Abstract
One of the most important natural sunlight absorbing substances in water is the chromophoric dissolved organic material (CDOM).Two series of CDOM samples from two Southwest Florida Rivers (Caloosahatchee (CR) and Shark (SR)) were characterized in terms of molecular mass (MM) and diffusion coefficients (D) by FIFO-FIFFF with absorbance and fluorescence detectors. The SR receives DOM from the Everglades and, by contrast, the CR arises from Lake Okeechobee in central Florida, and receives anthropogenic inputs and farming run-off. Both rivers extend to the Gulf of Mexico. Fluorescence identified, for both rivers, two different MM distributions in low salinity water samples: the first was centered at ∼1.7 kDa (CR) and ∼2 kDa (SR); the second, which gradually disappeared in the river plumes to below the detection limit in coastal waters, centered at ∼13 kDa for both rivers. Absorbance detected only one MM distribution centered at ∼2 kDa (CR) and 2.2--2.4 kDa (SR). Fluorescence in general peaked at a lower MM than absorbance, suggesting a different size distribution for fluorophores vs. chromophores. The differences observed between the rivers in the optical characteristics, MM distributions and D values suggest that the CDOM inputs, mixing rates, and photochemical degradation processes are different for these two rivers.During the year 2001 three cruises were undertaken in the coastal waters of Southwest Florida: one in the dry period (June) and two during the rainy season (September and November). The CDOM water samples collected during these cruises were characterized in terms of MM distribution and optical characteristics. On the basis of the results, water mass mixing seems to be the dominant factor in the area, but evidence of different sources of CDOM and degradation processes were observed. During the dry season the MM distribution did not change significantly and was centered at ∼1.4 kDa for chromophores and ∼1.1 kDa for fluorophores. Results suggest that chromophores were broken down to smaller MM compounds faster than fluorophores, indicating that the fluorescence moieties are more resistant to degradation/removal processes than the non-fluorescing compounds, even though the fluorophores were always centered at lower MM. The differences in the optical characteristics, MM distributions, and C concentration observed suggest that the CDOM sources, physical, and photochemical degradation processes change seasonally. (Abstract shortened by UMI.)