Conectividad dinámica y vulnerabilidad de los ecosistemas acuáticos en entornos agrícolas costeros: La Albufera de Valencia como caso de estudio

Coastal wetlands, considered indispensable for the many ecosystem services they provide to humans, are currently highly threatened by continuous anthropogenic pressures, especially from agricultural activity. Among the main impacts derived from agriculture are the extraction of freshwater reserves, the alteration of natural hydrological regimes, and the degradation of the chemical quality and trophic status of the natural aquatic ecosystems that make up these complex and dynamic natural sites. The main problem in developing and applying strategies for monitoring, conservation and restoration of agricultural wetlands lies mainly in the complex hydrology of these ecosystems. Therefore, the main objective of this doctoral thesis, using emerging tools and technologies in recent decades, is to evaluate in a comprehensive and multidisciplinary way the hydrological, ecological and environmental impact exerted by agriculture on the aquatic ecosystems that constitute the Albufera Natural Park (Valencia, Spain), a Mediterranean coastal wetland highly linked to rice cultivation, considering as a key element of its richness and vulnerability the connection and interdependence between its water bodies. To this end, firstly, based on the development of a mathematical adjustment derived from the analysis of satellite images, the flooding cycles of the wetland were studied for 15 years, taking into account the surface area and volume of flood water, and the correlation between these cycles and the water renewal of the Albufera lake was evaluated. On the other hand, the second study was a detailed analysis of limnological and ecological factors of the water bodies during the annual cycle of rice cultivation, considering the European directives and applicable regional regulations. The results were captured in cartographic layers, in order to verify relevant spatial differences and possible correlations with nearby agricultural activities and irrigation water management. Finally, a complementary ecotoxicological study was carried out at laboratory scale in order to integrate the spatial responses of colonization of the cladoceran species Daphnia magna, key aquatic organisms of biological quality in coastal lagoons, in environmental risk studies, also considering possible sublethal toxic effects on the swimming capacity and neurotransmitter activity of these organisms. The results obtained during the development of this doctoral thesis confirmed, firstly, that the Natural Park has a consistent hydrological regime regulated by the agricultural requirements of rice cultivation, not adapting to seasonal climatic variations, which affects the natural processes of water renewal of the lagoon. On the other hand, the generalized degraded and eutrophic state of the wetland is confirmed during the complete cycle of rice cultivation, not ensuring a good quality water inflow through its main fluvial axes, especially in the northern zone, where, in addition, irrigation water is mixed with inadequate effluents from the WWTPs to compensate the low ecological flow. The connectivity between water bodies and the flow of nutrients is confirmed, so that water management in the basin for rice cultivation modulates important limnological characteristics of the Albufera lake, which acts as the final sink before releasing nutrients and pollutants into the sea. Finally, ecotoxicological tests confirmed the acute toxic effect of the gradient mixture of pesticides on aquatic organisms, drastically inhibiting their colonization dynamics, as well as significantly and synergistically affecting their swimming behavior. Therefore, the results of this doctoral thesis serve as a tool of knowledge and support for the development of management plans that adapt to the spatial heterogeneity and dynamism of coastal agricultural wetlands. In addition, it provides tools for the development of environmental risk analysis methodologies that integrate connectivity and the flow of matter and energy between water bodies, helping to reduce the vulnerability of aquatic ecosystems to multiple anthropogenic pressures and degradation caused by agricultural activities.