DOC was measured using a Sievers M9 TOC analyser and quantified as Non-Purgeable Organic Carbon (NPOC) against MilliQ blanks and a Potassium hydrogen phthalate (KPH) standard. Replicate measurements had a coefficient of variation of ≤ 2 %. The instrument was calibrated between 1 and 50 mg L -1 using KPH, and subsequent KPH standards were all within 5 % of their calibrated value. Absorbance was measured between 200 and 400 nm at 2 nm intervals on a Shimadzu 1800 UV-Vis Spectrophotometer, using a 1 cm pathlength quartz cuvette. The instrument was baseline corrected us, and the sample was referenced against a MilliQ blank. DOC specific absorbance at 254 nm (SUVA254), a commonly used metric for aromaticity where a higher number is associated with a greater aromatic content, was calculated by dividing absorbance at 254 nm (in cm -1 ) by DOC concentration (in mg L -1 ) and multiplying by 100 .