ABSTRACT
Background: The management of invasive Tamarix genotypes depends on reliable and accurate information of their extent and distribution. This study investigated the utility of the multispectral Sentinel-2 imageries to map infestations of the invasive Tamarix along three riparian ecosystems in the Western Cape Province of South Africa. Methods: The Sentinel-2 image was acquired from the GloVis website (http://glovis.usgs.gov/). Random forest (RF) and support vector machine (SVM) algorithms were used to classify and estimate the spatial distribution of invasive Tamarix genotypes and other land-cover types in three riparian zones viz. the Leeu, Swart and Olifants rivers. A total of 888 reference points comprising of actual 86 GPS points and additional 802 points digitized using the Google Earth Pro free software were used to ground-truth the Sentinel-2 image classification. Results: The results showed the random forest classification produced an overall accuracy of 87.83% (with kappa value of 0.85), while SVM achieved an overall accuracy of 86.31% with kappa value of 0.83. The classification results revealed that the Tamarix invasion was more rampant along the Olifants River near De Rust with a spatial distribution of 913.39 and 857.74 ha based on the RF and SVM classifiers, respectively followed by the Swart River with Tamarix coverage of 420.06 ha and 715.46 hectares, respectively. The smallest extent of Tamarix invasion with only 113.52 and 74.27 hectares for SVM and RF, respectively was found in the Leeu River. Considering the overall accuracy of 85% as the lowest benchmark for a robust classification, the results obtained in this study suggests that the SVM and RF classification of the Sentinel-2 imageries were effective and suitable to map invasive Tamarix genotypes and discriminate them from other land-cover types.
Subject(s)
Ecosystem , Tamaricaceae , Rivers , Algorithms , SoftwareABSTRACT
Heavy metal polluted soils can be remediated using plants, a process called phytoremediation. However, high concentrations of heavy metals can negatively affect plant physiology and growth. We experimentally evaluated the effects of cadmium (Cd) on the growth, (i.e. height, shoot and biomass) and physiology (i.e. leaf chlorophyll and relative water contents) of Tamarix usneoides. In a greenhouse experiment, T. usneoides clones were subjected to a once off treatment of 100 mmol/l NaCl with three different Cd concentrations (6, 12, and 18 mg/kg) applied 3 times/week for eight weeks. We predicted that plant health would decrease with an increase in Cd concentration. Results revealed a 35.9% reduction in chlorophyll content between the 18 mg/kg Cd treated plants and the control, suggesting that T. usneoides experienced a reduction in photosynthetic rate, which in turn influenced the growth and relative water content (RWC) of the plant. Although T. usneoides' growth and physiology were significantly decreased at 12 and 18 mg/kg Cd concentrations, the plants tolerated up to 6 mg/kg Cd concentration, a level found in most anthropogenic Cd-contaminated soils. Tamarix usneoides should thus be confirmed as a good phytoremediation candidate once its ability to extract, translocate and concentrate Cd has been determined.
