Detecting heavy metal pollution of floodplain vegetation in a pot experiment using reflectance spectroscopy

ABSTRACT

Floodplain soils at the Elbe River are frequently polluted by heavy metals. Metal enrichments are linked to the composition of the floodplain’s plant community. Various studies have shown that soil characteristics, floodplain geomorphology and other factors may influence plant physiology and have demonstrated an overlapping of heavy metal pollution and growing conditions such as water and nutrient supply. The goal of this study was to assess and separate the current heavy metal contamination of the floodplain vegetation from other parameters using spectrometric laboratory measurements. A standardized pot experiment with floodplain vegetation in differently contaminated soils provided the basis for measurements. Various vegetation indices and spectral methods were used to normalize the spectral curve of the vegetation and to investigate the potential of different methods for separating plant stress in floodplain vegetation. The results of this study show the influence of heavy metals on the spectral characteristics of the focal plants. From 11 tested methods, 5 showed a significant correlation (R² > 0.6) to heavy metal content. Most methods with a significant correlation to heavy metal also showed a high correlation (R² > 0.5) to other investigated parameters such as chlorophyll content and nutrient content. Only the developed method (band depth at continuum removal spectra at 1725 nm (CR₁₇₂₅)) showed a significant relationship to the heavy metal load (R² = 0.644) and not to other parameters, and can therefore be used as a basis for further work in field studies in the context of heavy metal stress in floodplain plants.

KEYWORDS:

• Heavy metal pollution
• floodplain vegetation
• vegetation stress
• vegetation indices
• spectroscopy

Acknowledgements

We thank Prof. Ulrich Neue and Prof Jörg Rinklebe for their helpful comments on the experimental design, Dr Rainer Wennrich for providing the analytical process and Dr Ines Merbach for making possible and supporting the pot experiment.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by German Federal Foundation for the Environment [AZ 20006/859].