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Hyperspectral Remote Sensing to Detect Biotic and Abiotic Stress in Water Hyacinth, (Eichhornia Crassipes) (Pontederiaceae)

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Hyperspectral Remote Sensing to Detect Biotic and Abiotic Stress in Water Hyacinth, (Eichhornia Crassipes) (Pontederiaceae) Hyperspectral Remote Sensing to Detect Biotic and Abiotic Stress in Water Hyacinth, (Eichhornia crassipes) (Pontederiaceae) Report to the Water Research Commission by Solomon W. Newete, Barend F.N. Erasmus, and Marcus J. Byrne University of the Witwatersrand School of Animal, Plant and Environmental Sciences WRC Report No. 2037/1/13 ISBN 978-1-4312-0497-7 February 2014 Obtainable from Water Research Commission Private Bag X03 Gezina, 0031 [email protected] or download from www.wrc.org.za DISCLAIMER This report has been reviewed by the Water Research Commission (WRC) and approved for publication. Approval does not signify that the contents necessarily reflect the views and policies of the WRC, nor does mention of trade names or commercial products constitute endorsement or recommendation for use. © Water Research Commission ii Executive summary Water hyacinth is the most notorious aquatic weed in the world and it is known as one of the most efficient and productive plants on the planet. South Africa has released seven biocontrol agents against water hyacinth since 1974, none of which have achieved a satisfactory result to reduce the scourge compared to countries such as Uganda, Australia, Papua New Guinea and USA. As a result water hyacinth control in the country has shifted to integrated management, which combines the application of herbicides with biological control methods. However, this requires regular monitoring of the weed’s physiological status in relation to the habitat, in order to facilitate the decision when to intervene and what intervention measures are an appropriate and timely. Remote sensing (RS) of vegetation reflectance has the potential to be that monitoring tool. This report investigates the physiological status of water hyacinth grown with eight different heavy metals in a single-metal tub trial, three different simulated acid mine drainage (AMD) treatments in a pool trial under the influence of biocontrol agent from Neochetina spp., and in the Vaal River at the inlets of its tributaries, the Koekemoerspruit and the Schoonspruit. A hand-held spectrometer, the analytic spectral device (ASD), was used to measure reflectance. The hypothesis that hyperspectral RS can “see” the response of the plant to both the heavy metals and the biocontrol-induced stresses and their interactions was tested. Using the spectral indices associated with canopy chlorophyll content such as the modified normalized difference vegetation index (mNDVI), the linear extrapolation and the maximum first derivative methods that calculate the red edge position (REP), and the water band index (WBI), which determines the canopy water stress, the hyperspectral sensor was able to detect both the metal or AMD and weevil-induced plant stresses. These spectral indices resulted in a strong positive correlation with the actual leaf chlorophyll content, measured by a SPAD-502 chlorophyll meter, of which correlations with the mNDVI and the REP spectral indices were the greatest. Among the contaminants Cu, Hg, and Zn from the single-metal, tub trial and sulphate concentration exceeding 700 mg/L in the AMD pool trial were detected by the RS as stressful to the plants. These results were also consistent with the actual measurements of the different plant growth iii parameters and the weevils’ feeding and reproductive activities in both trials. The different growth parameters of water hyacinth showed that the plant was generally tolerant to most pollutants. Nevertheless, the few symptoms of plant stress due either to the phytotoxicity of the pollutants or feeding damage by the weevils, such as leaf chlorisis, reduction in leaf area, fresh weight of plant biomass and plant density, were detected in the RS. Similarly the RS results from the field trial showed that water hyacinth plants at the inlets of the Schoonspruit on the Vaal River grew bigger and healthier after the rain than before the rain and plants at the downstream site of the Schoonspruit inlet looked healthier than all the other sites. The consistent effects of the three metals (Cu, Hg and Zn) in the single-metal tub trial, and the medium and high AMD concentration treatments in the simulated AMD pool trial, and the increased pollution level after the rain, particularly on the Schoonspruit site, on the weevil’s activities and plant growth parameters with those found in RS data, confirm the feasibility of using the hyperspectral remote sensing (HRS) to identify both metal/AMD and weevil-induced plant stresses and accurately evaluate water hyacinth. Thus, the results of this study indicate that HRS has potential as a tool to assess the physiological status of water hyacinth from a remote position, to therefore inform management intervention in control of the weed. However, its use at a larger scale requires further studies. It also shows that although the general activities of the weevils decreased in response to metal pollution and AMD, the weevils nevertheless managed to cause some damage to the plants. Nevertheless, their use as biocontrol agents will be hindered by the pollutants and probably should be used synergistically with herbicides. iv Acknowledgements I am very grateful to both my supervisors Prof. Marcus Byrne and Prof. Barend Erasmus for supervising this project, and without their dedicated help and guidance this report would not have reached its final shape. I am greatly indebted to Prof. Marcus for all his time and comments on all the deliverables submitted to my funders the Water Research Commission (WRC). I also greatly thank Ms Isabel Weiersbye for her involvement as an advisor in this project and I am very much indebted for her valuable advice during the design of the project and during the analytical processing of my samples. I also thank her for covering all the expenses of the analysis and purchasing some of the equipment and chemicals used in this project and for generously paying my stipend in the first two years. The AngloGold Ashanti staff are thanked for all their cooperation during the setting of the floating cages at the Vaal River, for allowing me to work on the Vaal River near their mining sites and for their valuable advice concerning my safety at the site. I would like to thank Dr. Sashnee Raja for her continuous advice and facilitating all the logistical support, Prof. Deanne C. Drake for allowing me to use her laboratory and equipment and Dr. Moses Cho (CSIR) and Mr. David Furniss for assistance with ENVI software training. I am also very grateful to Mr. David Furniss for his help and advice during the setting of the Vaal River Experiment. And last but not least, I would like also to thank Dr. Des Conlong and Ms Denise Gillespie for their continuous supply of the water hyacinth weevils and Working for Water (WfW) for paying for the weevils and their shipment. Lutendo Mugwedi and my wife Azmera Debesay are thanked for their help during data collection. v vi Table of Contents Contents Pages Executive summary .................................................................................... iii Acknowledgements ...................................................................................... v Table of Contents ...................................................................................... vii List of Figures .............................................................................................. x List of Tables ............................................................................................. xv Problem statement .................................................................................. xvii Chapter 1 ...................................................................................................... 1 Introduction to water hyacinth and hyperspectral remote sensing ....... 1 1.1 The success of invasive plants ................................................................................. 1 1.2 Water hyacinth and environmental problems .......................................................... 2 1.3 Water hyacinth’s nutrient requirements................................................................... 3 1.4 Water hyacinth management ................................................................................... 4 1.4.1 The efficacy of Neochetina spp. .................................................................. 4 1.4.2 Metal accumulation by plants and their response to insect herbivory ......... 5 1.4.3 Integrated management of water hyacinth ................................................... 7 1.5 Remote sensing reflectance of plants using a spectrometer .................................... 7 1.5.1 Vegetation Indices (VIs) used in estimation of plant stresses ..................... 9 1.5.2 Hyperspectral versus Multispectral Sensors .............................................. 11 1.6 Aims and report outline ......................................................................................... 14 Chapter 2 .................................................................................................... 16 Hyperspectral remote sensing to evaluate water hyacinth physiological status.................................................................................... 16 2.1 Introduction ........................................................................................................... 16 2.1.1 Measurement of aquatic weeds with hyperspectral imagery ..................... 16 2.1.2 Use of the “red edge position” to determine plant stress ........................... 17 2.2 Materials and Methods
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