Controls on groundwater chemistry in a highly urbanised coastal area

Document Type: Original Research Paper

Authors

1 Department of Geology and Environmental Sciences, University of Buea, Cameroon, Department of Earth Sciences, Indian Institute of Technology Bombay, Mumbai, India, Institute of Geologic and Mining Research (IRGM), Yaoundé, Cameroon

2 Department of Geology and Environmental Sciences, University of Buea, Cameroon

3 Department of Earth Sciences, Indian Institute of Technology Bombay, Mumbai, India

4 Institute of Geologic and Mining Research (IRGM), Yaoundé, Cameroon

Abstract

Douala metropolitan city loated in the littoral province of Cameroon,has experienced a rapid
urbaniation and industralisation. The city depends heavily on groundwater as a resource. Due to ubiquitous
sources of pollution, groundwater quality and contamination has become an imprtant issue for this urban
groundwater supply. This study uses the major ion chemistry of groundwater together with the minerallogical
and chemical composition of sediments to investigate the chemical characteristics and contamination of
groundwater. An attempt has been made to identify the different factors controlling the chemical composition
of groundwater. Groundwater is acidic (4.1-6.9) and the chemistry is more influenced by atmospheric inputs
and anthropogenic activities than by aquifer water reactions. The ionic content of groundwater shows a large
variation with electrical conductivity ranging from 34.3-1021μs/cm. However, Cl and HCO3 are dominant
anions meanwhile Na and Ca are dominant cations. Groundwater from natural low residential areas has low
electrical conductivity and Ca-Na-HCO3 type where as the chemical composition of groundwater is shifted to
Ca-Na-Cl ( NO3+SO4)downstream with maximum electrical conductivity and high nitrate levels above the
guide limits occuring in the highly urbanised, settlements at the Cente of the study area.Groundwater is
vulnerable to acid deposition due to the resistant nature and the low level of base forming cations in the aquifer
sediments, which provides very little buffer for acid inputs.

Keywords