Geological and physiographic setting
The KCS is located in the Svecokarelian orogenic belt, which traverses large parts of Sweden and Finland. The bedrock is dominated by 1.92-1.87 Ga old migmatised meta-greywacke or paragneiss, which consists of metamorphosed sediments once deposited outside the Achaean Baltic Shield. The numerous hills in the area with peaks up to 400 m are largely derived from selective weathering of biotite-plagioclase schist in the valleys and more resistant veined gneiss at higher altitudes. Further inland, the meta-sediments are gradually replaced by 1.74-1.82 Ga old granite and granodiorite, which also occur as intrusions in the KCS along with minor intrusions of mafic rocks.
The Quaternary deposits are strongly influenced by the latest glaciation. Drumlins and crag-and-tails are aligned in a SSW direction as the inland ice was moving from NNW. The ice retreated ca. 10,200 a BP (Stroeven et al., 2016), leaving up to 30 m thick till in sheltered areas, but also bare bedrock in more exposed locations. In addition, the large Vindel River Esker passes through the lower parts of the KCS adding large deposits of glaciofluvial material (Fig. 1c). The Quaternary deposits are predominately of local origin, displaying a silicate-dominated chemistry with quartz>plagioclase>K feldspar>amphiboles as the main minerals (Lampa et al., 2020). In areas with low topographic relief, peat has built up generally forming oligotrophic minerogenic mires. At the termination of the deglaciation, approximately half of the KCS was located below the highest postglacial coastline (situated at ca 257 m above present sea level). This has resulted in locally >60 m deep sand and silt sediments that now cover the lower parts of the KCS, deposited by the Vindel River during the course of the isostatic rebound.

Long-term environmental trends

The boreal region encompassing the KCS has experienced some strong environmental trends during the last several decades. Changes in climate, land-use, and long-range transport of air pollutants all have had a role to play in explaining some of these decadal changes. Despite having a highly developed research infrastructure in place, the co-occurrence, interaction, and synchronicity of several human interventions complicate our efforts to disentangle the cause-and-effects responsible for all changes that can be observed. However, by combining long-time series, large-scale experiments, and modeling we are now beginning to understand the role climate change, land-use, and atmospheric pollution have had in the past and present, and predict which roles they will have in the future.
Here we highlight some of the major trends in forest biomass growth, lake ice extent, catchment hydrology, and water quality for the KCS (Fig. 3). While some of the trends can be directly related to changes in climate, such as the increasingly earlier lake ice-out, other trends are more likely related to atomospheric pollution, namely, the decline in stream calcium that relates to the recovery from acid deposition. Increased forest biomass production, stream water brownification, and increase in ET are likely caused by a combination of interacting factors. Such interactions, and the fact that some catchments respond while adjacent systems do not, call for the need of continued research to disentangle these cause-and-effect mechanisms. In addition, we urgently need to provide predictions for what these large-scale environmental changes will mean for northern environments. These include the direct and indirect effects on carbon and greenhouse gas (GHG) balances, atmospheric radiative forcing, terrestrial and aquatic biodiversity and water quality, but also for the industry and livelihood of communities in northern regions. Living up to these goals in an environment that is constantly changing, requires maintaining research infrastructures that take a landscape scale perspective and include the most important processes in the atmosphere, vegetation, soils, bedrock, and water, as well as the interactions between them.

Research infrastructure (max 2500 words)

The ambition of KCS is to take a holistic ecosystem perspective of the boreal landscape to understand, elucidate, and predict the role of internal and external drivers of catchment processes across a range of scales. In our approach, we combine state-of-the-art technology to capture various ecosystem processes with traditional research tools and basic environmental monitoring. This includes processes and dynamics of living and non-living ecosystem compartments, as well as the fluxes of energy, water, carbon, nutrients, metals, and other compounds within and between the atmosphere, lithosphere, cryosphere, and hydrosphere. In the KCS, we do this by combining a large, central, research facility – namely, the ICOS research tower – with supplemental infrastructures distributed across the entire landscape (Fig. 4). In addition to these facilities, the KCS also offers a number of large scale and/or long-term experimental facilities. Below we outline some of the most central of these facilities and data.