The water quality status of estuarine micro-system types along the coast of KwaZulu-Natal Province, South Africa

• Published in: Water S. A. 2023-07, Vol.49 (3), p.260-272
• Main Authors: Bate, G.C, Lemley, D.A, Nunes, M, Adams, J.B
• Format: Article
• Language: English
• Subjects: Anthropogenic factors; Biomass; Brackishwater environment; Catchment area; Catchments; Chlorophyll; Coastal zone; Coasts; Dissolved oxygen; Estuaries; Food chains; Food webs; Fresh water; Housing developments; Human influences; Hypotheses; Indicators; Land pollution; Land use; Nitrogen; Nonpoint source pollution; Phosphorus; Phytoplankton; Plankton; Point source pollution; Pollution; Pollution sources; Quality assessment; Wastewater; Water circulation; Water column; Water pollution; Water quality; Water quality assessments
• ISSN: 0378-4738
• DOI: 10.17159/wsa/2023.v49.i3.4038

A survey of the quality of water flowing from micro-system types to the ocean, along the subtropical east coast of South Africa, showed a wide variation in the concentrations of total nitrogen, phosphorus and phytoplankton biomass in the different systems located, in many cases, only a short distance from each other along the coastline. The origins of the high phytoplankton growth indicate pollutants caused by the land-use in this highly populated coastal region. The main agricultural activities in the area are sugarcane, permanent orchards, and forestry. The levels of N and P in the water varied from 'good' to 'poor', i.e., TN 0.15-3.99 mg*[L.sup.-1], TP 0.02-0.33 mg*[L.sup.-1] and chlorophyll-a from 0 to almost 45 [micro]g*[L.sup.-1]. Rapid coastal population densification appears to have been the cause of the pollution levels measured for total nitrogen, phosphorus, and phytoplankton biomass. Most of the micro-systems with a total modified peri-catchment above 80% were enriched by both TN and TP. While the hypothesis tested was that the main cause was residential development (e.g., septic tank effluent), it was not possible to show any statistical significance to support such a specific conclusion. Although these systems are small individually, the great number along the coastline warrants recognition as important sources of freshwater inflow and nutrients to the marine environment. KEYWORDS coastal pollution population agriculture wastewater phytoplankton