The post-drainage changes in vegetation composition and carbon balance were studied on four site types (from minero-to ombrotrophic conditions) in Lakkasuo mire, central Finland, by directly ...comparing undrained and drained parts (30 years ago) of the mire. Drainage had drastically changed the species composition of the sites, especially at the minerotrophic sites, where almost all Sphagna had been replaced by forest mosses. On the ombrotrophic sites much of the mire vegetation still remained 30 years after drainage. Drainage had decreased the C stores in ground vegetation on the minerotrophic sites but increased them on the ombrotrophic sites. The changes were, however, very small compared to the changes in the tree stand, where the C stores had increased at all sites (increasing with nutrient level). The change in peat C balance over the 30-year post-drainage period was negative on the most nutrient-rich site, and positive on the others, increasing with lower nutrient levels. The decrease in the peat C balance on the most nutrient-rich site was compensated by the greater increase in the tree stand C stores and the changes in the total C balance (peat+ tree stand+ ground vegetation) remained positive on all sites.
Surface–atmosphere energy exchange is strongly ecosystem-specific. At the same time, as the energy balance constitutes responses of an ecosystem to environmental stressors including precipitation, ...humidity and solar radiation, it results in feedbacks of potential importance for the regional climate. Northern peatlands represent a diverse class of ecosystems that cover nearly 6 × 106 km2 in the Boreal region, which makes the inter-comparison of their energy balances an important objective. With this in mind we studied energy exchange across a broad spectrum of peatlands from pristine fens and bogs to forested and agriculturally managed peatlands, which represent a large fraction of the landscape in Finland and Sweden. The effects of management activities on the energy balance were extensively examined from the micrometeorological point of view, using eddy covariance data from eight sites in these two countries (56º 12'–62º 11' N, 13º 03'–30º 05' E). It appears that the surface energy balance varies widely amongst the different peatland types. Generally, energy exchange features including the Bowen ratio, surface conductance, coupling to the atmosphere, responses to water table fluctuations and vapour pressure deficit could be associated directly with the peatland type. The relative constancy of the Bowen ratio in natural open mires contrasted with its variation in tree-covered and agricultural peatlands. We conclude that the impacts of management and the consequences of land-use change in peatlands for the local and regional climate might be substantial.
Drainage of peatlands is expected to turn these ecosystems into carbon
sources to the atmosphere. We measured carbon dynamics of a drained forested
peatland in southern Finland over 4 years, ...including one with severe drought
during growing season. Net ecosystem exchange (NEE) of carbon dioxide
(CO2) was measured with the eddy covariance method from a mast
above the forest. Soil and forest floor CO2 and methane
(CH4) fluxes were measured from the strips and from ditches with
closed chambers. Biomass and litter production were sampled, and soil
subsidence was measured by repeated levellings of the soil surface. The
drained peatland ecosystem was a strong sink of carbon dioxide in all studied
years. Soil CO2 balance was estimated by subtracting the carbon
sink of the growing tree stand from NEE, and it showed that the soil itself
was a carbon sink as well. A drought period in one summer significantly
decreased the sink through decreased gross primary production. Drought also
decreased ecosystem respiration. The site was a small sink for CH4,
even when emissions from ditches were taken into account. Despite the
continuous carbon sink, peat surface subsided slightly during the 10-year
measurement period, which was probably mainly due to compaction of peat. It
is concluded that even 50 years after drainage this peatland site acted as a
soil C sink due to relatively small changes in the water table and in plant
community structure compared to similar undrained sites, and the
significantly increased tree stand growth and litter production. Although the
site is currently a soil C sink, simulation studies with process models are
needed to test whether such sites could remain C sinks when managed for
forestry over several tree-stand rotations.
The urgent need to mitigate climate change has evoked a broad interest in better understanding and estimating nitrous oxide (N.sub.2 O) emissions from different ecosystems. Part of the uncertainty in ...N.sub.2 O emission estimates still comes from an inadequate understanding of the temporal and small-scale spatial variability of N.sub.2 O fluxes. Using 4.5 years of N.sub.2 O flux data collected in a drained peatland forest with six automated chambers, we explored temporal and small-scale spatial variability of N.sub.2 O fluxes. A random forest with conditional inference trees was used to find immediate and delayed relationships between N.sub.2 O flux and environmental conditions across seasons and years.
The most common forest management method in Fennoscandia is rotation forestry, including clear-cutting and forest regeneration. In clear-cutting, stem wood is removed and the logging residues are ...either removed or left on site. Clear-cutting changes the microclimate and vegetation structure at the site, both of which affect the site's carbon balance. Peat soils with poor aeration and high carbon densities are especially prone to such changes, and significant changes in greenhouse gas exchange can be expected. We measured carbon dioxide (CO2) and energy fluxes with the eddy covariance method for 2 years (April 2016–March 2018) after clear-cutting a drained peatland forest. We observed a significant rise (23 cm) in the water table level and a large CO2 source (first year: 3086±148 g CO2 m−2 yr−1; second year: 2072±124 g CO2 m−2 yr−1). These large CO2 emissions resulted from the very low gross primary production (GPP) following the removal of photosynthesizing trees and the decline of ground vegetation, unable to compensate for the decomposition of logging residues and peat. During the second summer (June–August) after the clear-cutting, GPP had already increased by 96 % and total ecosystem respiration decreased by 14 % from the previous summer. The mean daytime ratio of sensible to latent heat flux decreased after harvesting from 2.6 in May 2016 to 1.0 in August 2016, and in 2017 it varied mostly within 0.6–1.0. In April–September, the mean daytime sensible heat flux was 33 % lower and latent heat flux 40 % higher in 2017, probably due to the recovery of ground vegetation that increased evapotranspiration and albedo of the site. In addition to CO2 and energy fluxes, we measured methane (CH4) and nitrous oxide (N2O) fluxes with manual chambers. After the clear-cutting, the site turned from a small CH4 sink into a small source and from N2O neutral to a significant N2O source. Compared to the large CO2 emissions, the 100-year global warming potential (GWP100) of the CH4 emissions was negligible. Also, the GWP100 due to increased N2O emissions was less than 10 % of that of the CO2 emission change.
In peatlands drained for forestry, the soil carbon (C) or
carbon dioxide (CO2) balance is affected by both (i) higher
heterotrophic CO2-C release from faster decomposing soil organic matter
(SOM) and ...(ii) higher plant litter C input from more vigorously growing
forests. This balance and other greenhouse gas (GHG) sinks and sources in
managed lands are annually reported by national GHG inventories to the
United Nations Climate Change Convention. In this paper, we present a
revised, fully dynamic method for reporting the CO2 balance of drained
peatland forest soils in Finland. Our method can follow temporal changes in
tree biomass growth, tree harvesting and climatic parameters, and it is built
on empirical regression models of SOM decomposition and litter input in
drained peatland forests. All major components of aboveground and
belowground litter input from ground vegetation as well as live trees and trees that died naturally
are included, supplemented by newly acquired turnover rates of woody
plant fine roots. Annual litter input from harvesting residues is calculated
using national statistics of logging and energy use of trees. Leaching,
which also exports dissolved C from drained peatlands, is not included. The
results are reported as time series from 1990–2021 following the practice
in the GHG inventory. Our revised method produces an increasing trend of annual
emissions from 0.2 to 2.1 t CO2 ha−1 yr−1 for the period
1990–2021 in Finland (equal to a trend from 1.4 to 7.9 Mt CO2 yr−1 for the entire 4.3 Mha of drained peatland forests), with a
statistically significant difference between the years 1990 and 2021. Across the
period 1990–2021, annual emissions are on average 1.5 t CO2 ha−1 yr−1 (3.4 Mt CO2 yr−1 for 2.2 Mha area) in warmer southern
Finland and −0.14 t CO2 ha−1 yr−1 (−0.3 Mt CO2 yr−1
for 2.1 Mha area) in cooler northern Finland. When combined with data on the
CO2 sink created by the growing tree stock, in 2021 the drained peatland forest
ecosystems were a source of 1.0 t CO2 ha−1 yr−1 (2.3 Mt CO2 yr−1) in southern Finland and a sink of 1.2 t CO2 ha−1 yr−1 (2.5 Mt CO2 yr−1) in northern Finland. We
compare these results to those produced by the semi-dynamic method used earlier
in the Finnish GHG inventory and discuss the strengths and
vulnerabilities of the new revised method in comparison to more static
emission factors.
We compiled published peer-reviewed CO2, CH4, and N2O data on managed drained organic forest soils in boreal and temperate zones to revisit the current Tier 1 default emission factors (EFs) provided ...in the IPCC (2014) Wetlands Supplement: to see whether their uncertainty may be reduced; to evaluate possibilities for breaking the broad categories used for the IPCC EFs into more site-type-specific ones; and to inspect the potential relevance of a number of environmental variables for predicting the annual soil greenhouse gas (GHG) balances, on which the EFs are based. Despite a considerable number of publications applicable for compiling EFs being added, only modest changes were found compared to the Tier 1 default EFs. However, the more specific site type categories generated in this study showed narrower confidence intervals compared to the default categories. Overall, the highest CO2 EFs were found for temperate afforested agricultural lands and boreal forestry-drained sites with very low tree stand productivity. The highest CH4 EFs in turn prevailed in boreal nutrient-poor forests with very low tree stand productivity and temperate forests irrespective of nutrient status, while the EFs for afforested sites were low or showed a sink function. The highest N2O EFs were found for afforested agricultural lands and forestry-drained nutrient-rich sites. The occasional wide confidence intervals could be mainly explained by single or a few highly deviating estimates rather than the broadness of the categories applied. Our EFs for the novel categories were further supported by the statistical models connecting the annual soil GHG balances to site-specific soil nutrient status indicators, tree stand characteristics, and temperature-associated weather and climate variables. The results of this synthesis have important implications for EF revisions and national emission reporting, e.g. by the use of different categories for afforested sites and forestry-drained sites, and more specific site productivity categories based on timber production potential.
As soil microbial respiration is the major component of land CO.sub.2 emissions, differences in the functional dependence of respiration on soil moisture among Earth system models (ESMs) contributes ...significantly to the uncertainties in their projections.
Drainage of peatlands for forestry starts a succession of ground vegetation in which mire species are gradually replaced by forest species. Some mire plant communities vanish quickly following the ...water-level drawdown; some may prevail longer in the moister patches of peatland. Drainage ditches, as a new kind of surface, introduce another component of spatial variation in drained peatlands. These variations were hypothesized to affect methane (CH₄) fluxes from drained peatlands. Methane fluxes from different plant communities and unvegetated surfaces, including ditches, were measured at the drained part of Lakkasuo mire, Central Finland. The fluxes were found to be related to peatland site type, plant community, water-table position and soil temperature. At nutrient-rich fen sites fluxes between plant communities differed only a little: almost all plots acted as CH₄ sinks (-0.9 to -0.4 mg CH₄ m-² d-¹), with the exception of Eriophorum angustifolium Honck. communities, which emitted 0.9 g CH₄ m-² d-¹. At nutrient-poor bog site the differences between plant communities were clearer. The highest emissions were measured from Eriophorum vaginatum L. communities (29.7 mg CH₄ m-² d-¹), with a decreasing trend to Sphagna (10.0 mg CH₄ m-² d-¹) and forest moss communities (2.6 mg CH₄ m-² d-¹). CH₄ emissions from different kinds of ditches were highly variable, and extremely high emissions (summertime averages 182-600 mg CH₄ m-² d-¹) were measured from continuously water-covered ditches at the drained fen. Variability in the emissions was caused by differences in the origin and movement of water in the ditches, as well as differences in vegetation communities in the ditches. While drainage on average greatly decreases CH₄ emissions from peatlands, a great spatial variability in fluxes is emerged. Emissions from ditches constantly covered with water, may in some cases have a great impact on the overall CH₄ emissions from drained peatlands.
PDF
