Effects of drying and orientation to perennial refuges on aquatic biodiversity across two basins differing in aridity

A comprehensive spatial analysis of invertebrate diversity within intermittent stream networks: Responses to drying and land use

Freshwater ecosystems are highly vulnerable to the impacts of climate change, which affect both diversity and ecosystem functioning. Furthermore, these ecosystems face additional threats from human activities, such as changes in land use, leading to water pollution and habitat degradation. Intermittent streams represent nearly half of all fluvial systems and support a rich diversity adapted to cope with drying. This study examines the impact of drying and different land uses on the taxonomic and functional diversity of aquatic invertebrates in a Mediterranean intermittent stream network. By sampling 16 reaches seasonally, we hypothesised that longer dry-phase duration and agriculture would both reduce α-diversity, with drying dominating impacts on β-diversity over agricultural practices. We anticipated that drying and agriculture would alter species and trait compositions, favouring desiccation-tolerant and generalist taxa. Drying adversely affected the taxonomic and functional α-diversity of aquatic invertebrates, while it positively influenced β-diversity. Land use only affected α-diversity. Specifically, habitat heterogeneity and increased water nutrient levels within the stream network correlated positively with invertebrate diversity. However, the negative effects of drying were less pronounced in upstream forested regions with high habitat heterogeneity compared to downstream areas influenced by agriculture. Our research highlights the importance of preserving natural and forested streams in intermittent networks, particularly in headwater regions, thus facilitating recolonization when flow is restored throughout the stream network.