Exceptional hydrological stability of a Sphagnum-dominated peatland over the late Holocene

Abstract Lowering of the water table and substantial drying are observed in peatlands worldwide. A significant drying of European peatlands in the last 200–300 years influenced the vegetation, lowered carbon storage potential in peatlands, and modified microbial diversity. Here, we reconstructed in high resolution hydrological changes, local and extra-local vegetation composition, and fire activity based on a peat core from a Sphagnum-dominated peatland located in a young glacial landscape in Central Eastern Europe, NE Poland. The last ca. 1500 years of history of the Jaczno bog has been supported by a dense accelerator mass spectrometry (AMS) radiocarbon (14C) dating resolution: 20 dates per 400 cm of the peat profile. We also investigated changes in the functional and morphological traits of testate amoebae as well as the functional diversity of testate amoeba communities over time. Our reconstruction showed a rare case of hydrological stability in the peatland over the late Holocene, and no dry shifts were recorded during the study period. Relatively stable hydrological conditions and undisturbed Sphagnum growth enabled the bog to maintain notably high peat accumulation rates. Although increasing human impact has been recorded in the last ca. 400 years, we did not reconstruct strong disturbances (e.g., vast deforestations, intensive grazing or farming, fires) influencing the site. Compared with other hydrological records from Europe, the Jaczno bog was one of the few bogs in Central and Eastern Europe that did not experience drying during the Little Ice Age. Moreover, the traits and functional diversity of testate amoebae did not show any critical turnover. In the last 70 years, human impact on the site decreased, and the area became afforested. Unlike most of the European peatlands, the Jaczno bog possesses high water tables up to the present time. Therefore, our data suggest that nature conservation practices, which target high water tables, are essential to maintain peatlands as a sink and not as a source of carbon in the future.