Lake studies on CO 2 utilizing direct flux measurements (EC)

Transcription

1 Lake studies on CO 2 utilizing direct flux measurements (EC) Dr Anne Ojala University of Helsinki Department of Environmental Sciences Lake SMEAR Timo Vesala, Jukka Pumpanen, Jaana Bäck Utö ICOS April 2012

2 ICOS Global Carbon Cycle

3 Existing lacustrine EC studies Anderson et al. (1999). Estimating lake-atmosphere CO 2 exchange. Limnology & Oceanography 44: Morison et al. (2000). Very high productivity of the C 4 aquatic grass Echinocloa polystachya in the Amazon floodplain confirmed by net ecosystem CO 2 flux measurements. Oecologia 125: Eugster et al. (2003). CO 2 exchange between air and water in an arctic Alaskan and midlatitude Swiss lake: importance of convective mixing. Journal of Geophysical Research 108: doi: /2002JD Vesala et al. (2006). Eddy covariance measurements of carbon exchange and latent and sensible heat fluxes over a boreal lake for a full open-water perid. Journal of Geophysical Research Atmos 111, D doi: /2005jd Guerin & Abril (2007). Significance of pelagic aerobic methane oxidation in the methane and carbon budget of a tropical reservoir. Journal of Geophysical Research Biogeosci 112:G03006 Jonsson et al. (2008). Gas transfer rate and CO 2 flux between an unproductive lake and the atmosphere in northern Sweden. Journal of Geophysical Research 113:G doi /2008jg Huotari et al. (2011). Long-term direct CO 2 flux measurements over a boreal lake: Five years of eddy covariance data. Geophysical Research Letters 38, L18401, doi: /2011gl048753, 2011

4 Aquatic carbon cycling Vertical and later carbon fluxes Main components of lacustrine C cycle. The pink arrows represent the horizontal atmospheric (wind induced) CO 2 flow and the light blue the surface inflow and outflow of C. The straight arrows represent the groundwater flows and the black arrows in the water column the biologically mediated C cycle. The vertical red and blue arrows represent the physically mediated CO 2 flow so that the small arrows indicate diffusion between two layers and the big arrows the turbulentic and convective flows within a layer. The light blue color in the lake is the epilimnion and darker blue the hypolimnion. Modified from Eugster et al. (2003).

5 River Kymijoki expedition in 2009 Vertical and later carbon fluxes

6 CO 2 flux from River Kymijoki

7 Lake Valkea-Kotinen -studied in A typical boreal lake(?) Catchment area = 2/3 forest, 1/3 peatland Old growth forest Natural peatland Reference site Max depth 6 m, mean depth 2,5 m High DOC concentration low ph Majority of inorganic carbon in the form of CO 2 Belongs to the Finnish LTER network A site of the International Cooperative Programme on Integrated Monitoring of Air Pollution Effects on Ecosystems (ICP IM) Ample background data available Suitable for studies focusing on direct flux measurements (?)

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9 SMEAR II Station for Measuring Ecosystem Atmosphere Interactions Measurements since autumn 1995 SM EAR I Sweden Finland Norway SMEA R II Tampere Helsi nk i Russia St Petersburg Oslo Stockholm Tallinn Estonia Denmark Copenhagen Ri ga Latvia Lithuania Vilnius Minsk Belarus

10 Time series on CO 2 fluxes in Lake Valkea-Kotinen Annual flux: 77 (±11) g C m -2 yr -1 This is almost 30 times higher than the long-term (postglacial) carbon accumulation rate of 2.8 g m -2 yr -1 On average 10 % of the terrestrial NEE of the surrounding forest goes back to the atmosphere through the adjacent lake Huotari et al. (2011). Long-term direct CO 2 flux measurements over a boreal lake: Five years of eddy covariance data. Geophysical Research Letters 38, L18401, doi: /2011gl048753, 2011

11 Factors affecting the pco2

12 15 13 DOC (mg L -1 ) y = x y = x 5 Lake Pääjärvi Lake Ormajärvi 3 28 Apr 18 May 07 Jun 27 Jun 17 Jul 06 Aug 26 Aug 15 Sep 05 Oct 25 Oct 2004

13 Methane in Lake Pääjärvi after heavy rains Lateral transport Originates from the flooded riparian zone

14 Valkea-Kotinen: factors behind the CO 2 flux N.B. Fluxes were checked against PP, BP, community respiration, water quality parameters.

15 Lake-SMEAR instrumentation Eddy covariance measurements 2 m above water Li-Cor LI-7200 Enclosed CO 2 /H 2 O Analyzer (from June 2011 onwards) Gas fluxes, energy fluxes Metek sonic anemometer Net radiation and PAR above water Temperature profile in the water column 0.2, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 6.0, 8.0, 10.0, 12.0 m PT 100 CO 2 -concentration profile in the lake 0.5, 1.0, 1.5, 2.5 m Vaisala GMP 343 CO 2 probes + pumps Gas collection unit (silicone) Primary production/community respiration measurements ph, oxygen, conductivity 0.5 m YSI 6600 EDS water quality sensor PAR at 0.5 m depth under water Li-Cor LI-193SA Underwater PAR sensor Manual sampling for ph, DOC, O 2, CO 2, NH 4+, NO 3-, DON, P, 18 O, 13 C Maximum time interval 1 week Usually one month Background data

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17 Lake-SMEAR instumentation from 2010 onwards BVOC (Biogenic Volatile Organic Compounds) measurements with a closed chamber Summer 2012: continuous CH 4 flux measurements turbulence measurements internal waves & gas fluxes

18 CO 2 assimulation in photosynthesis Canopy respiration + BVOCs By courtesy of Dr Jukka Pumpanen Energy input Carbon in litter and root exudates CO 2, CH 4, N 2 O, BVOC, NH 3, amines CO 2, CH 4, N 2 O, BVOC, NH 3, amines CO 2, CH 4, N 2 O, BVOC, NH 3, amines Decomposition is catalyzed by enzymes emitted by microbes Lateral transport in runoff/drainage Riparian zone Aquatic systems, Photosynthesis, respiration, GHG emissions

19 Lake-SMEAR instrumentation STREAMS Inflow and outflow continuously monitore Water level monitoring continuously with Levelogger sensors CO 2 -concentration monitoring with Vaisala GMM220 CO 2 sensors All small/temporary streams/brooks sampled manually Intensive sampling campaign in spring 2012 New measurements: From 2012 onwards ph in main inflow/outflow continuously monitored

20 Studies in Valkea-Kotinen: continuous water column CO 2 -mesurements Pertti Hari & Jukka Pumpanen

21 CO2 (ppm) m 0.5 m

22 Comparison of methods Free water approach In vitro P-I -curves 14 C in situ incubations

23 Stream measurements outlet inlet Jul 05-Aug 10-Aug 15-Aug 20-Aug 25-Aug 30-Aug 04-Sep 09-Sep 14-Sep Aug-09 Aug-09 Sep-09 Sep-09 Sep-09 Sep-09 Sep-09 Sep-09 Oct-09 Oct-09 Puro CO2 (ppm) Puro CO2 Ranta CO2 Ranta T Puro T Ranta (T) 0 Outlet (mm) Inlet (mm) 0

24 First collaborative international paper on riverine CO 2 including data from Kuivajärvi now on its way Site Mean Discharge (L s -1 ) Mean Temp (ºC) Mean CO 2 (mg C L - 1 ) IQR (mg C L -1 ) FW MC (mg C L - 1 ) Ratio Mean:FW MC MK 0.71 (0-51.5) 8.17 ± ± 0.19 a AM 19.9 ( ) 4.36 ± ± 0.17 b CHS 0.92 ( ) 11.3 ± ± 0.95 b NY 1.45 ( ) 5.89 ± ± 0.94 ac HY 97.9 ( ) 7.93± ± 0.54 c

25 Riparian zone studies in Valkea- Kotinen NB Riparian zone an important source of DOC

26 DOC concentration in different compartments DOC concenctrations of different water compartmenst from study site Valkea-Kotinen The box extends from the 25th percentile to the 75th percentile, with the horizontal line at the median (50th percentile). Whiskers extend down to the smallest value and up to the highest value.

27 Time lags in CO 2 concentrations: rain event

28 Gas transfer coefficient Gas transfer velocity (cm h -1 ) in relation to wind speed (m s -1 ) (a) and effective heat flux (W m -2 ) (b). All the values are 6 h averages (n=457).

29 CO 2 CH 4 Lopez Bellido et al (JGR)

30 Lake Kuivajärvi EC data The CO 2 flux (g CO 2 m -2 day -1 ), net long-wave radiation, heat fluxes (daily averages) (W m -2 ) and precipitation (mm of rain day -1 ) throughout the measuring period. The black lines represent the measured values and the gaps in the lines are the missing data. The CO 2 flux, sensible heat flux and latent heat flux was measured with the EC and the net long-wave radiation and precipitation was provided by the SMEAR II station.

31 Truly interdisciplinary research Remarks Techniques already in use in environmental physics and terrestrial ecology introduced to aquatic ecology True integration of studies on soil ecology and limnology as well as atmospheric physics First comes physics, then biology So far created the world s longest EC data series on CO 2 exchange over a lake (and over a river) (lake) 40 days (river) Extensive data sets on lake ecosystem ecology New insights on functioning of lake ecosystems on landscape level Need for new approaches, methods

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