This study investigated patterns and controls of the seasonal and inter-annual variations in energy fluxes (i.e., sensible heat, H, and latent heat, lambda E) and partitioning of the water budget (i.e., precipitation, P; evapotranspiration, ET; discharge, Q; and soil water storage, Delta S) over five years (2001-2005) in a boreal oligotrophic fen in northern Sweden based on continuous eddy covariance, water table level (WTL), and weir measurements. For the growing season (May 1 to September 31), the 5 year averages (+/- standard deviation) of the midday (10:00 to 14:00 h) Bowen ratio (beta, i.e., H/lambda E) was 0.86 +/- 0.08. Seasonal and inter-annual variability of beta was mainly driven by lambda E which itself was strongly controlled by both weather (i.e., vapor pressure deficit, D, and net radiation, R-n) and physiological parameters (i.e., surface resistance). During the growing season, surface resistance largely exceeded aerodynamic resistance, which together with low mean values of the actual ET to potential ET ratio (0.55 +/- 0.05) and Priestley-Taylor alpha (0.89) suggests significant physiological constrains on ET in this well-watered fen. Among the water budget components, the inter-annual variability of ET was lower (199 to 298 mm) compared to Q (225 to 752 mm), with each accounting on average for 34 and 65% of the ecosystem water loss, respectively. The fraction of P expended into ET was negatively correlated to P and positively to R-n. Although a decrease in WTL caused a reduction of the surface conductance, the overall effect of WTL on ET was limited. Non-growing season (October 1 to April 30) fluxes of H, lambda E, and Q were significant representing on average -67%, 13%, and 61%, respectively, of their growing season sums (negative sign indicates opposite flux direction between the two seasons). Overall, our findings suggest that plant functional type composition, P and R-n dynamics (i.e., amount and timing) were the major controls on the partitioning of the mire energy and water budgets. This has important implications for the regional climate as well as for ecosystem development, nutrient, and carbon dynamics. Citation: Peichl, M., J. Sagerfors, A. Lindroth, I. Buffam, A. Grelle, L. Klemedtsson, H. Laudon, and M. B. Nilsson (2013), Energy exchange and water budget partitioning in a boreal minerogenic mire, J. Geophys. Res. Biogeosci., 118, 1-13, doi:10.1029/2012JG002073.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2012JG002073

Energy exchange and water budget partitioning in a boreal minerogenic mire

Rainfall partitioning by vegetation under Mediterranean conditions. A review of studies in Europe

Northern peatlands provide important global and regional ecosystem services (carbon storage, water storage, and biodiversity). However, these ecosystems face increases in the severity, areal extent and frequency of climate-mediated (e.g. wildfire and drought) and land-use change (e.g. drainage, flooding and mining) disturbances that are placing the future security of these critical ecosystem services in doubt. Here, we provide the first detailed synthesis of autogenic hydrological feedbacks that operate within northern peatlands to regulate their response to changes in seasonal water deficit and varying disturbances. We review, synthesize and critique the current process-based understanding and qualitatively assess the relative strengths of these feedbacks for different peatland types within different climate regions. We suggest that understanding the role of hydrological feedbacks in regulating changes in precipitation and temperature are essential for understanding the resistance, resilience and vulnerability of northern peatlands to a changing climate. Finally, we propose that these hydrological feedbacks also represent the foundation of developing an ecohydrological understanding of coupled hydrological, biogeochemical and ecological feedbacks. Copyright © 2014 John Wiley & Sons, Ltd.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/eco.1493

Hydrological feedbacks in northern peatlands

Methane (CH4) is produced in many natural systems that are vulnerable to change under a warming climate, yet current CH4 budgets, as well as future shifts in CH4 emissions, have high uncertainties. Climate change has the potential to increase CH4 emissions from critical systems such as wetlands, marine and freshwater systems, permafrost, and methane hydrates, through shifts in temperature, hydrology, vegetation, landscape disturbance, and sea level rise. Increased CH4 emissions from these systems would in turn induce further climate change, resulting in a positive climate feedback. Here we synthesize biological, geochemical, and physically focused CH4 climate feedback literature, bringing together the key findings of these disciplines. We discuss environment-specific feedback processes, including the microbial, physical, and geochemical interlinkages and the timescales on which they operate, and present the current state of knowledge of CH4 climate feedbacks in the immediate and distant future. The important linkages between microbial activity and climate warming are discussed with the aim to better constrain the sensitivity of the CH4 cycle to future climate predictions. We determine that wetlands will form the majority of the CH4 climate feedback up to 2100. Beyond this timescale, CH4 emissions from marine and freshwater systems and permafrost environments could become more important. Significant CH4 emissions to the atmosphere from the dissociation of methane hydrates are not expected in the near future. Our key findings highlight the importance of quantifying whether CH4 consumption can counterbalance CH4 production under future climate scenarios.

https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1002/2017RG000559

Methane Feedbacks to the Global Climate System in a Warmer World

Methane dynamics in northern peatlands: a review.

[1] Production and emission of peat gas has attracted great interest because substantial amounts of methane (CH4) are emitted to the atmosphere from peat soils. Many studies indicate supersaturation of CH4 in peat water, implying a high potential for gas bubble formation. However, observations of bubbles in peat are often only qualitatively described, and in most cases the presence of entrapped gas has been largely ignored in peatland studies. On the basis of a review of literature, a conceptual model of entrapped gas dynamics was developed and investigated using field and laboratory measurements at a poor fen in central Quebec. We investigated variations in production and volume of gas and the effect of this gas on trace gas emissions, peat buoyancy, and pore water chemistry during 2002 and 2003. Measurements made with moisture probes and subsurface gas collectors revealed that gas volume varied throughout the growing season in relation to hydrostatic and barometric pressure. Shifts in entrapped gas volume were also coincident with changes in dissolved pore water CH4. The presence of these bubbles has important biogeochemical effects, including the development of localized CH4 diffusion gradients, alteration of local flow paths affecting substrate delivery, peat buoyancy, and the potential episodic release of CH4 via ebullition events. These interactions must be included in peatland models to describe accurately the hydrology and greenhouse gas emissions from these ecosystems and to make predictions about their response to environmental change.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2004GB002330

Dynamics of biogenic gas bubbles in peat and their effects on peatland biogeochemistry

Surface energy fluxes and control of evapotranspiration from a Swedish Sphagnum mire.

A water budget was established for the open, undisturbed bog Stormossen, central Sweden, for the growing seasons of 1996 and 1997 as a part of the NOPEX project. The water budget was complemented with data on the spatial variation of groundwater levels and water contents in different microrelief elements (ridge, hollow and ridge margin). The seasonal (24 May to 4 October) rainfall, evaporation and runoff were 200, 256, and 43 mm in 1996, respectively, and 310, 286 and 74 mm in 1997, giving negative budgets of −99 mm in 1996 and −50 mm in 1997. Approximately 60% of the total budget was caused by storage changes in the upper 40 cm of the bog and 40% by swelling/shrinking in the layers below. This ‘mire breathing’ must be incorporated in future models of mire-water dynamics. The water content varied diversely among the different microrelief elements, much depending on the properties of moss and peat together with distance to water table. There also was a strong hysteresis in the relationships between groundwater level and measured volumetric water content, depending partly on pore-throat effects and partly on swelling/shrinking of the peat matrix. A seasonal variation of volumetric water content in a layer beneath water table was found to be larger than what could be justified by compression alone. We think that probable causes could be methane gas expansion together with temperature effects. The main conclusions of this study were: (i) water-transport and storage characteristics are distinctly different among hummocks, ridges and hollows, (ii) mire wetness cannot be deduced from groundwater levels only, and (iii) an important part of the total water storage was caused by swelling/shrinking of the peat, not by changes in unsaturated water content. Copyright © 2002 John Wiley & Sons, Ltd.

Water budget and surface-layer water storage in a Sphagnum bog in central Sweden

Continuous long-term measurements of soil-plant-atmosphere variables at a forest site

[1] Recent studies suggest that ebullition of biogenic gas bubbles is an important process of CH4 transfer from northern peatlands into the atmosphere and, as such, needs to be better described by models of peat carbon dynamics. We develop and test a simple ebullition model in which a threshold gas volume in the peat has to be exceeded before ebullition occurs. The model assumes that the gas volume varies because of gas production and variations in pressure and temperature. We incubated peat cores in the laboratory for 190 days and measured their volumetric gas contents and the ebullition flux. The laboratory results support the threshold concept and, considering the simplicity of the model, the calculated ebullition compared well with measured fluxes during the final 120 days with an r2 of 0.66. An improved, more realistic description would also include temporal and spatial variations in gas production and bubble retention terms.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2006GL027509

E. Kellner

Papers

Dynamics of biogenic gas bubbles in peat and their effects on peatland biogeochemistry

Surface energy fluxes and control of evapotranspiration from a Swedish Sphagnum mire.

Water budget and surface-layer water storage in a Sphagnum bog in central Sweden

Continuous long-term measurements of soil-plant-atmosphere variables at a forest site

Effect of temperature and atmospheric pressure on methane (CH4) ebullition from near-surface peats