Celio Chagas

Heavy Metals in Sediments and Runoff Waters in Soils of the Matanza River Basin, Argentina

Abstract Soil profiles near watercourses that drain rural areas with agricultural lands and pastures, as well as recreational zones and densely populated industrial centers, are directly influenced by human activities. Therefore, these soils condition the contamination dynamics of the aforementioned watercourses in a remarkable way. The present study deals with soils belonging to a first order subbasin. Pedons representative of positive areas located in slopes (B) and of alkaline sites close to the alluvial plane (T) were selected as study sites. In both cases, the land is used for extensive farming. Composite samples of the upper 5 cm of both soil types were treated either with vermicompost or phosphate fertilizer to study the effect of the addition of these elements on the runoff dynamics of heavy metals. Experiments using a rainfall simulator that formed drops on runoff microplots containing soil samples were carried out under laboratory conditions. The runoff obtained was analyzed for lead (Pb), zinc (Zn), cadmium (Cd), and nickel (Ni), both dissolved and particulate, following the Community Bureau of Reference (BCR) adaptation of the sequential extraction procedure. From these results, it was concluded that the use of high amounts of organic amendment produced important effects on the surface condition of the soils that determine a highly significant reduction in the delivery of suspended solids to watercourses. Amendments, however, may release heavy metals that flow through runoff avenues either as particulate or dissolved forms. Most of the heavy metal concentration is represented by the sediments produced by the runoff and not by the concentration of dissolved elements in runoff waters.

La textura del suelo como factor regulador de la adsorción de Escherichia coli en una cuenca de la Pampa Ondulada (Argentina)

Resumen es: El aumento de la carga animal vacuna en la Pampa Ondulada asociado a areas fragiles supone un importante riesgo de contaminacion biologica. Dicha contami...

Adsorption and affinity of Escherichia coli to different aggregate sizes of a silty clay soil

The sediments produced by water erosion are the main source of pollution of agricultural origin of surface water bodies. These sediments may be associated to bacteria, compromising the quality of nearby water bodies. Therefore, to understand this biological contamination, it is necessary to find out the adsorption capacity and bacterial affinity to aggregate sizes that may result in a differential sedimentation. To this end, in the present work, the distribution, adsorption capacity and affinity to different aggregate sizes of two strains of Escherichia coli in two liquid media of contrasting ionic strength were evaluated in a silty clay soil. The 2 μm, the 20–50 μm fraction was the one that showed the highest bacterial adsorption in both liquid media (37.9%). On the other hand, the highest values of bacterial affinity were found in the 20 to 50 μm fraction (coarse silt) in the low ionic strength media and 20–50 and >50 μm in the high ionic strength media. However, the bacterial strains used revealed only some trends in the modification of these variables. This work contributes to the development and implementation of strategies to mitigate pollution, such as control of sediment generation and its subsequent capture in filter strips.

Suspended sediment concentration controlling factors: an analysis for the Argentine Pampas region

ABSTRACT In the Argentine Pampas region, there is little information about sediment concentration in agricultural catchments. The aims of this work are: (1) to analyse fluctuations in sediment concentration and discharge, as a first attempt to characterize hysteresis patterns; and (2) to study sediment concentration controlling factors and to assess the importance of these factors using principal component analysis and a multiple regression model. Twenty-five events registered during 4 years in a 560 ha gauged basin of Argentina were studied. Analysis of data suggested a positive clockwise pattern. The multiple regression model was performed with three factors obtained by principal component analysis: runoff, precipitation and antecedent conditions. The model explained 83% of the variability of sediment concentration. The runoff factor contributed to modelled sediment concentration with the highest magnitude, followed by precipitation and antecedent condition factors. Although the watershed is under conservation tillage, rill erosion seems to be the main source of sediment concentration. Editor M.C. Acreman; Associate editor X. Fang