Origin of Dissolved Organic Carbon Studied by UV‐vis Spectroscopy

Dissolved organic carbon (DOC) distributions in water from Lake Ipê, 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, p(DOC), were highly correlated for the three depths. 77% of the surface, 85% for 1 m and bottom samples presented a variation between 20 dm3 g—1 cm—1 and 50 dm3 g—1 cm—1 of A(285 nm)/p(DOC), that characterizes the dissolved organic matter in lake water as essentially fulvic. The ratio A(254 nm)/p(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)/p(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 18 °C, 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.