The drawdown of the water level has been hypothesized to change peatlands from carbon (C) sinks to C sources to the atmosphere as a result of increased oxidation of organic matter. We measured the ...change in peat thickness (subsidence of peat surface) ca. 60 years after drainage in 273 peatland sites (875 points) representing three nutrient levels of pine fens and five macroclimatic regions from southern to northern Finland, and we calculated the changes in peat C densities and peat C stores using direct measurements and estimates drawn from regression models for C density derived in this study. On average, the peat surface had subsided ca. 22 plus or minus 17 cm (mean plus or minus SD), the C density had increased by 26 plus or minus 15 kg/m super(3), and the C stores had increased by 5.9 plus or minus 14.4 kg/m super(2) after drainage. Therefore, the hypothesis that drainage of peatland always makes them sources of C to the atmosphere is incorrect. We concluded that the post-drainage subsidence of peat surface was mainly caused by changes in the physical structure of peat after the removal of water while the oxidation of peat was of less importance. The changes in C density and C stores seemed to be dependent on the input of new C into the system through net primary production, especially through the fine roots of trees. Our results suggest that tree stand development plays an important role in the post-drainage C balance of peat soils.
Boreal mires encompass high diversity in species and habitats, many of which are endangered. In Finland, extensive use of peatlands has resulted in habitat fragmentation. A need for accurate and ...cost-efficient vegetation mapping and monitoring of habitat changes exists in mire conservation, restoration and peatland forestry. LiDAR is an emerging and excellent tool for probing the geometry of vegetation and terrain. Modern systems measure the backscattered signal accurately and also provide radiometric information. Experiments were carried out in a complex minerotrophic–ombrotrophic eccentric raised bog in southern Finland (61°47′N, 24.18′E). First, we tested discrete-return LiDAR for the modeling of mire surface patterns and the detection of hummocks and hollows, as well as the effect of mire plants on the Z accuracy of the surface echoes. Secondly, the response of different mire vegetation samples in LiDAR intensity was examined. Thirdly, we tested area-based geometric and radiometric features in supervised classification of mire habitats to discover the meaningful variables. The vertical accuracy of LiDAR in mire surface modeling was high: 0.05–0.10
m. A binary hummock-hollow model that was estimated from a LiDAR-based elevation model matched flawlessly in aerial images and had moderate explanatory power in habitat classification trials. The intensity of LiDAR in open-mire vegetation was mainly influenced by the surface moisture, and separation of vegetation classes spanning from ombrotrophic to mesotrophic vegetation proved to be difficult. Area-based features that characterize the height distribution of LiDAR points in the canopy were the strongest explanatory variables in the classification of 21 diverse mire site types. Actual qualifying differences in the ground flora were unattainable in the LiDAR data, which resulted in inferior accuracy in the characterization of ecohydrological conditions and nutrient level of open mires and sparsely forested wet sites. Mire habitat classification accuracy with LiDAR surpassed earlier results with optical data. The results suggested that LiDAR constitutes an efficient aid for monitoring applications. We propose the co-use of images and LiDAR for enhanced mapping of open mires and tree species.
In situ calibration and validation procedures are required until invariant geometric and radiometric features are discovered.
Drained organic forest soils in boreal and temperate climate zones
are believed to be significant sources of the greenhouse gases (GHGs) carbon
dioxide (CO2), methane (CH4) and nitrous oxide (N2O), ...but the
annual fluxes are still highly uncertain. Drained organic soils exemplify
systems where many studies are still carried out with relatively small
resources, several methodologies and manually operated systems, which
further involve different options for the detailed design of the measurement
and data analysis protocols for deriving the annual flux. It would be
beneficial to set certain guidelines for how to measure and report the data,
so that data from individual studies could also be used in synthesis work
based on data collation and modelling. Such synthesis work is necessary for
deciphering general patterns and trends related to, e.g., site types,
climate, and management, and the development of corresponding emission
factors, i.e. estimates of the net annual soil GHG emission and removal, which
can be used in GHG inventories. Development of specific emission factors
also sets prerequisites for the background or environmental data to be
reported in individual studies. We argue that wide applicability greatly
increases the value of individual studies. An overall objective of this
paper is to support future monitoring campaigns in obtaining high-value
data. We analysed peer-reviewed publications presenting CO2, CH4
and N2O flux data for drained organic forest soils in boreal and
temperate climate zones, focusing on data that have been used, or have the
potential to be used, for estimating net annual soil GHG emissions and removals.
We evaluated the methods used in data collection and identified major gaps
in background or environmental data. Based on these, we formulated
recommendations for future research.
Partitioning soil respiration (SR) into its components, heterotrophic and rhizospheric respiration, is an important step for understanding and modelling carbon (C) cycling in organic soils. However, ...no partitioning studies on afforested organic soil croplands exist. We separated soil respiration originating from the decomposition of peat (SR
P), and aboveground litter (SR
L) and root respiration (SR
R) in six afforested organic soil croplands in Finland with varying tree species and stand ages using the trenching method. Across the sites temporal variation in SR was primarily related to changes in soil surface temperature (−5
cm), which explained 71–96% of variation in SR rates. Decomposition of peat and litter was not related to changes in water table level, whereas a minor increase in root respiration was observed with the increase in water table depth. Temperature sensitivity of SR varied between the different respiration components: SR
P was less sensitive to changes in soil surface temperature than SR
L or SR
R. Factors explaining spatial variation in SR differed between different respiration components. Annual SR
P correlated positively with peat ash content while that of SR
L was found to correlate positively with the amount of litter on the forest floor, separately for each tree species. Root respiration correlated positively with the biomass of ground vegetation. From the total soil respiration peat decomposition comprised a major share of 42%; the proportion of autotrophic respiration being 41% and aboveground litter 17%. Afforestation lowered peat decomposition rates. Nevertheless the effect of agricultural history can be seen in peat properties for decades and due to high peat decomposition rates these soils still loose carbon to the atmosphere.
Natural peatlands accumulate carbon (C) and nitrogen (N). They affect the global climate by binding carbon dioxide (CO2) and releasing methane (CH4) to the atmosphere; in contrast fluxes of nitrous ...oxide (N2O) in natural peatlands are insignificant. Changes in drainage associated with forestry alter these greenhouse gas (GHG) fluxes and thus the radiative forcing (RF) of peatlands. In this paper, changes in peat and tree stand C stores, GHG fluxes and the consequent RF of Finnish undisturbed and forestry‐drained peatlands are estimated for 1900–2100. The C store in peat is estimated at 5.5 Pg in 1950. The rate of C sequestration into peat has increased from 2.2 Tg a‐‐1 in 1900, when all peatlands were undrained, to 3.6 Tg a‐‐1 at present, when c. 60% of peatlands have been drained for forestry. The C store in tree stands has increased from 60 to 170 Tg during the 20th century. Methane emissions have decreased from an estimated 1.0–0.5 Tg CH4‐‐C a‐‐1, while those of N2O have increased from 0.0003 to 0.005 Tg N2O‐‐N a‐‐1. The altered exchange rates of GHG gases since 1900 have decreased the RF of peatlands in Finland by about 3 mW m‐‐2 from the predrainage situation. This result contradicts the common hypothesis that drainage results in increased C emissions and therefore increased RF of peatlands. The negative radiative forcing due to drainage is caused by increases in CO2 sequestration in peat (‐‐0.5 mW m‐‐2), tree stands and wood products (‐‐0.8 mW m‐‐2), decreases in CH4 emissions from peat to the atmosphere (‐‐1.6 mW m‐‐2), and only a small increase in N2O emissions (+0.1 mW m‐‐2). Although the calculations presented include many uncertainties, the above results are considered qualitatively reliable and may be expected to be valid also for Scandinavian countries and Russia, where most forestry‐drained peatlands occur outside Finland.
Twenty chambers for measurement of soil CO2 efflux were compared against known CO2 fluxes ranging from 0.32 to 10.01 mumol CO2 m(-2) s(-1) and generated by a specially developed calibration tank. ...Chambers were tested on fine and coarse homogeneous quartz sand with particle sizes of 0.05-0.2 and 0.6 mm, respectively. The effect of soil moisture on chamber measurements was tested by wetting the fine quartz sand to about 25% volumetric water content. Non-steady-state through-flow chambers either underestimated or overestimated fluxes from -21 to +33% depending on the type of chamber and the method of mixing air within the chamber's headspace. However, when results of all systems tested were averaged, fluxes were within 4% of references. Non-steady-state non-through-flow chambers underestimated or overestimated fluxes from -35 to +6%. On average, the underestimation was about 13-14% on fine sand and 4% on coarse sand. When the length of the measurement period was increased, the underestimation increased due to the rising concentration within the chamber headspace, which reduced the diffusion gradient within the soil. Steady-state through-flow chambers worked almost equally well in all sand types used in this study. They overestimated the fluxes on average by 2-4%. Overall, the reliability of the chambers was not related to the measurement principle per se. Even the same chambers, with different collar designs, showed highly variable results. The mixing of air within the chamber can be a major source of error. Excessive turbulence inside the chamber can cause mass flow of CO2 from the soil into the chamber. The chamber headspace concentration also affects the flux by altering the concentration gradient between the soil and the chamber.
Recently, increased attention has been drawn to the greenhouse gas emissions of the Land use, Land use Change and Forestry (LULUCF) sector. In the Finnish LULUCF sector, the soil-originated emissions ...from the after-use of cutover peatland have become a more relevant question. This is due to the rapid increase in the number of former peat-harvesting sites, caused by the decline in the combustion of energy peat due to its high CO2 emissions. We conducted a nationally representative survey to study which after-use options of cutover peatlands are preferred by landowners. Based on the preferred after-use options, we estimated their impact on the national greenhouse gas emissions in the Finnish regions in 2035, and what factors influence the landowners’ choice of after-use options. We found that the four most popular after-use options for landowners were afforestation (71%), agriculture (24%), production of wind and solar power (22%) and rewetting (18%) when the respondent chose the three most attractive options. However, there were clear regional differences in the preferred after-use options, which might lead, if realized, to different soil-originated emissions at the regional level. The preferred after-use options could produce emissions of 0.35 million tonnes of carbon dioxide equivalent a year (Mt CO2 eq y−1) by 2035 in Finland. Most of these emissions (30.1%) would come from South Ostrobothnia in western Finland, mainly due to the indicated high interest in agricultural after-use. Most landowners prefer financially profitable after-use options, such as forestry, agriculture, as well as wind and solar energy production in cutover peatlands. However, environmentally oriented landowners favour many kinds of actions to support biodiversity, carbon sequestration, and water protection in cutover peatlands. It is crucial that economic productivity and the greenhouse gas sinks of cutover peatlands be considered simultaneously to meet the climate targets of the LULUCF sector in Finland.
•The landowners’ perspective of using cutover peatland was studied.•The landowners prefer financially profitable after-use options.•Forestry, agriculture, and wind and solar energy were the most popular options.•Landowners’ choices would increase the soil originated GHG emissions nationally.•Strengthening the dialogue between the landowners and climate policy is needed.
Vast areas of peatlands have been drained for forestry endangering their carbon sink function. Peatland rewetting aims at mitigating the situation through restoring the hydrology and vegetation of ...these areas. We compared the carbon dioxide (CO2) fluxes and phytomass on four pairs of rewetted and pristine peatland sites in Finland and Estonia, and described correlations between phytomass and CO2 fluxes. We measured the net ecosystem exchange of CO2 (NEE), respiration and photosynthesis over one growing season using manual chambers, and biomass of plant functional types (PFT) on rewetted sites and their pristine counterparts. Although pair-wise differences in the vegetation were small, pristine sites were on average stronger CO2 sinks than rewetted sites. Respiration was higher in hummocks while no differences were found in photosynthesis between hummocks and hollows. No clear relationship between the biomasses of PFTs and NEE was found. Generally, however, CO2 uptake decreased with increase in Sphagnum biomass.
In spite of advances in greenhouse gas research, the spatiotemporal CH4 and N2O dynamics of boreal landscapes remain challenging, e.g., we need clarification of whether forest–mire transitions are ...occasional hotspots of landscape CH4 and N2O emissions during exceptionally high and low ground water level events. In our study, we tested the differences and drivers of CH4 and N2O dynamics of forest/mire types in field conditions along the soil moisture gradient of the forest–mire ecotone. Soils changed from Podzols to Histosols and ground water rose downslope from a depth of 10 m in upland sites to 0.1 m in mires. Yearly meteorological conditions changed from being exceptionally wet to typical and exceptionally dry for the local climate. The median fluxes measured with a static chamber technique varied from −51 to 586 μg m−2 h−1 for CH4 and from 0 to 6 μg m−2 h−1 for N2O between forest and mire types throughout the entire wet–dry period. In spite of the highly dynamic soil water fluctuations in carbon rich soils in forest–mire transitions, there were no large peak emissions in CH4 and N2O fluxes and the flux rates changed minimally between years. Methane uptake was significantly lower in poorly drained transitions than in the well-drained uplands. Water-saturated mires showed large CH4 emissions, which were reduced entirely during the exceptional summer drought period. Near-zero N2O fluxes did not differ significantly between the forest and mire types probably due to their low nitrification potential. When upscaling boreal landscapes, pristine forest–mire transitions should be regarded as CH4 sinks and minor N2O sources instead of CH4 and N2O emission hotspots.
In spite of advances in greenhouse gas research, the spatiotemporal CH.sub.4 and N.sub.2 O dynamics of boreal landscapes remain challenging, e.g., we need clarification of whether forest-mire ...transitions are occasional hotspots of landscape CH.sub.4 and N.sub.2 O emissions during exceptionally high and low ground water level events. In our study, we tested the differences and drivers of CH.sub.4 and N.sub.2 O dynamics of forest/mire types in field conditions along the soil moisture gradient of the forest-mire ecotone. Soils changed from Podzols to Histosols and ground water rose downslope from a depth of 10 m in upland sites to 0.1 m in mires. Yearly meteorological conditions changed from being exceptionally wet to typical and exceptionally dry for the local climate. The median fluxes measured with a static chamber technique varied from -51 to 586 μg m.sup.-2 h.sup.-1 for CH.sub.4 and from 0 to 6 μg m.sup.-2 h.sup.-1 for N.sub.2 O between forest and mire types throughout the entire wet-dry period. In spite of the highly dynamic soil water fluctuations in carbon rich soils in forest-mire transitions, there were no large peak emissions in CH.sub.4 and N.sub.2 O fluxes and the flux rates changed minimally between years. Methane uptake was significantly lower in poorly drained transitions than in the well-drained uplands. Water-saturated mires showed large CH.sub.4 emissions, which were reduced entirely during the exceptional summer drought period. Near-zero N.sub.2 O fluxes did not differ significantly between the forest and mire types probably due to their low nitrification potential. When upscaling boreal landscapes, pristine forest-mire transitions should be regarded as CH.sub.4 sinks and minor N.sub.2 O sources instead of CH.sub.4 and N.sub.2 O emission hotspots.
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