Infilled Ditches are Hotspots of Landscape Methane Flux Following Peatland Re-wetting

Fine-Scale Spatial Variability of Greenhouse Gas Emissions From a Subantarctic Peatland Bog

Peatlands are recognized as crucial greenhouse gas sources and sinks and have been extensively studied. Their emissions exhibit high spatial heterogeneity when measured on site using flux chambers. However, the mechanism by which this spatial variability behaves on a very fine scale remains unclear. This study investigates the fine-scale spatial variability of greenhouse gas emissions from a subantarctic Sphagnum peatland bog. Using a recently developed skirt chamber, methane emissions and ecosystem respiration (as carbon dioxide) were measured at a submeter scale resolution, at five specific 3 × 3 m plots, which were examined across the site throughout a single campaign during the Austral summer season. The results indicated that methane fluxes were significantly less homogeneously distributed compared with ecosystem respiration. Furthermore, we established that the spatial variation scale, i.e., the minimum spatial domain over which notable changes in methane emissions and ecosystem respiration occur, was <0.56 m2. Factors such as ground height relative to the water table and vegetation coverage were analyzed. It was observed that Tetroncium magellanicum exhibited a notable correlation with higher methane fluxes, likely because of the aerenchymatous nature of this species, facilitating gas transport. This study advances understanding of gas exchange patterns in peatlands but also emphasizes the need for further efforts for characterizing spatial dynamics at a very fine scale for precise greenhouse gas budget assessment.

Peatland restoration increases water storage and attenuates downstream stormflow but does not guarantee an immediate reversal of long-term ecohydrological degradation

Peatland restoration is experiencing a global upsurge as a tool to protect and provide various ecosystem services. As the range of peatland types being restored diversifies, do previous findings present overly optimistic restoration expectations? In an eroding and restored upland peatland we assessed short-term (0-4 year) effects of restoration on ecohydrological functions. Restoration significantly reduced discharge from the site, transforming peat pans into pools. These retained surface water over half the time and were deeper during wet periods than before. In the surrounding haggs water tables stabilised, as drawdown during dry conditions reduced, increasing the saturated peat thickness. Despite these changes, there were no effects on photosynthesis, ecosystem respiration or dissolved organic carbon loads leaving the site. Soil respiration did not decrease as water tables rose, but methane emissions were higher from rewet pools. Restoration has had a dramatic effect on hydrology, however, consequent changes in other ecosystem functions were not measured in the 4 years after restoration. Whilst restoration is crucial in halting the expansion of degraded peatland areas, it is vital that practitioners and policymakers advocating for restoration are realistic about the expected outcomes and timescales over which these outcomes may manifest.

CH4 and CO2 emissions in water networks of rice cultivation regions

Rice cultivation regions have a high density of open water networks to meet the requirements of rice growth and production. These open water networks have a significant risk of carbon (C) emissions due to agricultural production, but the C emissions from these waters are not clearly recorded in previous studies. Therefore, this study aimed to explore the pattern and internal mechanism of methane (CH₄) and carbon dioxide (CO₂) emissions from multiple types of waters (i.e., river, fish pond, reservoir, and ditch) in a typical rice cultivation region in southwestern China. The annual CH₄ and CO₂ fluxes were higher in the downstream river (2.79-94.89 and 39.39-1699.98 mg m^-2 h^-1) and ditch (8.80-74.99 and 123.43-542.65 mg m^-2 h^-1, respectively) and lower in the reservoir (-0.67 to 3.45 and -239.15 to 141.50 mg m^-2 h^-1) (P < 0.05). The monthly trends of CH₄ and CO₂ fluxes from the middle river and ditch were driven by interactive reactions of rice cultivation practices and precipitation. In contrast, the emission patterns of CH₄ and CO₂ from the lower river, upper river, and fish pond were mainly driven by domestic sewage discharge, precipitation, and aquaculture practices, respectively. This study suggested that river and ditch were more sensitive to C emissions than other waters, and the rice production period was the critical period for controlling C emission. Although rice paddy soils yield more cumulative emissions of CH₄, water networks in rice cultivation regions were possible hotspots for C emissions due to the higher emission intensities, which were largely overlooked before. Thus, it is necessary to refine and promote practices to better mitigate C emissions from waters in rice cultivation regions in the future.

Overriding water table control on managed peatland greenhouse gas emissions

Global peatlands store more carbon than is naturally present in the atmosphere^1,2. However, many peatlands are under pressure from drainage-based agriculture, plantation development and fire, with the equivalent of around 3 per cent of all anthropogenic greenhouse gases emitted from drained peatland^3-5. Efforts to curb such emissions are intensifying through the conservation of undrained peatlands and re-wetting of drained systems⁶. Here we report eddy covariance data for carbon dioxide from 16 locations and static chamber measurements for methane from 41 locations in the UK and Ireland. We combine these with published data from sites across all major peatland biomes. We find that the mean annual effective water table depth (WTD_e; that is, the average depth of the aerated peat layer) overrides all other ecosystem- and management-related controls on greenhouse gas fluxes. We estimate that every 10 centimetres of reduction in WTD_e could reduce the net warming impact of CO₂ and CH₄ emissions (100-year global warming potentials) by the equivalent of at least 3 tonnes of CO₂ per hectare per year, until WTD_e is less than 30 centimetres. Raising water levels further would continue to have a net cooling effect until WTD_e is within 10 centimetres of the surface. Our results suggest that greenhouse gas emissions from peatlands drained for agriculture could be greatly reduced without necessarily halting their productive use. Halving WTD_e in all drained agricultural peatlands, for example, could reduce emissions by the equivalent of over 1 per cent of global anthropogenic emissions.

Towards a microbial process-based understanding of the resilience of peatland ecosystem service provisioning - A research agenda

Peatlands are wetland ecosystems with great significance as natural habitats and as major global carbon stores. They have been subject to widespread exploitation and degradation with resulting losses in characteristic biota and ecosystem functions such as climate regulation. More recently, large-scale programmes have been established to restore peatland ecosystems and the various services they provide to society. Despite significant progress in peatland science and restoration practice, we lack a process-based understanding of how soil microbiota influence peatland functioning and mediate the resilience and recovery of ecosystem services, to perturbations associated with land use and climate change. We argue that there is a need to: in the short-term, characterise peatland microbial communities across a range of spatial and temporal scales and develop an improved understanding of the links between peatland habitat, ecological functions and microbial processes; in the medium term, define what a successfully restored 'target' peatland microbiome looks like for key carbon cycle related ecosystem services and develop microbial-based monitoring tools for assessing restoration needs; and in the longer term, to use this knowledge to influence restoration practices and assess progress on the trajectory towards 'intact' peatland status. Rapid advances in genetic characterisation of the structure and functions of microbial communities offer the potential for transformative progress in these areas, but the scale and speed of methodological and conceptual advances in studying ecosystem functions is a challenge for peatland scientists. Advances in this area require multidisciplinary collaborations between peatland scientists, data scientists and microbiologists and ultimately, collaboration with the modelling community. Developing a process-based understanding of the resilience and recovery of peatlands to perturbations, such as climate extremes, fires, and drainage, will be key to meeting climate targets and delivering ecosystem services cost effectively.

Emission of CO2 and CH4 from a multi-ditches system in rice cultivation region: Flux, temporal-spatial variation and effect factors

Man-made multi-level ditches system is designed to irrigate, drain and collect runoff from surrounding fields. It is not only the conduit of water and field carbon, but also the linear-like wetland with complex carbon cycling. However, the contribution of ditches system to CO₂ and CH₄ emission has rarely been assessed. To understand the emission pattern of CO₂ and CH₄ from ditches, this study investigated the emission fluxes of CO₂ and CH₄ in a three-level ditches system in Chengdu Plain, China. The results showed that the emission of CO₂ and CH₄ ranged from 70.38 to 950.40 mg C m^-2 h^-1 and 6.51-74.99 mg C m^-2 h^-1, respectively, and was higher in spring and summer than other seasons in all ditches (P < 0.05). On the other hand, the emission of CO₂ and CH₄ increased along with the decreasing ditches size. Besides, it is found that the precipitation, water table depth and water DO concentration might contribute to the emission of CO₂, while CH₄ was possibly influenced by precipitation, water table depth, temperature, water DO and DOC concentration. Moreover, it is suggested that terrestrial external input and in-situ metabolism might be the main sources of C emission, and in-situ source might largely contribute to CH₄ emission. To reduce the C emission, it is necessary to improve fertilization and irrigation methods, limit soil pollutants transferring into ditches, and frequently dredge sediments in future.

Impact of water table levels and winter cover crops on greenhouse gas emissions from cultivated peat soils

Drainage and cultivation have turned peatlands from carbon (C) sinks into hotspots for greenhouse gas (GHG) emissions. Raising the water table and planting of winter cover crops are potential strategies to help reduce peat oxidation and re-initiate net C accumulation during the non-cropping period. However, the effects of these practices as well as their interactions on GHG emissions remain unclear. Here, we carried out an outdoor mesocosm experiment to elucidate the effect of water table levels (-30 cm and -50 cm) and winter cover crop cultivation (vetch, rye, no plant) on carbon dioxide (CO₂), nitrous oxide (N₂O) and methane (CH₄) fluxes during the winter period (November-April). Soil-atmosphere GHG exchange, GHG concentrations within the peat profile and soil water solute concentrations were monitored. Our results showed that high water table significantly reduced ecosystem respiration, while it had no net effect on N₂O and CH₄ fluxes. Uptake of available N by the cover crop significantly reduced nitrate in soil solution, thereby lowering the potential for leaching and both direct and indirect N₂O emissions. No interactive effects between water table levels and cover crops were detected for any of the measured GHG fluxes. Seasonal variations of GHG fluxes were positively correlated with soil air concentrations at -15 cm and -40 cm depths, which were further regulated by dissolved organic C, nitrate concentration, and anaerobic conditions in the soil. This study suggests that there is great potential to raise water table levels and introduce green cover crops to reduce GHG emissions. Further studies are needed to achieve a complete evaluation of these strategies outside of the growing season, which may provide a significant mitigation benefit in C-rich cultivated peatlands.

Annual gaseous carbon budgets of forest-to-bog restoration sites are strongly determined by vegetation composition

Large areas of naturally open peatland in western Europe were drained and planted with non-native conifers in the twentieth century. Efforts are currently underway to restore many of these sites. Ultimately, forest-to-bog restoration aims to bring back functional peatlands that can sequester carbon but there is a lack of empirical evidence for whether current approaches are effective. Using a chronosequence design, we compared the annual gaseous carbon balance of two forest-to-bog restoration areas with an open area not subject to afforestation. A closed chamber method was used to determine gas fluxes (Net Ecosystem Respiration, Gross Primary Productivity, Net Ecosystem Exchange (NEE) and methane (CH₄)) over a twelve-month period for locations spanning the range of peatland microtopography and vegetation communities. Relationships between gas fluxes, vegetation/cover and environmental factors were analysed and regression models used to estimate annual CO₂ and CH₄ budgets. During the study period, NEE estimates (total gaseous C expressed as CO₂-eq) showed a net sink for the unafforested (-102 g C m^-2 yr^-1) and oldest (-131 g C m^-2 yr^-1) restoration area (17 years post-restoration 'RES 17 YRS'), whilst the youngest restoration area (6 years post-restoration 'RES 6YRS'), was a net source (35 g C m^-2 yr^-1). We observed significantly higher CH₄ emissions from restoration areas dominated by Eriophorum angustifolium compared with other peatland vegetation types. Sampling points with higher cover of Sphagnum were found to be most effective for C sequestration. Overall, vegetation composition/cover was observed to be an important factor determining C emissions from forest-to-bog restoration areas. These results suggest that restoration is effective in returning the carbon sink function of peatlands damaged by commercial forestry and - depending on restoration techniques - timescales of >10 years may be required.

Drivers of Vegetation Development, Biomass Production and the Initiation of Peat Formation in a Newly Constructed Wetland

Newly constructed wetlands are created to provide a range of ecosystem services, including carbon sequestration. Our understanding of the initial factors leading to successful peat formation in such environments is, however, limited. In a new 100-ha wetland that was created north of Amsterdam (the Netherlands), we conducted an experiment to determine the best combination of abiotic and biotic starting conditions for initial peat-forming processes. Sediment conditions were the main driver of vegetation development, biomass production and elemental composition during the 3-year study period. Overall, helophytes (Typha spp.) dominated basins with nutrient-rich conditions, whereas nutrient-poor basins were covered by submerged vegetation, which produced about seven times less aboveground biomass than helophytes. The C/N ratios for all plant species and biomass components were generally lower under nutrient-rich conditions and were lower for submerged species than helophytes. Because total basin biomass showed five times higher shoot and ten times higher root and rhizome production for clay and organic than sand sediments, even with some differences in decomposition rates are the conditions in the nutrient-rich basins expected to produce higher levels of initial peat formation. The results suggest that addition of a nutrient-rich sediment layer creates the best conditions for initial peat formation by stimulating rapid development of helophytes.

Tree stem bases are sources of CH4 and N2 O in a tropical forest on upland soil during the dry to wet season transition

Tropical forests on upland soils are assumed to be a methane (CH₄ ) sink and a weak source of nitrous oxide (N₂ O), but studies of wetland forests have demonstrated that tree stems can be a substantial source of CH₄ , and recent evidence from temperate woodlands suggests that tree stems can also emit N₂ O. Here, we measured CH₄ and N₂ O fluxes from the soil and from tree stems in a semi-evergreen tropical forest on upland soil. To examine the influence of seasonality, soil abiotic conditions and substrate availability (litter inputs) on trace greenhouse gas (GHG) fluxes, we conducted our study during the transition from the dry to the wet season in a long-term litter manipulation experiment in Panama, Central America. Trace GHG fluxes were measured from individual stem bases of two common tree species and from soils beneath the same trees. Soil CH₄ fluxes varied from uptake in the dry season to minor emissions in the wet season. Soil N₂ O fluxes were negligible during the dry season but increased markedly after the start of the wet season. By contrast, tree stem bases emitted CH₄ and N₂ O throughout the study. Although we observed no clear effect of litter manipulation on trace GHG fluxes, tree species and litter treatments interacted to influence CH₄ fluxes from stems and N₂ O fluxes from stems and soil, indicating complex relationships between tree species traits and decomposition processes that can influence trace GHG dynamics. Collectively, our results show that tropical trees can act as conduits for trace GHGs that most likely originate from deeper soil horizons, even when they are growing on upland soils. Coupled with the finding that the soils may be a weaker sink for CH₄ than previously thought, our research highlights the need to reappraise trace gas budgets in tropical forests.

Multi-year net ecosystem carbon balance of a restored peatland reveals a return to carbon sink

Peatlands after drainage and extraction are large sources of carbon (C) to the atmosphere. Restoration, through re-wetting and revegetation, aims to return the C sink function by re-establishing conditions similar to that of an undrained peatland. However, the time needed to re-establish C sequestration is not well constrained due to the lack of multi-year measurements. We measured over 3 years the net ecosystem exchange of CO₂ (NEE), methane ( F CH 4 ), and dissolved organic carbon (DOC) at a restored post-extraction peatland (RES) in southeast Canada (restored 14 years prior to the start of the study) and compared our observations to the C balance of an intact reference peatland (REF) that has a long-term continuous flux record and is in the same climate zone. Small but significant differences in winter respiration driven by temperature were mainly responsible for differences in cumulative NEE between years. Low growing season inter-annual variability was linked to constancy of the initial spring water table position, controlled by the blocked drainage ditches and the presence of water storage structures (bunds and pools). Half-hour F CH 4 at RES was small except when Typha latifolia-invaded drainage ditches were in the tower footprint; this effect at the ecosystem level was small as ditches represent a minor fraction of RES. The restored peatland was an annual sink for CO₂ (-90 ± 18 g C m^-2  year^-1 ), a source of CH₄ (4.4 ± 0.2 g C m^-2  year^-1 ), and a source of DOC (6.9 ± 2.2 g C m^-2  year^-1 ), resulting in mean net ecosystem uptake of 78 ± 17 g C m^-2  year^-1 . Annual NEE at RES was most similar to wetter, more productive years at REF. Integrating structures to increase water retention, alongside re-establishing key species, have been effective at re-establishing the net C sink rate to that of an intact peatland.

Nitrogen and phosphorus enrichment effects on CO2 and methane fluxes from an upland ecosystem

Reactive nitrogen (N) deposition can affect many ecosystem processes, particularly in oligotrophic habitats, and is expected to affect soil C storage potential through increases in microbial decomposition rate as a consequence of greater N availability. Increased N availability may also result in changes in the principal limitations on ecosystem productivity. Phosphorus (P) limitation may constrain productivity in instances of high N deposition, yet ecosystem responses to P availability are poorly understood. This study investigated CO₂ and CH₄ flux responses to N and P enrichment using both short- (1year) and long-term (16year) nutrient addition experiments. We hypothesised that the addition of either N or P will increase CO₂ and CH₄ fluxes, since both plant production and microbial activity are likely to increase with alleviation from nutrient limitation. This study demonstrated the modification of C fluxes from N and P enrichment, with differing results subject to the duration of nutrient addition. On average, relative to control, the addition of N alone inhibited CO₂ flux in the short-term (-9%) but considerably increased CO₂ emissions in the long-term (+35%), reduced CH₄ uptake in the short term (-90%) and reduced CH₄ emission in the long term (-94%). Phosphorus addition increased CO₂ and CH₄ emission in the short term (+20% and +184% respectively), with diminishing effect into the long term, suggesting microbial communities at these sites are P limited. Whilst a full C exchange budget was not examined in the experiment, the potential for soil C storage loss with long-term nutrient enrichment is demonstrated and indicates that P addition, where P is a limiting factor, may have an adverse influence on upland soil C content.

Ancient dissolved methane in inland waters revealed by a new collection method at low field concentrations for radiocarbon (14C) analysis

Methane (CH₄) is a powerful greenhouse gas that plays a prominent role in the terrestrial carbon (C) cycle, and is released to the atmosphere from freshwater systems in numerous biomes globally. Radiocarbon (¹⁴C) analysis can indicate both the age and source of CH₄ in natural environments. In contrast to CH₄ present in bubbles released from aquatic sediments (ebullition), dissolved CH₄ in lakes and streams can be present in low concentrations compared to carbon dioxide (CO₂), and therefore obtaining sufficient aquatic CH₄ for radiocarbon (¹⁴C) analysis remains a major technical challenge. Previous studies have shown that freshwater CH₄, in both dissolved and ebullitive form, can be significantly older than other forms of aquatic C, and it is therefore important to characterise this part of the terrestrial C balance. This study presents a novel method to capture sufficient amounts of dissolved CH₄ for ¹⁴C analysis in freshwater environments by circulating water across a hydrophobic, gas-permeable membrane and collecting the CH₄ in a large headspace volume. The results of laboratory and field tests show that reliable dissolved δ¹³CH₄ and ¹⁴CH₄ samples can be readily collected over short time periods (∼4-24 h), at relatively low cost and from a variety of surface water types. The initial results further support previous findings that dissolved CH₄ may be significantly older than other forms of aquatic C, and is currently unaccounted for in many terrestrial C balances and models. This method is suitable for use in remote locations, and could potentially be used to detect the leakage of unique ¹⁴CH₄ signatures from point sources into waterways, e.g. coal seam gas and landfill gas.

Historical peat loss explains limited short-term response of drained blanket bogs to rewetting

This study assessed the short-term impacts of ditch blocking on water table depth and vegetation community structure in a historically drained blanket bog. A chronosequence approach was used to compare vegetation near ditches blocked 5 years, 4 years and 1 year prior to the study with vegetation near unblocked ditches. Plots adjacent to and 3 m away from 70 ditches within an area of blanket bog were assessed for floristic composition, aeration depth using steel bars, and topography using LiDAR data. No changes in aeration depth or vegetation parameters were detected as a function of ditch-blocking, time since blocking, or distance from the ditch, with the exception of non-Sphagnum bryophytes which had lower cover in quadrats adjacent to ditches that had been blocked for 5 years. Analysis of LiDAR data and the observed proximity of the water table to the peat surface led us to conclude that the subdued ecosystem responses to ditch-blocking were the result of historical peat subsidence within a 4-5 m zone either side of each ditch, which had effectively lowered the peat surface to the new, ditch-influenced water table. We estimate that this process led to the loss of around 500,000 m³ peat within the 38 km² study area following drainage, due to a combination of oxidation and compaction. Assuming that 50% of the volume loss was due to oxidation, this amounts to a carbon loss of 11,000 Mg C over this area, i.e. 3 Mg C ha^-1. The apparent 'self-rewetting' of blanket bogs in the decades following drainage has implications for their restoration as it suggests that there may not be large quantities of dry peat left to rewet, and that there is a risk of inundation (potentially leading to high methane emissions) along subsided ditch lines. Many peatland processes are likely to be maintained in drained blanket bog, including support of typical peatland vegetation, but infilling of lost peat and recovery of original C stocks are likely to take longer than is generally anticipated.

Management effects on greenhouse gas dynamics in fen ditches

Globally, large areas of peatland have been drained through the digging of ditches, generally to increase agricultural production. By lowering the water table it is often assumed that drainage reduces landscape-scale emissions of methane (CH₄) into the atmosphere to negligible levels. However, drainage ditches themselves are known to be sources of CH₄ and other greenhouse gases (GHGs), but emissions data are scarce, particularly for carbon dioxide (CO₂) and nitrous oxide (N₂O), and show high spatial and temporal variability. Here, we report dissolved GHGs and diffusive fluxes of CH₄ and CO₂ from ditches at three UK lowland fens under different management; semi-natural fen, cropland, and cropland restored to low-intensity grassland. Ditches at all three fens emitted GHGs to the atmosphere, but both fluxes and dissolved GHGs showed extensive variation both seasonally and within-site. CH₄ fluxes were particularly large, with medians peaking at all three sites in August at 120-230mgm^-2d^-1. Significant between site differences were detected between the cropland and the other two sites for CO₂ flux and all three dissolved GHGs, suggesting that intensive agriculture has major effects on ditch biogeochemistry. Multiple regression models using environmental and water chemistry data were able to explain 29-59% of observed variation in dissolved GHGs. Annual CH₄ fluxes from the ditches were 37.8, 18.3 and 27.2gCH₄m^-2yr^-1 for the semi-natural, grassland and cropland, and annual CO₂ fluxes were similar (1100 to 1440gCO₂m^-2yr^-1) among sites. We suggest that fen ditches are important contributors to landscape-scale GHG emissions, particularly for CH₄. Ditch emissions should be included in GHG budgets of human modified fens, particularly where drainage has removed the original terrestrial CH₄ source, e.g. agricultural peatlands.

Emissions of methane from northern peatlands: a review of management impacts and implications for future management options

Northern peatlands constitute a significant source of atmospheric methane (CH₄). However, management of undisturbed peatlands, as well as the restoration of disturbed peatlands, will alter the exchange of CH₄ with the atmosphere. The aim of this systematic review and meta‐analysis was to collate and analyze published studies to improve our understanding of the factors that control CH₄ emissions and the impacts of management on the gas flux from northern (latitude 40° to 70°N) peatlands. The analysis includes a total of 87 studies reporting measurements of CH₄ emissions taken at 186 sites covering different countries, peatland types, and management systems. Results show that CH₄ emissions from natural northern peatlands are highly variable with a 95% CI of 7.6–15.7 g C m⁻² year⁻¹ for the mean and 3.3–6.3 g C m⁻² year⁻¹ for the median. The overall annual average (mean ± SD) is 12 ± 21 g C m⁻² year⁻¹ with the highest emissions from fen ecosystems. Methane emissions from natural peatlands are mainly controlled by water table (WT) depth, plant community composition, and soil pH. Although mean annual air temperature is not a good predictor of CH₄ emissions by itself, the interaction between temperature, plant community cover, WT depth, and soil pH is important. According to short‐term forecasts of climate change, these complex interactions will be the main determinant of CH₄ emissions from northern peatlands. Drainage significantly (p < .05) reduces CH₄ emissions to the atmosphere, on average by 84%. Restoration of drained peatlands by rewetting or vegetation/rewetting increases CH₄ emissions on average by 46% compared to the original premanagement CH₄ fluxes. However, to fully evaluate the net effect of management practice on the greenhouse gas balance from high latitude peatlands, both net ecosystem exchange (NEE) and carbon exports need to be considered.

Methane Exchange in a Coastal Fen in the First Year after Flooding--A Systems Shift

Background

Peatland restoration can have several objectives, for example re-establishing the natural habitat, supporting unique biodiversity attributes or re-initiating key biogeochemical processes, which can ultimately lead to a reduction in greenhouse gas (GHG) emissions. Every restoration measure, however, is itself a disturbance to the ecosystem.

Methods

Here, we examine an ecosystem shift in a coastal fen at the southern Baltic Sea which was rewetted by flooding. The analyses are based on one year of bi-weekly closed chamber measurements of methane fluxes gathered at spots located in different vegetation stands. During measurement campaigns, we recorded data on water levels, peat temperatures, and chemical properties of peat water. In addition we analyzed the first 20 cm of peat before and after flooding for dry bulk density (DBD), content of organic matter and total amounts of carbon (C), nitrogen (N), sulfur (S), and other nutrients.

Results

Rewetting turned the site from a summer dry fen into a shallow lake with water levels up to 0.60 m. We observed a substantial die-back of vegetation, especially in stands of sedges (Carex acutiformis Ehrh). Concentrations of total organic carbon and nitrogen in the peat water, as well as dry bulk density and concentrations of C, N and S in the peat increased. In the first year after rewetting, the average annual exchange of methane amounted to 0.26 ± 0.06 kg m^-2. This is equivalent to a 190-times increase in methane compared to pre-flooding conditions. Highest methane fluxes occurred in sedge stands which suffered from the heaviest die-back. None of the recorded environmental variables showed consistent relationships with the amounts of methane exchanged.

Conclusions

Our results suggest that rewetting projects should be monitored not only with regard to vegetation development but also with respect to biogeochemical conditions. Further, high methane emissions that likely occur directly after rewetting by flooding should be considered when forecasting the overall effect of rewetting on GHG exchange.