John Couwenberg’s research while affiliated with Universität Greifswald and other places

Wetlands play an important role for water, carbon storage and biodiversity in the seasonally dry and hot environments of tropical savannas. Peatlands, which are permanent wetlands, are important as the carbon-richest parts of wetland ecosystems with a strong ability to store carbon, retain water and regulate its flow. With this first review on peatlands in the Cerrado we synthesize existing knowledge and gaps on their distribution and types in the biome including, vegetation, soil properties, carbon stocks and hydrogeomorphology. Peatlands are embedded in wetland complexes in valleys, groundwater-fed oligo- to mesotrophic, with wet grass- and shrubland, Vereda or riparian swamp forest vegetation. Average peat depth is 1.4 meters and soil carbon stocks in the first meter can be 9 times higher than in mineral soils under Cerrado dryland vegetation, reaching about 1000 t carbon per hectare. Total soil carbon stock estimates (3.19 Gt C) in peatlands equal 13.3% of the total soil carbon in the Cerrado in only 0.7% of its total area, although large uncertainties exist. Actual peatland occurrence appears to be more abundant than current soil and peat maps suggest. The high rate of transformation of the native vegetation into industrial agriculture and wood plantations, which affects large parts of the Cerrado, is a major cause for the degradation and the loss of peatlands and other wetlands. However, the extent of peatland degradation and resulting carbon losses remain unfathomed. We identified research needs such as better mapping and monitoring, and recommend including peatlands into wetland classification systems in Brazil.

Greenhouse gas (GHG) emissions from drained peatlands in the European Union (EU) significantly contribute to the total EU anthropogenic GHG emissions (6%). The lack of high-resolution spatial data in national monitoring systems hampers effective mitigation planning. We present detailed maps of land use, GHG emissions, and emission hotspots for EU peatlands. Results indicate that undrained peatlands and forest lands are prevalent at high latitudes, while grasslands and croplands dominate around latitudes 50°-55°. Three main emission hotspots are identified, all in the North Sea region: South-western England, Western Netherlands, and North-western Germany, accounting for 20% of EU peatland emissions on just 4% of the peatland area. This study highlights the necessity of targeted curbing of emissions from drained peatlands to meet EU climate goals and reveals substantial underreporting of emissions in current National Inventory Submissions to the UNFCCC, amounting to 59-113 Mt CO2-e annually. Our findings provide a crucial basis for policymakers to prioritize peatland rewetting to reduce GHG emissions.

The rewetting of formerly drained peatlands can help to counteract climate change through the reduction of CO 2 emissions. However, this can lead to resuming CH 4 emissions due to changes in the microbiome, favoring CH 4-producing archaea. How plants, hydrology and microbiomes interact as ultimate determinants of CH 4 dynamics is still poorly understood. Using a mesocosm approach, we studied peat microbiomes, below-ground root biomass and CH 4 fluxes with three different water level regimes (stable high, stable low and fluctuating) and four different plant communities (bare peat, Carex rostrata, Juncus inflexus and their mixture) over the course of a growing season. A significant difference in microbiome composition was found between mesocosms with and without plants, while the difference between plant species identity or water regimes was rather weak. A significant difference was also found between the upper and lower peat, with the difference increasing as plants grew. By the end of the growing season, the methanogen relative abundance was higher in the subsoil layer, as well as in the bare peat and C. rostrata pots, as compared to J. inflexus or mixture pots. This was inversely linked to the larger root area of J. inflexus. The root area also negatively correlated with CH 4 fluxes which positively correlated with the relative abundance of methanogens. Despite the absence or low abundance of methanotrophs in many samples, the integration of methanotroph abundance improved the quality of the correlation with CH 4 fluxes, and methanogens and methanotrophs together determined CH 4 fluxes in a structural equation model. However, water regime showed no significant impact on plant roots and methanogens, and consequently, on CH 4 fluxes. This study showed that plant roots determined the microbiome composition and, in particular, the relative abundance of methanogens and methanotrophs, which, in interaction, drove the CH 4 fluxes.

In 2011, MoorFutures® were introduced as the first standard for generating credits from peatland rewetting. We developed methodologies to quantify ecosystem services before and after rewetting with a focus on greenhouse gas emissions, water quality, evaporative cooling and mire-typical biodiversity. Both standard and premium approaches to assess these services were developed, and tested in the rewetted polder Kieve (NE-Germany). The standard approaches are default tier 1 estimation procedures, which require little time and few, mainly vegetation data. Based on the Greenhouse gas Emission Site Type (GEST) approach, emissions decreased from 1,306 t CO 2 e in the baseline scenario to 532 t CO 2 e in the project scenario, whereas 5 years after rewetting they were assessed to be 543 t CO 2 e per year. Nitrate release assessed via Nitrogen Emission Site Types (NEST) was estimated to decrease from 1,088 kg N (baseline) to 359 kg N (project), and appeared to be 309 kg N per year 5 years after rewetting. The heat flux − determined with Evapotranspiration Energy Site Types (EEST)-decreased from 6,691 kW (baseline) to 1,926 kW (project), and was 2,250 kW per year 5 years after rewetting. Mire-specific biodiversity was estimated to increase from very low (baseline) to high (project), but was only low 5 years after rewetting. The premium approaches allow quantifying a particular ecosystem service with higher accuracy by measuring or modelling. The approaches presented here have been elaborated for North-Germany but can be adapted for other regions. We encourage scientists to use our research as a model for assessing peatland ecosystem services including biodiversity in other geographical regions. Using vegetation mapping and indicator values derived from meta-analyses is a cost-efficient and robust approach to inform payment for ecosystem services schemes and to support conservation planning at regional to global scales.

The EU Nature Restoration Law (NRL) is critical for the restoration of degraded ecosystems and active afforestation of degraded peatlands has been suggested as a restoration measure under the NRL. Here, we discuss the current state of scientific evidence on the climate mitigation effects of peatlands under forestry. Afforestation of drained peatlands without restoring their hydrology does not fully restore ecosystem functions. Evidence on long-term climate benefits is lacking and it is unclear whether CO 2 sequestration of forest on drained peatland can offset the carbon loss from the peat over the long-term. While afforestation may offer short-term gains in certain cases, it compromises the sustainability of peatland carbon storage. Thus, active afforestation of drained peatlands is not a viable option for climate mitigation under the EU Nature Restoration Law and might even impede future rewetting/restoration efforts. Instead, restoring hydrological conditions through rewetting is crucial for effective peatland restoration.

Pollen deposition in small lakes and peatlands is composed of local pollen deposition arriving from the nearby vegetation and of regional pollen deposition arriving from farther away. The LOVE model aims to reconstruct past vegetation on a small local scale by extracting only the local pollen signal. To this end, pollen deposition from small sites is related to pollen deposition from large lakes with predominantly regional pollen deposition. We here present a new implementation of the LOVE model in the R environment for statistical computing that is more user friendly than existing implementations. It allows more readily application with fossil pollen data and facilitates extensive testing of the approach in simulated landscapes. The LOVE model derives from critical mathematical assumptions that strongly limit its application. We additionally present LOVEoptim as an adjusted approach to local-scale reconstructions. Other than in LOVE, past local plant abundances are approximated using numerical optimization. Tests in a simulated landscape, which is based on true landscape patterns from digital maps, show that both approaches are valid. Due to fewer mathematical assumptions, LOVEoptim is more widely applicable. The modeling results help to better interpret the spatial scale of vegetation reflected in LOVE/LOVEoptim reconstructions.

Drainage and agricultural use transform natural peatlands from a net carbon (C) sink to a net C source. Rewetting of peatlands, despite of high methane (CH4) emissions, holds the potential to mitigate climate change by greatly reducing CO2 emissions. However, the time span for this transition is unknown because most studies are limited to a few years. Especially, nonpermanent open water areas often created after rewetting, are highly productive. Here, we present 14 consecutive years of CH4 flux measurements following rewetting of a formerly long‐term drained peatland in the Peene valley. Measurements were made at two rewetted sites (non‐inundated vs. inundated) using manual chambers. During the study period, significant differences in measured CH4 emissions occurred. In general, these differences overlapped with stages of ecosystem transition from a cultivated grassland to a polytrophic lake dominated by emergent helophytes, but could also be additionally explained by other variables. This transition started with a rapid vegetation shift from dying cultivated grasses to open water floating and submerged hydrophytes and significantly increased CH4 emissions. Since 2008, helophytes have gradually spread from the shoreline into the open water area, especially in drier years. This process was periodically delayed by exceptional inundation and eventually resulted in the inundated site being covered by emergent helophytes. While the period between 2009 and 2015 showed exceptionally high CH4 emissions, these decreased significantly after cattail and other emergent helophytes became dominant at the inundated site. Therefore, CH4 emissions declined only after 10 years of transition following rewetting, potentially reaching a new steady state. Overall, this study highlights the importance of an integrative approach to understand the shallow lakes CH4 biogeochemistry, encompassing the entire area with its mosaic of different vegetation forms. This should be ideally done through a study design including proper measurement site allocation as well as long‐term measurements.