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Current approaches to environmental protection and development on land, along rivers and coastal zones, and in marine environments are struggling to effectively promote sustainability. This is partly due to limited understanding of how ecosystems are linked, and partly due to fragmented governance and management arrangements in the continuum from source to sea that hinders cooperation and strategic overview across connected systems. Meanwhile, the key flows that link ecosystems are being altered by climate change and by an intensification of human activities, which are also expanding offshore where management regimes are typically weak or nonexistent. This paper presents a conceptual framework to guide the design of future initiatives aimed at supporting green and blue growth in source-to-sea systems. It includes a taxonomy of key flows, elements to guide analysis and planning and a common framework for elaborating a theory of change. Assembling a governance baseline and engaging stakeholders are critical elements in the approach. The conceptual framework builds on recent experiences of pro-sustainability action in source-to-sea systems around the world, and the paper applies the theory of change framework to selected case studies in order to develop further insights.Keywords: Governance; Integrated management; Marine; River basin; Sustainable development; System linkages This is an Open Access article distributed under the terms of the Creative Commons Attribution Licence (CC BY-NC-SA 4.0), which permits copying, adaptation and redistribution for non-commercial purposes, provided the contribution is distributed under the same licence as the original, and the original work is properly cited

Changes in land use and land cover (LULC) are the leading contributors to the decline and loss of ecosystem services in the world. The present study covered the Central Rift Valley lakes basin in Ethiopia, focusing on the valley floor and the East and West escarpments, to analyze changes in LULC and to estimate associated losses in ecosystem service values (ESVs). Covering both upstream and downstream areas in the basin, the study addressed major gaps in existing studies by connecting the sources and sinks of material (e.g., sediment and water) in source-to-lake systems. Additionally, the study facilitated the identification of critical areas for conserving natural resources and reversing the decline of associated ESVs in the Central Rift Valley. A post-classification comparison approach was used to detect LULC changes between 1973 and 2020 using four Landsat images from 1973, 1990, 2005 and 2020. The value transfer valuation method was used to estimate the changes in ESVs due to LULC changes. Among the seven major identified LULC classes, farmlands, settlements, and bare lands showed positive changes, while forestlands, grasslands, shrublands and waterbodies showed negative changes over the last 47 years. The expansion of farmlands, for example, has occurred at the expense of grasslands, forestlands and shrublands. The changes in LULC over a period of 47 years resulted in a total loss of US $62,110.4 × 106 in ESVs. The contributors to the overall loss of ESVs in decreasing order are provisioning services (US $33,795.1 × 106), cultural services (US $28,981.5 × 106) and regulating services (US $652.9 × 106). The results imply that addressing the degradation of land and water resources is crucial to reversing the loss of ecosystem services and achieving the national Sustainable Development Goals (SDGs) related to food and water security (SDGs 2 and 6) and life on land (SDG 15).

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