Data of monitoring the Oplotnica River silicate catchment (Slovenia) using stable carbon and nitrogen isotopes

Herein, we present a dataset of the geochemical and isotopic characteristics of water collected from September 2012 to June 2014 to evaluate biogeochemical processes within the Oplotnica River silicate catchments. Additionally, we collected soil samples at Javorski creek to characterize the soil profiles using stable isotopes of carbon and nitrogen.
Discharge and temperature data for the Oplotnica River at the Perovec gauging station were gathered from the Slovenian environment agency. Temperature at both Javorski and Lukanjski creeks was measured on-site, while pH and conductivity were measured in the lab with Metrohm pH low ionic strength glass electrode and Pt1000 electroconductivity electrode, connected to Metrohm 712 Conductometer. Cations (Na+, K+, Ca2+, Mg2+, Mn2+, NH4+) were analyzed with Metrohm Metrosep C4-150/4.0 column without suppression and anions (NO3-, NO32-, SO42-, Cl-, PO43-) with Metrohm Metrosep A Supp 5-150/4.0 column with chemical suppression. Both connected in Metrohm Ion Chromatography modular system. Total alkalinity was measured with double-end point titration (pH=4.5, 4.2) measuring pH with Metrohm pH low ionic strength glass electrode and titrating with 0.01 M HCl controlled by Metrohm 702 SM Titrino titrator. Dissolved organic carbon (DOC) was measured with TOC analyser Shimadzu TOC-5000A as a difference between dissolved total carbon (DTC) and dissolved inorganic carbon (DIC).
Thermodynamic modeling was performed with the PHREEQC speciation program to evaluate pCO2 and the saturation state of calcite and dolomite.
The major solute composition of the analyzed surface water was as follows: Na+Ca2+Mg2+K+ and HCO3-SO42-Cl-NO3-. In surface water the δ13CDIC ranged from -26.1‰ to -1.4‰, and the 13CPOC from -28.2 to -22.3‰, and 15N from -2.2 to 2.6‰ (measured only in September 2012). 13Corg. ranged from -28.3 to -24.9‰, while 15N ranged from -4.9 to 5.4‰ at three soil profiles (up to a depth of 70 cm) at Tratice I, II and III locations at Javorski creek. Characteristic plants within catchment area have 13C in the range from -31.2 to -29.2‰ and 15N in the range from -8.0 to -5.5‰.
Data were collected through field and laboratory analyses. These data were used to calculate saturation indices, partial pressure of CO2 (SIcalcite, SIdolomite, pCO2), and to perform a mass balance calculation of carbon to determine the processes that contribute most to the isotopic composition of dissolved inorganic carbon (δ13CDIC). Furthermore, bicarbonate weathering intensity was calculated within the catchment area. The main conclusions are that the saturation index of calcite (SIcalcite) ranges from -6.1 to -1.9, and the saturation index of dolomite (SIdolomite) ranges from -12.7 to -4.2. The bicarbonate weathering intensity is 10.4 mmol/km²·s, which is typical for silicate catchments.