Flow alteration and wastewater inputs effects on freshwater communities in mediterranean rivers
- Autores: Jordi-René Mor
- Directores de la Tesis: Sergi Sabater i Cortés (dir. tes.), Isabel Muñoz Gràcia (codir. tes.)
- Lectura: En la Universitat de Girona ( España ) en 2019
- Idioma: español
- Tribunal Calificador de la Tesis: Núria Bonada i Caparrós (presid.), Dani Boix (secret.), Mark Ledger (voc.)
- Programa de doctorado: Programa de Doctorado en Ciencia y Tecnología del Agua por la Universidad de Girona
- Materias:
- Enlaces
- Tesis en acceso abierto en: TDX
- Resumen
River communities are determined by its adaptability to the regional constrains, physical and chemical conditions, food resources and biotic interactions. Mediterranean rivers have high hydrological variations, with marked flow reduction in summer and floods in autumn and spring according to regional precipitation patterns. These hydrological changes added to the high landscape heterogeneity and the combination between arid and temperate conditions makes the Mediterranean regions a diversity hotspot. However, human water demand in some Mediterranean areas is higher than water availability producing a scenario of water scarcity and increasing human pressures as dams and pollution on rivers.
The main objective of this thesis is to identify the effects of flow regulation and urban wastewater pollution on Mediterranean stream communities. Although the effects of dams and urban wastewater pollution are well known at different community levels, potential effects on Mediterranean communities and, specially, on food web and species interactions have received far less attention. The present thesis will focus on: i) determine the changes that the dam’s induced hydrological stability can produce on the food web structure (Chapter 1); ii) identify the effects of urban wastewater pollution on invertebrate community and functional traits under different hydrological conditions (Chapter 2); iii) analyse the effects that wastewater pollution could produce on the energy flow along the stream food web (Chapter 3).
To meet these objectives, several field surveys were carried out on different basins tributaries of the Ebro river (NE Iberian Peninsula). To determine the changes produced by dam’s induced water stability, a sampling survey was performed studying the longitudinal variation in the food-web structure in a highly-seasonal river. To identify the wastewater pollution effects on macroinvertebrate communities twelve sampling sites were sampled on summer 2015, autumn 2015 and spring 2016 up and downstream of the wastewater effluent. Ten of these sites were additionally sampled during spring 2016 to determine the pollution effects on stream food webs.
Hydrological stability caused by an irrigation dam on an intermittent stream increased the availability of autochthonous resources at the base of the food web. This, in turn, prompted a change from detritus-based to algal-based food webs downstream of the dam, increasing the richness of primary consumers. Additionally, flow stability favoured the entrance of terrestrial vegetation on the river bed as well as the predation of terrestrial invertebrates by stream top-predators. Overall, induced flow stability caused food-web structure to be longer and wider at intermediate trophic levels. However, despite a partial restitution of the flow regime, food-web structure did not recover 14 km of the dam, highlighting the overall effects of these impacts.
Pollution effects are enhanced under the lowest dilution situations produced on Mediterranean rivers; urban wastewater pollution favours the most tolerant invertebrate taxa and homogenises functional trait composition over time. Changes in functional traits were more evident during the seasonal low flow, when pollutant concentrations were at their highest downstream. However, the effects of urban wastewater pollution were not uniform, related to the local invertebrate communities variations according to the river substrata and stream size (i.e., width and discharge). Wastewater pollution reduces the energy efficiency transfer along the food web, with highest impacts on the highest trophic levels (i.e., predators). Predators show a reduction of its diet breadth, which added to a reduction of the predator-prey mass ratio and the decrease in the trophic efficiency transfer, suggest that wastewater polluted sites might be less resilient to other perturbations (e.g., floods).
The findings of this thesis highlight the importance of stream hydrology in determining ecosystem composition, stability and functioning.
