Assessing the Impact of Land Use Patterns on the Groundwater in the Shallow Coastal Aquifer of Eastern Dahomey Basin, Nigeria, Using Statistical and Water Quality Analysis

Abstract

Effective monitoring of groundwater quality is difficult in Sub-Saharan Africa countries due to rapid urbanisation and limited financial resources, but is required to meet the challenges of meeting targets for the UN's sustainable development goal 6 (SDG6) aimed at providing clean and potable drinking water for all. Science-led policy interventions are needed to set and meet Nigeria's national SDG6 targets, in particular for groundwater resource management. This study used the Groundwater Quality Index (GWQI) and statistical analysis to assess the impact of land use patterns on groundwater quality in the shallow aquifers of Eastern Dahomey Basin, Nigeria. Selected water quality parameters pH, EC, TDS, TH, Ca, Mg, Na, K, HCO , Cl, SO , NO , F and the trace metals As, Cd, Fe, Mn, Pb 3 4 3 and Si were analysed in 230 groundwater samples from boreholes and hand-dug wells between June 2017 and April 2018. The results were used to calculate the GWQI by assigning weight according to adverse impact on human health. A land use map of the area where irrigation may be of benefit was developed from a Landsat image using ArcGIS. Assessing the future use of groundwater for irrigation suggests the quality in some parts of the aquifer may be unsuitable based on the percentage of sodium (%Na), Kelly's ratio (KR), magnesium ratio (MR) and total hardness. Results of the GQWI revealed 44.8, 22.9 and 12.5% of water samples during the wet season fell in the class of excellent, good and moderate-quality respectively, while 8.3 %, 1.0 and 10.4 % fell in classes of poor, very poor and none potable water quality. Correlating the spatial distribution of the GWQI with the land use pattern map of the area revealed the least potable water is clustered around settlement areas, indicating groundwater quality has been impacted by municipal, industrial and agricultural waste. There is a need for waste management policy review and enforcement to support sustainable groundwater resource management and achieving the SDG6 goals