We explored how source-to-sea (S2S) thinking can strengthen research collaborations and innovation across Scotland. The S2S approach focuses on the interconnections between land, freshwater, and marine systems—helping inform cross-sector decision-making, address environmental trade-offs, and promote joined-up action on environmental and societal challenges. In Scotland, recent policy initiatives have highlighted the potential of the S2S approach to tackle biodiversity loss and climate change through cross-sectoral coordination and inform nature restoration finance models. However, its potential to shape research collaborations and research questions that address land-river-sea interlinkages —particularly those that can inform conservation planning, rural resilience and climate adaptation —remains largely unexplored.

Our SEFARI Gateway S2S Specialist Advisory Group (S2S Group) addressed this gap through a literature review and expert insights gathered during a UK-wide workshop. This case study outlines the key characteristics of the S2S approach; highlights research themes using the source-to-sea lens; provides a library of research projects implemented in Scotland and the UK; and provides insights from the members of the S2S Group for mainstreaming source-to-sea research in Scotland.

Stage

Results

Why S2S matters

The value of the S2S approach in improving resource management and governance is also clearly articulated by the Stockholm International Water Institute (SIWI), a global leader in water governance (e.g., Why Source-to-Sea Management). S2S projects are grounded in principles that help connect the dots, prioritise issues, target interventions effectively, minimise trade-offs, reduce duplication of effort, and promote long-term sustainability through broad stakeholder and community engagement. SIWI also provides guidance on a six-step implementation process (Figure2), which ensures that the S2S principles are applied.

Figure 2. The S2S approach: Implementation steps. Sources: see in-text.

The S2S approach complements other frameworks and theories

The Source-to-Sea (S2S) approach builds on and complements existing approaches by highlighting the ecological and social interdependencies across land, freshwater, and marine systems, particularly how upstream decisions and pressures affect downstream and coastal outcomes. It also strengthens environmental governance by filling critical gaps in existing frameworks and enabling the development of new, integrated models. It integrates with Integrated Water Resources Management (IWRM) and Integrated Coastal Zone Management (ICZM); aligns with One Health by recognising the interdependence of human, animal, and ecosystem health; and expands on Wholescape Thinking and the S2S Landscape approach. S2S also connects with community-led partnerships, such as in the Catchment-based approach (CaBA) and the ridge-to-reef (R2R) approach. It supports the synergies between interconnected Sustainable Development Goals (SDGs); resonates with the IPBES Nexus Assessment Report on the Interlinkages among on biodiversity, food, water, and health; and aligns with the source–sink conservation paradigm through integrated conservation planning of multi-realm species (e.g., Atlantic Salmon) and land-sea conservation planning’. Within the UK, it fits closely with Defra’s Systems Research Programme, which emphasises systems thinking to identify interlinkages and guide effective environmental decision-making.

Figure 3. Links of the S2S approach with other management and governance frameworks.

Key Research Themes

Source-to-sea research investigates how and why biophysical, ecological, and human-environment interactions occur and influence the source-to-sea system.

Peer-reviewed literature suggests bidirectional land-sea interactions, meaning activities inland affect coastal and marine ecosystems, and vice versa. Effective management must consider both directions to prevent unintended consequences and enhance system-wide resilience.

Currently, source-to-sea research is dominated by studies on biogeochemical flows and the impacts of agriculture, urbanisation, and forestry, with biodiversity, socio-economic dimensions, and restoration outcomes receiving less attention.

Peer-reviewed studies from Scotland highlight several thematic research areas and locations:

• Greenhouse gas emissions (GhGE): Studies on how land cover, seasonal variation and hydrology control the generation of greenhouse gasses (methane, carbon dioxide and nitrous oxide) from the River Clyde and the River Tay to their estuaries. This research is relevant to climate change mitigation by helping to determine what actions can reduce aquatic GhG generation and emissions.
• Land-derived carbon flows: Research on the factors affecting changes in dissolved organic matter across the peatland-to-coast continuum via the River Thurso to understand how much land-derived carbon is lost as carbon dioxide to the atmosphere or enters the coastal ocean.
• Carbon accumulation in saltmarsh sediments and biomass: Research on the sedimentation rate, organic carbon densities and terrestrial vs marine source apportionment of the organic carbon locked in saltmarsh soils, showing low accumulation rates and highlighting the need to protect already stored saltmarsh blue carbon.
• Peatland carbon sequestration in coastal sediments: Study on peatland carbon sequestration in West coast fjords (aka sea lochs)
• Saltmarsh management trade-off: Study on how land use, agriculture, and conservation priorities interact in saltmarshes, with implications for biodiversity and carbon storage.
• Harmful algal blooms (HABs) and disease-causing species: This work adopts a sea-to-source lens, tracing impacts from marine-based causes to coastal and inland activities and ecosystems. For example, studies explored how offshore and upstream nutrient loading and environmental changes may contribute to ecosystem, economic and human health risks. Research also examined the implications for HAB development, the siting of salmon farms, and the coastal food web from invertebrates to fish and mammals, such as seals. Work included developing early warnings of harmful summer blooms using sea surface temperature measurements.

Key research methods and tools

Tracking and monitoring key flows across the land-river-sea continuum is integral to source-to-sea research and its effective implementation. The choice of methods depends on which interlinkages and flows are being studied. In its simplest form, monitoring is designed to capture changes in key flows along source-to-sea transects. Key monitoring techniques include:

• Using multiple analytical tools together to study dissolved organic matter transformations.
• Visual observations to track plastic debris in rivers and coastal waters.
• High-precision particle size analysis, such as dynamic light scattering to characterise nanoplastics flows.
• A combination of surveillance (such as remote sensing with LIDAR or other approaches), field work studies, artificial intelligence (AI), local expertise, and mechanical engineering for intelligent, low-cost plastic litter removal.
• Environmental DNA (eDNA) - i.e., DNA present in the environment, including that which is shed through deposition of faeces or decay of tissue and present in unicellular organisms or viruses - for detecting changes in salmon habitat occupancy and responses to environmental stressors such as organic enrichment, saline intrusion, pathogens, predators, and species range shifts in near real-time.
• Biodiversity audits combining eDNA and metabarcoding assays that target a broad range of species across the tree of life (ToL-metabarcoding) in combination with water quality or other data to contextualise species presence or absence.
• Hi-tech underwater devices that, through the use of AI, allow for real-time phytoplanktonic species identification in the water around fish and shellfish farms (aka ‘virtual taxonomist’), thus providing an early warning of HABs that threaten public health and aquaculture and Scotland’s coastal livelihoods.

Key Research Projects

We reviewed completed and ongoing UK projects applying the source-to-sea lens, grouped by their primary application focus (Table 1). These projects illustrate the diverse applications of source-to-sea thinking.

Table 1. Thematic overview of research projects applying the source-to-sea (S2S) approach across the UK.

Connection with RESAS

We also explored opportunities for synergies between source-to-sea thinking and research implemented in the current SRP2022-2027-RESAS projects. Research at the James Hutton Institute on multi-purpose NBS and ‘Emerging Water Futures’ examines water, nutrient, and pollutant flows, with a focus on freshwater systems, while overlooking land-sea connections. SRUC’s research on the Vulnerability Of Remote Coastal Communities To Water Challenges: Perception, Valuation And Coping Mechanisms explored coastal community resilience to drought and flood risk. The Marine Science and Innovation Strategy reflects S2S principles through its emphasis on interdisciplinary science and evidence-based policy. Its current focus remains largely marine-centric with limited explicit attention to upstream–downstream coordination, or system-wide data integration. Future opportunities could involve much-needed upstream-downstream integration to strengthen governance links across coastal and inland areas. This could support sustainable solutions, in line with emerging priorities for holistic and inclusive approaches.

 Research Gaps

Our review shows that research integrating land, freshwater, and marine systems is gaining traction, and there is increasing recognition of the need for joined-up thinking and action from source to sea. Yet, source-to-sea thinking remains largely theoretical in many areas. In Scotland, we lack a clear understanding of the conditions under which limited data can support source-to-sea assessments and be scaled up to the extent at which resource management or conservation decisions are made.

Key areas where further work is needed include:

• Biological flows (e.g. species migration; trophic connectivity; source-sink dynamics, wherein some areas are net exporters of individuals and others are net importers).
• Social–ecological interlinkages (e.g. livelihoods, community dependence on ecosystems).
• Sea-to-land dynamics and their cascading inland effects.
• Restoration outcomes across interconnected ecosystems.
• Ecosystem service flows, especially land and marine resource use affect society-environment interactions and achieving SDGs such as those related to food security.
• Integrated use of monitoring tools (e.g. eDNA, remote sensing) across systems.
• Nature-based solutions (NBS): Current projects rarely assess optimal NBS placement to balance upstream–downstream trade-offs or deliver quantifiable S2S outcomes.

These gaps call for interdisciplinary source-to-sea research and integrated monitoring to connect land-use decisions, ecosystem services, and climate adaptation across the S2S continuum.

Future research directions for Scotland

Scotland has the opportunity to advance S2S research by building on existing evidence, but developing more integrated, system-wide approaches in several key areas:

• Land use and coastal ecosystem services – Future research can extend beyond carbon sequestration and habitat changes to understand the broader impacts of land use decisions on coastal ecosystems and resilience across the land-river-sea continuum. 
• Ecological and socio-economic impacts – There is potential for integrating the findings of fragmented studies on rural economies and their dependence on nature, with particular focus on bidirectional land-sea interactions and the combined effects of environmental changes on both biodiversity and local economies.
• Monitoring, technology & management – New tools like eDNA and remote sensing offer promise, but future research should prioritise their integration across land-freshwater-marine systems to support coordinated monitoring and management.
• Nature-based solutions (NBS) –Several NBS projects are currently implemented and planned, but research should focus on strategic project siting and design to balance upstream-downstream trade-offs for maximum quantifiable benefits at the source-to-sea scale.
• Conservation effectiveness and risk of overlooking S2S: Future research should address critical gaps in source–sink dynamics and planning to: avoid ‘ecological traps’ (where species may settle to seemingly suitable but low-quality habitats); improve habitat assessments and modelling (as simple presence or density measures may misrepresent true habitat value); and ensure that conservation efforts are directed towards the most important source habitats for sustaining populations. This includes refining metrics that go beyond local presence or density to identify S2S ecosystem health indicators.

Workshop insights

Our workshop brought together researchers, policymakers, and practitioners to explore Scotland’s readiness for Source-to-Sea (S2S) approaches (See S2S workshop report). Discussions centered around research collaborations, monitoring and research tool gaps, and funding needs. Participants confirmed persistent challenges-scientific discipline silos, fragmented monitoring frameworks, limited policy coordination, and siloed funding. However, they also identified clear opportunities for:

• A readiness assessment and better use of existing data to support demonstration S2S projects.
• Development of long-term monitoring frameworks, building on existing indicators and enabling open access to data and cross-sector collaboration.
• Technology innovation through combined high-tech and community-led approaches. Participants proposed launching a CivTech Challenge to stimulate new, accessible solutions for real-time source-to-sea surveillance and data integration.
• Cross-sectoral funding models, inspired by projects like Glenmorangie’s oyster restoration (DEEP), to unlock financing mechanisms for proof-of-concept projects. Participants highlighted the importance of funding from the Scottish Government (including through SEFARI Gateway and the SRP), the Scottish Funding Council and UKRI to support integrated, interdisciplinary research that addresses the identified evidence gaps.
• Cross-sectoral policy alignment, coordinated pilots, capacity-building, and embedding S2S into frameworks like the Natural Environment (Scotland) Bill. Participants stressed the timeliness of applying S2S thinking to integrate research to help achieve policy objectives for land use, water resources, the climate emergency, and nature restoration.

Participants agreed that clear policies, moving beyond compartmentalised funding to address interlinked problems, and stronger collaboration are essential to embed S2S in Scotland. Policymakers, like NatureScot, DAERA and the Environment Agency, are already raising awareness and building capacity, even without dedicated funding. Applying an S2S lens offers an opportunity to strengthen research innovation, bridge knowledge and implementation gaps across environmental domains, and account for different perspectives from communities and the industry. Applying the S2S approach would also help RESAS in delivering whole-system approaches.

Benefits

Documents

• Breaking down scientific silos: towards Source-to-Sea research in Scotland - Workshop Report