Multidisciplinary approach to a study of water and bottom sediment quality of streams associated with mixed land uses: Case study Del Gato Stream, La Plata (Argentina)

Surface water bodies receive a basin's wide diversity of pollutants, especially when there are mixed land uses. Among the many environmental tools to assess a body water quality, most studies use only a few. In addition these studies, usually, are focused only on a set of pollutants and an environmental matrix. The Del Gato Stream – a surface watercourse within of more populated area of Argentina – exemplifies the typically contrasting land uses around this area's streams. The predominant land uses along of the stream are agricultural in the upper, urban and industrial the middle, and animal husbandry in the lower subbasin. The aim of this study was to use a multidisciplinary approach to evaluate the environmental quality of that stream as a model of surface-water bodies within mixed-land-use regions in the Buenos-Aires metropolitan area. At each of the sampling sites – distributed along the stream as follows: 3 in the upper, 4 in the middle, 3 in the lower subbasin – general water parameters were measured; water and sediment samples taken for physical, chemical, microbiological, and ecotoxicological analysis; and the variables in each environmental matrix, analyzed separately and jointly. The stream presented a significant general deterioration, the middle subbasin with urban-industrial land use being the most impacted, where metals and metalloids recorded highest levels, and the rest of the measured parameters were also found at high levels. The upper subbasin had the highest quality, and the lower subbasin proved poor quality regarding microbiological variables, nutrients, and general water parameters. The tests included in the toxicity battery did not reflect a common pattern of toxicity along the watercourse. However, when they were integrated in the EDAR index, the middle subbasin was the most affected sector of the stream. Although, the usefulness of each analysis tool must be evaluated taking into account the objective of the study, if the aim is to know the general environmental quality of a stream, the multiple-factor analysis proved to be the most effective means in complex systems under the influence of great diversity of pollution sources. This study provides relevant information about the ecological quality of a stream representative of a region with scarce environmental information