Fluorescence properties of humic substances transformed in ectohumus horizons of Podzols affected by alkaline fly‐ash

Lignite burning is still the main source of energy in many countries, generating huge amounts of alkaline residues deposited in dumping sites, which affects the surrounding environment. There are only a few publications dealing with the effects on pH changes of surface horizons, but there are no reports on the impact on other soil properties. The aim of this paper was to characterize the changes occurring in the soil organic matter (SOM) of ectohumus horizons of Podzols located near the dumping site and at the control site. Conventional one‐dimensional, synchronous, and three‐dimensional fluorescence can provided a new information on differences in the structure of humic substances (HS), which are crucial constituents of SOM. Humic acid (HA) and fulvic acid (FA), originally present in the ectohumus horizon, indicated a lower degree of humification, and were characterized by a looser structure, than HS that were extracted from soils affected by fly‐ash. The neutralization of the soil reaction resulting from the deposition of fly‐ash favored the formation of higher humified HS, characterized by a higher concentration of aromatic rings in the core of the molecule and the presence of double conjugated bonds. The fluorescence technique could be applicable to monitor the chemical modification of soils in regions affected by ashes but also all factors changing soil pH. The conducted research has shown that fluorescence spectroscopy can be successfully used as a sensitive technique to characterize qualitatively structures of different organic substances present in terrestrial and aquatic systems.