Long-term rewetting of degraded peatlands restores hydrological buffer function

Carbon farming for climate change mitigation and ecosystem services - Potentials and influencing factors

Carbon Farming (CF) decreases atmospheric CO2 concentrations by increasing carbon stocks in soils and biomass. In addition to mitigating climate change, CF measures provide co-benefits through the supply of additional ecosystem services (ES). Integrating such benefits into a comprehensive assessment may increase the attractiveness of CF measures, increase adoption rates, and ultimately benefit climate and ecosystems. However, site-specific and measure-specific characteristics influence the impacts of CF measures. A comprehensive overview over CF impacts is lacking. We therefore analyzed six CF measures on cropland in the European temperate zone: (1) cover cropping, (2) introducing legumes or semi-perennial crops into crop rotations, (3) conversion to short rotation coppice, (4) agroforestry, (5) afforestation of marginal cropland, and (6) partial rewetting of drained organic soils. Through a structured literature review, we derived on-site climate change mitigation potentials, impacts on the supply of ES, and economic trade-offs, as well as influencing factors causing spatial heterogeneities. Our results show that the climate change mitigation potential varies strongly between and within CF measures. All measures can boost the supply of regulating ecosystem services, while trade-offs exist mainly with provisioning services and economic returns. Spatially heterogeneous effects in ES supply depend on local ES demand. As proof of concept, we mapped expected beneficial ES effects from 4 selected ES positively impacted by the measure (4) agroforestry in a GIS environment for Germany, as well as opportunity costs as an economic trade-off. The results suggest that strong co-benefits can be expected in areas where opportunity costs are high. Moreover, the CF measures with the highest climate change mitigation potential also imply the highest systemic change of the farm system. This constitutes a strong economic hurdle to implementation. We argue that payments for ES are needed to incentivize CF adoption and harness the beneficial effects on climate and ecosystems. Our findings provide a comprehensive view on the effect of CF measures and may support effective European climate change mitigation policy.

Wetscapes: Restoring and maintaining peatland landscapes for sustainable futures

Peatlands are among the world's most carbon-dense ecosystems and hotspots of carbon storage. Although peatland drainage causes strong carbon emissions, land subsidence, fires and biodiversity loss, drainage-based agriculture and forestry on peatland is still expanding on a global scale. To maintain and restore their vital carbon sequestration and storage function and to reach the goals of the Paris Agreement, rewetting and restoration of all drained and degraded peatlands is urgently required. However, socio-economic conditions and hydrological constraints hitherto prevent rewetting and restoration on large scale, which calls for rethinking landscape use. We here argue that creating integrated wetscapes (wet peatland landscapes), including nature preserve cores, buffer zones and paludiculture areas (for wet productive land use), will enable sustainable and complementary land-use functions on the landscape level. As such, transforming landscapes into wetscapes presents an inevitable, novel, ecologically and socio-economically sound alternative for drainage-based peatland use.

Production in peatlands: Comparing ecosystem services of different land use options following conventional farming

Majority of Dutch peatlands are drained and used intensively as grasslands for dairy farming. This delivers high productivity but causes severe damage to ecosystem services supply. Peatland rewetting is the best way to reverse the damage, but high water levels do not fit with intensive dairy production. Paludiculture, defined as crop production under wet conditions, provides viable land use alternatives. However, performance of paludiculture is rarely compared to drainage-based agriculture. Here, we compared the performances of six land use options on peatland following a gradient of low, medium, and high water levels, including conventional and organic drainage-based dairy farming, low-input grasslands for grazing and mowing, and high-input paludiculture with reed and Sphagnum cultivation. For each land use option, we conducted environmental system analysis on model farm system defined by a literature based inventory analysis. The analysis used five ecosystem services as indicators of environmental impacts with a functional unit of 1-ha peat soil. Ecosystem services included biomass provisioning, climate, water, and nutrient regulation, and maintenance of habitat. Results showed that drainage-based dairy farming systems support high provisioning services but low regulation and maintenance services. Organic farming provides higher climate and nutrient regulation services than its conventional counterpart, but limited overall improvement due to the persistent drainage. Low-intensity grassland and paludiculture systems have high regulation and maintenance services value, but do not supply biomass provisioning comparable to the drainage-based systems. Without capitalizing the co-benefits of regulation and maintenance services, and accounting for the societal costs from ecosystem disservices including greenhouse gas emission and nitrogen pollution, it is not likely that the farmers will be incentivized to change the current farming system towards the wetter alternatives. Sustainable use of peatlands urges fundamental changes in land and water management along with the financial and policy support required.

Carbon and climate implications of rewetting a raised bog in Ireland

Peatland rewetting has been proposed as a vital climate change mitigation tool to reduce greenhouse gas emissions and to generate suitable conditions for the return of carbon (C) sequestration. In this study, we present annual C balances for a 5-year period at a rewetted peatland in Ireland (rewetted at the start of the study) and compare the results with an adjacent drained area (represents business-as-usual). Hydrological modelling of the 230-hectare site was carried out to determine the likely ecotopes (vegetation communities) that will develop post-rewetting and was used to inform a radiative forcing modelling exercise to determine the climate impacts of rewetting this peatland under five high-priority scenarios (SSP1-1.9, SS1-2.6, SSP2-4.5, SSP3-7.0 and SSP5-8.5). The drained area (marginal ecotope) was a net C source throughout the study and emitted 157 ± 25.5 g C m^-2  year^-1 . In contrast, the rewetted area (sub-central ecotope) was a net C sink of 78.0 ± 37.6 g C m^-2  year^-1 , despite relatively large annual methane emissions post-rewetting (average 19.3 ± 5.2 g C m^-2  year^-1 ). Hydrological modelling predicted the development of three key ecotopes at the site, with the sub-central ecotope predicted to cover 24% of the site, the sub-marginal predicted to cover 59% and the marginal predicted to cover 16%. Using these areal estimates, our radiative forcing modelling projects that under the SSP1-1.9 scenario, the site will have a warming effect on the climate until 2085 but will then have a strong cooling impact. In contrast, our modelling exercise shows that the site will never have a cooling impact under the SSP5-8.5 scenario. Our results confirm the importance of rapid rewetting of drained peatland sites to (a) achieve strong C emissions reductions, (b) establish optimal conditions for C sequestration and (c) set the site on a climate cooling trajectory.

Responses of soil enzyme activities and bacterial community structure to different hydrological regimes during peatland restoration in the Changbai Mountain, northeast China

Appropriate hydrological management is critical for peatland restoration. An important prerequisite for peatland restoration is a recovery of soil biological processes. However, little is known about the effects of different hydrological management practices on soil biological processes during peatland restoration. In this study, the variations in soil properties, enzyme activities, and bacterial communities across different peatlands, namely natural peatland (NP), peatland restored under high water level (HR), peatland restored under alternating high-low water level (HLR), peatland restored under low water level (LR), and degraded peatland (DP), in the Changbai Mountains were investigated. Results showed that soil organic carbon, soil water content, and total nitrogen in NP were significantly higher than those in restored and degraded peatlands, and these soil properties in restored peatlands increased with the water level. The activities of soil hydrolases including β-1, 4-glucosidase, β-1, 4-n-acetylglucosidase, and acid phosphatase in NP were higher than in restored and degraded peatlands, while the activity of polyphenol oxidase in NP was the lowest. In restored peatlands, all measured enzyme activities decreased with the decline in water level. Both bacterial diversity and richness in NP were the lowest, while the highest diversity and richness were observed in HR. Redundancy analysis indicated that soil organic carbon, water level, soil water content, total nitrogen, and pH were the most important factors that affected the soil enzyme activities and bacterial community. Our findings give insight into the effects of different hydrological regimes on soil biological processes during peatland restoration. Maintaining a high water level early in the restoration process is more beneficial to restoring the ecological functions of peatlands than other hydrological regimes.

To store or to drain - To lose or to gain? Rewetting drained peatlands as a measure for increasing water storage in the transboundary Neman River Basin

Agriculture continues to place unwanted pressure on peatland functionality, despite international recognition calling for their conservation and restoration. Rewetting of peatlands is often the first step of restoration that aims towards improving the delivery of ecosystem services and their benefits for human well-being. Ongoing debates on peatland restoration in agricultural landscapes raise several issues based on the valuation of benefits achieved versus the costs of peatland restoration. Using the transborder Neman River Basin in North-Eastern Europe, this study aimed to quantify and evaluate the gains provided by peatland rewetting. To achieve this, this study estimated i) possible changes in water storage capacity from peatland restoration, ii) the value of expected benefits from restoration and iii) costs of restoration measures at the overarching basin level. Applying multiple assumptions, it was revealed that rewetting drained peatlands in the Neman River Basin could increase water retention by 23.6-118 M m³. This corresponds to 0.14-0.7% of the total annual Neman River discharge into the Baltic Sea. Unit increase of water retention volume due to rewetting ranged between 69 and 344 m³·ha^-1. The estimated water retention value ranged between 12 and 60.2 M EUR·year^-1. It was also shown that peatland rewetting at the scale of Neman River Basin would cost from 6.8 M and 51.5 M EUR·year^-1 depending on the selected scenario. Applying less expensive rewetting measures (non-regulated outflow from ditch blocks), the economic gains (as water storage ecosystem service of rewetted peatlands) from rewetting exceed the costs of rewetting. Thus, rewetting peatlands at a river-basin scale can be considered technically and economically efficient measures towards sustainable management of agricultural landscapes. The novel methodology applied in this study can be used when valuing trade-offs between the rewetting of drained peatlands and leaving them drained for the uncertain future of wetland agriculture.

Unmanned Aircraft System (UAS) Structure-From-Motion (SfM) for Monitoring the Changed Flow Paths and Wetness in Minerotrophic Peatland Restoration

Peatland restoration aims to achieve pristine water pathway conditions to recover dispersed wetness, water quality, biodiversity and carbon sequestration. Restoration monitoring needs new methods for understanding the spatial effects of restoration in peatlands. We introduce an approach using high-resolution data produced with an unmanned aircraft system (UAS) and supported by the available light detection and ranging (LiDAR) data to reveal the hydrological impacts of elevation changes in peatlands due to restoration. The impacts were assessed by analyzing flow accumulation and the SAGA Wetness Index (SWI). UAS campaigns were implemented at two boreal minerotrophic peatland sites in degraded and restored states. Simultaneously, the control campaigns mapped pristine sites to reveal the method sensitivity of external factors. The results revealed that the data accuracy is sufficient for describing the primary elevation changes caused by excavation. The cell-wise root mean square error in elevation was on average 48 mm when two pristine UAS campaigns were compared with each other, and 98 mm when each UAS campaign was compared with the LiDAR data. Furthermore, spatial patterns of more subtle peat swelling and subsidence were found. The restorations were assessed as successful, as dispersing the flows increased the mean wetness by 2.9–6.9%, while the absolute changes at the pristine sites were 0.4–2.4%. The wetness also became more evenly distributed as the standard deviation decreased by 13–15% (a 3.1–3.6% change for pristine). The total length of the main flow routes increased by 25–37% (a 3.1–8.1% change for pristine), representing the increased dispersion and convolution of flow. The validity of the method was supported by the field-determined soil water content (SWC), which showed a statistically significant correlation (R2 = 0.26–0.42) for the restoration sites but not for the control sites, possibly due to their upslope catchment areas being too small. Despite the uncertainties related to the heterogenic soil properties and complex groundwater interactions, we conclude the method to have potential for estimating changed flow paths and wetness following peatland restoration.

Restoration of Degraded Tropical Peatland in Indonesia: A Review

Tropical peatlands are fragile ecosystems with an important role in conserving biodiversity, water quality and availability, preventing floods, soil intrusion, erosion and sedimentation, and providing a livelihood for people. However, due to illegal logging, fire and conversion into other land use, the peatlands in Indonesia are under serious threat. Efforts to restore Indonesia’s tropical peatlands have been accelerated by the establishment of the Peatland Restoration Agency in early 2016. The restoration action policy includes the rewetting, revegetation and revitalisation of local livelihood (known as the 3Rs). This paper summarises the regulatory, institutional and planning aspects of peatland restoration, in addition to the implementation of the 3Rs in Indonesia, including failures, success stories, and the criteria and indicators for the success of peatland restoration.

Dissolved organic matter concentration, molecular composition, and functional groups in contrasting management practices of peatlands

About 91,300 ha of peatlands has been rewetted in western Europe since the mid-1990s. Still, it is unknown how long-term rewetting alters the dissolved organic matter (DOM) concentration, molecular composition, and functional groups. We examined these DOM characteristics in three peatland types subjected to 47- to 231-yr drainage and 18- to 24-yr rewetting to address this knowledge gap. Cold water-extractable DOM was characterized by pyrolysis field ionization mass spectrometry (Py-FIMS) and X-ray absorption near-edge structure (XANES) spectroscopy. The dissolved organic carbon (DOC) concentration in the rewetted forest peatland was 2.7 times higher than in the drained forest peatland. However, rewetting decreased the DOC concentrations by 1.5 and 4 times in the coastal peatland and percolation mire, respectively, compared with their respective drained peatlands at the topsoil horizons. The Py-FIMS analysis revealed that all nine DOM compound classes' relative abundances differed between the rewetted and drained forest peatland with the lower relative abundances of the labile DOM compound classes in the rewetted forest peatlands. However, most DOM compound classes' relative abundances were similar between the rewetted and drained coastal peatlands and percolation mires. The XANES also revealed nine carbon and seven nitrogen functional groups with no apparent differences between the two contrasting management practices. The influence of drainage and rewetting on DOC concentration and molecular composition depends on peatland type, drainage period, rewetting intensity, and peat degradation status that should be considered in future research for understanding DOM transformation and transportation from degraded and restored peatland ecosystems.

Impacts of historical ditching on peat volume and carbon in northern Minnesota USA peatlands

Peatlands play a critical role in terrestrial carbon (C) storage, containing an estimated 30% of global soil C, despite occupying only 3% of global land area. Historic management of peatlands has led to widespread degradation and loss of important ecosystem services, including C sequestration. Legacy drainage features in the peatlands of northern Minnesota, USA were studied to assess the volume of peat and the amount of C lost in the ~100 years since drainage. Using high-resolution Light Detection and Ranging (LiDAR) data, we measured elevation changes adjacent to legacy ditches to model pre-ditch surface elevations, which were used to calculate peat volume loss. We established relationships between volume loss and site characteristics from existing geographic information systems datasets and used those relationships to scale volume loss to all mapped peatland ditches in northern Minnesota (USA). We estimated that 0.165 ± 0.009 km³ of peat have been lost along almost 4000 km of peatland ditches. Peat loss upslope of ditches was significantly less than downslope (P < 0.001). Mean width of the entire ditch-effect zone was 333 ± 8.32 m. Using our volume loss estimates, literature estimates of oxidation, and mean bulk density and peat C% values from Minnesota peatlands, we calculate a total historic loss 3.847 ± 0.364 Tg C. Assuming a constant oxidation rate during the 100 years since drainage, euic and dysic peatlands within the ditch effect zone have lost 0.26 ± 0.08 and 0.40 ± 0.13 Mg C ha^-1 yr^-1, respectively, comparable to IPCC estimates. Our spatially-explicit peat loss estimates could be incorporated into decision support tools to inform management decisions regarding peatland C and other ecosystem services.