CONICET | Buscador de Institutos y Recursos Humanos

The Reconquista River is one of the mostpolluted rivers in Latin America. This paper aims atidentifying the dynamics of water quality in an areawith low or background concentrations of pollutantswithin the Reconquista River system in order tobetter define levels of pollution in the main system. Inorder to describe the dynamics of water quality in thebackground area, we propose a methodology basedon flow estimation with the instantaneous unithydrograph model and on measurements of physicaland chemical water variables under different hydrologicalconditions. Because of high dissolved oxygenand low ammonium and o-phosphate concentrations,the Arroyo Durazno, a tributary stream of theReconquista River, is defined as a background area.When a storm event begins, the concentration ofnitrates and the electrical conductivity diminish. Anincrease in dissolved organic carbon suggests animportant input of carbon from hillslope runoff. Theproportion of fulvic and humic acids also increases.On the receding limb of the hydrograph, nitrateconcentration was lower than during maximum flowand organic carbon concentration remained high.This behavior, known as the flushing effect,suggests that the soluble material accumulated inthe drainage area during dry periods is transported tothe stream by leaching or lixiviation and surfacerunoff, thus raising solute concentrations during thefirst few hours of the storm. Water quality changesrapidly, even in background areas, due to its dependenceon the flow. The methodology followed in thispaper can also be applied to other basins with similarcharacteristics. Due to the difficulty in definingbaseline areas for surface waters, a knowledge ofbackground water quality and its dynamics is essentialfor understanding pollution trends andanthropogenic impacts on rivers.

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