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

Author(s): E.U.Onweremadu, A.A.Ayoade, D.H.Ogbuagu, N.B.AC-Chukwuocha

The authors investigated the dynamics in spatial yields of primary production in the middle course of the Imo River in Etche, South-eastern Nigeria. 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 HORIBAU-10Water Quality Checker.Water samples were collected in 500 ml sterile containers for further laboratory analysis using standard methods. The light and dark bottle technique was employed in the measurement of primary production. Correlation coefficient (r) was used to establish relationships between physicochemical variables and primary production while the One-WayANOVAwas used to determine variance equality ofmeans in spatial yields.Means were further separated for the identification of variant productivity variables using the means plot. Wide variations were observed in turbidity (11.0-279.0, mean = 96.7 ± 9.3 NTU), DO (4.50-8.81,mean = 6.96 ± 0.14 mg/l), and sulphate (0.90-8.10, mean = 4.35 ± 0.25 mg/l) across the sampling locations. Gross and net primary production (GPP&NPP) aswell as community respiration (CR) ranged from0.01-1.12 (0.09 ± 0.02), 0.01-0.10 (0.04 ± 0.003), and 0.002-0.05 (0.02 ± 0.002) gCm-2d-1, respectively. Sampling location 1 showed the highest GPP, NPP, and CR of 0.09, 0.06, and 0.03 gCm-2d-1, respectivelywhile location 7 showed the least GPP of 0.06 gCm-2d-1, and locations 2-7 showed the least CRof 0.02 gCm-2d-1 each. At P<0.01, GPP correlated negatively with turbidity (r=-0.322) and sulphate (r=-0.297), NPP correlated positivelywith pH(r=0.404) and negativelywithDO( r=-0.567), turbidity (r=-0.592), nitrate (r=-0.435), phosphate (r=-0.365), and sulphate (r=-0.594) and CR correlated positively with pH (r=0.363) and negativelywithDO(r=-0.510), turbidity (r=-0.547), nitrate (r=- 0.405), phosphate (r=-0.304), and sulphate (r=-0.551).Variances inmeans of primary production variables showed inequality at P<0.05 at sampling locations 1 and 4. The observed oligotrophic production of the river was most probably due to low water nutrient levels, high turbidity and high relative humidity prevalent in the area.

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