Absorptivity Inversely Proportional to Spectral Slope in CDOM

Area of Science:

• Environmental Science
• Analytical Chemistry
• Spectroscopy

Background:

• The Bouguer-Lambert-Beer (BLB) Law's application to dissolved organic matter (DOM) is limited by overlapping chromophores with varying molar absorptivities (ε).
• Chromophoric DOM (CDOM) presents complex absorption spectra, hindering accurate quantification of dissolved organic carbon (DOC).
• Existing methods struggle with uniform DOC quantification across diverse aquatic environments.

Purpose of the Study:

• To demonstrate an inverse relationship between molar absorptivity (ε) and spectral slope (S) in CDOM absorption spectra.
• To expand the applicability of the BLB Law for uniform DOC quantification in various water types.
• To provide a method for interpreting DOM absorbance spectra and understanding its composition.

Main Methods:

• Analyzed absorption spectra of chromophoric DOM (CDOM) from diverse water bodies.
• Investigated the relationship between molar absorptivity (ε) at specific wavelengths and spectral slope (S).
• Correlated Gaussian peak width (W²) with ε and S to establish quantitative links.

Main Results:

• An inverse relationship between ε and S was confirmed for CDOM.
• ε values at 275 and 380 nm were found to be proportional to W², which is inversely proportional to S.
• The developed method achieved high accuracy (R² = 0.97) for quantifying DOC across a wide range (30-3000 μmol·L⁻¹) in inland, coastal, and pelagic waters.

Conclusions:

• The study successfully expands the applicability of the BLB Law for uniform DOC quantification in aquatic systems.
• The established relationship between ε and S offers valuable insights into DOM composition and properties.
• This advancement enables more effective CDOM monitoring using UV-vis spectroscopy on various scales.