Water hyacinth, or Eichhornia crassipes (Mart.) Solms, is an invasive and free floating water plant, native to South America that has often been marked as one of the world’s worst invasive aquatic species. It grows into large dense vegetable carpets that block sun energy transmission into shallow waters or even the lake bottom.
The objective of the presented study was to test a multi-sensor approach, combining several remote sensing methods at two different locations, with particular ecological and land use systems, in order to detect and monitor floating biomass, and assess the abundance and quantity of Eichhornia crassipes and similar floating macrophytes using MERIS, MODIS and Landsat 7-ETM imagery. The successful multi sensor approach resulted in temporal spatial patterns of floating biomass, enabling transformable quantifications for the detected floating biomass.
This study focused on two different water bodies in the tropical/subtropical zone: Lake Inle in Myanmar and Lake Victoria in east Africa. Only freely available Landsat ETM 7 imagery and MODIS, MERIS data from the last decade (2000 to 2011) were used in order to detect and assess the abun-dance of Eichhornia crassipes and similar floating macrophytes.
Several remote sensing index methods for detecting vegetation cover and floating biomass like NDVI and SAVI or MSAVI can be applied to detect any vegetation, including aquatic vegetation. A specific image analysis workflow to assess the spatial extent of aquatic vegetation on the lakes was created and tested in a semi-automated prototype. (Please consult the whole article for the detailed decription).
From 2000 to 2011, the spatial extent of sparse floating biomass fluctuated on both lakes within a range of more 3000 ha on the Inle Lake and more than 35000 ha in the Winam Gulf, without any significant trend. On the Inle Lake, the classification results show four peaks in 2000, 2002 2007-08 and 2011, which show a high frequency or periodicity and no significant correlation to the variability of dense floating vegetation. In the Winam Gulf, there were only three peaks of sparse floating vegetation in 2003, 2005 and 2010 measured in comparison to FUSILLI et al. (2011). The spatial extent of dense floating vegetation on the Inle Lake ranges between 250 ha and 1300 ha, showing large scale variations without a trend and only one peak in 2002. The dense floating vegetation in the Winam Gulf ranges from 1300 ha in 2006 to 11000 ha in 2007 with two peaks, and 16000 ha in 2010. The lack of intra-seasonal image collection available for this study limits the probability to identify any seasonal periodicity of water hyacinth abundance in the gulf.
Jan-Peter MUND, Dieter MURACH and André PARPLIES (2014): Monitoring and Quantification of Floating Biomass on Tropical Water Bodies. DOI: 10.1553/giscience2014s67