Spatio-Temporal Water Hyacinth Monitoring in the Lower Mondego (Portugal) Using Remote Sensing Data

Abstract

Monitoring invasive plant species is a crucial task to assess their presence in affected ecosystems. However, it is a laborious and complex task as it requires vast surface areas, with difficult access, to be surveyed. Remotely sensed data can be a great contribution to such operations, especially for clearly visible and predominant species. In the scope of this study, water hyacinth (Eichhornia crassipes) was monitored in the Lower Mondego region (Portugal). For this purpose, Sentinel-2 satellite data were explored enabling us to follow spatial patterns in three water channels from 2018 to 2021. By applying a straightforward and effective methodology, it was possible to estimate areas that could contain water hyacinth and to obtain the total surface area occupied by this invasive species. The normalized difference vegetation index (NDVI) was used for this purpose. It was verified that the occupation of this invasive species over the study area exponentially increases from May to October. However, this increase was not verified in 2021, which could be a consequence of the adopted mitigation measures. To provide the results of this study, the methodology was applied through a semi-automatic geographic information system (GIS) application. This tool enables researchers and ecologists to apply the same approach in monitoring water hyacinth or any other invasive plant species in similar or different contexts. This methodology proved to be more effective than machine learning approaches when applied to multispectral data acquired with an unmanned aerial vehicle. In fact, a global accuracy greater than 97% was achieved using the NDVI-based approach, versus 93% when using the machine learning approach (above 93%).

Impact of climate change on surface water resources in arid zones - the case of the Ykem watershed in the central plateau of Morocco

“…This study looks at changes in the surface area covered by water in the Ykem watershed, which is in the northwest of the central plateau of Morocco, between 1992 and 2021. The methodology is based on geospatialization tools [4], mainly remote sensing techniques that use publicly available data from Landsat and Sentinel satellite images. Second, data collected is analyzed by a GIS geographic information system [5], which quantifies spatio-temporal variations in water resources [6] using the Land Use index.…”

Biological invasions in the twenty-first century: a global risk

“…During the last few years, there has been increased concern about the impacts of biological invasions. There are multiple examples of detailed studies on the spectacular impacts of invasions on whole ecosystems, including for instance effects on genetic diversity and changes in ecosystem functioning (Strayer 2012;Simberloff et al 2013;Murphy and Romanuk 2014;Pádua et al 2022;Cordero et al 2023;Yang et al 2023).…”