Multiple-stressor impacts on mediterranean stream communities: responses to water scarcity and water pollution

Doutoramento em Restauro e Gestão Fluviais - Instituto Superior de Agronomia / Faculdade de Arquitetura / Instituto Superior Técnico. Universidade de Lisboa

Freshwater ecosystems are influenced by diverse anthropogenic stressors and natural disturbances producing interacting effects (synergies and antagonisms) often unpredicted based on their independent effects, and thereby represent a major concern to predict ecological changes and develop effective management and restoration strategies. The aim of this Thesis was to assess different responses of key stream biological elements (i.e., biofilms and macroinvertebrates) to the impact of main stressors acting in concert in Mediterranean rivers related with water scarcity and pollution (i.e., flow velocity reduction/stagnation and sewage contamination/hypoxia), using mesocosm approaches and evidences of a case study. In a first part, the effects of flow reduction and oxygen depletion conditions in two seasons were evaluated in macroinvertebrates behavioural and functional responses, conducting to evidences of changes in drift patterns and loss of trait diversity with potential impacts on ecosystem functioning and services. In a second part was investigated how single and combined effects of water flow stagnation and sewage contamination affect primary producers and primary consumers, showing that while stagnant water had an overall inhibitory effect, sewage inputs increased biological responses. Also, stressors combined effect revealed to be unfavourable for some biofilm assemblages (decreasing bacteria and algae diversity) while advantageous to other (increasing fungi diversity). In the last part, flow and water quality variations were followed over time in a Mediterranean urban stream, leading to observations of an impoverished community with low diversity and high abundance of tolerant taxa and resistance traits, which was associated with multiple-stressors patterns of urban ecosystems. Overall it was showed that the effects of representative multiple-stressor scenarios on Mediterranean stream biota are dependent on water scarcity conditions and that reductions on sewage inputs needs to be given priority by stream managers to prevent further degradation of these aquatic ecosystems

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