Seasonal dynamics of zooplankton composition and abundance in Thomas Dam Dambatta, Kano, Nigeria

Abstract

Seasonal dynamics of zooplankton composition and abundance as influenced by physicochemical parameters of Thomas Dam were studied between January and October, 2016. Zooplankton and water samples for physicochemical parameters were collected and analyzed fortnightly between 8:00 – 10:00 am using standard methods. Four sampling sites (A, B, C and D) were chosen on the Dam based on the vegetation pattern and impact of human activities. The mean range of physicochemical parameters studied were temperature (18.5 – 28.9 °C), pH (7.5 – 8.9), DO (4.8 – 9.1mg/L), BOD (2.2 – 4.9mg/L), turbidity (16.3 – 37.1 NTU), electrical conductivity (131.8 – 335.7µS/cm), TDS (140 - 386.6 mg/L), phosphate (0.15-1.13mg/L) and nitrate (0.14 - 4.78mg/L). Total dissolved solids, electrical conductivity, turbidity and nitrate recorded significant difference between wet and dry season (P<0.05). While no significant difference was observed between DO, BOD, phosphate, temperature and pH. Thirty two (32) species of zooplankton were identified belonging to Protozoa (4.3%), Cladocera (42.0%), Rotifera (29.6%) and Copepoda (24.1%) which accounted for 268.5org/L of the total faunal composition. Site A had the highest zooplankton density of 80.9org/L while site C recorded the least with 69.7org/L. Daphnia pulex had the highest species composition of 9.33org/L and Pleuronema sp. recorded the least with 0.07org/L. Seasonal variation indicated a strong positive relationship between physicochemical and zooplankton densities (P<0.05). Biotic Indices analyses of Shannon-wiener Index, Evenness Index and Margalef’s Index showed that zooplankton composition and abundance were highest during wet season than in dry season. However, Pearson Correlation Coefficient between zooplankton abundance and physicochemical parameters indicated strong positive relationship at p<0.01(2- tailed). The composition and abundance of zooplankton in Thomas Dam were affected by seasonal variation and fluctuation of physicochemical parameters during the study period. It is therefore recommended that uncontrolled discharge of agrochemicals around the Dam through irrigation and other human activities should be controlled in order to curtail degradation of the aquatic biota over a period of time.

Keywords: Seasonal dynamics, Physico-chemical parameters, Zooplankton composition, Diversity, Thomas Dam