1 / 20

Anne Ojala Timo Vesala, Jussi Huotari, Elina Peltomaa, Jukka Pumpanen, Pertti Hari

Carbon gas fluxes from a boreal lake. Anne Ojala Timo Vesala, Jussi Huotari, Elina Peltomaa, Jukka Pumpanen, Pertti Hari Üllar Rannik, Tanja Suni, Sampo Smolander, Andrey Sogachev and Samuli Launiainen. Department of Ecological and Environmental Sciences & Department of Physical Sciences.

valiant
Download Presentation

Anne Ojala Timo Vesala, Jussi Huotari, Elina Peltomaa, Jukka Pumpanen, Pertti Hari

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Carbon gas fluxes from a boreal lake Anne Ojala Timo Vesala, Jussi Huotari, Elina Peltomaa, Jukka Pumpanen, Pertti Hari Üllar Rannik, Tanja Suni, Sampo Smolander, Andrey Sogachev and Samuli Launiainen Department of Ecological and Environmental Sciences & Department of Physical Sciences 13 December 2007 HERC

  2. Rationale of the study • Boreal lakes can act as conduits of terrestrially fixed carbon • Importance of catchment area • studies in Amazonas by Richey et al. (2002) • Hanson et al. (2004): 14% of NEE of the surrounding watershed can be mineralized and vented to the atmosphere via the lake • Allochthonous vs. autochthonous carbon • DOC • Carbon source for heterotrophs • Microbial food webs • Kyoto protocol

  3. Study site: Lake Valkea-Kotinen • Pristine boreal lake • Surface area 0.041 km2 • Max depth 6.5 m, mean depth 2.5 m • high content of DOC • pH < 6 • inorganic carbon mostly in the form of CO2 • Headwater lake • Catchment area 0.30 km2 • Mainly old-growth forest • A true reference lake !

  4. Characteristics of the lake: stratification 2003 2004 • Temperature (ºC) • Short or incomplete spring turn over • meromixis • Steep summer stratification • Complete autumn turn over • Oxygen (g m-3) • Anoxic hypolimnion (below 2.5 – 3 m) • CH4 production • Autumn turn over

  5. Carbon gas measurements • Continuous CO2 flux measurements since summer 2002 • Eddy Covariance (EC) • Chamber measurements • Measurements based on water column CO2 concentrations • Throughout the growing seasons • Striking improvement in temporal resolution

  6. Results:Allochthonous carbon • Precipitation 30% higher in 2004 than in 2003 • peak in July • DOC (mg C l-1) in surface water • Clearly higher after July in 2004 • Slow recovery • Carry over to the next growing season

  7. Results:CO2 in the water column • CO2 concentration (mmol m-3) • Stratification in summer • Autumn turn over • Higher in 2004 2003 2004

  8. Comparison of different methods µmol m-2 s-1 Month *C&C = estimate based on CO2 concentration difference between the surface water and atmosphere

  9. Results:CO2 fluxes based on EC measurements • Seasonal pattern in CO2 exchange • fluxes higher during the fall turn-over than during the spring turn-over • lowest fluxes in summer

  10. Results:Process parameters • Community Respiration (R) and Primary Production (P) • CO2 production to consumption ratio (R to P) higher in 2004 than in 2003 • Carry-over effect in 2005? • R:P vs CO2 flux

  11. CO2 probes

  12. Surface water CO2 concentration: seasonal dynamics

  13. Determination of CO2 exchange in water g = CO2 exchange rate C = CO2 concentration Fa= CO2 flux from lake to the atmosphere Fu = CO2 flux from deep to surface

  14. Photosynthesis-irradiance response curves 6-10 September, 2006 11-15 September, 2006

  15. P-I Response Curve and Photosynthesis Estimate • Fall photosynthetic rate: • 0.35 g(CO2)m-2day-1 • Daily respiration: • 1.00 g(CO2)m-2day-1 • NEE • -0.65 g(CO2)m-2day-1 • Lake appeared as a small source of CO2 (submitted to Limnology and Oceanography: Methods)

  16. Small microplankton (20-50 µm) dominated in spring (37-73 %) and autumn (79-96 %) Large microplankton (> 50 µm) dominated (46-72 %) from the end of June till the end of September Peridinium Gonyostomum Size-fractionated PP at surface

  17. Picoplankton (0.2-2 µm) dominated (57-62 %) production in autumn Size-fractionatedPP at 1,5 meter zero

  18. Long-term changes in photosynthetic biomass Total biomass;decreasing trend (k = -1,4 x 10-2 g m-3 a-1) Gonyostomum semen;decreasing trend (k = -2,4 x 10-2 g m-3 a-1)

  19. CO2 fluxes from a larger lake:Lake Pääjärvi and an extreme weather event Summer time precipitation doubled >> a clear peak in CO2 flux - Not due to in-lake biological processes, but imported from the catchment area FC = chamber measurement ΔCO2 = concentration gradient method

  20. Remarks • Truly interdisciplinary research • Techniques already in use in environmental physics and terrestrial ecology introduced to aquatic ecology • True integration of studies on soil ecology and limnology • Spin-off projects • So far created the world’s longest EC data series on CO2 exchange over a lake • Extensive data sets on lake ecosystem ecology • New insights on functioning of lake ecosystems on landscape level • Not only DOC, but also CO2

More Related