AN INTRODUCTION TO THE PHYSICS AND CHEMISTRY OF SOME LAKES IN NORTHERN ZULULAND

Summary

1. Lakes Sibayi and Nhlange on the coastal plain of northern Zululand are warm shallow lakes which exhibit a complex pattern of stratification during summer. In Lake Sifungwe a permanent halocline was found at 10 metres. The source of this deep salt layer is the sea, to which the lake is connected via the Kosi estuary.

2. Dissolved oxygen never reaches limiting concentrations except in the deep salt layer of Lake Sifungwe. Variation in dissolved oxygen in Lake Nhlange can be correlated with river inflows rich in organic material.

3. Chemically the lakes are dominated by excess chloride varying from 135 mg/l in Lake Sibayi to greater than 3000 mg/l in Lake Nhlange and the surface waters of Lake Sifungwe.