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Si us plau utilitzeu sempre aquest identificador per citar o enllaçar aquest document: https://hdl.handle.net/2445/212800
Facing Global Change: Impacts of drying and human pressures on invertebrate diversity and organic matter processing in a Mediterranean stream network
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[eng] Intermittent rivers and ephemeral streams (IRES) currently constitute half of the global river network, occurring ubiquitously. Characterised by natural and periodic cessations of flow, IRES are proliferating due to global change, but face threats from different human-induced impacts such as water pollution, soil erosion, and habitat fragmentation. Notably, agriculture is one of the human activities with the greatest impact on freshwater ecosystems. This thesis examines the effects of drying and different land uses (natural and agricultural) on biodiversity and ecosystem functioning in a Mediterranean intermittent stream network, the Algars. These aspects are crucial for sustaining biogeochemical cycles and energy transfer within a system. Additionally, the thesis investigates the role of resistance strategies during dry phases in preserving aquatic diversity. Chapter 1 focuses on the impact of drying and land use on the functional and taxonomic α- and β-diversity of aquatic invertebrate communities during a hydrological year. Chapter 2 evaluates the roles of hyporheic refuges and invertebrate seedbanks during the dry phase in benthic assemblages under flowing conditions, assessing the taxonomic and functional responses across six intermittent streams. Chapter 3 investigates the influence of drying and land use on organic matter (OM) decomposition and fungal biomass throughout an intermittent stream network during a hydrological year. Chapter 1 reveals that drying negatively affects the taxonomic and functional α- diversity of aquatic invertebrates, but positively influences β-diversity. Land use predominantly affects α-diversity. Notably, habitat heterogeneity and elevated water nutrient levels in the stream network positively correlate with invertebrate diversity. The adverse effects of drying are less pronounced in upstream forested areas, which exhibit higher habitat heterogeneity, when compared to downstream agricultural regions. Chapter 2 identifies that seedbanks and hyporheic assemblages support up to 16% and 40% of the benthic assemblages, respectively. Diversity metrics vary between assemblage types in terms of taxonomic and functional richness. While no clear relationship can be established for diversity or the abundance of resistance traits with the dry phase duration, a negative linear relationship is observed between the abundance of resilience traits and the dry phase duration. Chapter 3 demonstrates that decomposition rates across the stream network negatively correlate with the duration of flow interruption. Dissolved inorganic nitrogen derived from agricultural activities mitigates the negative impact of drying on mass loss, enhancing it by up to threefold.However, with prolonged dry conditions, this effect diminishes. Increased canopy cover, particularly in natural areas, enhances OM processing. In summary, moderate agricultural activity within the small network studied can enhance diversity and ecosystem functioning. Nonetheless, increases in the frequency and duration of dry phases due to global change will reduce water availability, exacerbating the impacts of human pressures and threatening the survival strategies of aquatic species. This thesis significantly contributes to the understanding of the interactions between drying and land use in OM processing and biodiversity across a stream network. It underscores the importance of conserving natural and forested streams, especially in headwater regions, as potential refuges in intermittent networks.
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VIZA, Aida. Facing Global Change: Impacts of drying and human pressures on invertebrate diversity and organic matter processing in a Mediterranean stream network. [consulta: 4 de desembre de 2025]. [Disponible a: https://hdl.handle.net/2445/212800]