Application of multi-hydrochemical indices for spatial groundwater quality assessment: Ziway Lake Basin of the Ethiopian Rift Valley

Abraham Mechal,Tewodros Rango Godebo,Kristine Walraevens,Hassen Shube,Steffen Birk

doi:10.1007/s12665-021-10135-5

Abstract

The Ethiopian Rift Valley (ERV) is characterized by arid and semi-arid climate with groundwater as the most important water resource used for drinking and irrigation purposes. However, in the region, people are suffering from severe water scarcity exacerbated by climate effect. Besides water availability, endemic water quality issues are critical and affect the suitability of the water and human health risks. The present study evaluates the suitability of groundwater for drinking and agricultural purposes in the Ziway Lake Basin (ZLB) of the ERV. Groundwater used for drinking contains multiple inorganic contaminants in levels that surpass the World Health Organization recommended limits. The most frequent of these violations were for Na+, K+, HCO3−, F− and few samples for Mn, As, U, Pb and Mo. The modeled Drinking Water Quality Index (DWQI) values of the groundwater show wide variation ranging from 12.7 (Excellent category) to 714 (Unsuitable category) with mean value of 94. Likewise, Irrigation Water Quality Index (IWQI) computed by considering EC, SAR, Na%, RSC and PI of the groundwater varies from 13.2 to 520 with a mean value of 106. Both DWQI and IWQI values suggest that groundwater is generally of Excellent quality for drinking and irrigation use in the headwater regions of the ZLB and progressively becomes extremely Unsuitable toward the rift floor. The exceptionally high DWQI values to the west of Lake Ziway is mainly associated with the co-occurrence of multiple toxic elements from a groundwater from the Quaternary sediments and rhyolitic volcanic aquifers.

Highlights

Groundwater represents more than 90% of the world’s readily available freshwater resources (Boswinkel 2000) and has a vital role in supporting the life of mankind (WRI, UNEP, UNDP, World Bank 1998)
Irrigation Water Quality Index (IWQI) computed by considering Electrical Conductivity (EC), Sodium Adsorption Ratio (SAR), Na%, Residual Sodium Carbonate (RSC) and Permeability Index (PI) of the groundwater vary from 13.2 to 520 with mean value of 106. Both Drinking Water Quality Index (DWQI) and IWQI value suggest that groundwater is generally of Excellent quality for drinking and irrigation use in the headwater regions of the Ziway Lake Basin (ZLB) and progressively becomes extremely Unsuitable towards the rift floor
The Ethiopian Rift Valley (ERV), a volcano-tectonically active part of the East African Rift system, provides an example of the challenges to water supply posed by groundwater quality

Summary

Introduction

Groundwater represents more than 90% of the world’s readily available freshwater resources (Boswinkel 2000) and has a vital role in supporting the life of mankind (WRI, UNEP, UNDP, World Bank 1998). The Ethiopian Rift Valley (ERV), a volcano-tectonically active part of the East African Rift system, provides an example of the challenges to water supply posed by groundwater quality. The poor water quality in the region seems to be linked to the mobilization of contaminants naturally occurring in the volcanic rocks and lacustrine sediments and the enrichment of groundwater, e.g. with toxic elements (As, U, Mo and B), as it flows from rift escarpments to rift valley floor (UNDP 1973; Darling et al 1996; Gizaw 1996; Rango et al 2009, 2010, 2013)

Objectives

Methods

Findings

Conclusion