Dynamics of dissolved organic matter in seawaters and sediment pore waters from river-impacted coastal sea

As one of the world’s largest marginal seas, the South China Sea (SCS) plays an important role in regional and even global carbon budgets. Yet, understanding regarding DOM dynamics in coastal seawaters and sediment pore waters is still limited. Here, optical and molecular methods are utilized to investigate spatiotemporal dynamics of seawater dissolved organic matter (DOM) and composition of sediment pore water DOM in northern SCS. Generally, higher chromophoric and fluorescent DOM (CDOM and FDOM), coincident with higher CDOM molecular weight and humification index, are observed in summer monsoon than in the winter monsoon due to the seasonality of riverine runoffs. Nearshore surface seawaters were plume-affected whereas CDOM and FDOM of bottom waters were enhanced by inputs from sediment resuspension, leading to higher levels in bottom waters offshore. Furthermore, high abundance of condensed aromatics (~12.6±3.2%) and S-containing formulas (20±2%) were found in sediment pore waters, implying coastal sediment pollution caused by presumably anthropogenic activities. Common formulas shared by all pore water samples at different sites and depths are predominated by CHO-only molecular formulas (97%) which largely fall in the lignin-like/CRAMs(i.e., carboxyl-rich alicyclic molecules) category of the van Krevelen diagram. The study provides insights into the DOM dynamics in a river-impacted subtropical/tropical sea.

Presentation Preference: Oral

Primary Presenter: Meilian Chen, University of Tennessee, Knoxville (mchen51@utk.edu)

Authors:

Meilian Chen, University of Tennessee, Knoxville  (mchen51@utk.edu)

Qian Li, South China Sea Institute of Oceanology  (qianli@scsio.ac.cn)