T8 PM Measurement/ Estimation of Environmentally Relevant Physico-Chemical Properties
Tuesday, 15 November 2005: 1:50 PM - 5:30 PM in 337-338

(ZEP-1117-860495) Techniques for Determining UV Exposure in Coastal Waters: Case Study in South Florida.

Zepp, R¹, Shank, C², Fisher, W³, Miller, W⁴, Fichot, C⁴, Bartels, E⁵, Stabenau, E⁶, Moran, M⁴, Lee, R⁴, ¹ US EPA, NERL, Ecosystems Research Division, Athens, GA, USA² US EPA, National Research Council Associate, Athens, GA, USA³ US EPA, NHEERL, Gulf Ecology Division, Gulf Breeze, FL, USA⁴ University of Georgia. Dept. of Marine Sciences, Athens, GA, USA⁵ Mote Marine Laboratory, Summerland Key, FL, USA⁶ NOAA, Atlantic Oceanogrphic Marine Laboratory, Miami, FL, USA

ABSTRACT- The photosynthesis of coral reefs is inhibited by solar ultraviolet (UV) radiation and UV in combination with unusually high sea surface temperatures is believed to play an important role in coral bleaching. Although exposure to solar UV is an important determinant of corals condition, little is known about its variability in coastal regions where corals live. In this presentation we use a new technique based on remotely sensed ocean color to estimate UV attenuation in coastal areas. This technique is applied in a case study of the coral reefs in the South Florida region to estimate fluctuations in underwater solar spectral UV irradiance as a function of location and season. We demonstrate that colored dissolved organic matter (CDOM) controls the penetration of UV radiation in most locations in the Florida Keys and that microbial processing of seagrass and mangrove detritus are major sources of the CDOM. Suspended particles also play an important role in attenuating UV-A (315 to 400 nm), especially in the shallowest areas. UV-induced photoreactions coupled with microbial degradation are the primary loss pathways for the CDOM. Relationships between visible reflectance, UV attenuation, and absorption by colored dissolved organic matter (CDOM) in the ocean water are used along with SeaWiFS images of normalized water-leaving radiance to calculate the CDOM absorption and UV attenuation for the water over the coral reefs. Using this approach we used the satellite observations to compute diffuse attenuation coefficients in the UV region that were within 25% of the observed coefficients. (This abstract of a proposed presentation has been approved by the US EPA. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.)

Key words: uv exposure, corals, organic matter, remote sensing