Browsing by Subject "WATER-LEVEL DRAWDOWN"

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  • Bhuiyan, Md Rabbil; Minkkinen, Kari; Helmisaari, Helja-Sisko; Ojanen, Paavo; Penttila, Timo; Laiho, Raija (2017)
    Background and aims Estimation of root-mediated carbon fluxes in forested peatlands is needed for understanding ecosystem functioning and supporting greenhouse gas inventories. Here, we aim to determine the optimal methodology for utilizing ingrowth cores in estimating annual fine-root production (FRP) and its vertical distribution in trees, shrubs and herbs. Methods We used 3-year data obtained with modified ingrowth core method and tested two calculation methods: 'ingrowth-dividing' and `ingrowth-subtracting'. Results The ingrowth-dividing method combined with a 2-year incubation of ingrowth cores can be used for the 'best estimate' of FRP. The FRP in the nutrient-rich fen forest (561 g m(-2)) was more than twice that in the nutrient-poor bog forest (244 g m(-2)). Most FRP occurred in the top 20-cm layer (76-82 %). Tree FRP accounted for 71 % of total FRP in the bog and 94 % in the fen forests, respectively, following the aboveground vegetation patterns; however, in fen forest the proportions of spruce and birch in FRP were higher than their proportions in stand basal area. Conclusions Our methodology may be used to study peatland FRP patterns more widely and will reduce the volume of labour-intensive work, but will benefit from verification with other methods, as is the case in all in situ FRP studies.
  • Mathijssen, Paul J. H.; Kahkola, Noora; Tuovinen, Juha-Pekka; Lohila, Annalea; Minkkinen, Kari; Laurila, Tuomas; Väliranta, Minna (2017)
    Data on past peatland growth patterns, vegetation development, and carbon (C) dynamics during the various Holocene climate phases may help us to understand possible future climate-peatland feedback mechanisms. In this study, we analyzed and radiocarbon dated several peat cores from Kalevansuo, a drained bog in southern Finland. We investigated peatland succession and C dynamics throughout the Holocene. These data were used to reconstruct the long-term atmospheric radiative forcing, i.e., climate impact of the peatland since initiation. Kalevansuo peat records revealed a general development from fen to bog, typical for the southern boreal zone, but the timing of ombrotrophication varied in different parts of the peatland. Peat accumulation patterns and lateral expansion through paludification were influenced by fires and climate conditions. Long-term C accumulation rates were overall lower than the average values found from literature. We suggest the low accumulation rates are due to repeated burning of the peat surface. Drainage for forestry resulted in a nearly complete replacement of typical bog mosses by forest species within 40 years after drainage. The radiative forcing reconstruction suggested positive values ( warming) for the first similar to 7000 years following initiation. The change from positive to negative forcing was triggered by an expansion of bog vegetation cover and later by drainage. The strong relationship between peatland area and peat type with radiative forcing suggests a possible feedback for future changing climate, as high-latitude peatlands may experience prominent regime shifts, such as fen to bog transitions.
  • Ojanen, Paavo; Penttila, Timo; Tolvanen, Anne; Hotanen, Juha-Pekka; Saarimaa, Miia; Nousiainen, Hannu; Minkkinen, Kari (2019)
    Drainage of peatlands for forestry often leads to carbon dioxide (CO2) net emission from soil due to loss of peat. This emission can be compensated for by the increased tree growth. Hovewer, many drained peatlands have low tree growth due to nutrient limitations. Tree growth at these peatlands can be effectively increased by fertilization, but fertilization has been also found to increase decomposition rates. We studied the long-term effect of fertilization of low-productive forestry-drained peatlands on the complete ecosystem greenhouse gas exchange, including both soil and tree component, and accounting for CO2, methane and nitrous oxide. Five N-rich study sites (flark fens and a rich fen) and one N-poor ombrotrophic site were established. Fertilization had started at the study sites 16-67 years before our measurements. Fertilization considerably increased tree stand CO2 sink ( + 248-1013 g CO2 m(-2) year(-1)). Decomposition increased on average by 45% ( + 431 g CO2 m(-2) year(-1)) and litter production by 38% ( + 360 g CO2 m(-2) year(-1)). Thus, on average 84% of the increased decomposition could be attributed to increased litter production and 16% to increased soil CO 2 net emission due to increased loss of peat. Soil CO2 net emission correlated positively with water table depth and top soil N concentration. Fertilization increased soil CO2 net emission at the drained flark fens on average by 187 g CO2 m(-2) year(-1). At the rich fen, net emission decreased. The N-poor bog exhibited soil CO2 sink both with and without fertilization. Effects on methane and nitrous oxide emissions were small at most sites. The increase in tree stand CO2 sink was higher than the increase in soil CO2 net emission, indicating that fertilization has a climate cooling effect in the decadal time scale. Yet, as the fertilized plots at N-rich sites exhibited soil CO2 source or zero balance, continuation of fertilization-based forestry over several rotations would lead to progressive loss of ecosystem C. At the N-poor bog, fertilization-based forestry may have a climate-cooling effect also in the centennial time scale.
  • Minkkinen, Kari; Ojanen, Paavo; Penttilä, Timo; Aurela, Mika; Laurila, Tuomas; Tuovinen, Juha-Pekka; Lohila, Annalea (2018)
    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.
  • Kangas, Laura; Maanavilja, Liisa; Hajek, Tomas; Juurola, Eija; Chimner, Rodney A.; Mehtatalo, Lauri; Tuittila, Eeva-Stiina (2014)
  • Strakova, Petra; Larmola, Tuula; Andres, Javier; Ilola, Noora; Launiainen, Piia; Edwards, Keith; Minkkinen, Kari; Laiho, Raija (2020)
    Evidence of plant root biomass and production in peatlands at the level of species or plant functional type (PFT) is needed for defining ecosystem functioning and predicting its future development. However, such data are limited due to methodological difficulties and the toilsomeness of separating roots from peat. We developed Fourier transform infrared (FTIR) spectroscopy based calibration models for quantifying the mass proportions of several common peatland species, and alternatively, the PFTs that these species represented, in composite root samples. We further tested whether woody roots could be classified into diameter classes, and whether dead and living roots could be separated. We aimed to solve whether general models applicable in different studies can be developed, and what would be the best way to build such models. FTIR spectra were measured from dried and powdered roots: both "pure roots", original samples of 25 species collected in the field, and "root mixtures", artificial composite samples prepared by mixing known amounts of pure roots of different species. Partial least squares regression was used to build the calibration models. The general applicability of the models was tested using roots collected in different sites or times. Our main finding is that pure roots can replace complex mixtures as calibration data. Using pure roots, we constructed generally applicable models for quantification of roots of the main PFTs of northern peatlands. The models provided accurate estimates even for far distant sites, with root mean square error (RMSE) 1.4-6.6% for graminoids, forbs and ferns. For shrubs and trees the estimates were less accurate due to higher within-species heterogeneity, partly related to variation in root diameter. Still, we obtained RMSE 3.9-10.8% for total woody roots, but up to 20.1% for different woody-root types. Species-level and dead-root models performed well within the calibration dataset but provided unacceptable estimates for independent samples, limiting their routine application in field conditions. Our PFT-level models can be applied on roots separated from soil for biomass determination or from ingrowth cores for estimating root production. We present possibilities for further development of species-level or dead-root models using the pure-root approach.
  • Urbanova, Zuzana; Straková, Petra; Kastovska, Eva (2018)
    Various peatland restoration strategies developed during the last two decades have aimed to stop degradation and bring back the original hydrology, biodiversity and other peatland functions. This study evaluated progress 6-15 years after rewetting in vegetation development, physicochemical properties of peat, soil organic matter (SOM) quality and microbial activity in previously long-term drained bogs and spruce swamp forests (SSF) in comparison with pristine and long-term drained sites in the Bohemian Forest, Czech Republic. Long-term drainage led to overall ecosystem degradation, indicated by a change in vegetation composition, reduced decomposability of peat, with high content of recalcitrant compounds and decreased pH, and reduced soil microbial biomass and activity. The degradation was more pronounced in SSF, while bogs seemed to be relatively resistant to environmental changes caused by drainage. Post-rewetting progress has occurred with regard to vegetation composition, peat pH, microbial biomass and potential anaerobic CO2 and CH4 production, all of which tending towards characteristics of the pristine sites. However, overall SOM quality has not yet responded significantly, indicating that some peat properties and functions, such as C accumulation, need much longer periods of time to return to the original level.
  • Laine, Anna M.; Tolvanen, Anne; Mehtätalo, Lauri; Tuittila, Eeva-Stiina (2016)
    Young coastal fens are rare ecosystems in the first stages of peatland succession. Their drainage compromises their successional development toward future carbon (C) reservoirs. We present the first study on the success of hydrological restoration of young fens. We carried out vegetation surveys at six young fens that represent undrained, drained, and restored management categories in the Finnish land uplift coast before and after restoration. We measured plant level carbon dioxide (CO2) assimilation and chlorophyll fluorescence (Fv/Fm) from 17 most common plant species present at the sites. Within 5 years of restoration, the vegetation composition of restored sites had started to move toward the undrained baseline. The cover of sedges increased the most in response to restoration, while the cover of deciduous shrubs decreased the most. The rapid response indicates high resilience and low resistance of young fen ecosystems toward changes in hydrology. Forbs had higher photosynthetic and respiration rates than sedges, deciduous shrubs, and grasses, whereas rates were lowest for evergreen shrubs and mosses. The impact of management category on CO2 assimilation was an indirect consequence that occurred through changes in plant species composition: Increase in sedge cover following restoration also increased the potential photosynthetic capacity of the ecosystem. Synthesis and applications. Restoration of forestry drained young fens is a promising method for safeguarding them and bringing back their function as C reservoirs. However, their low resistance to water table draw down introduces a risk that regeneration may be partially hindered by the heavy drainage in the surrounding landscape. Therefore, restoration success is best safeguarded by managing the whole catchments instead of carrying out small-scale projects.