Biogeochemistry of Peat Deposits of the Holocene Section of the Vydrino Bog (Southern Baikal Region)

Abstract

The paper reports the detailed studies of drilling cores from peat deposits of the Vydrino bog with a thickness of 4.4 m and an age of 13 100 cal. years. The peat is composed of fen, transitional, and raised types. The early-diagenetic transformations of peat sediments are considered, and the distribution of elements, the formation of authigenic minerals, and the chemical composition of bog waters are studied. The destruction of organic matter begins from the upper intervals of peat at the early diagenetics stage. Pyrograms do not have clearly defined high-temperature peaks, “rudiments” of the macromolecular structure of kerogen, which indicates a low degree of transformation of peat organic matter. The high abundance of organotrophic, ammonifying, nitrifying, and phosphate-mobilizing microorganisms, and the low abundance of Fe- and Mn-oxidizing microorganisms, and sulfate-reducing bacteria are revealed. The presence of organotrophic microorganisms throughout the section indicates that the biogeochemical processes of the carbon cycle span the entire peat sequence. The low S(II) content indicates the low intensity of sulfate reduction. The fen peat is characterized by the high contents of Si, Al, Fe, Ca, Sr, Ba, Zr, La and anomalous contents of Cu, Zn, which is caused by the peatland formation under conditions of rich mineral nutrition. The ash part of the transitional peat demonstrates a decrease in the contents of Si, Fe, Sr, Br, K Si, Ca, Ba, Cu, Zn and La, which reflects the gradual weakening of the connection of the peat deposit with the underlying rocks. The near-surface horizon of raised peat is characterized by an increase in the contents of K, Mn, Zn, Hg, Pb and As, which is accompanied by an increase in atmospheric dust and anthropogenic impact on the bog ecosystem in the 20th and 21st centuries. The bog waters of the fen peat are characterized by the high contents of the main ions, Al, Fe, Mn, Sr, while the transitional peat shows a decrease in DOC, \({\text{SO}}_{4}^{{2 - }}\), \({\text{HCO}}_{3}^{ - }\), Al, Fe, Ni, Ca, Mg. The oligotrophic stage peat deposit layer is characterized by the development of Fe oxides and hydroxides, the presence of vivianite is noted for transitional peats, and the eutrophic stage layer includes rhodochrosite and sulfides of Fe, Cu, and Zn.