| 1. |
- Ijumulana, J., et al.
(författare)
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Spatial modeling of the occurrences of geogenic fluoride in groundwater systems and implications for the provision of safe drinking water in Tanzania
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Inadequate data and spatial dependence in the observations during geochemical studies are among the disturbing conditions when estimating environmental factors contributing to the local variability in the pollutants of interest. Usually, spatial dependence occurs due to the researcher’s imperfection on the natural scale of occurrence which affects the sampling strategy. As a consequence, observations on the study variable are significantly correlated in space. In this study, the machine learning approach was developed and used to study the environmental factors controlling the local variability in fluoride concentration in drinking water sources of northern Tanzania within the East African Rift Valley. The approach constituted use of the geographical information systems (GIS) technology, exploratory spatial data analysis methods, and spatial modeling at a local level. The environmental variables used to study the local variation in fluoride concentration include topography, tectonic processes, water exchanges between hydrogeological layers during lateral movement, the mineralization processes (EC), and pH. The study was based on 20 local spatial regimes determined using GIS based on water sources density in the four hydrogeological environments. The non-parametric (one-way Kruskal-Wallis sum ranks test and Multiple Comparisons Dunn Test), spatial statistics (Global Moran's I statistic), ordinary least squares (OLS) regression and spatial lag models were used to quantify the effects of topography, tectonic processes, water exchange between hydrogeological environments and waterphysiochemical parameters (pH and EC) on the spatial variability of fluoride concentrations in drinking water sources at a local scale. In the order of significance, the local spatial variation in fluoride concentration is influenced by the EC, topography, tectonic processes, pH and water exchange between hydrogeological layers during water movement. The results presented in this paper are crucial for safe water access planning in the naturally contaminated aquifers.
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| 2. |
- Quino Lima, Israel, 1980-, et al.
(författare)
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Geochemical mechanisms and spatio-temporal variation of the mobility of natural arsenic in shallowgroundwater and surface water in the hydrogeologic system of Lower Katari Basin, Bolivian Altiplano.
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Arsenic (As) contamination of drinking water is a world-wide problem. The natural origin of As, its mobility and transport are of great interest in Bolivian Altiplano due to its presence in mineral deposits, brines, hot springs and volcanic rocks. In this study a geochemical spatial-temporal approach was used to understand the sources and factors that control the mobilization and fate of As in water bodies as well as sediments of Lower Katari Basin (LKB). The results reveal that high levels of As, boron (B), manganese (Mn) and high salinity are present in shallow drinking water wells, which exceed the guideline values of the Bolivian regulation (NB-512) and WHO. The seasonal variation and its impact on water quantity, in addition to the load of solids and liquids of residual origin (Pallina River) represent risk of significant negative health impact for the communities at the banks of the Katari River. The first evaluation of the hydrogeological study indicates that the groundwater flow was observed in the direction southeast - northwest (SE - NW), which are showed in the sectors with interaction between groundwater and surface water. The spatial distribution of As varies considerably due to geological characteristics of the area as well as due to the heterogeneously distributed evaporites in the sediments; however, the highest concentrations of As are found in the alluvial sediments of the northern region. Sequential extraction of sediment along with geochemical modeling (mineral saturation indices) indicates that the iron (Fe) and aluminum (Al) oxides as well as their hydroxides are most important adsorbent minerals of As in central and southern region of LKB. The hydrochemistry of water bodies in LKB is strongly influenced by the interaction with the sediment constituents and by the spatial-temporal variations. Therefore, the determination of the distribution of As among the different geochemical fractions was useful to find the relative proportions of As transported by different chemical mechanisms and their spatial-temporal variation.
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| 3. |
- Quino Lima, Israel, 1980-, et al.
(författare)
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Hydrogeochemical contrasts in the shallow aquifer systems of the Lower Katari Basin and SouthernPoopó Basin, Bolivian Altiplano.
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Water sources for human consumption in regions such as the southeast of Lake Titicaca (Lower Katari Basin: LKB) and the south of Lake Poopó (Southern Poopó Basin: SPB) have high concentrations of arsenic (As) (>10 μg/L; WHO and NB-512 guideline value). These regions belong to the Bolivian Altiplano and characterized by a semiarid climate, slow hydrological flow, with geological formations of volcanic origin, in addition to brines and other mineral deposits. This study focuses in the comparision of the geochemical processes for the occurance of As, sources and its mobilization in groundwater (GW) in LKB and SPB. Samples of GW, surface water and sediments were collected from both the basins. The study found As (LKB: 0.8 - 288 μg/L and SPB: 2.6 - 207 μg/L), boron (B) (LKB: 96 - 2473 μg/L and SPB: 507 - 4359 μg/L), manganese (Mn) (LKB: 0.6 - 7259 μg/L) and salinity (LKB: 125 - 11740 μS/cm) are higher than the WHO guideline. The results indicate serious deterioration of GW quality that is apparently not safe for human consumption. The spatial distribution of As was observed in diverse geology of both the basins and it was heterogeneously distributed within the sediments. The highest As concentrations are found in the northern region of LKB and the PACK belt in SPB (both alluvial sediments). The dissolution and exchange of bases are the processes that govern the mineralization of GW. Whereas, sequential extraction of sediment and mineral saturation indices indicate the iron (Fe) and aluminum (Al) oxides as well as hydroxides are the most predominant mineral as potential sorbent of As. Nevertheless, solids and liquid from anthropogenic origin in surface water (LKB) are causing environmental problem for communities on the banks of river.
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