Table 1 Mann-Kendall statistical tests on the Log₁₀ TN vs. Log₁₀ TN:TP and Log₁₀ TP vs. Log₁₀ TN:TP between the two periods before (B-CUD) and after the construction of the upper dam (A-CUD)

B-CUD year

(1992–1999)

t _au

s

z

p value

Linear model

Log₁₀ TN vs. Log₁₀ TN:TP

−0.143

−4

−0.371

0.7105

Log₁₀ (TN:TP) = 2.52 − 0.119 × Log₁₀(TN)

Log₁₀ TP vs. Log₁₀ TN:TP

−0.714

−20

−2.351

0.0187

Log₁₀ (TN:TP) = 3.70 − 1.108 × Log₁₀(TP)

A-CUD year

(2000–2013)

t _au

s

z

p value

Linear model

Log₁₀ TN vs. Log₁₀ TN:TP

−0.187

−17

−0.876

0.3811

Log₁₀ (TN:TP) = 5.90 − 1.111 × Log₁₀(TN)

Log₁₀ TP vs. Log₁₀ TN:TP

0.868

−79

−4.270

0.0000

Log₁₀ (TN:TP) = 4.54 − 1.616 × Log₁₀ (TP)