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. 2023 Jun 24;9(7):e17474.
doi: 10.1016/j.heliyon.2023.e17474. eCollection 2023 Jul.

Depth profile of reservoir water quality in the Southwest of Ethiopia

Bizuneh Woldeab  1 , Argaw Ambelu  2 , Zewdu Efrem  3 , Siyoum Deribe  3 , Moa Megersa  4 , Tibebu Alemu  5 , Seid Tiku Mereta  3
Affiliations

Depth profile of reservoir water quality in the Southwest of Ethiopia

Bizuneh Woldeab et al. Heliyon. .

Abstract

The objective of this research was to investigate the variation of water quality parameters at different depths of the Gilgel Gibe I reservoir in Oromia Jimma zone during wet seasons. Five stations within the reservoir were selected, and water quality parameters were determined at four different depths (surface, 5 m, 10 m, and 15 m). Water quality parameters were analyzed on-site using a HACH, HQ40d portable multi-meter, and turbidity was measured using Wag tech turbidity meter and in the laboratory using the standard method. Comparison of water quality parameters among depths were conducted using one-way ANOVA and Tukey's pairwise comparisons with 5% significance level. The probable contributing source of the investigated physicochemical water quality parameters at different depth was identified using Principal components analysis. The results show that depth wise except for total suspended solids (TSS), total dissolved solids (TDS), total phosphorus (TP) and soluble reactive phosphorus (SRP) the rest showed statistically significant difference at p < 0.05 level. Negative correlations were found between depth and dissolved oxygen (DO), water temperature, pH, nitrate (N03-) and chlorophyll a (Chl.a) while positive correlations were found between electrical conductivity (EC), biochemical oxygen demand (BOD5), turbidity and N03-. The study revealed that the release of nutrients associated with increased concentration of BOD5 at the bottom depth caused low concentration of dissolved oxygen due to oxygen consumption. This was further aggravated through the decomposition of organic matter, indicating organic pollution resulting from runoff from the catchment. The presence of dense masses of blue-green algae in the pelagic zone of Gilgel Gibe I reservoir suggested the presence of ample nutrients for its blooming and significant reduction of water quality, indicating possible eutrophic conditions. Therefore, catchment management is required to protect aquatic life and the reservoir function as a whole from reservoir water quality degradation.

Keywords: Chlorophyll a; Eutrophication; Gilgel gibe; Organic matter; Physicochemical.

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Conflict of interest statement

The authors confirm that we have no conflicts of interest to disclose and all authors agreed for submission of this manuscript to the Journal. In addition, this research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Figures

Fig. 1
Fig. 1
Location of depth sampling sites at Gilgel Gibe I Reservoir.
Fig. 2
Fig. 2
Depth variation of water quality parameters based on median concentration (DO mg/L, Temperature °C, pH and BOD5 mg/L) at Gilgel Gibe I Reservoir. 0 m denotes surface.
Fig. 3
Fig. 3
Depth variation of water quality parameters based on median value (EC μS/cm, TDS mg/L, Turbidity NTU, and TSS mg/L) at Gilgel Gibe I Reservoir. 0 m denotes surface.
Fig. 4
Fig. 4
Depth variation of water quality parameters based on median concentration (NO3− mg/L, Chl.a mg/L, TP mg/L, and SRP mg/L) at Gilgel Gibe I Reservoir. 0 m denotes surface.
Fig. 5
Fig. 5
Scree plot showing the components to be considered.
Fig. 6
Fig. 6
PCA depth analysis of water quality parameters for Gilgel Gibe I Reservoir (the different depths, 0 m (surface), 5 m, 10 m and 15 m represented by square, dark square, circle, and triangle respectively).
Fig. 7
Fig. 7
Dense masses of Chl.a at Gilgel Gibe Reservoir I.
See this image and copyright information in PMC

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