Spectrofluorimetric study of dissolved organic matter in River Salaca (Latvia) basin waters

Dissolved organic matter (DOM) in surface waters influences mineral weathering, nutrient cycling, aggregation of particulate matter and photochemical reactions in waters and aquatic communities. In this study, the effectiveness of UV and fluorescence measurements in distinguishing the origin of DOM and processes within the river basin were analyzed using the River Salaca basin as an example. The basin of River Salaca is characterized by low anthropogenic pressure, however, the water color during the last few decades has increased (an effect known as brownification). As tools to study the composition of dissolved organic substances in waters of the River Salaca and its tributaries the use of UV and fluorescence spectroscopy was evaluated. The use of the fluorescence index (a ratio of the emission intensity at a wavelength of 450 nm to that at 500 nm) allowed us to distinguish sources of aquatic DOM, characterize processes in the water body basin and to follow the changes in organic matter composition. Synchronous scan fluorescence spectrometry was more informative than excitation emission spectra and, provided information on the basic structural features of DOM.