Hydrochemical Characterisation of High-Fluoride Groundwater and Development of a Conceptual Groundwater Flow Model Using a Combined Hydrogeological and Hydrochemical Approach on an Active Volcano: Mount Meru, Northern Tanzania

This study characterises 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. Additionally, we analyse the impact of rainwater recharge on groundwater chemistry by monitoring spring discharges during water sampling. The results 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.

Prospecting for safe (low fluoride) groundwater in the eastern African Rift: a multidisciplinary approach in the Arumeru District (northern Tanzania)

This research was aimed at finding fresh and safe groundwater easily deliverable to an area, located in northern Tanzania, within the western branch of the Rift Valley. The study area suffers from water shortage, moreover, 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 research consisting of geological, hydrogeological, hydro-chemical, geophysical and hydrological investigations. The study area stretches over 440 km2 and lies in the northern part of the Arumeru District, approximately 50 km from Arusha, the capital of the region. The Mount Meru (4565 m a.s.l.) and the Arusha National Park mark the boundary of the area, which includes 9 villages belonging to the Oldonyo Sambu and Ngarenanyuki Wards. The 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 on each other. Subordinate perched aquifers are present in sedimentary formations with local occurrence. The groundwater flow system has been interpreted on the basis of springs spatial distribution combined with lithological and the 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 grabens, faults, lava domes and tholoids. After the identification of the main fluoride source, an interference pattern among groundwater and high F surface water was drawn. Finally, some VES (Vertical Electrical Sounding) were performed that allowed an aquifer to be individuated within a structural high where the fluoride input is prevented. The drilling of a well, able to supply at least 3.8 l/s of low fluoride, drinkable water, successfully concluded the methodological approach for prospecting safe water in a semi-arid, naturally fluoride polluted region.

Assessment of permanence and stability in the territories of Kirk's dikdik (Rhynchotragus kirki) in Tanzania

ABSTRACTThe permanence and stability of 20 territories of the dikdik Rhynchotragus kirki, were studied at Arusha National Park Tanzania. Response criteria included the structure, size and vegetation attributes of territories, density of dikdik, and spatial distances between neighbouring territories. Fourteen of the territories studied were spatially fixed and stable while six were unstable. Two of the unstable territories were completely abandoned. Mean territory size was 0.11 and 0.13 ha during the rainy and dry seasons, respectively. 14.2% of circular territories and 42.9% of elliptical and kidney-shaped territories were stable. The figure of 55 dikdik km−2 sighted during morning censuses was lower than that for evening censuses by 13.5%. Spatial distance between territories ranged from 4.5 m to 100 m, an indication that population density might be a function of the size of suitable habitat. Although shrub canopy cover within stable territories decreased by 44.6% between 1982 and 1987, and some territories were realigned with changes in rainfall pattern, pair-bond was maintained by dikdik in 70% of the territories studied.