PHYSICAL AND CHEMICAL CHARACTERISTICS OF GROUNDWATER AND SURFACE WATER IN THE LAKE CHILWA BASIN, MALAWI

The physical and chemical properties of groundwater, streams and Lake Chilwa water were measured in the Lake Chilwa Basin in southern Malawi. The goal was to trace the origin of salinity in groundwater and Lake Chilwa water and their relationship to water-rock interactions and alluvial deposits respectively. Groundwater around the Lake Chilwa Basin are highly saline which has led to water shortages because of poor water quality. The hypothesize of the research was that highly saline groundwater and Lake Chilwa water results from water-rock interactions and alluvial deposits respectively or highly saline groundwater and Lake Chilwa water does not result from water-rock interactions and alluvial deposits respectively. The main objective was achieved from the following specific objectives: measuring the physical and chemical properties of water from tributaries, and groundwater, assessing the major ion concentrations of boreholes and Lake Chilwa water and investigating the major types of rocks within Lake Chilwa basin that may contribute to salinity of the lake and groundwater. Groundwater from 16 boreholes, 5 stream water samples and 3 samples from Lake Chilwa were collected using standard methods and investigated for temperature, pH, electrical conductivity and total dissolved solids (TDS). The expected results were that groundwater and Lake Chilwa water have higher ionic concentrations of HCO3-, Na+, Ca2+, Mg2+, K+, Cl-, F-, NO3-, SO42- and SiO2 than stream water because of weathering of silicate minerals and alluvial deposits respectively. Quality of streams water is adequate, and base flow to perennial streams is supported by shallow groundwater, efforts should be made to map shallow fresh groundwater aquifers for domestic and industrial use.