Browsing by Subject "Stratification"

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  • Alekseev, Alexander; Tomppo, Erkki; McRoberts, Ronald E; von Gadow, Klaus (Springer Singapore, 2019)
    Abstract The State Forest Inventory (SFI) in the Russian Federation is a relatively new project that is little known in the English-language scientific literature. Following the stipulations of the Forest Act of 2006, the first SFI sample plots in this vast territory were established in 2007. The 34 Russian forest regions were the basic geographical units for all statistical estimates and served as a first-level stratification, while a second level was based on old inventory data and remotely sensed data. The sampling design was to consist of a simple random sample of 84,700 circular 500 m2 sample plots over forest land. Each sample plot consists of three nested concentric circular subplots with radii of 12.62, 5.64 and 2.82 m and additional subplots for assessing and describing undergrowth, regeneration and ground vegetation. In total, 117 variables were to be measured or assessed on each plot. Although field work has begun, the methodology has elicited some criticism. The simple random sampling design is less efficient than a systematic design featuring sample plot clusters and a mix of temporary and permanent plots. The second-level stratification is mostly ineffective for increasing precision. Qualitative variables, which are not always essential, are dominant, while important quantitative variables are under-represented. Because of very slow progress, in 2018 the original plan was adjusted by reducing the number of permanent sample plots from 84,700 to 68,287 so that the first SFI cycle could be completed by 2020.
  • Alekseev, Alexander; Tomppo, Erkki; McRoberts, Ronald E.; von Gadow, Klaus (2019)
    The State Forest Inventory (SFI) in the Russian Federation is a relatively new project that is little known in the English-language scientific literature. Following the stipulations of the Forest Act of 2006, the first SFI sample plots in this vast territory were established in 2007. The 34 Russian forest regions were the basic geographical units for all statistical estimates and served as a first-level stratification, while a second level was based on old inventory data and remotely sensed data. The sampling design was to consist of a simple random sample of 84,700 circular 500m(2) sample plots over forest land. Each sample plot consists of three nested concentric circular subplots with radii of 12.62, 5.64 and 2.82m and additional subplots for assessing and describing undergrowth, regeneration and ground vegetation. In total, 117 variables were to be measured or assessed on each plot.Although field work has begun, the methodology has elicited some criticism. The simple random sampling design is less efficient than a systematic design featuring sample plot clusters and a mix of temporary and permanent plots. The second-level stratification is mostly ineffective for increasing precision. Qualitative variables, which are not always essential, are dominant, while important quantitative variables are under-represented. Because of very slow progress, in 2018 the original plan was adjusted by reducing the number of permanent sample plots from 84,700 to 68,287 so that the first SFI cycle could be completed by 2020.
  • Saarela, Taija; Rissanen, Antti J.; Ojala, Anne; Pumpanen, Jukka; Aalto, Sanni L.; Tiirola, Marja; Vesala, Timo; Jantti, Helena (2020)
    Freshwater ecosystems represent a significant natural source of methane (CH4). CH4 produced through anaerobic decomposition of organic matter (OM) in lake sediment and water column can be either oxidized to carbon dioxide (CO2) by methanotrophic microbes or emitted to the atmosphere. While the role of CH4 oxidation as a CH4 sink is widely accepted, neither the magnitude nor the drivers behind CH4 oxidation are well constrained. In this study, we aimed to gain more specific insight into CH4 oxidation in the water column of a seasonally stratified, typical boreal lake, particularly under hypoxic conditions. We used (CH4)-C-13 incubations to determine the active CH4 oxidation sites and the potential CH4 oxidation rates in the water column, and we measured environmental variables that could explain CH4 oxidation in the water column. During hypolimnetic hypoxia, 91% of available CH4 was oxidized in the active CH4 oxidation zone, where the potential CH4 oxidation rates gradually increased from the oxycline to the hypolimnion. Our results showed that in warm springs, which become more frequent, early thermal stratification with cold well-oxygenated hypolimnion delays the period of hypolimnetic hypoxia and limits CH4 production. Thus, the delayed development of hypolimnetic hypoxia may partially counteract the expected increase in the lacustrine CH4 emissions caused by the increasing organic carbon load from forested catchments.
  • Kari, Elina; Merkouriadi, Ioanna; Walve, Jakob; Leppäranta, Matti; Kratzer, Susanne (2018)
    Seasonal sea ice cover reduces wind-driven mixing and allows for under-ice stratification to develop. These under-ice plumes are a common phenomenon in the seasonal sea ice zone. They stabilize stratification and concentrate terrestrial runoff in the top layer, transporting it further offshore than during ice-free seasons. In this study, the effect of sea ice on spring stratification is investigated in Himmerfjärden bay in the NW Baltic Sea. Distinct under-ice plumes were detected during long ice seasons. The preconditions for the development of the under-ice plumes are described as well as the typical spatial and temporal dimensions of the resulting stratification patterns. Furthermore, the effect of the under-ice plume on the timing of the onset and the maximum of the phytoplankton spring bloom were investigated, in terms of chlorophyll-a (Chl-a) concentrations. At the head of the bay, bloom onset was delayed on average by 18 days in the event of an under-ice plume. However, neither the maximum concentration of Chl-a nor the timing of the Chl-a maximum were affected, implying that the growth period was shorter with a higher daily productivity. During this period from spring bloom onset to maximum Chl-a, the diatom biomass was higher and Mesodinium rubrum biomass was lower in years with under-ice plumes compared to years without under-ice plumes. Our results thus suggest that the projected shorter ice seasons in the future will reduce the probability of under-ice plume development, creating more dynamic spring bloom conditions. These dynamic conditions and the earlier onset of the spring bloom seem to favor the M. rubrum rather than diatoms.
  • Alligier, Maud; Barres, Romain; Blaak, Ellen E.; Boirie, Yves; Bouwman, Jildau; Brunault, Paul; Campbell, Kristina; Clement, Karine; Farooqi, I. Sadaf; Farpour-Lambert, Nathalie J.; Fruhbeck, Gema; Goossens, Gijs H.; Hager, Jorg; Halford, Jason C. G.; Hauner, Hans; Jacobi, David; Julia, Chantal; Langin, Dominique; Natali, Andrea; Neovius, Martin; Oppert, Jean Michel; Pagotto, Uberto; Palmeira, Antonio L.; Roche, Helen; Ryden, Mikael; Scheen, Andre J.; Simon, Chantal; Sorensen, Thorkild I. A.; Tappy, Luc; Yki-Järvinen, Hannele; Ziegler, Olivier; Laville, Martine (2020)
    Heterogeneity of interindividual and intraindividual responses to interventions is often observed in randomized, controlled trials for obesity. To address the global epidemic of obesity and move toward more personalized treatment regimens, the global research community must come together to identify factors that may drive these heterogeneous responses to interventions. This project, called OBEDIS (OBEsity Diverse Interventions Sharing - focusing on dietary and other interventions), provides a set of European guidelines for a minimal set of variables to include in future clinical trials on obesity, regardless of the specific endpoints. Broad adoption of these guidelines will enable researchers to harmonize and merge data from multiple intervention studies, allowing stratification of patients according to precise phenotyping criteria which are measured using standardized methods. In this way, studies across Europe may be pooled for better prediction of individuals' responses to an intervention for obesity - ultimately leading to better patient care and improved obesity outcomes.
  • European Interferon Beta Pregnancy; Nordic MS Pregnancy Interferon Be; Korjagina, Marta; Hakkarainen, Katja M.; Burkill, Sarah; Verkkoniemi-Ahola, Auli; Korhonen, Pasi (2021)
    Background: Previous studies reported no increase in the prevalence of adverse pregnancy outcomes after exposure to interferon-beta (IFN-beta). However, no study has investigated if the prevalence of these outcomes after IFN-beta exposure is modified by maternal and newborn characteristics. Our objective was to describe the stratified prevalence of adverse pregnancy outcomes among women with multiple sclerosis (MS) exposed only to IFN-beta or unexposed to any MS disease modifying drugs (MSDMDs). Methods: This population-based cohort study using Finnish (1996-2014) and Swedish (2005-2014) register data included pregnancies of women with MS exposed only to IFN-beta 6 months before or during pregnancy (n=718) or unexposed to MSDMDs (n=1397). The outcome prevalences were described stratified by maternal and newborn characteristics, with 95% confidence intervals (CIs). Confounder-adjusted analyses were performed if the prevalence results indicated modified effect of IFN-beta in specific strata. Results: The stratified analysis indicated that the prevalence of serious (anomaly or stillbirth) and other adverse pregnancy outcomes was similar among the exposed and unexposed, with no statistically significant difference. Among women treated for MS >5 years, serious adverse pregnancy outcomes occurred in 4.3% (95%CI: 1.98.3%) of pregnancies exposed only to IFN-beta 6 months before or during pregnancy and in 2.7% (95%CI: 1.25.0%) of unexposed pregnancies. The confounder adjusted analyses did not support the hypothesis that MS