Methodology:

Samples for dissolved iron and manganese analysis were syringe-filtered immediately in the field through 0.45 µm filters into pre-cleaned 15 mL Eppendorf Tubes, before acidification to pH ~ 1.7 using reagent grade HNO3- (AnalaR 65% Normapur, VWR, IL, USA). The analysis of dissolved Fe and Mn was then completed using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) (PerkinElmer Elan DRC II, MA, USA). Precision errors of the analyses were < 5% according to repeat analyses of mid-range standards, with a detection limit of 1.0 ug L-1. No contaminants were detected above this limit in the analyses of blank deionised water samples. Samples for major ion analysis (here Ca2+, Mg2+, Na+, K+, Cl-, NO3-, SO42-) were also filtered in the same manner (but not acidified) and stored in 50 mL Corning centrifuge tubes after being triple rinsed with filtrate. The analysis was conducted on Dionex DX90 Ion Chromatographs with a detection limit of 0.02 mg L-1 for the lowest, undiluted analysis. Precision errors for these ions were all <5% for mid-range standards.

Charge balance calculations were used to provide the indicative values of HCO3-.

Samples for the determination of dissolved methane and carbon dioxide concentrations as well as delta13C-CH4 and delta13C-DIC of the waters were taken directly from the spring following immersion, complete filling and sealing of a 22 mL Wheaton bottle with a crimp-top lid with septum. The samples were stored inverted under water at 4 degC until analysis. The analysis of the CH4 was performed by gas-chromatography on a Shimadzu GC-2014 instrument equipped with a methaniser and flame ionisation detector, using a 30 m GS-Q, 0.53 mm internal diameter column with N2 as a carrier gas at a flow rate of 8 mL/minute, and injection, oven and detector temperature of 60, 40 and 240 degC, respectively. The sample size was 100 uL and the sample run time was 3 minutes at 40 degC. Concentrations of dissolved CH4 were obtained according to a mass balance calculation for the samples, in which a known volume of N2 was injected into sample vials to create a headspace. After shaking and equilibration (2 h) the CH4 partitioned into the headspace was analysed by GC-FID and the corresponding mass in the gas and aqueous phase was determined by Henry's law, to obtain a final concentration in the water sample. Calibration gas standards were prepared by serial dilution of certificated 60% CH4: 40% CO2 mixed gas using O2-free N2 as the balance gas. The method detection limit was 10 ppm for CH4 in the headspace sample and the analytical precision error was < 5%.

Analysis of dissolved methane isotopic composition and concentration was performed using the gas headspace equilibration technique (5mls sampled water were injected into a Viton-stoppered, He-flushed 120 mL glass serum vial). 10mls of the headspace was then flushed through a 2 mL sample loop, and injected onto a 25 m MolSieve column within an Agilent 7890B GC attached to an Isoprime100 Isotope Ratio Mass Spectrometer (IRMS). Analytical precision errors for samples > 3 ng-C were better than 0.3 per mille for isotopic values, and < 3.5% for concentration, based on methane standard injections. Delta13CDIC was measured by a Continuous Flow Isotopic Ratio Mass Spectrometer (Thermo-Finnegan Delta V with gasbench interface) and an error of 0.1 per mille. All delta13CDIC and delta13CCH4 values are reported vs. the Vienna Pee Dee Belemnite standard.

Samples for water isotope analysis were collected as unfiltered 20 mL aliquots in a screw-top HDPE bottle. The bottles were subsampled into 1.5 mL vials with septa closures and loaded into the auto-sampler tray of a CDRS instrument (Picarro V 1102-i model). Each sample was injected and measured 6 times using 2.5 uL of water for each injection. Together with the samples, two secondary international standards (USGS 64444 and USGS 67400)...(6)

Data quality:

See lineage for precision errors.

For missing analyses or lost/damaged samples, cells are marked "n.d." (not determined). Results below detection limit are marked "b.d." (below detection).