Assessment of nitrate concentrations in the shallow groundwater aquifer of Maiduguri and environs, Northeastern Nigeria

Abstract

Abstract Maiduguri and environs lie in the semi-arid region of Nigeria, characterized by low rainfall of approximately 600 mm per annum and high evapotranspiration of over 2000 mm per annum. Surface water is largely seasonal with rivers flowing for about three months in a year, although the Alau dam is an exception whose water is treated for supply to about 30% of the citizens of Maiduguri. Therefore, perennial water supply to the inhabitants is from groundwater, with the shallow Upper aquifer the dominant source. Assessment of quality of this water is thus fundamental. This is because of its susceptibility to contamination as a result of poor waste disposal from a rapidly growing population and industrialization. Water samples from 128 shallow boreholes were used to measure the EC, NO3 and temperature using appropriate meters, in addition to taking the site coordinates. The values of the EC and NO3 were used to evaluate the quality of this shallow groundwater. The results show a linear relationship between EC and NO3, which indicate that NO3 is a major contribution to the EC. NO3 concentrations in some boreholes are over 700 ppm; considerably higher than the WHO and NSDWQ permissible limit of 50 ppm. These boreholes are in wards of older settlements and with high population density. Most of the water from boreholes having lower than 50 ppm average NO3 are from wards that have low population density and usually of recent settlement. Although, for borehole sites close to the river channel, their NO3 concentrations are low due to dilution. Distribution of the NO3 concentrations over the study area indicates that the age of settlement and population density the major controls. There is the need to assess and constrain the source and mechanism of NO3 leaching into the groundwater of this area. Ultimately, there will be a need to develop modern human waste disposal systems that will enhance protection and/or minimize groundwater contamination.