Recent vegetation history from a swampy environment to a pond based on macromolecular organic matter (lignin and fatty acids) and pollen sedimentary records

International audienceEvidence of environmental and vegetation changes in the catchment area of a small pond created artificially during the Middle Ages from a swampy area was provided by coupling palynology data and a detailed study of macromolecular organic matter (OM). Tetramethylammonium hydroxide (TMAH) thermochemolysis after solvent extraction was used to characterize macromolecular OM and particularly lignin and fatty acids (FAs). Molecular ratios such as TAR(FA), C-16:1/C16: 0 and C-18:1/C-18:0 were calculated to characterize the FAs incorporated into the macromolecular OM. Moreover, syringyl vs. vanillyl phenols (S/V) and cinnamyl vs. vanillyl phenols (C/V) molecular ratios were investigated to fingerprint the lignin sources. These different markers suggested that the swampy area was dominated by a non-woody angiosperm input and gave rise to pond status over a period of several centuries. Indeed, TAR( FA) correlated with the aquatic contribution, which became predominant after creation of the pond. The use of ratios of total acid phenols to the total aldehyde phenols of syringyl or vanillyl units (Ad/Al-( s), Ad/Al-( v)), which are related to the degree of oxidation of lignin, revealed the irregular operation of oxidative conditions