<p>Peat bogs are terrestrial wetland ecosystems where waterlogging prevents the complete decomposition of plant material. Therefore, organic matter production exceeds its decomposition, resulting in net peat accumulation. However, anthropogenic pressures, such as drainage for forestry, significantly affects those systems' biogeochemistry. Drainage lowers the originally high water table, increasing the oxic peat layer depth, which changes the dynamics of peat soil greenhouse gas (GHG) fluxes. Moreover, change dynamics can differ in peatland types. While GHG fluxes from drained minerotrophic and ombrotrophic peatlands are relatively well studied, drained transitional peatlands require additional accurate data for different spatio-temporal conditions.<br />This study aims to estimate the magnitude and temporal variability of soil GHG fluxes in three drained transitional bog forests in southeastern Estonia with different tree compositions, dominated respectively by Downy Birch (<em>Betula pubescens</em>), Norway Spruce (<em>Picea abies)</em>&#160;and Scots Pine (<em>Pinus sylvestris</em>), in addition to one drained raised bog forest dominated by Scots Pine. Ongoing sampling campaigns run twice a month from April 2022 to March 2023. Soil CO<sub>2</sub> fluxes (heterotrophic soil respiration; n=6) are measured using a dark dynamic chamber connected to EGM-5 Portable CO<sub>2</sub> Gas Analyzer. To estimate soil CO<sub>2</sub> (forest floor respiration), N<sub>2</sub>O and CH<sub>4</sub> fluxes, gas concentration samples are collected at 20-minute intervals during an hour-long session using manual static chambers (n=6) and are analyzed with Shimadzu GC-2014 gas chromatography. Soil environmental parameters (water table depth, soil temperature and moisture) are measured simultaneously with GHG measurements at each site.<br />Preliminary results (April 2022 &#8211; December 2022) show that sites with greater depth of oxic peat layer were, on average, stronger emitters of CO<sub>2</sub> (forest floor respiration) and net CH<sub>4</sub> sinks. The birch site had the highest average CO<sub>2</sub> flux (103.6 &#177; 9.96 mg C m<sup>&#8722;2</sup> h<sup>&#8722;1</sup>, mean &#177; SE), while the drained raised bog pine forest site had the lowest (59.9 &#177; 4.82 mg C m<sup>&#8722;2</sup> h<sup>&#8722;1</sup>). The transitional bog sites were net CH<sub>4</sub> sinks, with the birch site being the largest (&#8722;85.85 &#177; 7.41 &#956;g C m<sup>&#8722;2</sup> h<sup>&#8211;1</sup>), in contrast to the drained raised bog pine forest being a net source (33.92 &#177; 20.38 &#956;g C m<sup>&#8722;2</sup> h<sup>&#8722;1</sup>). The nitrogen-rich spruce site had the largest N<sub>2</sub>O emissions (27.64 &#177; 9.88 &#956;g N m<sup>&#8722;2</sup> h<sup>&#8722;1</sup>), with the highest fluxes in April and May (with a maximum of 309.84 &#956;g N m<sup>&#8722;2</sup> h<sup>&#8722;1</sup>). Further analysis of soil GHG fluxes and linkage to soil chemical, physical and environmental parameters will help determine and explain the magnitude and temporal variability of drained transitional bog forest's GHG fluxes and, consequently, highlight the importance of disturbance of these sensitive ecosystems.</p>
<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&#8217; 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 (&#8722;48.9 &#177; 12.9 &#956;g m<sup>&#8722;&#8205;2</sup> h<sup>&#8722;&#8205;1</sup>), whereas the reference fen studied had a higher emission potential of 396&#160;&#177;&#160;214 &#956;g m<sup>&#8722;&#8205;2</sup> h<sup>&#8722;&#8205;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&#160;&#177;&#160;10.49 &#956;g m<sup>&#8722;&#8205;2</sup> h<sup>&#8722;&#8205;1</sup>) than drier sites (17.97&#160;&#177;&#160;4.8 &#956;g m<sup>&#8722;&#8205;2</sup> h<sup>&#8722;&#8205;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>
<p>Organic soils are one of the largest natural terrestrial carbon stores, especially in boreal, temperate, and tropical wet climates. In these environments, scarcity of oxygen due to soil wetness has enabled the accumulation of organic carbon deposits over the past millennia. In Europe, organic soils account for only 3% of total agricultural land. Yet, they play a significant role in meeting Europe's 2030 and 2050 climate change mitigation targets. However, drainage of these soils, as a common management practice aiming for higher agricultural productivity, transforms these carbon-rich soils into a significant GHG source.</p> <p>Water-level management practices are critical in agriculture to minimize soil degradation and nutrient leaching. Fluctuations in water levels may alter soil physical and chemical conditions and potentially cause GHG emissions. Deep draining leads to an increase in carbon dioxide (CO<sub>2</sub>) and nitrous oxide (N<sub>2</sub>O) emissions due to increased soil mineralization. On the other hand, methane (CH<sub>4</sub>) emissions are lower compared to natural wetlands where soil drainage and tillage do not occur. Land use, climate zone, soil nutrient status, fertilization, and drainage status are closely related to estimating GHG budgets from managed sites on organic soils.</p> <p>Available data on actual GHG emissions from drained and nutrient-rich organic soils under different management practices show considerable variation. Therefore our study's main objectives are: (I) to update GHG emission factors for organic soils in drained croplands and grasslands and (ii) to calculate soil carbon and nitrogen budgets applicable to the Baltic countries. A two-year study was conducted from January 2021 to December 2022 to assess the impact of drainage and land use on GHG fluxes in the Baltic countries.</p> <p>Fluxes in croplands and perennial grassland on nutrient-rich organic soils with different drainage conditions were determined by groups: (I) excessively drained croplands, (II) excessively drained grasslands, (III) moderately drained grasslands, (IV) rewetted grasslands, and (V) non-managed fens as reference sites. Measurements were done monthly (Latvia and Lithuania) or twice per month (Estonia) using the manual static dark chamber method (N<sub>2</sub>O, CH<sub>4</sub>), the dynamic transparent chamber method for net ecosystem exchange, and the dynamic dark chamber for soil heterotrophic respiration (CO<sub>2</sub>). In addition, we measured associated environmental parameters (water table level, soil moisture and temperature, and solar radiation). For biomass analyses, we took samples once in the measurement period.</p> <p>Our preliminary results show that all grasslands were annual CH<sub>4</sub> sinks, while fens soils in natural status were a source of CH<sub>4</sub>. All studied sites were N<sub>2</sub>O sources on an annual basis, and croplands were the strongest emitters, as was expected. Higher N<sub>2</sub>O emissions and temporal variability were associated with sites characterized by high groundwater levels with high seasonal fluctuations. Soil heterotrophic respiration fluxes peaked over all the study sites during the summer. As the last field campaign shortly ended, more detailed data analyses will be presented at the conference.</p> <p><em>This research was supported by the LIFE programme project "Demonstration of climate change mitigation potential of nutrients rich organic soils in Baltic States and Finland", (2019-2023, LIFE OrgBalt, LIFE18 274CCM/LV/001158).</em></p>
<p>Methane (CH<sub>4</sub>) has high global warming potential, and its atmospheric concentration is increasing rapidly at the present rate of 0.3% yr<sup>-1</sup>. Forest ecosystems cover a large part of the biosphere and play a significant role in climate change. Upland forest soils are considered as important terrestrial sinks for atmospheric CH<sub>4</sub>; however, the complex interactions between microbial processes of CH<sub>4</sub> production and oxidation, and environmental drivers are not well understood. Balance of CH<sub>4</sub> in the forest ecosystems depends on two main natural processes, i.e., anaerobic methanogenesis and aerobic methanotrophy, driven by multiple environmental factors. A forest ecosystem's ability to exchange CH<sub>4</sub> depends on the soil type, environmental conditions, species composition, living trees and deadwood, age and health conditions of the tree stand, and their CH<sub>4</sub> balance can vary between seasons and years.</p><p>In this study, we present long-term CH<sub>4</sub> fluxes (from 2015 to 2019) in a 60-200-year-old coniferous forest site of Scots pine (Pinus sylvestris) grown on loose sandy soil in Soontaga research station (58&#176;01'N 26&#176;04'E) in Estonia. The fluxes of CH<sub>4</sub> were measured every two weeks, using a manual static soil chamber (n = 6) and gas chromatography method. Air temperature, precipitation and humidity, and soil moisture and temperature (10 cm depth) were measured continuously. The average annual temperature and precipitation recorded were 7.3 + 1.0 &#176;C and 54.3 + 3.9 mm, respectively.</p><p>The results showed that mature pine forest soil was an annual net sink of CH<sub>4</sub>: &#8722;21.14 + 0.59 g ha<sup>&#8722;&#8205;1</sup> yr<sup>-1 </sup>(mean + SE). No significant difference (p&#160;<&#160;0.05) was found between the soil CH<sub>4</sub> uptake and tree age. Methane uptake correlated negatively (r<sup>2&#160;</sup>= 0.61, p&#160;<&#160;0.05) with soil temperature and showed similar seasonal dynamics being highest during the vegetation period (Apr-Oct) and lowest during the non-vegetation period (Nov-Mar). The highest CH<sub>4</sub> uptake (&#8722;36.93 g ha<sup>&#8722;&#8205;1</sup>) was observed in July 2018, the warmest and driest month during the overall period. Even though soil moisture was only weakly correlated (r<sup>2</sup>&#160;=&#160;0.15, p&#160;<&#160;0.05) with CH<sub>4</sub> uptake, the CH<sub>4</sub> flux was affected by precipitation. As a result of this, it is noticed that CH<sub>4</sub> uptake in the cold and wet conditions decreased with increasing precipitation in winter and increased with warming during warm and dry conditions in summer.</p><p>Concluded, our coniferous pine forest was sequestering CH<sub>4</sub> during the investigated five years. The soil CH<sub>4</sub> uptake could be explained by CH<sub>4</sub> oxidation at optimal temperature in the water-unsaturated surface soil regulating the soil's microbial activity.</p>
<p>Nutrient-rich organic soils are one of the largest key sources of greenhouse gas (GHG) emissions in cool moist climate regions in Europe, and around 15 Mha of wetlands are drained for forestry across the world's temperate and boreal areas. Drainage promotes the decomposition of the organic material stored in these naturally water-saturated organic soils, turning the wetland from a carbon sink into an emitter of CO<span xml:lang="EN-US"><span><sub>2</sub></span></span>. Lower soil water content in drained histosols leads to reduced CH<sub>4</sub> emission, while N<span xml:lang="EN-US"><span><sub>2</sub></span></span>O emission can increase due to increased mineralization and more favorable conditions for nitrification. However, detailed information of GHG emissions from drained organic soils under different land use and management in the hemiboreal zone is still scarce.&#160;&#160;</p><p xml:lang="EN-US"><span xml:lang="EN-US">We conducted a full-year study at drained peatland sites with different land uses to assess the impact of drainage and land-use on GHG fluxes in Estonia. We investigated ten sites: (I) five forests with different tree species, (II) three grasslands with different water regimes, (III) cropland and (IV) natural wetland (fen). The GHG fluxes were measured twice per month using the manual static (CH</span><sub>4</sub> and N<sub>2</sub>O) and dynamic (heterotrophic respiration (CO<span xml:lang="EN-US"><span><sub>2</sub></span></span>)) closed chamber method from Jan 2020 to Dec 2021. Additionally, groundwater level, soil temperature and moisture were measured hourly with automatic loggers to determine soil conditions.&#160;&#160;&#160;</p><p xml:lang="EN-US"><span xml:lang="EN-US">Our preliminary results show that all drained forest soils were annual CH<sub>4</sub> sinks (&#8722;59.4 &#177; 2.5 &#181;g m</span><span xml:lang="EN-US"><span><sup>-2</sup></span></span> h<sup>-1</sup>, mean &#177; SE). However, CH<span xml:lang="EN-US"><span><sub>4</sub></span></span> uptake from the&#160;studied fen, crop and grasslands were lower, &#8211;13.2 &#177; 4.4, -12.2 &#177; 2.0 and -8.2 &#177; 3.3 &#181;g m<span xml:lang="EN-US"><span><sup>-2</sup></span></span> h<sup>-1</sup>, respectively, while grassland with poor drainage soil was a less source of CH<sub>4 </sub><span xml:lang="EN-US">emission. Most of the sites were annual emitters of N</span><sub>2</sub>O; forest sites were higher emitters (15.9 &#177; 2.3 &#181;g m<sup>-2</sup> h<sup>-1</sup>) than cropland (12.7 &#177; 4.1 &#181;g m<span xml:lang="EN-US"><span><sup>-2</sup></span></span> h<sup>-1</sup>) and fen soils (6.3 &#177; 1.1 &#181;g m<span xml:lang="EN-US"><span><sup>-2</sup></span></span> h<sup>-1</sup>). N<sub>2</sub>O fluxes from grasslands depend on drainage intensity and the site with poor drainage emitted less. Higher N<span xml:lang="EN-US"><span><sub>2</sub></span></span>O emissions and temporal variability were associated with sites where the water level had high seasonal fluctuations. Soil CO<sub>2</sub> fluxes (heterotrophic respiration) were highest from grasslands and peaked over all the study sites during the summer. Methane flux had a statistically significant correlation with water level and soil moisture, while N<sub>2</sub>O flux was controlled by soil temperature, having higher emissions in a warmer season. <span xml:lang="EN-US">The results provide insights into GHG fluxes over temporal and spatial scales and indicate the need for mitigation measures and further enhancement of modeling tools for climate-friendly land management practices in nutrient-rich organic soils.&#160;&#160;</span>&#160;</p><p xml:lang="EN-US"><span xml:lang="EN-US">This research was supported by the LIFE programme project &#8220;Demonstration of climate change mitigation potential of nutrients rich organic soils in Baltic States and Finland&#8221;, (2019-2023, LIFE OrgBalt</span>, LIFE18 274CCM/LV/001158)<span>&#160;</span></p>
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