3. Materials and methods
A total of 63 samples were collected from the Zuli River Catchment and
these samples were divided into five types:
precipitation
(n=5), groundwater (n=20), river water (n=25), soil, and river suspended
particulates (n=13)(Fig. 1). Local precipitation of headwaters was
sampled monthly from May to September for one season (Fig. 1). TDS and
pH measurements were performed in the field with a calibrated portable
Multi-Parameter Analyzer (HACH HQ40D; typical EMC deviation: ±0.1 pH,
±1% of TDS). Water samples were filtered in the field at 0.45 μm for
hydrochemistry analyses and acidified for cations and87Sr/86Sr analysis to pH <
2 with ultrapure HNO3. For the hydrochemistry analysis,
the water samples with TDS >1000 mg/l were diluted to TDS
less than 500 mg/l. Samples for Boron isotopic analysis were collected
in a separate bottle.
All chemical compositions of the samples (n=50) were analyzed at the
State Key Laboratory of Hydrology-Water Resources and Hydraulic
Engineering, Hohai University, China. Major cations were analyzed by
inductively coupled plasma-atomic emission spectrograph (ICP-AES)
(Instrumental Error <5.0%), and major anions were analyzed by
ion chromatography (ICS-2000) (Instrumental Error <2.0%).
For strontium isotopes, the isotopic compositions of Sr (n=18; Table 1)
were determined by TIMS (Thermal Ionization Mass Spectrometry, Triton,
VG354) with nine Faraday collectors at the Institute of Geochemistry,
Nanjing Nantai. The 87Sr/86Sr value
for the standard NIST987 was 0.710236 ± 0.000007 (2r, n=62) during the
measurement period of our samples. The total blank for Sr was less than
0.5 ng, negligible with respect to the total strontium in the analyzed
precipitation samples.
Boron isotopes (n=28; Table 1) were analyzed using a Neptune Plus
MC-ICP-MS (Nanjing) with an ESI PFA 50 μL/min nebulizer in a quartz
cyclonic spray chamber. The isotopic standard
(11B/10B) standard
NIST 951 =4.04362. To reduce the memory effect, continuous washing with
3% HNO3 and 1% HNO3 and Millipore
water in sequence for ~25 min was conducted. The final
isotopic compositions are reported as δ11B= 1000
(Rsample/Rstandard-1). The average
internal analytical precision (n=100) and the external reproducibility
of the measured 11B/10B ratios of
200 ng/mL NIST 951 are ±0.02 ‰ (2 SE) and 0.11 ‰ (2σ), respectively.