Photochemical and microbial degradation of dissolved organic matter in the Lake Superior watershed.

Abstract

Photodegradation of dissolved organic matter (DOM) due to ultraviolet (UV) exposure can have important consequences for coastal zone productivity. The availability of UV radiation to aquatic environments has increased due to ozone depletion. Chromophoric DOM affects the amount of light penetration in a water column. Ecosystem productivity depends in part on the input of DOM into a coastal zone. DOM can protect animals, plants, and microbes from damaging UV light by acting as sunscreen, resulting in increased ecosystem productivity. Alternatively, DOM can decrease ecosystem productivity by absorbing light needed for photosynthesis and forming reaction products that are harmful to coastal zone biota. Increased urbanization of watersheds and seasonal differences in weather patterns change the delivery pathways, reactivity, input, and energy flow of DOM into aquatic systems. Understanding the input and reactivity of DOM in coastal systems as a function of land urbanization and season will help determine the fate of irradiated organic matter and its potential role as a sunscreen in coastal waters. The consequences of energy flow from UV radiation to DOM in aquatic systems will provide useful preliminary data to be used for land-use planning in tributary regions. This study also provides data useful for predictive models of the fate of irradiated organic chemicals and the resultant impact on water quality. In this paper, the study of watershed urbanization and season on the input and photodegradation of DOM in coastal waters is discussed based on organic carbon analysis, UV-Visible spectrophotometry, microbial processing of DOM, and terrestrial (land-use) analysis.