Replicated mesocosm study on the role of natural ultraviolet radiation in high CDOM, shallow lakes

PATRICIA PÉREZ,; MARCELA FERRARO,; GABRIELA CUSMINSKY,; HORACIO ZAGARESE

Photechemical And Photobiological Sciences

Año: 2003 vol. 2 p. 118 - 123

The role of ultraviolet radiation on shallow, high CDOM (colored dissolved organic matter) lakes was investigatedduring two consecutive summers (1999 and 2000) in replicated mesocosms (rectangular fiberglass tanks). Eachtank (volume: 300 L; depth: 40 cm) was covered with a layer (∼3 cm) of sediment from lake El Toro (40
14 S; 70
22 W) and filled with filtered water. The experimental design consisted of two treatments: full natural radiation(UV-exposed) and natural radiation without ultraviolet radiation (UV-shielded). UV-exposed and UV-shieldedtreatments differed in most studied variables as revealed by repeated measures ANOVA. UV-exposed tanks displayedlower CDOM levels (dissolved absorbance) of lower average molecular size (absorbance ratio between 250 and365 nm), higher bacterial biomass, and lower chlorophyll a concentration. The effect on consumers (rotifers andcrustaceans) was less noticeable. The results are consistent with UV stimulation of bacteria production mediated byhigher rates of CDOM photobleaching, and the photoinhibition of planktonic algae. Thus, a major effect of UVRin shallow, high CDOM ecosystems appears to be the stimulation of heterotrophic pathways and a simultaneousinhibition of photoautotrophs.