The response of humic substances to soil acidification and freezing

Fluorescence spectroscopy studies of humic substance fractions isolated from permanently frozen sediments of Yakutian coastal lowlands

“…For instance it was clearly reported that the sequential resinalkali extraction-fractionation technique (Shirshova,1991;Shirshova et al, 2006a,b) offers advantages in characterizing soil HS as it allows milder isolation conditions compared to the classical procedure thereby preserving the native structure of HS (Shirshova and Yermolayev, 1990;Shirshova and Khomutova, 1994;Shirshova et al, 1999). In the present work we made use of the above mentioned extraction technique to isolate humic and/or humic-like fractions from permafrost sediments.…”

“…The investigation is concerned with permafrost aleurites syncryogenic sediments of different genesis and age collected from borehole Shirshova and Khomutova (1994) and used for comparison. cores in the permafrost as described in Kholodov et al (2003).…”

Spectroscopic characterization of humic acid fractions isolated from soil using different extraction procedures

“…2) that alkali-extracted HAs, as compared to resin-extracted ones, contain more structures with aromatic CMC double bonds, the differences in the fluorescence spectra of these fractions may be attributed to the internal quenching. To minimize the inner filter effect as well as to eliminate its influence on the exciting light within the sample, the following conditions were met: (i) the concentration of HA solutions used for fluorescence measurements was around 12 mg C/l (Shirshova and Khomutova, 1994), and their spectral absorbances did not exceed the value of 0.4 (Zimmermann et al, 1997); (ii) the spectral absorbance values of HA samples were brought into one-to-one correspondence at the excitation wavelength (Belin et al, 1993).…”

“…Synchronous fluorescence spectra were obtained by scanning both k ex and k em simultaneously over the range of k ex 300-520 nm, keeping a constant wavelength difference of D = k em À k ex = 18 nm (Senesi et al, 1991). Each HAs sample was dissolved in 0.05 M NaHCO 3 and 0.1 M NaOH to obtain solutions at concentrations of 25 mg/l, and then the spectral absorbance values of all HA solutions used for fluorescence measurements were adjusted by dilution with 0.05 M NaHCO 3 and 0.1 M NaOH, respectively, to 0.3 1 at the excitation wavelength of 337 nm according to the recommendations in Belin et al (1993), Shirshova and Khomutova (1994) and Zimmermann et al (1997). Fluorescence measurements were performed after equilibrating the prepared solutions for 4, 48, and 86 h at room temperature.…”

“…Resins remove the HSs fraction stabilized through cation-binding (Edwards and Bremner, 1965). To separate weakly cation-bound HSs from strongly cation-bound ones, sulfonate and carboxylate resins are used in succession (Shirshova and Khomutova, 1994;Shirshova et al, 1999). Final extraction with aqueous alkaline solution isolates humic materials that have not been removed by resins.…”