Two experiments were set up to track chemical changes of organic matter in the Muskegon River watershed. An outdoor incubation experiment was set up to track chemical changes due to microbial activity at six sites from Cedar Creek to Lake Michigan. Changes in the concentration of tannins and lignins (of exclusively terrestrial origin), bacterial abundance and dissolved organic carbon (DOC) concentration were measured before and after the incubation. DOC increased from Cedar Creek to Muskegon Lake as the water traveled further along land gathering terrestrial inputs, but rapidly decreased in concentration as the water mixed into Lake Michigan. Tannin and lignin concentration varied only slightly during the microbial incubation.

A photochemical experiment was set up in the lab to track chemical changes in the water due to “sunlight” exposure at the Muskegon Lake site. Tannin and lignin concentration, bacterial abundance, DOC concentration and a colored dissolved organic matter (CDOM) spectrum were collected throughout the photo exposure. The concentration of tannins and lignins actually increased during the UV exposure in the light bottles, which was contrary to our prediction. The CDOM spectra clearly showed a decrease in CDOM concentration due to the “sunlight”, suggesting that photochemically released phenol-like compounds are likely responsible for the apparent increase in tannin or lignin concentration in irradiated water.