Assessment of variations in dissolved organic matter in contrasting streams in the Pampas and Patagonian regions (Argentina)

Dissolved organic matter (DOM) is the major source of carbon in aquatic environments and may be derived from allochthonous or autochthonous sources. This study presents the first DOM characterisation in streams from two contrasting Argentinean regions (the Pampas and Patagonia). We found that dissolved organic carbon (DOC) concentrations and absorption coefficients at 254 and 350 nm (a254 and a350) were higher in Pampean than in Patagonian streams. DOM from streams in both regions contained compounds with high molecular weight and highly variable a350 per DOC; it has been suggested that this could be an indicator of lignin content. The characterisation of DOM reflects the agricultural signal and the effect of autochthonous sources in Pampean streams, whereas a more pristine condition with high input from terrestrial environments was recorded in Patagonian streams. No sign of DOM photodegradation was observed in either region. Fluorescence-based indices suggest a more recent input of DOM in Pampean streams, whereas a highly humified component was recorded in Patagonian streams. The combined use of absorbance and fluorescence-based techniques was useful for understanding the quantity and quality of DOM in these contrasting regions in Argentina.