Colored Dissolved Organic Matter (CDOM)

The effects of dissolved organic matter on the color and clarity of water can be seen in this photograph of a Florida estuary. The stark contrast is a result of canal drainage from agricultural lands with highly concentrated dissolved organic matter matter.

CDOM, or yellow substances as they are sometimes referred to, are that component of the water that is a result of organic detritus deteriorating, which releases tannins into the water, much like a tea bag, staining the water yellow to brown. Organic detritus naturally occurs as decaying plant matter, like leaves, and decaying phytoplankton produced within a water body. However, CDOM can be increased by human activities, which include nutrient enrichment, leading to phytoplankton growth, increasing the amount of decaying phytoplankton. CDOM can also be increased by point source pollution from pulp and paper mills or wetland drainage.

The resulting color change is a result of the selective absorption of some of the light energy by the dissolved material. The graph above shows the spectral absorption for three increasing concentrations of an analog solution of dissolved organic matter. In each case, the curve is similar, meaning absorption is simply increasing with increasing concentrations.

Absorption is greatest near the 400 nm end of the spectrum, meaning the CDOM is taking in most of the energy of the blue wavebands. When this affect is combined with the strong absorption of red light by water itself, the water appears to be green or yellow to brownish in color depending on the amount of CDOM present.

Examples of of water bodies almost exclusively dominated by CDOM include black water swamps of the southeastern United States, brown water lakes, draining peat bogs in the northeast U.S. and Canada, and portions of the Pocomoke River, east of the Chesapeake Bay.