In a field study, we examined the relationship between vegetation, abiotic factors and the CO exchange dynamics of a cut-away peatland 20 years after production had ended. The main objective was to determine the effect of rewetting on the CO exchange dynamics, measured separately in Eriophorum vaginatum tussocks and intertussocks (almost non-vegetated surfaces) using closed-chamber techniques, one growing season before and three growing seasons after the rewetting treatment. Rewetting lowered total respiration (R ) and increased gross photosynthesis (P), which resulted in a higher incorporation of CO into the system. The seasonal CO balance for the almost continuously submerged section of the rewetted site became positive 2 years after rewetting (9.1 g CO-C m), and it was still higher in the 3rd year (64.5 g CO-C m), i.e. the system accumulated carbon. In the driest section of the rewetted site the seasonal balance increased strongly, but the balance was still negative during the 3 years following rewetting with losses from the system of 44.1, 26.1, 38.3 g CO-C m in 1995, 1996 and 1997 respectively. At the control site seasonal balance during 1995-1997 varied between ecosystem C losses of 41.8 and 95.3 in an area with high Eriophorum cover and between 52.1 and 109.9 g CO-C m with lower cover. Simulation of a cut-away peatland with dense Eriophorum vegetation (Eriophorum cover 70%) showed that if the water level (WT) is low, the seasonal CO balance of the ecosystem can reach the compensation point of no net C change (P = R) only if weather conditions are favourable, but with a high WT the seasonal CO balance would be positive even under varying weather conditions. It can be concluded that with dense Eriophorum vegetation a restored cut-away peatland acts as a functional mire and becomes a sink for atmospheric CO.
A high-resolution plant macrofossil analysis was applied to investigate wetness dynamics in a southern Finnish boreal bog, Kontolanrahka, during the last 5000 years. The chronological control and the age—depth model were based on 40 AMS radiocarbon dates. Pollen analysis provided information on regional-scale vegetation changes. Macrofossil analysis revealed prominent changes in vegetation assemblages during the late Holocene, indicating fluctuations in water-table. The reconstruction suggests that at the coring point, which nowadays is a relatively wet lawn, habitat type has repeatedly varied between transient communities similar to those currently represented in dry hummocks, very wet lawns and even hollows. In order to quantify historical changes in water-table, Generalized Additive Models (GAM) were used to investigate the current relationships between surface plant species and water-table depth. Modern water-table measurements and a survey of associated plant communities along moisture gradients provided data for GAM-analyses. The plant species showed unimodal distributions with apparent optima and narrow tolerances along the water-table gradient. A transfer function for water-table reconstruction was created by calibrating plant macrofossil records against the modern vegetation/water-table relationship using the weighted averaging partial least squares (WA-PLS) regression method. The quantitative water-table reconstruction for the late Holocene showed that the water-table depth had varied between 38 and 2.5 cm, the root mean square error of prediction being 3 cm. The detected historical wet and dry shifts were compared with other similar data from Finland, Sweden and Estonia, and from Western Europe. Despite some similarities, especially during the last c. 1000 years, noticeable differences in timing and duration occur, suggesting they may not have been driven only by climate, but also by local factors, including surface fires.
Mires forming an ecohydrological gradient from nutrient-rich, groundwater-fed mesotrophic and oligotrophic fens to a nutrient-poor ombrotrophic bog were studied by comparing potential methane (CH(4)) production and methanogenic microbial communities. Methane production was measured from different depths of anoxic peat and methanogen communities were detected by detailed restriction fragment length polymorphism (RFLP) analysis of clone libraries, sequencing and phylogenetic analysis. Potential CH(4) production changed along the ecohydrological gradient with the fens displaying much higher production than the ombrotrophic bog. Methanogen diversity also decreased along the gradient. The two fens had very similar diversity of methanogenic methyl-coenzyme M reductase gene (mcrA), but in the upper layer of the bog the methanogen diversity was strikingly lower, and only one type of mcrA sequence was retrieved. It was related to the Fen cluster, a group of novel methanogenic sequences found earlier in Finnish mires. Bacterial 16S rDNA sequences from the fens fell into at least nine phyla, but only four phyla were retrieved from the bog. The most common bacterial groups were Deltaproteobacteria, Verrucomicrobia and Acidobacteria.
Natural peatlands accumulate carbon (C) and nitrogen (N). They affect the global climate by binding carbon dioxide (CO2) and releasing methane (CH4) to the atmosphere; in contrast fluxes of nitrous oxide (N2O) in natural peatlands are insignificant. Changes in drainage associated with forestry alter these greenhouse gas (GHG) fluxes and thus the radiative forcing (RF) of peatlands. In this paper, changes in peat and tree stand C stores, GHG fluxes and the consequent RF of Finnish undisturbed and forestry‐drained peatlands are estimated for 1900–2100. The C store in peat is estimated at 5.5 Pg in 1950. The rate of C sequestration into peat has increased from 2.2 Tg a‐‐1 in 1900, when all peatlands were undrained, to 3.6 Tg a‐‐1 at present, when c. 60% of peatlands have been drained for forestry. The C store in tree stands has increased from 60 to 170 Tg during the 20th century. Methane emissions have decreased from an estimated 1.0–0.5 Tg CH4‐‐C a‐‐1, while those of N2O have increased from 0.0003 to 0.005 Tg N2O‐‐N a‐‐1. The altered exchange rates of GHG gases since 1900 have decreased the RF of peatlands in Finland by about 3 mW m‐‐2 from the predrainage situation. This result contradicts the common hypothesis that drainage results in increased C emissions and therefore increased RF of peatlands. The negative radiative forcing due to drainage is caused by increases in CO2 sequestration in peat (‐‐0.5 mW m‐‐2), tree stands and wood products (‐‐0.8 mW m‐‐2), decreases in CH4 emissions from peat to the atmosphere (‐‐1.6 mW m‐‐2), and only a small increase in N2O emissions (+0.1 mW m‐‐2). Although the calculations presented include many uncertainties, the above results are considered qualitatively reliable and may be expected to be valid also for Scandinavian countries and Russia, where most forestry‐drained peatlands occur outside Finland.
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