Uncovering sediment pollution sources: A comparative assessment of two South African Estuaries

Abstract

Richards Bay Harbour is South Africa's largest and busiest deep-water port by tonnage, and this ongoing shipping and port activities will expectedly result in metal contamination issues. The adjacent Mhlathuze Estuary is a nature reserve with a long history with Richards Bay Harbour and may be prone to metal contamination from multiple sources. The study investigates the sources of contaminated sediments in these two South African estuaries arising from their proximity to various anthropogenic activities. Investigating these sources of contamination is crucial for developing effective pollution control strategy since Richards Bay Harbour and Mhlathuze Estuary are regarded as estuaries of national conservation importance in South Africa. To provide further insights, sediment samples were acid digested and quantified for metal concentrations using Inductively coupled plasma-optical emission spectrometry (ICP-OES). Multivariate (SIMPROF and cluster) analysis was used to identify how sampling sites in Richards Bay Harbour and Mhlathuze Estuary were grouped based on sediment metal concentrations. Results of pollution load index for Richards Bay Harbour showed site 4 to be heavily polluted, while site 3 in Mhlathuze Estuary showed moderate pollution. Multivariate analysis (SIMPROF and cluster) further revealed sites related to anthropogenic activities and those that were unpolluted. Engaging this advanced analysis enhanced the ability to delineate potential pollution sources and further helped in the identification of the main contributors to sediment pollution. The findings indicate that port and industrial activities are the major contributors to sediment contamination at the estuaries. The results provide specific insights into the sources of pollution, informing targeted environmental management and policy-making efforts to protect and improve the estuarine environments.