El uso de bioensayos crónicos en Daphnia magna para la evaluación ambiental de un arroyo urbano en Tierra del Fuego (Argentina)

Abstract

The development of urbanization has a negative impact on aquatic environments, making them the final receptors for a variety of anthropic substances, many of which lead to eutrophication. In Ushuaia (Tierra del Fuego), the Arroyo Buena Esperanza (ABE) has been subjected to these impacts. Its water quality decreases as the stream crosses the urban zone and discharges into Bahía Encerrada (BE). However, it is unknown whether its waters are toxic to the biota. We evaluated the water quality of the ABE all along its path through the urban zone and at its mouth in the BE through the effect on survival (48 hours) and growth (21 days) of Daphnia magna. Acute and chronic bioassays were conducted with D. magna neonates exposed to waters from four sites of the ABE: one with no urban impact, one with intermediate impact, and two with high impact. Water quality decreased as the stream crosses the urban zone, finding high values of ammonia, phosphates, particulate organic matter, total suspended solids and coliform bacteria; caused by the contribution of untreated sewage effluents. The survival of D. magna at 48 hours was close to 100%, which indicates the absence of acute toxicity of the water. The individual biomass varied according to the site and the time tested, increasing gradually but not evenly between sites. The organisms exposed to the most impacted sites presented higher biomass and growth rate in comparison to the sites with the least impact. This is linked to the poorer water quality of the impacted sites. The growth of D. magna was an environmental diagnostic tool with high applicability for the detection of sublethal effects of the waters of Fuegian streams, which adequately complements the environmental monitoring.