Holocene vegetation and hydrologic changes inferred from molecular vegetation markers in peat, Penido Vello (Galicia, Spain)

Peat molecular chemistry reflects a combination of plant input and decomposition. Both vegetation community and the degree of decomposition of plant remains are highly dependent on depth and fluctuation of the water table and thus peat organic matter (OM) chemistry reflects past hydrological conditions. Changes in hydrology according to the OM composition (by pyrolysis-gas chromatography/mass spectrometry, pyrolysis-GC/MS) in a high-resolution sampled monolith of an 8000 years old peat deposit are presented. Analysis of 18 modern vegetation species resulted in molecular markers for Erica spp., Deschampsia flexuosa, Juncus bulbosus and Carex binervis, in addition to more general markers which enabled differentiation between woody, grass and moss vegetation. Factor analysis of 106 pyrolysis products quantified for all peat samples enabled identification of mineral (Factor 1) and hydrological (Factor 2) conditions of the bog. Depth profiles of vegetation markers showed good agreement with those of the scores of both factors and enabled the identification of 14 relatively wet periods, dating to 1430-1865 AD, 930-1045 AD, 640 AD, 270-385 AD, 190-215 AD, 135 AD, 45 BC-15 AD, 260-140 BC, 640-440 BC, 1055-960 BC, 1505-1260 BC, 2300 BC, 4190-2945 BC and 5700-5205 BC, which show excellent agreement with other palaeoclimatic studies in Europe. The results emphasize the importance of high-resolution sampling, in combination with the use of multiple vegetation markers and other peat OM characteristics for a proper interpretation of a peat record.