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.
Dodoma city, central Tanzania, seats in a semi-arid region of East Africa with limited rains and surface water resources. Consequently, the area largely depends on shallow and deep aquifers for its freshwater needs. Owing to harsh climatic conditions, chronic lack of year-round surface water bodies and, limited development of water distribution infrastructures, over year's local people have nurtured, developed and, passed on important indigenous knowledge (IK) on exploiting and managing shallow aquifers (SAs). However, there is no clear documented administrative plans for the SAs and the roles of IK, which is widely practised in developing SDWs and managing SAs, are not properly documented. This study intended to assess the extent of shallow dug wells (SDWs) utilization and contribution of IK on management of SAs of indigenous people of Dodoma Municipality. The methods followed include critical field observations, measurements and, focus group discussions done during both the dry season (Sep.-Oct. 2013) and wet season (Dec. 2013-Feb. 2014). The results show that SDWs occur widely in the city, particularly in the suburbs, where they often serve as the only sources of freshwater and heavily dependent by the populace. It is clear that there is rich IK on management of SAs including on groundwater exploration, digging, water allocation, pricing, and even on water quality and, water treatment skills. The aforementioned IK clearly contribute to water sufficiency to the populace and general management of groundwater such as enhancing recharge mechanisms where about 1% of local rainfall is recharged through a network of SDWs compared to ~ 5-10% that is naturally being recharged by rainfall through the vadose zone. Thus, as much as the current policy framework and groundwater managers do not recognize the roles of IK and contributions of SDWs as key water sources, it is clear that IK contributes to the groundwater management and SDWs already support large part of the society. While it is globally appreciated that vital skills on SDWs management are vanishing, local people in Dodoma still retain them and should, therefore, be preserved. It is further recommended that IK are strengthened, improved and most importantly, incorporated in the local water resources management plans that already advocate on integrated approaches but which clearly ignores the IK and the local people's efforts to explore and manage water resource, particularly SAs.
The Hombolo dam (HD), in central Tanzania, is a shallow reservoir characterized by high salinity that limits its use for human activities. The origin of the salinity, mechanisms of reaching and concentrating in the dam remain unclear. These were assessed using hydrogeochemical facies, water type evolutions and mapping. The source of HD salinity was identified to be shallow groundwater (SG) and runoff from a seasonal floodplain with NaCl-rich lithological materails, along Little Kinyasungwe River that feeds the dam. The NaCl-rich lithological units, about 5-7 km upstream of the dam, were highly concentrated with NaCl to the extent that the local community was commercially separating table salt from them. The physicochemical parameters from these NaCl-rich lithological materials were well represented in HD and nearby groundwater sources, which suggests active water interactions. Water type evolution and surface hydrology assessments clearly showed that SG in the salty-floodplain was influenced by evaporation (ET) and was periodically carried to the HD. Clearly; HD water had high chemical similarity with the nearby SG. This agrees with previous studies that HD is partly fed by the local aquifer. However, this is the first attempt at mapping its physical origin. The origin of HD salinity was further supported by the spatial distribution of electrical conductivity (EC), where very high EC (up to 21,230 lScm ) was recorded in SG within the NaCl-rich lithological unit while water sources far away from the NaClrich materials had much lower EC values. Thus, the study disagrees with previous conclusions that HD salinity was sorely due to high dam surface ET but is primarily due to geological reasons. Comparisons of HD with a nearby Matumbulu dam (MD), another earthen dam in climatologically similar settings, reveals that MD water was less saline/ mineralised. This further shows that HD high salinity is most likely a geologic phenomenon, but local climatic factors, namely high ET, decreasing rainfall and warming trends are likely to have concentrated the salts further. Although HD is widely/ideally used for grape vine irrigation, it was clearly revealed that its prolonged usage would potentially affect the soil and grape productivity due to high salinity.
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