Four Eastern Cape estuaries, the Kromme, Gamtoos, Swartkops and Sundays Estuaries have a permanent connection to the adjacent ocean, but differ in the amount of freshwater inflows as well as in the land-use patterns in their respective catchment areas. The nutrient loading to the four estuaries in terms of phosphate, nitrate, nitrite and ammonia therefore varies. The aim of the study was to show how the nutrient loads received by the estuaries differ, and how they act as filters for nutrients. Discriminant analysis revealed such contrasts: The lower reaches of the four estuaries are similar in their inorganic nutrient concentrations, but concentrations diverge in their upper reaches and in the inflowing river water.

Keywords: filtering capacity of estuaries, nutrient loading, phosphate, nitrate, nitrite, ammonia, South Africa

Water SA Vol. 31(4) 2005: 483-490