Water
sampling and geochemical
measurements were performed before initiating the experiment and subsequently
at time intervals of 30 min to 30 h for up to 200 h. Measurements
of pH and redox potential (Eh) were performed in conjunction with
water sampling. The pH electrode (VWR Symphony) was calibrated to
NIST-traceable 4, 7, and 10 buffer solutions. The electrode performance
was regularly checked, and recalibration was performed as necessary.
The performance of the redox electrode (Accumet) was verified using
ORP calibration solution (Orion). The water samples were collected
in PE syringes, passed through 0.2 μm polyethersulfone (PES)
syringe filter membranes, stored in high-density PE (HDPE) bottles,
and refrigerated until analysis. Inorganic anions (NO3–, NO2–, and SO42–) were quantified by ion chromatography (ICS2100;
Dionex Corporation) on nonacidified samples. Total Se was quantified
by inductively coupled plasma–optical emission spectroscopy
(SPECTROBLUE SOP, SPECTRO Analytical Instruments GmbH, Germany) on
samples acidified to pH < 2 with trace-metal-grade nitric acid
(Thermo Fisher Scientific). Spectrophotometric (DR2800; HACH Chemical
Co.) determination of total ammonium (NH4+)
concentrations (by the Nessler method) was performed for samples from
B3 and B4, which initially contained NO3–.
sampling and geochemical
measurements were performed before initiating the experiment and subsequently
at time intervals of 30 min to 30 h for up to 200 h. Measurements
of pH and redox potential (Eh) were performed in conjunction with
water sampling. The pH electrode (VWR Symphony) was calibrated to
NIST-traceable 4, 7, and 10 buffer solutions. The electrode performance
was regularly checked, and recalibration was performed as necessary.
The performance of the redox electrode (Accumet) was verified using
ORP calibration solution (Orion). The water samples were collected
in PE syringes, passed through 0.2 μm polyethersulfone (PES)
syringe filter membranes, stored in high-density PE (HDPE) bottles,
and refrigerated until analysis. Inorganic anions (NO3–, NO2–, and SO42–) were quantified by ion chromatography (ICS2100;
Dionex Corporation) on nonacidified samples. Total Se was quantified
by inductively coupled plasma–optical emission spectroscopy
(SPECTROBLUE SOP, SPECTRO Analytical Instruments GmbH, Germany) on
samples acidified to pH < 2 with trace-metal-grade nitric acid
(Thermo Fisher Scientific). Spectrophotometric (DR2800; HACH Chemical
Co.) determination of total ammonium (NH4+)
concentrations (by the Nessler method) was performed for samples from
B3 and B4, which initially contained NO3–.