Spatial and temporal variability of groundwater quality in Barotse floodplain and surrounding areas, western Zambia.
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Date
2022
Authors
Mweemba, Sinkombo
Journal Title
Journal ISSN
Volume Title
Publisher
The University of Zambia
Abstract
Groundwater is one of the most valuable natural resources, which supports human health, economic development and ecological diversity. More than half of the households in Barotse Floodplain and surrounding areas depend on groundwater as the main source of portable water supply. A groundwater quality status review has shown that information and data on groundwater quality in this area is not available. The risk of groundwater contamination is growing due an increase in potential threats posed by anthropogenically induced effects of land use and climate change. It is against this background that spatialtemporal variability of groundwater quality between 2018 and 2019 was undertaken. Purposive sampling was used to collect 50 water samples in dry the season and 69 samples in the wet season for physio-chemical and microbiological analysis. Physio- chemical and microbiological parameters were assessed on-site using potable pH and conductivity meters and at the Geochemical and Environmental Engineering Laboratories from the University of Zambia. At the laboratories, the samples were analysed using standard methods i.e. membrane filtration technique for coliforms whereas chemical analysis was done after APHA(1998). Temporal variation between the dry and wet season was assessed using the ANOVA whereas spatial variation was analysed by comparing the concentration of selected parameters along Lukulu to Mongu, Mongu to Senanga and Kalongola to Kalabo Transect. Characterisation of groundwater type was done with the aid of the Piper diagram. Furthermore, the suitability of water for drinking was assessed by comparing the values obtained in the field and laboratory analysis with World Health Organisation (WHO, 2008) and Zambia Bureau of Standards (ZABS, 2008) limits. It was observed that the concentration of physio-chemical parameters was relatively low and fell within the WHO (2008) and ZABS (2008) guidelines for drinking water except for iron (0.36 to 9.20mg/l), nitrate (10.65 to 30.90 mg/l), sulphate (478mg/l) and sodium (244mg/l). In addition, heavy metals (copper, lead, cadmium, manganese, cobalt, zinc, and chromium) were found to be below detection limits of < 0.006 mg/l. This implies that the current large-scale mining activities taking place upstream in North-western province has not yet affected the groundwater quality of Barotse Floodplain. Sampling points close to communities which have pit latrines and soak-aways within the radius of 30m registered
too-numerous-to-count (TNTC). Total coliforms were found in 52% of the sampled water points whereas 30% of the samples registered the presence of faecal coliforms. Statistical
analysis of ANOVA for all parameters showed that there was no significant seasonal variation in groundwater quality since the Fcritical was greater than P-Value at 0.05 or 95% level of significance. The seasonal variations observed in microbiological parameters were attributed to anthropogenic causes (human faecal material) resulting from the use of pit latrines and open defecation. Spatial variations between different water points were observed along Lukulu to Mongu, Mongu to Senanga and Kalongola to Kalabo transects. The variations were attributed to the different chemical combination (ionic exchange reactions, mixing processes, evaporation and silicate weathering) stemming from the geology and soil types. Parameters found with concentrations above the standard for drinking water such as nitrates < 0.001to 30.9mg/l, iron (<0.006mg/l to 9.2mg/l), coliforms (0/100ml of water) to Too Numerous to Count (TNTC) were mapped as hot spots. The mean abundance of major cations is, Na+ > K+ > Ca+2 > Mg+2 whereas the major anions are, SO4−2 >HCO3− > Cl− . The hydrochemical facies of groundwater show that Na (Cl) HCO3 and MgHCO3 are the major water type in the study area. The coliforms, nitrate and iron were identified as the major groundwater contaminants. Drivers of groundwater
quality variations in the study areas are attributed to both anthropogenic activities and natural processes such as low and high flooding patterns and chemical combination stemming from the geology and different soil type. It is evident from the study that the major contaminants of groundwater in Barotse Floodplain and Surrounding areas are iron, nitrates and coliforms. The concentration of these parameters was considerably above the WHO (2008) and ZABS (2008) guidelines for drinking water. Therefore, they were mapped as hot spots. The study also forms an
important baseline from which future changes in groundwater quality will be compared. The study recommends the establishment of a groundwater monitoring network for
observation of both the quality and quantity of groundwater in Barotse Floodplain and Surrounding areas.
Description
Thesis for the Master of Science Degree in Integrated Water Resources Management.