The Influence of Rewetting on Vegetation Development and Decomposition in a Degraded Fen

The rewetting technique border irrigation was installed in a degraded fen peatland in northeastern Germany. Because of the prevailing site conditions, the technique resulted in two different rewetting variants (surface irrigation and temporary inundation) at the study site. This paper reports on the practicability of this technique and the influence of rewetting on vegetation development, decomposition processes and soil nutrient availability, and the possibilities for renewed peat accumulation. The technique proved to be suited for rewetting fen sites with a continuous slope, deep peat layer with low hydraulic conductivity, and upstream water recharge facilities. A subsidence of the ground‐water levels during the summer months, however, could not be avoided in dry years. The vegetation changed slowly from species‐poor grassland into typical fen plant communities, despite rewetting and soil tillage. Species richness, however, was higher in the surface irrigation than in the temporary inundation variant. A sufficient water supply proved to be absolutely necessary to retard decomposition processes because higher decomposition of root materials (i.e., higher k values) occurred under temporary inundated conditions. Generally, the higher water content in the soil after rewetting led to a lower nitrate‐N–to–ammonium‐N ratio in the topsoil in both rewetting variants. In the surface irrigation variant the mineral nitrogen content (Nmin) of the topsoil decreased from 7.8 to 4.4 g N/m², which is also correlated with the increase in water content of the soil. The low Nmin levels of fens which were never deeply drained (0.9–2.8 g N/m²), however, were not reached within the observation period of 3 years.     

Restoration of peat‐forming vegetation by rewetting species‐poor fen grasslands

Questions: Does succession of rewetted species‐poor fen grasslands display similar trends when different water levels, sites and regions are compared? Will restoration targets as peat growth and waterfowl diversity be reached? Location: Valley fen of the river Peene (NE‐Germany) and the Hanság fen (Lake Neusiedler See, NW‐Hungary). Methods: Analysis of permanent plot data and vegetation maps over a period of up to seven years of rewetting. The general relations between newly adjusted water levels and changes in dominance of helophytic key species during early succession are analysed considering four rewetting intensities (water level classes) and eight vegetation types (Phalaris arundinacea type, Carex type, Glyceria maxima type, Phragmites australis type, Typha type, aquatic vegetation type, open water type and miscellaneous type). Results: The initial period of balancing the site conditions and vegetation is characterised by specific vegetation types and related horizontal vegetation structures. Most vegetation types displayed similar trends within the same water level class when different sites and regions were compared. A significant spread of potentially peat forming vegetation with dominance of Carex spp. or Phragmites as desired goal of restoration was predominantly restricted to long‐term shallow inundated sites (water level median in winter: 0–30 cm above surface). Open water patches as bird habitats persisted mainly at permanent inundated sites (water level median in winter > 60 cm above surface). Conclusions: Site hydrology appeared as a main force of secondary succession. Thus the rewetting intensity and restoration targets have to be balanced adequately.     

Vegetation controls methane emissions in a coastal brackish fen

Climate change and associated sea level rise will likely affect coastal ecosystems and lead to more frequent inundations. Plants are an important control for methane (CH₄) emissions in peatlands because the metabolism of the living plant can either enhance or attenuate CH₄ emissions and plant litter supplies an easily available carbon source for methanogenesis. Here we compare the contribution of various dominant plant species to methane emissions in a degraded, rewetted coastal brackish fen at the southern Baltic Sea coast in Northeast Germany. We analyse one year of bi-weekly static closed chamber data gathered at measurement spots that were located in different mono-dominant vegetation stands (Bolboschoenus maritimus (L.) Palla, Schoenoplectus tabernaemontani (C.C.Gmel.) Palla, Carex acutiformis Ehrh.). Furthermore, data on water level, water temperature, conductivity (sulphate), and several peat characteristics were recorded. Generally, the annual methane emissions were low with an average across vegetation stands of 14 kg CH₄ ha^?1 a^?1, which we related to high decomposition of peat after drainage and to relatively low water levels in summer. Nevertheless, methane emissions varied between different vegetation types with significantly higher methane fluxes (31.8 ± 5.7 kg CH₄ ha^?1 a^?1) from Bolboschoenus maritimus stands compared to Carex acutiformis and Schoenoplectus tabernaemontani stands (4.3 ± 1.2 and 5.7 ± 2.4 kg CH₄ ha^?1 a^?1, respectively). None of the environmental variables that have been recorded can explain this difference. Thus, vegetation composition seems to be an important driver for methane emissions in coastal brackish fens and may therefore be crucial with regard to recreation measures.     

Change in fluxes of carbon dioxide,methane and nitrous oxide due to forest drainage of mire sites of different trophy

Northern peatlands accumulate atmospheric CO₂ thus counteracting climate warming. However, CH₄ which is more efficient as a greenhouse gas than CO₂, is produced in the anaerobic decomposition processes in peat. When peatlands are taken for forestry their water table is lowered by ditching. We studied long-term effects of lowered water table on the development of vegetation and the annual emissions of CO₂, CH₄ and N₂O in an ombrotrophic bog and in a minerotrophic fen in Finland. Reclamation of the peat sites for forestry had changed the composition and coverage of the field and ground layer species, and increased highly the growth of tree stand at the drained fen. In general, drainage increased the annual CO₂ emissions but the emissions were also affected by the natural fluctuations of water table. In contrast to CO₂, drainage had decreased the emissions of CH₄, the drained fen even consumed atmospheric CH₄. CO₂ and CH₄ emissions were higher in the virgin fen than in the virgin bog. There were no N₂O emissions from neither type of virgin sites. Drainage had, however, highly increased the N₂O emissions from the fen. The results suggest that post-drainage changes in gas fluxes depend on the trophy of the original mires.     

Changes of methane and nitrous oxide emissions in a transition bog in central Germany (German National Park Harz Mountains) after rewetting

During the last decades, various renaturation programmes have been initialized to recover nutrient sink and ecological functions of peatlands by rewetting. Rewetting, however, often results in the formation of hotspots for methane (CH₄) emissions and in temporal dieback of local vegetation. The present study aimed at quantifying changes of CH₄ and nitrous oxide (N₂O) emissions in a peatland currently under continuous rewetting conditions. Emissions where studied at a permanently flooded site and a non-flooded peat site with fluctuating water tables by using common closed chamber method. The permanently flooded site revealed extremely high CH₄ emissions (up to 1195 mg C m^?2 d^?1) which were positively correlated with temperature, nutrient content, dissolved organic carbon and nitrogen concentration of the peat soil water. In contrast, the non-flooded peat site, with lower and fluctuating water tables (WT), showed significantly lower CH₄ emissions and an increasing trend of CH₄ release associated with a generally increasing WT caused by the progressing rewetting process. Lower N₂O emissions (<24 µg N m^?2 d^?1) were observed at the flooded site. By contrast, the non-flooded peat site with fluctuating WT showed significantly higher N₂O emissions (up to 4178 µg N m^?2 d^?1), in particular at high temperatures during summer time. The present results indicate that permanently flooded conditions during rewetting processes might cause higher CH₄ emissions compared to fluctuating WT which in contrast might enhance N₂O emissions. In total, however, no decreasing trend for CH₄ emissions throughout the five-year renaturation period could be found. At least for N₂O we observed a decreasing trend during rewetting.     

Assessing greenhouse gas emissions from peatlands using vegetation as a proxy

Drained peatlands in temperate Europe are a globally important source of greenhouse gas (GHG) emissions. This article outlines a methodology to assess emissions and emission reductions from peatland rewetting projects using vegetation as a proxy. Vegetation seems well qualified for indicating GHG fluxes from peat soils as it reflects long-term water level, affects GHG emissions via assimilate supply and aerenchyma and allows fine-scaled mapping. The methodology includes mapping of vegetation types characterised by the presence and absence of species groups indicative for specific water level classes. GHG flux values are assigned to the vegetation types following a standardized protocol and using published emission values from plots with similar vegetation and water level in regions with similar climate and flora. Carbon sequestration in trees is accounted for by estimating the annual sequestration in tree biomass from forest inventory data. The method follows the criteria of the Voluntary Carbon Standard and is illustrated using the example of two Belarusian peatlands.     

Land use of drained peatlands: Greenhouse gas fluxes,plant production,and economics

Drained peatlands are hotspots for greenhouse gas (GHG) emissions, which could be mitigated by rewetting and land use change. We performed an ecological/economic analysis of rewetting drained fertile peatlands in a hemiboreal climate using different land use strategies over 80 years. Vegetation, soil processes, and total GHG emissions were modeled using the CoupModel for four scenarios: (1) business as usual—Norway spruce with average soil water table of ?40 cm; (2) willow with groundwater at ?20 cm; (3) reed canary grass with groundwater at ?10 cm; and (4) a fully rewetted peatland. The predictions were based on previous model calibrations with several high‐resolution datasets consisting of water, heat, carbon, and nitrogen cycling. Spruce growth was calibrated by tree‐ring data that extended the time period covered. The GHG balance of four scenarios, including vegetation and soil, were 4.7, 7.1, 9.1, and 6.2 Mg CO₂eq ha^?1 year^?1, respectively. The total soil emissions (including litter and peat respiration CO₂ + N₂O + CH₄) were 33.1, 19.3, 15.3, and 11.0 Mg CO₂eq ha^?1 year^?1, respectively, of which the peat loss contributed 35%, 24%, and 7% of the soil emissions for the three drained scenarios, respectively. No peat was lost for the wet peatland. It was also found that draining increases vegetation growth, but not as drastically as peat respiration does. The cost–benefit analysis (CBA) is sensitive to time frame, discount rate, and carbon price. Our results indicate that the net benefit was greater with a somewhat higher soil water table and when the peatland was vegetated with willow and reed canary grass (Scenarios 2 and 3). We conclude that saving peat and avoiding methane release using fairly wet conditions can significantly reduce GHG emissions, and that this strategy should be considered for land use planning and policy‐making.     

Dynamics of soil biogeochemical gas emissions shaped by remolded aggregate sizes and carbon configurations under hydration cycles

Changes in soil hydration status affect microbial community dynamics and shape key biogeochemical processes. Evidence suggests that local anoxic conditions may persist and support anaerobic microbial activity in soil aggregates (or in similar hot spots) long after the bulk soil becomes aerated. To facilitate systematic studies of interactions among environmental factors with biogeochemical emissions of CO₂, N₂O and CH₄ from soil aggregates, we remolded silt soil aggregates to different sizes and incorporated carbon at different configurations (core, mixed, no addition). Assemblies of remolded soil aggregates of three sizes (18, 12, and 6 mm) and equal volumetric proportions were embedded in sand columns at four distinct layers. The water table level in each column varied periodically while obtaining measurements of soil GHG emissions for the different aggregate carbon configurations. Experimental results illustrate that methane production required prolonged inundation and highly anoxic conditions for inducing measurable fluxes. The onset of unsaturated conditions (lowering water table) resulted in a decrease in CH₄ emissions while temporarily increasing N₂O fluxes. Interestingly, N₂O fluxes were about 80% higher form aggregates with carbon placement in center (anoxic) core compared to mixed carbon within aggregates. The fluxes of CO₂ were comparable for both scenarios of carbon sources. These experimental results highlight the importance of hydration dynamics in activating different GHG production and affecting various transport mechanisms about 80% of total methane emissions during lowering water table level are attributed to physical storage (rather than production), whereas CO₂ emissions (~80%) are attributed to biological activity. A biophysical model for microbial activity within soil aggregates and profiles provides a means for results interpretation and prediction of trends within natural soils under a wide range of conditions.     

Carbon balance and radiative forcing of Finnish peatlands 1900–2100 – the impact of forestry drainage

Natural peatlands accumulate carbon (C) and nitrogen (N). They affect the global climate by binding carbon dioxide (CO₂) and releasing methane (CH₄) to the atmosphere; in contrast fluxes of nitrous oxide (N₂O) in natural peatlands are insignificant. Changes in drainage associated with forestry alter these greenhouse gas (GHG) fluxes and thus the radiative forcing (RF) of peatlands. In this paper, changes in peat and tree stand C stores, GHG fluxes and the consequent RF of Finnish undisturbed and forestry‐drained peatlands are estimated for 1900–2100. The C store in peat is estimated at 5.5 Pg in 1950. The rate of C sequestration into peat has increased from 2.2 Tg a^‐‐1 in 1900, when all peatlands were undrained, to 3.6 Tg a^‐‐1 at present, when c. 60% of peatlands have been drained for forestry. The C store in tree stands has increased from 60 to 170 Tg during the 20th century. Methane emissions have decreased from an estimated 1.0–0.5 Tg CH₄‐‐C a^‐‐1, while those of N₂O have increased from 0.0003 to 0.005 Tg N₂O‐‐N a^‐‐1. The altered exchange rates of GHG gases since 1900 have decreased the RF of peatlands in Finland by about 3 mW m^‐‐2 from the predrainage situation. This result contradicts the common hypothesis that drainage results in increased C emissions and therefore increased RF of peatlands. The negative radiative forcing due to drainage is caused by increases in CO₂ sequestration in peat (‐‐0.5 mW m^‐‐2), tree stands and wood products (‐‐0.8 mW m^‐‐2), decreases in CH₄ emissions from peat to the atmosphere (‐‐1.6 mW m^‐‐2), and only a small increase in N₂O emissions (+0.1 mW m^‐‐2). Although the calculations presented include many uncertainties, the above results are considered qualitatively reliable and may be expected to be valid also for Scandinavian countries and Russia, where most forestry‐drained peatlands occur outside Finland.     

CH4 production and oxidation processes in a boreal fen ecosystem after long‐term water table drawdown

Fens, which extend over vast areas in the Northern hemisphere, are sources of the greenhouse gas CH₄. Climate change scenarios predict a lowering water table (WT) in mires. To study the effect of WT drawdown on CH₄ dynamics in a fen ecosystem, we took advantage of a WT drawdown gradient near a ground water extraction plant. Methane fluxes and CH₄ production and oxidation potentials were related to microbial communities responsible for the processes in four mire locations (wet, semiwet, semidry, and dry). Principal component analyses performed on the vegetation, pH, CH₄, and WT results clearly separated the four sampling locations in the gradient. Long‐term lowering of WT was associated with decreased coverage of Sphagnum and aerenchymatic plants, decreased CH₄ field emissions and CH₄ production potential. Based on mcrA terminal restriction fragment length polymorphism the methanogen community structure correlated best with the methane production and coverage of aerenchymatic plants along the gradient. Methanosarcinaceae and Methanocellales were found at the pristine wet end of the gradient, whereas the Fen cluster characterized the dry end. The methane‐oxidizing bacterial community consisted exclusively of Methylocystis bacteria, but interestingly of five different alleles (T, S, R, M, and O) of the particulate methane monooxygenase marker gene pmoA. The M allele was dominant in the wet locations, and the occurrence of alleles O, S, and T increased with drainage. The occurrence of the R allele that characterized the upper peat layer correlated with CH₄ oxidation potential. These results advance our understanding of mire dynamics after long‐term WT drawdown and of the microbiological bases of methane emissions from mires.     

The role of vegetation in methane flux to the atmosphere: should vegetation be included as a distinct category in the global methane budget?

Currently, the global annual flux of methane (CH₄) to the atmosphere is fairly well constrained at ca. 645 Tg CH₄ year^?1. However, the relative magnitudes of the fluxes generated from different natural (e.g. wetlands, deep seepage, hydrates, ocean sediments) and anthropogenic sources remain poorly resolved. Of the identified natural sources, the contribution of vegetation to the global methane budget is arguably the least well understood. Historically, reviews of the contribution of vegetation to the global methane flux have focused on the role of plants as conduits for soil-borne methane emissions from wetlands, or the aerobic production of methane within plant tissues. Many recent global budgets only include the latter pathway (aerobic methane production) in estimating the importance of terrestrial vegetation to atmospheric CH₄ flux. However, recent experimental evidence suggests several novel pathways through which vegetation can contribute to the flux of this globally important, trace greenhouse gas (GHG), such as plant cisterns that act as cryptic wetlands, heartwood rot in trees, the degradation of coarse woody debris and litter, or methane transport through herbaceous and woody plants. Herein, we synthesize the existing literature to provide a comprehensive estimate of the role of modern vegetation in the global methane budget. This first, albeit uncertain, estimate indicates that vegetation may represent up to 22 % of the annual flux of methane to the atmosphere, contributing ca. 32–143 Tg CH₄ year^?1 to the global flux of this important trace GHG. Overall, our findings emphasize the need to better resolve the role of vegetation in the biogeochemical cycling of methane as an important component of closing the gap in the global methane budget.     

Environmental and physical controls on northern terrestrial methane emissions across permafrost zones

Methane (CH₄) emissions from the northern high‐latitude region represent potentially significant biogeochemical feedbacks to the climate system. We compiled a database of growing‐season CH₄ emissions from terrestrial ecosystems located across permafrost zones, including 303 sites described in 65 studies. Data on environmental and physical variables, including permafrost conditions, were used to assess controls on CH₄ emissions. Water table position, soil temperature, and vegetation composition strongly influenced emissions and had interacting effects. Sites with a dense sedge cover had higher emissions than other sites at comparable water table positions, and this was an effect that was more pronounced at low soil temperatures. Sensitivity analysis suggested that CH₄ emissions from ecosystems where the water table on average is at or above the soil surface (wet tundra, fen underlain by permafrost, and littoral ecosystems) are more sensitive to variability in soil temperature than drier ecosystems (palsa dry tundra, bog, and fen), whereas the latter ecosystems conversely are relatively more sensitive to changes of the water table position. Sites with near‐surface permafrost had lower CH₄ fluxes than sites without permafrost at comparable water table positions, a difference that was explained by lower soil temperatures. Neither the active layer depth nor the organic soil layer depth was related to CH₄ emissions. Permafrost thaw in lowland regions is often associated with increased soil moisture, higher soil temperatures, and increased sedge cover. In our database, lowland thermokarst sites generally had higher emissions than adjacent sites with intact permafrost, but emissions from thermokarst sites were not statistically higher than emissions from permafrost‐free sites with comparable environmental conditions. Overall, these results suggest that future changes to terrestrial high‐latitude CH₄ emissions will be more proximately related to changes in moisture, soil temperature, and vegetation composition than to increased availability of organic matter following permafrost thaw.     

Greenhouse gas fluxes from tropical peatlands in south‐east Asia

The lowland peatlands of south‐east Asia represent an immense reservoir of fossil carbon and are reportedly responsible for 30% of the global carbon dioxide (CO₂) emissions from Land Use, Land Use Change and Forestry. This paper provides a review and meta‐analysis of available literature on greenhouse gas fluxes from tropical peat soils in south‐east Asia. As in other parts of the world, water level is the main control on greenhouse gas fluxes from south‐east Asian peat soils. Based on subsidence data we calculate emissions of at least 900 g CO₂ m^?2 a^?1 (～250 g C m^?2 a^?1) for each 10 cm of additional drainage depth. This is a conservative estimate as the role of oxidation in subsidence and the increased bulk density of the uppermost drained peat layers are yet insufficiently quantified. The majority of published CO₂ flux measurements from south‐east Asian peat soils concerns undifferentiated respiration at floor level, providing inadequate insight on the peat carbon balance. In contrast to previous assumptions, regular peat oxidation after drainage might contribute more to the regional long‐term annual CO₂ emissions than peat fires. Methane fluxes are negligible at low water levels and amount to up to 3 mg CH₄ m^?2 h^?1 at high water levels, which is low compared with emissions from boreal and temperate peatlands. The latter emissions may be exceeded by fluxes from rice paddies on tropical peat soil, however. N₂O fluxes are erratic with extremely high values upon application of fertilizer to wet peat soils. Current data on CO₂ and CH₄ fluxes indicate that peatland rewetting in south‐east Asia will lead to substantial reductions of net greenhouse gas emissions. There is, however, an urgent need for further quantitative research on carbon exchange to support the development of consistent policies for climate change mitigation.     

The effect of biomass harvesting on greenhouse gas emissions from a rewetted temperate fen

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^?2 a^?1 and 2–5 g m^?2 a^?1, 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 CO₂‐equivalents: 18 t ha^?1 a^?1). 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^?1 a^?1 of CO₂‐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^?1 CO₂‐equivalents could possibly be achieved by rewetting; this excludes additional savings by fossil fuel replacement.     

A synthesis of methane emissions from 71 northern,temperate, and subtropical wetlands

Wetlands are the largest natural source of atmospheric methane. Here, we assess controls on methane flux using a database of approximately 19 000 instantaneous measurements from 71 wetland sites located across subtropical, temperate, and northern high latitude regions. Our analyses confirm general controls on wetland methane emissions from soil temperature, water table, and vegetation, but also show that these relationships are modified depending on wetland type (bog, fen, or swamp), region (subarctic to temperate), and disturbance. Fen methane flux was more sensitive to vegetation and less sensitive to temperature than bog or swamp fluxes. The optimal water table for methane flux was consistently below the peat surface in bogs, close to the peat surface in poor fens, and above the peat surface in rich fens. However, the largest flux in bogs occurred when dry 30‐day averaged antecedent conditions were followed by wet conditions, while in fens and swamps, the largest flux occurred when both 30‐day averaged antecedent and current conditions were wet. Drained wetlands exhibited distinct characteristics, e.g. the absence of large flux following wet and warm conditions, suggesting that the same functional relationships between methane flux and environmental conditions cannot be used across pristine and disturbed wetlands. Together, our results suggest that water table and temperature are dominant controls on methane flux in pristine bogs and swamps, while other processes, such as vascular transport in pristine fens, have the potential to partially override the effect of these controls in other wetland types. Because wetland types vary in methane emissions and have distinct controls, these ecosystems need to be considered separately to yield reliable estimates of global wetland methane release.     

Full carbon and greenhouse gas balances of fertilized and nonfertilized reed canary grass cultivations on an abandoned peat extraction area in a dry year

Bioenergy crop cultivation on former peat extraction areas is a potential after‐use option that provides a source of renewable energy while mitigating climate change through enhanced carbon (C) sequestration. This study investigated the full C and greenhouse gas (GHG) balances of fertilized (RCG‐F) and nonfertilized (RCG‐C) reed canary grass (RCG; Phalaris arundinacea) cultivation compared to bare peat (BP) soil within an abandoned peat extraction area in western Estonia during a dry year. Vegetation sampling, static chamber and lysimeter measurements were carried out to estimate above‐ and belowground biomass production and allocation, fluxes of carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) in cultivated strips and drainage ditches as well as the dissolved organic carbon (DOC) export, respectively. Heterotrophic respiration was determined from vegetation‐free trenched plots. Fertilization increased the above‐ to belowground biomass production ratio and the autotrophic to heterotrophic respiration ratio. The full C balance (incl. CO₂, CH₄ and DOC fluxes from strips and ditches) was 96, 215 and 180 g C m^?2 yr^?1 in RCG‐F, RCG‐C and BP, respectively, suggesting that all treatments acted as C sources during the dry year. The C balance was driven by variations in the net CO₂ exchange, whereas the combined contribution of CH₄ and DOC fluxes was <5%. The GHG balances were 3.6, 7.9 and 6.6 t CO₂ eq ha^?1 yr^?1 in RCG‐F, RCG‐C and BP, respectively. The CO₂ exchange was also the dominant component of the GHG balance, while the contributions of CH₄ and N₂O were <1% and 1–6%, respectively. Overall, this study suggests that maximizing plant growth and the associated CO₂ uptake through adequate water and nutrient supply is a key prerequisite for ensuring sustainable high yields and climate benefits in RCG cultivations established on organic soils following drainage and peat extraction.     

Functional-Structural Analysis of Nitrogen-Cycle Bacteria in a Hypersaline Mat from the Omani Desert

Anaerobic microbial activity in northern peat soils most often results in more carbon dioxide (CO ₂ ) production than methane (CH₄) production. This study examined why methanogenic conditions (i.e., equal molar amounts of CH₄ production and CO₂ production) prevail so infrequently. We used peat soils from two ombrotrophic bogs and from two rheotrophic fens. The former two represented a relatively dry bog hummock and a wet bog hollow, and the latter two represented a forested fen and a sedge-dominated fen. We quantified gas production rates in soil samples incubated in vitro with and without added metabolic substrates (glucose, ethanol, H₂/CO₂). None of the peat soils exhibited methanogenic conditions when incubated in vitro for a short time (< 5 days) and without added substrates. Incubating some samples > 50 days without added substrates led to methanogenic conditions in only one of four experiments. The anaerobic CO₂:CH₄ production ratio ranged from 5:1 to 40:1 in peat soil without additions and was larger in samples from the dry bog hummock and forested fen than the wet bog hollow and sedge fen. Adding ethanol or glucose separately to peat soils led to methanogenic conditions within 5 days after the addition by stimulating rates of CH₄ production, suggesting CH₄ production from both hydrogenotrophic and acetoclastic methanogenesis. Our results suggest that methanogenic conditions in peat soils rely on a constant supply of easily decomposable metabolic substrates. Sample handling and incubation procedures might obscure methanogenic conditions in peat soil incubated in vitro.     

Multivariate regulation of soil CO2 and N2O pulse emissions from agricultural soils

Climate and land‐use models project increasing occurrence of high temperature and water deficit in both agricultural production systems and terrestrial ecosystems. Episodic soil wetting and subsequent drying may increase the occurrence and magnitude of pulsed biogeochemical activity, affecting carbon (C) and nitrogen (N) cycles and influencing greenhouse gas (GHG) emissions. In this study, we provide the first data to explore the responses of carbon dioxide (CO₂) and nitrous oxide (N₂O) fluxes to (i) temperature, (ii) soil water content as percent water holding capacity (%WHC), (iii) substrate availability throughout, and (iv) multiple soil drying and rewetting (DW) events. Each of these factors and their interactions exerted effects on GHG emissions over a range of four (CO₂) and six (N₂O) orders of magnitude. Maximal CO₂ and N₂O fluxes were observed in environments combining intermediate %WHC, elevated temperature, and sufficient substrate availability. Amendments of C and N and their interactions significantly affected CO₂ and N₂O fluxes and altered their temperature sensitivities (Q₁₀) over successive DW cycles. C amendments significantly enhanced CO₂ flux, reduced N₂O flux, and decreased the Q₁₀ of both. N amendments had no effect on CO₂ flux and increased N₂O flux, while significantly depressing the Q₁₀ for CO₂, and having no effect on the Q₁₀ for N₂O. The dynamics across DW cycles could be attributed to changes in soil microbial communities as the different responses to wetting events in specific group of microorganisms, to the altered substrate availabilities, or to both. The complex interactions among parameters influencing trace gas fluxes should be incorporated into next generation earth system models to improve estimation of GHG emissions.     

Where old meets new: An ecosystem study of methanogenesis in a reflooded agricultural peatland

Reflooding formerly drained peatlands has been proposed as a means to reduce losses of organic matter and sequester soil carbon for climate change mitigation, but a renewal of high methane emissions has been reported for these ecosystems, offsetting mitigation potential. Our ability to interpret observed methane fluxes in reflooded peatlands and make predictions about future flux trends is limited due to a lack of detailed studies of methanogenic processes. In this study we investigate methanogenesis in a reflooded agricultural peatland in the Sacramento Delta, California. We use the stable‐and radio‐carbon isotopic signatures of wetland sediment methane, ecosystem‐scale eddy covariance flux observations, and laboratory incubation experiments, to identify which carbon sources and methanogenic production pathways fuel methanogenesis and how these processes are affected by vegetation and seasonality. We found that the old peat contribution to annual methane emissions was large (~30%) compared to intact wetlands, indicating a biogeochemical legacy of drainage. However, fresh carbon and the acetoclastic pathway still accounted for the majority of methanogenesis throughout the year. Although temperature sensitivities for bulk peat methanogenesis were similar between open‐water (Q₁₀ = 2.1) and vegetated (Q₁₀ = 2.3) soils, methane production from both fresh and old carbon sources showed pronounced seasonality in vegetated zones. We conclude that high methane emissions in restored wetlands constitute a biogeochemical trade‐off with contemporary carbon uptake, given that methane efflux is fueled primarily by fresh carbon inputs.     

Key variables controlling the vegetation of a cool-temperate mire in northern Japan

Abstract. In the cool-temperate Bibi Mire, Hokkaido, Japan, valley fens and flood-plain fens have quite different vegetation. The main variables controlling the vegetation were all hydrological: mean water level, water level fluctuation and surface water flow. Chemical factors such as electrical conductivity, dissolved oxygen and related peat decomposition were less important. The pH was about neutral and has little effect. The flood-plain fen developed under fluctuating water table conditions. The dominant species are Calamagrostis langsdotffii and Carex pseudocuraica. When temporal inundation occurs in the rainy or typhoon seasons, the submergence stimulates bud germination of the stoloniferous C. pseudocuraica, which can rapidly elongate its stolons upward. Some large floating peat mats occurred in the flood-plain fen zone. On these mats some Alnus japonica saplings establish and patches of alder forest can arise. Here the water level was higher than in the peripheral alder forest zone. The valley fen is dominated by Carex lasiocarpa var. occultans and/or C. limosa. It is formed under stable water table conditions in the inundated parts of the mire -where the non-inundated wet areas are dominated by alder trees. In the area where the surface water is flowing, these two fen sedges grow in deeper water since the high oxygen content is considered to compensate the flooding stress.