Biological invasions are responsible for some of the most devastating impacts on the world’s ecosystems. Freshwater ecosystems are among the worst affected, with biological invasion posing serious threats not only to freshwater biodiversity, but to the important ecosystem services it provides. Tackling the impact of these invaders on our freshwater ecosystems is currently a major challenge, and one that requires detailed information on both invasive species distribution and spread. While these concerns are relevant globally, there is an urgent need to conduct research of this nature in countries such as South Africa, where freshwater resources are becoming increasingly pressured.

This project utilises freely available satellite data and the processing capabilities of cloud computing platforms to map the distribution of the worst invasive aquatic alien plant, Water Hyacinth Eichhornia crassipes across South African waterbodies to explore reasons for its occurrence and identify optimal biological control release strategies. PhD student Geethen Singh is undertaking this valuable research in collaboration with Chevonne Reynolds, Benjamin Rosman and Marcus Byrne of the University of the Witwatersrand.

Invasive aquatic alien plant species present a serious threat to South Africa’s freshwater resources as they increase water loss through evapotranspiration. Water weeds can increase water loss by 130–180%. Water body area and the percentage cover of invasive aquatic weeds on these impoundments are crucial information needed to facilitate the removal and management of these weeds. However, field assessments to obtain this information are often too time-consuming, costly and labour intensive. Freely available satellite images are an alternative and cost-effective approach to reliably and frequently assess the coverage of surface water weeds. In this way, the extent of water weed infestation and its associated drivers can be identified and tracked.

Once an invasive alien species has established itself it can be difficult or even impossible to stop or slow down the invasion. Thus, the early and rapid detection of invasive alien species is needed to make management targeted, feasible and effective. Consequently, there is an urgent need for techniques that enable consistent, fast and accurate monitoring. This will allow invasion biologists to systematically monitor invasive alien species over the introduction, establishment and secondary dispersal phases of the invasion process, across large areas with a reduced risk of accidental invasive alien plant dispersal by field personnel. Geethen is making use of semi-automated satellite image analysis techniques, such as semantic segmentation of freely available Landsat, Sentinel-1 and Sentinel-2 imagery to map the distribution of water hyacinth at a national level. 

Furthermore, Geethen is undertaking this analysis within Google Earth Engine, a cloud computing platform that allows scientists and managers the ability to produce up-to-date maps of surface water extent and percentage plant cover. 

Activities in 2021

  • Over the last year, Geethen has made excellent progress in identifying the dominant factors determining the occurrence of water hyacinth at a national level and has put together a framework that can be used to identify candidate biocontrol release strategies.
  • Geethen presented the results of his first two PhD chapters at the Invasion Biology Symposium held at the University of Fort Hare.
  • Geethen attended the Deep Learning Indaba X 2022 at the University of Pretoria.
  • Geethen visited the Norwegian Institute for Nature Research (NINA) and the University of Oslo for three weeks to present a one-day Google Earth Engine workshop and collaborate with NINA researchers.

Highlights

  • Geethen submitted his PhD thesis for examination and will graduate in 2023.
  • Geethen co-authored a research paper through collaboration with researchers from NINA.
  • Geethen released a python package (GEEML) to download data from Google Earth Engine.

Key co-supporters
DSi-NRF CoE grant.

Research team 2022
Dr Chevonne Reynolds (APES, Wits)
Dr Benjamin Rosman (Applied Maths, Wits)
Prof. Marcus Byrne (APES, Wits)

Student:  Geethen Singh (PhD, Wits)