Beyond "The limits to peat bog growth'': Cross-scale feedback in peatland development

Copyright by the Ecological Society of America 2006, for personal or educational use only. Article is available at <http://dx.doi.org/10.1890/0012-9615(2006)076[0299:BTLTPB]2.0.CO;2

Bridging the gap between models and measurements of peat hydraulic conductivity

Peat saturated hydraulic conductivity, Ksat, declines strongly with increasing degree of decomposition, providing a potentially important negative ecohydrological feedback that may buffer peatlands from climate-induced drying. However, the quantitative nature of this relationship is poorly understood. We measured downcore changes in Ksat and carbon-to-nitrogen concentration quotients (C/N) in fourteen shallow (~0.5 m deep, 0.1 m diameter) peat cores from a Swedish raised bog. We used the C/N measurements to approximate the fraction of original peat mass remaining. A linear mixed effects (LME) model predicts log10(Ksat) from i) our C/N-derived estimate of fractional remaining mass; ii) depth; iii) microhabitat (hummock, hollow); and iv) location (treeless bog center, treed bog margin). The LME model indicated no significant random effects or interactions between predictors, so we derived a non-linear multiple regression (NLMR) model to predict Ksat on its original scale. Both LME and NLMR models predict that Ksat decreases exponentially with depth and that Ksat is lower beneath hollows than beneath hummocks for equivalent depths below the surface. Fractional remaining mass was an important predictor in the LME model, but not in the NLMR model. The distinction between central and marginal areas of the bog was not an important predictor. We demonstrate for the first time that the relationship between fractional remaining mass and Ksat is log-linear, and suggest revisions that should be made to peatland development models. In particular, depth – usually ignored in modeling studies – exerted a strong control over Ksat ndependently of decomposition and should be included explicitly in model algorithms

Resource contrast in patterned peatlands increases along a climatic gradient

Copyright by the Ecological Society of America 2010, for personal or educational use only. Article is available at <http://dx.doi.org/10.1890/09-1313.1

The Importance of CH₄ Ebullition in Floodplain Fens

Uncertainty in estimates of CH4 emissions from peatlands arise, in part, due to difficulties in quantifying the importance of ebullition. This is a particular concern in temperate lowland floodplain fens in which total CH4 emissions to the atmosphere (often measured as the sum of diffusive and plant‐mediated fluxes) are known to be high, but few direct measurements of CH4 ebullition fluxes have been made. Our study quantified CH4 fluxes (diffusion, plant‐mediated, and ebullition) from two temperate floodplain fens under conservation management (Norfolk, UK) over 176 days using funnels and static chambers. CH4 ebullition was a major component (>38%) of total CH4 emissions over spring and summer. Seasonal variations in quantifiable CH4 ebullition fluxes were marked, covering six orders of magnitude (5 × 10−5 to 62 mg·CH4·m−2·hr−1). This seasonal variability in CH4 ebullition fluxes arose from changes in both bubble volume flux and bubble CH4 concentration, highlighting the importance of regular measurements of the latter for accurate assessment of CH4 ebullition using funnels. Soil temperature was the primary control on CH4 ebullition fluxes. Elevated water level was also associated with increased CH4 ebullition fluxes, with a distinct increase in CH4 ebullition flux when water level rose to within 10 cm of the peat surface. In contrast, CH4 ebullition flux decreased steadily with increasing plant cover (measured as vascular green area). Ebullition was both steady and episodic in nature, and drops in air pressure during the two‐day funnel deployments were associated with higher fluxes

An experimental study on the response of blanket bog vegetation and water tables to ditch blocking

We studied the effect of ditch blocking on vegetation composition and water-table depths in a blanket peatland. Measurements were made for a period of four years (water tables) and five years (vegetation) in the inter-ditch areas of three experimental treatments: (i) open ditches, (ii) ditches blocked with closely-spaced dams and (iii) ditches partially infilled with peat and blocked with dams. It is often assumed that ditch blocking will lead to an increase in the abundance of Sphagnum and, potentially, a reduction in the abundance of sedges, particularly the cotton grasses. However, our data show no treatment effects on the abundance of either group. We did find an effect of time, with the abundance of both sedges and Sphagnum spp. varying significantly between some years. For the sedges there was no systematic change over time, while for the Sphagnum spp. abundance tended to increase through the study period. This systematic change was not related to a measure of the vigour of the sedges, although vigour was lower towards the end of the study compared to the beginning. Our vegetation data are consistent with our water-table data. As with plant type abundance, we did not find any statistically significant differences in water-table depths between treatments, both for annual averages and summer averages. We comment on why ditch blocking does not seem to have affected water tables and vegetation composition at our study site

The effect of temperature on growth and competition between Sphagnum species

Peat bogs play a large role in the global sequestration of C, and are often dominated by different Sphagnum species. Therefore, it is crucial to understand how Sphagnum vegetation in peat bogs will respond to global warming. We performed a greenhouse experiment to study the effect of four temperature treatments (11.2, 14.7, 18.0 and 21.4°C) on the growth of four Sphagnum species: S. fuscum and S. balticum from a site in northern Sweden and S. magellanicum and S. cuspidatum from a site in southern Sweden. In addition, three combinations of these species were made to study the effect of temperature on competition. We found that all species increased their height increment and biomass production with an increase in temperature, while bulk densities were lower at higher temperatures. The hollow species S. cuspidatum was the least responsive species, whereas the hummock species S. fuscum increased biomass production 13-fold from the lowest to the highest temperature treatment in monocultures. Nutrient concentrations were higher at higher temperatures, especially N concentrations of S. fuscum and S. balticum increased compared to field values. Competition between S. cuspidatum and S. magellanicum was not influenced by temperature. The mixtures of S. balticum with S. fuscum and S. balticum with S. magellanicum showed that S. balticum was the stronger competitor, but it lost competitive advantage in the highest temperature treatment. These findings suggest that species abundances will shift in response to global warming, particularly at northern sites where hollow species will lose competitive strength relative to hummock species and southern species