Aquatic Sciences Meeting, Albuquerque 2001

SS02 Photochemical Reactions In Surface Waters: A Major Issue in the 21st Century? (Environmental Connections)

Date: Thursday, February 15, 2001, Time: 2:00:00 PM

Location: San Miguel

Osburn, C, L, NRC-Naval Research Laboratory, Washington, DC, USA, cosburn@ccs.nrl.navy.mil

Morris, D, P, Lehigh University, Bethlehem, PA, USA, dpm2@lehigh.edu

Hargreaves, B, R, Lehigh University, Bethlehem, PA, USA, brh0@lehigh.edu

Zagarese, H, E, Consejo Nacional de Investigaciones Cientificas y Tecnicas, Bariloche, Argentina, zagarese@infovia.com.ar

MODELING THE CONTRIBUTION OF UV RADIATION TO THE PHOTOBLEACHING OF CDOM IN TEMPERATE LAKES FROM NORTH AND SOUTH AMERICA

The effect of UV-B radiation on the decrease in the dissolved absorption coefficient (a_d) of several North and South American lakes was estimated to be <20% compared to UV-A and blue light radiation, based on a summary spectral weighting function (SWF) calculated for the photobleaching (PB) of chromophoric dissolved organic matter (CDOM). The SWF was able to explain 80-90% of the observed variance in exposures of filtered epilimnial lake water to solar radiation. We were also able to predict PB results obtained for exposures of water from other South American lakes (mean error 14.5%). A Monte Carlo simulation based on the SWF model predicted PB values that did not differ significantly (p=0.003) from measured values pooled across lakes and dates from static depth incubations of filtered water from two Pennsylvania lakes. The SWF also predicted changes in the a_d of the mixed layer of the two PA lakes during 1999, especially during periods when watershed input of CDOM is minimal. Though the contribution of biologically-damaging UV radiation to overall PB was estimated to be small, these results suggest that photobleaching plays a central role in regulating the transparency of UVR in the mixed layer of temperate lakes.

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Aquatic Sciences Meeting, Albuquerque 2001

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