Hyperspectral reflectance features of water hyacinth growing under feeding stresses of Neochetina spp. and different heavy metal pollutants

Abstract

Spectral signatures of water hyacinth grown with biocontrol agents (Neochetina eichornia and N. bruchi) and various heavy metal pollutants were collected at the plant canopy level using a hand-held spectrometer to detect biocontrol agent and heavy metal-induced plant stresses and the interaction between the two stressors. Water hyacinth was grown in 65L tubs, each with a single treatment, from one of; As (1 mg/L), Au (1 mg/L), Cu (2 mg/L), Fe (0.5, 2 and 4 mg/L), Hg (1 mg/L), Mn (0.5, 2 and 4 mg/L), U (1 mg/L) and Zn (4 mg/L), with the exception of the control treatment. Spectral measurements were taken before and after the addition of the weevils. Several spectral indicators of plant stress including RE_NDVI, mNDVI705, mSR, PRI, red-edge position (REP) calculated using first derivative and linear extrapolation and WBI (to detect water stress) were used to identify biotic and abiotic induced plant stresses of water hyacinth. The spectral indicators of both metal and weevil plant stressors were correlated with the leaf chlorophyll content from the SPAD readings at the end of the experiment. Correlation results of mNDVI(sub705) was the highest followed by REP_LE. Cu-, Hg-, and Zn-treated plants showed significantly lower chlorophyll contents compared with the control treatment. A similar trend with four additional treatments (As, Fe-M, Mn-L and Mn- H) was seen after the release of the weevils, indicating plant stress due to feeding by the biocontrol agent. These results indicate that hyperspectral remote sensing has potential as a tool to determine the health status of water hyacinth from a remote location, to inform management interventions in the control of the weed. However, its usage at a larger scape requires further studies.