DOI: 10.5061/dryad.08kprr532
title: Rewetting does not return drained fen peatlands to their old selves

description: 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.
description: See 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.<br> 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.<br> 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.<br> 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.<br> 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 &lt;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.<br> 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 &gt;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.
description: 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.