Interdisciplinary studies for the knowledge of the groundwater fluoride contamination in the eastern African rift: Meru district - North Tanzania

This research was aimed at finding fresh and safe groundwater easily deliverable to an area, located in Northern Tanzania. The study area suffers water shortage, due to widespread alkaline volcanism, high fluoride contents (F- up to 70 mg/l) affects the groundwater. The achievement of this goal has been pursued through a multidisciplinary approach research. The study area stretches over 440 km2 and lies in the northern part of the Arumeru District. Climate is semi-arid, with dry and relatively rainy seasonal alternance. Four principal hydrogeological complexes have been identified within different lithologies. They occur within volcanic formations, singularly or superimposed each other. Subordinate perched aquifers are present in sedimentary formations with local occurrence. The groundwater flow system has been interpreted on the base of springs spatial distribution joined with lithological and geometrical reconstruction of the aquifers. The dominant pattern consisting of multidirectional flow from the higher elevation area in the south, towards the lower area in the north is complicated by the occurrence of structures such as graben, faults, lava dome and tholoids. After the identification of the main fluoride source, an interference pattern among groundwater and high F surface water was drown. Finally, an aquifer to be individuated within a structural high where the fluoride input is prevented and in which a well was drilled, able to supply at least 3.8 l/s of low fluoride

Bonds, lone pairs, and shells probed by means of on-top dynamical correlations

The Electron Localization Function (ELF) by Becke and Edgecombe [J. Chem. Phys. {\bf 92}, 5397 (1990)] is routinely adopted as a descriptor of atomic shells and covalent bonds. Since the ELF and its related quantities find useful exploitation also in the construction of modern density functionals, the interest in complementing the ELF is linked to both the quests of improving electronic structure descriptors and density functional approximations. The ELF uses information which is available by considering parallel-spin electron pairs in single-reference many-body states. In this work, we complement this construction with information obtained by considering antiparallel-spin pairs whose short-range correlations are modeled by a density functional approximation. As a result, the approach requires only a contained computational effort. Applications to a variety of systems show that, in this way, we gain a spatial description of the bond in H$_2$ (which is not available with the ELF) together with some trends not optimally captured by the ELF in other prototypical situations

Il Metodo ESAS per la modellizzazione del rischio di desertificazione: applicazione in un'area della Sardegna nord-occidentale

GIS elaboration was applied to assess the sensivity to Desertification of an area of north western Sardinia. The ESAs model was used (Environmentally Sensitive Areas to desertification, developed by MEDALUS III EC – DG RES project. The model makes use of 15 indicators grouped into 4 classes: soil, vegetation, climate, land management. For each indicator independent layers are produced according to a pre-defined weights system and are then processed to create four synthetic indexes. Finally, the sensitivity index is produced as a geometric average. The implementation highlighted the high sensitivity of the concerned area

Hydrogeological and geophysical investigations for groundwater in the Arumeru District (Northern Tanzania)

Due to water shortage, in the wards of Ngarenanyuki and Oldonyosambu (Arumeru District, Northern Tanzania), the per capita daily water consumption is 8 liters as.average, The avaleability goes down to 3-4 liters in the dry seasons when most of the population cannot resort to seasonal ponds or streams and so it is compelled to concentrate around the few perennial water points. This datum is quite far from the Millennium Goal objectives that foresee a quantity of at least 20 l/d/p (litres per day per person) for the Development Countries population, within 2015. Problems are also related to water quality, in particular, the high concentration of fluoride that characterises the waters in East Africa Rift System

Hydrogeology and hydrogeochemistry of an alkaline volcanic area: the NE Mt. Meru slope (East African Rift – Northern Tanzania)

The objective of this study is to analyze the geochemical conditions associated with the presence of fluoride (F−) in the groundwater of an area of Northern Tanzania. The studied aquifers are composed of volcanic rocks such as phonolitic and nephelinitic lavas, basalts, lahars of various ages and mantling ash. Sedimentary rocks consisting of fine-grained alluvial and lacustrine deposits occur as well. Samples collected from springs, borehole and surface water, during two monitoring surveys, were analyzed for the various physico-chemical and isotopic parameters. The geochemical composition of water is typically sodium bicarbonate. High values of F− (up to 68 mg l−1) were recorded. The highest values of fluoride agreed with the highest values of pH, sodium and bicarbonate. Dissolution of major ions, exchange processes and precipitation of Ca2+ from supersaturated solutions joined with the local permeability and hydraulic gradients, control the fluoride mobilization and the contamination of the area

Prospecting for safe (low fluoride) groundwater in the Eastern African Rift: the Arumeru District (Northern Tanzania)

A multidisciplinary research effort, including geological, hydrogeological, hydro-chemical, geophysical and hydrological investigations, was aimed at locating a source of safe groundwater for a district of northern Tanzania, within the western branch of the East Africa Rift Valley, where water shortage is common and much of the surface water carries unacceptable levels of dissolved fluoride. The 440 km2 study area lies in the northern part of Arumeru district and is dominated by Mt. Meru (4565m a.s.l.). The local climate is semi-arid, with distinct wet and dry seasons. Four hydrogeological complexes were identified, occurring within different volcanic formations, either alone or superimposed upon one another. The groundwater flow system was interpreted from the spatial distribution of the springs, combined with a lithology- and geometry-based reconstruction of the aquifers. The dominant pattern consists of a multi-directional flow from the higher elevations in the south towards the lower areas in the north, but this is complicated by structures such as grabens, faults, lava domes and tholoids. After the identification of the major fluoride source, an interference pattern between groundwater and high fluoride surface water was drawn. Finally, vertical electrical soundings were performed to define the location of aquifers in regions where release of fluoride was prevented. The methodological approach for the prospecting of safe water in a semi-arid, fluoride polluted region was validated by the drilling of a 60m deep well capable of supplying at least 3.8 l/s of low fluoride, drinkable water

Caratterizzazione ambientale delle acque del Golfo dell’Asinara (Sardegna) attraverso l’uso di spettrofluorimetria laser e immagini telerilevate

The general objective of this research (financed by L.R. 7 of the Autonomous Region of Sardinia for the period May 2010 –May 2012) is to calibrate bio-optical algorithm for more accurate estimates of phytoplanktonic Chl-a in the Asinara Gulf (Northern Sardinia, Italy) using remote sensing data and in situ measurements. The “sea truth” values of Chl-a were obtained with the new laser spectrofluorometric apparatus CASPER (Compact and Advanced laser SPEctrometeR – Patent ENEA). CASPER permitted not only to quantify values of Chl-a but also to detect other algal pigments (phycoerythrin, phycocyanin), chromophoric dissolved organic matter (CDOM), proteins-like components (tyrosine, tryptophan), and qualitative data on the presence of hydrocarbons and oil pollution. At the moment “sea truth” data of Chl-a were just compared to standard chlorophyll products of MODIS OC3 algorithm. In order to reach better results, the bio-optical algorithm is going to be recalibrated according to the measurements of CASPER during the next year, thus providing new estimates of phytoplanktonic Chl-a in the Asinara Gulf

An Innovative and high-speed technology for sweater monitoring of Asinara Gulf (Sardinia- Italy)

Laser induced fluorescenze technique for sea water monitoring allows no-time consuming, non-invasive and non-destructive controls. In this study, the performance of the new shipboard laser spectrofluorometric CAS-PER (Compact and Advanced Laser Spectrometer –ENEA Patent) for monitoring phytoplankton community composition was examined. The prototype CASPER is based on double laser excitation of water samples in the UV (266 nm) and visible (405 nm) spectral region and a double water filtration in order to detect both quantitative data, such as choromophoric dissolved organic matter (CDOM), proteins-like components (tyrosine, tryptophan), algal pigments (chlorophylls a and b, phycoerythrin, phycocyanin, different pigments of the carotenoid groups) and qualitative data on the presence of hydrocarbons and oil pollutants. Sea water samples from different depths have been collected and analyzed from August 2010 through November 2011 in the Gulf of Asinara (N-W Sardinia). Several sampling stations were selected as sites with different degree of pollution. The accuracy and the reliability of data obtained by CASPER have been evaluated comparing the results with other standard measurements such as: Chlorophyll a (Chl a) data obtained by spectrophotometric method and total phytoplankton abundance in terms of density and class composition. Spectral deconvolution technique was developed and integrated with CASPER system to assess and characterize a marker pigments and organic compounds in situ and in vivo. Field studies confirmed CASPER system capability to effectively discriminate characteritistic spectra of fluorescent water constituents, contributing to decrease the time-consuming manual analysis of the water samples in the laboratory

Runoff coefficient and average yearly natural aquifer recharge assessment by physiography-based indirect methods for the island of Sardinia (Italy) and its NW area (Nurra)

Runoff estimation and water budget in ungauged basins is a challenge for hydrological researchers and planners. The principal aim of this study was the application and validation of the Kennessey method, which is a physiography-based indirect process for determining the average annual runoff coefficient and the basin-scale water balance. The coefficient can be calculated using specific physiographic characteristics (slope, permeability and vegetation cover) and a parameter that defines climatic conditions and does not require instrumental data. One of the main purposes of this study was to compare the average annual runoff coefficient obtained using the Kennessey method with the coefficients calculated using data from 30 instrumented drainage basins in Sardinia (Italy) over 71 years (from 1922 to 1992). These measurements represent an important and complete historical dataset from the study area. Using the runoff coefficient map, the method was also applied to assess the effective annual recharge rate of the aquifers of the Calich hydrogeological basin in the Nurra Plain (Alghero, NW Sardinia-Italy). The groundwater recharge rate was compared with rates calculated using the standard water balance method. The implementation of the method at the regional and basin scales was supported by GIS analyses. The results of the method are promising but show some discrepancies with other methodologies due to the higher weights given to the physiographic parameters than to the meteorological parameters. However, even though the weights assigned to the parameters require improvements, the Kennessey method is a useful tool for evaluating hydrologic processes, particularly for water management in areas where instrumental data are not available.</br

Analysis of salinization processes in the coastal carbonate aquifer of Porto Torres (NW Sardinia, Italy)

The Porto Torres (NW Sardinia) coastal aquifer is hosted in the carbonate rocks of the Miocene succession, which fills a NNW oriented half-graben. This aquifer is an important contributor to the fresh water supply of the local area. It is increasingly being degraded by salinization processes, mainly associated with intense groundwater over-exploitation. A combined hydrochemical and hydrogeological study has been carried out to identify the origin of the salinity in the groundwater. The behavior of the major ions showed that the changes in the chemical composition of the groundwater have been mainly controlled by the encroachment of seawater, accompanied by cation exchange reactions. Since seawater intrusion is a dynamic process, an Hydrochemical Facies Evolution Diagram, HFE-D (Gimenez Forcada, 2010) approach was taken to establish whether the aquifer was in the seawater intrusion or in the freshening phase. The assessment model developed provides regional authorities with a basic tools for sustainable water management in the framework of multi-disciplinary research activities aiming to combat and/or mitigate desertification and land degradation processes