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Multiple stressors on aquatic ecosystems under Mediterranean conditions

The Ecotoxicology group of IMDEA Water, and in particular Dr. Alba Arenas Sánchez, has carried out a study for the last four years whose main objective was to contribute to a better understanding of the individual and combined effects of hydrological variability and pollution in aquatic ecosystems of Mediterranean regions. The project consisted of a broad literature review, an extensive monitoring study in upper part of the Tagus river basin and laboratory studies simulating water stress and chemical pollution. Some key findings of this project and links to scientific articles published are presented below:

First, it was observed that there is little current knowledge about the problem, with few experimental studies and little variety of organisms studied.1

Key contaminant mixtures were usually formed by <5 compounds, in most cases potentially exerting a chronic toxicity risk for aquatic ecosystems, despite some metals (Cu, Zn) and pesticides (chlorpyrifos, diuron) which could also exert acute risks. Sub-lethal/behavioural/endocrine effects of pharmaceuticals should also be considered.2,3

Once compounds have been prioritized, temporal patterns of exposure, as well as potential interactive effects, are recommended to be considered in risk assessment. 2,3

The inclusion of non-priority potentially hazardous substances at a basin level should be considered in specific management plans, after proper cost-effective validation through monitoring.

The assessment of macroinvertebrate responses to chemical pollution under hydrological stress showed enhanced negative effects of pollution during drought or water scarcity periods in terms of species richness, functional richness and functional diversity. The seasonality observed in these responses suggests that current regulatory procedures for the assessment of ecological status of Mediterranean water bodies (at least at a national level) may need to be adapted, covering periods with the highest ecological disturbance (i.e. drought periods apart from spring-base flow periods). 

The microcosm study performed in the laboratory showed that environmental conditions related to water scarcity may influence chemical fate and the vulnerability of zooplankton communities to chemical stress. High temperature resulted in faster response but higher recovery potential of the zooplankton community. Slight drought and chemical interaction after rewetting was observed due to pesticide degradation when desiccation occurred, as maximum hydrological stress period. Overall, a high resilience capacity to the ecosystem‘s contraction and desiccation was observed.4

This study set light to improve water quality and management actions in Mediterranean surface water bodies. Still, more studies in this direction are needed, considering different drought and pollution levels, timing of stressors, identifying sensitive life-stages and understanding food web interactions.

This work is part of the PhD project of Dra. Alba Arenas Sánchez, directed by Dr. Andreu Rico and Professor Marco Vighi, and defended last September the 6th, 2019 at the University of Alcalá de Henares. 

This thesis is available in the archives of the Ministry and in the library of the UAH

 


1 Effects of water scarcity and chemical pollution in aquatic ecosystems: State of the art https://doi.org/10.1016/j.scitotenv.2016.07.211

2 Identification of contaminants of concern in the upper Tagus river basin (central Spain). Part 1: Screening, quantitative analysis and comparison of sampling methods https://doi.org/10.1016/j.scitotenv.2019.02.250

3 Identification of contaminants of concern in the upper Tagus river basin (central Spain). Part 2: Spatio-temporal analysis and ecological risk assessment https://doi.org/10.1016/j.scitotenv.2019.02.286

4 Effects of increased temperature, drought, and an insecticide on freshwater zooplankton communities https://doi.org/10.1002/etc.4304