Mapping and monitoring the spatial distribution of eichhornia crassipes (water hyacinth) in the Hartbeespoort dam, South Africa, using remote sensing datas

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2019

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Keebine, Galaletsang Latoya

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Abstract

The rapid spread of Eichhornia crassipes (water hyacinth) has caused negative ecological, economic and social impacts in warm tropical and sub-tropical countries globally. The invasive taxa of Eichhornia species are presently listed among 100 of the most undesired species globally. However, the absence of current information about the temporal and spatial dispersion of water hyacinth infestation has deterred the control and monitoring efforts employed against the weed. Thus, monitoring and detection of water hyacinths are crucial in order to provide trustworthy and precise information about the spatial dispersal and the level of water hyacinth infiltration into native environments. This study investigates the ability of Sentinel-2 MSI and Landsat-8 OLI imagery for mapping the spatial extent of the water hyacinth invasion in the Hartbeespoort Dam, North West Province, South Africa, using the random forest classifier. Images utilised in this study were acquired within a period of 24 hours of each other; 26 October 2018 and 27 October 2018, respectively. Both sensors, Sentinel2 MSI and Landsat-8 OLI, similarly achieved high overall accuracies of 93.13% and 89.88% respectively. Although, Sentinel-2 MSI was better at distinguishing water hyacinth from other LULCC in the area, as shown by the 91.75% producers accuracy for water hyacinth, whereas the delineation of water hyacinth from the Landsat-8 OLI imagery achieved a moderately high 80.41% producers accuracy. The study additionally utilised historical Landsat 7 ETM+ data and change detection analysis to infer on the success of physical control measures previously employed against the weed in the dam for 2007 and 2009. The change detection statistic showed that the physical control of water hyacinth is to an extent successful, but requires a long-term implementation to avoid greater re-infestation of water by water hyacinth. The result not only demonstrates that Sentinel-2 MSI and Landsat-8 OLI imagery are able to detect and correctly delineate water hyacinth distribution from other LULCC but that the multispectral sensors do so with high-accuracy. Moreover, they indicate the possibility of monitoring water hyacinth infestations on a regular basis, by integrating data from various sensors. The high accuracies provide an opportunity for the mapping of the spatial extent of the intrusive alien plants to be performed on a regular basis utilising freely available data of high quality. The restoration of ecological functions and processes, by physically controlling water hyacinth invasion, through Metsi A Me programme and Working for Water programme is plausible and a functional long-term strategy

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A research report submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in partial fulfillment of the requirement for the degree of Master of Science GIS and Remote Sensing at the School of Geography, Archaeology & Environmental Studies May 2019 Johannesburg, South Africa

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