Effect of lead on zooplankton dynamics in Challawa River, Kano State, Nigeria

Abstract

Lead concentration was determined with the aid of Atomic Absorption Spectrophotometer while zooplankton were collected with the aid of plankton net and analysed microscopically to assess their diversity and density in the Challawa River at four selected sites on fortnight basis between July 2006 and December 2007. The mean lead concentration was between 125 mg/L and 2.84 mg/L, far above maximum acceptable and allowable concentrations in drinking water of 0.05 mg/L and 0.10 mg/L respectively (WHO, 1996). The mean zooplankton density ranged between 3.09 Org/L and 10.26 Org/L. Only five protozoan, two insect, four copepod (plus one naplius I), one cladoceran and five rotifer species were identified during the study. The river quality decreased down stream, with least plankton recovery of 4 species at the industrial effluent inflow site and highest off-stream (site A) with 14 species. The site that experiences a direct inflow of industrial effluent was the most polluted (Odum’s Index = 0.22). Significant differences occurred in the lead concentration between the sites (P<0.01) and the seasons (P<0.05). The lead concentration at the sampling sites was negatively correlated with zooplankton diversity (r = -0.28734). It was feared that consumption of raw Challawa River water can over time lead to bioaccumulation of this heavy metal with possible negative consequences on health and wellbeing of man. Likewise, the low zooplankton diversity and density in this river could largely be attributed to its poor physicochemical status that had detrimental effect on them especially at the industrial effluent inflow site.

Key words: Challawa River, lead, zooplankton dynamics, pollution, Kano-Nigeria.