Distinct variations in fluorescent DOM components along a trophic gradient in the lower Fox River-Green Bay as...

Area of Science:

• Environmental Chemistry
• Aquatic Science
• Organic Geochemistry

Background:

• Dissolved organic matter (DOM) plays a crucial role in aquatic ecosystems, influencing nutrient cycling and carbon transport.
• Understanding DOM composition and lability is essential for managing water quality in river-lake interfaces.
• The Fox River-Green Bay system is a seasonally hypereutrophic environment with dynamic water quality changes.

Purpose of the Study:

• To investigate variations in molecular weight distributions and fluorescent components of DOM along a river-to-bay transect.
• To characterize the DOM source and quality changes in the lower Fox River-Green Bay.
• To evaluate the efficacy of the one-sample PARAFAC approach for analyzing DOM.

Main Methods:

• Coupling flow field-flow fractionation (FFF) for size-separation with fluorescence excitation-emission matrix (EEM) and PARAFAC analysis.
• Utilizing a one-sample PARAFAC approach for detailed DOM characterization.
• Measuring concentrations of dissolved organic carbon and nitrogen, chromophoric DOM, and specific UV absorbance.

Main Results:

• DOM quality, indicated by decreasing DOC, DON, and specific UV absorbance, showed a strong riverine source and significant changes along the transect.
• Colloidal DOM (>1 kDa) remained a relatively constant proportion (71%) of bulk DOM, though its concentration decreased.
• Fluorescent components varied, with humic-like components (C475, C410) decreasing from river to bay, while protein-like components (C320, C290) increased.

Conclusions:

• DOM composition and quality are strongly influenced by the riverine source and undergo dynamic changes in the estuarine environment.
• The relative abundance of refractory humic-like DOM (C475) was conservative, while semi-labile humic-like DOM (C410) decreased towards the bay.
• Protein-like DOM components increased towards the bay, suggesting autochthonous production and reflecting the trophic gradient. The one-sample PARAFAC approach proved effective for DOM analysis.