Biosphere-atmosphere exchanges of carbon, water and energy
A combined Integrated ICOS atmosphere-ecosystem station is located in
the center of KCS (Fig 1). ICOS is a pan-European research
infrastructure with the mission to produce standardized, high-precision,
and long-term observations of greenhouse gases and to facilitate
research to understand the carbon cycle (www.icos-cp.eu/). The ICOS
Svartberget infrastructure has been in operation since 2014 within ICOS
Sweden. The atmosphere and ecosystem stations were officially labelled
and designated as ICOS Europe stations in 2017 and 2019, respectively.
All data collected are quality controlled by central thematic centers
and made openly available via the ICOS Carbon Portal
(https://data.icos-cp.eu/portal).
The atmosphere station conducts measurements of concentrations of
CO2, carbon monoxide (CO), methane
(CH4), as well as air temperature and humidity at three
levels (35, 85, 150 m height). At 150 m, concentrations of14CO2 and13CO2 are also measured with lower
time resolution (i.e. by periodic flask sampling). The atmospheric
concentration measurements have a footprint of several hundred
kilometers and in combination with other atmospheric measurement
stations in Northern Europe capture subcontinental scale conditions.
The ecosystem station provides measurements of CO2,
water (i.e. evapotranspiration), and energy fluxes using the eddy
covariance (EC) technique. These measurements (conducted at 34.5 m
height) have a footprint of several hundred meters representing the
specific ecosystem conditions in the vicinity of the tower, including
catchments C2 and C7. In addition, key meteorological (i.e. radiation,
temperature, wind, humidity, precipitation) and soil environmental
(temperature, moisture, heat flux and water table level) variables are
continuously monitored on the tower and along four soil depth profiles,
respectively. Permanent sample plots for inventories of tree and
understory vegetation biomass, species, leaf area, phenology and leaf
chemistry, as well as litter fall give additional information on the
biotic ecosystem properties.
The ICOS infrastructure also serves as a platform for establishing and
connecting external research projects. For instance, the installation of
two more EC systems at 60 and 85m height along the ICOS tower provides
additional estimates of CO2, CH4, water
and energy exchanges at the landscape scale (i.e. few km radius),
roughly spanning the area of the KCS (Chi et al., 2019). Integration of
these landscape EC measurements with aquatic fluxes of carbon species
via stream runoff has resulted in a first estimate of the net landscape
carbon balance (NLCB) for the KCS (Chi et al., 2020). In addition, the
combination of EC and sapflow measurements around the ICOS tower has
provided an opportunity to partition the forest water cycle components
(Kozii et al., 2020). Furthermore, the concentration measurement profile
including several levels along the 150 m tall tower has enabled
investigations of atmospheric organic pollutants (Bidleman et al. 2017),
as well as water isotope and mercury dynamics. The ICOS tower structure
also hosts multispectral sensors, phenology cameras and UAVs within the
SITES-Spectral infrastructure to collect spectral data for estimating
ecosystem vegetation properties at various spatial and temporal scales.