Peatlands are strategic areas for climate change mitigation because of their matchless carbon stocks. Drained peatlands release this carbon to the atmosphere as carbon dioxide (CO 2). Peatland rewetting effectively stops these CO 2 emissions, but also re-establishes the emission of methane (CH 4). Essentially, management must choose between CO 2 emissions from drained, or CH 4 emissions from rewetted, peatland. This choice must consider radiative effects and atmospheric lifetimes of both gases, with CO 2 being a weak but persistent, and CH 4 a strong but short-lived, greenhouse gas. The resulting climatic effects are, thus, strongly time-dependent. We used a radiative forcing model to compare forcing dynamics of global scenarios for future peatland management using areal data from the Global Peatland Database. Our results show that CH 4 radiative forcing does not undermine the climate change mitigation potential of peatland rewetting. Instead, postponing rewetting increases the longterm warming effect through continued CO 2 emissions.

The growing demand for bioenergy increases pressure on peatlands. The novel strategy of wet peatlands agriculture (paludiculture) may permit the production of bioenergy from biomass while avoiding large greenhouse gas emissions as occur during conventional crop cultivation on drained peat soils. Herein, we present the first greenhouse gas balances of a simulated paludiculture to assess its suitability as a biomass source from a climatic perspective. In a rewetted peatland, we performed closed-chamber measurements of carbon dioxide, methane, and nitrous oxide exchange in stands of the potential crops Phragmites australis, Typha latifolia, and Carex acutiformis for two consecutive years. To simulate harvest, the biomass of half of the measurement spots was removed once per year. Carbon dioxide exchange was close to neutral in all tested stands. The effect of biomass harvest on the carbon dioxide exchange differed between the 2 years. During the first and second year, methane emissions were 13-63 g m À2 a À1 and 2-5 g m À2 a À1, respectively. Nitrous oxide emissions lay below our detection limit. Net greenhouse gas balances in the study plots were close to being climate neutral during both years except for the Carex stand, which was a source of greenhouse gases in the first year (in CO 2 -equivalents: 18 t ha À1 a À1). Fifteen years after rewetting the net greenhouse gas balance of the study site was similar to those of pristine fens. In addition, we did not find a significant short-term effect of biomass harvest on net greenhouse gas balances. In our ecosystem,~17 t ha À1 a À1 of CO 2 -equivalent emissions are saved by rewetting compared to a drained state. Applying this figure to the fen area in northern Germany, emission savings of 2.8-8.5 Mt a À1CO 2 -equivalents could possibly be achieved by rewetting; this excludes additional savings by fossil fuel replacement.

Closed chamber measurements for methane emission estimation are often carried out with opaque chambers to avoid heating of the headspace. However, mainly in wetlands, some plants possess an internal convective gas transport which quickly responds to changes in irradiation. These plants have also been found to often channel a large part of the released methane in temperate fens. We compare methane fluxes derived from transparent versus opaque chambers on Carex-, Phragmites-, and Typha-dominated stands of a temperate fen. Transparent chamber fluxes almost doubled opaque chamber fluxes in the convective transporting Phragmites stand. In Typha, a trend of higher fluxes determined with the transparent chambers was detectable, whereas in Carex, transparent and opaque chamber fluxes did not differ significantly. Thus, opaque chambers bias the outcome of methane measurements, depending on dominant vegetation. We recommend the use of transparent chambers when determining emissions of convective plants or extrapolating fluxes to larger scales.

Manual closed‐chamber measurements are commonly used to quantify annual net CO2 ecosystem exchange (NEE) in a wide range of terrestrial ecosystems. However, differences in both the acquisition and gap filling of manual closed‐chamber data are large in the existing literature, complicating inter‐study comparisons and meta analyses. The aim of this study was to compare common approaches for quantifying CO2 exchange at three methodological levels. (1) The first level included two different CO2 flux measurement methods: one via measurements during mid‐day applying net coverages (mid‐day approach) and one via measurements from sunrise to noon (sunrise approach) to capture a span of light conditions for measurements of NEE with transparent chambers. (2) The second level included three different methods of pooling measured ecosystem respiration (RECO) fluxes for empirical modeling of RECO: campaign‐wise (19 single‐measurement‐day RECO models), season‐wise (one RECO model for the entire study period), and cluster‐wise (two RECO models representing a low and a high vegetation status). (3) The third level included two different methods of deriving fluxes of gross primary production (GPP): by subtracting either proximately measured RECO fluxes (direct GPP modeling) or empirically modeled RECO fluxes from measured NEE fluxes (indirect GPP modeling). Measurements were made during 2013–2014 in a lucerne‐clover‐grass field in NE Germany. Across the different combinations of measurement and gap‐filling options, the NEE balances of the agricultural field diverged strongly (–200 to 425 g CO2‐C m−2). NEE balances were most similar to previous studies when derived from sunrise measurements and indirect GPP modeling. Overall, the large variation in NEE balances resulting from different data‐acquisition or gap‐filling strategies indicates that these methodological decisions should be made very carefully and that they likely add to the overall uncertainty of greenhouse gas emission factors. Preferably, a standard approach should be developed to reduce the uncertainty of upscaled estimates.

Many raised bogs in Central Europe are in an unfavorable state: drainage causes high emissions of carbon dioxide (CO 2 ) and nitrous oxide (N 2 O), while rewetting may result in high methane (CH 4 ) emissions. Also, the establishment of typical bog species is often hampered during restoration. Measures like topsoil removal (TSR) or introduction of target vegetation are known to improve restoration success in other systems, but experiences on bogs after long-term agricultural use are scarce and their climate effects including carbon losses from TSR are unknown. In a field trial in north-western Germany, consisting of seven plots (intensive grassland, IG, and six restoration approaches), we explored the effects of rewetting, TSR and Sphagnum introduction on greenhouse gas (GHG) emissions. We measured GHG fluxes to obtain two-year GHG budgets and applied a radiative forcing model to assess the time-dependent climate effects. Existing uncertainty of decomposition processes in the translocated topsoil has been incorporated by different topsoil accounting scenarios. According to our data, rewetting alone reduced CO 2 emissions by approximately 75% compared to IG, but substantially increased CH 4 emissions. After TSR and rewetting, on-site CO 2 emissions were close to zero or, with Sphagnum introduction, net negative while CH 4 emissions remained very low. The climatic warming effect of TSR including C export becomes less climate warming than rewetting nutrient-rich peatlands after a few decades. For raised bog restoration, we therefore recommend a TSR sufficient to achieve nutrient-poor and acidic conditions needed for rapid Sphagnum establishment.

Abstract. Carbon (C) sequestration in soils plays a key role in the global C cycle. It is therefore crucial to adequately monitor dynamics in soil organic carbon ( SOC) stocks when aiming to reveal underlying processes and potential drivers. However, small-scale spatial (10-30 m) and temporal changes in SOC stocks, particularly pronounced in arable lands, are hard to assess. The main reasons for this are limitations of the well-established methods. On the one hand, repeated soil inventories, often used in long-term field trials, reveal spatial patterns and trends in SOC but require a longer observation period and a sufficient number of repetitions. On the other hand, eddy covariance measurements of C fluxes towards a complete C budget of the soil-plant-atmosphere system may help to obtain temporal SOC patterns but lack small-scale spatial resolution.To overcome these limitations, this study presents a reliable method to detect both short-term temporal dynamics as well as small-scale spatial differences of SOC using measurements of the net ecosystem carbon balance (NECB) as a proxy. To estimate the NECB, a combination of automatic chamber (AC) measurements of CO 2 exchange and empirically modeled aboveground biomass development (NPP shoot ) were used. To verify our method, results were compared with SOC observed by soil resampling.Soil resampling and AC measurements were performed from 2010 to 2014 at a colluvial depression located in the hummocky ground moraine landscape of northeastern Germany. The measurement site is characterized by a variable groundwater level (GWL) and pronounced small-scale spatial heterogeneity regarding SOC and nitrogen (Nt) stocks. Tendencies and magnitude of SOC values derived by AC measurements and repeated soil inventories corresponded well. The period of maximum plant growth was identified as being most important for the development of spatial differences in annual SOC. Hence, we were able to confirm that AC-based C budgets are able to reveal small-scale spatial differences and short-term temporal dynamics of SOC.

AbstractPeatlands are strategic areas for climate change mitigation because of their matchless carbon stocks. Drained peatlands release this carbon to the atmosphere as carbon dioxide (CO2). Peatland rewetting effectively stops these CO2 emissions, but also re-establishes the emission of methane (CH4).Essentially, management must choose between CO2 emissions from drained or CH4 emissions from rewetted peatland. This choice must consider radiative effects and atmospheric lifetimes of both gases, with CO2 being a weak but persistent and CH4 a strong but short-lived greenhouse gas. The resulting climatic effects are, thus, strongly time-dependent. We used a radiative forcing model to compare forcing dynamics of global scenarios for future peatland management using areal data from the Global Peatland Database. Our results show that CH4 radiative forcing does not undermine the climate change mitigation potential of peatland rewetting. Instead, postponing rewetting increases the long-term warming effect of continued CO2 emissions. Warnings against CH4 emissions from rewetted peatlands are therefore unjustified and counterproductive.

Within a full‐factorial laboratory experiment, three different designs and two modifications of typical manual closed chamber setups were tested for sealing integrity. Tests were performed using a simple method, based on injections of single CO2 pulses. Chamber designs differed in V:A‐ratio and chamber‐collar sealing (water, rubber‐foam, rubber‐tube). All chambers were tested with and without pressure vent and fan. Our results indicate significant differences in sealing integrity due to chamber‐collar sealing strategy. Especially rubber sealing turned out to be characterized by a certain non‐reliability. The effect of vent and fan, however, was of minor importance. The proposed setup is an effective way to assess the airtightness of manual chambers for subsequent field studies.