Chromophoric dissolved organic matter in summer in a coastal mariculture region of northern Shandong Peninsula, North Yellow Sea

摘要

Four field cruises were carried out in a mariculture region of the northern Shandong Peninsula from June to September 2017. The concentration of dissolved organic carbon (DOC) together with the absorbance and fluorescence indices of chromophoric dissolved organic matter (CDOM) were measured. The parallel factor analysis model identified four unique fluorescent components consisting of two protein components identified as tyrosine-like Cl and tryptophan-like C2, and two humic-like components C3 and C4. The DOC, CDOM absorption coefficient at 350 nm (a(350)) and protein-like components C1 and C2 exhibited obvious monthly variations particularly. However, the monthly variation of humic-like components C3 and C4 was not significantly different. Spatially, the a(350) and fluorescent components C1-C4 were higher in the nearshore area and decreased towards the offshore area. The humification index, fluorescence index and biological index indicated the predominant autochthonous and microbial sources of CDOM. In the surface water, phytoplankton was assessed as the contributor to 11.6-35.2% of the CDOM, and 9.0-37.4%, 9.1-37.4%, 7.8-18.7% and 11.4-19.9% of the CDOM were identified as C1, C2, C3 and C4, respectively. The river inputs, especially the Xin'an River, have an important impact on DOM dynamics. In the bottom water, microbial aerobic degradation of sinking biogenic particles is an important source of humic-like components, which contributed 9.1%, 18.7% and 48.5% to C3 in July, August and September, and 14.6%, 16.3%, 18.0% and 26.6% to C4 from June to September, respectively.