The hydrochemistry of rivers in KwaZulu-Natal

S De Villiers

doi:10.4314/wsa.v31i2.5202

Abstract

The chemistry of the major elements of KwaZulu-Natal river water draining the eastern Drakensberg Escarpment was monitored in October 2003 and compared to data obtained previously along the western Drakensberg Escarpment, i.e. the Caledon and Upper Orange Rivers. The data obtained in these two surveys reveal no significant differences in the Mg, Ca, Na, K and HCO 3 -content of rivers draining similar lithologies, despite slightly different climatic regimes and different suspended loads. The implication is that lithology is the dominant control on the major element chemistry of river water draining the Drakensberg. However, in the north-western part of KwaZulu-Natal, drought-stricken at the time of sampling, evaporation-induced concentration results not only in evaporite formation, but dramatic changes in river and stream water chemistry. Elevated levels of minor constituents such as NO3 also indicate that in cultivated areas anthropogenic activities have an impact on water quality and composition.

Highlights

The chemistry of unpolluted freshwater systems such as rivers is primarily controlled by the lithology of the drainage basin and weathering stoichiometry (Meybeck, 1987; Dupré et al, 2003)
This study investigates whether the relationship between river water chemistry and lithology demonstrated for rivers draining the western Drakensberg Escarpment, i.e. the Caledon and Upper Orange Rivers, holds along the eastern Drakensberg Escarpment
Since Drakensberg basalt is found only above an altitude of approximately 1 800 m along the escarpment, the results suggest that Mg/K and Ca/K can be used as indicators of the relative altitude from which river water along the escarpment was sourced

Summary

Introduction

The chemistry of unpolluted freshwater systems such as rivers is primarily controlled by the lithology of the drainage basin and weathering stoichiometry (Meybeck, 1987; Dupré et al, 2003). Most of the rivers sampled in KwaZulu-Natal drain rocks of the Karoo Supergroup, i.e. the same lithological provinces as the Caledon and Upper Orange Rivers. Samples KZN1 to KZN12 in western KwaZulu-Natal drain rocks and sediments belonging to the Karoo Supergroup, as do KZN13 to KZN15 in the north-western part of the province.

Results

Conclusion