Assessing the effectiveness of mechanical methods in controlling water hyacinth using multi-temporal remote sensing data and machine learning techniques

The Blesbokspruit Wetland Reserve is a critical ecosystem in South Africa that has been impacted by the aggressive invasive water hyacinth (Eichhornia crassipes), which invades freshwater resources and threatens water quality and ecosystem services. The plant can spread rapidly over short intervals, creating thick and dense layers on the top surface of freshwater bodies, affecting freshwater resources. Thus, monitoring the management of water hyacinths is essential to protect water resources affected by the presence of this plant. Therefore, this research tests the applicability of multiseries Sentinel-2 (S2) Multispectral Imager data with machine learning algorithms, Random Forest (RF) and Support Vector Machines (SVM) to monitor the effectiveness of mechanical methods in managing water hyacinth in a wetland reserve from 2018 to 2024 in a Google Earth Engine environment. During the analysis, multi-series S2 images were acquired during these periods, namely before and after the intervention that occurred every three months of each year in the reserve, to assess the spatio-temporal variation of the distribution of water hyacinth. The results showed that RF and SVM were able to discriminate the spatio-temporal distribution of Eichhornia crassipes by obtaining an overall accuracy of 93.42% and 92.08%, respectively. A significant reduction in the spatial coverage of water hyacinth after each intervention was observed. However, a subtle regrowth of 35% to less than 16% between 2018 and 2024 occurred after a month of manual plant removal, which required extra resources for continued monitoring. Thus, the research highlights the potential of new generation multispectral data in identifying problematic areas, which will assist reserve managers and nature conservators in devising effective management strategies to control the spread of alien invasive species in a timely and effective manner, thus preserving wetland resources which align with the Sustainable Development Goals (SDG 6).