Methodology:

The pH was determined using standard, portable meter and electrodes (Hanna Instruments, UK) calibrated using fresh pH 4 and 7 buffers. The other parameters required analysis of a filtered sample, which was undertaken immediately after melting. For both DOC and TDIC, a 50mL aliquot was filtered through a Whatman GFF filter paper (notional pore space: 0.7 µm) and stored in pre-rinsed 40 mL glass vials for DOC analyses using the membrane conductometric method. This employed a Sievers 5310 Analyser with UV and persulphate digestion (detection limit 0.01 mg L-1 and < 5% precision errors according to repeat analysis of mid-range (0.4 mg L-1) standards.

For NH4+ we employed the fluorescence technique described by Taylor et al (2007), using a Turner Instruments Aquafluor fluorometer, with a 375 nm excitation LED and a 420 nm long pass filter for emission detection. The samples were incubated for typically three to five hours in order to optimise the intensity of the fluorescence and enable a detection limit of 0.1 µg L-1. The same device was also used to provide an optical measure of the abundance of fluorescent DOC in the filtered samples. Untreated samples were allowed to equilibrate to room temperature and the average of three fluorescence readings taken at the same wavelengths used for the NH4+ detection. These excitation/emission wavelengths are used as an industry standard for the detection of chromophoric dissolved organic matter or 'CDOM' and readings are used here to assess whether there were any changes in the source of the DOC.

Melted snow or ice (300-900 mL) was filtered under low pressure onto 25 mm GF/F filters (combusted at 450°C for 5 hours). All sample and filter handling was conducted under low light and low temperature conditions and in an acid-free environment. Filters were stored in glassine envelopes in -80°C until further analysis (1-8 weeks). Filters were then added to clean glass scintillation vials with 10 ml of 80% methanol for extraction. Chlorophyll-a standards (Anacystis nidulans, Sigma) were made just prior to analysis (0, 1, 2, 5, 10, 50, 100, 200, 500 and 1000 µg L-1). Triplicate measurements were conducted using the Turner Designs Aquafluor fluorometer with excitation at 395 + 65 nm. The accuracy was tested by repeated use of blanks, chlorophyll standards and a solid standard.

Samples from the first survey at each site were also subject to analysis after 0.45 µm filtration (WCN paper) to ion chromatography, with a detection limit of 1 ppb and precision errors of 5% or better on mid-range calibration solutions.

Data collection:

Instruments used include:

Turner Instruments Aquafluorometer

Sievers 5310 Analyser

Dionex DX90

Apogee SQ100 pyranometer