Browsing by Subject "CO2 flux"

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  • Lohila, Annalea (2008)
    Finnish Meteorological Institute Contributions
  • Kankaala, Paula; Arvola, Lauri; Hiltunen, Minna; Huotari, Jussi; Jones, Roger I.; Hannu, Nykänen; Ojala, Anne; Olin, Mikko; Peltomaa, Elina; Peura, Sari; Rask, Martti; Tulonen, Tiina; Vesala, Sami (2019)
    Recent increases in terrestrial dissolved organic carbon (DOC) concentrations in northern inland waters have many ecological consequences. We examined available data on carbon cycles and food webs of 2 boreal headwater lakes in southern Finland. Basic limnology and catchment characteristics of a pristine lake, Valkea-Kotinen (VK), were monitored over the past 25 years while the lake has undergone browning and DOC increased from similar to 11 to 13 mg L-1. Pronounced changes in the early 2000s represent a regime shift in DOC concentration and color. Lake Alinen Mustajarvi (AM) was manipulated for 2 years by additions of labile DOC (cane sugar), raising the DOC concentration from similar to 10 to 12 mg L-1, but not changing light conditions. The 2 different approaches both revealed increased concentrations and efflux of carbon dioxide (CO2) from the lakes and thus net heterotrophy and changes in the pelagic community structure following an increase in DOC concentration. Long-term monitoring of VK revealed a decline in phytoplankton primary production (PP) along with browning, which was reflected in retarded growth of young (1-2-year-old) perch. In the experimentally manipulated lake (AM), PP was not affected, and the growth of young perch was more variable. The results suggested the importance of a pathway from labile DOC via benthic invertebrates to perch. Although provided with this extra resource, the food chain based on DOC proved inefficient. Long-term monitoring and whole-lake experimentation are complementary approaches for revealing how freshwater ecosystems respond to climate and/or atmospheric deposition-induced changes, such as browning.
  • Matkala, Laura (Helsingfors universitet, 2013)
    Boreal peatlands contain approximately one third of the global soil carbon and are considered net sinks of atmospheric CO2. Water level position is one of the main regulators of CO2 fluxes in northern peatlands because it controls both the thickness of the aerobic layer in peat and plant communities. However, little is known about the role of different plant functional groups and their possible interaction with changing water level in boreal peatlands with regard to CO2 cycling. Climate change may also accelerate changes in hydrological conditions, changing both aerobic conditions and plant communities. To help answer these questions, this study was conducted at a mesocosm facility in Northern Michigan where the aim was to experimentally study the effects of water levels, plant functional groups (sedges, shrubs and mosses) and the possible interaction of these on the CO2 cycle of a boreal peatland ecosystem. The results indicate that Ericaceous shrubs are important in the boreal peatland CO2 cycle. The removal of these plants decreased ecosystem respiration, gross ecosystem production and net ecosystem exchange rates, whereas removing sedges did not show any significant differences in the flux rates. The water level did not significantly affect the flux rates. The amount of aboveground sedge biomass was higher in the low water level sedge treatment plots compared to the high water level sedge plots, possibly because the lowered water level and the removal of Ericaceae released nutrients for sedges to use up.
  • Park, Sung-Bin; Knohl, Alexander; Migliavacca, Mirco; Thum, Tea; Vesala, Timo; Peltola, Olli; Mammarella, Ivan; Prokushkin, Anatoly; Kolle, Olaf; Lavric, Jost; Park, Sang Seo; Heimann, Martin (2021)
    Climate change impacts the characteristics of the vegetation carbon-uptake process in the northern Eurasian terrestrial ecosystem. However, the currently available direct CO2 flux measurement datasets, particularly for central Siberia, are insufficient for understanding the current condition in the northern Eurasian carbon cycle. Here, we report daily and seasonal interannual variations in CO2 fluxes and associated abiotic factors measured using eddy covariance in a coniferous forest and a bog near Zotino, Krasnoyarsk Krai, Russia, for April to early June, 2013-2017. Despite the snow not being completely melted, both ecosystems became weak net CO2 sinks if the air temperature was warm enough for photosynthesis. The forest became a net CO2 sink 7-16 days earlier than the bog. After the surface soil temperature exceeded similar to 1 degrees C, the ecosystems became persistent net CO2 sinks. Net ecosystem productivity was highest in 2015 for both ecosystems because of the anomalously high air temperature in May compared with other years. Our findings demonstrate that long-term monitoring of flux measurements at the site level, particularly during winter and its transition to spring, is essential for understanding the responses of the northern Eurasian ecosystem to spring warming.