Electric conductivity and temperature variations within a raised bog in Finland: implications for bog development

Abstract

The deeper parts of raised bogs in Europe have been long regarded as hydraulically stagnant. However, recent reports describe seasonal water movements and solute transport through the deeper layers of some North American bogs, possibly affecting their carbon budgets. Such water movements were not observed in Haukkasuo, a typical raised bog in southeastern Finland, which was thoroughly mapped with a new electric conductivity and temperature probe during four seasons and two successive years. The measured temperature variations can be explained by thermal conduction without convective heat transfer so that the deeper peat layers (2-3 m) reach their highest temperatures in the winter, which possibly affects the methane production. A minimum conductivity (low solute concentration) in the vertical profiles indicates the transition from minerotrophic to ombrotrophic stage of bog development. The seasonal and annual conductivity variations are insignificant, but the conductivity cross-sections of the bog show systematic patterns suggesting slow but persistent advective transport of solutes. The bog mound seems to drive a flow system, which under the central dome forces dilute surface waters to the basal layers, where they pick up nutrients on their way to the discharge sites near the margins. Such translocation of solutes is expected to excite the peat decay at the margins and slow it down near the bog centre. This promotes further doming of the 10 000-year-old bog, which will keep on sequestering carbon although the methane emissions may increase near its margins.