Photodegradation of natural organic matter exposed to fluctuating levels of solar radiation

HORACIO ZAGARESE; MONICA DIAZ,; FERNANDO PEDROZO,; MARCELA FERRARO,; WALTER CRAVERO,; BARBARA TARTAROTTI,

JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY

Año: 2001 vol. 61 p. 35 - 45

1011-1344

Irradiation of natural water samples with natural or artificial UVR typically results in a progressive loss of color and decreasedabsorbance; a process often referred to as photobleaching. In a typical photobleaching experiment, samples are exposed to a relativelyconstant level of artificial or natural UVR. However, under most natural situations, the vertical mixing of the water within the uppermixed layer results in strong and periodic fluctuations in UV irradiance. In this paper, we present the results of an experiment in whichnatural lake water was exposed to solar radiation in quartz tubes that were incubated either at fixed depths or rotating within the watercolumn.We found differences between rotating and fixed samples in (i) photobleaching, (ii) nutrient release, and (iii) subsequent use byalgae and bacteria. The evidence presented in this study demonstrated that photochemical processes might be affected by vertical watermotion. The reasons for such differences remain largely unknown. Although we offer a potential explanation for such differences, ourproposed mechanism is based on a post-hoc analysis of the data and should be taken solely as a working hypothesis for future research.