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: 2:15:00 PM

Location: San Miguel

Reche, I, , Universidad de Granada, Granada, Spain, ireche@goliat.ugr.es

Pace, M, L, Institute of Ecosystem Studies, Millbrook, USA, pacem@ecostudies.org

Cole, J, J, Institute of Ecosystem Studies, Millbrook, USA, colej@ecostudies.org

INFLUENCE OF WATER CHEMISTRY ON DISSOLVED ORGANIC MATTER PHOTOBLEACHING

Photobleaching of dissolved organic matter (DOM) affects light climate and bacterial carbon mineralization influencing rates of heterotrophy in aquatic ecosystems. Variability in photobleaching has been associated with the intrinsic nature of DOM and the chemical environment where the diverse molecules are dissolved. In this work, we present experimental evidences of the influence of water chemistry on photobleaching rates. We performed a set of experiments designed to determine: 1) if identical DOM manifests a variable susceptibility to photobleaching in water with different acid-neutralizing capacity (ANC); 2) if photobleaching changes are linked to specific cations and/or anions; and 3) if these changes are constant over the absorption spectrum. Experimental increases of ANC led to higher initial absorptivities and faster photobleaching rates at 440 nm. This experimental pattern was comparable to that previously observed among lakes that vary in ANC. Photobleaching was 2-3 times faster when carbonate was the source of alkalinity relative to bicarbonate. The pattern of increased photobleaching with increased ANC, however, was not observed at shorter wavelengths. We speculate that the mechanism of increased photobleaching at 440 nm with changes in ANC is related to interactions between ions and the configuration of molecules of humic and fulvic acids as has been observed in soils.

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Aquatic Sciences Meeting, Albuquerque 2001

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