Photochemical transformation of dissolved organic matter to dissolved inorganic carbon

Abstract

Coloured dissolved organic matter (CDOM) and dissolved inorganic carbon (DIC) photoproduction rate (dDIC/dt) were measured at two marine time series stations (coastal station L4; 50.25°N, 4.22°W and open-shelf station E1; 50.03°N, 4.37°W) and three rivers (river Dart, 50.59°N, 3.91°W; river Erme, 50.38°N, 3.92°W; and river Plym; 50.46°N, 4.04°W) all located in South-West England. Sampling was done during February-April 2016, when eleven samples were analysed. Additional data collected previously, during May-June 2015, was incorporated into the data analysis presented here. This project observed a correlation between CDOM and dDIC/dt during both periods (p-value = 8.32x10-3 (2015) and 2.39x10-5 (2016)). Both datasets show an understudied relationship, the seasonal variability of both CDOM and dDIC/dt. Different slopes were observed in their correlations (0.0340±0.0055μmol m L-1 h-1 (2015) and 0.0939±0.0118μmol m L-1 h-1 (2016)), seasonal variation being the most probable cause. However, the slope for oceanic water during the 2016 period (0.0302±0.0108μmol m L-1 h-1) was in the range of the slope for all the data during the 2015 period. This would suggest that major changes in CDOM and dDIC/dt are only observed in fluvial water, although compositional changes between the different water types may also influence this result.