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Chromophoric dissolved organic matter composition and load from a coastal river system under variable flow regimes
Ruchi Bhattacharya1, Christopher L Osburn2
1Dept. of Earth and Environmental Sciences, University of Waterloo, Waterloo, ON N2L 3G1, Canada.
The Science of the Total Environment
|November 24, 2020
Summary
Episodic high flows significantly increase the export of terrestrial chromophoric dissolved organic matter (CDOM) from river catchments, impacting coastal water quality and carbon cycling. Low flows export more microbially processed CDOM, influencing estuarine processes.
Area of Science:
- Environmental Science
- Biogeochemistry
- Coastal Ecology
Background:
- Chromophoric dissolved organic matter (CDOM) from rivers affects coastal biogeochemical processes, water quality, and carbon budgets.
- Quantifying CDOM fluxes, especially reactive vs. recalcitrant forms, under varying flow conditions remains a knowledge gap.
Purpose of the Study:
- To characterize CDOM composition and fluxes under variable flow conditions in a SE USA coastal river basin.
- To assess the impact of episodic and base-flow conditions on terrestrial CDOM export and estuarine processing.
Main Methods:
- Analysis of stream dissolved organic carbon (DOC) concentrations.
- Characterization of CDOM optical properties using parallel factor analysis (PFAnalysis).
- Flux calculations under variable flow regimes.
Main Results:
- Episodic flows exported 70% of terrestrial CDOM, with a 3-fold flux increase during events.
- High flows were dominated by humic acid-like CDOM, with reduced in-stream microbial degradation.
- Low flows exported more microbially derived CDOM, readily processed in estuaries.
- The Neuse River's annual CDOM yield was 5-6 times higher than larger rivers due to wetland coverage.
Conclusions:
- Coastal watersheds, particularly those with extensive wetlands, export substantial reactive CDOM during high flows, impacting estuarine carbon dynamics and water quality.
- These findings are crucial for predicting coastal carbon cycling under climate change and informing management strategies.
