitation. This has led to the accumulation of pollutants in the atmosphere and the poor washout of pollutants.

Dynamics of sulfate and basic cations in soil solution as affected by gypsum fertilization in an Ultisol of Southern Brazil

ABSTRACTThe objective of this study was to evaluate the short-term dynamics of chemical species of sulfate and the main basic cations in the soil solution affected by the application of different sulfur (S) rates using agricultural gypsum. The experiment was carried out in an Ultisol with 14% clay, managed under no-tillage for 14 yrs in Southern Brazil. Four rates of S (0, 5, 10 and 20 kg of S ha−1) were evaluated using agricultural gypsum (CaSO4) as S-source. The soil solution was collected using porous capsule lysimeters before and at 9, 17, 37, 60, 76 and 109 d after the gypsum application, at depths of 20 and 60 cm. Surface application of gypsum rapidly increases the sulfate concentration in the soil solution at 20 cm depth. However, in less than 30 d, the effect of the S rates on the soil solution at 20 cm was minimal, with an increase in sulfate concentration in the soil solution at 60 cm depth after 17 d. Sulfated fertilization via agricultural gypsum at rates greater than 10 kg ha−1 in sandy soil with low cation exchange capacity increased the mobility of Ca and Mg in the soil profile.

Hydrochemical Diversity of a Large Alluvial Aquifer in an Arid Zone (Draa River, S Morocco)

Abstract In arid areas, with rivers functioning episodically, alluvial resources are the main source of water. Considering the intensified regulation of discharge in montane catchments, supplying the intermittent rivers, in the nearest future alluvial aquifers will gain key importance for the functioning of people in arid zones. The research aimed to investigate the diversified chemistry of alluvial waters typical of large intermittent river valleys in hot arid zones as well as to analyse processes determining the water chemistry and affecting its diversity. The detailed study, carried out in October 2015, covered the Draa river valley (1100 km total length) in the region of the Mhamid Oasis. The examined water was sampled from all wells found in the study area. Concentrations of the main cations: Ca2+, Mg2+, K+, Na+, NH4 +, and Li+, anions: Cl−, SO4 2−, HCO3 −, and NO3 −, as well as trace elements: Al, As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Sr, and Zn, were identified. Results were analysed with statistical, hydrochemical, and geochemical modelling methods. Alluvial waters of the eastern and western part of the oasis differed in concentrations of numerous components, what resulted from the regulation of irrigation. Specific electrical conductivity showed a 3.5-fold increase, from 3800 to 13800 μS/cm, consistent with the direction of water flow in the oasis, from east to west. Even a greater rise was observed for ions: Cl− (6x), Na+ (5.5x), Mg2+ (5.0x), Ca2+, and SO4 2− (3.5x). Such a composition indicated multiionic hydrochemical type of waters dominated by Na+ and Cl−. Additionally, high Pearson correlation coefficients were recorded for Na+ and Cl− (0.98) as well as Mg2+ and Cl− (0.97). The saturation index suggested that the main water components originated from dissolving of minerals such as halite, anhydrite, sylvite, and gypsum. Groundwater chemistry in the Mhamid Oasis was determined mainly by geogenic processes, such as dissolving of evaporates, precipitation of carbonate minerals, and ion exchange.

Ion substitution induced formation of spherical ceramic particles

How to precipitate ceramic nano- and microspheres in water based solutions only using inorganic ions is a challenge. In this study, spherical particles of alkaline earth phosphates and fluorides were synthesized using a precipitation reaction. Substituting ions, through inhibition of crystal growth, was used to induce sphere formation and to alter the morphology, size and composition of the spheres. The difference in ionic radius between the substituting ion (Mg, Ca and Sr) and the main cation (Sr and Ba) influenced the critical concentration to allow for sphere formation as well as the crystallinity. The larger difference, the lower was the concentration needed to form spheres. Low concentrations of Mg was enough to generate amorphous spheres of Sr- and Ba-phosphates whereas higher concentrations were needed if the radius difference were smaller. An increasing degree of substitution leads to a decrease in crystallinity of precipitated particles. The degree of substitution was determined to 16–55% where a low degree of ion substitution in the phosphates resulted in the formation of spheres (500–800 nm) with rough surfaces composed of apatite like phases. A higher degree of substitution resulted in amorphous spheres (500 nm- 1 μm) with smooth surfaces.

Effects of low-molecular weight organic acids on the transport of graphene oxide nanoparticles in saturated sand columns

The impact of low-molecular weight organic acids (LMWOAs) on the transport of graphene oxide (GO) nanoparticles in saturated quartz sand was investigated. The different LMWOAs such as acetic acid, glycolic acid, malonic acid, and tartaric acid were used in experiments. The effects of LMWOAs on the transport of GO were markedly dependent upon organic acid species. In general, the transport enhancement effects followed the order of tartaric acid > malonic acid > glycolic acid > acetic acid, the regular pattern might be related to amount and type of functional groups of LMWOAs. Additionally, the different enhanced ability of LMWOAs was determined by their molecular weight. In the presence of Na+, the main deposition mechanism was ascribed to steric hindrance and competition between LMWOA and GO for deposition sites on grain surfaces under acidic conditions (i.e., pH 4.0 and 5.0). Batch adsorption experiments indicated the extents of competitive adsorption between LMWOAs and GO on quartz sand. In addition, the DLVO theory was not applicable to describe the transport of GO in the presence of LMWOAs at pH 5.0. Nevertheless, electrostatic and steric repulsion, existing between GO and sand grains, were the most important deposition mechanisms under the neutral condition (i.e., pH 7.0). When Ca2+ was the main cation in the background solution, the transport enhancement effects followed quite similar order to those of Na+, mainly due to different complexing strength of organic acids.

Sulfate variations as a natural tracer for conduit‐matrix interaction in a complex karst aquifer

AbstractLarge areas of Europe, especially in the Alps, are covered by carbonate rocks, and karst springs are an important source for drinking water supply. Because of their high variability and heterogeneity, understanding the hydrogeological functioning is of particular importance for protection of karst aquifers. In this study, hydrogeochemical investigations characterized the water of a spring draining a complex carbonate‐gypsum karst system in the Alps. The reaction of the spring to a rainfall event was examined to identify the relevant hydrological processes controlling the hydrochemistry of the spring, and to understand water‐rock interactions and conduit–matrix exchange. A fast and marked reaction of discharge and electrical conductivity was observed. The main cations are Ca2+ and Mg2+, which showed a distinct decrease after the rainfall. Bicarbonate and sulfate were identified as major anions. Although HCO3− showed only minor fluctuations, SO42− decreased by 72% after the rain event. Comparisons of ion ratios show that both carbonate and gypsum rocks influence the water chemistry of the spring. The rainfall event caused a dilution effect, but dilution alone cannot explain the observed water chemistry. A conceptual model of the spring behaviour during low‐flow and high‐flow conditions, including conduit–matrix interaction, was developed, which can explain the observations. This study aims to give new insights into the highly dynamic exchange processes between karst conduits and the surrounding matrix, and the results demonstrated that (a) during low‐flow conditions, the spring is characterized by high sulfate content, but after rainfall events, the water chemistry is dominated by bicarbonate. These findings show the dependency of water chemistry from the lithology; (b) a change in water chemistry is associated with a significant shift from low‐flow to high‐flow conditions; (c) conduit–matrix exchange is an important factor as shown by the discharge–sulfate relationship and clearly influences the behaviour of the spring.

The Complex Fine-Tuning of K⁺ Fluxes in Plants in Relation to Osmotic and Ionic Abiotic Stresses.

As the main cation in plant cells, potassium plays an essential role in adaptive responses, especially through its involvement in osmotic pressure and membrane potential adjustments. K+ homeostasis must, therefore, be finely controlled. As a result of different abiotic stresses, especially those resulting from global warming, K+ fluxes and plant distribution of this ion are disturbed. The hormone abscisic acid (ABA) is a key player in responses to these climate stresses. It triggers signaling cascades that ultimately lead to modulation of the activities of K+ channels and transporters. After a brief overview of transcriptional changes induced by abiotic stresses, this review deals with the post-translational molecular mechanisms in different plant organs, in Arabidopsis and species of agronomical interest, triggering changes in K+ uptake from the soil, K+ transport and accumulation throughout the plant, and stomatal regulation. These modifications involve phosphorylation/dephosphorylation mechanisms, modifications of targeting, and interactions with regulatory partner proteins. Interestingly, many signaling pathways are common to K+ and Cl−/NO3− counter-ion transport systems. These cross-talks are also addressed.

Relationship between Soil Salinization and Groundwater Hydration in Yaoba Oasis, Northwest China

Precipitation is scarce and evaporation is intense in desert areas. Groundwater is used as the main water source to develop agriculture in the oases. However, the effects of using groundwater on the ecological environment elicit widespread public concern. This study investigated the relationship between soil salinity and groundwater characteristics in Yaoba Oasis through in situ experiments. The relationship of the mineral content, pH, and main ion content of groundwater with soil salt was quantitatively evaluated through a gray relational analysis. Four main results were obtained. First, the fresh water area with low total dissolved solid (TDS) was usually HCO3− or SO42− type water, and salt water was mostly Cl− and SO42−. The spatial distribution of main ions in groundwater during winter irrigation in November was basically consistent with that during spring irrigation in June. However, the spatial distribution of TDS differed in the two seasons. Second, soil salinization in the study area was severe, and the salinization rate reached 72.7%. In this work, the spatial variability of soil salinization had a relatively large value, and the values in spring were greater than those in autumn. Third, the soil in the irrigated area had a high salt content, and the salt ion content of surface soil was higher than that of subsoil. A piper trilinear diagram revealed that Ca2+ and K+ + Na+ were the main cations. SO42−, Cl−, and HCO3− were the main anions, and salinization soil mainly contained SO42−. Fourth, the changes in soil salt and ion contents in the 0–10 cm soil layer were approximately similar to those of irrigation water quality, both of which showed an increasing trend. The correlation of surface soil salinity with the salinity of groundwater and its chemical components was high. In summary, this study identified the progress of irrigation water quality in soil salinization and provided a scientific basis for improving the oasis ecosystem, maintaining the healthy development of agriculture, managing oasis water resources, and policy development. Our findings can serve as a reference for other, similar oasis research.

Hydrochemical Characteristics and Water Quality Assessment of a Zn-Pb Mine Waters in Yunnan Southwest China

Water samples (rivers, streams, mine adits, tailings ponds) from Jinding zinc-lead polymetallic mining area and Bi River Basin were analysed for 32 indicators including major hydrochemical components and heavy metals. The correlation analysis of water chemical parameters and Gibbs diagram show that the water composition of the Bi River is influenced by human activities in addition to the rock weathering. In the streams, the main cations and anions are derived from the rock weathering of formations rich in gypsum, calcite and dolomite. Nemerow comprehensive pollution index method was performed to evaluate water quality. The water of streams and one pond is clean. Mine adits water pollution level is medium-heavy pollution. The water samples flowing through the mining area and from tailings ponds are heavy polluted.

Zn sorption on Ca-illite and Ca-smectite: experiment and modelling

To predict Zn behaviour in soil, the retention properties of clay minerals plays a relevant role. In a continental environment, Ca is the main cation in solution. Soil reactivity may be reduced to sorption properties of Zn and Ca on illite and smectite, the major clay minerals in soil. With this assumption, a multi-site ion exchanger model has successfully been applied to the Zn sorption on Ca-illite and Ca-smectite. New batch experiments performed in this study enabled to collect sorption data for Zn on Ca-illite by concentration and pH isotherms. Zn sorption reversibility was then verified. These sorption data were modelled successfully with a multi-site ion exchanger (MSIE) formalism by using four sorption site types. Zn sorption isotherms on smectite were retrieved from literature and interpreted following the MSIE formalism. The obtained selectivity coefficients may be thereafter put into ion exchange models to describe the Zn sorption in natural environments.

Optimal Fluoride Concentration in Drinking Water as a Function of Calcium Content

Fluoride (F-) is known to have both beneficial and adverse effects on humans, depending on the total intake. Drinking water, usually obtained from groundwater, is the primary source of fluoride intake. Estonian aquifer systems differ from each other in bedding conditions, hydraulic parameters and chemical composition and fluorides are released into the groundwater mostly through water-rock interaction. The present study bases on long term groundwater monitoring data and was undertaken to assess the occurrence of fluoride values in abstracted drinking water over the whole of Estonia and their relation to groundwater’s calcium content. Fluoride concentration in 4404 water samples ranges from 0 to 6.71 mg/l. Values higher than 1.5 mg/l were detected in 8 % of samples, mostly in Silurian-Ordovician aquifer system, composed of limestones and dolomites. Low fluoride area in southern Estonia coincides with the outcrop of Devonian sedimentary rocks, where the major source of drinking water is terrigenous Middle-Devonian aquifer system. The occurrence of fluorides is correlated to variations in groundwater chemical type, which is the function of the proportional content of main cations and anions. The highest F- values prevail in wells, which produce the water with low Ca2+ content and vice versa. Thus, the content of calcium ions in groundwater has an important effect on fluoride concentration, insofar as Ca is an element that removes F from water through CaF2 formation and precipitation. Generally, in terrigenous aquifer systems consisting of sand- and siltstones the optimal fluoride content (0.7-1.2 mg/l) is achieved at the calcium concentration within 30-120 mg/l, in carbonaceous Silurian-Ordovician aquifer calcium content which provides the optimal fluoride amount in carbonaceous aquifer system is 150-340 mg/l.

Detection of leakage paths at the Wanyao dam body in Southwest China by hydrochemical analysis and tracer testing

Leakage at the Wanyao dam body was studied using a combined approach of field exploration, hydrochemical analysis and tracer testing. The objective of study was to determine the location of the water leakage paths at the dam. A hydraulic connection was observed between exploration boreholes of dam crest and drain holes at drainage gallery during the period of drilling. This connection shows that there were some defects in the dam. The hydrochemical compositions and characteristics of the water samples involved the main anions and cations, total dissolved solids, electrical conductivity, pH and water temperature which were analyzed and evaluated by correlation and cluster analysis. The results indicated that a close hydraulic connection existed between water from the dam body and reservoir water, particularly reservoir water from Sections III and IX. Tracer testing results demonstrated further existence of leakage paths between reservoir water and Sections III and IX. Also, there were multiple leakage paths in Section IX compared with a single path of Section III. Furthermore, the leakage location of upstream concrete faces in the vertical and horizontal directions was determined accurately with the measured electrical conductivity of receiving points. The experimental data provide a strong foundation and basis for maintaining and reinforcing the dam.

Structural Features, Physicochemical, and Optical Characteristics of Lithium Niobate Crystals Grown from Boron-Doped Melts

Chemical interactions in the Li2O−B2O3−Nb2O5 system, as well as certain features of crystallization of LiNbO3 crystals growing from melts containing nonmetal impurities, are considered. It is shown that boron changes the structure of the melt and has a significant impact on the structure and physical characteristics of LiNbO3 : В crystals, practically not entering the lithium niobate structure. Notable changes and certain features were found in the Raman spectra of grown LiNbO3 : В crystals, which indicates changing the sequence of the main cations and vacancies along a crystal polar axis and distortion of the oxygen octahedrons. Meanwhile, the distortion of the oxygen octahedrons is anisotropic. LiNbO3 : В crystals have a higher structural homogeneity than congruent crystals, and are close in the number of NbLi defects to a crystal with a stoichiometric composition, differing from it by a substantially less photorefraction effect.

Natural background levels and seasonal influence on groundwater chemistry of the Upper São Francisco karst region, MG, Brazil

ABSTRACT: Karst aquifers are large water reservoirs that supply approximately 25% of the world population. They are also extremely sensitive to contamination, demanding knowledge on groundwater quality regarding base level conditions for the main cations and anions. Knowing the Natural Background Level (NBL) values of these waters becomes an indispensable measure to understand aquifers and hydrochemical anomalies, either from anthropogenic or geogenic origin. This paper aimed to provide a hydrochemical characterization and to propose NBL 90% values for the little-studied groundwater of the Sao Miguel River watershed, Upper Sao Francisco River, MG, Brazil. NBL 90% values were estimated using statistical analyses followed by an analysis of seasonal influence on observed concentrations. The water was classified as calcium bicarbonate, with the highest NBL 90% values occurring during the rainy season for Ca 2+ , K + , HCO 3 - , SO 4 2- , Cl - , NO 3 - , and As 3+ . On the other hand, Mg 2+ , Na + , PO 4 3- , and Zn 2+ presented reduction in concentration during this season. Nitrate, phosphate and chloride anomalies (values above NBL 90%) are directly related to human action. Thus, monitoring and proposing NBL 90% values were an essential tool to help in understanding the hydrochemical behavior of waters in this watershed.

The hydrogeochemistry and geothermometry of the thermal waters in the Mouil Graben, Sabalan volcano, NW Iran

The emerging temperature of thermal springs within the Mouil Graben in the Sabalan volcano, a primary prospect for a geothermal power plant in Iran, varies from about 24 to 80 °C. The investigation was carried out by analyzing hydrogeochemistry (i.e., main cations and anions, trace elements and heavy metals) and environmental isotopes (i.e., δ18O, δ2H, tritium, and δ18C) of water from cold and thermal springs, deep wells and the Khiavchay River over the period from 1979 to 2016. The results were also combined with those from a geo–structural survey. The findings reveal that the ascending geothermal fluids around the summit of the Sabalan volcano primarily move into the Mouil Graben fault system where the intersection of the caldera rim faults and the main oblique-slip faults occur at the lowest topographic elevation around the volcano as an emergent dome. The waters in the graben can be categorized into four clusters G1 to G4. The thermal springs which are categorized into groups G1 and G2 result from the contribution of geothermal waters and/or the condensation of the geothermal steam into near–surface waters. The spring waters of group G1 are characterized by being of the chloride water type with the highest values for temperature and EC. The waters of this group predominantly result from the contribution of geothermal water and are then more appropriate for geothermometry. The spring waters of group G2 are characterized by acidic–sulfate water type with lower values for temperature and EC. The waters of this group which predominantly arise from the condensation of geothermal steam, are mainly cold and enriched by H2S into near–surface waters or steam heated waters and are not appropriate for thermometry. Notably, δ18O of the G1 water samples has a significant positive shift while in the G2 water samples there is either no shift or a small positive shift. The cold spring waters with a low δ18O ratio (G3 and G4) originate from precipitation percolated into the surrounding highlands. Moreover, it can be concluded that the controlling silica phase in the Mouil reservoir is quartz and the average temperature calculated by the quartz geothermometer (maximum steam loss) for the water samples from the deep wells is about 225–230 °C which is near the range of values determined in the deep wells (230–242 °C). The temperatures calculated for the water samples from the deep wells by the cation geothermometers of Na–K (169–349 °C), Na–K–Ca 174 to higher than 300 °C), Na–K–Ca–Mg (268 to higher than 350 °C), Mg–Li (167–266 °C), and Na–Li (226–258 °C) are higher than the temperature range determined in the deep wells (230–242 °C). The average temperature calculated for the water samples from the springs of group G1 using all the silica geothermometers (<196 °C) and the cation geothermometers of Na–K (236–290 °C), Na–K–Ca (194–221 °C), Na–K–Ca–Mg (more than 350 °C), and Mg–Li (∼64–126 °C) is different from the temperature range measured in the deep wells except that calculated by the Na–Li geothermometer (173–250 °C and 226 °C on average) which is relatively close to the measured range. The common discharging gas from the deep wells is CO2 (about 98% of the total gas). It seems that the volatile gases discharging from the deep wells come from a mixture of crustal/mantle and meteoric gas. The deep well gas samples lie well below the air saturation water line.

Major Ionic Features and Possible Controls in the Groundwater in the Hamatong River Basin

In order to study the major ion chemistry and controls of groundwater, 59 groundwater samples were collected and their major ions measured in the Hamatong River Basin. The hydrogeochemical characteristics of groundwater in this basin were analyzed by means of mathematical statistics, Piper triangular diagrams, Gibbs figures, and ionic relations, and the water chemical evolution and ion sources of the Hamatong River Basin were determined. The results showed that Ca2+ was the main cation in the groundwater, accounting for 22.1% to 72.4% of the total cations, with an average value of 48.7%. HCO3- was the main anion, accounting for 35.3% to 97.5% of the total anions, and with an average value of 80%. Total dissolved solids concentration ranged from 93.3 mg·L-1 to 521.1 mg·L-1 with a median value of 219.1 mg·L-1. The hydrochemical types of groundwater are HCO3-Ca, HCO3-Ca·Mg, and HCO3-Ca·Na. Chemical weathering rates of carbonates and silicates were estimated, and the chemical composition of groundwater samples located in the middle of Gibbs model indicated that the major chemical process of groundwater was controlled by rock weathering. Silicate weathering is believed to significantly contribute to dissolved solute compositions, and carbonate weathering played an important role as the source of dissolved ions.

Impact of Mainstream Backwater on the Water Environment of the Tributaries of the Three Gorges Reservoir at Low Water Level

To prevent the eutrophication of tributaries and guarantee water quality and safety in the Three Gorges Reservoir, research on the impact of mainstream backwater on tributary water environments is of great significance. The investigation and sampling of the Yangtze mainstream and its major tributaries in the reservoir region were performed from August 7 to August 12, 2016, through which the overall hydrochemical environment of the Three Gorges Reservoir has been revealed, and the impact of mainstream backwater on the hydrochemical characteristics of main tributaries has been determined during the low water level operation period. The results showed the following:① The electrical conductivity of the mainstream varied from 291 μS·cm-1 to 336 μS·cm-1, whereas that of the mainstream backwater unaffected zone of the tributary varied from 183.7 μS·cm-1 to 518 μS·cm-1. The electrical conductivity of the mainstream backwater affected zone of the tributary varied from 267 μS·cm-1 to 330 μS·cm-1, which was close to the mainstream variation range. ② The variation range of the δD and δ18 O values of the mainstream were -81.60‰--75.16‰ and -11.57‰--0.26‰, whereas that of the mainstream backwater unaffected zone of tributaries were -59.94‰--43.67‰ and -9.00‰--6.04‰; those of the mainstream backwater affected zone of tributary were -77.85‰--50.75‰ and -11.06‰--7.33‰, which showed the same pattern as those of electrical conductivity and mass concentration of main anions and cations. This means that the mainstream affected the waterbody composition of tributaries through backwater as well as the chemical characterization of tributary water. The extent of mainstream backwater influence on tributaries was negatively correlated to the distance between the tributary estuary and Three Gorges Dam as well as tributary discharge. The hydrochemical characteristics of the mainstream backwater unaffected zone of the tributary were related to the tributary catchment properties. Tributaries with denser populations and higher proportions of cultivated land have poorer water quality. Mainstream backwater can pollute tributaries of better water quality and optimize those with poor water quality.

Growth of Rhodes grass and leaching of ions from seawater neutralized bauxite residues after amendment with gypsum and organic wastes

A 32-week leaching column study was carried out in the greenhouse to investigate the effects of incorporation of gypsum, cattle manure, biosolids, gypsum plus cattle manure and gypsum plus biosolids into the topsoil layer (0–10 cm) on growth of Rhodes grass, and on root distribution and chemical and microbial properties in the topsoil and subsoil (10–30 cm) layers of seawater neutralized bauxite residues. The columns were leached for a period of 8 weeks prior to sowing Rhodes grass and during that time the bulk of the salts accumulated during seawater neutralization were leached out. The main cation leached was Na+ and the main balancing anions were Cl− and SO42−. During this period the pH of leachates rose from 7 to 8 up to 9–10. At the end of the study, exchangeable Na and pH were lowered in the surface horizon by all treatments with a combination of gypsum plus organic amendments having the greatest effect. The latter treatments also caused a significant decrease in pH, extractable Al and exchangeable Na in the subsoil. Rhodes grass dry matter production followed the order Control < gypsum < cattle manure = gypsum plus cattle manure < biosolids = gypsum plus biosolids. Growth of roots into the subsoil layer was inhibited in the Control and gypsum treatments but when organic amendments were applied, 50% or more of root dry matter was recovered in the subsoil layer. It was concluded that incorporating a combination of gypsum and organic matter into the surface soil is an effective strategy for revegetation of bauxite residue.

Análise hidroquimíca e da aplicação de diferentes métodos de avaliação da qualidade da água subterrânea em aquíferos costeiros em Osório – RS

Este trabalho teve por objetivo analisar a qualidade da água subterrânea de poços ponteira, que captam água de aquíferos livres na região de Osório (RS), e avaliar a aplicação de diferentes índices de qualidade da água subterrânea. Para o desenvolvimento do estudo foi realizada a coleta de amostras de água subterrânea em 15 poços ponteira, a interpretação de dados físico-químicos e bacteriológicos, e a aplicação de índices de avaliação da qualidade da água. A análise dos resultados indicou que as águas subterrâneas da região, na sua maioria, apresentam baixas concentrações para os principais cátions e ânions, e baixos valores de pH e condutividade elétrica. A comparação dos resultados das análises com os Valores Máximos Permitidos da portaria do Ministério da Saúde Nº 2914/11 indicou a ocorrência de problemas de qualidade, em 14 poços, provocadas por alterações em diferentes parâmetros, como: pH, amônia, ferro, cor, alumínio, manganês, turbidez, Coliformes Totais e E.coli. A aplicação do Índice de Qualidade da Água Subterrânea indicou a ocorrência de 4 poços com águas de péssima qualidade, 2 de boa qualidade e 9 de ótima qualidade. O cálculo do Índice Relativo de Risco evidenciou a ocorrência de 4 poços que apresentaram valores mais elevados. A Avaliação de Risco à Saúde indicou a ocorrência de 2 poços que apresentaram risco não carcinogênico. A análise da aplicação de diferentes índices demonstrou a existência de uma discrepância nos resultados, visto que para aplicação de cada um dos índices são utilizados diferentes parâmetros. Assim, em estudos de avaliação de qualidade da água subterrânea, devem ser utilizados mais de um tipo de índice, para que seja possível identificar e avaliar com maior precisão, as alterações de quali-dade desse recurso hídrico.