Origin of dissolved organic carbon studied by UV-vis spectroscopy

Dissolved organic carbon (DOC) distributions in water from Lake Ipe, MS, Brazil, were investigated. The samplings were performed monthly (surface, 1 m depth, and bottom) from June 1999 to June 2000. Absorbance at 285 nm and DOC concentrations in mg dm(-3), rho(DOC), were highly correlated for the three depths. 77% of the surface, 85% for 1 m and bottom samples presented a variation between 20 dm(3) g(-1) cm(-1) and 50 dm(3) g(-1) cm(-1) of A(285 nm)/rho(DOC), that characterizes the dissolved organic matter in lake water as essentially fulvic. The ratio A(254 nm)/rho(DOC) was also sensitive for fulvic matter, and an A(250 nm)/A(365 nm) = 4 ratio was characteristic of strongly colored waters. The ratios A(436 nm)/rho(DOC) for the three depths also showed a significant correlation. The predominance of fulvic acid is explained by environmental characteristics such as the tropical climate, temperatures above 18degreesC, and the lake environment. It was demonstrated that the variation in the water carbon content due to different compartments in the lake can be monitored by UV-vis spectroscopy ratios.