Abrupt ombrotrophication of a boreal aapa mire triggered by hydrological disturbance in the catchment

Abstract

Summary1. Hydrological changes due to drainage and climate warming can have great impact on the ecosystem balance of boreal mires. The possibility of ombrotrophication, i.e. the development from fen to bog, in response to altered hydrology has not been previously tested. Here, recent changes in vegetation and surface peat are studied in an aapa mire, a typical boreal mire system dominated by fen vegetation. Drainage in the catchment from 1968 onwards led to the change from richly minerogenous to ombrogenous hydrology, thus providing a long-term ombrotrophication experiment. 2. A sequence of aerial photographs (1941, 1953, 1965, 1974, 1984, 1995, 2005) revealed a dramatic shift from fen vegetation to the nearly complete dominance of peat mosses (Sphagnum) within two decades after the catchment disturbance. 3. A distinct change from Carex peat to Sphagnum peat at the average depth of 23.3 cm (SE 0.8 cm) was found in 18 peat cores. All of the new Sphagnum peat had accumulated within the last four decades. This was verified by the relationship of age and rooting depth of 37 small pines (Pinus sylvestris) and by two pollen density profiles. The ratio Ca ⁄ Mg diminished towards the surface of peat profiles indicating change from minerogenous to ombrogenous hydrology. In accordance, extremely low pH (range 3.8-4.2) and conductivity (average 14.5 ls cm )1 ) were measured in the surface pore water. 4. The average total dry mass of new Sphagnum peat was 7042 g m )2 (SE 442) and the recent apparent rate of carbon accumulation was 100.6 g m )2 year )1 (SE 6.3), as calculated for a 35-year period and 50% carbon content. 5. Synthesis. Remarkable potential for vegetation change and increase of peat growth is demonstrated in boreal aapa mires. Ombrotrophication can be initiated within a few decades in response to reduced input of minerogenous water. Future changes in the hydrological cycle, as indicated by climate change models, are similar to the impact of catchment disturbance in aapa mires. Diminished total water budgets during the summer cause a decrease of minerogenous input and a drawdown of water level, both of which may promote the growth of Sphagnum over fen vegetation.

Methanotrophy induces nitrogen fixation during peatland development

“…This pattern implies that methanotrophic N 2 fixation contributes to rapid N accumulation in the fen stages. The predicted warming conditions in the northern latitudes (27) may impact on boreal peatland development in two ways: At the southern limit of permafrost, melting is promoting a reverse succession from ombrotrophic bog to fen ecosystem, whereas at the southern border of the fen region (aapamires, wet fen-dominated peatland complexes) drainage due to increased evapotranspiration may accelerate ombrotrophication, i.e., succession toward bog ecosystem (28). Our results indicate that these successional changes are likely to lead to changes in N 2 dynamics.…”

Fine‐scale dynamics and community stability in boreal peatlands: revisiting a fen and a bog in Sweden after 50 years

“…If the peat accumulation process continues in a fen, the peat surface will eventually disconnect from the minerotrophic ground water and the fen transforms into a bog. The fen-bog transition (ombrotrophication) has traditionally been described as a unidirectional slow autogenic succession (Zobel 1988), but recent research describes how rapid these shifts may occur (Granath et al 2010, Tahvanainen 2011. For example, Granath et al (2010) showed that the absence of flooding can allow Sphagnum to expand in rich fens, thereby resulting in an ecosystem shift to a poor fen or bog within decades.…”

Microsatellite variation in three calcium-tolerant species of peat moss detected specific genotypes of Sphagnum warnstorfii on magnesium-rich bedrock

“…Sphagnum mosses are a dominant component of peatlands, a habitat covering more than three percent of the global land area, making up at least half of the world's wetlands, storing one third of the global carbon pool and harbouring many endangered species (Tahvanainen 2011, Loisel et al 2012, Rydin & Jeglum 2013. Two contrasting ecosystems occur within peatlands, dominated either by Sphagnum species or 2015) indicate that both calcium and magnesium are toxic for peatland mosses, but that S. warnstorfii is able to tolerate high levels of magnesium, we determined whether magnesium tolerance coincides with genetic structure at a broad geographical scale.…”