Inferring Ecosystem Function from Dissolved Organic Matter Optical Properties: A Critical Review.

Area of Science:

• Environmental Science
• Biogeochemistry
• Optical Oceanography

Background:

• The study of dissolved organic matter (DOM) has evolved from analyzing complex mixtures to understanding its role in carbon (C) cycling.
• The application of optical properties for DOM analysis in biogeochemical systems is currently under debate.
• Existing research often treats DOM from different ecosystems as distinct, potentially overlooking shared characteristics.

Purpose of the Study:

• To critically review the use of optical properties for dissolved organic matter (DOM) analysis across atmospheric, marine, and terrestrial ecosystems.
• To establish a framework for interpreting common DOM optical metrics (FI, HIX, SUVA254) based on ecosystem variables.
• To investigate the similarities and differences in DOM optical properties across various biosphere subdivisions.

Main Methods:

• Conducted an extensive literature survey of DOM optical property measurements.
• Employed a categorical approach to analyze data across atmospheric, marine, and terrestrial biospheres and their subdivisions.
• Utilized a rubric of ecosystem variables (e.g., productivity, C cycling rate, water quality) to interpret optical metrics.
• Performed case studies and a meta-analysis for each biosphere and subdivision.

Main Results:

• Found substantial overlap in characteristic distributions for fluorescence index (FI), humification index (HIX), and specific ultraviolet absorbance at 254 nm (SUVA254) across different ecosystems.
• Observed that chromophores and fluorophores from diverse ecosystems may share more similarities than previously assumed.
• Demonstrated that ecosystem context is crucial for interpreting DOM optical metrics.

Conclusions:

• Optical properties of DOM are valuable indicators for understanding ecosystem function and carbon cycling.
• DOM optical metrics like FI, HIX, and SUVA254 exhibit characteristic patterns that can be linked to ecosystem variables.
• Researchers should consider ecosystem connectivity and avoid "if this, then that" conclusions when interpreting DOM optical data.