Introduction

Water is an essential life sustainer on the planet; it is indispensable to life, and in numerous water-dependent processes, a kind of bloodstream of the biosphere (Ripl 2003). It is crucial in the industrial production of goods and services necessary for our daily lives, as well as in the production of food, in social life, and families’ daily lives (Falkenmark 1997). Because water is recognized an essential part of the livelihoods, the water right became a central issue, and water security was strongly attached to the human right to water (Saito 2018).

Whether fresh or salty, water is a unique resource, a continuum linked by the hydrological cycle that knows no limits, and environmental boundaries cannot contain it. The hydrological cycle is usually understood as a natural and continuous process independent of the presence or absence of human activity (Maidment 1993), and this naturalness of the hydrological cycle is based on the idea of ​​a natural course of water circulation (Horton 1931).

Despite this apparent independence, this cycle can be affected by human activities, damming rivers, withdrawing groundwater, or polluting water bodies, altering the speed of circulation in the hydrological cycle, leading to alteration of coastal and open ocean. Climate change has brought a new nature and magnitude of impacts on water cycle affecting water resources’ supply and demand (IPCC 2022; Little et al. 2017; Marengo et al. 2017; Ribeiro Neto et al. 2016; Wilhite et al. 2014). These events draw us into a future scenario with greater water scarcity, where conflicts between water uses become increasingly evident, even in countries with high water availability (Miletto et al. 2017; World Bank UN-DESA 2017).

The nature of water shows how the management of fresh and saltwater resources is cross-sectoral and linked to many activities and investments in the use of water resources and other sectors. An integrated approach is needed to address these problems and find ways to mitigate, adapt and conserve water resources because water tends to be managed segment by segment or sector by sector. Integrated Water Resources Management (IWRM) and Integrated Coastal Management (ICM) have been presented to find sustainable solutions to these problems. IWRM represents a process promoting the coordinated development and management of water, land, and related resources, increasing economic and equitable social welfare without compromising the sustainability of vital ecosystems (GWP 2000). ICM is a process to maintain or restore ecological integrity and improve quality of life by developing economies in coastal and marine socio-ecological systems (Eger et al. 2021).

Despite these efforts, the current arrangements for governance and management of water resources are poorly suited to balance the diverse and often conflicting management objectives, priorities of social actors, and institutional arrangements in different geographic segments from the source of the watercourse to marine systems. Because of this, a new approach showed up proposing to manage together fresh and salty water resources: the Source-to-sea (S2S) approach. The S2S concept concerns key flows in the “continuum” of the system, referring to the continuity of the water system from land to ocean, encompassing all the land area that is drained by a river system, its lakes and tributaries (the river basin), connected aquifers and downstream recipients including deltas and estuaries, coastlines and near-shore waters, the adjoining sea and continental shelf as well as the open ocean (Granit et al. 2017a; Mathews et al. 2019).

The three approaches’ overall objective is to improve the governance and management of water resources for human well-being and ecosystem sustainability. They all advocate a broad view of water-related issues, and call for an integrated approach across sectors and scales. The question is whether they overlap themselves and/or to what extent they are complementary. The objective of this research was to identify the relationships and convergences between the three approaches and in which aspect the Source-to-sea approach brings novelty to ensure better governance and management of fresh and marine water resources to guarantee water security and conservation of waters and their sustainability.

Methods

This research aims to understand the emergence of the Source-to-sea approach and to identify the relationships and convergences with the IWRM and ICM approaches, trying to see if they are integrative, complementary, or competitive.

An issue that permeates the understanding of governance and management approaches is the terminology used. Because there is no general convention, different terms are often used to express the same perception and meanings. Therefore, this requires repeatedly exploring documents, articles, and reports to capture meaning and intent (Monteiro et al. 2020). Depending on how they are placed, meanings vary a lot, demanding interpretation work by the researcher. To face this, content analysis was developed to identify the intentions and perceptions of each approach´s concepts, principles, and dimensions. According to Bardin (1977), content analysis is a set of communication analysis techniques aimed at obtaining, through systematic procedures and objectives of the description of the content of messages, quantitative or qualitative indicators that allow the inference of knowledge related to the conditions of communication: production, and reception, of these messages.

Content analysis can help select key issues that can help advance the global debate, analyzing different content of messages, concepts, and knowledge structures and grouping some of them in the same category, even addressed with different names, so that a set of categories is produced.

The research was planned and carried out in 03 stages: Planning and literature review, content analysis, and validation and results.

The first phase: Planning and Literature review. It was the organizational phase consisting of the theme definition, pre-analysis, and selection of documents referring to the three approaches. The defined theme of the study revolved around the innovative Source-to-sea approach. It became clear that knowing if the approach was innovative was important. Therefore, it was deemed crucial to explore its relationship with other pertinent approaches concerning water resources and the coastal zone. Consequently, the research question was formulated to assess and compare the Source-to-sea, IWRM, and ICM approaches and answer if they were integrative, complementary, or competitive. For this, it was necessary to identify documents, articles, and books, among others, that brought concepts, principles, and applications of the three approaches. To proceed with the research, the first keywords were defined, including: “Water resources,” “Source-to-sea,” “IWRM,” “ICM,” “Integrated management of water resources,” “Integrated management of coastal zones,” “Integrated coastal management,” “Integrated Coastal planning,” and also in a dismembered way such as: “coastal management,” “coastal governance” “watershed management.” Then, using the “and” operator between them in the search expression, the terms “management,” “governance,” “concept,” “principles,” “integration,” “implementation,” and “practices” were added, among others that emerged as the research progressed due to the high number of documents presented in each research. The process was carried out in 03 steps, each destined to an approach and then the crossing between the steps. For example, in step 1, the search was carried out with the keyword “Source-to-sea,” adding the connectors mentioned above. All fields were searched using Scopus, Web of Science, and Google Scholar databases. In this phase, 335 documents were selected.

The Second phase: Content analysis. After a preliminary selection of literature, it was necessary to analyze the elements according to the objectives of this research and classify them. A floating reading of the base of documents selected in the first phase, exclusion and choice of documents. In this phase, 234 documents were removed, and 101 were selected to support the research. The selected documents were submitted to classification of elements, analysis, the definition of categories, and the first version of the matrix were carried out. It’s important to emphasize that the analysis occurred in the thematic field. The process of classifying elements according to selected criteria is called categorization (Richardson 2012). To create the categories, which means reducing the text to categories, the texts were cut at a semantic level (unitizing), looking for the core of the meanings. In classifying the categories, an attempt was made to follow the characteristics of exhaustiveness, exclusivity, concreteness, homogeneity, and objectivity (Richardson 2012).

The third phase: validation and results. After a preliminary analysis with an initial set of categories, while the matrix was analyzed, a deeper analysis and complimentary review of the literature was performed to fill in gaps in the preliminary selection of literature. This resulted in the addition of 15 documents, the revision and confirmation of the categories, and adaptation and matrix re-analysis, interpretation, and discussion of the categories.

A matrix containing the final categorization was created based on the Leopold matrix (Leopold et al. 1971) for the treatment and interpretation of the data obtained. The methodological approach applied in this work is represented in Fig. 1. The matrix was used to compare the three approaches (IWRM, ICM, S2S), and it was filled with graphical symbols that could express how each category was considered in each approach based on literature. The discussion section presents the analysis of the matrix results and the theoretical and methodological implications that can guide the understanding, choice, and implementation of these approaches.

Fig. 1
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Methodological approach applied in this work

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Results and discussion

Approaches in a given field encompass principles, guidelines, goals, and objectives with specific focuses that influence the way their structures are proposed. Therefore, it is essential to analyze and identify how these focuses are addressed in each approach, as well as whether the specificity of one approach is present in others or if they discuss and incorporate such specificity conceptually into their plans. These differences are crucial for the characterization of each approach. The categorization was important to understand these aspects, whether the contributions advance the sustainable use and conservation of water resources and water security or even in which aspects the sole focus is similar or equal concepts and structures but addressed with different names. The results of this categorization originated eight categories: integration, segments, key flows, governance and management, monitoring and evaluation, blue and green economy, gender, and water value. The definitions of each category and the documents used to define and analyze them are presented in Table 1.

Table 1 Category definition
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The results obtained through the content analysis are represented in the results matrix (Fig. 2). The matrix presents eight categories and the relationships between the approaches within each category, so it was filled in considering the characteristics defined in each category.

For the eight categories, S2S was fully committed to 6 of them (Integration, Segments, Key flows, Governance and Management, Monitoring and Evaluation, Blue and Green Economy, Gender, and Water Value), and it was partially committed to 2 of them (Gender, Water Value). IWRM was fully committed to 5 of them (Integration, Governance and Management, Monitoring and Evaluation, Gender, and Water Value), and it was partially committed to 3 of them (Segments, Key flows, Blue and Green Economy). And ICM was fully committed to only 3 of them (Integration, Governance and Management, Monitoring and Evaluation) and partially committed to the other 5 categories (Segments, Key flows, Blue and Green Economy, Gender, Water Value). The segments category was analyzed as a composed result of its sub-categories, and only S2S was considered fully committed because it presented this commitment in all its sub-categories representing segments of the water bodies.

Fig. 2
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Matrix with the results of the 08 categories. The black full circle means that the characteristics are present in the approach, the circle with partial filling is used when the approach has part of the defined characteristics, and the unfilled (empty) circle is when the characteristics are not included in the approach

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Integration

The integration in the three approaches seeks to apply a systemic vision to deal with water resources Thus all of them were classified as fully-committed to this category.

For IWRM, integration must occur within and between two categories: the natural system and the human system considering the variability of time and space (GWP 2000). Integration into the natural system is associated with the recognition of the requirements for the coastal zone and the continuum that unites them through the flow of water, and it is concerned with the integration between surface and groundwater, catchment and basin management, water quality and quantity, and upstream and downstream water. Human system integration involves understanding the natural system, its capacity, vulnerability, and limits. This means ensuring that government policies consider the implications for development, risks, and uses of water resources. Intersectoral integration needs an enabling environment: clear institutional roles and functions of the various administrative levels, stakeholders, and management instruments. It also includes ensuring stakeholders’ participation in decisions. Thus, considering the system natural and human, the ecosystem approach and participatory approach are included within the concept (UNESCO 2009; Smith and Clausen 2015). IWRM aims the integration and coordination of planning, development, management, and policy formulation in the water and cognate sectors, linking social and economic development with the protection of natural ecosystems (Van Beek and Arriens 2014; Varis et al. 2014).

The integrative approach is also essential for ICM because, in addition to allowing internal consistency between policies and programs, it makes planning associated with the reality of implementation, encompassing for example Marine Protected Areas (MPA) networks, Marine Spatial Planning (MSP), and Integrated Coastal Zone Management (ICZM). Integration in the coastal/marine context considers the dimensions of intersectoral integration (horizontal integration); spatial integration (between the aquatic and terrestrial environment), intragovernmental (vertical integration); and interdisciplinary science and management integration (Cicin-Sain et al. 1998; Hong and Lee 2001; Portman 2018). In the ICM, the cumulative impacts of the relevant activities on the ecosystem and its services become the organizing framework for management. It is intended to directly address the long-term, sustainable delivery of ecosystem services and the resilience of coastal and marine ecosystems to perturbations (Eger et al. 2021; Rosenberg and Sandifer 2009).

The Source-to-sea approach is based on systems thinking to deal with complexity (Granit et al. 2017a). S2S adopts a systemic approach that looks at the water resource through the prism of the water cycle: marine water and fresh water are part of the same continuum, of the same cycle, and what happens in this continuum (the anthropogenic intervention) impacts this system as a whole (Belete et al. 2021; Falkenmark 2005; Granit et al. 2014; Linton 2008; Vörösmarty et al. 2004). In this way, it adopts ecosystemic, participatory, and adaptive approaches that recognize human beings, with their cultural diversity, are an integral component of many ecosystems. The associated human population and economic/social systems are considered integral parts of the ecosystem (UNEP/GPA 2006). International integration is highlighted in diplomatic relations between administrative borders and political processes (Fallon et al. 2022; Pahl-Wostl et al. 2012; Söderbaum and Granit 2014).

The Source-to-Sea (S2S) approach stands out for its comprehensive and integrative perspective compared to the GIRH and ICM approaches. While the other approaches focus on managing water resources in their specific contexts, S2S transcends these boundaries. It seeks to innovate by considering the complete water cycle and its connections across different environments. It adopts a holistic view of the water cycle, considering the interdependence between natural, human, economic, and social systems. The approaches also have a lot in common, such as considering participation and being adaptive, for example. Therefore, even though S2S advances in integration, including the proposal to integrate the two approaches, it should consider the experience that IWRM and ICM have accumulated over time and bring this accumulated knowledge together with its broader vision in negotiations and in diplomatic relations between administrative borders and political processes.

Segments

There are many arguments, proposals, definitions of IWRM and how to implement it, as well as the appropriate scales for intervention. What predominates are approaches at national policy, river basin, and sub-basin levels. It was emphasized at the Johannesburg World Summit on Sustainable Development – WSSD that water should be managed in a basin-wide context, under the principles of good governance and public participation (WSSD 2002). Water resources boundaries rarely coincide with administrative boundaries, whether surface or groundwater. At this point, IWRM emphasizes that legal frameworks need to be conceived from an international level into regional and national levels (Davis 2007; GWP 2000; Rahaman and Varis 2005; Savenije and Van der Zaag 2008; SIWI 2020). Therefore, the main GIRH targeted segments are Land resources and terrestrial systems – river basins, freshwater systems, and estuaries and deltas. It also recognizes the need for freshwater managers to identify the needs of coastal zones and for coastal plans need to support IWRM.

ICM focuses on coastal zones, their relationship with the sea, territorial ordering, and the use of coastal waters. It aims at integration with regional development at national and cross-border policy levels. It also recognizes that the complexity of water resources in coastal zones goes beyond administrative limits and the search for cooperation and transboundary policies (Cicin-Sain et al. 1995; Cicin-Sain and Belfiore 2005; Eger et al. 2021; Godschalk and Burns 2019; Oliveira et al. 2020). The dynamic balance of coastal regions requires integrated and multiple approaches capable of considering ecological, social, and economic characteristics as integral parts of a system as a whole. This comprehensive view of coastal management must include coastal and catchment areas in the same landscape unit, as human pressures on these regions can affect coastal landscapes and vice versa. In this open system, changes in land use and transportation resources or the supply zones of the basins on both sides of the river corridors are reflected downstream to coastal waters, affecting the integrity of marine ecosystems (Cantasano and Pellicone 2014). Therefore, ICM’s main targeted segments are Land resources and terrestrial systems, including coastal and urban areas, estuaries and deltas, coastline and nearshore waters. It also recognizes the upstream-downstream connections and the need for dialogue and harmonization between IWRM, Marine Management, and Land Use Plan.

The Source-to-sea approach aims to improve understanding of the linkages between freshwater, terrestrial, coastal, and marine systems, to support efforts to promote coordinated governance of all these systems and provide a foundation for decision-makers and planners (Weinberg et al. 2021). Fresh, coastal, and marine waters are interconnected as part of the hydrological cycle, moving across political and disciplinary boundaries, on land, underground, through the air, and through exchanges within and between biomes and beings. They are at various scales, from global to regional and local to river basins to oceans. What defines the Source-to-sea system is precisely this vision of the single system, which includes rivers basins, aquifers, downstream receptors, including deltas and estuaries, shorelines, and near-shore waters, maritime and continental shelves, and the open sea. (Granit et al. 2017a; Rocha Loures 2021). In the S2S approach, in defining an appropriate scale for analysis in a particular source-to-sea system, the scale can range from one or more segments that are closely connected to a river basin and downstream recipient, a sea and its drainage area to the connections of the global system (Mathews et al. 2019; Wang et al. 2021). Consequently, S2S main targeted segments are Land resources and terrestrial systems, including watersheds, freshwater systems, estuaries and deltas, coastline and nearshore waters, adjoining sea and continental shelf, and open ocean.

As shown in Fig. 3 the Source-to-sea encompasses all the segments that the other approaches (IWRM and ICM) only partially include in their analysis.

Key flows

The first Dublin Statement principle, water as a finite and vulnerable resource, recognizes that a fixed amount of water per period of time is available by the hydrological cycle and that this total amount cannot be significantly altered by human actions, even considering the progress in water desalination in some countries. However, it also recognizes that humans can affect water resource productivity and reduce water availability and quality by altering flow regimes in surface water systems (GWP 2000).

However, integrated river basin planning already recognized that water flow unites the physical and human characteristics within a river basin (Schramm 1980). IWRM considers the environmental flow as the quantity, quality, and timing of water flows necessary to sustain ecosystems. The condition in which ecosystems and their services are sustained is essentially a socio-political decision: it can be established by international conventions or national policies, and environmental flow allocation can be negotiated between water users to maintain ecosystems in the desired condition (Sadoff and Muller 2009; Sadoff et al. 2015).

Coastal zones are complex and dynamic due to their elements and interactions. The coastline undergoes constant changes, as it is a place of integration and a buffer zone between land and ocean. Therefore, the category of key flows is also partially present in the ICM considering three aspects of water flow: freshwater and saltwater flows and the interface between them. In the analyzed articles, the references to flows are mainly to ecosystem services or the impacts often generated by this land-ocean interaction (Broadley et al. 2022; Cicin-Sain and Belfiore 2005; Jean et al. 2018; Lins-de-Barros 2017; Lu et al. 2018; Rasch et al. 2005; Sklar and Browder 1998).

The comprehension of the upstream-downstream interactions is crucial because of the sediment balance, changes in the water flow, and the increasing loads of nutrients and a variety of chemicals that impact downstream the health of coastal and marine ecosystems. The impact also happens upstream, such as the rise in river water levels due to tides, which are related to flooding and saltwater intrusion into deltas. The Coastal ecosystems adjust to this cyclical effect, but coastal morphology changes can lead to saltwater intrusion further inland. Although arguing in favor of integration with IWRM, the first one encompassing the latter and vice-versa depending on the point of view (Cicin-Sain et al. 1998; Olsen 2003b), in practice, key interconnections and flows still remain in the perception and solutions remain fragmented into the continuum.

The S2S approach looks at the water resource through the prism of the water cycle: marine water and fresh water are part of the same continuum, of the same cycle, and what happens in this continuum impacts this system as a whole, including the human component and its changes as part of this cycle (Granit et al. 2017b; Rocha Loures 2021; Steffen et al. 2004). The S2S approach is similar to and supported by the River Continuum Concept (Vannote et al. 1980). This means the centrality of the flow driven, that is, focused and sustained in the flow processes, seeking, from the flow, to establish lateral connections (in the case of a river continuous, the connection between the light energy input, the production of biomass and the interactions between the physical environment and the biotic environment; in the case of S2S, the interactions between the diagnosis of pressure and impacts, management and governance).

Thus, the first element of the S2S conceptual framework is the key flows - water, sediments, pollutants, biota, materials, and ecosystem services - that connect subsystems in the continuum (Fig. 3) at different spatial scales and that bring impacts or benefits to the system (Granit et al. 2016). The state of each flow can be affected by activities in the other flows. Thus, the approach is structured in the combination of elements set that help identify courses of action that are suitable for a given S2S system, starting by identifying the flows and issues that are priorities.

For this category, it was the S2S approach the only one that was classified as fully-committed to this category. The others presented a weak and thus partial commitment, with focus only on isolated flow such as water or sediments.

Fig. 3
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Key flows that connect geographies from source-to-sea

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Governance and management

The three approaches have water resources governance and management in their proposals and thus, all of them were classified as fully-committed to this category.

There is no single definition of governance, and depending on the context, different approaches and different views and definitions can emerge. Additionally, there is frequently a certain confusion about what governance is and what concerns management (Varis et al. 2014; Woodhouse and Muller 2017). The distinction between governance and management is an important aspect that permeates the ICM and S2S approach. Governance deals with the values, policies, laws, and institutions by which a set of issues is addressed, defining the scenario in which management takes place. Management is the process by which human and material resources are harnessed to achieve a known objective within a known institutional framework and it can be seen as the time to apply the approach after building the enabling environment through governance (Olsen 2003a).

There is a great convergence in the proposals/guide of implementation plans of the approaches in terms of establishing a progressive spiral process (loop cycles) with steps to be followed, where each cycle brings the lessons learned (learning and adaptive approach) and may indicate new scopes. Depending on the approach, these spiral processes differ in some aspects, but in terms of the theoretical vision of continuity and evolution, they are similar.

For the IWRM, water governance is the range of political, social, economic, and administrative systems in place to develop and manage water resources and deliver water services at different levels of society, and achieving good water governance requires creating an enabling environment that facilitates efficient public and private sector initiatives and stakeholder involvement. The enabling environment involves policies, legal frameworks, investment and financing structures (GWP 2000; Rogers and Hall 2003; Sadoff et al. 2015). IWRM is moving towards distributed governance, and the Dublin principles clearly reflect this concept, addressing the relevance of meaningful decentralization at the lowest appropriate level (Rahaman and Varis 2005; SIWI 2020).

IWRM proposes national IWRM plans to plan the coordinated development and management of water resources that provide frameworks and guidance on how to address development problems, including issues of water allocation and pollution. This roadmap is proposed to guide changes from fragmented approaches to more integrated approaches, identifying actions and a set of management instruments embedded in a broad framework of policies, legislation, funding structure, and institutions with clearly defined roles (UN-Water GWP 2007).

For the ICM, governance requires thinking in terms of nested systems because different environmental and social issues, conditions, and actions impact and are impacted at higher and lower levels of an ecosystem and hierarchy of governance (Eger et al. 2021; Olsen et al. 1999). ICM is an umbrella term for other related processes, tools, and concepts such as Coastal Management or Coastal Resource Management, ecosystem-based management (EBM), marine protected area (MPA), and marine spatial planning (MSP), among others (Ehler 2003). The choice of an issue or a set of issues to be addressed must consider how responsibility and decision-making authority are distributed within a layered governance system, and consider relevant issues and proposed objectives of the immediately higher level of the governance system (Olsen et al. 2009).

Management in the ICM approach aims to restore or improve the specific qualities of coastal ecosystems and their human societies, enabling development and conservation in specific places, whether from a community to the coast of a nation. It also emphasizes that the instruments, indicators, and their management processes must be designed for periods longer than 4 to 6 years than currently used by governments to make possible to monitor the progress of initiatives and promote their adaptation and expansion of scope (Olsen 2003c; Ferreira et al. 2021).

The S2S approach takes a critical view of current water resources governance and management arrangements. Part of the problem is that there are many overlapping management frameworks on the continuum of water resources from land to open sea - it is several approaches to be applied to the same body of water, such as IWRM, ICM, MPA, and MSP, among others (Fig. 4), and that governance structures typically deal with freshwater and saltwater separately, where institutional and administrative structures of governments, as much as laws, have different departments for marine and freshwater issues (Granit et al. 2014). To design an appropriate course of action, S2S proposes a thorough governance analysis to understand past and existing governance and management systems - their strengths, weaknesses, or absences - and to consider the issues that are priorities for setting the governance baseline and identify the consequences of actions that did not take the system as a whole into account (Juda and Hennesssey 2001; Olsen et al. 2011). The S2S management cycle helps understandthe pressures and drivers of changed key flows, selecting the appropriate scale of intervention and stakeholder engagement, and establishing a Theory of Change (ToC) that will guide planning and implementation (Mathews et al. 2019).

Fig. 4
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Overlapping or weak governance and management frameworks in the water continuum—Adapted from Granit et al. (2014)

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Monitoring and evaluation

IWRM defends the need to develop a monitoring and evaluation system to accompany the implementation process, monitor the results, and evaluate progress to learn from the information obtained and refine the projects, programs, policies, plans, or strategies. The availability of this information is also necessary to promote the participation and support of civil society while ensuring accountability and generating public and private political support for the investment made. An important part of this process is the creation of indicators (Bertule et al. 2017). The GWP Toolbox suggests some criteria that can be used to guide and assess the quality of indicators, such as the SMART criteria (Specific, Measurable, Attainable, Relevant, Time-bound) and the SPICED criteria (Subjective, Participatory, Interpreted and communicable, Cross-checked, Empowering, Diverse and disaggregated) (GWP 2022).

In the ICM, the implementation of projects or programs matures through the completion of each management cycle and it is essential to analyze and understand the results that coastal management works to achieve. Usually, the first cycle starts with the most pressing issues linked to a specific geographic area. Thus, it is important to understand the sequences of impacts that accumulate as the plan develops and is implemented. The ICM suggests using The Orders of Outcomes to build this trajectory. This framework groups the results along this trajectory to make it possible to understand progress and trace new advances toward more sustainable forms of development. The structure establishes 4 orders, 3 intermediate and one final which measure sustainable coastal development, that is, at what level the balance of social and environmental qualities has reached in terms of intergenerational equity and perspectives on social and environmental conditions and trends (Olsen 2003b, c; USAID 2009).

S2S advances the proposal for a monitoring and evaluation framework. It incorporates the observations, concerns, and recommendations from the IWRM and ICM approaches and extends the process. In the structure proposed by S2S, it is necessary to develop a ToC to guide the process of adaptation and change and the application of the structure of The Orders of Outcomes for monitoring and evaluation. According to Weiss (1995), ToC is a theory of how and why an initiative works. Stein and Valters (2012) add that this can be understood as a way of describing a set of assumptions that explain both the mini-steps that lead to a goal of long-term and the connections between these activities and the results of an intervention or program. A defining feature of the structure of the theory of change proposed by the S2S approach is precisely this recognition of complexity in which economic, political, and diplomatic factors are as important as science and engineering in governance and management (Granit et al. 2017b; Söderbaum and Granit 2014; Stein and Valters 2012). GWP also hinted at adopting ToC in its latest IWRM global strategy for 2020–2025 (Saito 2019).

In this process, the concern is whether the necessary results (reports, trained people) have been generated, whether the quality of program activities is adequate, and how the program is responding to external events that are shaping the socio-political context in which the program is inserted and operating. In S2S, the systems thinking together with the Order of Outcomes structure can help fill gaps in water management and monitoring where frequently it is not clear the process for achieving this objective or how the progress in this direction will be monitored and evaluated. ToC in S2S can help monitoring and evaluation as it offers a sequence of tangible results that, if pursued over long periods, can lead to increasingly sustainable stages (Granit et al. 2017b; UNEP/GPA 2006).

It can be said that all of them (IWRM, ICM, S2S) were classified as fully-committed to this category.

Blue and green economy

In order to achieve sustainable development, the issue of economic development has to be integrated with more emphasis on governance and management approaches to ensure the balance and adequacy of society’s economic development to the capabilities of nature. For this to be consolidated, specific mechanisms and measures are being incorporated, such as the concept of the green and blue economy (Bekmurzaev and Dadaev 2021; Lee et al. 2020; UN Environment 2018; World Bank UN-DESA 2017; European Commission 2013; Falkenmark and Rockström 2010; UNCSD 2012).

UNEP (2011) defines the green economy as a low-carbon, resource-efficient, and socially inclusive economy, resulting in improved human well-being and social equity, while significantly reducing environmental risks and ecological scarcities. The IWRM has brought up the issue of green growth in some case studies. However, the discussion is still in its infancy, and a long way needs to be traced so that, within the policies and plans linked to the water sectors, they are integrated with other sectors in search of efficiency. In this aspect, the conceptual framework nexus water-energy-food (Hoff 2011) has complemented the discussions in the IWRM approaches. Its framework seeks to promote actions toward a green economy because it deals with the interdependencies between key sectors; seeks to determine and resolve trade-offs between increasing demands; and aims to achieve water, energy, and food security without compromising sustainability (Griesinger and Michels-Brito 2022).

In relation to the blue economy, the ICM has advanced in the discussion of governance and in the design of its management initiatives. The blue economy concept has developed alongside the green economy to consider the economic benefits generated by coasts and oceans in all aspects of economic activity (Pereira 2020). The Blue Economy partly encompasses the concept of ocean-based economies, however, this concept goes far beyond that, conceptualizing the oceans as development spaces.

The framework of the S2S approach aims to improve the understanding of systems linked to the water cycle, including the economic development of societies, and it explicitly embraces “green” and “blue” economic development theories. In this way, S2S identifies economic growth sectors with the potential to enhance environmental sustainability in general (green) and in coastal and marine areas in particular (blue), showing the opportunities for sustainable economic growth in interconnected systems by the fresh and salty water continuum (Granit et al. 2017b). As a result, it breaks with the molds of the “brown” development model, where the oceans are perceived as a means of free resource extraction and waste disposal and incorporate oceanic values ​​and services in economic modeling and decision-making processes (UNCSD 2012).

In summary, the blue and green economies are contemplated in the S2S approach and partially reflected in the IWRM and ICM. The S2S has as one of its main objectives in its conceptual structure to guide the design of future initiatives to support “green” and “blue” growth. Developing the green and blue economy through good governance and management is to outline the path to sustainable development. The IWRM and ICM work with the green and blue economy in some programs and forums, but they do not have the blue and green growth as an objective contemplated in their framework.

Gender

IWRM has advanced in the context of governance and management of water resources so that the understanding of what gender integration means have expanded, going beyond the issue of women’s integration. The Integration must take place from all gender perspectives, from differences in needs, uses and practices, employment, and entrepreneurship to access to resources, adaptability, and mitigation of men, women, and non-binary individuals in water planning and management, ensuring participation in all decision-making forums. Gender equality and social inclusion became core values at IWRM, and they are presented in this way in the Dublin Statement (GWP 2000). This means mainstreaming gender into all policies across the board, linking water and other relevant policy areas (Grant 2017). This direction is in line with what today proposes the goals of Sustainable Development Goals 6, 5, and 14 (GWP UNEP-DHI 2021; Niasse 2017; UNGA 2015; Water Europe 2019).

The gender issue in the ICM has also been discussed and introduced in many programs and projects (Olsen 2003b; Bennett 2005; de la Torre-Castro et al. 2017; Pravalprukskul and Resurreccion 2018; USAID 2009; Wabnitz et al. 2021). This insertion was both to enhance the participation of stakeholders and to promote equitable benefits distribution, reducing inequalities. However, the question is not structured at the principle level, as in the IWRM. The gender discussion has appeared with more emphasis when addressing vulnerability to climate change (Diamond and Lellement 2014; Miletto et al. 2017; Nagel 2015). Nonetheless, the ICM recognizes the need to analyze basic social information, including gender and demographic variables, so operational strategies are more effective.

According to Diamond (2003), the need for gender mainstreaming in the planning and implementation of ICM programs needs to be much more than a simple matter of adding more female staff or adding a female member to a committee or just scheduling a small generation activity income for women in an ICM program. Many experiences have been accumulating in ICM approaches, and the perception that equity is not an optional choice but a transformative perspective necessary for coastal management to become more integrated and inclusive has been consolidating. We do not argue that ICM programs and projects are not developing approaches to gender mainstreaming, but in the conceptual articles analyzed in this work, gender mainstreaming does not feature prominently.

The S2S approach has its structure focused on the sustainable promotion of human well-being, equity, and social justice. However, the gender issue appears incipient in the articles dealing with the approach, perhaps because the approach is recent, despite its construction having taken place over time based on results obtained in different programs. For example, Berggren and Liss Lymer (2016), in their study on the links between the freshwater and marine targets in the 2030 Agenda, seek, in addition to understanding these links, to identify the gaps between SDGs 6 and 14 through the S2S vision, the issue of vulnerability of women and girls excel in sanitation and hygiene.

Mathews et al. (2019) show in the S2S implementation guide that ensuring gender representation increases engagement and strengthens the strategies and objectives outlined. Tengberg and Valencia (2017), on identifying the main aspects of integration and evaluation of implementation in natural resource management projects through systemic thinking, highlighted the need for equity to be brought into planning. The projects presented showed that where there was a priority to integrate women, the success of the programs was higher.

Therefore, in this category, IWRM stands out against the ICM and S2S approaches and can contribute to these approaches evolving in the integration of gender for coastal zones and marine environments in a complementary way, sharing experiences and tools.

Water value

IWRM brings in its conceptual structure the question of the value of water. The value of water begins with a principle 1 approach, where there is a recognition that water is a finite resource. Because it is a finite resource, the management of this resource needs to be judicious, and its value must be included in this aspect. Seeing water as a free common good, without considering its value, can lead to harmful competition, overexploitation, and degradation of the resource (Hardin 1968; Ostrom 1999). This is why IWRM principle 4 considers water as an economic good, and thus having value (Rogers et al. 1998).

The discussion of water as an economic good and its value generates different interpretations and great confusion. Agenda 21, in Chap. 18, sought to direct the issue by referring to water as an economic good but also as a social good, bringing a distinction between valuation (use value that involves regulatory and economic means) and charging (economic instruments that are complementary used to guarantee institutional control over access and use) (UNCED 1992). This confusion persists and two major schools of thought can be distinguished when considering water as a economic good, according to Savenije and Zaag (2002): (1) the first one defends that water should be priced according to its economic value and the market will guarantee the balance of uses; (2) the second one argues that water as an economic good is a decision-making process integrated into allocation decisions without necessarily involving financial transactions. However, in a different way of thinking, water can be valued as a common, not as a good: water can be viewed as part of humanity’s common heritage, and thus, water is not merchandise (P7 Summit of the World’s Seven Poorest Countries 2000). Bakker (2007) recognize the political differences between the “Commons” versus the “Commodity” nature of water.

The GWP (2000) states that the total value of water includes its economic value (value to users of water, net benefits from return flows and from indirect uses, and adjustment for social objectives) and the intrinsic value. O High-Level Panel on Water (HLPW) outcome document – Making Every Drop Count (HLPW 2018), suggested five principles to value water: (1) recognize and embrace the multiple values of water, including deep interconnections between human needs, well-being social and economic, spiritual beliefs and the viability of ecosystems; (2) Reconcile values and build trust in an equitable, transparent and inclusive way, dealing with trade-offs and emphasizing that inaction generates higher costs; (3) Valuing, managing and protecting all water sources; (4) Promote education and public awareness of the intrinsic value of water, and (5) Invest and innovate.

The issue also is approached from different avenues within IWRM, such as the value of ecosystem services and the need for healthy systems for these services to be maintained.

The three approaches explore the issue of service provision, economic instruments, and financing, but this topic is not the subject of discussion as Water Value category within ICM and S2S. ICM and S2S do not present water’s value in their principles; the theoretical debate does not take place in both ICM and S2S.

Therefore, in this category, IWRM stands out from the ICM and S2S approaches and it can contribute to these approaches evolving in this debate.

Comparing the three approaches—a quick overview

The IWRM, ICM and S2S approaches bring their own principles, guidelines, goals, and objectives, which influence the way their structures are proposed. The categorization helped to establish key points to focus comparison, so that this effort can result productive to help advance water management. Categorization also helped to clarify how each approach addresses the sustainable use and conservation of water resources and water security or even in which aspects these approaches present similar or equal concepts and structures but addressed with different names.

The Integration category is present in all three approaches. However, the integrative view of the S2S approach is based on systemic thinking to deal with complexity, which expands the systemic view of the water resource, turning its concerns to the interaction between the parts, the flows, processes and control mechanisms. Therefore, S2S considers the water cycle as a hydrosocial cycle and proposes that the integration is between river basins, coastal areas, and the marine system. In the segments category, S2S stands out because its main targeted segments encompass all segments that the IWRM and ICM include, and, in addition, it adds the open ocean segment. Regarding the Key-flows category, the S2S approach was the only one that was classified as fully compromised. The first element of its conceptual structure is the main flows that connect subsystems in the continuum at different spatial scales and that bring impacts or benefits to the system.

The three approaches were rated as fully-committed to the governance and management category. However, the S2S approach takes a critical view of current water resource governance and management arrangements. Considers that part of the problem is the fact that multiple approaches are applied to the same body of water (in the same continuum), and governance structures are also segment driven and sectorally fragmented. This fragmentation in the way of approaching water resources has deep roots. For example, university programs usually deal with freshwater and saltwater separately; marine sciences are taught in one department and terrestrial ecosystems in another. A similar situation exists in governance structures, where ministries and local authorities have different departments for marine and freshwater issues. The approach advocates for the need to break these silos and understand interconnections to enable better actions across sectors and administrative boundaries. At the core of the approach are Key Flows that link the terrestrial system to the oceans, showing impacts and connections between sectors and guiding solutions that address these diverse trade-offs and nexuses. This doesn’t mean that actions shouldn’t be coordinated at the most appropriate level, but rather that systemic thinking must be present to identify solutions that not only improve the problem locally but also avoid causing larger impacts and problems in other interconnected areas or in the whole system.

Regarding the monitoring and evaluation category, IWRM, ICM, and S2S were classified as fully-committed. S2S advances the proposal for a monitoring and evaluation framework. It incorporates the observations, concerns, and recommendations from the IWRM and ICM approaches and extends the process. Monitoring needs to occur at all stages of the management cycle to enable adaptation during implementation and governance adjustments to ensure a conducive environment. In the S2S approach, systemic thinking, combined with the use of the Theory of Change, has demonstrated the capacity to fill gaps in water monitoring and evaluation.

The blue and green economies are contemplated in the S2S approach and partially reflected in the IWRM and ICM. The S2S has as one of its main objectives in its conceptual structure to guide the design of future initiatives to support “green” and “blue” growth. The IWRM and ICM work with the green and blue economy in some programs and forums, but they do not have the blue and green growth as an objective contemplated in their framework. In the Gender Category, IWRM stands out against the ICM and S2S approaches. IWRM can contribute to these approaches evolving in the integration of gender for coastal zones and marine environments in a complementary way, sharing experiences and tools. Finally, for the Water Value category, IWRM hegemonically recognizes water as an economic good as one of the fundamental principles that guide its structure, in opposition to the idea of water as commons. This principle generates a critical debate within the water sector that influences governance and management. ICM and S2S do not present the Water Value in their principles. At this point, IWRM can bring an excellent contribution for these approaches to evolve in this debate, not least because water is the link and permeates all sectors and resources that generate values in which the approaches are engaged.

Therefore, taking into consideration these “Gender” and “Water Value” categories, the S2S approach needs to deepen the discussion and incorporate the advancements that GIRH has achieved to strengthen its objective of guiding green and blue growth, as indicated by the “Blue and Green Economy” category so that in fact this growth truly represents sustainable development guided by the principles of the SDGs.

The IWRM and ICM are complementary. Nonetheless, their vision remains fragmented in practice because, as we saw in this study, governance and management occur separately despite the recognition that they are interconnected by the upstream-downstream flow. At this point, the S2S approach comes to contribute by uniting them in a common point: water. The S2S approach integrates and, at the same time, complements IWRM and ICM. S2S is based on understanding Earth as a unique system and fresh and marine water systems as a single continuum, acting strictly “in this common ground” between IWRM and ICM, with the key flows connecting the segments and, in consequence, these two approaches.

Conclusion

This research aimed to understand the Source-to-sea approach and identify its relationships and convergences with the approaches of IWRM and ICM and answer the question of whether they are integrative, complementary, or competitive. We used content analysis as part of the investigation method so that it was possible to identify the intentions and perceptions of the concepts, principles, and dimensions adopted by each approach. The classification of elements resulted in 8 categories. Based on Leopold’s matrix, we created a base matrix to process and analyze the relationships between the approaches.

The categorization was useful to establish key points to focus comparison, so that this effort can result productive to help advance water management. Because categorization worked with the core of the sentences meaning and not with precise words employed to communicate ideas, it also helped to clarify if these approaches present similar or equal concepts and structures but addressed with different names.

Based on the key points (categories), S2S, IWRM and ICM were compared to see if they were integrative, complementary, or competing. At the end, it was concluded that the S2S approach brings new elements, revitalizes some methods, and strengthens the governance and management structure of freshwater and marine water resources, enabling a new vision in the continuum where IWRM and ICM are part of the process within a new perspective.

Nonetheless, It is important that this review can be expanded addressing more case studies. It is also critical to identify relationships and connections with landscape approaches. The approach encompasses interdependence and ecological and human influences, which makes it essential to understand how this human-space-water-climate interaction occurs. Considering these aspects, landscape approaches can probably contribute to the S2S approach in understanding these relationships.