Abstract
More than 25 % of Tanzanian depends on groundwater as the main source of water for drinking, irrigation and industrial activities. The current trend of land use may lead to groundwater contamination and thus increasing risks associated with the usage of contaminated water. Nitrate is one of the contaminants resulting largely from anthropogenic activities that may find its way to the aquifers and thus threatening the quality of groundwater. Elevated levels of nitrate in groundwater may lead to human health and environmental problems. The current trend of land use in Tanzania associated with high population growth, poor sanitation facilities and fertilizer usage may lead to nitrate contamination of groundwater. This paper therefore aimed at providing an overview of to what extent human activities have altered the concentration of nitrate in groundwater aquifers in Tanzania. The concentration of nitrate in Tanzanian groundwater is variable with highest values observable in Dar es Salaam (up to 477.6 mg/l), Dodoma (up to 441.1 mg/l), Tanga (above 100 mg/l) and Manyara (180 mg/l). Such high values can be attributed to various human activities including onsite sanitation in urban centres and agricultural activities in rural areas. Furthermore, there are some signs of increasing concentration of nitrate in groundwater with time in some areas in response to increased human activities. However, reports on levels and trends of nitrate in groundwater in many regions of the country are lacking. For Tanzania to appropriately address the issue of groundwater contamination, a deliberate move to determine nitrate concentration in groundwater is required, as well as protection of recharge basins and improvement of onsite sanitation systems.
Highlights
BackgroundGroundwater makes up to over 95 % of the world’s available freshwater resources and is the main source of drinking water for a large percentage of the world’s population (Bowell et al 1996; Brindha and Elango 2011)
Geology and geomorphology play a significant role on storage, transportation and quality of the groundwater, whereas precipitation plays a significant role on the groundwater recharge (Taylor et al 2012)
Highest values were observed in urban areas of Dar es Salaam, Dodoma and Tanga where the concentration of nitrate in some aquifers was higher than 400 mg/l
Summary
Groundwater makes up to over 95 % of the world’s available freshwater resources and is the main source of drinking water for a large percentage of the world’s population (Bowell et al 1996; Brindha and Elango 2011). The annual total rainfall ranges from less than 500 mm in central parts to more than 1,000 mm in wet areas, the coastal regions and the Islands of Zanzibar and Pemba may receive about 1,500 mm (Sumner 1983; Nicholson 1996; Basalirwa et al 1999; McSweeney et al 2014) Such precipitation may facilitate groundwater recharge significantly if other factors like geology, geomorphology and land cover are good. The soft formations of Tanzania include the Mesozoic to Cenozoic sediments in the coastal areas, inland basins (mainly karoo sediments), rift valley sediments together with recent volcanic and fluvial sediments (Kashaigili 2012) Due to their primary porosity, sedimentary rocks are potential for accumulation of appreciable groundwater resource (Fetter 2001). A full understanding of the natural concentration, possible sources and biogeochemical transformation of nitrate is required for a successful groundwater management strategy
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