Evaluation of Sentinel-2 for water quality monitoring in a eutrophic estuary in South Africa

Authors

  • Marié E Smith 1. Coastal Systems and Earth Observation Research Group, Council for Scientific and Industrial Research (CSIR), Rosebank 7700, Cape Town, South Africa; 2. Department of Oceanography, University of Cape Town, Rondebosch 7700, Cape Town, South Africa https://orcid.org/0000-0001-6781-2343
  • Daniel A Lemley 1. Botany Department, Nelson Mandela University, Gqeberha 6031, South Africa; 2. DSI/NRF Research Chair in Shallow Water Ecosystems and the Institute for Coastal and Marine Research, Gqeberha 6031, South Africa https://orcid.org/0000-0003-0325-8499
  • Emily Whitfield 1. Botany Department, Nelson Mandela University, Gqeberha 6031, South Africa; 2. DSI/NRF Research Chair in Shallow Water Ecosystems and the Institute for Coastal and Marine Research, Gqeberha 6031, South Africa https://orcid.org/0000-0002-6900-8823
  • Janine B Adams 1. Botany Department, Nelson Mandela University, Gqeberha 6031, South Africa; 2. DSI/NRF Research Chair in Shallow Water Ecosystems and the Institute for Coastal and Marine Research, Gqeberha 6031, South Africa https://orcid.org/0000-0001-7204-123X

DOI:

https://doi.org/10.17159/wsa/2025.v51.i3.4190

Keywords:

Sentinel-2, water quality, chlorophyll a, atmospheric correction, South Africa

Abstract

This study evaluates the utility of Sentinel-2 satellite products for monitoring spatial and temporal changes in chlorophyll a (Chl-a) concentration within an urban, eutrophic estuary. Four atmospheric correction (AC) processors, namely Acolite, C2RCC, Sen2Cor, and Polymer, are assessed together with eight different parameterisations of three high-biomass-appropriate empirical Chl-a retrieval algorithms, namely the 2-band, 3-band and normalised difference chlorophyll index (NDCI). The best performance is achieved using Sen2Cor and the NDCI, which provides an average absolute percentage difference, bias, and correlation of 173%23.8% and 0.853 (p < 0.05), respectively, which improves to 61.7%, 5.4% and 0.843 (p < 0.05), respectively, for conditions where Chl-a > 10 mg/m3. These results indicate that an appropriately configured NDCI algorithm applied to the default Sentinel-2 Level 2 product can be used for routine aquatic water quality monitoring applications for mesotrophic and eutrophic estuaries in the South African context. Monitoring approaches for estuary water quality are essential, as there is an increase in urban runoff and untreated inputs from malfunctioning wastewater treatment systems. The results inform water quality monitoring and management of similar sized estuaries globally. Remote sensing can complement in situ measurements and provide a holistic overview of a system.

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Published

2025-07-22

Issue

Vol. 51 No. 3 July (2025): Water SA

Section

Research paper

License

Copyright (c) 2025 Marié E Smith, Daniel A Lemley, Emily Whitfield, Janine B Adams

Creative Commons License

This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.

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The content of this journal is licensed under a Creative Commons Attribution Licence.  Users are permitted to read, download, copy, distribute, print, search or link to the full texts of the articles in this journal under the terms of this Licence, without asking prior permission from the publisher or the author, provided the source is attributed. Copyright is retained by the authors.

How to Cite

Marié E Smith (2025) “Evaluation of Sentinel-2 for water quality monitoring in a eutrophic estuary in South Africa”, Water SA, 51(3 July). doi:10.17159/wsa/2025.v51.i3.4190.