DOM Background-Optics

Colin A. Stedmon (taken from Ph.D. thesis introduction chapter (2004)

The fraction of DOM that absorbs light is referred to as CDOM (coloured dissolved organic matter). Modern-day research into CDOM has evolved from the overlap of branches of three different research fields;

i) aquatic optics (research into the controls of intensity and spectral quality of underwater light, e.g. Markager & Vincent (2000)),

ii) ocean colour remote sensing (the use of satellite measurements of water colour to estimate distributions of algal biomass among other parameters, e.g. Tassan (1988)),

iii) biogeochemistry of carbon (research into the carbon cycling, e.g. Stedmon & Markager 2001).

The optical properties of CDOM are defined by its chemical properties. This allows us to use optical measurements as a proxy for DOM, with the assumption that the processes influencing CDOM are also influencing the non-coloured fraction. It is debatable how valid this assumption is. CDOM may not represent a considerable fraction of the DOM pool in certain environments (e.g. oligotrophic clear water lakes). However in most aquatic environments there are measurable quantities of CDOM. The chemical complexity of DOM leaves no alternative. Detailed chemical analysis suffers from the same weaknesses. Although exact concentrations can be measured, the uncharacterised material overwhelmingly dominates and it’s ecological role is largely unknown. Absorption and fluorescence measurements have their advantages in being rapid and relatively cheap. They are therefore well suited to routine analysis and large-scale intercomparisons.

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This text is taken from my Ph.D. thesis introduction chapter (2004).