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The Salar de Olaroz, located in the Argentine Puna, is one of the largest lithium deposits of the world. Lithium extraction requires large amounts of fresh and brackish water, creating pressure on wetlands of these desert environments. The knowledge of the aquatic fauna of the area is of interest to monitor impacts of these extractive activities. In this work, a study of the Chironomidae (Diptera) prior to mining is carried out in order to understand the structure of the Chironomidae assemblage at morphospecies level, with the aim of evaluating its spatial and seasonal variation, relating changes in the assemblage to some environmental variables. Quantitative biological samples and environmental variables of interest were taken and registered in three streams during four season in three consecutive years (2013-2015). Our results show that the Chironomidae assemblage could respond to variables related with discharge by decreasing its richness. Some morphotypes (e.g., Podonomus, Parametriocnemus, Limnophyes and Polypedilum) associated with changes in pH, decreases in dissolved oxygen and water velocity, and increases of finer sediments could disappear from the area.

The aim of this work is to evaluate the ecological quality of waters along an environmentally heterogeneous basin, using macroinvertebrate biotic indices (BI). Twelve sampling sites were selected in the Río Grande basin, following an altitudinal gradient across the Puna, Monte and Yungas ecoregions. Sampling was conducted in the dry and rainy seasons, during three consecutive years (2012 to 2014). At each site, physico-chemical parameters were measured and benthic macroinvertebrates were collected. Principal component analysis (PCA) was applied to explore environmental variability in terms of physico-chemical parameters. The water quality of the basin was assessed by means of different biotic indices. Correlation analyses were performed between the biotic indices and the physicochemical parameters. Altitude, NaCl, total dissolved solids (TDS) and electrical conductivity were higher at the Puna and Monte sites, while river discharge, width and depth were higher at the Yungas sites. Biotic indices suggested good water quality. The BMWP (Biomonitoring Working Party) and family richness were the most suitable indices to simultaneously compare the rivers of the different ecoregions. The change in the composition of macroinvertebrate assemblages was observed at an altitude of 1500 m a. s. l., separating arid and humid zones and coinciding with inflection points of conductivity, NaCl and TDS.

Una gran parte del noroeste argentino (NOA) está ocupada por zonas áridas vulnerables al avance de las actividades humanas. En este trabajo se caracterizaron los ensambles de macroinvertebrados de los ríos de esas zonas, para lo cual se emplearon distintos índices bióticos a fin de evaluar su respuesta y posible aplicación en la región. En las provincias de Catamarca y La Rioja fueron muestreados 15 ríos y arroyos, en diferentes períodos (23 sitios en total). Se tomaron muestras Surber (dos o tres por sitio) y se registraron datos ambientales. Se realizaron análisis de correspondencia canónica (CCA) para estudiar las relaciones entre los datos ambientales y los ensambles de macroinvertebrados, y se aplicaron diferentes índices bióticos. En total fueron identificados 59 taxa, de los cuales Diptera fue el más rico (12 familias). La máxima diversidad alfa encontrada correspondió a 29 taxa, mientras que la mínima fue 1. Los taxa más abundantes fueron Andesiops peruvianus, Meridialaris tintinnabula, Austrelmis (larva), Orthocladiinae, Smicridea, Helicopsyche y Heleobia. El CCA reveló que la conductividad eléctrica y el ancho húmedo son factores clave que influyen en la estructura de los ensambles de macroinvertebrados. Entre los índices bióticos utilizados, el de las Sierras de San Luis (IBSSL) mostró la mayor concordancia con el estado ecológico de los ambientes estudiados. Algunos de los sitios investigados poseen una diversidad similar a sitios de zonas áridas de la Argentina, como Cuyo (provincias de San Luis y Mendoza) y la provincia de Catamarca, pero de menor riqueza que los de Patagonia. Los resultados muestran que el IBSSL se puede usar en la región, pero aún deben realizarse ajustes en los valores de corte, tanto para este índice como para otros empleados. Por esta razón, y para mejorar su valor explicativo, se requiere de estudios más detallados que incluyan sitios impactados en diferente grado. https://doi.org/10.25260/EA.18.28.2.0.645 Foto: kataix.umag.cl/sib-aysen/

The present study was conducted to assess the effect of rainbow trout introduction on benthic invertebrate communities, stratified as epibenthos and infauna. Two main questions are explored: 1) do the trout-invaded streams show a different community structure than the streams with autochthonous fish?, and 2) does the presence of trout affect differentially the epibenthos and the infauna? Epibenthic and infaunal samples, drift samples and fish stomach content were sampled four times from three stations to assess the impact of rainbow trout (Oncorhynchus mykiss) on the invertebrate aquatic fauna. Only one species of native fish was recorded in the studied sites, the siluriform Trichomycterus corduvense. Both fish species were found always in allopatry. The trout-invaded site has a different community structure than the other streams with a much lower abundance of large and active epibenthic taxa (e.g., Perlidae, Gripopterygidae, Hydropsychidae, Leptoceridae, Elmidae adults) and an increase in the importance of infaunal organisms (Chironomidae, Oligochaeta). Diversity indices showed alternating and opposite high and low values along time in trout-free and invaded sites.