The effect of redox conditions on sphagnum acid thermochemolysis product distributions in a northern peatland

摘要

Thermally assisted hydrolysis and methylation (THM) in the presence of tetramethylammonium hydroxide (TMAH) of a range of layers in eight peat cores from the Ryggmossen peatland (central Sweden) was carried out. This yielded a complex mixture including components Ⅰ (methylated 4-isopropenylphenol (IUPAC name: 1-methoxy-4-(prop-1-en-2-yl)benzene)), Ⅱa/b (methylated cis/trans 3-(4'-hydroxyphen-1-yl)but-2-enoic acid (IUPAC names: (E/Z)-methyl 3-(4-methoxyphenyl)but-2-enoate)) and Ⅲ (methylated 3-(4'-hydroxyphen-1-yl)but-3-enoic acid (IUPAC name: methyl 3-(4-methoxyphenyl)but-3-enoate)) which have been assigned as products from "bound" sphagnum acid. The proportion of the individual sphagnum acid products relative to total Sphagnum yield revealed the simultaneous degradation of all four components in the unsaturated layer (which is characterised by oxic conditions) concomitant with the decrease of the total Sphagnum yield. Following their degradation in the surficial oxic layer, the total amounts of the sphagnum acid thermochemolysis products stabilise in the deeper seasonally saturated peat. With a further increase in burial depth, in the permanently saturated anoxic peat, the distribution of thermochemolysis products becomes dominated by Ⅰ. The increase of σ_Ⅰ% relative to σ_(Ⅱa/b and Ⅲ)% indicates that the mode of binding of sphagnum acid into the peat changes as a function of burial depth and hence position relative to the water table. Therefore the relative amounts of the four sphagnum acid THM products show some promise as indicators of redox conditions in young surficial peats.