Influence of a summer storm event on the flux and composition of dissolved organic matter in a subtropical river, China

Dissolved organic matter (DOM) has not been studied fully for tropical and subtropical rivers, in particular during storm events. DOM dynamics during a summer storm event in June, 2011 were examined in a subtropical river (the North Jiulong River, China). Stormwater runoff was sampled for measurement of dissolved organic C (DOC), absorption spectroscopy and fluorescence excitation emission matrix spectroscopy (EEMs). Three different fluorescent components were identified using parallel factor analysis (PARAFAC), including humic-like C1 and C3, and C2 as a combination of humic-like and protein-like fluorophores. The flux of DOC increased fivefold from 0.4 kg s−1 at baseflow to 2.0 kg s−1 at peak flow. Chromophoric DOM (CDOM) and fluorescent components also showed large increases with stormflow. The flux of DOC was similar during the rising and falling hydrographs at equal water discharge, while those of CDOM and fluorescent components were much higher during the falling-hydrograph. Carbon specific CDOM absorption coefficient at UV (SUVA254) and the fraction of C3 which fluoresced at long emission wavelength correlated positively to each other but negatively to absorption spectral slope ratio (SR) and C2%. They showed notable temporal variations indicative of increases in aromaticity, C3% and average molecular weight of DOM during the storm event. Changes in DOM composition lagged behind those in DOM flux. Changes in the flux and quality of DOM during the storm event, which were monitored effectively by absorption spectroscopy and EEMs–PARAFAC, could affect biogeochemical processes in the river and receiving coastal waters.