Effective landscape-scale restoration hinges on a truly integrated source-to-sea approach—one that recognises rivers, estuaries and coasts as a single interconnected ecological system rather than separate management units. Without this holistic perspective, conservation efforts in any part of the continuum risk being undermined by pressures arising from elsewhere. For example, seascape restoration can be undermined by upstream nutrient and sediment inputs, while pressures within estuaries can disrupt migratory species and the ecological connectivity on which they depend, with consequences that extend far into freshwater catchments.
While the principles of source-to-sea management are well-established in both policy and practice, implementation remains fragmented. Conservation and restoration efforts continue to be shaped by disciplinary boundaries and ecosystem-based silos. Freshwater scientists often focus on river catchments, where nature-based solutions are increasingly embedded within restoration practice, while marine ecologists tend to focus on brackish estuaries and coastal habitats such as saltmarshes, native oyster beds and seagrass meadows. Consequently a critical component of the source-to-sea continuum is frequently overlooked: tidal freshwater and low-salinity zones at the top of estuaries.
These zones exist in disciplinary limbo; too fresh for marine scientists and too tidal for limnologists, they have become the blind spot in restoration planning. Yet they are far from peripheral. Tidal freshwater zones act as dynamic ecological gateways, mediating the exchange of water, sediments, nutrients, organic matter and organisms between freshwater rivers and brackish estuaries. Despite
their importance, they are among the most impacted and vulnerable of estuarine areas exposed to intensive land-use pressures, development and the emerging threat of “estuarine squeeze”, where rising sea levels compress these habitats against fixed in-stream barriers.
Despite their functional significance, tidal freshwater zones remain largely absent from restoration agendas, which typically focus on either fluvial upstream systems or marine downstream habitats. This fragmentation limits the effectiveness of source-to-sea approaches and constrains opportunities to enhance ecological resilience across connected landscapes.
In this talk, we argue that tidal freshwater zones represent the missing link in integrated source-to-sea management. Drawing on new spatial analyses from across England and Wales, we identify where these systems are most at risk and present a vision for their restoration. Through nature-based solutions, including the re-establishment of tidal freshwater marsh habitats, we can reconnect fragmented ecosystems, support climate adaptation and strengthen ecological resilience from source to sea.
If we are to achieve meaningful landscape-scale restoration, we must move beyond conventional disciplinary and management boundaries. Restoring tidal freshwater zones offers an opportunity to transform fragmented conservation actions into a unified strategy for source-to-sea resilience.
Dr Sally Little is a Senior Lecturer in Environmental Science at Nottingham Trent University, specialising in aquatic ecology across the freshwater, estuarine and marine continuum. Her research focuses on understanding the impacts of climate change and other anthropogenic pressures on these systems, and developing nature-based solutions and ecosystem restoration approaches that enhance ecological resilience across the source-to-sea continuum.
Dr Little is an internationally recognised researcher in estuarine and coastal science and environmental restoration. She is the Immediate Past President and a Trustee of the Estuarine and Coastal Sciences Association (ECSA), a Trustee of the Clean Rivers Trust, and serves as a specialist advisor on a number of national research and restoration initiatives. Through these roles, she works closely with academic, government and industry partners to translate research into policy and practice, supporting evidence-based approaches to river, estuarine and coastal management.
