Temporary streams are widespread and often occur in catchments dominated by agricultural land uses. Drying and agriculture can both negatively impact aquatic communities, for example by decreasing dissolved oxygen concentrations and increasing fine sediment deposition. However, the combined effects of drying and agriculture have rarely been studied. We used 98 macroinvertebrate samples collected from the perennial (n = 49) and temporary (n = 49) headwaters of the Hampshire Avon, England. We quantified the proportion of agriculture surrounding each site, assigned samples to high (n = 62) and low (n = 36) agricultural land use categories, and tested whether variability in community composition differed between perennial and temporary reaches and between high and low agricultural categories. We also tested whether the occurrence of temporary stream specialist species (including a nationally rare stonefly) was affected by agriculture. Regardless of agriculture, temporary reach communities were more variable than those in perennial reaches, suggesting drying is a bigger influence than agriculture in shaping headwater communities. Within temporary reaches, communities were comparably variable regardless of agriculture, whereas agriculture increased variability among perennial reach communities. The occurrence of temporary stream specialists was unaffected by agriculture. Our results suggest that tolerance of drying by temporary stream communities and their specialist species promotes tolerance of agriculture. However, drying, agriculture and other human pressures are intensifying, with potentially detrimental impacts for the long-term stability of headwater temporary stream communities.

Temporary streams are widespread and diverse in cool, wet countries such as the UK. Here, the chalk streams of south and east England are among the UK’s most iconic rivers, and their ‘winterbourne’ reaches naturally dry in response to fluctuating groundwater levels. Chalk streams are celebrated for their international rarity, high water quality, biodiversity, and provision of cultural ecosystem services, but are also subject to a breadth of human impacts including eutrophication and geomorphological degradation. In addition, climate change and water abstraction are increasing the spatial and temporal extent of their dry phases. River managers thus need tools to assess the ecological health of winterbourne chalk streams regardless of whether they are wet or dry. This presentation will introduce winterbourne chalk streams and explore research done by academic and practitioner collaborators to improve their biomonitoring. We will discuss research guiding the adaptation of current biomonitoring methods for use during flowing phases, then will focus on our use of newly collected field data to evaluate plant and invertebrate communities (including both their terrestrial and aquatic species) as biomonitors that enable ecological health assessments during dry phases. We call for testing, adaptation and use of our approaches to promote effective dry-phase biomonitoring to inform evidence-based management strategies that protect biodiversity in winterbournes and a diverse range of other drying rivers and streams.

In rivers, detrital organic matter (OM) is decomposed by diverse communities of organisms, including microorganisms and invertebrates, along the river network and across terrestrial-aquatic boundaries. Drying naturally fragments most rivers, disrupting network-scale connectivity and thus preventing communities from reaching and consuming their resources, thereby modifying OM transfers across ecosystems. However, little evidence of the effects of drying on network-scale OM cycling and dependent communities exists. We examined the effects of fragmentation by drying on the structure of consumer communities and ecosystem functioning within interacting aquatic-terrestrial river ecosystems. To do so, we monitored leaf resource stocks, invertebrate communities and decomposition rates in the instream and riparian habitats of 20 sites in a river network naturally fragmented by drying. Although instream resource quantity and quality increased with drying severity, decomposition decreased due to changes in invertebrate communities and particularly leaf-decomposer abundance. Invertebrate-led decomposition peaked at intermediate levels of upstream connectivity (i.e. proportion of permanently flowing reaches upstream), suggesting that intermediate levels of fragmentation can promote the functioning of downstream ecosystems. Relationships between invertebrate community structure and decomposition instream were weaker at sites with low connectivity and high drying severity, suggesting that such conditions can promote mismatches between communities and their functioning. Decomposition instream was correlated to decomposition in the riparian area, revealing one of the first network-scale evidence of the links between ecosystem functions across terrestrial-aquatic boundaries. Our river network-scale study thus confirms the paramount effect of drying on the dynamics of resources, communities and ecosystem functioning in river networks.

Intermittent rivers are dynamic habitats that seasonally cease to flow, resulting in a dry phase suitable for colonisation by terrestrial invertebrates. This study aimed to identify dispersal patterns of flying and ground-dwelling invertebrates during the dry phase of the intermittent karst Krčić River in the Mediterranean region of Croatia. Flying invertebrates were sampled in the dry riverbed and riparian habitats using cross-vane window traps in July 2021. In addition, wind speed and directionality were measured continuously. Simultaneously, ground-dwelling invertebrates were collected using pitfall traps in the dry riverbed, riparian, and upland karst habitats. The activity patterns of flying invertebrates differed significantly between day and night, with no direction preference, suggesting that they both laterally colonise and use the dry riverbed as a corridor. We recorded a positive correlation between windspeed and the catch of flying invertebrates in the dry riverbed, suggesting colonisation as part of the aerial plankton. Taxa richness of the ground-dwelling invertebrates was significantly higher in riparian habitats than in dry riverbed and upland habitats, indicating possible spillover. A similar pattern was found for spider assemblages but not for orthopterans. Carabid beetle species richness, abundance, and diversity were significantly higher in the dry riverbed and riparian habitats than in upland habitats. The colonisation of a dry riverbed by flying and ground-dwelling terrestrial invertebrates increases the diversity and may support ecosystem functioning in intermittent rivers. Furthermore, our results indicate that dry rivers with their riparian vegetation may act as a refuge for terrestrial invertebrates during the hot Mediterranean summer.

Freshwaters are biodiversity hotspots, but among the most threatened habitats on Earth. They provide habitat for threatened and endangered organisms, support crucial biogeochemical cycles and provide key ecosystem services to people. In the Anthropocene Era, river networks are increasingly drying due to climate change and human alterations to flow regimes. Currently, rivers and streams that naturally do not flow all year round represent the dominant type of flowing water on Earth, with 51–60% of the mapped global river network. After being overlooked for decades, the ecological effects of flow intermittence have been intensively studied in the past 15 years and we are now gradually gaining understanding of drying impacts at the river network scale, where fragmentation alters spatiotemporal patterns of flows of sediments, nutrients and both aquatic and terrestrial organisms. As an interdisciplinary group of 80+ scientists from Europe, North and South America and China, the European project DRYvER is modelling the current and future hydrological, ecological and socio-economical responses of river networks to drying. Here, we will present our preliminary results related to the effects of current drying on 9 river networks scattered across Europe and South America.