Study of heavy metal contamination in river floodplains using the red-edge position in spectroscopic data

One of the major environmental problems resulting from the regular flooding of rivers in Europe is the heavy metal contamination of soils. Various studies have shown that soil contamination may influence plant physiology and, through changes in leaf pigment concentrations, influence reflectance spectra. The main objective of this case study was to study whether the red-edge position ( REP) of vegetation spectra may provide information on soil contamination by heavy metals in river floodplains. The use of the maximum first derivative, smoothing methods ( like polynomial fitting and the inverted Gaussian function) and interpolation methods based on just a few spectral bands were evaluated for a test site in the floodplain of the river Waal in the Netherlands. On selected transects, heavy metal concentrations of soil samples and reflectance spectra of the growing vegetation using a field spectroradiometer were measured. A significant negative correlation between the REP and heavy metal concentration was found using the maximum first derivative method ( R-2 = 0.64). The first derivative spectra in this study showed the presence of more than one peak within the red-edge region, as found by other authors. This phenomenon requires further detailed research using very fine spectral measurements.