Surface water program
The hydrology and water chemistry program has been a central feature of the KCS program since the beginning. The 50 ha C7 catchment (also called Svartberget or Nyänget in earlier work) is located in the central part of the research station and was established in 1980 and marks the start of what today is the KCS. Since 1984, the two sub-catchments that feed C7 have also been monitored, one completely forested (Västrabäcken, C2) and the other dominated by a mire (Kallkälsmyren, C4). In 2002, the KCS expanded further and now includes 10 nested sub-catchments that are continously monitored in the 6790 ha Krycklan catchment (including C2, C4 and C7; see Fig. 1 and Table 1). Heated huts allow year around measurements at C7 since 1982, at C2 and C4 since 2011, at C5 (a lake outlet) since 2012, and at C13 since 2014. The details of the hydrological monitoring program was presented by Karlsen et al. (2016a, b), while additional with-in lake measurements are being conducted in Stortjärn (Denfeld et al. 2020).
In total, ~12,000 stream water samples have been collected and analyzed from KCS stream sites. Regular sampling began at C7 in 1985, at C2 and C4 in 1990, and at most of the remaining sites in 2003 (Table 1). Most samples have been analyzed for basic chemistry (pH, major cat- and anions), dissolved and/or total organic carbon (DOC and/or TOC). Absorbance spectra (from 190 to 1100 nm) and dissolved inorganic carbon (DIC) have been part of the standard protocol since 2003. On selected samples, analysis of a suite of stable and radioactive isotopes (18O, D, 14C,13C, 15N, 54/56Fe,206/207/208Pb, 226Ra,230Th, 234/238U), trace elements (including Hg, Pb, Rare Earth Elements (REE)) and persistent organic pollutants (PCBs, HCB and other) have also been included (see Laudon et al. 2011; Lidman et al. 2014; Josefsson et al. 2016; Tiwari et al. 2017; Ingri et al. 2018).
In addition to the regular sampling program a number of high-frequency, real-time measurements are now being conducted, especially in the central KCS area including streams C2, C4, C5, C6 and C7 (Fig 1d) using carbon dioxide (CO2) and dissolved oxygen sensors, and measurements of absorbance spectra (Lupon et al. 2019, Riml et al., 2019; Gomez-Gener et al. 2020). The purpose of these is to capture rates of aquatic metabolism in relation to terrestrial contributions, but also to better understand the rapid, dynamic and non-linear stream biogeochemical responses to weather and climatic events that cannot be captured by the relatively infrequent sampling program.