Interactions of ultraviolet‐B radiation, mixing, and biological activity on photobleaching of natural chromophoric dissolved organic matter: A mesocosm study

• DOI: 10.4319/lo.2000.45.2.0278
• Publication Date: 2010-06-02T08:24:19Z
• Authors: Robert F. Whitehead; Stephen de Mora; Serge Demers; Michel Gosselin; Patrick Monfort; Behzad Mostajir
• Keywords: Photobleaching; Mesocosm; Absorbance; Photosynthetically active radiation; Spectral slope; Ultraviolet

A natural planktonic assemblage from the St. Lawrence Estuary was isolated in eight 1,500‐liter outdoor meso‐cosms and subjected to combinations of fast or slow mixing regimes with solar radiation artificially enhanced ultraviolet‐B (UVB, 280–320 nm) radiation. The interdependent evolution dissolved organic carbon (DOC), absorption by chromophoric matter (CDOM), chlorophyll a (Chl ), particulate (POC), bacterial abundance mesocosms followed over 10‐d period. There net increase Chl , POC, DOC all systems time; however, slower treatments had less accumulation than faster mixing. All displayed weak correlations POC . significant effect UVB on concentrations these bulk properties not observed any mesocosms. strong correlation CDOM absorbance loss (photobleaching) absorbed dose treatments, having larger losses rates. Photobleaching wavelength dependent, resulting an spectral slope time. Thus, although photobleaching may result deeper penetration light at wavelengths, ratios ultraviolet‐A (UVA) photosynthetically active (PAR) are reduced. unexpected, no proportional increases photo‐bleaching #x002BUVB treatments. Comparisons different indicate that interactions biological activity, mixing, situ field can influence and/or photoreactivity there is possible role for production CDOM.