Sandy rivers across continents: the impact of sediment pollution on benthic invertebrates and epipelic diatoms assemblages.The Paraná River case study

EBERLE, E.; BLETTLER, M.J.M.; AMSLER, M.L.; OBERHOLSTER, P.J.; DE KLERK, A.R.; TRUTER, J.C.; MARCHESE, M.; GONZALES, C

Buenos Aires

Congreso; SETAC Latin America 11th Biennial Meeting; 2015

SETAC Latin America

A collaborative study between the National Institute of Limnology (Argentina) and the Council for Scientific and Industrial Research (South Africa) was performed in the Paraná River, one of the largest in the world, with the aims to determine levels of pollution and its influence on the benthic macroinvertebrates Buenos Aires 2015 SETAC Latin America 11th Biennial Meeting Abstract Book 108 and epipelic diatoms assemblages. We performed the samplings in the main channel, in a large secondary channel of its floodplain, the Colastiné River and in a minor tributary, Las Conchas River. Higher concentrations of As (>5,9 mg/kg), Cr (>37,3 mg/kg) and Ni (>18 mg/kg; according to MacDonald et al. 2000) as well as Cu, Pb, Ni and Zn were found in the Colastiné River approximately 2 km downstream a localized sewage discharge. In addition, diatoms usually associated with organic contaminants were also recorded at this sampling station. Otherwise, dangerous concentrations of heavy metal pollutants were not detected in Las Conchas River as well as in the Paraná main channel. Another sampling station was located near Las Conchas mouth where this tributary joins with a small branch of the Paraná River. Flow velocity diminishes abruptly at this confluence creating favourable hydraulic conditions for sedimentation of fine sediments (silts and clays supplied by the Paraná and Las Conchas). Though the concentrations of As, Cr, Cu, Pb, Hg, Ni, Zn at this site were lower than the admissible limits, their values were 40-100% higher than in the other sampling stations along the Paraná and Las Conchas Rivers. This fact would show the potential of localized areas to accumulate pollutants along river channels. Note that areas where the interaction of morphology and hydraulics prompts sedimentation seem to be optimal places to measure pollution since, otherwise, pollutants would be carried in suspension without been detected in a current bottom sediment sampling. Furthermore, the invasive bivalve Limnoperna fortunei was only recorded in the areas of highest concentration of pollutants (at the confluence station and downstream of sewage discharge). This species has the potential for bioaccumulation of pollutants, making them available when ingested by fish predators. This study shows that sampling techniques may be improved with interdisciplinary approaches involving the interaction of river morphology, flow configuration, sedimentology and ecotoxicology