Variability in the rate of CDOM photobleaching and its control in lakes

FERRARO, MARCELA; MORRIS, DONALD; ZAGARESE, HORACIO; HARGREAVES, BRUCE; SOTO, DORIS; DE LOS RÍOS, PATRICIO; JARAMILLO, JORGE; PÉREZ, ALEJANDRA PATRICIA; AÑÓN SUÁREZ, DIEGO

Santiago de Compostela, España

Congreso; American Society of Limnology and Oceanography; 2005

American Society of Limnology and Oceanography

Photobleaching potential of CDOM to UV radiation was measured in 99 water samples collected from lakes of Argentina, Chile, and Antarctica. A standardized laboratory technique for measuring photobleaching potential was developed and utilized in this study. Photobleaching potential was defined as the rate constant (Kb) for the wavelength specific loss of absorbance for the duration of exposures to light. Rate constants were converted to wavelength specific absorbance half-lives (J). A first order kinetic model for photobleaching was confirmed for standards and lake samples. Both laboratory and solar exposure to UVR provided similar rates of photobleaching across most of the UV-a and UV-b spectrum (difference < +/-10%). Values of J varied from 0.6 d to 16.9 d for the lakes investigated in this study. Photobleaching rates for Antarctic lakes were significantly higher than for South American lakes (p<0.001). No significant difference in photobleaching rate was observed between fresh and saline lakes or between climate or ecogeographic regions. Multivariate models of photobleaching based on chemical and optical properties explained the greatest amount of variance in photobleaching among lakes.