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We conducted a multidisciplinary study at the watershed scale of an andesitic-type volcanic island in order to better characterize the hydrogeological functioning of aquifers and to better evaluate groundwater resources. A heliborne Time Domain ElectroMagnetic (TDEM) survey was conducted over Martinique in order to investigate underground volcanic structures and lithology, characterized by high lateral and vertical geological variability and resulting in a very high heterogeneity of their hydrogeological characteristics. Correlations were made on three adjacent watersheds between resistivity data along flight lines and geological and hydrogeological data from 51 boreholes and 24 springs, showing that the younger the formations, the higher their resistivity. Correlation between resistivity, geology and transmissivity data of three aquifers is attested: within the interval 10–100 ohm m and within a range of 1 to 5.5 Ma, the older the formation, the lower its resistivity, and the older the formation, the higher its transmissivity. Moreover, we demonstrate that the main geological structures lead to preferential flow circulations and that hydrogeological watersheds can differ from topographical watersheds. The consequence is that, even if the topographical watershed is small, underground flows from an adjacent watershed can add significant amounts of water to such a catchment. This effect is amplified when lava domes and their roots are situated upstream, as they present very high hydraulic conductivity leading to deep preferential groundwater flow circulations. We also reveal, unlike basaltic-type volcanic islands, that hydraulic conductivity increases with age in this andesitic-type volcanic island. This trend is interpreted as the consequence of tectonic fracturing associated with earthquakes in this subduction zone, related to andesitic volcanic islands. Finally, our approach allows characterization in detail of the hydrogeological functioning and identification of the properties of the main aquifer and aquitard units, leading to the proposition of a hydrogeological conceptual model at the watershed scale. This working scale seems particularly suitable due to the complexity of edifices, with heterogeneous geological formations presenting high lateral and vertical variability. Moreover, our study offers new guidelines for accurate correlations between resistivity, geology and hydraulic conductivity for volcanic islands. Finally, our results will also help stakeholders toward a better management of water resources.

For more than half a century airborne electromagnetic (AEM) methods have been used worldwide for cost-effective resistivity mapping of areas larger than several hundred km2. The technical developments and intensive use of these systems, principally in mining exploration during the first decades, led to the development of helicopter transient EM (HTEM) systems. Since the 2000s these systems provide the best lateral and vertical resolution for environmental exploration, and they still keep a good depth of investigation allowing the exploration from the first meters to depths of several hundred meters. This chapter focuses on helicopter borne transient electromagnetic (HTEM) systems, which are well suited for the detection of low resistive targets such as salt water intrusion in coastal zones. AEM methods are based on the diffusive induction phenomenon. It is a key tool for building realistic hydrogeological models; however it requires an understanding of its limits, and some insight into data processing modeling is necessary. They require careful processing, and removal of cultural EM noise, present in most survey areas, is mandatory in order to get high quality results. Accurate modeling of the data and of the system is also critical. The modeling is most often based on least-square optimization algorithms giving smooth or layered model descriptions of ground. In this chapter we describe the AEM method in detail and we discuss processing and inversion of data. To demonstrate the results from an investigation, we end the chapter with a case study of a SkyTEM survey made in the volcanic island of Mayotte where key geological structures and salt water intrusion were successfully mapped.

Twenty-four AIDS patients, who underwent gastrointestinal evaluation, died from their disease and were autopsied. Seven had Cytomegalovirus colitis (group I) and 17 did not (group II). Clinical manifestations, digestive lesions, and infections were compared in the two groups. Chronic watery diarrhea was present in all the patients with colitis but was also present in 65% of the patients without colitis. Hematochezia was present only in the group with colitis (one of seven patients) but appeared late in the diarrheal course, due to necrotizing colitis. No other difference were noted between the two groups (mean duration of diarrhea, frequency and nature of the other infections). As for group I specifically, colonic ulcerations due to Cytomegalovirus were present in all the patients, varying from punctate and superficial erosions to deep ulcerations, with granular and friable intervening mucosa. Severe colonic lesions appeared during the course of Cytomegalovirus colitis in two patients who developed lethal necrotizing colitis. Finally, the clinical and pathologic features of these seven cases were compared to other reports of Cytomegalovirus infection of the colon.

We studied the gastrointestinal manifestations in 26 cases of AIDS. The patients belonged to two different epidemiological groups: the first group included thirteen french homosexual men, the second group included 6 Haitians, 6 Africans and a Pakistanian, none of them admit homosexual activity. The clinical manifestations were: chronic watery diarrhea in 17 cases, bloody diarrhea in 2 cases; loss of weight in the 26 cases; dysphagia in five cases; jaundice in one patient (due to Kaposi sarcoma of the ampulla of Vater). The digestive lesions found, alone or associated, were necrotizing enteritis (2), ulcerative colitis (1), pseudomembranous colitis (1), Candida esophagitis (10), erythematous duodenitis (6), proctitis (4), Kaposi sarcoma (3), diffuse (2) or localized (1). Thirteen patients out of the 26 presented opportunistic digestive infections due to one or several germs. These were 10 cases of esophageal infection (due to Candida albicans) and 8 cases of enterocolonic infection due to Cytomegalovirus (3 cases), Cryptosporidium (3 cases), Mycobacterium avium intracellulare (1 case), Cryptococcus neoformans (1 case). The other digestive infections cases were due to non-opportunistic pathogens: Entamoeba histolytica (3 cases); Giardia lamblia (3 cases); Strongyloides stercoralis (2 cases); Salmonella typhi (2 cases); Shigella (1 case); Herpes simplex virus (1 case). No difference was noticed between the homosexual and the heterosexual groups with respect to the nature and the frequency of the digestive infections.