Design and optimization of a weight-of–evidence approach to risk characterization in sediments affected by co2 acidification/diseño y optimización de un enfoque basado en el peso de la evidencia para la caracterización del riesgo en sedimentos afectados por la acidificación del co2

Resumen

The increases of carbon dioxide (CO2) in the marine environment may occur by different natural and anthropogenic sources. Studies have been performed in the last years in order to assess the potential adverse effects on marine organisms associated with the acidification related to this enrichment of CO2. However, none of these studies have designed under an integrative point of view using multiples lines of evidence. An integrated approach based on the use of multiple lines of evidence (LOEs) was designed and executed in this Thesis as an effective way to evaluate the environmental risk related to CO2 enrichment in coastal environments. Different LOEs were integrated under a weight-of-evidence (WOE) approach to characterize the risks associated with this acidification. For this purpose, chemical analysis, toxicity tests, ecological integrity of macrobenthic community and bioaccumulation analysis were used as LOEs that were performed using sediments from two coastal areas located in Spain and Brazil. The sediment samples used for each LOEs were exposed to a range of pH levels to mimic different scenarios of acidification by enrichment of CO2. The obtained results were linked so for each LOE assessed using three different models of WOE: a) tabular matrix based on statistical significance (p < 0.05) compared to the reference case, b) significance by pie charts showing three levels of statistical differences (p < 0.05 significantly different and positive effect; 0. 1 ≥ p > 0.05 significantly different but moderate effect; and p > 0.1 not significantly different) between the treatments and sampling stations, and c) multivariate analysis by means of factor analysis using principal component as extraction method. The results using WOE indicated that the adverse effects start to be detected when the pH reaches values of pH 7.0 that considerably enhancing at pH 6.5 using the stations from Spain and at pH 6.0 using the stations from Brazil. Dissolved metals such as As, Fe, Cu, Ni and Zn showed increase their concentrations and contribute to toxic effects to marine organisms in acidified conditions using the sediment stations from Spain whereas the metals As, Zn and Ni in seawater, and Cr, As and Cu in elutriate have demonstrated increase their mobility related to the increase in the concentrations of protons (H+) and cause toxic effects to the organisms exposed to the sediments from Brazil. Furthermore, the findings of the study suggested that the sediment contamination is a very important factor in an environmental risk assessment related to enrichment of CO2 since the metals can increase their bioavailability at lower pH values. The results of the ecological integrity studies by means of the macrobenthic communities showed to be strongly correlated with the contamination of the sediment tested. The WOE has shown a powerful tool able to identify and distinguish the difference between the causes of the adverse effects. It allows to identify if the effects are related to the acidification and/or associated with the chemical contamination measured „per se‟. The present study is the first attempt in the world that compares these scenarios of enrichment of CO2 to relate the cause and effects under an integrated approach using different sediment contamination conditions. Therefore, this Thesis provide useful information of the risks related to CO2 enrichment and can contribute not only with the environmental impacts researches but also in supporting the international organs in their discussion and decisions making to protect the marine ecosystems.