Relationship between lake level fluctuations (WLFs) and water
quality parameters
A significant correlation (p < 0.01) was found between
nine water quality parameters (conductivity, depth, TP,
PO43–, WQI, DO, temperature,
turbidity, and NO3–) and DLTM (Table
II). Only, one parameter (SiO44–) was
significantly (p < 0.01) correlated with the yearly
amplitude (WLamp) in Lake Baringo indicating the DLTM to be a better
predictor of water quality in the lake at an inter-annual scale. Except
for the depth and different forms of nitrogen
(NO3–,
NO2– and
NH4+) which had negative correlations
with DLTM, other parameters demonstrated positive concordance with
increasing DLTM over time in the lake.
NH4+ that ranged from 21.75 to 48.8 µg
L-1, also showed significant negative correlation (r =
-0.64, p < 0.05) with DLTM over time in the lake.
Silicate ions (SiO44–) ranged from
18.92 to 27.43 mg L-1 across all years (2008-2021).
SiO44– did not demonstrate a
concordance with DLTM but showed a positive significant correlation with
yearly amplitude of lake levels (r = 0.70, p = 0.008) indicating the ion
is tracked by short-term changes in the lake. There was no significant
concordance between Chl-a, and TN with any of the WLFs indices over time
in the lake. The water quality index (WQI) as a measure of the lake
water quality was significantly correlated with the DLTM (r = 0.80,p = 0.001) and not the lake water level amplitude, WLamp (Table
II). The Gaussian 4 parameter unimodal model further provided a
significant fit (p < 0.05) to the relationship between
WQI and DLTM (R² = 0.89) and not with the lake amplitude (Figure 6a and
b) indicating that a range of DLTM of ≥ 2 m and in the range of 6.5 to
≥10 m provided a good water quality of the lake as WQI approached the
WHO recommended value of WQI ≤ 100, while DTLM values of ≤ 2 m resulted
into poor water quality. The Gaussian, 4-parameter model: WQI = 314.68 +
1252.05*exp(-0.5*((x - 3.88)/2.2)²) yielded a significant relationship
(p = 0.0024 ) between WQI and DLTM (R² = 0.89) (Figure 6). These
results indicated that the water quality index (WQI) was lowest in years
closest to the highest long-term mean (DLTM = 9.9 m) and increased with
decreasing lake water levels.