Seasonal discharge and chemical flux variations of rivers flowing into the Bayhead canal of Durban Harbour,South Africa

The uMhlatuzana, uMbilo and aManzimnyama river catchments located on the eastern seaboard of the KwaZulu-Natal province, South Africa, form the core of urbanization and industrialization, contributing the only natural freshwater inflows to the Bayhead Canal portion of the Durban Harbour. In this study, seasonal discharges and physico–chemical water properties were used to quantitatively determine the material mass transport capacity of the river systems on the basis of hydrographic inputs and chemical loading from the surrounding land use sectors. The mass transport of the total dissolved solids (TDS), ammonia (NH₄), phosphorous (P), aluminum (Al), calcium (Ca), copper (Cu), chromium (Cr), mercury (Hg), potassium (K), magnesium (Mg), sodium (Na), nickel (Ni), lead (Pb), sulphur (S) and vanadium (V) was determined for each river. Results indicated that land use, seasonality and river flow were significant determinants for the material loading in the rivers and the receiving port waters. The spatio-temporal distribution patterns of chemical fluxes indicated that industrial activity associated with the aManzimnyama canal contributed the most, with regards to TDS, NH₄, Ca, K, Mg, Na, S and V, loading in both wet and dry seasons, as well as Al, Cu, Hg and Pb during the dry season. Similarly, industrial activity associated with the uMbilo/uMhlatuzana Canal at the lower reaches accounted for the highest P, Al, Cu and Pb fluxes in the wet season alone. Fluxes of these parameters are used to explain the observed elemental concentrations and patterns of the receiving port waters of the Bayhead Canal.