Table 1 Physico-chemical parameters of water in Opa Reservoir’s tributaries (September 2004–July 2005)

Water temperature (^°C)

26.14 ± 0.95

26.23 ± 0.65

26.37 ± 1.43

0.050

0.952

pH

7.30 ± 0.14

7.31 ± 0.16

7.57 ± 0.17

4.660

0.048

EC (μS/cm)

122.59 ± 12.58

170.76 ± 77.57

207.89 ± 68.62

4.576

0.071

DO (mg/L)

5.31 ± 0.71

4.62 ± 0.68

5.11 ± 1.01

1.221

0.345

BOD₅ (mg/L)

1.71 ± 0.40

1.72 ± 0.60

2.21 ± 0.71

1.156

0.367

Total alkalinity (mgCaCO₃/L)

44.16 ± 7.46

56.50 ± 37.42

77.50 ± 35.90

2.351

0.186

Total acidity (mgCaCO₃/L)

25.50 ± 3.78

25.00 ± 4.54

26.83 ± 6.01

0.149

0.864

Organic carbon (mg/L)

2.82 ± 1.03

2.02 ± 1.16

2.02 ± 0.63

1.19

6.751

Ca²⁺ (mg/L)

9.58 ± 2.06

15.50 ± 7.77

20.96 ± 7.26

6.824

0.032

Mg²⁺ (mg/L)

2.23 ± 0.69

3.65 ± 2.75

7.37 ± 4.04

4.551

0.070

NO₃⁻ (mg/L)

1.26 ± 0.21

1.27 ± 0.22

1.14 ± 0.23

0.564

0.591

PO₄³⁻ (mg/L)

0.71 ± 0.28

0.51 ± 0.21

0.26 ± 0.09

7.83

0.022