Abstract
Introduction: Water quality assessment is essential for monitoring and managing
freshwater resources, particularly in ecologically and culturally significant areas
like the Cradle of Humankind World Heritage Site (COHWHS). This study aimed to
predict and map the spatio-temporal patterns of both optically and non-optically
active water quality parameters within small inland water bodies located in
the COHWHS.
Methods: High-resolution Sentinel-2 Multispectral Instrument (MSI) satellite data
and two random forest models (Model 1 [consisting of sensitive spectral bands]
and Model 2 [consisting of spectral bands + indices]) were used alongside In-situ
measurements of chlorophyll-a, suspended solids, dissolved oxygen (DO), pH,
Temperature, and electrical conductivity (EC) were integrated to establish
empirical relationships and assess spatial variability across high-flow and lowflow
conditions.
Results: The results indicated that DO could be predicted with the highest
accuracy under low-flow conditions, followed by EC. Specifically, Model 2
achieved an R2 of 0.88 and an RMSE of 1.37 for DO, while Model 1 achieved
an R2 of 0.63 and an RMSE of 291.48 for EC. For optically active parameters,
suspended solids showed the highest prediction accuracy under high-flow
conditions using Model 2 (R2p = 0.55; RMSE = 118.19). Due to the overpixelation
of other smaller water bodies within the COHWHS in Sentinel-2
imagery, Cradlemoon Lake was selected to show distinct seasonal (high- and
low-flow) and spatial variations in optically and non-optically active water quality
parameters.
Discussion: Variations in the results were influenced by runoff dynamics and
upstream pollution: lower Temperatures and suspended solids under low-flow
conditions increased DO concentrations, whereas higher suspended solid
concentrations under high-flow conditions likely reduced light penetration,
OPEN ACCESS
EDITED BY
Xiaojun Li,
INRAE Nouvelle-Aquitaine Bordeaux, France
REVIEWED BY
Pedzisai Kowe,
Midlands State University, Zimbabwe
Liqiao Tian,
Wuhan University, China
Tarek Seleem,
Suez Canal University, Egypt
*CORRESPONDENCE
Mahlatse Kganyago,
mahlatsek@uj.ac.za
RECEIVED 19 May 2025
ACCEPTED 03 July 2025
PUBLISHED 21 July 2025
CITATION
Ngamile S, Kganyago M, Madonsela S and
Mvandaba V (2025) Characterising the spatiotemporal
patterns ofwater quality parameters in
the cradle of humankind world heritage site
using Sentinel-2 and random forest regressor.
Front. Remote Sens. 6:1631403.
doi: 10.3389/frsen.2025.1631403
COPYRIGHT
© 2025 Ngamile, Kganyago, Madonsela and
Mvandaba. This is an open-access article
distributed under the terms of the Creative
Commons Attribution License (CC BY). The use,
distribution or reproduction in other forums is
permitted, provided the original author(s) and
the copyright owner(s) are credited and that the
original publication in this journal is cited, in
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No use, distribution or reproduction is
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terms.
Frontiers in Remote Sensing 01 frontiersin.org
TYPE Original Research
PUBLISHED 21 July 2025
DOI 10.3389/frsen.2025.1631403
resulting in lower spectral reflectance and chlorophyll-a levels. These findings
highlight the potential of Sentinel-2 MSI data and machine learning models for
monitoring dynamic water quality variations in freshwater ecosystems.