Degradation legacy and current water levels as predictors of carbon emissions from two fen sites

Drainage-induced shifts in physicochemical peat properties are irreversible on a decadal time span. We investigated whether carbon emissions from fen peat can be estimated using two proxies: current water levels and peat properties (as affected by drainage history, i.e. degradation legacy). We collected bare peat monoliths from a long-term drained and an undrained fen. In a crossed design, half of the monoliths was kept wet and the other half was drained. Highest carbon dioxide (CO2) emissions came from the originally undrained peat under low water levels (607 mmol m-2 d-1). Overall, CO2 emissions were primarily determined by drainage history, with 141 % higher emissions from the originally undrained peat. In addition, low current water levels correlated with 42 % higher emissions. Highest methane (CH4) emissions were measured in the originally undrained peat under high water levels (123 mmol m-2 d-1). Overall, CH4 emissions were primarily determined by current water levels, with 430 % higher emissions under high water levels. In addition, the originally undrained peat had 180 % higher emissions. The lower C efflux from originally drained peat correlated with lower concentrations of methanogens and of easily-degradable carbon substrate (cellulose). We conclude that substrate limitation in long-term drained fens ensures low baseline carbon emissions, which provides opportunities for renewed carbon sequestration by rewetting

Stable isotopes (d(13)C, d(15)N) and biomarkers as indicators of the hydrological regime of fens in a European east-west transect

Peatland degradation is tightly connected to hydrological changes and microbial metabolism. To better understand these metabolism processes, more information is needed on how microbial communities and substrate cycling are affected by changing hydrological regimes. These activities should be imprinted in stable isotope bulk values (delta N-15, delta C-13) due to specific isotopic fractionation by different microbial communities, their metabolic pathways and nutrient sources. We hypothesize that stable isotope values and microbial abundance are correlated and act as indicators of dif-ferent hydrological regimes. We sampled an East-West transect across European fens in 14 areas and conducted a stable isotope (delta C-13, delta N-15) and membrane fatty acid (mFA) analysis. Within each area an undrained, drained and rewetted site was selected. Rewetted sites were separated based on when rewetting occurred. We found differences in the upper layers of all sites in microbial-derived mFAs and stable isotope values corresponding to hydrological re-gimes. The highest and lowest quantities of microbial-derived mFAs were measured in undrained and drained sites, respectively. Fungal-derived mFAs were especially lower in drained sites. Simultaneously, delta N-15 stable isotope values were highest in drained sites. In addition, stable isotope values and microbial-derived mFAs showed distinct depth trends. In undrained sites stable isotopes values slightly increased with depth. In drained sites, delta N-15 values decreased downwards, whereas delta C-13 values increased. Overall microbial-derived mFAs decreased with depth. These patterns presumably result from anoxic conditions and high peat recalcitrance in the deeper layers. In sites with short time of rewetting, the microbial-derived mFAs and stable isotope values were similar to values of drained sites, while with increasing rewetting time values shifted to those of undrained sites. We conclude that biomarkers indicate that stable isotope values reflect specific microbial metabolic processes, which differ with hydrological regimes, and thus could indicate both drainage and rewetting in fens

Recovery of fen peatland microbiomes and predicted functional profiles after rewetting

Many of the world’s peatlands have been affected by water table drawdown and subsequent loss of organic matter. Rewetting has been proposed as a measure to restore peatland functioning and to halt carbon loss, but its effectiveness is subject to debate. An important prerequisite for peatland recovery is a return of typical microbial communities, which drive key processes. To evaluate the effect of rewetting, we investigated 13 fen peatland areas across a wide (>1500 km) longitudinal gradient in Europe, in which we compared microbial communities between drained, undrained, and rewetted sites. There was a clear difference in microbial communities between drained and undrained fens, regardless of location. Community recovery upon rewetting was substantial in the majority of sites, and predictive functional profiling suggested a concomitant recovery of biogeochemical peatland functioning. However, communities in rewetted sites were only similar to those of undrained sites when soil organic matter quality (as expressed by cellulose fractions) and quantity were still sufficiently high. We estimate that a minimum organic matter content of ca. 70% is required to enable microbial recovery. We conclude that peatland recovery after rewetting is conditional on the level of drainage-induced degradation: severely altered physicochemical peat properties may preclude complete recovery for decades

Rewetting does not return drained fen peatlands to their old selves

Peatlands, in particular groundwater-fed fens of the temperate zone, have been drained for agriculture, forestry and peat extraction for a long time and on a large scale. Drainage turns peatlands from a carbon and nutrient sink into a respective source, diminishes water regulation capacity at the landscape scale, causes continuous surface height loss and destroys their typical biodiversity. Over the last decades, drained peatlands have been rewetted for biodiversity restoration and, as it strongly decreases greenhouse gas emissions, also for climate protection. With the dataset published here, we quantified restoration success by comparing 320 rewetted fen peatland sites to 243 near-natural peatland sites of similar origin across temperate Europe with regards to biodiversity (vegetation), ecosystem functioning (hydrology, geochemistry) and land cover characteristics based on remote sensing. Vegetation data comes as species-specific cover values. Hydrology data covers on average 2.3 years and minimally one full year and comes as median, minimum, and maximum water table depth. Geochemistry consists of pH and electrical conductivity of the pore water (0-60 cm), bulk density and organic matter content of the top soil layer (0-30 cm), all sampled in summer for all sites included here alongside the vegetation data sampling. Land cover characteristics contain 208 spectral-temporal metrics for a full annual time series of Copernicus Sentinel-2 A/B data for 2018.Several taxa included in this dataset are at risk from a harmful human activity, in accordance to Chapman 2008 (https://docs.gbif.org/sensitive-species-best-practices/master/en/) we therefore report the georeferences denatured to 0.1 degrees (~10 km). Data may be supplied at finer scales on request under the conditions of a written data agreement. Missing values are coded as NA, zeros are true and measured values. Funding provided by: European Social FundCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100004895Award Number: ESF/14-BM-A55-0027/16 to ESF/14-BM-A55-0035/16Funding provided by: BiodivERsA*Crossref Funder Registry ID: Award Number: DFG JO 332/15-1Funding provided by: BiodivERsA*Crossref Funder Registry ID: Award Number: BELSPO BR/175/A1Funding provided by: BiodivERsA*Crossref Funder Registry ID: Award Number: NCN 2016/22/Z/NZ8/00001Funding provided by: Ministerium für Bildung, Wissenschaft und Kultur Mecklenburg-VorpommernCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100014848Award Number: ESF/14-BM-A55-0027/16 to ESF/14-BM-A55-0035/16Funding provided by: BiodivERsACrossref Funder Registry ID: Award Number: DFG JO 332/15-1See methods section of the accompanying paper for details about data collection and processing; see ReadMe-file for parameter explanation. Potential sites were found through literature search and contacting the respective authors. All such authors providing data were included as co-authors and we included all data from fen ecosystems of temperate Europe which were drained and had a dateable rewetting action and all sites without direct drainage history as confirmed by local experts and remote sensing. We included all sites that provided data for at least two of the following four response clusters in order to obtain comparable datasets for these clusters: (1) vegetation, (2) hydrology, (3) geochemistry, (4) land cover characteristics. We included all available datasets fitting to the definitions laid out above. Sampling for vegetation and geochemistry occurred in summer for all sites. Vegetation sampling consisted of complete lists of vascular plants and bryophytes (539 species in total) based on 16 m² (median, ranging between 12 and 25 m²) with estimates of individual plant species cover. All vegetation data collections included in this study aimed at full species lists and used comparable methodologies, i.e. estimating species-specific cover values. Studies focusing on specific taxa or just reporting the dominant species were excluded from the analyses. Geochemical sampling quantified pH and electrical conductivity of the pore water (0-60 cm) and bulk density and organic matter content of the top soil layer (0-30 cm). Hydrological data relied on on continuous are at least monthly manual sampling for on average, 2.3 years, and a minimum of at least one full year. Land cover characteristics were sampled after the fact for all sites for which the required remote sensing prodcuts were available in the year 2018. Data was collected for different purposes over different years. The data owners are included as co-authors. Vegetation data is the estimated aboveground cover of all vascular plants and bryophytes (539 species in total) within a 16 m² (median, ranging between 12 and 25 m²) plot noted down by experts with pen on paper. Hydrological data is based on 269 piezometers with dataloggers, 91 piezometers related to a datalogger in a transect, 216 piezometers with manual measurements of at least one year and biweekly or monthly readings of the water table depth relative to the peat surface. Geochemical data consisted of pH and electric conductivity of the pore water extracted in the field and measured directly with portable pH-sensors and conductivity sensors. Bulk density was quantfied based on volumetric field samples (0-30cm depth) in relation to their dry weight after drying to constant weight in a drying cabinet. Organic matter was quantified as the loss on ignition of these dry samples. Land cover characteristics: spectral-temporal metrics for a full annual time series of Copernicus Sentinel-2 A/B data for 2018. The Sentinel-2 A/B constellation provides optical imagery of the Earth's surface between ~0.49 - ~2.2 µm in ten spectral bands and at 10 – 20 m ground sampling distance at a theoretical acquisition frequency of 2.5 – 5 days. We here acquired all available Sentinel-2 A/B imagery for 2018 with cloud cover <70% from the ESA API Hub. We used all valid observations to derive spectral-temporal metrics from the time series. Spectral temporal metrics are statistical measures (e.g. average, minimum, maximum, quartiles, …) per spectral band or index (e.g. MNDWI = (green - short wave infrared)/(green + short wave infrared)) using all available cloud- and shadow-free observations over time. The median count of clear-sky-observations per pixel across the sites is 45, while 90% of all sites featured 27 clear-sky observations or more. Both data processing to Analysis Ready Data as well as calculating spectral-temporal metrics was performed through the Framework for Operational Radiometric Correction for Environmental monitoring. Our analysis included data averaged over 3x3 pixels around the center plot location of the site. Different spatial aggregations (e.g. single pixels, 5x5 pixels around the center plot) led to highly similar results, implying that the intra-site variability was robust around locations of the vegetation survey. The inclusion of an annual series of Sentinel-1 synthetic aperture radar data (temporal metrics for VV and VH polarization, IW swath at 10 m resolution) for the same year did not affect the results. Spatial scale: temperate fen ecosystems of Europe. Timing: Data was collected between 1994 and 2019 with sampling for vegetation and geochemistry occurring once per site with known year and time since rewetting for the rewetted sites but different years between sites. Hydrology was monitored for >1 year at each site (see above for details and rationale), again with known time periods per site and different timing for different sites. Land cover characteristics were sampled for all sites for the year 2018 as decribed above