As/P relationship in pampean stream: in situ experiments and periphyton colonizations

RODRIGUEZ CASTRO, CAROLINA; GUASCH, HELENA; GIORGI, ADONIS; VILCHES CAROLINA.

Buenos Aires

Congreso; Society of Environmental Toxicology and Chemistry Latin America (SETAC Latin America); 2015

SETAC

In small fluvial systems, biogeochemical processes are attributed largely to periphyton as these communities contribute in its selfpurification, capturing nutrients and accumulating or transforming many pollutants. However, the response of aquatic organisms to arsenic, a metalloid present in Pampean streams, can alter these functions. This is due to the chemical similarity between arsenate (AsO43-) and phosphate (PO43-). Some studies claim that As uptake produces irreversible damage to the P transport system of cells. In other cases, there is a competition for uptake. This damage could affect P uptake of algae and therefore its ability to depurate the surrounding environment. However, higher affinity of cells to P reduces the impact of As in the presence of nutrient excess. Following the observations made at organism level, interaction between P and As given at community and ecosystem scales would be expected. Ecotoxicological studies are enriched when they cover the widest range of organization levels, because each level allows a different kind of inferences. But discriminating between environmental variability and the pressure of a contaminant on the biota is very complex. Field experiments provide results that integrate ecological realism and the effect of a contaminant in interaction with other natural factors that also act on organisms. Therefore, the aim of this study was to evaluate whether the effect of P and As interaction on the structure and function of periphyton can be detected at ecosystem scale or it becomes obscured by the action of other interacting factors. Nutrient addition experiments, open metabolism and photosynthetic parameters measurement were performed at reach scale and also periphyton colonization was performed in situ and then transported to the laboratory for in vitro dose-response tests. Experiments and colonization were conducted in Pampean streams with different levels of As and P, providing natural treatments. It was noted that periphytic communities were very P retentive. Also, As produced toxicity on the periphytic community, both functionally and structurally, affecting photosynthetic parameters. It was also observed that the presence of As had an effect on the retention of P in microcosm, which was not detected at ecosystem level, as nutrient retention parameters did not follow a pattern associated with As levels and metabolism associated with P levels, regardless of the levels of As.