Spatial Distribution and Degradation of CDOM in the Minjiang River in Summer

Abstract

The composition, distribution, and degradation of chromophoric dissolved organic matter (CDOM) in the lower reach and estuary of the Minjiang River were analyzed using fluorescence excitation-emission matrices-parallel factor analysis (EEMs-PARAFAC) and microbial and photochemical degradation experiments. The results show that there are three types of fluorescence components in the study area:humic-like, tyrosine-like, and tryptophan-like. The humic-like components are the main components in the river zone, while the protein-like components become dominant with increasing salinity in the estuary. The change of the CDOM abundance shows a notable spatial distribution pattern. The absorption coefficient a(280) of CDOM is lower in the river, increases after entering the urban area, shows a decreasing trend in the suburbs, and rapidly declines in the estuary. A conservative estimate of the contribution of the Fuzhou urban area to the CDOM of the Minjiang River is 8%. The a(280) in the river is susceptible to microbial and photochemical degradation and the degradation percentages are (28±8)% and (44±7)%, respectively. The bioavailability and photochemical reactivity of a(280) are much higher in the river than in the estuary. The humic-like, tyrosine-like, and tryptophan-like components show a higher photochemical reactivity in the river, with degradation percentages of (75±0.5)%, (58±21)%, and (73±3)%, respectively. The fluorescent components are not labile with respect to microbial degradation and humic-like components are accumulated after 28 days of microbial culture.