DETERMINATION OF SOLUBLE SALTS IN INTERSTITIAL WATER OF FLUVIAL SEDIMENTS BY IE-HPLC

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Abstract

An ionic exchange high resolution liquid chromatography (IE-HPLC) method for determination of cations and anions in interstitial water of sediments, affluent and effluent of dams is proposed in this paper. Cations: Na+, Ca2+, K+, and Mg2+ and anions: Cl-, CO3(2-), NO3- and SO4(2-) were analyzing by IE-HPLC method. Optimized analytical conditions were validated in terms of accuracy, recovery and detection limit. The method of flame spray atomic absorption spectrophotometer (AAS) was used as an additional method for the determination of Ca and Mg. It must be indicated that cations may be analyzed by several analytical methods such as AAS, ICP, etc., but there are not enough methods to analyze anions; IE-HPLC methods are good alternative to determine these ions. The aim of this study was to determine ions in interstitial water in the affluent and effluent of the Chilean dams Cogotí, Corrales, La Paloma, Rapel and Recoleta in order to determine if the water is suitable for irrigation or human consumption and estimate the effect of dams on water quality. The results indicate that the highest concentrations observed were for the cations: Ca2+ (mean 43.5 mgL-1), Na+ (mean 16.4 mgL-1), Mg2+ (mean 12.6 mgL-1), and K+ (mean 2.3 mgL-1). The highest concentration of anions was found for CO3(2-) (mean 55.9 mgL-1); the concentrations of SO4(2-), Cl- and NO3- reached 59.3 mgL-1, 12.8 mgL-1 and 27.0 mgL-1, respectively. The results indicate that although the origin of soluble salts is lithogenic, the high concentrations of these salts found in some places indicate anthropogenic effect, either by direct or indirect discharges or by diffuse pollution. These high concentrations may be significant, considering that these waters are used mainly for irrigation, which would affect the quality of agricultural soils irrigated with this moderately saline water.

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Rapid planetesimal formation in turbulent circumstellar discs

Anders Johansen, Jeffrey S. Oishi, Mordecai-Mark Mac Low … (2007)

The initial stages of planet formation in circumstellar gas discs proceed via dust grains that collide and build up larger and larger bodies (Safronov 1969). How this process continues from metre-sized boulders to kilometre-scale planetesimals is a major unsolved problem (Dominik et al. 2007): boulders stick together poorly (Benz 2000), and spiral into the protostar in a few hundred orbits due to a head wind from the slower rotating gas (Weidenschilling 1977). Gravitational collapse of the solid component has been suggested to overcome this barrier (Safronov 1969, Goldreich & Ward 1973, Youdin & Shu 2002). Even low levels of turbulence, however, inhibit sedimentation of solids to a sufficiently dense midplane layer (Weidenschilling & Cuzzi 1993, Dominik et al. 2007), but turbulence must be present to explain observed gas accretion in protostellar discs (Hartmann 1998). Here we report the discovery of efficient gravitational collapse of boulders in locally overdense regions in the midplane. The boulders concentrate initially in transient high pressures in the turbulent gas (Johansen, Klahr, & Henning 2006), and these concentrations are augmented a further order of magnitude by a streaming instability (Youdin & Goodman 2005, Johansen, Henning, & Klahr 2006, Johansen & Youdin 2007) driven by the relative flow of gas and solids. We find that gravitationally bound clusters form with masses comparable to dwarf planets and containing a distribution of boulder sizes. Gravitational collapse happens much faster than radial drift, offering a possible path to planetesimal formation in accreting circumstellar discs.