The impacts of water table dynamics on greenhouse gas emissions and phosphorus leaching in managed boreal peatlands

Pristine boreal peatlands store vast reserves of terrestrial carbon and have a net cooling impact on climate in the long term. Peatland drainage increases CO₂ and N₂O emissions and decreases CH₄ emissions, leading to a net warming impact on climate. For example, cultivated peatlands can have high greenhouse gas (GHG) emissions per area and are therefore attractive targets for national aims to reduce GHG emissions. Raising water table depth (WTD) level can decrease the climate-warming impact. However, as drainage changes peat properties, the WTD elevation may lead to additional leaching of e.g. redox-sensitive phosphorus (P), which often restricts primary production in freshwaters. To support environmentally sound climate actions, we aimed to study the simultaneous impacts of different WTD conditions on GHG emissions and P leaching in variably managed peatlands.

Our study sites include cultivated peatland plots with different peat thicknesses, peatland forest, abandoned peat field, and pristine peatland. The chemical potential for P retention in different soil depths was studied using chemical extractions of soil. The GHG emissions in field conditions were studied with year-round GHG emission inventories, which were conducted with chamber methods in snow-free conditions and otherwise with the snow-gradient method. Besides the effect of WTD, also the effects of vegetation and several environmental variables were considered. The simultaneous effects of different WTD conditions (saturation, slowly lowering WTD, quick fluctuations) on GHG emissions and P leaching were studied using intact soil profiles with a column experiment in controlled conditions.

Our results help to find the best water management solutions considering both GHG emissions and P leaching. This knowledge is especially important in countries with large areas of drained peatlands and attempts to lower both GHG emissions and nutrient leaching. Sometimes land use changes may be unavoidable, and our studies with different land use options also support decision-making in these situations.