Research

The measurements of energy and matter exchange between forest ecosystem and the atmosphere are carried out since 1996 at our Forestry Field Station for Measuring Ecosystem-Atmosphere Relationship (SMEAR II) located in Hyytiälä, southern Finland. The measurements cover, among others, flux monitoring of CO₂, H₂O and CH₄ on a regular basis, topped with occasional measurement campaigns for N₂O, O₃, CO, VOCs (volatile organic compounds) and COS (carbonyl sulfide). The fluxes are determined applying micrometeorological techniques (including gradient and eddy-covariance methods), automatic and manual chambers for soil, woody-tissue and shoot components, and soil gradient method. SMEAR II forms a unique facility for soil-tree-atmosphere continuous measurements that have been used in several international projects and during field courses and summer schools.

Since 2012, an eddy-covariance (EC) flux measurements system is studying the carbon dioxide and water vapour exchange between the atmosphere and forest at ecosystem level also in Värriö Subarctic Research Station for Measuring Ecosystem-Atmosphere Relationship (SMEAR I, established in 1991). The station is located at the Arctic-alpine timberline in Värriö strict nature reserve, Finnish Lapland

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. In 2009, lake measurements were started at Lake Kuivajärvi in Hyytiälä. 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. 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.

Boreal wetlands are one of the largest pools of organic carbon on Earth. At present, up to 30% of the Earth's organic carbon is thought to be contained in the Boreal peat deposits. This massive storage, however, seems to become more and more unstable as climate change gains pace. Apart from accumulating carbon thanks to plant photosynthesis, natural wetlands affect the global greenhouse gas balance by emitting methane (CH₄). They are the largest single CH₄ source into the atmosphere. Processes leading to CH₄ emissions from wetlands are generally known, but their relative contributions, trends and controls often remain obscure. With the prospects of drastic global changes becoming realistic, it is of capital importance to forecast the dynamics of peatland carbon storage and CH₄ emissions in this context. We study peatland - atmosphere interactions with a range of measurements and modelling approaches, the key combination aimed at disentangling the complexity of those ecosystems.

We approach different aspects of the peatland - atmosphere interactions at the biggest South Finnish natural mire of Siikaneva. Two measurement stations are operating currently in the fen and bog areas of the wetland. Both have EC setups for measuring the turbulent fluxes of energy, CO₂, H₂O and CH₄, and a set of meteorological and soil measurements. CH₄ fluxes related to belowground processes (production, oxidation and transport) are explored with stable isotope labelling experiment and continuous real-time measurements of the natural abudance of belowground isotopes (see "MIso" project for more information). We closely interact with the University of Eastern Finland, who perform a range of ecological measurements, including e.g. vegetation sampling and monitoring and chamber measurements of the greenhouse gas fluxes.

In January 2013 an intensive measurement campaign was started in Nummela to study the GHG balance using eddy covariance flux measurement of heat, CO₂, H₂O and CH₄, and a set of meteorological measurements.

West Siberia houses some of the vastest wetlands of the world, by scale comparable only with those of Canada. However, a large fraction of the Siberian wetland diversity remains unexplored due to remoteness of many areas and underdeveloped infrastructure. Measurements at the Mukhrino field station were initiated in 2015 jointly with the Yugra State University. The station equipment is similar to that in the Siikaneva stations.

Large eddy simulations (LES) are a popular fluid dynamics tool for simulating turbulent flow. LES resolves explicitly large eddies and parameterizes small eddies using a subgrid-scale model. The parallelized LES model (PALM) is designed for simulating atmospheric and oceanic flows on massively parallel computer architectures. PALM can be used in concurrence with Lagrangian Stochastic (LS, see below) modelling: PALM can resolve a desired 3-dimensional flow field which can be transferred into a LS model that calculates the composition, distribution and trajectory of particles, which have been released during the simulation. The spatial distribution of particles is used for calculating the scalar concentration and flux, in addition to their source areas (footprints). In our group, this modelling setup is used for simulating flow over an idealized chess-board like pattern of grass and forest. In both cases, the footprints are calculated based on released particles.

Lagrangian Stochastic modelling (LS) solves the paths of particles in a given turbulent flow. LS models are used for dispersion simulations within a canopy and the atmospheric boundary layer. The model is capable to account for turbulence statistics and dispersion inside canopy, driven by the canopy leaf area profiles and density, and skewed turbulence in the convective boundary layer. The research areas of interest are dispersion and deposition of gases and atmospheric aerosols, including particles of biogenic origin, and also evaluation of the source statistics contributing to micrometeorological flux and concentration measurements, the footprint functions.

EddyUH is an advanced software for processing raw eddy covariance data, developed and maintained by our group. A substantial amount of instruments (sonic anemometers and gas analyzers) are supported, and standardized procedures are fully implemented in EddyUH. In order to advance methodical issues concerning especially CH₄, N₂O, COS, O₃ and VOCs fluxes, most updated corrections and methods for EC flux estimates for these gases have been also included. EddyUH is flexible and easy to use thanks to a simple graphical user interface (GUI) and different data plotting tools. It is freely available for research purposes.

In addition to developing the processing software, we also develop the eddy covariance flux measurement technique, especially related to different corrections needed in the flux processing and post processing phases.