Spectral and fluorescent properties of humic acids from various peat samples

Abstract

The aim of the study. To identify differences in absorption spectra and the fluorescent properties of humic acids under different formation conditions.  

Location and time of the study. Fluorescence studies were carried out for aqueous solutions of peat aliquots isolated from samples of debitumenized high-moor peat, located at different depths and hence of humidity of the oligotrophic bog complex in the Mezensky district of the Arkhangelsk region.

Methods. Absorption and fluorescence spectra were recorded using a CM2203 spectrofluorimeter (Solar, Belarus) in standard quartz cuvettes for fluorometry. Fluorescence was recorded at excitation wavelengths of 260, 310, 360 nm.

Results. During the humification process and with the increasing duration of peat drying, the fluorescence intensity of the studied samples increased.The wavelength of the fluorescence maximum and its intensity depend on the wavelength of the excitation light. A "blue shift" of the fluorescence maximum was recorded with an increase in the excitation wavelength from 260 to 310 nm for the studied samples obtained from high-moor peat.

Conclusions. This study of the fluorescence spectra of the water extracts from peat enabled to reveal the properties of their emission characteristics. The "blue shift" of the fluorescence maximum that we discovered with an increase in the excitation wavelength from 260 to 310 nm for samples isolated from high-moor peat in the Mezensky District of the Arkhangelsk Region is consistent with similar shifts obtained for the dissolved organic matter in the surface layer of the Kara Sea and the bays of Novaya Zemlya, for aqueous extracts of saline soils in Northern Dagestan, and for industrial humic preparations from peat and sapropel. The fluorescent properties of humic acids are sensitive to the origin of the organic raw materials from which they are isolated and can be useful both for determining the influence of the environment and for assessing systems under anthropogenic pressure.