A survey of zooplankton diversity of Challawa river, Kano and evaluation of some of its physico-chemical conditions

Abstract

Between July 2006 and December 2007 changes in some physico-chemical and biological conditions of Challawa River were assessed by collecting water samples from it, except for temperature, pH and Secchi disc transparency that were measured in situ, at four selected sites on fortnight basis between 8:00 – 10:00a.m.. The results revealed that the minimum and maximum temperature, pH, electrical conductivity, secchi disc transparency, dissolved oxygen, biochemical oxygen demand and zooplankton densities were 15.5-31.5oC, 3.67-8.69, 44.0-4865.0μScm¯1, 0.04- 0.149M, 0.20-9.15mg/L, 1.30-19.80mg/L and 0.00-45.30Org/L respectively. Significant differences occurred between the wet and dry season values of temperature, pH, and Secchi disc transparency (P0.01 for electrical conductivity. However, no significant difference was found between the seasons in terms of dissolved oxygen, biochemical oxygen demand and zooplankton distribution (P>0.05). Zooplankton density was found to correlate positively with pH, secchi disc transparency and dissolved oxygen among others. Eighteen (18) zooplankton species were identified and include protozoa, 5 (22.78%); insecta 2(11.11%); copepoda, 5(27.78%); cladocera, 1(5.55%); and rotifera, 5(27.78%). The first two sites before the above that were off stream had higher zooplankton diversity and appeared to be unpolluted. Although the river generally had low zooplankton diversity, perhaps due to low transparency among other factors that limit phytoplankton growth, the discharge of untreated effluent into the river could be said to cause pollution in a localized state at the effluent inflow site. It was recommended that appropriate authorities should ensure that neighboring industries comply with emission standards set out by government with the view to minimizing the negative effects of their actions on both humans and aquatic biodiversity of the river. Similarly, it was recommended that there should be continual monitoring of the biological and physico-chemical status of the river, which appears to be neglected by the concerned authorities at present so that appropriate actions can take place before the situation go out of hand. Key words: Physico-chemical, zooplankton, season, Challawa River, Kano