Release of dissolved organic matter (DOM) in an autotrophic and productive stream in Pampean region

The aim of our study was to analyze dissolved organic carbon processing at a reach of a productive Pampean stream and to determine DOM retention efficiencies under a wide range of hydrological conditions. This study was carried out in Las Flores stream, a third-order stream located in the Luján River basin in the northeast of the Buenos Aires province, Argentina. We selected a 2.2 km reach of Las Flores stream. On each sampling occasion, we collected water samples at the end of the reach, at two upstream tributaries, and at the potential hydrological contributors (end members) to stream flow. We determined DOC concentration and DOM optical properties in the stream and end members by combining absorbance–fluorescence spectroscopy techniques. The reach acts as a reactor for DOC concentration at baseflow condition, when in situ production processes prevailed. However, DOC is passively transported downstream at high flow condition. We found that humic and more degraded compounds predominate in DOM at the end of the reach. According to this, we proposed that both protein-like and humic-like compounds are produced at the study reach through in situ production processes, such as biological production from periphyton and macrophytes decomposition.