Lignin depolymerization products as biomarkers of the organic matter sedimentary record in 210Pb–137Cs-dated lake sediments

The composition and concentration of lignin phenols (used as biomarkers of organic matter quality gradients) and granulometric and mineral composition were studied, in order to document land cover variations, in a dated (using the 210Pb method, validated with 137Cs distribution) sediment core from a small lake (Pusty Staw) in the coastal Baltic Sea area. Substantial gradients were found in the granulometric composition. These were attributed to varying erosion caused by deforestation and afforestation of the catchment area. Extrapolation of the dating to deep core layers showed that the deforestation layer originated from 1730 AD, close to a period of deforestation found in historical records. The core dating was validated by matching a peak in the 137Cs profile with the 1986 Chernobyl accident. Changes in the use of the catchment area caused substantial shifts in organic matter composition and quality, as suggested by the gradients of syringyl (S), cinnamyl (C), and vanillic (V) phenols derived from CuO/alkaline oxidation of lignin. The lignin component of the sedimentary organic matter originated primarily from angiosperm woody material (S/V = 0.8; C/V = 0.4). A new lignin parameter, called delta (Δ), indicating the burden of lignin-derived organic matter deposited in sediments with mineral matter, shows changes between the uppermost and middle zones of the core. An increased ratio of vanillic acid (Ad) to vanillone (Al) in the uppermost sediment layers was noticed and attributed to the inflow of degraded organic matter washed out from the catchment area soil. Principal component and cluster analysis indicated the lignin load and quality as the main factors distinguishing the organic material in the core sections. Both the lignin load and quality gradients were in agreement with the lithology of the core, showing the steepest gradients at the boundaries of core sections deposited prior to/after the deforestation/afforestation events.