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Hydrogeological investigation of a volcanic aquifer system on the flanks of Mount Meru, Northern Tanzania
No full textIn the Arusha volcanic region in northern Tanzania, within the eastern branch of the East African Rift System, water shortage is common and much of the surface water and groundwater contain fluoride (F⁻) concentration above the WHO limit (1.5 mg/L) recommended for drinking water. The groundwater is the main source of drinking water in the area. Prolonged intake of this high F⁻ water has caused dental and skeletal fluorosis among the local population. Limited studies particularly concerning the aquifer structure, groundwater potential, groundwater flow systems, and localities of low F⁻ groundwaters have been conducted in the area. In this study, primary data (field collected) and secondary data were used to study the aquifer characteristics, hydrochemistry, hydrogeochemistry, groundwater recharge, groundwater flow systems, and hydrothermal reservoir in the study area. The delineation of the aquifer structure and estimation of its hydraulic properties have been conducted with the aim of investigating the groundwater potential for different geological formations, to provide comprehensive knowledge for proper groundwater utilisation and management. The groundwater level monitoring was done for uncovering the spatiotemporal variation of groundwater levels in the aquifer and analysing the groundwater level response to rainfalls. Moreover, the characterisation of high F⁻ groundwater in the aquifer system has been done to understand the temporal and spatial changes in the groundwater chemistry, develop a conceptual groundwater flow model, and evaluate the hydrogeochemical processes responsible for temporal and spatial changes in the groundwater chemistry with the aim of identifying localities of low and high F⁻ groundwaters for the purpose to come up with guidelines to provide groundwater that can be used for drinking water supply without health impacts on the population. Lastly, the estimation of the temperature and circulation depth of the hydrothermal reservoir below the ash cone of Mount Meru was done to explore a possibility of finding low-temperature geothermal energy resources on the flanks of Mount Meru and develop a conceptual model for the hydrothermal reservoir in the area.
The delineation of the aquifer structure using litho-hydrostratigraphical cross-sections and estimation of the hydraulic parameters using single well pumping tests show that the aquifer system on the flanks of Mount Meru is a sloping aquifer with sloping beds. On the far east of the eastern flank, the aquifer is composed of debris avalanche deposits, while on the north-eastern and west flanks the aquifer is composed of weathered fractured lava, whereas on the south-western flank, the aquifer is composed of different layers: pyroclastics on the top, weathered fractured lava, weathered pyroclastics, and again weathered fractured lava at the bottom. The aquifer is semi-confined on the north-eastern flank, by overlying debris avalanche deposits acting as an aquitard, while unconfined elsewhere. The transmissivity of the aquifer on the north-eastern flank is substantially increasing with increasing depth, while on the south-western flank, the transmissivity of the aquifer is variable, both at the shallow depth (exploited by hand-dug wells) and at larger depth (exploited by boreholes); indicating aquifer heterogeneity. On the north-eastern flank, the topmost part of the aquifer, exploited by hand-dug wells, has a low transmissivity (T=1.3 m2/d) and potential for smaller withdrawals for local water supply with limited consumption, while the upper part of the aquifer, captured by boreholes, has an intermediate transmissivity (T=35 m2/d) and potential for local water supply, whereas the deeper part of the aquifer has a high transmissivity (T=788 m2/d) with potential of somewhat regional importance. On the western flank, the aquifer has a very low transmissivity (T= 0.4 m2/d) and potential for local water supply with limited consumption. On the south-western flank, on average, the topmost part of the aquifer, exploited by hand-dug wells, has very low to intermediate transmissivity (range of T: 0.3–19 m2/d), leading to variable potential for smaller withdrawals for local water supply (private consumption), whereas the deeper part of the aquifer, captured by boreholes, has low to intermediate transmissivity (range of T: 9–43 m2/d) and potential for local water supply.
For the analysis of the groundwater level response to rainfall in the shallow aquifer system on the flanks of Mount Meru, a conceptual model of groundwater flow has been defined, related to sloped aquifers, localised recharge, and propagation of groundwater waves (or pulses). The model has been used to explain the piezometric time series in the area. Groundwater flow on and around Mount Meru is occurring in shallow aquifers on the slopes of the mountain. Because of the large topographic differences and steepness of the slopes as well as the depositional mechanism, aquifer beds and layer bottoms show significant tilt and groundwater flow is not only controlled by piezometric gradients but also by gravity effects. The conceptual model was verified in the time series from monitored wells on all sides of the mountain and can explain the water level variations that are observed. Thus, the estimation of groundwater recharge using the water-table fluctuation (WTF) method or using models that utilise Darcy’s flow equation is unfit for the estimation of the diffuse recharge in the area. On the south-western flank of Mount Meru, the water level variations are very smooth, indicating a high hydraulic diffusivity in this aquifer. The geomorphology of the landscape in the study area plays a great role in controlling the groundwater flow paths. The general groundwater flow system on each flank is involving a multidirectional flow from the higher elevation areas, including the parasitic cones, towards the lower areas.
The characterisation of high-fluoride groundwater in the aquifer system on the flanks of Mount Meru, focusing on parts of the flanks that were only partially or not at all covered by previous research, and the analysis of the impact of rainwater recharge on groundwater chemistry by monitoring spring discharges during water sampling show that the main groundwater type in the study area is NaHCO3 alkaline groundwater (average pH = 7.8). High F⁻ values were recorded: in 175 groundwater samples, the concentrations range from 0.15 to 301 mg/L (mean: 21.89 mg/L, median: 9.67 mg/L), with 91% of the samples containing F⁻ values above the WHO health-based guideline for drinking water (1.5 mg/L), whereas 39% of the samples have Na+ concentrations above the WHO taste-based guideline of 200 mg/L. The temporal variability in F⁻ concentrations between different seasons is due to the impact of the local groundwater recharge. We recommend that a detailed ecohydrological study should be carried out for the low-fluoride springs from the high-altitude recharge areas on the eastern and northwestern flanks of Mount Meru inside Arusha National Park. These springs are extracted for drinking purposes. An ecohydrological study is required for the management of these springs and their potential enhanced exploitation to ensure the sustainability of this water extraction practice. Another strategy for obtaining safe drinking water could be to use a large-scale filtering system to remove F⁻ from the groundwater.
The investigation of the localities of low and high F⁻ groundwaters using the conceptual groundwater flow model and hydrogeochemical system analysis in the aquifer system in the study area for the purpose to come up with guidelines to provide groundwater that can be used for drinking water supply without health impacts on the population, shows that the groundwater chemistry of F⁻-rich NaHCO3 alkaline groundwater in the area is controlled by dissolution of weathering aluminosilicate minerals (especially Na-K-feldspars), dissolution of F⁻-bearing minerals, the precipitation of carbonate minerals as secondary products and the dissolution of magmatic gases. Evaporative concentration of solutes, precipitation and redissolution of evaporitic salts may locally play a role, especially on the north-eastern flank of Mount Meru. The low F⁻ groundwaters which can be used for drinking water supply without health impacts under the WHO limit (1.5 mg/L) are the low-fluoride springs from the high-altitude recharge areas on the eastern and north-western flanks of Mount Meru inside Arusha National Park, whereas on the western flank the groundwater meets the Tanzanian limit (4.0 mg/L). On the south-western flank, the shallow aquifer composed of alluvium deposits at lower elevations, shows F⁻ values that meet the Tanzanian limit. One of the three investigated deep boreholes on this flank also meets the Tanzanian limit, this suggests a possibility of finding more localities of relatively low F⁻ groundwaters in the deep aquifer. Yet, in general, the deposits at lower elevations (the debris avalanche deposits, mantling ash, alluvial fan deposits and lake deposits) are found to contain high to very high F⁻ values, whereas the deposits at high elevations (pyroclastics and lavas) contain groundwater of low F⁻ values. Thus, the internal texture and grain size of geological formations (causing variable weatherability), the burial depth of these formations (less weathering at depth) and the water residence times are the factors determining the groundwater mineralisation and F⁻ concentrations in the area. Deposits that are more weathered (e.g., debris avalanche deposits, mantling ash, alluvial fan deposits and lake deposits) have higher F⁻ values, whereas deposits at larger burial depths (e.g., fractured weathered lava) are less weathered and have low F⁻ values. Groundwater with a longer residence time (i.e., mature water) has a high F⁻ value, whereas groundwater with a shorter residence time (i.e., young water) has a low F⁻ value. The study identified that the deep hydrothermal system has influence on the high F⁻ groundwaters on the eastern and north-eastern flanks of Mount Meru.
The estimation of the temperature and circulation depth of the hydrothermal reservoir below the ash cone of Mount Meru by using classical solute geothermometry analysis of the two hydrothermal springs located at the foot of the ash cone shows that, using silica geothermometers, the estimated reservoir temperatures range from 50–90 °C (average temperature: 75 °C), indicating a low-temperature hydrothermal reservoir. We would expect higher temperature on an active volcano, such as Mount Meru, the low temperature can be attributed to a great extent of cold groundwater mixing with the hydrothermal waters. The estimated circulation depth of the hydrothermal springs ranges from 0.6–1.4 km deep; the circulation depth may be shallower, since the faster velocity along the fractures will result in shallower depth of circulation (and water-rock interaction). Therefore, there is a possibility of finding low-temperature geothermal energy resources on the eastern flank of Mount Meru since the deep hydrothermal system has influence on the groundwater chemistry on the eastern and north-eastern flanks of Mount Meru. A preliminary conceptual model for the hydrothermal reservoir in Mount Meru is presented in this thesis. We recommend further working towards proving the existence of a potential groundwater reservoir below the ash cone, as well as a detailed analysis of the hydrothermal system in the area
Hydrological System and Water Balance of Ungauged Crater Lakes of the Northern Crater Highlands
Get PDFThis research article was published in the Tanzania Journal of Engineering and Technology, Vol. 42 No. 3, 2023The study aimed to unveil the hydrological system and water balance
of the ungauged crater lakes with major focus on the Emakati Lake
which occupy 46% of the Empakaai Crater associated to the East
African Rift Valley and form part of the Northern Crater Highlands.
Water samples for analysis of NO3- , Cl- and stable isotopes (2H and
18O) were collected from the Emakat lake, springs of the inner, outer
and the foot of the Empakaai Crater rims. A combination of satellite
data such as digital elevation model (DEM), Climate Hazards Group
Infrared Precipitation with Station data (CHIRPS), net shortwave solar
radiation, surface temperature, and the computation methods such as
Curve Number (CN) Model, DeBruin–Keijman (D-K) Model enabled
the computation of water balance components such as Lake level
changes, precipitation, runoff and evaporation. Results show that,
evaporation (1694.57 mm) surpasses rainfall (878.68 mm) of the
Empakaai Crater results of higher enrichments of δ18O and δ2H in the
lake ranging between 3.28⁰/₀₀ to 3.96⁰/₀₀ and 31.99 to 33.93⁰/₀₀
compared to springs which range between -5.18 to -4.05⁰/₀₀ and -26.62
to -19.48⁰/₀₀ respectively. Springs plots to the left and above of both the
GMWL and TMWL, implying that they receive direct recharge from
rainfall. The water balance in the area shows that, groundwater flow
plays a major role on the lakes hydrological system as it contributes
about 22,004,361.12 m3/year as the groundwater inflow to Emakat
Lake which is about 56% of the lake’s total inflow and about
22,734,274.00 m3/year as groundwater outflow which is about 63% of
total lake outflow. This imply that, the lake depends less on the weather
condition and hence ensuring the sustainability of the ecosystem of the
Empakaai crater and the downstream
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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