Département Eaux de surface

Swiss geosciences are at the heart of major national and global challenges that our society is facing, including climate change and weather extremes, long-term environmental trends, natural hazards (e.g. landslides, floods,
seismic and volcanic events), the energy transition towards a green and blue economy, sustainable management of natural resources (e.g. water, soils, ecosystems, critical metals, building materials), and the increasing interest
towards extra-terrestrial life and resources. In order to remain at the forefront of geosciences research and provide the fertile environment necessary for groundbreaking findings addressing these societal challenges, the Swiss Geosciences Community proposes five large infrastructures, organised into four pillars built on a common datadriven research foundation. [...]

Mesomediterranean vegetation with abundant evergreen broadleaved trees and shrubs is dominant along the coast of northern Greece. Well-dated palynological records are available from the inland submediterranean zone, where evergreen broadleaved trees and shrubs are absent or rare, but less is known about the vegetation history of the coastal area. For instance, it is unclear when and why evergreen broadleaved vegetation expanded during the Holocene. Here we present a new record from a mesomediterranean site, Limni Volvi, near the coast of the Aegean Sea. To understand Holocene vegetation history, we combined palynology, microscopic charcoal analysis and biogeochemical proxies (Ti, Ca, RABD_655–680max). At the start of the Holocene, open steppe vegetation and high fire activity prevailed around Limni Volvi. Afforestation by deciduous trees was likely delayed compared to sites further inland, due to the lack of moisture at the start of the Holocene, but vegetation composition was generally similar (i.e. submediterranean), with barely any evergreen broadleaved element. Around 8150 cal. BP (6200 cal. BC) trees and shrubs declined in the open woodlands or parklands, and the landscape returned to steppe conditions at 8000 cal. BP (6050 cal. BC), likely because of drier and colder conditions during the "8.2 ka event." Around the same time, cultural indicators suggest the start of Neolithic agriculture in the region. The present-day mesomediterranean vegetation with evergreen oaks only began to develop after 6000–5000 cal. BP (4050–3050 cal. BC), likely in response to increasing winter temperatures and reduced frost occurrence, further advantaged by human impact during the past 3600 years.

Research and management of hydropeaked rivers largely overlook the ecological impacts of recurring flow fluctuations, such as fish stranding, on ecosystem health. This article synthesizes scientific and grey literature, field studies, and experiments to assess the effects of frequent hydropeaking on fish. Findings show that hydropeaking frequency significantly affects the ecological integrity of alpine rivers, with an average of three daily down-ramping events. Despite some evidence of behavioral adaptation of fish to recurrent flow fluctuations, this adaptation appears insufficient to counter the cumulative effect of a series of single hydropeaking events. Larval and juvenile fish are particularly vulnerable, with stranding impacts extending to the population and community levels. Effective mitigation should prioritize reducing the cumulative impact of recurring hydropeaks while ensuring single-event ramping rates and flow amplitudes remain within ecological limits. To effectively safeguard sensitive habitats, targeted mitigation efforts informed by an understanding of habitat dynamics are critical. Furthermore, maintaining lateral connectivity within river systems is essential for supporting resilient fish populations, especially where hydropeaking mitigation possibilities are limited. Finally, this study identifies future research directions on hydropeaking frequency and its ecological effects.