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Aims Drained peatlands are a major source of greenhouse gases (GHG). Paludiculture is the production of biomass under wet and peat preserving conditions. Despite the growing recognition as GHG mitigation measure, the potential influence of climate warming on paludiculture is still unknown. Methods For two years, we quantified the exchange of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) using manual chambers and surveyed the vegetation composition of warmed and control sites at a near-natural bog and two Sphagnum farming areas in North-Western Germany. Passive warming was achieved using Open Top Chambers (OTC). Results OTCs significantly increased air and soil temperatures, while soil moisture, humidity and light availability differed only marginally. The latter was considered when calculating gross primary production. Warming tended to increase vascular plant cover, but differences to the control plots were still small after two years. Emissions of CO2 and CH4 increased with warming, dominated by CH4 at the near-natural bog and by CO2 at the paludiculture areas, where vegetation was in a successional stage and topsoils temporarily dried out during summer. N2O emissions were negligible at the near-natural bog and ceased with increasing biomass at the paludiculture sites. Interannual variability was high due to a heatwave in the second measurement year. Conclusions Climate warming could increase GHG emissions from near-natural bogs and Sphagnum farming. In the latter case, this puts even more emphasis on water management systems ensuring high water table depths during dry periods. Further, control of vascular plants might both reduce CH4 emissions and improve biomass quality.

Drained organic soils are large sources of anthropogenic greenhouse gases (GHG) in many European and Asian countries. In Germany, they account for more than 7% of the national GHG emissions. Carbon dioxide (CO2) forms the vast majority of emissions from these soils and is thus the main target for mitigation measures. Bog peatlands are mainly found in North-Western Germany and frequently used for high-intensity grassland use. Further, former peat extraction areas are restored for nature protection. While restoration has decades of tradition, paludiculture and active water management in agriculture are comparatively new.Here, we will compile data on GHG exchange of bog peatlands and highlight recent results on water management by ditch blocking and subsurface irrigation, on Sphagnum paludiculture and on restored bog peatlands. Groundwater levels are usually considered as the major control for both CO2 and methane (CH4) emissions. The effects of water management on CO2 emissions are strongly depending on the site. Surprisingly, raising the groundwater level by subsurface irrigation in a grassland under bog peat to levels considered as acceptable even in restoration projects did not only fail to reduce CO2 emissions, but raised them compared to deeply drained control parcel. These results might be explained by an interaction of increased soil moisture in the topsoil and improved nutrient retention during phases of high soil temperatures and, at the same time, by limitations of microbial activity due to low soil moisture at the control parcels. However, at a second grassland site with subsurface irrigation, this did not occur, but a combination with grassland renewal caused extremely high nitrous oxide emissions. In contrast, both re-wetting for restoration purposes and Sphagnum farming reliably reduce GHG emission or may even lead to a carbon sink. Here, the effects of the groundwater level on CO2 and, even more, on CH4 emissions in a Sphagnum farming experiment were partially overridden by vegetation development dynamics.

Conventional agriculture on peatlands requires drainage, but this practice causes high emissions of the greenhouse gases (GHG) carbon dioxide (CO2) and nitrous oxide (N2O). Paludiculture is an option to mitigate these adverse environmental effects while maintaining productive land use. Whereas the GHG exchange of paludiculture on rewetted bog peat, i.e. Sphagnum farming, is relatively well examined, data on GHG emissions from fen paludicultures is still very scarce. As typical fen paludiculture species are aerenchymous plants, the release of methane (CH4) is of particular interest when optimising the GHG balance of such systems. Topsoil removal is an option to reduce the CH4 emissions upon rewetting but retaining a nutrient rich topsoil might foster the biomass growth.In this project, Typha angustifolia, Typha latifolia, and Phragmites australis are grown at a fen peatland formerly used as grassland. Water levels will be kept at the surface or slightly above it. In parts of the newly created polder surrounded by a peat dam, the topsoil is removed. Four smaller sub-polders are installed to separate the effects of topsoil removal and water level. Here, the water levels can be adjusted independently from the main polder. Greenhouse gas exchange is measured for all three species with and without topsoil removal. Additionally, a reference grassland site close by and a site on the dam are included in the measurements. GHG measurements are carried out every two to four weeks on a campaign basis using manual chambers and a portable analyser for both CH4 and CO2. Here we present GHG balances of the first two years after planting the paludicultures.Despite of imperfect water management during the first year after planting, all paludiculture species were both a net CO2 and GHG sink regardless the topsoil treatment. During this period, fluctuating water levels resulted in low CH4 emissions while N2O emissions were of greater importance regarding the GHG balance. Due to more stable water levels in the second year, higher methane emissions are expected. Carbon export by the first biomass harvest will also be taken into account.

For two years, we quantified the exchange of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) at two different large-scale Sphagnum farming sites. At both, peat extraction left a shallow layer of highly decomposed peat and low hydraulic conductivities. One site was characterized by preceding multi-annual inundation and irrigated by ditches, while the other one was inoculated directly after peat extraction and irrigated by ditches and drip irrigation. Further, GHG emissions from an irrigation polder and the effect of harvesting Sphagnum donor material at a near-natural reference site were determined. GHG mitigation potentials lag behind the results of less decomposed sites, although our results were also affected by the extraordinary hot and dry summer 2018. CO2 exchanges ranged between -0.6 and 2.2 t CO2-C ha−1 y−1 and were mainly influenced by low water table depths. CH4 emissions were low with the exception of plots with higher Eriophorum covers, while fluctuating water tables and poorly developing plant covers led to considerable N2O emissions at the ditch irrigation site. The removal of the upper vegetation at the near-natural site resulted in increased CH4 emissions and, on average, lowered CO2 emissions. Overall, best plant growth and lowest GHG emissions were measured at the previously inundated site. At the other site, drip irrigation provided more favourable conditions than ditch irrigation. The size of the area needed for water management (ditches, polders) strongly affected the areal GHG balances. We conclude that Sphagnum farming on highly decomposed peat is possible but requires elaborate water management.

Background: There is considerable uncertainty about the actual size of the global soil organiccarbon (SOC) pool and its spatial distribution due to insufficient and heterogeneous data cover-age. Aims: We aimed to assess the size of the German agricultural SOC stock and develop a stratification approach that could be used in national greenhouse gas reporting. Methods: Soils from a total of 3104 sites, comprising 2234 croplands, 820 permanent grasslands and 50 sites with permanent crops (vineyards, orchards) were sampled in a grid of 8 x 8 km to a depth of 100 cm in fixed depth increments. In addition, a decade of management data was recorded in a questionnaire completed by farmers. Two different approaches were used to stratify cropland and grassland mineral soils and derive homogeneous groups: stratification via soil type (pedogenesis) and via SOC-relevant soil properties. Results: A total of 146 soils were identified as organic soils, which stored by far the highest average SOC stock of528–201 Mg ha–1 in 0–100 cm depth. Of the mineral soils, croplands and permanent crops stored on average 61–25 and 62–25 Mg ha–1 in 0–30 cm (topsoil) and 35–30 and 44–28 Mg ha–1 in 30–100 cm (subsoil), while permanent grasslands stored significantly more SOC (88–32 and 47–50 Mg ha–1 in topsoil and subsoil). Overall, topsoils stored 67–14% and subsoils 33–14% of total SOC stocks. Soil C:N ratio, clay content and ground-water level were major factors that explained the spatial variability of SOC stocks in mineral soils. Accordingly, Podzols, Gleysols and Vertisols were found to have the highest SOC stocks. Conclusions: Stratification via soil properties yielded the most comparable cropland and grassland strata and is thus preferable for estimating land-use change effects, e.g., for greenhouse gas inventories. In total, 2.5 Pg C are stored in the upper 100 cm of German agricultural soils, making them the largest organic carbon pool in terrestrial ecosystems of Germany. This bares a large responsibility for the agricultural sector and society as a whole to maintain and, if possible, enhance this pool.

Natural raised temperate bogs are characterized by Sphagnum-dominated vegetation, facing increasing threats by vascular plant encroachment in the recent past. The VESBO-project is investigating the influence of this shift in vegetation composition on the water and carbon cycle in a rewetted bog in north-west Germany. Two study sites were established in close proximity on the same former peat extraction area, one showing near-natural Sphagnum-dominated vegetation and one exhibiting an increasingly dense birch stand and Eriophorum vaginatum cover, low in Sphagnum density.As methane (CH4) emissions from rewetted bogs are of strong interest regarding the greenhouse gas balance, one focus of our project is to disentangle how vascular plant encroachment is influencing total ecosystem CH4 emissions and to quantify the contribution of different plant functional types, especially in relation to the different peat water levels on both sites. Besides this, little is known about the diurnal cycle in CH4 emissions and which bio-meteorological parameters are its drivers.We used closed chambers in combination with the Picarro GasScouter G4301 to measure methane fluxes on-site. The measurements were performed every 3-4 weeks over one year and on multiple plots equipped with different chamber designs: soil chambers which were located either on hummocks (Eriophorum-dominated) or hollows (Sphagnum-dominated) and branch/leaf chambers for Betula-branches and Eriophorum-leaves. In order to more precisely quantify the influence of birch roots on the gas exchange, the soil plots were further divided into plots located in close proximity and separated from birch trees.The campaigns included transparent and opaque measurements over the course of the day to cover both the diurnal and annual ranges of soil temperature and photosynthetic active radiation, as well as to capture net ecosystem exchange and respiration.We will show the preliminary results of the methane fluxes from September 2020 to October 2021. They indicate that the methane fluxes increased strongly with soil temperature and water level. Further analysis will relate the CH4 emissions to plant functional groups and flux-driving parameters.In conclusion, the available data will provide valuable information on the contribution and the drivers of methane emissions to the greenhouse gas emissions in bogs, which is particularly important for planning and reporting of rewetting and restoration activities in peatlands.

Global change is expected to have adverse effects on the carbon (C) storage function of Sphagnum peat bogs. However, the consequences of the interaction of different aspects of global change for peatland C dynamics have not been systematically assessed yet.The aim of this study is to examine how interactions between rising air temperatures, declining ground water levels (WL) and nitrogen eutrophication affect C exchange of both natural and degraded Sphagnum bog ecosystems.A greenhouse experiment with Sphagnum papillosum planted on packed bog peat soil columns has been carried out in the vegetation period of 2021. Three different mean annual air temperature and WL treatments (ambient, + 1 °C, + 3 °C and 0 cm, 7 cm,15 cm below peat surface, respectively), three different amounts of nitrogen (N) input (5, 25 and 50 kg N/(ha*a)) and two different types of peat substrate (slightly and highly decomposed) were combined in a fully factorial design.Three measurement campaigns with manual chambers were conducted over the course of the vegetation period to quantify CO2 and CH4 fluxes for each treatment combination. Soil temperature was measured continuously as explanatory variable. During each measurement campaign, three or more measurements using opaque chambers were conducted per soil column to assess the variation of ecosystem respiration (Reco) and CH4 exchange over the range of soil temperatures. To quantify the impact of the imposed environmental treatments on moss C-uptake capacity (GPPsat), one measurement at an irradiation close to moss light saturation point (ca. 600-800 µmol/(s*m2); determined prior to the experiment) was conducted per column using a chamber illuminated by a LED grow light. Directly before each of these measurements, the mosses were light adapted to this irradiation intensity for 15 minutes.Linear flux calculation and several steps of automated and manual filtering were applied to the data and a model describing the relationship between soil temperature and Reco was fitted.Preliminary results indicate that GPPsat was affected negatively by higher air temperatures in summer, but positively in autumn. A negative response to a drop in WL was observed only after several weeks.Reco increased in columns with lower WL and at higher temperatures and showed a fast response to treatment variation (< two weeks). The effect of the lowered WL seemed to increase at higher temperatures.WL strongly affected CH4 fluxes with highest emissions observed in high WL treatments. In contrast, there seemed to be a net uptake of CH4 in low temperature and low WL columns. No effect of diurnal air or soil temperature variations on CH4 exchange could be observed, but emissions were higher in summer than in autumn. No short term effect of N eutrophication on any flux component could be detected.The results of the study will provide insights into the effects of projected future environmental changes on Sphagnum bog peatlands. The findings can be used to optimize the management of natural, rewetted or commercially used Sphagnum peatlands with regard to the reduction of greenhouse gas emissions.

Soil hydraulic properties are frequently obtained from evaporation experiments. Different methods exist to infer soil hydraulic properties from these experiments. Commonly proposed is the ‘direct method’ (or ‘Simplified Evaporation Method’) by which soil hydraulic properties are calculated analytically. An alternative is given by inverse parameter optimization (‘inverse method’). Although soil hydraulic properties are frequently estimated by the ‘direct method’, only very few studies have focused on the question how accurate derived parameters can reproduce laboratory measurements. This can be achieved by modeling the water flow with a processed based numerical forward model, e.g. with HYDRUS-1D. Here, we applied the ‘direct method’ and ‘inverse method’ to a large dataset of evaporation experiments on 431 organic soil samples. The derived soil hydraulic parameters were used in HYDRUS-1D simulations and their performance in reproducing measured states and fluxes was compared. As an additional analysis, we tested how water contents at the permanent wilting point can aid stabilizing parameter estimation by adding information on water retention in the dry range. For all methods, soil hydraulic properties were determined with the soil hydraulic functions of van Genuchten-Mualem and Peters-Durner-Iden. The results show that parameters derived with the ‘direct method’ do often not well reproduce measured pressure heads over the complete pressure head range of the evaporation experiments when they were used for HYDRUS-1D simulations (mean objective function value 0.05831). Parameters derived by the ‘inverse method’ provided a better performance in the HYDRUS-1D simulations if the full pressure head range of the evaporation experiments was considered (mean objective function value 0.00099), but a weaker performance when focusing on wet conditions (pressure heads >−100 cm). Constraining the ‘inverse method’ by additional soil moisture measurements at permanent wilting point improved the prediction of the soil moisture at dry conditions. For the full pressure head range, the hydraulic functions of Peters-Durner-Iden performed better than the ones of van Genuchten-Mualem.

In wetlands, the water budget is traditionally quantified by measuring the hydrologic components including precipitation, evapotranspiration and surface water-groundwater inflows and outflows. However, the reliability of measurements is often questioned due to the difficulty of rigorously monitoring all components of the water budget. Quantifying the rainfall event to water table response ratio is an alternative approach with minimal need for data commonly collected in peatland studies. However, the method has been used only in a limited number of biophysical settings including different microforms, hydroclimatic and hydrogeological settings. The objectives of this study are to quantify the reactivity of the water table to precipitation for different pristine peatlands located in different hydroclimatic conditions and to provide quantitative assessments of water storage of as many peatlands as possible. To do so, site-specific hourly water table and precipitation measurements was collected from northern peatlands worldwide. In total, data from more than 30 sites were retrieved from 8 research groups. For all peatlands, water-table depths varied between 80 cm below the peat surface and 10 cm above the peat surface. The results highlight that the hydrology of all peatlands is characterized by a shift from an environment that can store water to an environment that contributes to rapid outflow, and this is a uniform feature across sites. However, for peatlands with the lowest water storage capacities, this shift occurs during relatively moderate rainfall events (40 mm) or successive small rainfall events. Blanket peat bog best embodied this type of hydrological response. For peatlands with the highest water storage capacity, this shift occurs following multiple moderate to large precipitation events (40 mm – 80 mm) and it is strongly enhanced by the shift from high to low evaporative periods. The peatlands with the highest storage capacity are raised bogs with deep water-table. These conditions are best observed in peatlands located in geographical settings with high evaporation rates. Among all the peatlands, maximum water storage capacity for given rainfall events was equal to ≈150 mm. These analyses also confirm that the water table rise caused by precipitation events contain sufficient information to constrain water storage variations around monitored wells peatlands for a wide array of biophysical settings.

The vast majority of peatlands in the North German Plain are cultivated as grassland. Intensive drainage measures are a prerequisite for conventional agricultural use of peatlands, but this practice causes high emissions of greenhouse gases (GHG), mainly carbon dioxide (CO2). Thus, raising the water levels is necessary to reduce or stop CO2 emissions. Water management options such as submerged drains (SD) and ditch blocking (DB) are discussed as a potential compromise between maintaining the trafficability for intensive grassland use and reducing the GHG emissions. Furthermore, grassland renewal is regularly practiced to improve the fodder quality for dairy farming; however, this might cause additional release of GHGs, especially nitrous oxide (N2O). Here, we present results of a four-year study on the GHG emissions from an intensively used grassland on fen peat equipped with SD and DB. Additionally, the effect of grassland renewal by shallow ploughing and direct sowing was evaluated.The target groundwater levels were set to -0.30 m below ground. In the first year, the water management system was optimized. In the following years, mean annual water levels at the parcels with SD were -0.23 m and at the parcels with DB -0.37 m. The groundwater level at the SD parcels was around 0.18 m higher than at the conventionally drained control parcels. Thus, water management by SD enabled us to even surpass the target water levels. However, year two and three of the study were dryer than usual, the differences between the SD parcels and the control parcels are expected to be lower in wet years. DB, in contrast, raised the water levels only marginally.During the first three years, control parcels with ditch drainage emitted 27-49 t CO2-eq. ha-1 a-1. This is within the typical range of emissions from grasslands on fen peat in Germany. On average, the parcels with SD showed slightly lower emissions than the drained control parcels, but these were highly variable (16-60 t CO2-eq. ha-1 a-1). Due to similar groundwater levels the emissions from the parcel with DB (23-43 t CO2-eq. ha-1 a-1) were comparable to the drained control parcels. Reasons for the high CO2 emissions despite increased groundwater levels by SD remain so far unclear. Both types of grassland renewal lead to higher N2O emissions during the first year after renewal. Afterwards, effects became ambiguous. Results from the fourth measurement year (2020) will be presented as well. So far, the data seems to support the results of the previous years.

Peatland restoration projects are important to mitigate climate change, loss of biodiversity and sustain and develop ecosystem services of peatlands. National and global strategies which address the effects of peatlands on climate change and nature conservation as well as the social and economic compatibility of peatland restoration projects are needed. The regional focus of these strategies is crucial for prospective restoration projects as well as for the measurements used to identify regions with high potential for realisation of peatland restoration along with sufficient impact on GHG reduction and nature conservation.Therefore, we aim to identify regions in Germany in which the potential of realisation of restoration projects is high. Further, we identify important restrictions at regional scale which hinder potential peatland restoration projects.We assembled a set of regional indicators and analysed the available GIS-data on the nationwide scale of Germany. Indicators comprise natural (e.g. precipitation surplus), legislative (e.g. protected and priority areas) and economic (e.g. land use, marginal return) conditions. Each identified indicator was categorised based on its relevance for the feasibility of implementing peatland restoration projects. Using landscape structure analyses, regions throughout Germany with good prospective for the realisation of peatland restoration projects were identified. These highlighted regions show high potential for optimising and/ or maximising the ecosystem services of peatlands. To characterise the region based on the indicators used, short profiles were created for each resulting region. We recommend to take the analysing method and these highlighted regions into account when developing nationwide strategies for peatland management in Germany.

Drainage is necessary for conventional agriculture on peatlands, but this practice causes high emissions of the greenhouse gases (GHG) carbon dioxide and nitrous oxide. Paludiculture is an option to mitigate these adverse environmental effects while maintaining productive land use. Whereas the GHG exchange of paludiculture on rewetted bog peat, i.e. Sphagnum farming, is relatively well examined, data on GHG emissions from fen paludicultures is still very scarce. As typical fen paludiculture species are all aerenchymous plants, the release of methane is of particular interest when optimising the GHG balance of such systems. Topsoil removal is, on the one hand, an option to reduce methane emissions as well as phosphorus release upon rewetting, but on the other hand, nutrient-rich topsoils might foster biomass growth.In this project, Typha angustifolia, Typha latifolia, and Phragmites australis are grown at a fen peatland formerly used as grassland. Water levels will be kept at the surface or slightly above it. In parts of the newly created polder, the topsoil will be removed. To be able to separate the effects of topsoil removal and water level, four smaller sub-polders will be installed. Greenhouse gas exchange will be measured with closed manual chambers for all three species with and without topsoil removal as well as at a reference grassland site close by.

Peat soils shrink and become very hydrophobic when dried. Both properties may cause inaccuracies when applying laboratory methods for soil hydraulic properties that have been developed and tested for mineral soils. This study aimed to compare different methods for the determination of the water retention of peat soils near permanent wilting point (pF 3.5 to 4.2). Three common methods were tested: two pressure apparatus (ceramic plate [Soilmoisture] vs. membrane [eijkelkamp]) and a dew-point potentiameter (WP4C, Decagon Devices, Inc.), which is based on the equilibrium of soil water potential with air humidity. We used both field-moist peat samples and samples that had been rewetted after oven-drying. We found that there was no systematic difference between the two pressure apparatus. Low moisture variability among replicates and dew-point potentiameter measurements that indicated a drainage to pF 4.2 support the use of pressure apparatus for the determination of water retention near permanent wilting point. Despite a rewetting time of 2 wk including periodic mixing, rewetted oven-dried samples showed lower soil moistures at pF 3.5 and 4.2 than field-moist ones. This severe and long-lasting hysteresis effect was strongest for less decomposed peat samples. Thus, field-moist samples should be used. This makes the classical dew-point potentiameter measurement protocol, which is based on defined water additions to oven-dried samples, unsuitable for peat samples.

Soil needs to be dried in order to determine water content, soil organic carbon content (SOC) and total nitrogen content (N). Water content is commonly measured using standard methods that involve drying temperatures of 105–110 °C. Recommended drying temperatures differ for the determination of SOC and N. However, at moderate drying temperatures, microbial activity might lead to organic matter mineralisation and nitrification, and thus to an underestimation of SOC and N. Furthermore, low drying temperatures might not dewater soils sufficiently to correctly determine water content or bulk density. Chemical processes such as thermal decomposition and volatilisation might occur at higher temperatures. This raises the question of whether the same sample can be used to determine water content, SOC and N. Further, the effect of drying, especially at different temperatures, on basal respiration of peat soils determined by incubation experiments is so far unknown. Effects of drying temperature might be especially severe for peat soils, which have high SOC and water contents. This study systematically evaluated the effect of different drying temperatures (20, 40, 60, 80 and 105 °C) on the determination of mass loss (proxy for water content), SOC and N over a wide range of 15 different peat soils comprising amorphous, Sphagnum and sedge peat substrate. The investigated peat soils had SOC contents ranging from approximately 16.8–52.5% with different degrees of decomposition. They were thus separated into two ‘peat groups’ (amorphous and weakly decomposed). In a subsequent investigation, an incubation experiment was carried out on a subset of five peat soils to investigate the pre-treatment effect of different drying temperatures on basal respiration. The results showed that amorphous samples should be dried at 105 °C to determine water content. The weakly decomposed peat soils in the study had reliable water contents for drying temperatures above 60 °C. For temperatures below 80 °C, the determined SOC and N were biased by residual water. This could be corrected for weakly decomposed samples, but for amorphous samples only for drying temperatures ≥60 °C. Thus, mineralisation of soil organic matter is likely to take place at lower drying temperatures which are not recommendable especially for amorphous peat prone to high mineralisation rates. This is supported by the results of the incubation experiment: The effect of peat type (amorphous topsoil vs. weakly decomposed subsoil) was greater than the effect of different drying temperatures, which nonetheless affected respiration rates. The differences between all five soils were consistent, irrespective of the drying temperature. Thus, incubation experiments might be possible using peat dried at moderate temperatures. © 2021 The Authors

Organic soils are the most important source of dissolved organic carbon (DOC) in surface water. To date, most studies have focused on natural and re-wetted peatlands, but in Central Europe a large proportion of organic soils are drained and under agricultural use. Furthermore, measures such as deep ploughing or sand addition have been conducted to improve trafficability and have resulted in topsoil horizons consisting of a peat-sand mixture. Very little is known about DOC losses from such soils. Moreover, peat soils frequently feature both mobile zones, characterised by active water and solute transport, and immobile zones, which exchange solutes with the mobile zone by diffusion. Surprisingly, however, the effects of this dual porosity on DOC transport have not yet been explored. This study investigated the physicochemical controls on DOC concentrations in a peat-sand mixture by means of a saturated column experiment with undisturbed columns. The soil came from a former bog in northern Germany where peat layers remaining after peat extraction were mixed with the underlying mineral soil by ploughing. Three pumping rates and two levels of electrical conductivity (EC) were applied. The transport properties of the soil were obtained by analysing breakthrough curves of potassium bromide using the transport model STANMOD, which is based on the two-region non-equilibrium concept. The results of the column study were compared to DOC concentrations measured bi-weekly for two years at the field site from where the columns were taken. Despite a similar texture and soil organic carbon (SOC) content, the fraction of the mobile zone in the columns varied between 51% and 100% of total porosity. Thus even heavily degraded organic soils mixed with sand still showed a dual porosity comparable to degraded peat soils. Percolating the columns with the high EC solution caused low pH values, probably due to ion exchange and cation bridging. The combination of high EC and low pH greatly decreased DOC concentrations at the outlet of the columns. DOC concentrations decreased and fluxes increased as the pumping rates increased. Taking pore water velocity in the mobile zone into account could help to explain the differences between the columns. Overall, transport of DOC did not seem to be limited by production of DOC, but by rate-limited exchange processes. In contrast to the column experiment, field concentrations of DOC were much higher and were not related to pH, but increased with higher electrical conductivity. These higher concentrations could be explained by low pore water velocities and the slightly higher SOC content in the field. This first experiment on DOC transport in peat-sand mixtures taking the dual-porosity nature of organic soils into account clearly demonstrated the importance of pore water velocity and thus the residence time for DOC concentrations. While hydrochemical conditions are frequently addressed in laboratory studies, there is a need for improved understanding of their interaction with hydrology and soil-physical properties, especially when attempting to interpret DOC data on different spatial and temporal scales.

This study was conducted in the course of a fen rewetting project in NE Germany aiming to restore a heavily drained spring-percolation mire used as pasture land for more than 100 years. Shallow top soil removal (TSR) up to 40 cm was applied to remove the upper degraded peat layer in order to eliminate accumulated nutrients and unwanted seed banks as well as generating material for infilling drain ditches and building dams. This measure has well known positive effects on species development, but very little was known about the phosphorus (P) status in the newly exposed peat soils and porewater. Therefore, we investigated (i) the P mobilisation potential of surface peat soils, (ii) net P release rates in intact soil cores with different degree of peat decomposition, and (iii) P concentrations in porewater of rewetted fen areas with TSR compared to areas without removal and refilled drain ditches. We highlighted that TSR strongly reduced the P mobilisation potential and thereby also the concentration of dissolved P in the porewater at the peat surface. Furthermore, we found low net P release rates close to 0 mg P m−2 d−1 (median, n = 9) in the cut-over areas with less degraded peat similar to those documented for natural fens. Despite of high P concentrations up to 2.6 mg L−1 in rewetted areas without TSR (about 50% of total peatland area) there was no evidence of elevated P export to other low-nutrient areas of the fen or in a close-by lake due to high P retention capacity of the iron-rich degraded peat (molar Fe:P ratios >10). It can be concluded that TSR is a suitable measure to recover nutrient poor conditions in rewetted fens in a relatively short timeframe instead of decades to centuries compared to rewetting measures without TSR. This measure is highly recommended if degraded peatlands are characterised by a low P retention capacity or low molar Fe/P ratios in degraded peat (

During the last century, drainage turned the majority of the bogs and fens in Germany into productive agricultural land, causing substantial emissions of greenhouse gases (GHG). The project ‘SWAMPS’ focuses both on maintaining the trafficability for conventional intensive grassland use and on the reduction of GHG emissions by managing the groundwater level by submerged drains and blocked ditches. Here, we aim to evaluate the interaction of water table management and a severe mice infestation on the emissions of carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4).We set up two field sites on both fen and bog peat in North-Western Germany. Submerged drains were installed at a distance of 4 to 5 m and with a target ditch level of 45 to 50 cm below mean soil surface. On the parcels with blocked ditches, the target ditch level is adjusted at 30 to 35 cm. The control parcels are drained by ditches and/or drainage pipes. Since 2017, diurnal CO2 flux measurement campaigns have been realised once every three to four weeks with transparent and opaque chambers and a portable gas analyser. CH4 and N2O samples are taken biweekly and additionally more frequently after fertilizer application.However, our experimental design was disrupted when, after an extremely dry summer and a dry and mild winter, the mice population grew strongly in 2019. We monitored both the number of mouse holes and the damage by mice. At the bog site, nearly no grass was left at the control site at the end of the year, while at the fen site, less, but still significant damage was observed. In this year, this was typical for the situation in North-Western Germany, where around 150,000 ha of grassland were severely damaged by mice. The sites with water table management were less effected by mice, but as food became scarce, they started to move into these wetter areas as well.Despite higher water levels, CO2 emissions in 2019 were partially higher than in previous years, especially at those sites affected by mice. With this presentation, we would like to discuss the effects of mice damage on soil respiration and on possibilities to disentangle water management effects from this (experimental and agricultural) calamity.

Boreal and temperate peatlands cover less than 3% of the earth's surface but store nearly 30% of the terrestrial carbon. Natural raised bogs are characterized by a Sphagnum-moss dominated vegetation cover. The majority of bogs has been used for peat extraction or agriculture for centuries, but in the last decades the focus on restoration to protect climate and biodiversity was increasing. This includes the re-establishment of quasi-natural hydrological conditions as well as of ecosystem-typical vegetation.Recently, a change in species composition of restored bogs from Sphagnum-dominated bryophyte communities to multi-layered tree and graminoid vegetation was observed. Current investigations report contradictory effects for the impact on throughfall, evapotranspiration (ET), gross primary productivity, respiration, net CO2 balance (NEE) as well as soil carbon sink strength. A final conclusion with respect to altered ecosystem functioning through changing conditions for vegetation development in the light of climate change is missing.The VESBO project aims at the mechanistic analysis of ET, NEE and soil carbon sink strength of a restored, atlantic-temperate raised bog during vascular plant encroachment. The two study areas are former peat extraction sites, with one being Sphagnum-dominated while the other one has been populated by Betula pubescens during the last years. Focus will be placed on the partitioning of total ecosystem ET and NEE fluxes by Eddy Covariance and chamber measurements in situ into bryophyte, graminoid and tree contributions. Results are used to parameterize a modern soil-vegetation-atmosphere-transport model able to simulate bryophyte and vascular plant layers on peat soil. The model, jointly with the empirical data, is used to quantify seasonal changes in plant functional group flux contributions depending on altered environmental conditions. The holistic process understanding is of high relevance for the NEE estimation of restored bog ecosystems under changing climatic conditions and vegetation compositions. The knowledge about different interactions of plant functional groups with mass and energy fluxes of the bog ecosystem will be valorised by the assessment of restoration and emission mitigation measures throughout Europe.

Intact peatland ecosystems are efficient sinks of atmospheric carbon dioxide (CO2). Disturbance, e.g. by drainage to transform peatlands into agricultural land, causes high emissions of the greenhouse gases (GHG) CO2 and nitrous oxide (N2O). Our Project “Gnarrenburger Moor” focuses on the evaluation of the effects of submerged drains on GHG emissions and dissolved solute losses from bog peat under intensive grassland management. Due to installation of the water management system, grassland renewal was necessary at one of our two experimental grassland sites, both being located in Northwest Germany and subjected to similar management in the past. Here, we report on the initial year of the project, which was dominated by the impact of grassland renewal as target groundwater levels were only reached after several months.The reference site, representing common region-specific grassland management on peat, is deeply drained by tile drains, while submerged drains were installed at the project site to achieve constantly high water levels of 30 to 40 cm below ground. Both sites are equipped with eddy covariance towers for CO2 measurements and 6 plots for manually measuring N2O and methane (CH4) with closed chambers. Water samples for the analysis of phosphorus and nitrogen species are collected from ditches, tile drains and suction plates at 15, 30 and 60 cm depths. Measurements started in March 2019, i.e. approximately one month before the grassland renewal. The mechanical renewal involved mulching of the old grass sward and grading the surface of the site. Due to very dry conditions, growth of grass species was poor and the site was mulched and re-seeded again in July 2019. Target groundwater levels were reached in September 2019.During the initial year of our study, grassland renewal substantially dominated the response of the system. From April to November, net ecosystem exchange of the project site was approximately 400 g C m-2 higher than that of the reference site. When including carbon input and output from organic fertilizer and harvest on the reference site, the project site is still by far (around 140 g C m-2) a larger source. When the bare soil and raising groundwater levels coincided between July and September, N2O fluxes and dissolved nitrogen and phosphorus concentrations drastically increased at the project site. N2O fluxes were partially 100 times higher than at the reference site. The next years will show whether an operational water management system and a fully developed grass sward will turn the project site with submerged drains into a smaller source of GHGs than the reference site.

In this study, time series over 14 years of climate, stream flow, land management, nitrate-nitrogen (NO3--N) concentrations and losses were analyzed to identify potential drivers for temporal trends at two tile-drained catchments under cropland use in northeastern Germany. Mean annual NO3--N concentrations were 9.7 (drainage plot) and 6.8 mg l-1 (ditch catchment), while mean annual NO3--N losses amounted to 22 and 20 kg ha-1, respectively. Results indicated decreasing trends for discharge, NO3--N concentrations and losses, and N surpluses at both the drainage plot and the ditch catchment scale. However, a significant downward trend was only detected for flow-weighted mean annual NO3--N concentrations of the ditch water. A significant positive relationship between annual discharge and mean annual NO3--N concentrations of the ditch underlines the importance of the hydrologic conditions on the NO3--N concentrations. No direct relationships were found between NO3--N concentrations and N surpluses. We conclude that the decreasing NO3--N concentrations could be primarily attributed to decreasing discharge rates. The possible impact of reduced N surpluses was overridden by the hydrologic conditions in the catchment. The statistically significant downward trend of flow-weighted mean annual NO3--N concentrations in the ditch water suggests, however, a positive effect of reduced N surpluses on stream water quality. Our analysis has further shown that effects of land management aiming at reducing N surpluses might only become visible with a delay of years or even decades.

Peat soils offer numerous functions from the global to the local scale: they constitute the biggest terrestrial carbon storage, form important nutrient filters and provide hydrological buffer capacities. They represent an important share of soils suitable for agriculture in temperate and boreal Europe, pressurized by increasing demands for production. Cultivated peat soils, however, show strong alterations of soil physical and chemical properties, accompanied by extreme mineralization rates, land surface subsidence, soil and water quality deterioration and thus crop failure.The aim of this study is to report soil physical and chemical properties of fen peat soils under typical agricultural management in six European countries in contrast to the technical and economical assessment of the managing farmers. We conducted standardized soil mapping, soil physical/chemical analysis, ground water table monitoring and farm business surveys across 46 sites in Germany, The Netherlands, Denmark, Estonia, Finland and Sweden.The results showed a strong impact of agricultural management on fen peat soil properties across Europe. Peat depth ranged from -0.2 to -4.7 m below ground (on average -1.1 m). The majority of sites were deeply drained, showing annual mean soil water levels of -0.6 m with summer draw downs to -0.93 m. Soil profiles exhibited strong gradients of humification with soil depth, showing fully degraded topsoils (von Post 10 down to -0.2 m), reaching weaker degradation (Bulk density, porosity and available field capacity consistently reflected the degradation gradient, whereas hydraulic conductivity and penetration resistance showed no trend. Soil organic carbon was strongly reduced in the topsoil horizons (25% on average) and reached only in horizons below -0.6 m values of on average 45%. Total nitrogen and pH values showed no clear depth gradient. The soil carbon stock ranged from 100 to 500 t/ha for the unsaturated horizons and increases up to 2000 t/ha in the permanently saturated subsoil. The economic relevance of organic soils varied greatly across countries and although farms were settled in organic soil rich regions, 72% of farms had an average share of peat soil of only 23%. The main reasons farmers attributed yield losses on organic soils to were (by importance), high ground water levels, unsuitable water management, and ponding/hydrophobic soils independent of the land use, strongly contrasting the measured water levels. Overall, in the perception of interviewed farmers, the economic success of land use on organic soils in the future will be mostly depended on financial shortcomings due to increasing water logging and inevitably increasing drainage costs agreed on by 65% and 69% of interviewed farmers.

Drained organic soils are large sources of anthropogenic greenhouse gases (GHG) in many European and Asian countries. Therefore, these soils urgently need to be considered and adequately accounted for when attempting to decrease emissions from the Agriculture and Land Use, Land Use Change and Forestry (LULUCF) sectors. Here, we describe the methodology, data and results of the German approach for measurement, reporting and verification (MRV) of anthropogenic GHG emissions from drained organic soils and outline ways forward towards tracking drainage and rewetting. The methodology was developed for and is currently applied in the German GHG inventory under the United Nations Framework Convention on Climate Change (UNFCCC) and the Kyoto Protocol. Spatial activity data comprise high resolution maps of land-use, type of organic soil and mean annual water table (WT). The WT map was derived by a boosted regression trees model from data of more than 1000 dipwells. Emissions of carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4) were synthesized from a unique national data set comprising more than 250 annual GHG balances from 118 sites in most land-use categories and types of organic soils. Measurements were performed with harmonized protocols using manual chambers. Non-linear response functions describe the dependency of CO2 and CH4 fluxes on mean annual WT, stratified by land-use where appropriate. Modelling results were aggregated into “implied emission factors” for each land-use category, taking into account the uncertainty of the response functions, the frequency distribution of the WT within each land-use category and further GHG sources such as dissolved organic carbon or CH4 emissions from ditches. IPCC default emission factors were used for these minor GHG sources. In future, response functions could be applied directly when appropriate WT data is available. As no functional relationship was found for N2O emissions, emission factors were calculated as the mean observed flux per land-use category. In Germany, drained organic soils emit more than 55 million tons of GHGs per year, of which 91% are CO2. This is equivalent to around 6.6% of the national GHG emissions in 2014. Thus, they are the largest GHG source from agriculture and LULUCF. The described methodology is applicable on the project scale as well as in other countries where similar data are collected.

Drained peatlands are hotspots of carbon dioxide (CO2) emissions from agricultural soils. As a consequence of both drainage-induced mineralisation and anthropogenic mixing with mineral soils, large areas of former peatlands under agricultural use underwent a secondary transformation of the peat (e.g. formation of aggregates). These soils show contents of soil organic carbon (SOC) at the boundary between mineral and organic soils. However, the carbon (C) dynamics of such soils have rarely been studied so far. The aim of the present study was to evaluate the vulnerability of soil organic matter (SOM) to decomposition over the whole range of peat-derived soils under agriculture including very carbon rich mineral soils (76–526 g kg−1 SOC). A total of 62 soil samples covering a broad range of soil and site characteristics were selected from the sample set of the German Agricultural Soil Inventory. Potential CO2 production was measured by aerobic incubation. Fen and bog peat samples were grouped into disturbance classes according to their soil properties. Specific basal respiration rates (SBR), i.e. CO2 fluxes per unit SOC, showed the highest values for the most disturbed samples for both fen peat (13.9 ± 6.0 μg CO2-C g SOC−1 h−1) and bog peat (10.9 ± 4.7 μg CO2-C g SOC−1 h−1). Respiration rates of bog peat increased more strongly with an increasing degree of disturbance than those of fen peat. Perhaps counterintuitively, SOM vulnerability to decomposition thus increased with an increasing degree of disturbance and a decreasing SOC content, indicating positive feedback mechanisms as soon as peat soils are disturbed by drainage. Furthermore, the variability of the SBR increased drastically with increasing degree of disturbance. The turnover of SOM in less disturbed peat samples tended to be higher in samples with higher nitrogen (N) content, higher pH value and lower C:N ratio, while plant-available phosphorus was important for the mineralisation of more severely disturbed peat. However, clear correlations between a single soil property and SBR could not be identified. The high potential of CO2 emissions from organic soils with a low SOC content implies that mixing organic soil with mineral soil does not seem to be a promising option for mitigating greenhouse emissions.

The tracking of land use since 1990 presents a major challenge in greenhouse gas (GHG) reporting under the United Nations Framework Convention on Climate Change (UNFCCC) and the Kyoto Protocol because there is often limited availability of data, especially for the base year of 1990. There is even less land management and soil moisture data, which are needed to track climate change mitigation activities since soil moisture is one of the main drivers of GHG emissions of organic soils. Information is also needed for the reporting of land-based activities such as grazing land management or wetland drainage and rewetting of organic soils. Different spatial and thematic resolutions of land-use data produce inconsistent time series with a strong overestimation of land-use change (LUC) if not adequately accounted for. Our aim was to create a consistent time series of land use since 1990 that is in line with GHG reporting under the UNFCCC and the Kyoto Protocol by combining official cadastral data with colour-infrared aerial photography used for biodiversity monitoring in six federal states in northern and eastern Germany. We developed a generic hierarchical classification by land use, management and drainage status, and a translation key for data harmonisation into a consistent time series. This time series enabled the quantification of LUC on organic soils between 1992 and 2013 in a spatially explicit manner. Furthermore we used this time series to develop indicators for changes in land management and drainage to evaluate the success of protection statuses on peatland restoration. The study area encompassed one million hectares, half of which had some type of legal nature protection status. Areas with no protection status tended to become more intensively farmed and drier, while highly protected areas (e.g. Natura 2000) showed the opposite trend. Land-use trends also differed greatly between federal states. In Schleswig-Holstein organic soils tended to become drier during the study period, while in Mecklenburg-Western Pomerania they tended to become wetter overall. The trends and differences in LUC between federal states were linked to German reunification, changes in the European Common Agricultural Policy (CAP) and Germany's Renewable Energy Act (EEG). A large-scale peatland protection programme also had major impact. In conclusion, our study demonstrates how data derived for biodiversity monitoring and other highly detailed land-use data can be used to track changes in land use, management and drainage status in accordance with the reporting requirements under the UNFCCC and the Kyoto Protocol.

The construction of consistent time series of land use presents a key challenge when accounting for elective land use-based activities under the Kyoto Protocol (wetland drainage and rewetting (WDR), cropland management (CM) and grazing land management (GM)), in which current land use-driven greenhouse gas emissions are compared to a reference situation in 1990. This case study is the first to demonstrate the feasibility of using high-resolution land-use proxies from different datasets for Kyoto accounting in a data-rich case study region in Germany. The study region is characterised by organic soils and has been subject to significant nature conservation measures, including land-use changes, reductions in land-use intensity and changes in groundwater table depth. A consistent time series of 20 years of land use with a spatial resolution of 0.01 ha was created from various fine-grained spatial datasets for organic soils in the Dromling nature park by applying a newly developed ⿿translation key⿿. The translation key accounted for systematic differences in legends and thematic resolution. We also tested whether the land-use datasets served as trustworthy proxies for groundwater table depth. Land use in the Dromling nature park became less intensive during the study period of 1992⿿2012. The greatest land-use change (142 ha year ⿿1 , 1.14% year ⿿1 ) occurred between 2000 and 2008. This was in line with management measures undertaken in the nature park. The centre of the nature park became wetter and there was an increase in the share of grassland and more natural vegetation types. The groundwater table correlated with land use and land-use intensity on organic soils in the study area throughout the entire period. Land-use changes were accompanied by altered groundwater tables, except for the conversion from cropland to grassland. Our study indicates that detailed land-use time series can serve as a semi-quantitative proxy for groundwater depth, but that any robust quantitative assessment of water table changes requires in situ data, e.g. from a network of dipwells. Therefore, the combination of land-use and dipwell data provided an accurate basis for estimating GHG emission reductions from drained organic soils since 1990, which is the centre of the Kyoto activity WDR, but also part of afforestation/reforestation (AR) and deforestation (D), forest management (FM), CM and GM. Even the detailed land-use time series on its own would fulfil the requirements for WDR accounting, although with considerable uncertainty about the drainage status of the organic soils. We present the study area of organic soils as a showcase for combining the difficult issues of monitoring changes in land-use intensity as well as in soil wetness, the latter being most relevant for organic soils. The methodology is equally applicable to and relevant for mineral soils.

Accurate and effective determination of soil bulk density (BD) is needed to monitor soil organic C (SOC) stocks and SOC stock changes. However, BD measurements are often lacking in soil inventories and BD is estimated by pedotransfer functions with substantial uncertainty. In a systematic method comparison, we evaluated different methods for BD determination in the field by comparing the performance of MINI (5 cm3) and BIG (250 cm3) sample rings and of three driving hammer probes differing in diameter, material, and extraction method. Bulk density determined with 100-cm3 sample rings was defined as the reference method (REF). All methods were tested at five depth increments in nine subplots at four sites with differing soil texture and SOC content. All methods determined BD in the depth increments with low systematic error (8% for probes and 2% for sample rings). The random error of the probe samples was, on average, 50% higher than that of the ring samples when the cores of the probes were adequately corrected for compaction or stretching. The BD was significantly overestimated (by 2%) when determined with MINI rings, and the variation in BD was not reduced with BIG sample rings rather than the smaller REF sample rings. The performance of the driving hammer technique varied widely among probe types and sites. The sheath probe had the smallest systematic error of all probes tested and is recommended for soil inventories. All methods for estimating BD had smaller errors than pedotransfer functions.

Drainage turns peatlands from natural carbon sinks into hotspots of greenhouse gas (GHG)emissions from soils due to alterations in hydrological and biogeochemical processes. As a consequence of drainage-induced mineralisation and anthropogenic sand addition, large areas of former peatlands under agricultural use have soil organic carbon (SOC)contents at the boundary between mineral and organic soils. Previous research has shown that the variability of GHG emissions increases with anthropogenic disturbance. However, how and whether sand addition affects GHG emissions remains a controversial issue. The aim of this long-term incubation experiment was to assess the influence of hydrological and biogeochemical soil properties on emissions of carbon dioxide (CO 2 ), nitrous oxide (N 2 O)and methane (CH 4 ). Strongly degraded peat with sand addition (peat-sand mixtures)and without sand addition (earthified peat)was systematically compared under different moisture conditions for fen and bog peat. Soil columns originating from both the topsoil and the subsoil of ten different peatlands under grassland use were investigated. Over a period of six months the almost saturated soil columns were drained stepwise via suction to −300 hPa. The CO 2 fluxes were lowest at water-saturated and dry soil moisture conditions, resulting in a parabolic dependence of CO 2 fluxes on the water-filled pore space (WFPS)peaking at 56–92% WFPS. The highest N 2 O fluxes were found at between 73 and 95% WFPS. Maximum CO 2 fluxes were highest from topsoils, ranging from 21 to 77 mg C m −2 h −1 , while the maximum CO 2 fluxes from subsoils ranged from 3 to 14 mg C m −2 h −1 . No systematic influence of peat type or sand addition on GHG emissions was found in topsoils, but CO 2 fluxes from subsoils below peat-sand mixtures were higher than from subsoils below earthified peat. Maximum N 2 O fluxes were highly variable between sites and ranged from 18.5 to 234.9 and from 0.2 to 22.9 μg N m −2 h −1 for topsoils and subsoils, respectively. CH 4 fluxes were negligible even under water-saturated conditions. The highest GHG emissions occurred at a WFPS that relates – under equilibrium conditions – to a water table of 20–60 cm below the surface in the field. High maximum CO 2 and N 2 O fluxes were linked to high densities of plant-available phosphorus and potassium. The results of this study highlight that nutrient status plays a more important role in GHG emissions than peat type or sand addition, and do not support the idea of peat-sand mixtures as a mitigation option for GHG emissions.

Nitrate–nitrogen (NO3–N) as well as dissolved organic carbon (DOC) and nitrogen (DON) concentrations and losses were studied for three and two years, respectively, in a small catchment dominated by a degraded peatland used as intensive grassland. Concentrations in the shallow groundwater were spatially and temporally very variable, with NO3–N being the most dynamic component (7.3 ± 12.5 mg L−1) and ranging from 0 to 79.4 mg L−1. Average NO3–N concentrations of 10.3 ± 5.4 mg L−1 (0 to 25.5 mg L−1) in the ditch draining the catchment and annual NO3–N losses of 19, 35 and 26 kg ha−1 confirmed drained peatlands as an important source of diffuse N pollution. The highest NO3–N losses occurred during the wettest year. Resulting from concentration of 2.4 ± 0.8 mg L−1 (0.7 to 6.2 mg L−1), DON added a further 4.5 to 6.4 kg ha−1 to the N losses and thus formed a relevant (15%) component of the total N losses. Ditch DOC concentrations of 24.9 ± 5.9 mg L−1 (13.1 to 47.7 mg L−1) resulted in DOC losses of 66 kg ha−1 in the wet year of 2006/2007 and 39 kg ha−1 in the dry year of 2007/2008. Ditch DOC concentration were lower than the groundwater DOC concentration of 50.6 ± 15.2 mg L−1 (14.9 to 88.5 mg L−1). Both DOC and N concentrations were governed by hydrological conditions, but NO3–N reacted much faster and clearer on rising discharge rates than DOC, which tended to be higher under drier conditions. In the third year of the study, the superposition of a very wet summer and land use changes from grassland to arable land in a part of the catchment suggests that, under re-wetting conditions with a high groundwater table in summer, NO3–N would diminish quickly, while DOC would remain on a similar level. Further intensification of the land use, on the other hand, would increase N losses to receiving water bodies.

Drained peatlands are hotspots of carbon dioxide (CO2) emissions from agriculture. As a consequence of both drainage-induced mineralisation and anthropogenic mixing with mineral soils, large areas of former peatlands under agricultural use now contain soil organic carbon (SOC) at the boundary between mineral and organic soils and/or underwent a secondary transformation of the peat (e.g. formation of aggregates). However, low carbon organic soils have rarely been studied since previous research has mainly focused on either mineral soils or true peat soils. The aim of the present study was to evaluate the soil organic matter (SOM) vulnerability of the whole range of organic soils including very carbon rich mineral soils (73 g kg−1 −1) and to identify indicators for mineralisation of such anthropogenically disturbed organic soils. Using a large sample pool from the German Agricultural Soil Inventory, 91 soil samples were selected covering a broad range of soil and site characteristics. Fen and bog samples were grouped into disturbance classes according to their pedogenetic features. Potential CO2 production by aerobic incubation was then measured. Specific basal respiration rates (SBR) per unit SOC showed the highest potential emissions for heavily disturbed fen (12.1 ± 5.0 µg CO2-C g SOC−1 h−1) and moderately disturbed bog samples (10.3 ± 5.2 µg CO2-C g SOC−1 h−1). Surprisingly, SOM vulnerability increased with an increasing degree of disturbance and a decreasing SOC content, indicating positive feedback mechanisms as soon as peat soils are disturbed by drainage. Furthermore, with increasing degree of disturbance the variability of the SBR increased drastically, but correlations between soil properties and SBR could not be identified. Respiration rates increased more strongly with an increasing degree of disturbance in bog than in fen samples. Peat properties that positively influenced the turnover of SOM in less disturbed soil samples were mainly pH value and nitrogen content, while phosphorus was important for the mineralisation of increasingly disturbed samples and bog peat in general. Furthermore, a narrow carbon-to-nitrogen ratio correlated strongly with potential emissions. Given the high potential of CO2 emissions from organic soils with a low SOC content, mixing with mineral soil does not seem to be a promising option for decreasing emissions.

© 2018 by the authors. Water table depth (WTD) is one of the key variables controlling many processes in peatlands. Reliable WTD estimates based on remote sensing data would advance peatland research from global-scale climate monitoring to field-scale ecosystem management. Here, we evaluate the relationship between ENVISAT Advanced Synthetic Aperture Radar (ASAR) C-band backscatter (σ°) and in situ observed WTD dynamics over 17 peatlands in Germany covering deeply-drained to natural conditions, excluding peatlands dominated by forest or inundation periods. The results show increasing σ° with shallower WTD (=wetter conditions), with average temporal Pearson correlation coefficients of 0.38 and 0.54 (-) for natural (also including disturbed and rewetted/restored states) and agriculturally-used drained peatlands, respectively. The anomaly correlation further highlights the potential of ASAR backscatter to capture interannual variations with values of 0.33 and 0.43 (-), for natural and drained peatlands. The skill metrics, which are similar to those for evaluations of top soil moisture from C-band over mineral soils, indicate a strong capillary connection between WTD and the 'C-band-sensitive' top 1-2 cm of peat soils, even during dry periods with WTD at around -1 m. Various backscatter processing algorithms were tested without significant differences. The cross-over angle concept for correcting dynamical vegetation effects was tested, but not superior, to constant incidence angle correction. ispartof: REMOTE SENSING vol:10 issue:4 status: published

Summary Nitrate is one of the most important sources of pollution for surface waters in tile-drained agricultural areas. In order to develop appropriate management strategies to reduce nitrate losses, it is crucial to first understand the underlying hydrological processes. In this study, we used Principle Component Analysis (PCA) and Linear Discriminant Analysis (LDA) to analyze 212 discharge events between 2004 and 2011 across three spatial scales (68 events at the collector drain, 72 at the ditch, and 72 at the brook) to identify the controlling factors for hydrograph response characteristics and their influence on nitrate concentration patterns. Our results showed that the 212 hydrological events can be classified into six different types: summer events (28%), snow-dominated events (10%), events controlled by rainfall duration (16%), rainfall totals (8%), dry antecedent conditions (10%), and events controlled by wet antecedent conditions (14%). The relatively large number of unclassified events (15%) demonstrated the difficulty in separating event types due to mutually influencing variables. NO 3 -N concentrations showed a remarkably consistent pattern during the discharge events regardless of event type, with minima at the beginning, increasing concentrations at the rising limb, and maxima around peak discharge. However, the level of NO 3 -N concentrations varied notably among the event types. The highest average NO 3 -N concentrations were found for events controlled by rainfall totals (NO 3 -N = 17.1 mg/l), events controlled by wet antecedent conditions (NO 3 -N = 17.1 mg/l), and snowmelt (NO 3 -N = 15.2 mg/l). Average maximum NO 3 -N concentrations were significantly lower during summer events (NO 3 -N = 10.2 mg/l) and events controlled by dry antecedent conditions (NO 3 -N = 11.7 mg/l). The results have furthermore shown that similar hydrological and biogeochemical processes determine the hydrograph and NO 3 -N response on storm events at various spatial scales. The management of tile-drained agricultural land to reduce NO 3 -N losses should focus explicitly on flow events and, more specifically, active management should preferably be conducted in the winter season for discharge events after snowmelt, after heavy rain storms and when the soil moisture conditions are wet.

© 2018 IEEE. Groundwater table depths (WTD) control peat formation and greenhouse gas emissions from peatlands. Therefore, monitoring WTD is of great interest for restoration and climate change mitigation actions. In shallow groundwater systems such as peatlands, moisture in the topsoil is influenced by and often in hydrostatic equilibrium with WTD. Sentinel-1 provides C-band radar data with high temporal and spatial resolution. Since backscattered microwave radiation is sensitive to the soils’ dielectric permittivity of the first centimeters, radar data provides a promising tool to obtain spatial information not only on soil moisture but also on WTD. We evaluate the correlation between time series of backscatter coefficients σ 0 and WTD measured in situ at > 50 dip wells using a change detection approach. Study area is the Drömling peatland in Germany. Overall, we observe an increase in σ 0 with shallower WTD. For a few sites and time periods σ 0 also decreased during wettest conditions and related partial inundation. Preliminary results from the Drömling peatland show that temporal correlation coefficients vary strongly among sites and reach on average 0.57. Time series indicate that the σ 0 -WTD dependency partly disappears during summer. ispartof: pages:7793-7796 ispartof: International Geoscience and Remote Sensing Symposium (IGARSS) vol:2018-July pages:7793-7796 ispartof: IGARSS location:Valencia date:22 Jul - 27 Jul 2018 status: Published online

Summary Soil moisture is one of the key parameters controlling biogeochemical processes in peat and other organic soils. To understand and accurately model soil moisture dynamics and peatland hydrological functioning in general, knowledge about soil hydraulic properties is crucial. As peat differs in several aspects from mineral soils, the applicability of standard hydraulic functions (e.g. van Genuchten–Mualem model) developed for mineral soils to peat soil moisture dynamics might be questionable. In this study, the hydraulic properties of five types of peat and other organic soils from different German peatlands have been investigated by laboratory evaporation experiments. Soil hydraulic parameters of the commonly-applied van Genuchten–Mualem model and the bimodal model by Durner (1994) were inversely estimated using HYDRUS-1D and global optimization. The objective function included measured pressure heads and cumulative evaporation. The performance of eight model set-ups differing in the degree of complexity and the choice of fitting parameters were evaluated. Depending on the model set-up, botanical origin and degree of peat decomposition, the quality of the model results differed strongly. We show that fitted ‘tortuosity’ parameters τ of the van Genuchten–Mualem model can deviate very much from the default value of 0.5 that is frequently applied to mineral soils. Results indicate a rather small decrease of the hydraulic conductivity with increasing suction compared to mineral soils. Optimizing τ did therefore strongly reduce the model error at dry conditions when high pressure head gradients occurred. As strongly negative pressure heads in the investigated peatlands rarely occur, we also reduced the range of pressure heads in the inversion to a ‘wet range’ from 0 to −200 cm. For the ‘wet range’ model performance was highly dependent on the inclusion of macropores. Here, fitting only the macropore fraction of the bimodal model as immediately drainable additional pore space seems to be a practical approach to account for the macropore effect, as the fitting of the full bimodal model led to only marginal further improvement of model performance. This keeps the number of parameters low and thus provides a model that is more easily managed in pedotransfer function development and practical applications like large scale simulations. Our findings point out first options to improve the performance of the frequently-used simple single-domain models when they are applied to organic soils. We suggest further performance evaluation of these models during wetting periods when they are known to fail to describe preferential and non-equilibrium flow phenomena.

Anthropogenic drainage of peatlands releases additional greenhouse gases to the atmosphere, and dissolved carbon (C) and nutrients to downstream ecosystems. Rewetting drained peatlands offers a possibility to reduce nitrogen (N) and C losses. In this study, we investigate the impact of drainage and rewetting on the cycling of dissolved C and N as well as on dissolved gases, over a period of 1 year and a period of 4 months. We chose four sites within one Atlantic bog complex: a near-natural site, two drained grasslands with different mean groundwater levels and a former peat cutting area rewetted 10 years ago. Our results clearly indicate that long-term drainage has increased the concentrations of dissolved organic carbon (DOC), ammonium, nitrate and dissolved organic nitrogen (DON) compared to the near-natural site. DON and ammonium contributed the most to the total dissolved nitrogen. Nitrate concentrations below the mean groundwater table were negligible. The concentrations of DOC and N species increased with drainage depth. In the deeply-drained grassland, with a mean annual water table of 45 cm below surface, DOC concentrations were twice as high as in the partially rewetted grassland with a mean annual water table of 28 cm below surface. The deeply drained grassland had some of the highest-ever observed DOC concentrations of 195.8 ± 77.3 mg L−1 with maximum values of >400 mg L−1. In general, dissolved organic matter (DOM) at the drained sites was enriched in aromatic moieties and showed a higher degradation status (lower DOC to DON ratio) compared to the near-natural site. At the drained sites, the C to N ratios of the uppermost peat layer were the same as of DOM in the peat profile. This suggests that the uppermost degraded peat layer is the main source of DOM. Nearly constant DOM quality through the profile furthermore indicated that DOM moving downwards through the drained sites remained largely biogeochemically unchanged. Unlike DOM concentration, DOM quality and dissolved N species distribution were similar in the two grasslands and thus unaffected by the drainage depth. Methane production during the winter months at the drained sites was limited to the subsoil, which was quasi-permanently water saturated. The recovery of the water table in the winter months led to the production of nitrous oxide around mean water table depth at the drained sites. The rewetted and the near-natural site had comparable DOM quantity and quality (DOC to DON ratio and aromaticity). 10 years after rewetting quasi-pristine biogeochemical conditions have been re-established under continuously water logged conditions in the former peat cut area. Only the elevated dissolved methane and ammonium concentrations reflected the former disturbance by drainage and peat extraction. Rewetting via polder technique seems to be an appropriate way to revitalize peatlands on longer timescales and to improve the water quality of downstream water bodies.

Peatlands are a major source of dissolved organic carbon (DOC) for aquatic ecosystems. Naturally high DOC concentrations in peatlands may be increased further by drainage. For agricultural purposes, peat has frequently been mixed with sand, but the effect of this measure on the release and cycling of DOC has rarely been investigated. This study examined the effects of (i) mixing peat with sand and (ii) water table depth (WTD) on DOC concentrations at three grassland sites on shallow organic soils. The soil solution was sampled bi-weekly for two years with suction plates at 15, 30 and 60cm depth. Selected samples were analysed for dissolved organic nitrogen (DON), δ13CDOM and δ15NDOM. Average DOC concentrations were surprisingly high, ranging from 161 to 192mgl-1. There was no significant impact of soil organic carbon (SOC) content or WTD on mean DOC concentrations. At all sites, DOC concentrations were highest at the boundary between the SOC-rich horizon and the mineral subsoil. In contrast to the mean concentrations, the temporal patterns of DOC concentrations, their drivers and the properties of dissolved organic matter (DOM) differed between peat-sand mixtures and peat. DOC concentrations responded to changes in environmental conditions, but only after a lag period of a few weeks. At the sites with a peat-sand mixture, temperature and therefore probably biological activity determined the DOC concentrations. At the peat site, the contribution of vegetation-derived DOM was higher. The highest concentrations occurred during long, cool periods of waterlogging, suggesting a stronger physicochemical-based DOC mobilisation. Overall, these results indicate that mixing peat with sand does not improve water quality and may result in DOC losses of around 200kg DOCha-1a-1. publisher: Elsevier articletitle: Effect of past peat cultivation practices on present dynamics of dissolved organic carbon journaltitle: Science of The Total Environment articlelink: http://dx.doi.org/10.1016/j.scitotenv.2016.07.121 content_type: article copyright: © 2016 The Authors. Published by Elsevier B.V. ispartof: Science of the Total Environment vol:574 pages:1243-1253 ispartof: location:Netherlands status: published