Estimation of primary production along gradients of the middle course of Imo River in Etche, Nigeria

Dynamics in spatial yields of primary production in the middle course of the Imo River in Etche, South-eastern Nigeria has been investigated. At seven sampling locations along the course of the river, in situ measurements for water temperature, pH, turbidity, and dissolved oxygen (DO) were made with HORIBA U-10 Water Quality Checker. The light and dark bottle technique was used to measure primary production. Wide variations were observed in turbidity (11.0-279.0, mean = 96.7 ± 9.3 NTU), DO (4.50-8.81, mean = 6.96 ± 0.14mg/l), and sulphate (0.90-8.10, mean = 4.35 ± 0.25mg/l) across the sampling locations. Gross and net primary production (GPP & NPP) as well as community respiration (CR) ranged from 0.10-11.2 (0.9 ± 0.2), 0.1-1.0 (0.4 ± 0.03), and 0.02-0.5 (0.2 ± 0.02) mgO2l-1d-1, respectively. Sampling location 1 showed the highest GPP, NPP, and CR of 0.9, 0.6, and 0.3 mgO2l-1d-1, respectively while location 7 showed the least GPP of 0.6 mgO2l-1d-1, and locations 2-7 the least CR of 0.2mgO2l-1d-1each. At P<0.01, GPP correlated negatively with turbidity (r=-0.322) and sulphate (r=-0.297), NPP correlated negatively with turbidity (r=-0.592), nitrate (r=-0.435), phosphate (r=-0.365), and sulphate (r=-0.594) and CR correlated negatively with turbidity (r=-0.547), nitrate (r=-0.405), phosphate (r=-0.304), and sulphate (r=-0.551). Marked variance in means of primary production attributes at P<0.05 was mostly observed in sampling locations 1 and 4.The observed oligotrophic production of the river was most probably due to low nutrient levels and high turbidity, which blankets off sunlight necessary for photosynthesis.