# Substantial Mitigation Potential for Greenhouse Gases Under High Water Levels in a Cultivated Peatland in the Arctic

## TL;DR

Raising water levels in Arctic peatlands can reduce greenhouse gas emissions and even create net carbon sinks, but careful management is needed to balance environmental and agricultural goals.

## Contribution

Demonstrates that elevated water tables in Arctic peatlands can turn them into net GHG sinks under specific conditions.

## Key findings

- Maintaining a water table between −0.5 and −0.25 m reduced CO2 emissions and created a net GHG sink.
- Biomass harvesting led to significant carbon depletion, even at high water tables.
- Arctic summer photoperiod enhanced CO2 uptake, improving mitigation efficacy.

## Abstract

Drained cultivated peatlands are recognized as substantial global carbon emission sources, prompting the exploration of water level elevation as a mitigation strategy. However, the efficacy of raised water table level (WTL) in Arctic/subarctic regions, characterized by continuous summer daylight, low temperatures and short growing seasons, remains poorly understood. This study presents a two‐year field experiment conducted at a northernmost cultivated peatland site in Norway. We used sub‐daily CO2, CH4, and N2O fluxes measured by automatic chambers to assess the impact of WTL, fertilization, and biomass harvesting on greenhouse gas (GHG) budgets and carbon balance. Well‐drained plots acted as GHG sources as substantial as those in temperate regions. Maintaining a WTL between −0.5 and −0.25 m effectively reduces CO2 emissions, without significant CH4 and N2O emissions, and can even result in a net GHG sink. Elevated temperatures, however, were found to increase CO2 emissions, potentially attenuating the benefits of water level elevation. Notably, high WTL resulted in a greater suppression of maximum photosynthetic CO2 uptake compared to respiration, and, yet caused lower net CO2 emissions due to a low light compensation point that lengthens the net CO2 uptake periods. Furthermore, the long summer photoperiod in the Arctic also enhanced net CO2 uptake and, thus, the efficacy of CO2 mitigation. Fertilization primarily enhanced biomass production without substantially affecting CO2 or CH4 emissions. Conversely, biomass harvesting led to a significant carbon depletion, even at a high WTL, indicating a risk of land degradation. These results suggest that while elevated WTL can effectively mitigate GHG emissions from cultivated peatlands, careful management of WTL, fertilization, and harvesting is crucial to balance GHG reduction with sustained agricultural productivity and long‐term carbon storage. The observed compatibility of GHG reduction and sustained grass productivity highlights the potential for future paludiculture implementation in the Arctic.

Elevating the water table in Arctic cultivated peatlands can substantially reduce greenhouse gas emissions, and even turn these systems into net GHG sinks. Fertilization enhanced biomass production but did not significantly affect CO2 or CH4 emissions, while biomass harvesting led to net carbon loss. The findings highlight the importance of integrated water, fertilization, and harvest management to balance climate mitigation and agricultural productivity in northern peatlands.