Soil CH4 and N2O fluxes from drained nutrient-rich peatland forests in Estonia and Latvia

Abstract

<p>In the terrestrial biosphere, peatlands represent the most important long-term soil carbon storage. They cover only 3% of the land surface but are responsible for about one-third of the total. Ecosystem degradation and changes made in hydrology may affect the biogeochemistry of peatlands and, together with projected global warming, may lead to significant changes in greenhouse gas fluxes. Aeration of peatlands increases organic matter's aerobic decomposition and enhances wetlands’ change from a net carbon sink to a carbon dioxide source and low soil water content in drained histosols results in lower CH<sub>4</sub> emissions. In contrast, N<sub>2</sub>O emissions may increase due to increased mineralization and more favorable conditions for nitrification.</p><p>However, soil CH<sub>4</sub> and N<sub>2</sub>O fluxes in peatlands are spatially and temporally (interannual, seasonal) variable, and there is little detailed information on drained nutrient-rich organic soils in the hemiboreal zone. We conducted a two-year study in drained peatland forests with different tree species Scots pine<em> </em>(<em>Pinus sylvestris</em>), Norway spruce (<em>Picea abies</em><em>), </em>birch<em> </em>(<em>Betula sp</em><em>.</em>), and black alder (<em>Alnus glutinosa</em>) and with various water levels and a natural wetland (fen) as a reference site in Estonia and Latvia from January 2021 to December 2022.</p><p>CH<sub>4</sub> and N<sub>2</sub>O fluxes were measured twice per month using the manual static chamber method. Environmental parameters in soil, such as groundwater level, temperature, and moisture were monitored and stored hourly by a data logger. Detailed studies of soil physio-chemical parameters and microbial community were conducted to relate greenhouse gas fluxes with environmental conditions.</p><p>Our preliminary results for the first year showed that all drained forest soils with low groundwater levels were annual methane sinks (−48.9 ± 12.9 μg m<sup>−‍2</sup> h<sup>−‍1</sup>), whereas the reference fen studied had a higher emission potential of 396 ± 214 μg m<sup>−‍2</sup> h<sup>−‍1</sup>. In contrast, birch and alder forests with poorly drained soils consumed less CH<sub>4</sub> and were annual emitters than artificially drained sites. Methane flux had a statistically significant correlation with water level and soil temperature. Most of the sites were annual emitters of N<sub>2</sub>O; wetter forest sites were higher emitters (21.0 ± 10.49 μg m<sup>−‍2</sup> h<sup>−‍1</sup>) than drier sites (17.97 ± 4.8 μg m<sup>−‍2</sup> h<sup>−‍1</sup>). Higher N<sub>2</sub>O emissions and temporal variability were associated with sites where water levels exhibited large seasonal fluctuations. N<sub>2</sub>O flux was controlled by soil temperature and moisture content, and emission peaks occurred in spring (freeze-thaw period).</p><p>This research was supported by the LIFE programme project "Demonstration of climate change mitigation potential of nutrients rich organic soils in the Baltic States and Finland", (2019-2023, LIFE OrgBalt, LIFE18 274CCM/LV/001158).</p>