Spatial and seasonal characterization of water quality in the Ouémé River basin (Republic of Benin, West Africa)

Abstract

T HE STUDY aims at evaluating the quality of the water in the Ouémé River basin. Data were collected from October 2014 through September 2015. Physico-chemical parameters were assessed and the concentrations of dissolved heavy metals were determined. The results show both physical and chemical pollutions of the water according to a nonlinear pollution gradient. The middle basin up to the height of the city of Kaboua appears to be the most polluted segment. The Delta region, near the coast, is the second most polluted segment, and the remaining parts of the basin are the least polluted. Pollutant concentrations are highest during the low flow season. Cluster analysis and Principal Component Analysis (PCA) of sampled sites reveals that Atchakpa-Rejet and Kaboua have high concentrations of nitrite, nitrate, ammonium, orthophosphate, conductivity, TDS, pH, calcium, magnesium, and total hardness. Kpassa, Bétérou, and Atchakpa-Bethel have high dissolved oxygen and high transparency values. All other sites have high alkalinity. During the low flow season, Cd, Pb, Zn and Cu were detected at concentrations exceeding ecological standards in most of the sites. The Water Quality Index (WQI) ranged from 52.7 to 80.9, meaning that water in that river basin can be classified either as marginal quality, moderately polluted, or good quality for aquatic life. Overall, water in the Oueme River basin is under high and increasing influence of human activities.

Heavy Metal Content of Water in Ikwu River (Umuahia, Nigeria): Pollution Indices and Health Risk Assessment Approach

“…Manganese, chromium, and nickel had values that exceeded limits only during the dry months. This observed trend could also be attributed to season and anthropogenic influences as observed in iron, lead, and cadmium (Etesin et al, 2013;Houssou et al, 2017;Haque et al, 2019).…”

“…Grützmacher et al (2013) and CGWB (2014) defined geogenic sources as levels that exceeded permissible limits without any direct or indirect link to anthropogenic activities and could have negative health effects. Little or no precipitation, low flow rate, higher air temperatures, and higher evaporation during the dry months contribute to the concentration and higher values of the metals (Etesin et al, 2013;Houssou et al, 2017;Haque et al, 2019). The dry periods or seasons are also associated with increased human visitations and activities because rivers and streams are major sources of water for drinking and most domestic activities in the region (Onyele and Anyanwu, 2018;Anyanwu and Umeham, 2020a, b).…”

An index approach to heavy metal pollution assessment of Eme River, Umuahia, Nigeria

“…The seasonal variations observed could be attributed to low precipitation, higher atmospheric temperatures resulting in higher evapotranspiration rates leading to concentration and higher values in the dry season while lower values during the wet season may be due to dilution by rain water (Atobatele & Olutona, 2013;Etesin et al, 2013;Houssou et al, 2017). Zinc and copper were generally low and within limits.…”

Spatio-Temporal Assessment of Zooplankton Fauna of Uta Ewa Estuary, Akwa Ibom State, Nigeria.

“…Higher temperatures were recorded between December 2019 and February 2020, which was the peak of the dry season. In the tropics, the wet season results in lower water temperatures while the dry season brings about higher temperatures (Anyanwu, 2012;Etesin et al, 2013;Houssou et al, 2017). Idowu et al (2013) reported that the higher water temperatures recorded during the dry season could be as a result of low precipitation, high atmospheric temperature and low relative humidity.…”