Detecting changes and trends in atmospheric composition and understanding their impact on the stratosphere and upper troposphere is necessary for establishing the scientific links and feedback between climate change and atmospheric composition.

The primary objective of ACTRIS is to provide the 4D-variability of clouds and of the physical, optical and chemical properties of short-lived atmospheric species, from the surface throughout the troposphere to the stratosphere, with the required level of precision, coherence and integration.

At both stations, Hyltemossa and Norunda, the installations and parallel measurements are ongoing under 2017 as they replace former measurement sites.

The measurements in Norunda replace the measurements in Aspvreten, a rural site about 80 km SW of Stockholm.

The equipment for Hyltemossa is moved from the Vavihill site, about 20 km WSW from Hyltemossa.

Previous studies have shown that clear-cuts, which are the result of the dominating harvesting method in Sweden, cause large emissions of CO₂ during 10-20 years. Our own measurements in Norunda also indicate significant emissions of the powerful greenhouse gases methane (CH₄) and nitrous oxide (N₂O) from clear-cuts.

It is important to understand how general this picture is and if there are alternative management strategies that maintain a high forest productivity but with smaller negative impacts on the climate and the environment.

Hyltemossa and Norunda are only two out of several stations within this project.

Click to get more information.

The understanding of carbon emissions from tree roots is needed in order to model the internal carbon dynamics in a tree unity and to estimate tree growth in future climate, for example. Tree roots emit carbon as a result of their vital functions, growth and root exudation but those fluxes are difficult to measure and quantify in natural field conditions due to the location below the soil surface and the close interaction between tree roots, symbiotic mycorrhiza and bulk soil. Commonly, CO₂ emissions are monitored on forest floor but that flux includes also CO₂ arising from heterotrophic respiration i.e. from the decomposition of soil organic matter. These different sources of CO₂ interact as well since trees allocate carbon to mycorrhiza which can boost the decomposition of soil organic matter, a phenomenon known as rhizosphere priming effect.

The plots were installed in Norunda in late summer 2015 whereas the measurements started in 2016. The campaign will be running until the end of 2017.

Map of the four sites where CO₂ emissions are measured on forest floor both on trenched and control plots.

For this study, we have installed over 100 soil chambers at the Norunda site, to measure seasonal and spatial variability of CO₂ and CH₄ surface fluxes. Chamber data have been collected throughout the growing season of 2014 and again in 2016, to allow for analysis of seasonal and annual variability. The measured fluxes together with tower flux measurements from the main tall tower and four short towers on the clear-cut site are linked using the footprint model of Kljun et al. (2015).

We conducted an airborne survey of the Norunda site in 2011, collecting high-resolution LiDAR and hyperspectral data of an area of 4 km x 4 km centered at the Norunda flux tower. Maps of digital elevation, tree height, canopy height, and leaf area index were derived on the basis of the LiDAR data. Soil moisture maps were derived from the digital elevation data and ground water table observations.

This unique combined dataset will give us a new insight of greenhouse gas sources and sinks at the Norunda site and will allow us to improve upscaling of greenhouse gas fluxes to the boreal landscape.

References
Kljun, N., P. Calanca, M.W. Rotach, H.P. Schmid, 2015: A simple two-dimensional parameterisation for Flux Footprint Prediction (FFP), Geoscientific Model Development, 8, 3695-3713. DOI 10.5194/gmd-8-3695-2015

Sundqvist E., A. Persson, N. Kljun, P. Vestin, L. Chasmer, C. Hopkinson, A. Lindroth, 2015: Upscaling of methane exchange in a boreal forest using soil chamber measurements and high-resolution LiDAR elevation data, Agricultural and Forest Meteorology, 214-215, 393-401. DOI 10.1016/j.agrformet.2015.09.003.

Precipitation is collected during the warm season as bulk deposition at two rural background sites, one located in the very south of Sweden (Hallahus on Söderåsen) and the other on the east coast close to Nyköping (Aspvreten). Aspvreten is closing down in 2017 and sampling will now be carried out at Norunda instead.

Each sample is analyzed for approximately 130 different substances, including also a number of pesticides not registered for use within Sweden in order to investigate also transboundary, long-range transport and deposition of both banned and currently used pesticides.

Data are open and can be found, in Swedish, here.

The monitoring program is financed by the Swedish Environmental Protection Agency. Monitoring of pesticides in air is currently performed only at Hallahus.

We installed 12 automated chambers in combination with a gas analyzer to determine CO₂ and CH₄ fluxes at hourly resolution. A combination of transparent and opaque chambers provides data on the net ecosystem CO₂ exchange (NEE), ecosystem respiration (ER) and heterotrophic respiration (Rh). Rh is determined on experimental vegetation-removal plots. Using a mass balance approach, hourly estimates of gross and net primary production (GPP, NPP) and autotrophic respiration (Ra) are derived. An additional stable isotope analyzer connected to the automated chamber system provides continuous measurements of the ¹³CO₂ signatures and allows us to further quantify the contributions from CH₄ oxidation and decomposition of organic matter to Rh. Concurrent measurements of abiotic variables and biotic data from phenology cameras, spectral sensors and manual vegetation inventory are used to explore the separate controls of the individual component fluxes from hourly to seasonal time scales.

The first approach is based on detailed measurements of the plot-scale carbon balance carried out in 50 forest plots (10m radius) which were selected from a grid of 550 inventory plots across the Krycklan catchment spanning various soil types, species and stand age classes. In each of the selected plots, measurements of the forest floor CO₂ exchange and heterotrophic respiration are conducted using the closed chamber technique. Additional measurements include litterfall, leaf area index as well as tree and understorey biomass production. CO₂ exchange data is also collected with chambers from lake and mire ecosystems. Using high-resolution Lidar data, plot-level information will be up-scaled to estimate the carbon balance of the entire forest landscape. The second approach is based on tall tower eddy covariance measurements. For this purpose, instrumentation was installed at the ICOS-Svartberget 150m tall flux tower located within the Krycklan catchment. These measurements provide a direct estimate of the landscape carbon balance by integrating all vertical CO₂ fluxes over the catchment area. The lateral aquatic carbon export is estimated with a network of weirs and combined with the vertical CO₂ exchange to obtain the full carbon balance of the forest catchment.

NordSpec is an infrastructure for collecting spectral data for ecosystem monitoring. The spectral measurements are conducted year-round using robust equipment in order to capture seasonal signals from vegetation. This information is used as ground reference information for remotely sensed observations from satellite, and for learning more about the dynamics of vegetation. NordSpec is currently focused on field sites in the Nordic countries, but also includes sites beyond, e.g. Greenland, Senegal and the Sudan.

SITES Spectral is an infrastructure for collecting spectral data for ecosystem monitoring. Through this initiative SITES can provide data for research related to climate change, carbon and greenhouse gas balances, phenology, general ecology and biodiversity and plant science.