Hidrología: investigaciones actuales

Surface soil moisture is important to understand environmental systems and dielectric constant is a convenient physical parameter to describe this. Dielectric Mixing models relate the effective dielectric constant of a heterogeneous medium with the properties of constituent materials. The dielectric properties of the soil is known to have dependence on Soil moisture content along with other factors like texture, frequency, salinity etc. In this investigation, experimental data of Dielectric Constant of various types of soil has been taken at 1.4 GHz and 18 GHz to fit unknown parameters in modified Rayleigh mixing model. Calculation of Effective dielectric constant and emissivity of different types of soil has been carried out and using modified Debye formulation, spread in relaxation and relaxation frequency is also obtained. Effective dielectric constant increases with rise in volumetric Soil Moisture, while the emissivity decreases. Further the emissivity increases with the increase in Roughness parameter. Relaxation Frequency (f_r) and spread of relaxation (α) are identified as microscopic parameters to characterize the soil texture along with volumetric moisture. These parameter values decreases with an increase in soil moisture. These data can be obtained in laboratory and field conditions and can be of interest to agricultural scientists.

The current research examined the level of surface and groundwater contamination near a municipal solid waste landfill site in Tunis City. The site of Jebel Chakir is the largest and the first controlled in Tunisia, in operation since May 1999. It receives 1800 tons/day of municipal solid waste incoming from great Tunis. Water quality parameters (physico-chemical and heavy metals) of leachate, surface and groundwater samples were analyzed. The mean concentrations of all measured parameters except Salinity, Na2SO4 and Mg in groundwater conform to the stipulated World Health Organization potable water standards and the Tunisian Standard for Drinking Water Quality. The current results show insignificant impact of the landfill operations on surface and the groundwater resource. The existing soil stratigraphy at the landfill site consisting of clay intercalated with clay gypsum or chalky is deduced to have significantly influenced natural attenuation of leachate into the groundwater resource. The research recommends an upgrade of the solous landfill to a standard that would guarantee adequate protection of both the surface and the groundwater resources in the locality.

A “salt-free”, automated purge-and-trap sampling method, with gas chromatographic-mass spectrometric detection for simultaneous detection of 2-methylisoborneol (2-MIB) and geosmin (GSM) was developed. The preliminary procedure involved purging a 25 mL water sample, at 80^°C for 11 min, with helium gas, and trapping onto a Tenax sorbent. Target analytes were desorbed with helium gas onto the gas chromatograph, coupled to a mass spectrometer, via a transfer line. Chromatographic separation was performed on HP5-MS capillary column (30 m x 0.25 mm x 0.25 μm), followed by mass spectrometric detection in the selected ion monitoring mode. During the preliminary method optimization and development stages, inconsistencies were noted regarding the relative ratios of ions m/z 95 and 107, two ion fragments frequently used for identification and subsequent quantitation of 2-MIB. NIST reference mass spectra, liquid auto sampler injection of commercial standards of the target analytes, and gas chromatographic retention times were used to confirm peak identification on the chromatograms of aqueous standards analyzed by purge-and-trap, with mass selective detection. The effect of mass spectrometer source temperature and use of a 6 mm drawout plate in the source body, on the relative ratios of m/z 95, 107, 108, for 2-MIB, and m/z 111, 112, 125, for GSM, and precision, was investigated. It was found that use of the latter had no significant effect on the ratios. The observed data indicated that 2-MIB dehydrates to 2-methyl-2-bornene (2-M-2-B) during the purge-and-trap cycle conditions used, presumably when the sample is initially purged at 80^°C. The relative retention times were ± 9.2min, ± 12.0min and ± 15.2min, for 2-M-2-B, 2-MIB and GSM, respectively, under the gas chromatographic conditions. Preliminary results indicate suitability of the technique for trace analysis of GSM in water samples over the 5-100 ng/L analytical range.