Carbon dioxide emissions from reed canary grass during two growing seasons after restoration of an abandoned agricultural peat soil

Reed canary grass (RCG) can be a suitable energy crop on abandoned agricultural peatland as it can be harvested for more than 10 years without re-establishment, and nutrient recycling to rhizomes lowers the fertilizer demand. A field near Mala in Sweden was restored by improving drainage and sowing RCG in 2010. In the first growing season, CO2 emissions from the soil were lower and groundwater level and soil water content higher for the RCG field than for a nearby unrestored field. Possible reasons were peat compaction by agricultural machinery in the restored field and higher transpiration and respiration from vegetation in the unrestored field. In the second growing season, the groundwater level was raised in some restored plots and CO2 emissions and RCG growth were found to be unaffected by this practice

Surface energy exchange in pristine and managed boreal peatlands

Surface-atmosphere energy exchange is strongly ecosystem-specific. At the same time, as the energy balance constitutes responses of an ecosystem to environmental stressors including precipitation, humidity and solar radiation, it results in feedbacks of potential importance for the regional climate. Northern peatlands represent a diverse class of ecosystems that cover nearly 6 x 10(6) km(2) in the Boreal region, which makes the inter-comparison of their energy balances an important objective. With this in mind we studied energy exchange across a broad spectrum of peatlands from pristine fens and bogs to forested and agriculturally managed peatlands, which represent a large fraction of the landscape in Finland and Sweden. The effects of management activities on the energy balance were extensively examined from the micrometeorological point of view, using eddy covariance data from eight sites in these two countries (56 degrees 12'-62 degrees 11' N, 13 degrees 03'-30 degrees 05' E). It appears that the surface energy balance varies widely amongst the different peatland types. Generally, energy exchange features including the Bowen ratio, surface conductance, coupling to the atmosphere, responses to water table fluctuations and vapour pressure deficit could be associated directly with the peatland type. The relative constancy of the Bowen ratio in natural open mires contrasted with its variation in tree-covered and agricultural peatlands. We conclude that the impacts of management and the consequences of land-use change in peatlands for the local and regional climate might be substantial.Peer reviewe

Relationship between ecosystem productivity and photosynthetically-active radiation for northern peatlands

We analyzed the relationship between net ecosystem exchange of carbon dioxide (NEE) and irradiance (as photosynthetic photon flux density or PPFD), using published and unpublished data that have been collected during midgrowing season for carbon balance studies at seven peatlands in North America and Europe. NEE measurements included both eddy-correlation tower and clear, static chamber methods, which gave very similar results. Data were analyzed by site, as aggregated data sets by peatland type (bog, poor fen, rich fen, and all fens) and as a single aggregated data set for all peatlands. In all cases, a fit with a rectangular hyperbola (NEE = α PPFD Pmax/(α PPFD + Pmax) + R) better described the NEE-PPFD relationship than did a linear fit (NEE = β PPFD + R). Poor and rich fens generally had similar NEE-PPFD relationships, while bogs had lower respiration rates (R = −2.0μmol m−2s−1 for bogs and −2.7 μmol m−2s−1 for fens) and lower NEE at moderate and high light levels (Pmax = 5.2 μmol m−2s−1 for bogs and 10.8 μmol m−2s−1 for fens). As a single class, northern peatlands had much smaller ecosystem respiration (R = −2.4 μmol m−2s−1) and NEE rates (α = 0.020 and Pmax = 9.2μmol m−2s−1) than the upland ecosystems (closed canopy forest, grassland, and cropland) summarized by Ruimy et al. [1995]. Despite this low productivity, northern peatland soil carbon pools are generally 5–50 times larger than upland ecosystems because of slow rates of decomposition caused by litter quality and anaerobic, cold soils

Global Research Alliance N2O chamber methodology guidelines : Summary of modeling approaches

Acknowledgements Funding for this publication was provided by the New Zealand Government to support the objectives of the Livestock Research Group of the Global Research Alliance on Agricultural Greenhouse Gases. Individual authors work contribute to the following projects for which support has been received: Climate smart use of Norwegian organic soils (MYR, 2017-2022) project funded by the Research Council of Norway (decision no. 281109); Scottish Government's Strategic Research Programme, SuperG (under EU Horizon 2020 programme); DEVIL (NE/M021327/1), Soils-R-GRREAT (NE/P019455/1) and the EU H2020 project under Grant Agreement 774378—Coordination of International Research Cooperation on Soil Carbon Sequestration in Agriculture (CIRCASA); to project J-001793, Science and Technology Branch, Agriculture and Agri-Food Canada; and New Zealand Ministry of Business, Innovation and Employment (MBIE) core funding. Thanks to Alasdair Noble and the anonymous reviewers for helpful comments on a draft of this paper and to Anne Austin for editing services.Peer reviewedPublisher PD

Methane dynamics in the subarctic tundra : combining stable isotope analyses, plot- and ecosystem-scale flux measurements

Methane (CH4) fluxes were investigated in a subarctic Russian tundra site in a multi-approach study combining plot-scale data, ecosystem-scale eddy covariance (EC) measurements, and a fine-resolution land cover classification scheme for regional upscaling. The flux data as measured by the two independent techniques resulted in a seasonal (May-October 2008) cumulative CH4 emission of 2.4 (EC) and 3.7 gCH(4) m(-2) (manual chambers) for the source area representative of the footprint of the EC instruments. Upon upscaling for the entire study region of 98.6 km(2), the chamber measured flux data yielded a regional flux estimate of 6.7 gCH(4) m(-2) yr(-1). Our upscaling efforts accounted for the large spatial variability in the distribution of the various land cover types (LCTs) predominant at our study site. Wetlands with emissions ranging from 34 to 53 gCH(4) m(-2) yr(-1) were the most dominant CH4-emitting surfaces. Emissions from thermokarst lakes were an order of magnitude lower, while the rest of the landscape (mineral tundra) was a weak sink for atmospheric methane. Vascular plant cover was a key factor in explaining the spatial variability of CH4 emissions among wetland types, as indicated by the positive correlation of emissions with the leaf area index (LAI). As elucidated through a stable isotope analysis, the dominant CH4 release pathway from wetlands to the atmosphere was plant-mediated diffusion through aerenchyma, a process that discriminates against C-13-CH4. The CH4 released to the atmosphere was lighter than that in the surface porewater, and delta C-13 in the emitted CH4 correlated negatively with the vascular plant cover (LAI). The mean value of delta C-13 obtained here for the emitted CH4, 68.2 +/- 2.0 %, is within the range of values from other wetlands, thus reinforcing the use of inverse modelling tools to better constrain the CH4 budget. Based on the IPCC A1B emission scenario, a temperature increase of 6.1 degrees C relative to the present day has been predicted for the European Russian tundra by the end of the 21st Century. A regional warming of this magnitude will have profound effects on the permafrost distribution leading to considerable changes in the regional landscape with a potential for an increase in the areal extent of CH4-emitting wet surfaces.Peer reviewe

FLUXNET-CH₄ synthesis activity: objectives, observations, and future directions

We describe a new coordination activity and initial results for a global synthesis of eddy covariance CH4 flux measurements

Substantial hysteresis in emergent temperature sensitivity of global wetland CH₄ emissions

Wetland methane (CH4) emissions (FCH4 ) are important in global carbon budgets and climate change assessments. Currently, FCH4 projections rely on prescribed static temperature sensitivity that varies among biogeochemical models. Meta-analyses have proposed a consistent FCH4 temperature dependence across spatial scales for use in models; however, sitelevel studies demonstrate that FCH4 are often controlled by factors beyond temperature. Here, we evaluate the relationship between FCH4 and temperature using observations from the FLUXNET-CH4 database. Measurements collected across the globe show substantial seasonal hysteresis between FCH4 and temperature, suggesting larger FCH4 sensitivity to temperature later in the frost-free season (about 77% of site-years). Results derived from a machine-learning model and several regression models highlight the importance of representing the large spatial and temporal variability within site-years and ecosystem types. Mechanistic advancements in biogeochemical model parameterization and detailed measurements in factors modulating CH4 production are thus needed to improve global CH4 budget assessments.s

Substantial hysteresis in emergent temperature sensitivity of global wetland CH4_{4} emissions

Wetland methane (CH$_{4}$) emissions (F$_{CH_{4}}$) are important in global carbon budgets and climate change assessments. Currently, F$_{CH_{4}}$ projections rely on prescribed static temperature sensitivity that varies among biogeochemical models. Meta-analyses have proposed a consistent F$_{CH_{4}}$ temperature dependence across spatial scales for use in models; however, site-level studies demonstrate that F$_{CH_{4}}$ are often controlled by factors beyond temperature. Here, we evaluate the relationship between F$_{CH_{4}}$ and temperature using observations from the FLUXNET-CH$_{4}$ database. Measurements collected across the globe show substantial seasonal hysteresis between F$_{CH_{4}}$ and temperature, suggesting larger F$_{CH_{4}}$ sensitivity to temperature later in the frost-free season (about 77% of site-years). Results derived from a machine-learning model and several regression models highlight the importance of representing the large spatial and temporal variability within site-years and ecosystem types. Mechanistic advancements in biogeochemical model parameterization and detailed measurements in factors modulating CH$_{4}$ production are thus needed to improve global CH$_{4}$ budget assessments

Carbon dioxide exchange in a peatland ecosystem

Micrometeorological measurements of carbon dioxide exchange were made in an open peatland in north central Minnesota during two growing seasons (1991 and 1992). The vegetation at the site was dominated by Sphagnum papillosum, Scheuchzeria palustris, and Chamaedaphne calyculata. The objective of the study was to examine the diurnal and seasonal variations in canopy photosynthesis (P) and develop information on the net ecosystem CO2 exchange. The two seasons provided contrasting microclimatic conditions: as compared with 1991, the 1992 season was significantly wetter and cooler. Canopy photosynthesis was sensitive to changes in light, temperature, and moisture stress (as indicated by water table depth and atmospheric vapor pressure deficit). Under moderate conditions (temperature 18–28°C, vapor pressure deficit 0.7–1.5 kPa, and water table near the surface) during the peak growth period, midday (averaged between 1000–1400 hours) P values ranged from 0.15 to 0.24 mg m−2 s−1. Under high-temperature (30°–34°C) and moisture stress (water table 0.16–0.23 m below the surface and vapor pressure deficit 2.2–3.0 kPa) conditions, midday P was reduced to about 0.03–0.06 mg m−2 s−1. There was a high degree of consistency in the values of P under similar conditions in the two seasons. Seasonally integrated values of the daily net ecosystem CO2 exchange indicated that the study site was a source of atmospheric CO2, releasing about 71 g C m−2 over a 145-day period (May-October) in 1991. Over a similar period in 1992, however, this ecosystem was a sink for atmospheric CO2 with a net accumulation of about 32 g C m−2. These results are consistent with previous investigations on CO2 exchange in other northern wetland sites during wet and dry periods