Abstract
This study examined the relationship between the leaf reflectance of different seasons and the concentration of heavy metal elements in leaves, such as Co, Cu, Mo, and Ni in a post-mining area. The reflectance spectra and leaf samples of three typical plants were measured and collected in a whole growth cycle (June, July, August, and September). The Red Edge Position (REP), Readjustment Normalized Difference Vegetation Index (RE-NDVI), and Photochemical Reflectance Index (PRI) were extracted and used to explore its relation with the heavy metals concentrations in leaves between different seasons. The results show that all three Vegetation Indices (VIs) were insensitive indicators for monitoring the metal effects of vegetation in different seasons, which showed similar trends. Based on this, the Continuum Removal Indices (CRIs) were proposed from the continuum removed approach and extended for detecting the effects of heavy metal pollution over a full growth cycle. The relationship between the metal concentrations and CRIs of different plants was respectively analyzed by Stepwise Multiple Linear Regression (SMLR) and Partial Least Squares Regression (PLSR). It is found that a significant correlation exists between the band depth and the concentration of Cu and Ni based on the White birch data sets using the PLSR, resulting in a small deviation from the established relationships. Compared with VIs, the approach of coupling CRIs and multiple regressions was effective for improving the estimation accuracy. The presented study provides a detection model of leaf heavy metals that can be adapted to different growing cycles, even an arbitrary growing cycle.
Highlights
One of the major environmental problems resulting from mining areas is the metal pollutants [1,2,3]
Since S1 and S2 are probably three to five times the metal concentration of the plant leaves at S0, it is clear that two sites are affected by heavy metal pollution
Our study compared the simulated ability of the three Vegetation Indices (VIs) and Continuum Removal Indices (CRIs) of heavy metal concentrations in leaves of different seasons
Summary
One of the major environmental problems resulting from mining areas is the metal pollutants [1,2,3]. When plants uptake excessive concentrations of heavy metals in soil, their growth will lead to a certain extent of harmful changes, such as a decrease in chlorophyll content and/or changes in the leaf internal structure [7,8]. These directly or indirectly influence the spectral feature of the plant leaves [9,10]. Exploring the spectral response of the plant leaves by metal-induced stress is of the utmost importance for monitoring the phytoremediation of metal mine-polluted land or finding the concealed deposits using remote sensing techniques, with its advantages of fast dynamic, subtle recognition, and nondestructive detection
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