SUMMARYAs demand for oil increases, production from large oil fields is declining at 4-5% annually, and the world production of oil is expected to peak around 2010. In the meantime, there is one liquid fuel that is renewable and can be used in vehicles without major modification of the engine-it is biofuel (biomass fuel). Ethanol is an alcohol-based fuel produced by fermenting and distilling crops such as corn, barley, wheat, and the like. There are a few issues to be discussed regarding the use of ethanol biofuel: (i) there is a possibility that more energy is used to grow and process the raw material (e.g. corn) into ethanol than is contained in the ethanol itself; (ii) it is unclear whether the adoption of ethanol fuel will increase greenhouse gas; and (iii) a common objection to biofuel production is that it could divert agricultural production away from food crops (i.e. subsidized food burning). After analysis of these issues, biofuel production from wood (forest) residues is considered a sustainable approach to a renewable energy-based society.
Duckweed species, particularly Lemna minor, are widely found in freshwaters all over the world. This macrophyte provides multiple ecosystems’ functions and services, but its excessive proliferation can have negative environmental impacts (including ecological and socio-economic impacts). This work explores the use of remote sensing tools for mapping the dynamics of Lemna minor in open watercourses, which could contribute to identifying suitable monitoring programs and integrated management practices. The study focuses on a selected section of the Lis River (Portugal), a small river that is often affected by water pollution. The study approach uses spatiotemporal multispectral data from the Sentinel-2 satellite and from 2021 and investigates the potential of remote sensing-based vegetation and water indices (Normalized Difference Vegetation Index (NDVI), Green Normalized Difference Vegetation Index (GNDVI), Normalized Difference Aquatic Vegetation Index (NDAVI), Green Red Vegetation Index (GRVI), Normalized Difference Water Index (NDWI)) for detecting duckweeds’ infestation and its severity. The NDAVI was identified as the vegetation index (VI) that better depicted the presence of duckweeds in the surface of the water course; however, results obtained for the other VIs are also encouraging, with NDVI showing a response that is very similar to NDAVI. Results are promising regarding the ability of remote sensing products to provide insight into the behavior of Lemna minor and to identify problematic sections along small watercourses.
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