Data of snapshot sampling in Ishikari River basin

The six study sites lie
within the Ishikari River basin in Hokkaido, northern
Japan. The forested mountain area of the Ishikari basin can be divided
into two main parts depending on geology: the Yubari Mountain Range, which is
underlain by sedimentary bedrock, and the eastern part of the basin, which is
underlain by igneous rock formed by the activity of volcanic groups, including the
Daisetsuzan and Mt. Tokachi. The S-SE, S-NA, and S-PO study sites were located
on the Yubari Mountain Range and underlain by sedimentary bedrock, and the V-IS,
V-PE, and V-KU study sites were located around the Daisetsuzan volcanic group
and underlain by volcanic bedrock.
Spring and stream water
were sampled for chemical analysis and discharge rates were measured during
baseflow conditions at points with different catchment areas.
Streamflow velocity was
measured by a propeller flow velocity meter (CR-11; Miura-Rika Inc., Sapporo,
Japan). Discharge was calculated by multiplying the cross-sectional area by the
stream velocity. Specific discharge was calculated as the measured discharge
rate divided by the catchment area obtained from the Geospatial Information
Authority of Japan’s 10 × 10-m digital elevation models using QGIS 3.4 software
(QGIS Development Team).

The samples were filtered
through a GF/F filter with 0.63-µm pores in a laboratory. The samples were
sealed in polyethylene bottles and refrigerated at 2°C until analysis. The
solute concentrations were analyzed in a laboratory. Anion and cation concentrations were measured using ion chromatography (Dionex
ICS-1100; Thermo Fisher Scientific, Waltham, MA, USA), and SiO2
concentrations were measured using an auto-analyzer (QuAAtro 2-HR; BLTEC,
Osaka, Japan).