Ivan Mammarella, Kukka-Maaria Erkkilä, Maria Provenzale, Timo Vesala
The aim of the lake measurements is to decipher lake-landscape and lake-atmosphere interactions. The role of lakes in the terrestrial carbon cycle is of major interest, as well as the lake-atmosphere gas and heat exchange and their effects to the physics and biology of a lake. The coupling between a lake ecosystem and the atmosphere was studied at Lake Valkea-Kotinen, Lammi, from 2002 to 2009 (Vesala et al. 2006; Nordbo et al. 2011). In 2009, lake measurements were started at Lake Kuivajärvi in Hyytiälä (Figure 1, Mammarella et al. 2015). The fluxes of carbon dioxide (CO2), water vapor, heat and momentum are measured on a raft with the eddy-covariance technique. The water temperature profile is measured continuously to determine the changes in heat storage of the lake, and the CO2 profile of the lake is measured to determine the mixing layer CO2 concentrations. The river inlet and outlet temperature, water depth and nutrient and carbon concentrations are monitored. There are also annual campaigns in Kuivajärvi, focused on e.g. VOCs and measurement method comparisons and development (Erkkilä et al., 2018; Provenzale et al., 2018). In 2012, similar lake measurements were started also on Lake Vanajanselkä, near Hämeenlinna. The setup includes an eddy covariance system, located at the end of a narrow peninsula in Hattula, that measures CO2, water vapor, heat and momentum fluxes. The water CO2 concentration, PAR and temperature are also measured.
The fluxes between a lake and the atmosphere depart much from those observed between a forest and the atmosphere (Vesala et al. 2012). Lakes Valkea-Kotinen and Kuivajärvi are on average a CO2 source during the open water period (Huotari et al. 2011; Mammarella et al. 2015). Lake Vanajanselkä is also on average a source, albeit smaller than the two other lakes, probably due to its highly eutrophic state. The capability of the lakes to store large amounts of heat leads to a heat flux from the atmosphere to the lake in spring and summer and a heat efflux in fall and early winter. The constantly wet surface causes the channelling of available energy to latent heat flux whereas the sensible heat flux remains smaller (Nordbo et al. 2011). On Lake Kuivajärvi, the heat flux seems to be the most important factor governing lake-atmosphere CO2 flux, and taking heat fluxes into account makes GHG exchange estimates better (Erkkilä et al., 2018).
The micrometeorological measurements at Lake Valkea-Kotinen have also been used for improving weather forecasts. Manrique-Suñén et al. (2013) evaluated the tiling method, often used in numerical weather prediction models to describe a heterogeneous surface: simulations over a forest site (SMEAR II) and Lake Valkea-Kotinen were compared and pros and cons of the tiling method were highlighted. An example of a measured and simulated water temperature profile is in Figure 2. Stepanenko et al. (2014) compared five lake models for Lake Kuivajärvi and compared simulated fluxes and temperature profile to measurements.
Prof. Lauri Arvola, Lammi Biological Station, University of Helsinki
Department of Forest Sciences, University of Helsinki
Finnish Meteorological Institute
European Centre for Medium-Range Weather Forecasts (ECMWF)
Lake Model Intercomparison Project (Lake-MIP)
University of Eastern Finland
Finnish Environment Institute
Anne Ojala, Department of Environmental Sciences, Faculty of Biological and Environmental Sciences, UHEL
Prof. Patrick Crill, Stockholm University , Sweden
Dr. David Bastviken, Linköping Univeristy, Sweden
Prof. Sally MacIntyre, University of California – Santa Barbara, USA
Dr. Victor Stepanenko, Moskow State University , Russia
Dr. Arkady Terzhevik, Northern Water Problems Institute, Russian Academy of Sciences, Russia
Dr. Leonid Golubyatnikov, A.M. Obukshov Institute of Atmospheric Physics, Russian Academy of Sciences, Russia
Provenzale, M., Ojala, A., Heiskanen, J., Erkkilä, K-M., Mammarella, I., Hari, P. and Vesala, T. (2018). High-frequency productivity estimates for a lake from free-water CO2 concentration measurements. Biogeosciences, 15(7), 2021-2032. https://doi.org/10.5194/bg-15-2021-2018
Erkkilä, K-M., Ojala, A., Bastviken, D., Biermann, T., Heiskanen, J. J., Lindroth, A., Peltola, O., Rantakari, M., Vesala, T. and Mammarella, I. (2018). Methane and carbon dioxide fluxes over a lake: comparison between eddy covariance, floating chambers and boundary layer method. Biogeosciences, 15(2), 429-445. https://doi.org/10.5194/bg-15-429-2018
Heiskanen, J. J., Mammarella, I., Ojala, A., Stepanenko, V., Erkkilä, K., Miettinen, H., … Nordbo, A. (2015). Effects of water clarity on lake stratification and lake-atmosphere heat exchange. Journal of Geophysical Research: Atmospheres, 120, 7412–7428. https://doi.org/10.1002/2014JD022938
Mammarella, I., Nordbo, A., Rannik, Ü., Haapanala, S., Levula, J., Laakso, H., … Vesala, T. (2015). Carbon dioxide and energy fluxes over a small boreal lake in Southern Finland. Journal of Geophysical Research: Biogeosciences, 120, 1–19. https://doi.org/10.1002/2014JG002873
Heiskanen J J, Mammarella I, Haapanala S, Pumpanen J, Vesala T, MacIntyre S, Ojala A (2014) Effects of cooling and internal wave motions on gas transfer coefficients in a boreal lake. Tellus B 2014, 66, 22827, http://dx.doi.org/10.3402/tellusb.v66.22827.
Stepanenko, V., Jöhnk, K., & Machulskaya, E. (2014). Simulation of surface energy fluxes and stratification of a small boreal lake by a set of one-dimensional models. Tellus A, 1, 1–18. http://doi.org/10.3402/tellusa.v66.21389
Manrique-Suñ én A, Nordbo A, Balsamo G, Beljaars A, Mammarella I (2013) Representing land surface heterogeneity: Offline analysis of the tiling method. J.Hydrometeorol. 14:850-867. 10.1175/JHM-D-12-0108.1
Huotari J, Ojala A, Peltomaa E, Nordbo A, Launiainen S, Pumpanen J, Rasilo T, Hari P, Vesala T (2011) Long-term direct CO2 flux measurements over a boreal lake: Five years of eddy covariance data. Geophys.Res.Lett. 38:L18401. 10.1029/2011GL048753
Mammarella I, Nordbo A, Rannik Ü, Haapanala S, Ojala A, Peltola O, Heiskanen J, Pumpanen J, Vesala T (in prep.) Long term eddy covariance fluxes of energy and carbon dioxide over a boreal lake in southern Finland.
Nordbo A, Launiainen S, Mammarella I, Leppäranta M, Huotari J, Ojala A, Vesala T (2011) Long-term energy flux measurements and energy balance over a small boreal lake using eddy covariance technique. J. Geophys. res. 116:1-17. 10.1029/2010JD014542
Vesala T, Huotari J, Rannik Ü, Suni T, Smolander S, Sogachev A, Launiainen S, Ojala A (2006) Eddy covariance measurements of carbon exchange and latent and sensible heat fluxes over a boreal lake for a full open-water period. J. Geophys. res. 111:D11101.
Vesala T, Eugster W and Ojala A. 2012. Eddy Covariance Measurements over Lakes. In: Eddy Covariance - A practical guide to measurements and data analysis (M. Aubinet, T. Vesala and D. Papale). Springer, the Netherlands, 365-376.