Acidification of shallow groundwater in the unconfined sandy aquifer of the city of Douala, Cameroon, Western Africa: implications for groundwater quality and use

Abstract

The alluvial aquifer underlying the city of Douala comprises shallow Quaternary deposits where groundwater is the main source for domestic and drinking purposes. Shallow groundwater in the area show signs of acidification with average pH range of 3.8-6.8. Long-term groundwater chemistry data (1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013), hydrogeochemical and R mode factor analysis were used to establish the acidification process of shallow groundwater and also determine possible origin and implications for water quality and use in the area. Twenty-six groundwater sample points, three streams and three rain sample points were studied seasonally in the 2006-2008 and the 2010-2013 study periods. The data were compared with result of a study, 7 years earlier (1998)(1999). The results show evidence of acidification manifested by depletion of HCO 3 , a decrease in the pH and increase in SO 4 and NO 3 concentrations of shallow groundwater. Average groundwater pH range is 3.of water samples fall within the range of pH (6.5-8.5) for potable water according to WHO (1993). The alkalinity/acid neutralizing capacity of the shallow groundwater has decreased significantly coupled with increase in the number of zero alkalinities recorded in the 2010-2013. The shallow groundwater is generally undersaturated with common carbonate minerals (calcite, dolomite), therefore providing insufficient acid buffer. Principal component analysis in combination with hydrogeochemical studies revealed that four main factors are responsible for the groundwater chemistry and acidity: (1) acid atmospheric deposition, (2) anthropogenic activities (industrial effluent discharges and acid spill, (3) chemical weathering, and (4) coastal atmospheric deposition/cation exchange. In general, the shallow groundwater is not suitable for drinking and domestic purposes with respect to the low pH and elevated nitrate concentration. In view of the implications such as increase in corrosion and increased mobilization of toxic elements (e.g. Al, Pb, Cu, Zn, Mn) as well as their possible harmful effect on health, it is recommended that the causes, rate of acidification and the mobility of trace elements be investigated with more details.

Factors Influencing the Shallow Groundwater Quality in Four Districts with Different Characteristics in Urban Area (Douala, Cameroon)

“…Few studies have been carried out [19]- [24] and established the level of nitrate concentration in shallow groundwater is up to 160 mg/l. These studies show the nitrate to be of anthropogenic origins.…”

“…The Bependa district presents a wider range of pH-values ( Figure 5) and the most acidic sample being BE 12 (pH = 3.5) while Logpom pH-value distribution is narrow (4.6 -5.3) and relatively close to the input function (5.5 -5.8) [23]. [24] showed that the acidity of groundwater in Quaternary alluvium of Douala may have resulted from origins such as; acid rain, coastal atmospheric deposition, anthropogenic activities and cation exchange from marine sodium with Figure 6 is a display of the EC which gives the total ion content of water samples [39]. It shows a higher and wider range (332 -1646 µS/cm) in Bependa than in Ndogbong (103 -483 µS/cm), Logpom (42 -250 µS/cm) and Ndogpassi (2 -57.5 µS/cm).…”

Variable water quality of domestic wells emphasizes the need for groundwater quality monitoring and protection: Stinkwater, Hammanskraal, Gauteng

“…Studies of groundwater quality across Africa are numerous, and include rural (Grimason et al, 2013), urban (Mangore andTaigbenu, 2004) and peri-urban (Mokuolu et al, 2017), as well as agricultural (Esterhuizen et al, 2014), industrial (Takem et al, 2015) and domestic (Vala et al, 2011) studies. Most of these studies reveal decreases in groundwater quality related to human activities at the surface.…”

Importance of Rocks and Their Weathering Products on Groundwater Quality in Central-East Cameroon

“…Alkalinity indicates the ability for groundwater to neutralize the inputs of acidity, and generally consists of the bicarbonate (HCO 3 ) and the carbonate (CO 3 2− ) concentration. High alkalinity values might lead to a high buffering capacity [30]. [33].…”