Aiba Reservoir was sampled between March, 2004 and February, 2005 for physico-chemical studies. Air temperatures ranged from 20.00-30.50 o C (mean ± s.e: 26.33 ± 0.26 o C), water temperature ranged from 25.00-35.00 o C (mean ± s.e: 29.26 ± 0.19 o C), pH ranged from 5.53-9.48 (mean ± s.e: 7.98 ± 0.11), dissolved oxygen ranged from 1.75-11.20 mgO 2 /l (mean ± s.e: 7.23 ± 0.20 mgO 2 /l), alkalinity ranged from 42.50-85.00 mg/l (mean ± s.e: 65.20 ± 0.85 mg/l), total hardness ranged from 12.00-59.00 mg/lCaCO 3 (mean ± s.e: 45.13 ± 0.90 mg/lCaCO 3), conductivity ranged from 6.80-126.40 mV (mean ± s.e: 67.03 ± 4.04 mV), and turbidity ranged from 12.50-143.75 FTU (mean ± s.e: 40.74 ± 3.60 FTU). The physico-chemistry of Aiba Reservoir exhibited spatio-temporal variation. Two-way analysis of variance of physico-chemical parameters showed obvious seasonality for pH, conductivity and turbidity, suggesting that these parameters play major roles in the limnology of the reservoir. Factor analysis shows pH, conductivity, temperature and dissolved oxygen as important parameters contributing to the annual variability. Dissolved oxygen is a more important parameter during the wet season, while alkalinity is more important during the dry season for the reservoir. Hardness and alkalinity values suggest that the reservoir water is good for aquaculture.

Abstract:The physicochemical variables and cyanobacteria of Mid-Cross River, Nigeria, were studied in six stations between March 2005 and August 2006 to determine the relationship between water quality and cyanobacteria abundance. Canonical Correspondence Analysis (CCA) showed that biological oxygen demand (BOD), dissolved oxygen, pH, water velocity, width and depth were important environmental factors that influenced cyanobacteria abundance. Trace metals, phosphate and nitrate increased significantly from values of previous studies indicating increased eutrophication of the river but were weakly correlated with cyanobacteria abundance and could be scarcely regarded as regulating factors. A higher cyanobacteria abundance was recorded during the wet season in most of the sampled stations. The dominant cyanobacteria included Microcystis aeruginosa, Aphanizomenon flos-aquae, Oscillatoria limnetica and Anabaena spiroides. The toxins produced by these species could degrade water quality. The factors favouring cyanobacteria abundance were identified as increased pH, width and depth. Increase in cyanobacteria abundance was associated with reduction in dissolved oxygen and increase in BOD values. Rev. Biol. Trop. 57 (1-2): 33-43. Epub 2009 June 30.