Methodology:

Samples for trace metal analysis were filtered using pre-rinsed 0.45um Whatman Puradisc Aqua 30 syringe filters and stored in 15mL Eppendorf Tubes after immediate acidification to pH 1.7 using reagent grade HNO3 (AnalaR 65% Normapur, VWR, IL, USA). Samples for major ions were stored in sterile 50 mL centrifuge tube after filtration and rinsing.

Analysis of Fl-, Cl-, NO3-, and SO42- employed a Dionex ICS90 ion chromatography module calibrated in the range 0 - 2 mg L-1. Precision errors for these ions ranged from 0.9 % (SO42-) to 1.6 % (PO43-) and the limit of detection (three times the standard deviation of ten blanks) was < 0.05 mg L-1. A Skalar Autoanalyser, was employed for quantification of dissolved Si (detection limits 0.1 mg L-1, available for 2015 only) using standard colorimetric methods. Concentrations of cations Ca2+, Mg2+, Na+ and K+ were determined by ICP-OES using a Thermo Fisher iCAP 7400 Radial ICP-OES with an internal standard of 1ppm Y, a limit of detection of 0.07 mg L-1 or better and precision errors < 3.65%. For Al, Co, Fe, Mn, Ni, Sr, Ti, and Zn we employed a Thermo Fisher iCAPQc ICP-MS, with internal standard of 1 ppb Rh, a limit of detection < 0.7 ppb and precision 3.2% or better. Accuracy of each method was assessed by analysing freshwater certified reference standards throughout the analyses.

Data quality:

For missing analyses or lost samples, cells have been left blank. Results below detection limit are marked 'b.d.'