Seasonal and Spatial Patterns in Water Quality and in Situ Responses of Daphnia Magna along River Kaduna, Nigeria

Abstract

Variations in biochemical oxygen demand and dissolve oxygen affect aquatic organisms and have the potential to disrupt the ecological equilibrium of aquatic ecosystems. This study examined the effects of these environmental factors on the growth, reproduction and survival response of Daphnia magna at various sampling sites with differing levels of pollution in the River Kaduna, Nigeria, during both the dry and wet seasons.  The physicochemical changes and the structure and dynamics of the D. magna community were monitored bi-monthly. In situ bioassays involving D. magna were conducted twice at five sampling locations in River Kaduna, Nigeria. Exposure was followed by reported measurements of growth, survival, and reproduction at 7 and 14 days. Mean station dissolved oxygen ranged from 2.75 to 4.15 mg/L, while biochemical oxygen demand ranged from 1.47 to 2.13 mg/L. Growth values were higher in wet season than dry season values at Stations 1 – 4; reproductive values were higher in dry season values at Stations 1 and 3, higher in the wet season values at Station 2, and equal at Station 4. This study assessed field bioassay screen of organism responses associated with ambient water conditions. The findings show that in stations with low pollution levels in the River Kaduna, Nigeria, higher DO levels promote improved D. Magna growth and reproductive function.