With the intensifying threat of climate change, the need for effective mitigation solutions has become urgent. The question of how best to implement such solutions was a topic of debate in the recent EU parliament elections.

One potential strategy is wetland restoration. Drained peatlands, which are significant carbon sources, are estimated to release the equivalent of 5% of the global man-made greenhouse gas (GHG) emissions. When rewetted, these peatlands can shift from carbon sources to carbon sinks, uptaking rather than releasing carbon.

However, as Dr. Aram Kalhori explains, the transition from a source to sink is not so straightforward. This is a finding from her scientific article published earlier this year. In her study she used long term data from a rewetted peatland to reveal remarkable changes in their GHG emissions over time. Although the peatland eventually became a CO2 sink, the study revealed deviations from the Intergovernmental Panel on Climate Change (IPCC) standards, providing insights for improving rewetting efforts. 

ESCI: The IPCC and many national governments have pre-established numbers for GHG emissions before and after rewetting. Could you explain how they are determined?

Kalhori: IPCC emission factors are mostly based on short-term datasets. These datasets often lack information in terms of changes in emissions over time and their trends. Also, the spatial coverage of in-situ GHG measurements across peatlands is limited.

In Germany, the underlying dataset used in the national GHG inventories are primarily based on chamber measurements. Measurements conducted with this technique usually cover a maximum area of 2 m2. A key limitation of chamber measurements is their restricted temporal coverage. As typically, data collection usually occurs over one or two weeks per month, at most, and usually only during the vegetation period. Thus, annual emission estimations are extrapolated from these limited measurements. 

So, while these measurements offer valuable insights, they often don’t capture emissions at the ecosystem scale or over extended time periods. The broader diversity and complexity of the whole rewetted ecosystems are often overlooked, limiting the accuracy of the assessment for long term environmental monitoring.

ESCI: How did you address these limitations in your study?

Kalhori: In our research, we use Eddy Covariance (EC) towers, which provide measurements over a much larger footprint area compared to chamber methods. For example, a 3-meter EC tower, can measure GHG fluxes across a 300-meter radius, offering a more comprehensive view of the ecosystem compared to the plot-scale chamber measurements.

To capture GHG exchanges, or fluxes, we require gas analysers to measure gas concentrations and sonic anemometers to measure wind components. They are all mounted on the EC towers. In addition, we incorporate several ancillary sensors to monitor critical environmental factors affecting GHG fluxes, such as air and soil temperature, water level, incoming and outgoing radiation, precipitation, and ground heat exchanges. These combined measurements provide a better understanding of the entire ecosystem, capturing the dynamic interactions and the impact of environmental conditions on the GHG fluxes of the ecosystem.

ESCI: Your research shows it takes longer than expected to achieve the IPCC and national government scientific bodies’ standards. Could you elaborate on why?

Kalhori: Rewetting should not be considered as an instant fix – it is not as simple as an on/off switch, so you can't just assume, after rewetting, the ecosystem immediately becomes a CO2 sink.

These are natural systems. Their complexity makes it unrealistic to expect an immediate transition following rewetting. What’s essential is continuous monitoring of GHG emissions on a yearly basis to capture the transient changes.

On our site, we observed that CO2 emissions started to decrease after rewetting, but this didn’t happen immediately in the following year. We show that there were still annual CO2 emission trends following rewetting, though we did see a decreasing trend of both CO2 and methane (CH4) emissions over the course of the study period.

ESCI: You used long-term data from a rewetted peatland in Northeast Germany for this study. Is it common to use such long-term datasets to assess the impacts of rewetting? 

Kalhori: Long term datasets like what we produce from our rewetted site and used in our study are still limited and relatively uncommon. While there is a growing emphasis in the EU, particularly in countries like Germany and perhaps the UK, to establish a larger network of GHG flux monitoring systems for rewetted peatlands, continuous measurements remain limited. 

A major challenge is translating this scientific data into knowledge that policymakers can act upon. The question is: Do we have sufficient and cohesive information on GHG emissions from all wetland types and conditions? While some datasets do exist, they are often fragmented and not readily available in a systematic way.

At the moment, there are ongoing consortiums and projects aiming at expanding the wetlands’ GHG flux monitoring system within the EU and even on a global scale. For instance, I am currently leading a work package in a consortium focused on enhancing knowledge and solutions to fast-track wetland restoration across Europe: WET HORIZONS. One of our key goals is to create an open-access database that compiles harmonized GHG datasets and associated environmental variables from wetlands within the EU. This database will help update the commonly used emission factors (EF)s to higher-tier, more precise EFs, that are classified both spatially and temporally. Such initiatives are critical not only for improving scientific understanding of wetland conditions and their impacts but also for securing the necessary funding and support to sustain long-term monitoring efforts. Without this, many important measurements are at risk of being discontinued due to lack of resources. To summarize, while there is still room to improve, progress in creating a large network of flux towers across various wetland ecosystems has improved considerably over the past two decades. 

ESCI: What do your results mean for environmental management or peatland restoration policy? 

Kalhori: Our study definitely calls for a more comprehensive monitoring system introducing sustainable management scenarios for rewetted sites within Germany. Since we're observing the transition from a CO2 source to a sink taking several years after rewetting, it is clear that immediate action is required to rewet drained peatlands and not to wait any longer. Individual sites may continue to emit GHGs for an extended period, depending on different management practices and site-specific conditions. This variability emphasizes the importance of tailored land restoration strategies and the need for adaptive management.

There is often a gap between the research community and decision makers, which can sometimes result in a lack of sustained funding for long term monitoring projects. Policymakers require robust, extensive, and consistent data to develop effective legislation and land management strategies. In our case, other work packages within the WET HORIZONS consortium are dedicated to assuring that our findings directly inform land restoration policies. We aim to provide the data needed for informed and timely decision-making on peatland rewetting and management practices and bridge the gap between research and policy, enabling more measurement-based strategies for peatland restoration.

ESCI: How would you suggest we approach wetland restoration with a forward-looking and long-term lens?

Kalhori: It's essential to account for the changing climate conditions we're already beginning to observe: such as changes in the precipitation patterns and projections of a warmer and potentially drier future due to extreme climate events like droughts. Thus, managing water level and vegetation monitoring would become increasingly important as these changes continue to happen. 

For that reason, it would be very crucial to implement effective rewetting practices that are adaptable to future climate scenarios that consider the resiliency of rewetted ecosystems for being effective in mitigating emissions in the long term. 

ESCI: How does this research fit into the WET HORIZONS project?

Kalhori: We aim to fill the gap in the current knowledge of GHG emissions and datasets in wetland regions, assess the impacts of current and future climate extremes on the trajectory of EFs, and ultimately estimate the total mitigation potential of wetlands based on different site characteristics.

My research primarily focuses on collecting field measurements, which provide in-situ data for WET HORIZONS. The idea is to integrate these field measurements with modeling efforts, from another work package, to define the temporal phases of GHG emissions in restored wetlands and provide guidance on the application of updated EFs at a larger scale.

ESCI: Can a rewetted wetland ever go back to its original state?

Kalhori: Based on existing studies and our observations, peatlands that have been drained for agricultural or grassland use, have experienced extensive degradation. We're therefore dealing with significantly altered systems and associated hydrological changes. 

Peat formation is a process that takes thousands of years, which means we can't expect these ecosystems to fully go back to their pristine state simply by rewetting them.

From a climatic mitigation perspective, rewetting plays a critical role as one of the natural climate-based solutions; however, it must be done in an optimized way to convert the system into a CO2 sink as promptly as possible. Achieving this will also facilitate other benefits of rewetting, such as enhanced biodiversity, filtering out nutrients, and water retention.

That said, while we do observe a source to sink transition, restoring peatlands to their full ecological capacity is a complex process that requires careful management and ongoing monitoring.

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