Atsushi Kawachi

Hydrogeochemistry and groundwater salinization in an ephemeral coastal flood plain: Cap Bon, Tunisia

Abstract The Wadi Al Ayn plain is a coastal system on the eastern coast of Cap Bon in northeastern Tunisia. The area is known for its intensive agriculture, which is based mainly on groundwater exploitation. The aim of this study is to identify the sources of groundwater salinization in the Wadi Al Ayn aquifer system and deduce the processes that drive the mineralization. Surface water and groundwater samples were taken and analysed for major ions and stable isotopes. The geochemical data were used to characterize and classify the water samples based on a variety of ion plots and diagrams. Stable isotopes are useful tools to help us understand recharge processes and to differentiate between salinity origins. The oilfield brines infiltrated from the sandy bed of Wadi Al Ayn comprise the main source of groundwater salinization in the central part of the plain, while seawater intrusion is mainly responsible for the increased salinity in the groundwater of the coastal part of the plain (at Daroufa). Citation Chekirbane, A., Tsujimura, M., Kawachi, A., Isoda, H., Tarhouni, J., and Benalaya, A., 2013. Hydrogeochemistry and groundwater salinization in an ephemeral coastal flood plain: Cap Bon, Tunisia. Hydrological Sciences Journal, 58 (5), 1097–1110.

Identification of 6-octadecynoic acid from a methanol extract of Marrubium vulgare L. as a peroxisome proliferator-activated receptor γ agonist

6-Octadecynoic acid (6-ODA), a fatty acid with a triple bond, was identified in the methanol extract of Marrubium vulgare L. as an agonist of peroxisome proliferator-activated receptor γ (PPARγ). Fibrogenesis caused by hepatic stellate cells is inhibited by PPARγ whose ligands are clinically used for the treatment of diabetes. Plant extracts of Marrubium vulgare L., were screened for activity to inhibit fibrosis in the hepatic stellate cell line HSC-T6 using Oil Red-O staining, which detects lipids that typically accumulate in quiescent hepatic stellate cells. A methanol extract with activity to stimulate accumulation of lipids was obtained. This extract was found to have PPARγ agonist activity using a luciferase reporter assay. After purification using several chromatographic methods, 6-ODA, a fatty acid with a triple bond, was identified as a candidate of PPARγ agonist. Synthesized 6-ODA and its derivative 9-octadecynoic acid (9-ODA), which both have a triple bond but in different positions, activated PPARγ in a luciferase reporter assay and increased lipid accumulation in 3T3-L1 adipocytes in a PPARγ-dependent manner. There is little information about the biological activity of fatty acids with a triple bond, and to our knowledge, this is the first report that 6-ODA and 9-ODA function as PPARγ agonists.

Plausibility of freshwater lenses adjacent to gaining rivers: Validation by laboratory experimentation

The occurrence of freshwater lenses in saline aquifers adjoining gaining rivers has recently been demonstrated as being theoretically possible by way of analytical solution. However, physical evidence for freshwater lenses near gaining rivers is limited largely to airborne geophysical surveys. This paper presents the first direct observations of freshwater lenses adjacent to gaining rivers, albeit at the laboratory scale, as validation of their plausibility. The experimental conditions are consistent with the available analytical solution, which is compared with laboratory observations of lens extent and the saltwater flow rate, for various hydraulic gradients. Numerical simulation shows that dispersion can account for the small amount of mismatch between the sharp-interface analytical solution and laboratory measurements. Calibration and uncertainty analysis demonstrate that accurate mathematical predictions require calibration to laboratory measurements of the lens. The results provide unequivocal proof that freshwater lenses can persist despite gaining river conditions concordant with theoretical lenses predicted by the analytical solution, at least within the constraints of the experimental setup. This article is protected by copyright. All rights reserved.

Quantification of Groundwater-Saline Surface Water Interaction in a Small Coastal Plain in North-East Tunisia using Multivariate Statistical Analysis and Geophysical Method

  Amultivariate statistical analysis used with geophysical investigation enabled the assessment of interaction between saline surface water and groundwater in the coastal plain of Wadi Al Ayn and Daroufa in CapBon peninsula, north-east Tunisia. The application of the Principal Component Analysis (PCA) identified the end members which contribute to groundwater recharge: the wastewater infiltrated from Wadi Al Ayn, the oilfield brine infiltrated to the aquifer through the sandy bed of Wadi Al Ayn, the intruded seawater near Wadi Daroufa in the downstream region and the fresh groundwater flowing from the upstream region. The contribution of wastewater in groundwater recharge varies from 1.4% in the upstream region of Wadi Al Ayn to 77% near its downstream part. The fraction of oilfield brine mixed with groundwater in the alluvial aquifer under Wadi Al Ayn varies from 1% to 13%; whereas the fraction of intruded seawater into the coastal part of the aquifer near Daroufa region varies from 2% to 21%.

Electrochemical detection of phenolic estrogenic compounds at clay modified carbon paste electrode

A simple and sensitive electroanalytical method was developed to determine the Endocrine Disrupting chemical 4-tert-octylphenol on clay modified carbon paste electrode (Clay/CPE). The electrochemical response of the proposed electrode was studied by means of cyclic and square wave voltammetry. It has found that the oxidation of 4-tert-octylphenol on the clay/CPE displayed a well-defined oxidation peak. Under these optimal conditions, a linear relation between concentrations of 4-tert-octylphenol current response was obtained over range of 7.26×10−6 to 3.87×10−7 with a detection and quantification limit of 9.2×10−7 M and 3.06×10−6 M, respectively. The correlation coefficient is 0.9963. The modified electrode showed suitable sensitivity, high stability and an accurate detection of 4-tert-octylphenol. The modified electrode also relevant suitable selectivity for various phenolic estrogenic compounds.

Effect of Water Flow on Larval Settlement in The Nagura Amparu Tidal Lagoon

This study analyses settlement process of megalopa, which is final stage of crab larva, on a tidal lagoon based on population sampling of juvenile crabs and numerical simulation of larval settlement. Population sampling was carried out 3 times in settlement period, detailed distribution of the juveniles were grasped. The observed results indicated many megalopae have settled down at around points of 0.2 meters elevation. In addition, it seemed that the positions where many juveniles inhabited are near stagnation point. Then, to grasp the relationship between larval settlement and flow field, numerical tracer chasing by 2-D Lagrangian model was conducted. This study brought up tractive force as settlement parameter of tracer. By comparison the distribution, the calculated result with considering tractive force agreed with the observed result. Additionally, the results in spring tide are more reasonable than neap and middle tides, thus, megalopae may reinvade to the lagoon and settle down in the spring tide practically.