Exploring greenhouse gas emissions in wetlands: rewetted organic soils vs constructed agricultural ponds
Short description
This research project investigates the effects of wetland rewetting to answer the question of whether methane emissions from open water are greater in rewetted peatlands compared to constructed wetlands on mineral soils. The study is designed to answer the question of whether there is a difference in greenhouse gas emissions from constructed wetlands and rewetted peatlands, and whether it is possible to scale up methane emissions using the amount of chlorophyll in the water. The project involves extensive field studies with sampling and analysis of water quality, algal biomass, gas and sediment.
Background
Over the past few decades, Sweden has actively implemented a holistic approach to the preservation and administration of wetlands. Noteworthy initiatives include the restoration of peatlands, covering 7000 hectares since 2010, and the establishment of wetlands on mineral soils, totaling 7900 hectares since 2010. This endeavor aims to counteract the historical degradation of wetlands, along with the vital ecological functions they provide, stemming from widespread drainage practices in the 19th and 20th centuries.
In contrast to creating wetlands on mineral soils, which creates new greenhouse gas (GHG) emissions, the act of rewetting a drained organic soil used for agriculture has the potential to yield GHG reductions of up to 27 tons of CO2 equivalent (GWP 100) per hectare per year. Given the pressing urgency of climate change and the Paris Agreement, it is disconcerting that the majority of wetlands in Sweden have been established on mineral soils. This calls for a critical reevaluation of existing policy guidance.
Aim of this study
Our study will ascertain whether methane emissions from open water in rewetted organic soils consistently exceed emissions from constructed wetlands on mineral soils. This has been superficially tested previously, but using small, underpowered datasets, therefore giving inconsistent results, leaving a critical gap in our understanding. On the one hand, the amount of organic material in the rewetted soil may exacerbate methane emissions simply due to high availability of sustenance for methanogens. On the other hand, methanogens use labile organic compounds which may be just as prevalent in the sediments of constructed wetlands.
Given that constructing wetlands on mineral soils introduces new net GHG (particularly CH4) emissions on areas with no prior emissions, while rewetting reduces previous emissions or leads to renewed sequestration, a thorough investigation is necessary to determine whether rewetting of organic soils, regardless of WTD, should universally be prioritized over constructing new wetlands on mineral soils.
This knowledge is crucial for establishing policy guidance for future establishment or restoration of wetlands funded by the Swedish government through Våtmarkssatsningen, as well as within Landsbygdsprogrammet. It is also essential for meeting climate mitigation targets set by both national and international climate regulations, such as the European Climate Law.