This story first appeared in the SERC quarterly Newsletter Spring 2007

Sun Bleaching the Marshes

In the marshy tributaries of the Chesapeake Bay colored dissolved organic material, such as the tannin from fallen leaves is a major reservoir of organic carbon. CDOM, as it’s called, plays a central role in aquatic ecosystems, affecting carbon budgets, nutrient availability and ecosystem productivity. As such an influential component of the system, it’s a major focus of researchers in the Photobiology lab.

A recent paper by Maria Tzortziou, Patrick Neale and Chris Osburn published in Photochemistry and Photobiology examines how exposure to sunlight changes the properties of colored dissolved organic matter (CDOM) in the waters of the Chesapeake Bay.

CDOM absorbs sunlight in the visible and UV spectral regions, preventing the sun’s rays from reaching the plants and animals below. That can be a good thing, because it absorbs a lot of the harmful UVB radiation and acts as a natural sunscreen for marine organisms. Under certain conditions, solar radiation can change the chemical composition of CDOM and affect its optical properties, something the scientists call photo-degradation and photo-bleaching.

These chemical alterations can result in the release of important trace gases such as Carbon monoxide, carbon dioxide and others. Photo-degradation can also transform CDOM into unstable forms of carbon carbonyl compounds that are readily available for consumption by microbial communities. This in turn affects microbial activity in the water and the cycling of carbon in coastal ecosystems.

The new study shows how CDOM samples from different sources in the Rhode River (marshes, watershed, mouth to the Chesapeake Bay) differ in their susceptibility to photochemical degradation.

According to Tzortziou, this work clears up some previous confusion about CDOM photo-bleaching and describes a new and relatively simple model for predicting the effects of solar exposure on CDOM.

“A model like this is needed for modeling water quality in the Chesapeake Bay and understanding carbon cycling/degradation in coastal waters,” she said.

For more information, or to reach Dr. Tzortiou, please contact SERC science writer Kristen Minogue.