Natural pollution (As, F) and eutrofication (N, P) in the basin of El Divisorio stream, Argentina

The interrelation between hydrochemistry and hydrodinamicswas analyzed in the basin of El Divisorio stream. Thiswas to gain undestanding in the magnitude, distribution of toxicions (As, F) and behaviour in the discharge of main nutrients (P,N) contributing to the eutrofication of Paso de las Piedras Dam.During two years, 47 sites were sampled determining several parameters:geographical position for each sampling point, phreaticlevel depth, and As, F, PO4 and N-NO3 concentrations. Repeatedmeasures, Fisher test, correlation and regression analysis were appliedto all variables. Highly significant space and time differences(P<0.01) with increments of 0.3 m were detected for isohypses. Atevery site, differences with a variable degree of significance wererecognized for chemical parameters (As, F, PO4 and N-NO3). Hydrodinamicsbehaves mainly in accord with the seasonal rainfallcontribution; run off affects some of the hydrochemical parametersgiving rise to a variability that influences water quality. N-NO3 andPO4 concentrations are the main factors that cause eutroficationexpressed through algae bloom episodes and deterioration of storedwater quality. P is the critical element and in the dry periods thehighest contribution is through groundwater flux and to a lesserextent by the continuous discharge of surface water. In the periodof greater runoff, these elements incorporated to the sedimentarycharge as a result of soil erosion, and coming by fertilizers and pesticidesare transported in suspension towards the reservoir.