Search

Hydrological drought is a process of natural desiccation mainly due to large shortage of rainfall events. Reduced precipitations and prolonged droughts are spreading worldwide and threaten the integrity of aquatic ecosystems. Most Mediterranean streams have an intermittent flow which may become more variable and with larger duration of their no-flow periods under climate change. The enlargement of the dry period can importantly influence the ecosystem functioning, altering the microbiota inhabiting the streambed sediment as well as the processes they carry out (e.g. nutrients cycling). Consequently, hydrological alterations can reduce, limit or change microbial community functions, structure and composition, and therefore compromise the overall aquatic ecosystem functioning. The main objectives of this thesis are to study the responses of bacteria archaea and fungi inhabiting sediment to prolonged dry phase events and to wet episodes, spacing from punctual rains to rewetting events La sequía hidrológica es un proceso de desecación natural debido principalmente a la gran escasez de eventos de lluvia. Las precipitaciones reducidas y las sequías prolongadas se están extendiendo por todo el mundo y amenazan la integridad de los ecosistemas acuáticos. La mayoría de las corrientes mediterráneas tienen un flujo intermitente que puede volverse más variable y con una mayor duración de sus períodos sin flujo bajo el cambio climático. La ampliación del período seco puede influir de manera importante en el funcionamiento del ecosistema, alterando la microbiota que habita en el sedimento fluvial, así como los procesos que llevan a cabo (por ejemplo, el ciclo de nutrientes). En consecuencia, las alteraciones hidrológicas pueden reducir, limitar o cambiar las funciones, la estructura y la composición de la comunidad microbiana y, por lo tanto, comprometer el funcionamiento general del ecosistema acuático. Los objetivos principales de esta tesis son estudiar las respuestas de bacterias, arqueas y hongos que habitan en sedimentos a eventos prolongados de fase seca y episodios húmedos, espaciando desde lluvias puntuales hasta eventos de rehumectación Programa de Doctorat en Ciència i Tecnologia de l'Aigua

Intermittent rivers and ephemeral streams (IRES) encompass fluvial ecosystems that eventually stop flowing and run dry at some point in space and time. During the dry phase, channels of IRES consist mainly of dry riverbeds (DRBs), prevalent yet widely unexplored ecotones between dry and wet phases that can strongly influence the biogeochemistry of fluvial networks. DRBs are often overlooked because they do not strictly belong to either domain of soil or freshwater science. Due to this dual character of DRBs, we suggest that concepts and knowledge from soil science can be used to expand the understanding of IRES biogeochemistry. Based on this idea, we propose that DRBs can be conceptually understood as early stage soils exhibiting many similarities with soils through two main forces: i) time since last sediment transport event, and ii) the development status of stabilizing structures (e.g. soil crusts and/or vascular plants). Our analysis suggests that while DRBs and soils may differ in master physical attributes (e.g. soil horizons vs fluvial sedimentary facies), they become rapidly comparable in terms of microbial communities and biogeochemical processes. We further propose that drivers of DRBs biogeochemistry are similar to those of soils and, hence, concepts and methods used in soil science are transferable to DRBs research. Finally, our paper presents future research directions to advance the knowledge of DRBs and to understand their role in the biogeochemistry of intermittent fluvial networks., Earth-Science Reviews, 188, ISSN:0012-8252, ISSN:1872-6828

Surface-groundwater interactions in intermittent rivers and ephemeral streams (IRES), waterways which do not flow year-round, are spatially and temporally dynamic because of alternations between flowing, non-flowing and dry hydrological states. Interactions between surface and groundwater often create mixing zones with distinct redox gradients, potentially driving high rates of carbon and nutrient cycling. Yet a complete understanding of how underlying biogeochemical processes across surface-groundwater flowpaths in IRES differ among various hydrological states remains elusive. Here, we present a conceptual framework relating spatial and temporal hydrological variability in surface water-groundwater interactions to biogeochemical processing hotspots in IRES.

Surface-groundwater interactions in intermittent rivers and ephemeral streams (IRES), waterways which do not flow year-round, are spatially and temporally dynamic because of alternations between flowing, non-flowing and dry hydrological states. Interactions between surface and groundwater often create mixing zones with distinct redox gradients, potentially driving high rates of carbon and nutrient cycling. Yet a complete understanding of how underlying biogeochemical processes across surface-groundwater flowpaths in IRES differ among various hydrological states remains elusive. Here, we present a conceptual framework relating spatial and temporal hydrological variability in surface water-groundwater interactions to biogeochemical processing hotspots in IRES.