Botanical composition of peat and degree of peat decomposition in three temperate peatlands

Abstract

Models of peat accumulation assume that peat decomposition occurs mostly above the water table, with little or no decomposition once peat enters the deeper, saturated, anoxic zone. However, few such measurements of peat decomposition exist. In this paper we quantified differences in degree of decomposition, botanical composition, and organic chemical composition of peat from three temperate peatlands with different water table levels. All sites had a thick layer of herbaceous peat, capped by a layer of Sphagnum peat. The lignin content and degree of decomposition, measured by the pyrophosphate index, generally increased with depth. Analysis of the lignin with cupric oxide (CuO) oxidation revealed most of the chemical differences between peat deposits occurred in the upper, aerated peat layer, as expected. The upper layer of Sphagnum peat was characterized by high p-hydroxyl phenolic yield, whereas Sphagnum peat below the water table exhibited a high degree of humification and high yield of vanillyl oxidation products despite being of similar botanical composition. Surprisingly, herbaceous peat below the water table was similar in terms of degree of decomposition to younger herbaceous peat. The results confirm that peat decomposition occurs mostly above the water table, although botanical source, climate, and local hydrology interact to create multiple trajectories in peat chemistry.