Analysis of water hyacinth (Eichhornia crassipes) infestation in a river branch using Sentinel-2 satellite data

The worldwide spread of invasive aquatic plants in freshwater environments often leads to serious environmental (including ecological and socio-economic) problems, which requires a deeper knowledge of the extent of infestations (in time and space), and the abundance and propagation rates of aquatic weeds in invaded water systems. In particular, water hyacinth (Eichhornia crassipes) has become a threat to many aquatic environments: by presenting a rapid reproductive capacity; water hyacinth outcompetes other aquatic plant species, forming dense free-floating mats, which in many instances completely cover fresh-water surfaces. The infestation leads to several impacts that are hazardous to aquatic systems, disables human uses of surface waters, and affects hydraulic infrastructures (e.g., waterways, pumping stations). In general, the water hyacinth’s fast growth rate is explained, to a large extent, by eutrophication in water bodies.

This study explores the use of remote sensing tools to characterize the presence of water hyacinth in a river environment, aiming at new insights into the detection, observation, and mapping of this invasive plant using multispectral based vegetation indices and water indices, such as NDVI and NDWI. The study focuses on a small watercourse located in the downstream part of the Mondego River Valley, in Portugal. Multi-temporal data were acquired by multispectral satellite Sentinel-2; the data spatial resolution is 10 m. Results from this study show that the new generation sensors’ data have the potential to better detect the spatial distribution of invasive plant species and temporal dynamic changes in their incursion level, compared to data collected during (traditional) time costly ground-based surveys. The remote sensing approach provides a baseline to inform planners and decision-makers and a framework for developing water hyacinth management and important eradication strategies.