The Khibiny alkaline massif on the Kola Peninsula (Fig. 1d) consists of
igneous rocks with titanite and apatite-nepheline deposits (Kogarko,
2018). The massif is surrounded by two larger lakes: the Umbozero Lake
to the east and the Imandra Lake to the west with lake areas of 320 and
880 km2, respectively (Fig 1; Dauvalter and Kashulin,
2010; Dinu et al., 2020). The Khibiny mountain valleys (Fig. 1e) are
characterized by sandy till deposits and a forest-tundra ecosystem,
while the higher plateaus (with mountain peaks up to 1000 meter above
the Umbozero and Imandra Lakes) hold mostly weathered rocks
and
Arctic tundra (Pereverzev, 2010). The average annual temperature for the
Khibiny massif was −0.59 °C between 1993 and 2017 according to data from
the Climatic Research Unit (CRU) at the University of East Anglia
described by Harris et al. (2014; see Supporting Information S1 on
details). For the same time period, the annual average precipitation was
715 mm/yr and annual average actual evapotranspiration was 290 mm/yr
(based on CRU data and same calculation procedure as for the Imetjoki
catchment). About 210 days per year were snow covered between 1998 and
2007 (Callaghan et al., 2011). The southwestern part of the Khibiny
massif is drained by the Belaya River that has a catchment area of 142
km2 and an average annual discharge of 1900 l/s (ID 22
in Fig. 1; derived from CRU data following the water balance calculation
steps of Fischer et al. 2020) before reaching the Imandra Lake.
Furthermore, the Belaya River (main branch) starts at the outlet of the
Bolshoy Vudyavr Lake gathering tributary inflows from the Yuksporiok,
Saamsky and Vudyavriok sub-catchments (Fig. 1e). The southeastern part
of the massif is drained by the Vuonnemiok Stream with an annual average
discharge of 1300 l/s (ID 25 in Fig. 1; based on water balance
calculations) that empties in the Umbozero Lake. Kirovsk City is the
main settlement in the Khibiny massif where there are five
apatite-nepheline ore deposits (Fig. 1e) that have been actively mined
since the 1930s. They are now owned by the company PhosAgro. The mining
activity has led to elevated surface water concentrations of strontium
(Sr) and aluminum (Al), as well as copper (Cu), zink (Zn), nickel (Ni)
and chromium (Cr) in the Yuksporiok and Vuonnemiok basins (Efimov et
al., 2019; Malinovsky et al., 2002). The Kola Peninsula also hosts
several Cu-Ni ore smelters that have for decades emitted large volumes
of sulfur dioxide into the air resulting in acid rain and high sulfur
and metal atmospheric deposition (Moiseenko and Bazova, 2016).
Field campaigns and analyses
Surface water sampling and measurement campaigns were conducted in the
Imetjoki catchment in the spring (end of May during snowmelt) and in the
late summer (end of August) of 2017. Apart from element concentrations
and general water quality parameters (e.g., pH, dissolved organic carbon
etc.; presented in Fischer et al. 2020) sulfur isotopes
(δ34SSO4-values in
SO42-) were measured. In total 11
locations were sampled for sulfur isotopes and sulfur concentrations in
the spring and 13 locations were sampled in the summer (the latter used
here for comparison, being presented in Fischer et al., 2022). Nine
sampling locations were common for both campaigns. The sampling
locations were distributed over the upstream areas (undisturbed by
mining; IDs 1‒2 in Fig.1), the mining site itself (directly affected by
AMD; IDs 3‒9), and downstream of the mining site (IDs 10‒12, 14). Two
adjacent rivers were also sampled for reference (IDs 13, 15). The same
sampling and analysis procedures were followed in both the spring and
summer campaigns as described in Fischer et al. (2022), making the
results directly comparable. The sulfur isotopic composition was
determined from collecting 2L water samples that were dripped through
ion exchange resin columns to collect the sulfate in water and for
easier transportation to the laboratory. Instrumental analyses were
carried out with an elemental analyzer (CarloErba NC2500) coupled to a
stable isotope ratio mass spectrometer (Finnigan Thermo Delta plus;
analytical accuracy was ±0.2‰) at the laboratories of the Department of
Geological Sciences at Stockholm University. Sulfur isotopes are
reported in parts per million (‰) through the δ-notation relative to the
Vienna-Canyon Diablo Troilite (V-CDT) standard: