1. Introduction
1.1 Background of sustainable development goals
The United Nations sustainable development goals (SDGs) simultaneously address some of society's greatest challenges while also accommodating for sustainable use and extraction of the world's natural resources. Many of these SDGs lack specific quantitative indicators and data, while other SDGs that do have these essentials are only slowly progressing towards their ideal deadline (often 2030), one of which is SDG 14, Conserve and sustainably use the oceans, seas and marine resources for sustainable development. For example, target 14.2: Protect and restore ecosystems, has the indicator, ‘proportion of national exclusive economic zones managed using ecosystem-based approaches’, but no data exist despite having a target completion date of 2020 (Goal 14, 2021) (Supplementary Table S1.1). Pursuit of economic productivity (e.g. agricultural output), infrastructure, energy and waste management improvements are still compromising ecosystems, despite progress towards achieving SDGs and their intent on reducing tradeoffs and incentivizing co-benefits among the SDGs (Gordon et al., Reference Gordon, Finlayson and Falkenmark2010; van Zanten & van Tulder, Reference van Zanten and van Tulder2020). Nexus approaches and biodiversity recovery plans have highlighted two key opportunities for improved SDG implementation: (1) linking among and within human–nature systems and (2) expanding research towards aquatic systems for sustainability initiatives (Arthington, Reference Arthington2021; Liu et al., Reference Liu, Hull, Godfray, Tilman, Gleick, Hoff, Pahl-Wostl, Xu, Chung, Sun and Li2018). One could argue that any progress for human well-being, including biodiversity and its services, will require functioning and healthy freshwater ecosystems – particularly rivers – with natural or near natural flows, or environmental flows as a surrogate of the natural condition (Arthington, Reference Arthington2021). The premise that a modified water cycle can enhance water security at the cost of biodiversity has led to the precept of environmental flows in managing highly modified and regulated rivers across the world (Arthington et al., Reference Arthington, Bhaduri, Bunn, Jackson, Tharme, Tickner, Young, Acreman, Baker, Capon, Horne, Kendy, McClain, Poff, Richter and Ward2018; Grill et al., Reference Grill, Lehner, Thieme, Geenen, Tickner, Antonelli, Babu, Borrelli, Cheng, Crochetiere, Macedo, Filgueiras, Goichot, Higgins, Hogan, Lip, McClain, Meng, Mulligan and Zarfl2019; Vörösmarty et al., Reference Vörösmarty, McIntyre, Gessner, Dudgeon, Prusevich, Green, Glidden, Bunn, Sullivan, Liermann and Davies2010).
Environmental flows are ‘the quantity, timing, and quality of water flows required to sustain freshwater and estuarine ecosystems and the human livelihoods and well-being that depend on these ecosystems’ (Arthington et al., Reference Arthington, Bhaduri, Bunn, Jackson, Tharme, Tickner, Young, Acreman, Baker, Capon, Horne, Kendy, McClain, Poff, Richter and Ward2018). In 2007, prior to the enactment of the SDGs, 750 scientists, economists, engineers, resource managers and policy-makers from over 50 countries proclaimed that environmental flows are the foundation for many water-related SDGs, and summarized this intent in what is now known as the Brisbane Declaration (Arthington et al., Reference Arthington, Naiman, Mcclain and Nilsson2010) (Supplementary Figure S2.1). The SDGs were developed with reference to existing international commitments that express the most relevant global priorities (Kim, Reference Kim2016), but the inclusion of environmental flows and rivers was not explicit. A decade later the revised declaration re-emphasized ‘an urgent call for action to protect and restore environmental flows and aquatic ecosystems for their biodiversity, intrinsic values, and ecosystem services, as a central element of integrated water resources management, and as a foundation for achievement of water-related SDGs’ (Arthington et al., Reference Arthington, Bhaduri, Bunn, Jackson, Tharme, Tickner, Young, Acreman, Baker, Capon, Horne, Kendy, McClain, Poff, Richter and Ward2018).
Despite evidence indicating that rivers are directly and indirectly linked to many of the SDGs and their targets, SDG targets have not typically included provisions and indicators for rivers and their appropriate management, which would enable resilient outcomes. The importance of river health for food value that is provided by river-based fisheries is a direct example of one way that rivers affect SDG 14 through target 14.4, which measures the sustainable management of fisheries (Opperman et al., Reference Opperman, Orr, Baleta, Garrick, Goichot, McCoy, Morgan, Turley and Vermeulen2018). An indirect example would be the extraction of groundwater to support agricultural production (Falke et al., Reference Falke, Fausch, Magelky, Aldred, Durnford, Riley and Oad2011), which would support SDG target 2.4, ‘sustainable food production and resilient agricultural practices’. This gap emphasizes a key consideration for the future progress of the SDGs; if river systems sit at the crossroads among and between SDGs, how will resilient rivers be achieved if SDG progress inherently comes with tradeoffs? Furthermore, what pathways in policy, research and management are necessary to achieve this future, particularly for the ecosystems in which rivers are connected? The precedence of this gap becomes readily apparent as the global conditions of rivers degrade.
SDG 6 (‘Ensure access to water and sanitation for all’) has four targets that are directly related to river systems: wastewater and water quality (6.3), freshwater stress and water-use efficiency (6.4), integrated water resources management and transboundary cooperation (6.5) and protection of freshwater systems (6.6). Trends for these targets are progressing positively, but there is a substantial data gap with most data for these indicators coming from high-GDP countries (United Nations Environment Programme, 2021b). Additionally, some of the indicators used within this target are subject to criticism as they may not reflect actual ecosystem condition but just metrics of water body change (Ladel et al., Reference Ladel, Mehta, Gulemvuga and Namayanga2020; Vanham et al., Reference Vanham, Hoekstra, Wada, Bouraoui, de Roo, Mekonnen, van de Bund, Batelaan, Pavelic, Bastiaanssen, Kummu, Rockström, Liu, Bisselink, Ronco, Pistocchi and Bidoglio2018). For indicators focused on effective management, increased management may not translate to appropriate management actions. As illustrated in the monitoring methodology of indicator 6.6.1, metrics are prefaced with the condition: ‘The direction [of an indicator] is recorded as either positive or negative but the use of this terminology does not necessarily imply a positive or negative state of the water-related ecosystem being monitored’ (United Nations Environment Programme, 2021a, 2021b; UN-Water, 2017). To accelerate progress for SDG 6 targets globally, five areas of action have been suggested by the latest SDG 6 report, which are: (1) capacity development, (2) data and information, (3) innovation, (4) financing and (5) governance. One pathway that incentivizes development of these areas simultaneously is the participation of institutions in the SDG 6 IWRM Support programme, where numerous tools and packages are available to facilitate adoption. Parts of the scientific community consider SDG 6 progress as ‘off-track’ and at the will of other SDGs that require substantial water resources. The dilemma of tradeoff and synergies sits at the forefront of SDG 6 progress and the progress of other SDGs, including SDG 14 (Essex et al., Reference Essex, Koop and Van Leeuwen2020). Progress in SDG 6 should support progress in SDG 14, but the strength of this relationship is understudied.
1.2 Current status of rivers and freshwater biodiversity
Rivers and freshwater biodiversity have systematically been altered and degraded for many centuries, with the vast majority of rivers over 1000 km in length being no longer free-flowing (Grill et al., Reference Grill, Lehner, Thieme, Geenen, Tickner, Antonelli, Babu, Borrelli, Cheng, Crochetiere, Macedo, Filgueiras, Goichot, Higgins, Hogan, Lip, McClain, Meng, Mulligan and Zarfl2019). In Europe, for example, more than 1 million barriers fragment river systems (Belletti et al., Reference Belletti, Garcia de Leaniz, Jones, Bizzi, Börger, Segura, Castelletti, van de Bund, Aarestrup, Barry, Belka, Berkhuysen, Birnie-Gauvin, Bussettini, Carolli, Consuegra, Dopico, Feierfeil, Fernández and Zalewski2020) and indications of the status of freshwater fish biodiversity, such as in the living planet index, have reported declines of over 70% for both anadromous and potamodromous fishes (Deinet et al., Reference Deinet, Scott-Gatty, Rotton, Twardek, Marconi, McRae, Baumgartner, Brink, Claussen, Cooke, Darwall, Eriksson, Garcia de Leaniz, Hogan, Royte, Silva, Thieme, Tickner, Waldman and Berkhuysen2020). Conflicts concerning water rights have consequences ranging from lawsuits to armed violent conflicts, which occur both within and between nations (Levy & Sidel, Reference Levy and Sidel2011). Furthermore, pressures from climate change, such as seasonal and decadal droughts, pose potentially harmful outcomes to both perennial river systems (Kovach et al., Reference Kovach, Dunham, Al-Chokhachy, Snyder, Letcher, Young, Beever, Pederson, Lynch, Hitt, Konrad, Jaeger, Rea, Sepulveda, Lambert, Stoker, Giersch and Muhlfeld2019) and intermittent rivers (Datry et al., Reference Datry, Larned and Tockner2014).
Tickner et al. (Reference Tickner, Opperman, Abell, Acreman, Arthington, Bunn, Cooke, Dalton, Darwall, Edwards, Harrison, Hughes, Jones, Leclère, Lynch, Leonard, McClain, Muruven, Olden and Young2020) urged that an emergency recovery plan for freshwater biodiversity loss is needed and emphasized that the current SDGs (as well as Aichi Biodiversity Targets – Convention on Biological Diversity) need substantial refinement to better serve rivers more comprehensively. One of the major similarities between this recovery plan and the Brisbane Declaration was the recognition of the absence of environmental flow targets and management. Arguably, the most critical SDG that fails to mention the importance of rivers and environmental flows to its own success is SDG 14 – ‘Life below water’. Even prior to the development of the SDGs, the obvious connection between rivers and marine systems was not consistently included in the fisheries policy arena, nor has this connection been articulated in SDG 14 and its targets (Elliott et al., Reference Elliot, Lynch, Phang, Cooke, Cowx, Claussen, Dalton, Darwall, Harrison, Murchie, Steel and Stokes2022). To fulfil the targets proposed by SDG 14, clear recognition of riverine resilience in both policy and practice is needed.
1.3 Connecting SDG 14 to rivers
River systems contribute to marine ecosystem form and functioning, resilience and ecosystem services, but they do not feature in SDG 14. Instead, freshwater systems are integrated in several other SDGs, for example in SDG 15 – ‘Life on land’ and SDG 6 – ‘Clean water and sanitation’. This disconnect fails to show the mutual opportunities that can benefit the sustainability and resilience of both freshwater and marine systems. The SDG 14 targets 14.1 – reduce marine pollution, 14.2 – protect and restore ecosystems, 14.3 – reduce ocean acidification, and 14.5 – conserve coastal and marine areas, are broad marine ecosystem goals, but they are being influenced by society's current interactions with rivers and watersheds. For example, experts have demonstrated that 70–80% of marine plastic pollution originates from land-based activities and makes its way to the sea via rivers (Duncan et al., Reference Duncan, Davies, Brooks, Chowdhury, Godley, Jambeck, Maddalene, Napper, Nelms, Rackstraw and Koldewey2020). Furthermore, the fisheries-focused targets of SDG 14 do not currently account for the inland fisheries sector (Elliott et al., Reference Elliot, Lynch, Phang, Cooke, Cowx, Claussen, Dalton, Darwall, Harrison, Murchie, Steel and Stokes2022) and dependency on resilient river ecosystems, despite the importance of this sector in supporting some of the world's most vulnerable populations (Funge-Smith & Bennett, Reference Funge-Smith and Bennett2019). Additionally, SDG 14 neglects to incorporate how rivers may influence marine fish production, habitat loss, fisheries economics and fisheries policy.
This review aims to demonstrate links between rivers and marine ecosystems with regards to SDG 14's targets, such that policy and management strategies relevant to achieving sustainability goals can be proposed. In this review we present recent literature and specific examples illustrating how rivers and their environmental flows directly or indirectly link to SDG 14's progress or lack of progress. We also show how key actions recommended by the river science community can help build win-win sustainability outcomes for rivers and marine ecosystems. This review is separated into three main themes building off the SDG 14 targets and their means of implementation: (1) rivers contribute to marine and estuary ecosystem resilience (targets 14.1, 14.2, 14.3, 14.5); (2) resilient rivers are part of global fisheries sustainability concerns (targets 14.4, 14.6, 14.7, 14.B) and (3) enhancing marine policy and research from a river and environmental flows perspective (targets 14.A, 14.C). An overview of targets and indicators is provided in the Supplementary information. The first two themes present how rivers are relevant to the above listed SDG targets, assess existing indicators with or without the consideration of rivers, and provide potential mutual sustainability opportunities to improve marine ecosystems. The last theme focuses on joint policy opportunities between freshwater and marine ecosystems. We also include in a specific case study for the Mekong river highlighting the key findings from the review in an applied context.
2. Rivers contribute to marine and estuary ecosystem resilience
2.1 Relevance of river processes to SDG 14
Marine debris and nutrient pollution from land-based activities are predominantly transported to coastal and marine ecosystems by rivers (Duncan et al., Reference Duncan, Davies, Brooks, Chowdhury, Godley, Jambeck, Maddalene, Napper, Nelms, Rackstraw and Koldewey2020; Harris et al., Reference Harris, Westerveld, Nyberg, Maes, Macmillan-Lawler and Appelquist2021; Schmidt et al., Reference Schmidt, Krauth and Wagner2017; Strokal et al., Reference Strokal, Spanier, Kroeze, Koelmans, Flörke, Franssen, Hofstra, Langan, Tang, van Vliet, Wada, Wang, van Wijnen and Williams2019, Reference Strokal, Kahil, Wada, Albiac, Bai, Ermolieva, Langan, Ma, Oenema, Wagner, Zhu and Kroeze2020). For example, an estimated 1.15–2.41 million tonnes of plastic debris flow from rivers into oceans every year with temporal variations attributed to river hydrodynamics (Lebreton et al., Reference Lebreton, Van Der Zwet, Damsteeg, Slat, Andrady and Reisser2017). The Mekong river, for example, accounts for an estimated 40,000 tonnes of plastic into the world's oceans each year. The wide spectrum of plastic debris sizes, chemical additives and chemical compositions transported by rivers poses multiple environmental hazards for the receiving freshwater and marine ecosystems (van Emmerik & Schwarz, Reference van Emmerik and Schwarz2020). Similarly, river basins that encompass agriculture production can transport large quantities of nutrient pollution, such as nitrogen and phosphorus, from point and non-point sources to marine ecosystems (Strokal et al., Reference Strokal, Ma, Bai, Luan, Kroeze, Oenema, Velthof and Zhang2016). One example of this is the Mississippi river, where decades of nutrient runoff has resulted in a hypoxic dead zone in the Gulf of Mexico (Tian et al., Reference Tian, Xu, Pan, Yao, Bian, Cai, Hopkinson, Justic, Lohrenz, Lu, Ren and Yang2020; Turner & Rabalais, Reference Turner and Rabalais2003). The flow rate of a river is a major process that affects the delivery of nutrient loading (Pinckney et al., Reference Pinckney, Paerl, Tester and Richardson2001). Predicted increases in eutrophication and hypoxia events, as well as plastic pollution from rivers, have affected and will continue to affect fisheries and food webs in the marine environment (Borrelle et al., Reference Borrelle, Ringma, Law, Monnahan, Lebreton, McGivern, Murphy, Jambeck, Leonard, Hilleary, Eriksen, Possingham, Frond, Gerber, Polidoro, Tahir, Bernard, Mallos, Barnes and Rochman2020; Rabalais et al., Reference Rabalais, Turner, Díaz and Justić2009). Flooding, magnified by climate change and deforestation, could potentially increase these impacts further (Polvi et al., Reference Polvi, Lind, Persson, Miranda-Melo, Pilotto, Su and Nilsson2020), for example, via washing microplastic particles present in soil and other terrestrial environments into waterways (Mouyen et al., Reference Mouyen, Longuevergne, Steer, Crave, Lemoine, Save and Robin2018; Vogelsang et al., Reference Vogelsang, Lusher, Dadkhah, Sundvor, Umar, Ranneklev, Eidsvoll and Meland2019).
Aside from the transportation of pollutants, the provisioning and regulating services from rivers play a vital role in coastal and marine ecosystem resilience. For instance, access to freshwater is essential for mangrove productivity (Santini et al., Reference Santini, Reef, Lockington and Lovelock2015), and transport and deposition of riverine sediments can have strong linkages to coastal zones and fisheries (Broadley et al., Reference Broadley, Stewart-Koster, Burford and Brown2022; Darnaude et al., Reference Darnaude, Salen-Picard, Polunin and Harmelin-Vivien2004; Kondolf et al., Reference Kondolf, Gao, Annandale, Morris, Jiang, Zhang, Cao, Carling, Fu, Guo, Hotchkiss, Peteuil, Sumi, Wang, Wang, Wei, Wu, Wu and Yang2014a, Reference Kondolf, Rubin and Minear2014b). In addition, water extraction and diversion is expected to increase in many areas around the world and the current availability of groundwater will not meet the needs of 1.7 billion people in the near future, particularly in North America and Asia (Gleeson et al., Reference Gleeson, Wada, Bierkens and van Beek2012). One extreme example is the Colorado river, where these water-development needs have resulted in the river no longer reaching the ocean (Pitt et al., Reference Pitt, Kendy, Schlatter, Hinojosa-Huerta, Flessa, Shafroth, Ramírez-Hernández, Nagler and Glenn2017). Building upon this predicament, natural phenomena, such as droughts and floods, can also influence river-connected coastal ecosystems by interrupting salinity dynamics (Lee et al., Reference Lee, Black, Bosserel and Greer2012), increasing mangrove mortality (Saintilan et al., Reference Saintilan, Rogers, Kelleway, Ens and Sloane2019), and changing fisheries production (Ferguson et al., Reference Ferguson, Ward, Ye, Geddes and Gillanders2013; Gillson et al., Reference Gillson, Suthers and Scandol2012).
2.2 Evaluating SDG 14 indicators and identifying mutual opportunities
Target 14.1 (reduce marine pollution) seeks to prevent and significantly reduce all forms of pollution using an index focused on coastal areas that shares complementary goals with SDG 12.4: ‘responsible management and production of chemicals and waste’. Despite having an earlier proposed completion date of 2025 instead of 2030, indexes for these targets have only been recently approved (Recuero Virto, Reference Recuero Virto2018; United Nations Environment Programme, 2021a, 2021b). The new eutrophication index focuses primarily on water quality levels in the marine environment (e.g. chlorophyll-a, dissolved inorganic nitrogen, dissolved inorganic phosphorus), while the new marine plastic debris index focuses on floating debris in the ocean as well as beach litter (United Nations Environment Programme, 2021a, 2021b). Both of these indexes include monitoring parameters concerning rivers (e.g. river discharge, river water quality, river litter), but are relegated to ‘level 3’, which are supplementary indicators and not described in detail. The eutrophication index suggests that hydrology data are needed to quantify nutrient export, but instead focuses on discharge and retention. Shifting river measurements to a supplemental priority limits the potential to tackle SDG 14 issues before they enter the marine environment. In order to include riverine measurements into SDG 14 progress we highlight a more holistic array of datasets that could enable evidence-based decision-making and address issues at the source (Supplement 2).
While many marine systems are threatened by both sea and river sources, ecosystem-based management seems to be a top management priority for SDG 14, as one indicator for target 14.2 seeks to quantify the number of countries using ecosystem-based approaches to manage marine areas (United Nations Environment Programme, 2021a, 2021b). The scope of this management approach is often designed primarily to address marine issues at regional scales (Link, Reference Link2017), such as fisheries management regimes that are already seeking ecosystem management programmes through policy initiatives (Link, Reference Link2017). Extending this management approach to include rivers, estuaries and seas may require a meta-ecosystem perspective that emphasizes cross-ecosystem flows (Gounand et al., Reference Gounand, Harvey, Little and Altermatt2018). This has been recognized in recent river basin-to-ocean scale plastic waste management programmes and frameworks (Mathews et al., Reference Mathews, Tengberg, Sjödin and Liss Lymer2019; Moura et al., Reference Moura, Falcão, da Silva, Neto, Montenegro and da Silva2020). Combining efforts between marine, estuarine and freshwater ecosystem-based management to manage nature's contributions to people (Pascual et al., Reference Pascual, Balvanera, Díaz, Pataki, Roth, Stenseke, Watson, Başak Dessane, Islar, Kelemen, Maris, Quaas, Subramanian, Wittmer, Adlan, Ahn, Al-Hafedh, Amankwah, Asah and Yagi2017), and achieve SDG 14 targets could be a synergistic outcome, but would also require extensive planning (Langhans et al., Reference Langhans, Domisch, Balbi, Delacámara, Hermoso, Kuemmerlen, Martin, Martínez-López, Vermeiren, Villa and Jähnig2019; Needles et al., Reference Needles, Lester, Ambrose, Andren, Beyeler, Connor, Eckman, Costa-Pierce, Gaines, Lafferty, Lenihan, Parrish, Peterson, Scaroni, Weis and Wendt2015).
Including river impact radius is a valuable approach to evaluate how rivers may impact marine regions given ocean processes (Fredston-Hermann et al., Reference Fredston-Hermann, Brown, Albert, Klein, Mangubhai, Nelson, Teneva, Wenger, Gaines and Halpern2016). One example, the dispersal capabilities of plastic pollution via large oceanic currents, means that plastic emissions from rivers can threaten sensitive marine habitats and protected areas far beyond their immediate near-shore and coastal environments (Harris et al., Reference Harris, Westerveld, Nyberg, Maes, Macmillan-Lawler and Appelquist2021; Huserbråten et al., Reference Huserbråten, Hattermann, Broms and Albretsen2022; Lebreton et al., Reference Lebreton, Van Der Zwet, Damsteeg, Slat, Andrady and Reisser2017) (Figure 1). In addition, Lindo (Reference Lindo2020) showed that terrestrial species can conduct transoceanic dispersal by riding on top of macroplastic debris, which has the potential to introduce new species in non-native habitats. Since most marine plastic pollution originates from land-based activities, often via rivers (Duncan et al., Reference Duncan, Davies, Brooks, Chowdhury, Godley, Jambeck, Maddalene, Napper, Nelms, Rackstraw and Koldewey2020; Sundt et al., Reference Sundt, Schulze and Syversen2014), filling the knowledge gap of relations between river networks health and the presence of plastic pollution in the marine environment could support a connected ecosystem management approach (Azevedo-Santos et al., Reference Azevedo-Santos, Brito, Manoel, Perroca, Rodrigues-Filho, Paschoal, Gonçalves, Wolf, Blettler, Andrade, Nobile, Lima, Ruocco, Silva, Perbiche-Neves, Portinho, Giarrizzo, Arcifa and Pelicice2021). This could be particularly important in relation to the push to conserve large parts of the ocean through marine protected areas (MPAs), which is one of SDG 14's most often achieved targets. The success of MPAs and conservation areas may diminish if they do not have measures in place to manage widely dispersing threats emanating from rivers. Achieving many SDG 14 targets depends on the range at which these issues impact marine systems and goes beyond the river delta.
Figure 1. Map showing how major ocean currents and gyres can widely disperse pollutants, such as plastics, from rivers to MPAs. Projected using a Spilhaus projection, which distorts the map to fit all oceans into a single plane. This ‘fish’ view of oceans demonstrates how interlinked the plastic pollution problem is given the range of dispersal capabilities of plastics. Data for plastic output and dispersal were provided by Harris et al. (Reference Harris, Westerveld, Nyberg, Maes, Macmillan-Lawler and Appelquist2021) and Esri basemaps were used for currents and elevation. MPAs came from protectedplantet.net (UNEP-WCMC, 2019).
Actionable recommendations from the Brisbane Declaration, across governance, management and research bodies suggest the development of adaptive management frameworks that focus on balancing environmental flows for both human and ecological water requirements (Arthington et al., Reference Arthington, Bhaduri, Bunn, Jackson, Tharme, Tickner, Young, Acreman, Baker, Capon, Horne, Kendy, McClain, Poff, Richter and Ward2018). An environmental flows programme focused on river–estuary connections could forge new paths to identify key moments to implement mitigation measures (Stein et al., Reference Stein, Gee, Adams, Irving and Van Niekerk2021). The timing and magnitude of river discharge predictions could, for example, provide insights on plastic dispersal ranges in relation to coast types (Harris et al., Reference Harris, Westerveld, Nyberg, Maes, Macmillan-Lawler and Appelquist2021), or could also be used by managers to know when to clean litter traps to avoid bypass or overflow during a flood event. An environmental flows style framework may also enable development of high-resolution, down-scaled estuarine indexes that provide predictions of ecosystem-wide scenarios given hydrological changes (Van Niekerk et al., Reference Van Niekerk, Taljaard, Adams, Lamberth, Huizinga, Turpie and Wooldridge2019). If ecosystem-based management regimes are achieved in the marine/estuary environment, large-scale flow experiments may help evaluate water management actions for both the river and estuary (Olden et al., Reference Olden, Konrad, Melis, Kennard, Freeman, Mims, Bray, Gido, Hemphill, Lytle, McMullen, Pyron, Robinson, Schmidt and Williams2014).
A failure to accommodate a connected ecosystem perspective may result in lasting changes of the biophysical processes that connect rivers and coastal ecosystems (Thom et al., Reference Thom, Rocheta, Steinfeld, Harvey, Pittock and Cowell2020). Furthermore, overlooking connections between SDG 6 and SDG 14 could result in achieving one SDG, but negatively affect the other (Wang et al., Reference Wang, Janssen, Bazin, Strokal, Ma and Kroeze2022). Developing policies that support both river ecosystem needs as well as estuary and marine needs may improve adoption of environmental flow principles and management. Environmental flow-based management shows promising restoration outcomes for historically over-utilized rivers, and can produce benefits for both rivers and estuaries when appropriately funded (Kendy et al., Reference Kendy, Flessa, Schlatter, de la Parra, Hinojosa Huerta, Carrillo-Guerrero and Guillen2017). Further research to investigate flow–ecology relationships and ecosystem services that directly benefit rivers, estuaries and seas across a range of taxa and industries would also be beneficial (Arthington et al., Reference Arthington, Bhaduri, Bunn, Jackson, Tharme, Tickner, Young, Acreman, Baker, Capon, Horne, Kendy, McClain, Poff, Richter and Ward2018).
3. Resilient rivers are part of the global fisheries sustainability opportunity
3.1 Relevance of river processes to SDG 14
The SDGs do not recognize inland fisheries explicitly, and certainly do not recognize overfishing in lakes and rivers (Allan et al., Reference Allan, Abell, Hogan, Revenga, Taylor, Welcomme and Winemiller2005; Elliot et al., Reference Elliot, Lynch, Phang, Cooke, Cowx, Claussen, Dalton, Darwall, Harrison, Murchie, Steel and Stokes2022; Lynch et al., Reference Lynch, Cowx, Fluet-Chouinard, Glaser, Phang, Beard, Bower, Brooks, Bunnell, Claussen, Cooke, Kao, Lorenzen, Myers, Reid, Taylor and Youn2017), despite fisheries from freshwater ecosystems (connected or unconnected to the marine environment) provide food security, primary protein and nutrition supply to some of the world's least developed nations and roughly 158 million people (Ainsworth et al., Reference Ainsworth, Cowx and Funge-Smith2021; Funge-Smith & Bennett, Reference Funge-Smith and Bennett2019; McIntyre et al., Reference McIntyre, Liermann and Revenga2016). It is important to point out that this issue also affects developed countries for a variety of fishery types (Driscol, Reference Driscol2015; Embke et al., Reference Embke, Rypel, Carpenter, Sass, Ogle, Cichosz, Hennessy, Essington and Zanden2019). Often inland fisheries are highly dispersed, lack infrastructure and management capacity, consist of artisanal or small-scale fishing, are lower in economic value and result in a subsistence-oriented harvest. The combination of these factors makes understanding impacts difficult (Bartley et al., Reference Bartley, Graaf, Valbo-Jørgensen and Marmulla2015). Progress towards improving inland fisheries, as suggested by the United Nation's Rome Declaration (Cooke et al., Reference Cooke, Nyboer, Bennett, Lynch, Infante, Cowx, Beard, Bartley, Paukert, Reid, Funge-Smith, Gondwe, Kaunda, Koehn, Souter, Stokes, Castello, Leonard, Skov and Taylor2021), has become constrained by these limitations and in many cases freshwater fisheries are heavily fished (Lynch et al., Reference Lynch, Bartley, Beard, Cowx, Funge-Smith, Taylor and Cooke2020). Most recently, a 10-year fishing moratorium for the Yangtze river was put into effect on 1 January 2021, which affects roughly 250,000 fishers according to mainstream media (Xiaoyi & Yameng, Reference Xiaoyi and Yameng2021). Drastic management actions, such as fishery closures, can help restore biodiversity and combat overfishing, but can work against the livelihoods and rights (e.g. ancestral, cultural, access arrangements, food security) of small-scale and subsistence fishers.
The construction and removal of water infrastructure (i.e. dams, water diversions, power plants and levees) is an example of a drastic ecosystem intervention that poses both opportunities and challenges for inland fisheries (Grill et al., Reference Grill, Lehner, Thieme, Geenen, Tickner, Antonelli, Babu, Borrelli, Cheng, Crochetiere, Macedo, Filgueiras, Goichot, Higgins, Hogan, Lip, McClain, Meng, Mulligan and Zarfl2019). On the one hand, fishery production of a reservoir can provide ways to increase capture and develop aquaculture, although it rarely replaces the lost river fisheries. On the other hand, barriers may generally result in reductions in fish catches, loss of biodiversity and interruption of ecosystem processes (Hughes, Reference Hughes2021; Petts, Reference Petts1984). They may also prevent migration of diadromous and potadromous fishes if appropriate fish passage facilities are not installed (Winemiller et al., Reference Winemiller, Mcintyre, Castello, Fluet-Chouinard, Giarrizzo, Nam, Baird, Darwall, Lujan and Harrison2016). In extreme cases, large-scale water diversions could both fundamentally change flows within river systems and contribute to water scarcity (Shumilova et al., Reference Shumilova, Tockner, Thieme, Koska and Zarfl2018).
Dams are designed for many purposes, which results in a complex array of impacts for both freshwater and diadromous fishes (Barbarossa et al., Reference Barbarossa, Schmitt, Huijbregts, Zarfl, King and Schipper2020). Often, such infrastructure development involves neither fishing communities in the planning nor discussions around needs for fish passage or other mitigation measures. For example, floodplain fisheries in the Mekong river basin that depend on annual flood regimes have encountered conflict with rice farmers as their levees and water management structures are used to convert floodplains into rice production (Lynch et al., Reference Lynch, Baumgartner, Boys, Conallin, Cowx, Finlayson, Franklin, Hogan, Koehn, McCartney, O'Brien, Phouthavong, Silva, Tob, Valbo-Jørgensen, Vu, Whiting, Wibowo and Duncan2019). Similar conflicts among inland fisheries and irrigation needs have been shown in the Murray–Darling basin (Lynch et al., Reference Lynch, Baumgartner, Boys, Conallin, Cowx, Finlayson, Franklin, Hogan, Koehn, McCartney, O'Brien, Phouthavong, Silva, Tob, Valbo-Jørgensen, Vu, Whiting, Wibowo and Duncan2019). Tributaries that are unobstructed by dams can still be affected by main stem rivers that are dammed because of the backwater effects of inundation and disconnection of migratory fish pathways (swimways) (Worthington et al., Reference Worthington, van Soesbergen, Berkhuysen, Brink, Royte, Thieme, Wanningen and Darwall2022). Riverine capture fisheries, such as the Murray–Darling basin, Brazilian Amazon and the Columbia river, are minimizing further deterioration by supporting science-based management and adapting governance for a shared water body (Cooke et al., Reference Cooke, Nyboer, Bennett, Lynch, Infante, Cowx, Beard, Bartley, Paukert, Reid, Funge-Smith, Gondwe, Kaunda, Koehn, Souter, Stokes, Castello, Leonard, Skov and Taylor2021).
Systems that cannot overcome the challenges associated with existing capture fisheries have also considered further development of aquaculture (Valenti et al., Reference Valenti, Barros, Moraes-Valenti, Bueno and Cavalli2021). Aquaculture is an independent production system that has the potential to increase the economic benefits of these fisheries, but has many economic limitations and risks for inland fishing communities as well (Lynch et al., Reference Lynch, Cowx, Fluet-Chouinard, Glaser, Phang, Beard, Bower, Brooks, Bunnell, Claussen, Cooke, Kao, Lorenzen, Myers, Reid, Taylor and Youn2017). Eutrophication from aquaculture may work against ecosystem management goals intended to reduce excess nutrients and algal blooms in rivers (Wang et al., Reference Wang, Beusen, Liu and Bouwman2020). Lack of regulations, inspections and monitoring can result in the escapement of non-native aquaculture farmed species, which threaten native biodiversity (Nobile et al., Reference Nobile, Cunico, Vitule, Queiroz, Vidotto-Magnoni, Garcia, Orsi, Lima, Acosta, da Silva, do Prado, Porto-Foresti, Brandão, Foresti, Oliveira and Ramos2020). Opportunities to address some of these issues can be seen in Chinese freshwater aquaculture where dramatic changes to reach long-term sustainability initiatives are occurring: eliminating fertilizer application for fish culture, combining aquaculture with rice culture systems, increasing emphasis on aquaponics use, prioritizing culture of indigenous fish species, and increasing regulation (Wang et al., Reference Wang, Li, Gui, Liu, Ye, Yuan and De Silva2018). Subsidies geared to enhance more sustainable practices of freshwater aquaculture can also increase economic benefits and profitability without jeopardizing ecosystem integrity (Aheto et al., Reference Aheto, Acheampong and Odoi2019; Guillen et al., Reference Guillen, Asche, Carvalho, Fernández Polanco, Llorente, Nielsen, Nielsen and Villasante2019).
For marine systems, ending harmful subsidies that enable illegal, unreported and unregulated fishing practices is critical to prevent overfishing and promote sustainability of fish stocks. Conversely, in freshwater systems, fisheries can be harmed by subsidies or incentives that enable barrier construction, unsustainable aquaculture production, sand mining and other undesired by-products, which can alter natural flow regimes, reduce biodiversity and decrease the productivity of fish communities (Ainsworth et al., Reference Ainsworth, Cowx and Funge-Smith2021; Arantes et al., Reference Arantes, Fitzgerald, Hoeinghaus and Winemiller2019; Hackney et al., Reference Hackney, Darby, Parsons, Leyland, Best, Aalto, Nicholas and Houseago2020; Kano et al., Reference Kano, Dudgeon, Nam, Samejima, Watanabe, Grudpan, Grudpan, Magtoon, Musikasinthorn, Nguyen, Praxaysonbath, Sato, Shibukawa, Shimatani, Suvarnaraksha, Tanaka, Thach, Tran, Yamashita and Utsugi2016; Pelicice et al., Reference Pelicice, Azevedo-Santos, Vitule, Orsi, Lima Junior, Magalhães, Pompeu, Petrere and Agostinho2017). Subsidies for detrimental developments on rivers directly contribute to the degradation of ecosystem resilience and productivity, jeopardizing any existing fishing enterprises. For example, Badcock and Lenzen (Reference Badcock and Lenzen2010) found that global financial subsidies for hydropower totalled 116 billion USD between 1960 and 2007. The total subsidies for all dams, not just hydropower, during this time period is unclear, but recent estimates of large hydroelectric projects (over 50 MW) was 16 billion USD in 2018 (United Nations Environment Programme & Frankfurt School-UNEP Centre, 2019) and for small hydropower development it was approximately 170 million euros in 2018 (Gallop et al., Reference Gallop, Vejnović and Pehchevski2019).
Disagreement among stakeholders has made it unclear whether hydropower should be expanded to assist with efforts to decarbonize energy production and whether subsidies, such as the Kyoto Protocol's clean development mechanism, should be used to support this initiative (Ascher, Reference Ascher2021; Fearnside, Reference Fearnside2015; Zarfl et al., Reference Zarfl, Lumsdon, Berlekamp, Tydecks and Tockner2015). As the cost of installing wind, solar and battery storage decreases, developing countries must decide on which renewable energy sources to invest (Thieme et al., Reference Thieme, Tickner, Grill, Carvallo, Goichot, Hartmann, Higgins, Lehner, Mulligan, Nilsson, Tockner, Zarfl and Opperman2021). Construction of hydropower dams is not only considered a viable means to meet SDG 7 (ensure access to affordable, reliable, sustainable and modern energy for all), but is a key investment goal for both hydropower developers and some global funding agencies (World Commission on Dams, 2000). Figure 2 highlights hydropower financing flows from 2000 to 2019, and according to the International Renewable Energy Agency (2022), total transactions reached 92.51 billion USD. The top five recipients were Brazil, Nigeria, Pakistan, Lao PDR and Ethiopia, and the largest donor was China. The implications for global financing of hydropower projects are directly linked to the future resilience of river systems, environmental flows and fishing-related targets of SDG 14, and many other food security-related SDGs as well as energy-related SDGs. The accessibility and increase of water security may provide opportunities for SDG 2 (end hunger, achieve food security and improved nutrition and promote sustainable agriculture) if agricultural development is pursued at the cost of SDG 14. Synergies between SDG 14, SDG 2 and SDG 3 (ensure healthy lives and promote well-being for all at all ages) become more realistic if a healthy river ecosystem is maintained. Tradeoffs and synergies among SDGs is not a new issue but solutions are often case-by-case specific where there is potential for conflict among stakeholders (Thieme et al., Reference Thieme, Tickner, Grill, Carvallo, Goichot, Hartmann, Higgins, Lehner, Mulligan, Nilsson, Tockner, Zarfl and Opperman2021).
Figure 2. Bee-swarm plot showing the hydropower finance transactions by financing type from 2000 to 2019. Regions on the y-axis are the location of the recipient country. Data were retrieved from International Renewable Energy Agency (2022) and plotted using RAWGraphs (Mauri et al., Reference Mauri, Elli, Caviglia, Uboldi and Azzi2017).
3.2 Evaluating SDG 14 indicators and identifying mutual opportunities
Fishing at sustainable levels, implementing policies to restrict harmful fishing subsidies, increasing economic output of fisheries, and providing support for small-scale fishers (targets 14.4, 14.6 and 14.B) could be readily adapted to inland fisheries. One of the greatest challenges lies in the international characteristics of many of the world's large rivers. These transboundary rivers may have complex socio-ecological relationships concerning fishing, which may lead to conflict among different stakeholders (Ainsworth et al., Reference Ainsworth, Cowx and Funge-Smith2021). For example, water abstraction from adjacent aquifers may also have multinational dimensions, issuing another series of challenges. Polycentric-governance is a potential opportunity that can supplement or even replace existing state-based governance systems to better accommodate transboundary issues in a flexible manner (Baltutis & Moore, Reference Baltutis and Moore2019). Improving science-based management for these systems may be challenging for migratory species that cross political boundaries and ecosystems. The likely suspects framework is one potential approach that attempts to unify management of Atlantic salmon (Salmo salar) across its life history, which includes both marine and freshwater systems (Bull et al., Reference Bull, Gregory, Rivot, Sheehan, Ensing, Woodward and Crozier2022). The ‘swimway’ management approach is a recommendation for freshwater migratory fish species that span multiple basins and political jurisdictions (Pracheil et al., Reference Pracheil, Pegg, Powell and Mestl2012; Worthington et al., Reference Worthington, van Soesbergen, Berkhuysen, Brink, Royte, Thieme, Wanningen and Darwall2022). Similarly, creating agreements for sustainable societal developments may require cooperation at multiple scales throughout a river basin to avoid power hierarchies (e.g. upstream and downstream socio-political dynamics).
Prohibiting certain fishing activities and river development subsidies that contribute to unsustainable practices and less resilient marine and freshwater systems will require different strategies. Many large rivers intersect with multiple countries that may have competing interests in regards to both energy and food production (e.g. the Mekong river intersects China, Myanmar, Thailand, Lao PDR, Cambodia and Vietnam). Implementation of international instruments focused on dam development incentives – particularly for developing and least developed countries – may need to operate at a transnational scale to avoid conflict over downstream water requirements. Unless mechanisms are in place to override activities in the watershed, there is always the risk that countries will act independently. For example, proposed dam development projects in free-flowing rivers over 500 km are focused in Asia, South America and Africa, which have the potential to: (1) affect some of the world's largest river basins and deltas; (2) involve multiple countries and (3) have implications for estuaries and marine environments (Thieme et al., Reference Thieme, Tickner, Grill, Carvallo, Goichot, Hartmann, Higgins, Lehner, Mulligan, Nilsson, Tockner, Zarfl and Opperman2021). Where aquaculture is being developed, careful consideration should be warranted to ensure artisanal fisheries are not substituted by aquaculture production. In the case of sand mining, regulating and monitoring, which is often not conducted, is just beginning to understand longitudinal impacts on the river system and the connected marine system (Hackney et al., Reference Hackney, Darby, Parsons, Leyland, Best, Aalto, Nicholas and Houseago2020).
Application of legal, regulatory, policy or institutional frameworks for riverine small-scale fisheries can be improved by developing inclusive adaptive management programmes that incorporate fisher values and knowledge. Emphasis is particularly focused on full and equal participation of small-scale fishing communities and associated cultures for all parts of the governance process: planning, assessment, implementation, monitoring and management. This approach may present opportunities to subsidize sustainable development projects that can directly increase economic benefits from river fisheries. This co-development approach also provides a straightforward opportunity in making the planning process gender-inclusive, which has met resistance historically, despite high proportions of the workforce being women (Bartley et al., Reference Bartley, Graaf, Valbo-Jørgensen and Marmulla2015; Biswas et al., Reference Biswas2018; Harper et al., Reference Harper, Adshade, Lam, Pauly and Sumaila2020).
For riverine or reservoir capture fisheries, opportunities exist to optimize dam operations to integrate with fish life history requirements. However, such options are often hard to design and even harder to predict (Holtgrieve et al., Reference Holtgrieve, Arias, Ruhi, Elliott, Nam, Ngor, Rasanen and Sabo2018; Olden et al., Reference Olden, Konrad, Melis, Kennard, Freeman, Mims, Bray, Gido, Hemphill, Lytle, McMullen, Pyron, Robinson, Schmidt and Williams2014; Richter & Thomas, Reference Richter and Thomas2007; Sabo et al., Reference Sabo, Ruhi, Holtgrieve, Elliott, Arias, Ngor, Rasanen and Nam2017; Williams, Reference Williams2018). The Brisbane Declaration suggests environmental flows should be assessed well before the development of new dams, and actively incorporated within the planning process once development commences (Arthington et al., Reference Arthington, Bhaduri, Bunn, Jackson, Tharme, Tickner, Young, Acreman, Baker, Capon, Horne, Kendy, McClain, Poff, Richter and Ward2018). Adopting an adaptive management approach for existing large infrastructure may also help promote environmental flows in a cost-effective manner (Olden et al., Reference Olden, Konrad, Melis, Kennard, Freeman, Mims, Bray, Gido, Hemphill, Lytle, McMullen, Pyron, Robinson, Schmidt and Williams2014). For systems where reservoir development is appropriate, consideration of multi-purpose operation and optimization could increase co-benefits as opposed to single-purpose implementation (Bhaduri et al., Reference Bhaduri, Bogardi, Siddiqi, Voigt, Vörösmarty, Pahl-Wostl, Bunn, Shrivastava, Lawford, Foster, Kremer, Renaud, Bruns and Osuna2016). Dams have broad socio-ecological impacts upstream and downstream of their reservoir (Richter et al., Reference Richter, Sandra, Carmen, Thayer, Bernhard, Allegra and Morgan2010), and this issue persists well after the lifespan of the dam has surpassed and restoration is needed (Bellmore et al., Reference Bellmore, Pess, Duda, O'Connor, East, Foley, Wilcox, Major, Shafroth, Morley, Magirl, Anderson, Evans, Torgersen and Craig2019; Hansen et al., Reference Hansen, Forzono, Grams, Ohlman, Ruskamp, Pegg and Pope2019; Perera et al., Reference Perera, Smakhtin, Williams, North and Curry2021; Tullos et al., Reference Tullos, Collins, Bellmore, Bountry, Connolly, Shafroth and Wilcox2016). Broader discussion and debate now concern how funds and subsidies are allocated for dams and their anticipated impacts (Hirsch, Reference Hirsch2010; Thieme et al., Reference Thieme, Tickner, Grill, Carvallo, Goichot, Hartmann, Higgins, Lehner, Mulligan, Nilsson, Tockner, Zarfl and Opperman2021).
4. Case study snapshot: SDG 14 and environmental flow implications for the Mekong river and its delta
The Mekong river is one of the world's most important rivers. It is among the largest in terms of discharge, it is a ‘hotspot’ for freshwater aquatic biodiversity and the river basin supports a population of approximately 60 million people, where 70% of communities are rural and rice farming and fishing are primary occupations. Living aquatic resources, including fish and other aquatic animals, make a vital contribution to regional food security and nutrition, cash income and employment and have strong cultural and religious significance. More than 2.3 million tonnes of fish and a further 0.6–0.9 million tonnes of other aquatic organisms, valued at an estimated 17 billion USD, are harvested annually from the Lower Mekong basin (LMB) downstream of China (Nam et al., Reference Nam, Phommakon, Vuthy, Samphawamana, Hai Son, Khumsri, Peng Bun, Sovanara, Degen and Starr2015)
The resilience of the Mekong basin hinges on the extent of multiple anthropogenic stressors: (1) climate change, (2) dams, (3) sediment mining, (4) groundwater extraction, (5) sea level rise, (6) land-use change, (7) fragmentation, (8) pollution, (9) non-native species and (10) water abstraction (Best & Darby, Reference Best and Darby2020). These stressors directly or indirectly affect the flows in the system, ecosystem functioning of the river's delta and the integrity of the adjacent marine ecosystem. For example, some may directly impact the artisanal fisheries and exploitation of aquatic products along the river, and will have indirect impacts on the fishery, subsistence agriculture and the delta by altering flow dynamics and the movement of sediments (Dugan et al., Reference Dugan, Barlow, Agostinho, Baran, Cada, Chen, Cowx, Ferguson, Jutagate, Mallen-Cooper, Marmulla, Nestler, Petrere, Welcomme and Winemiller2010). The large dams in the Mekong – particularly those in China and the major tributaries of the LMB – alter the flow regime, but also block or alter the passage of aquatic biota and sedimentary materials. The large run-of-river hydropower plants in the mainstream of the LMB also impact movement of aquatic biota and sediments but are less prone to alter the hydrology, except in the few hundred kilometres downstream of the dam where hydropeaking occurs. The size of the migratory fish resource at risk from dams on the Mekong mainstream alone has been estimated at 0.7–1.6 million tonnes per year (equivalent to approximately 30–60% of the annual catch in the Mekong) (DHI, 2015; Mekong River Commission, 2021). This is a conservative estimate because it does not account for the economic benefits that flow from the trade and processing of fish products.
One of the insidious impacts will be the capture of sediments in the impoundments that will fundamentally alter the river form and functioning (Hackney et al., Reference Hackney, Vasilopoulos, Heng, Darbari, Walker and Parsons2021). It is estimated that 96% of the 160 million tonnes historically deposited in the South China Sea (Kondolf et al., Reference Kondolf, Gao, Annandale, Morris, Jiang, Zhang, Cao, Carling, Fu, Guo, Hotchkiss, Peteuil, Sumi, Wang, Wang, Wei, Wu, Wu and Yang2014a, Reference Kondolf, Rubin and Minear2014b) (now estimated at 87 million tonnes per year; Darby et al., Reference Darby, Hackney, Leyland, Kummu, Lauri, Parsons, Best, Nicholas and Aalto2016) will be captured and deplete the sediment deposition in the floodplain and coastal regions. This problem with sediment depletion by the dams is exacerbated by sand and gravel mining in the lower basin, with around 55 million tonnes removed annually, considerably more than what is naturally transported in the system under the current damming regime (Hackney et al., Reference Hackney, Vasilopoulos, Heng, Darbari, Walker and Parsons2021). The further consequences of this loss in sediment is the reduction in nutrient transport and thus productivity of aquatic plants and animals, especially in the flood plain areas of the LMB (Kondolf et al., Reference Kondolf, Schmitt, Carling, Darby, Arias, Bizzi, Castelletti, Cochrane, Gibson, Kummu, Oeurng, Rubin and Wild2018), and also in the South China Seas fisheries, which currently yields about 500,000–726,000 tonnes per year. In addition, the sediment depletion is leading to considerable coastal erosion, which is currently up to 12 m per year (DHI, 2015), affecting mangrove forests and nursery areas of many fish and shellfish species.
These changes brought about by the flow regulation and sediment depletion have a considerable impact on achieving SDG 14 and targets 14.4 and 14.B in terms of stock recovery and sustaining small-scale fisheries. The disruption to ecosystem functioning, reduction in extent and duration of flooding in the LMB, erosion of coastal habitat and loss of productivity of coastal fisheries in the South China Sea all compromise the extensive small-scale and subsistence fisheries, and ultimately access to critical aquatic resources that sustain millions of people in the region. To bridge the gap between SDG 14 targets and the guiding environmental flow principles of the Brisbane Declaration, we highlight how this dual approach can address the Mekong river's most pressing challenges. Table 1 provides an overview of SDG 14 targets in relation to the organizational units as proposed in the Brisbane Declaration to highlight how environmental flow guidance can mutually benefit both riverine goals and marine-focused targets. The mentioned references support and describe the critical issue in more detail and also highlight how alternative definitions of environmental flows that emphasize the inclusion of sediments and transported material (de Jalón et al., Reference de Jalón, Bussettini, Rinaldi, Grant, Friberg, Cowx, Magdaleno and Buijse2016) may be critical to connected riverine–marine systems.
Table 1. Overview of possible actions that organizational bodies could undertake for addressing critical river and marine issues in the Mekong river basin and delta
Structure and guidance of this table builds off the ideas proposed in the Brisbane Declaration (Supplement S2). Targets 14.3, 14.6 and 14.7 were removed as no direct linkage to the river or catchment is present for this system. This table is not a comprehensive list but is to highlight the largest issues for this international system and encourage others to consider a similar evaluation for their own river-to-sea continuum.
The Mekong river system has a variety of issues that span waste management, natural resources and political challenges that are both directly and indirectly related to the environmental flows of the system. Supplementary Figure S2.1 showcases the Brisbane Declaration as primary components of a ‘planetary’ gear system, how each component relates to the six primary themes of the declaration and are scaled to the three different stakeholder organizations: leadership and governance, management and research. This illustrates the profound importance of a cooperatively driven system maintained by scientifically rigorous data as key requirements for future advancement and application of environmental flows. Using the ‘planetary gear’ view and the Brisbane Declaration as inspiration, we applied its framework of leadership and governance, management and research to show possible mutual opportunities that can benefit the river and the marine system (Table 1). Of course, not all of SDG 14's targets are applicable, which is to be expected for any river system. The main takeaway from Table 1 is to showcase how river–marine issues can be readily shown as win-win opportunities and it is anticipated that other river systems can develop site-specific strategies and achieve similar mutual outcomes. Bringing together stakeholders from both systems will ideally bring about a more cohesive and functioning operation towards conservation goals and sustainable development.
5. Enhancing marine outcomes through river and catchment policy
The current relationship between society and the global water cycle is unsustainable (Abbott et al., Reference Abbott, Bishop, Zarnetske, Minaudo, Chapin, Krause, Hannah, Conner, Ellison, Godsey, Plont, Marçais, Kolbe, Huebner, Frei, Hampton, Gu, Buhman, Sara Sayedi and Pinay2019). Environmental flows comprise primarily the surface water aspects of freshwater use; however, while important, contextualizing such efforts into broader water planetary boundaries may yield even greater outcomes (Gleeson et al., Reference Gleeson, Wang-Erlandsson, Zipper, Porkka, Jaramillo, Gerten, Fetzer, Cornell, Piemontese, Gordon, Rockström, Oki, Sivapalan, Wada, Brauman, Flörke, Bierkens, Lehner, Keys and Famiglietti2020). The previous sections highlighted the reliance between river health and marine ecosystem health as well as their direct benefits to society. To maintain the resiliency of well-managed systems and recover the resilience of impacted systems, pathways via policy and management need to be identified and implemented. Special attention to the challenges that prevent linking these systems is ideal areas to develop scale-appropriate legislation, management approaches and policy. In the following sections, we showcase how scalable policies are critical to incorporating environmental flow opportunities.
There are many layers of policy and stakeholders that need to be taken into consideration for policies to function as intended. For example, at the highest level (the transnational level), the European Union Water Framework Directive (WFD-2000/60/EC) is designed to improve surface and groundwater conditions while also linking with the EU Marine Strategy Framework Directive (MSFD). Both policies promote using scalable management plans: for freshwater systems a river basin management system, and for marine systems an integrated coastal management system and an ecosystem-based approach. This push comes from the EU's green deal strategy to become the world's first climate-neutral continent (European Commission. Directorate General for Maritime Affairs and Fisheries, 2019). Although it is unclear how hydropower and dams will be involved during this transition to pursue carbon-neutral energy sources, the marine directive MSFD identified the need for additional measures to address riverine-sourced issues concerning plastic pollution and nutrient runoff. Enhancing policy-driven environmental flow management and data collection in areas such as regulation of rivers, freshwater aquaculture and nutrient runoff, as well as understanding any relationships between flow and hypoxic dead zone areas, and relationships between flow and sensitive habitats, could mutually benefit rivers and marine systems. Other systems could follow suit with their own transnational cooperation, or look to others such as the International Joint Commission (North America: USA and Canada boundary waters), Orange-Senqu River Basin Commission (Africa: Botswana, Namibia, Lesotho and South Africa) or the Mekong River Commission (mentioned in the case study) (Raadgever et al., Reference Raadgever, Mostert, Kranz, Interwies and Timmerman2008).
After transnational agreements, lower on the scale are national laws and regional policies, which more directly influence and regulate how rivers will interact with marine systems. One example that includes the whole range of regulations is the Baltic Sea eutrophication governance. Nine coastal countries (Denmark, Estonia, Finland, Germany, Latvia, Lithuania, Poland, Russia and Sweden) surround the Baltic Sea, and despite mitigations such as wastewater treatments and better agricultural practices in the 1980s and 1990s, the amount of nutrients and sediment that is transported from land-to-river-to-sea is still high. The intergovernmental organization The Helsinki Convention (HELCOM) consists of the nine surrounding coastal countries and the EU as contracting parties. In their work of approaching the objective of a good environmental status and sustainability, they use the instrument Baltic Sea Action Plan (BSAP) (Baltic Sea Action Plan – HELCOM, 2021) and co-operate with management authorities for each river basin. In the BSAP, it is concluded that the nutrient load is still high, and establishment of buffer zones is mentioned as one example of action. Protection of riparian zones along streams and lakes will influence the nutrient loading to the aquatic system since riparian zones filter water, nutrients and sediment (Hasselquist et al., Reference Hasselquist, Mancheva, Eckerberg and Laudon2020). The current removal of protection of riparian buffers in Sweden can function as an example where the Swedish environmental objectives conflict with Agenda 2030 global goals at a national level. Here, the goal of ‘Zero eutrophication’ collides with the goal of a ‘Varied agricultural landscape’, where one goal promotes protection of the riparian buffers and the other one sets to limit buffers to open up the landscape.
Lowest on the scale are local laws, policies and ordinances that can shape how society interacts with rivers before they reach the marine environment. Broadly speaking, storm-water management (Harding et al., Reference Harding, Tagal, Ylitalo, Incardona, Davis, Scholz and McIntyre2020), ice and salt management in colder climates (Szklarek et al., Reference Szklarek, Górecka and Wojtal-Frankiewicz2022) and road development (Kemp & O'Hanley, Reference Kemp and O'Hanley2010) are commonplace in urban settings and directly affect a variety of environmental flow criteria and indirectly affect SDG 14 targets. Terrestrial-focused policies, such as bans or reductions of single-use plastics, can be either national in their implementation or fragmented at a variety of different scales (Adam et al., Reference Adam, Walker, Bezerra and Clayton2020). In the rural setting, land developments may not be concentrated making it harder to enforce and regulate industrial waste products directly entering rivers. For example, in China poor regulation and environmental measures in combination with rural development growth allowed industries to operate without proper waste treatment facilities, resulting in a public health crisis (Wang et al., Reference Wang, Webber, Finlayson and Barnett2008).
At every level of the policy-making environment the problem of the ranking and prioritization of SDG goals exists, both in legislative arenas and implementation. An emerging example that intersects multiple scales concerns SDG 9 (Build resilient infrastructure, promote sustainable industrialization and foster innovation) where infrastructure development, particularly in developing countries, is directed towards increased development in rural areas where ecosystem integrity is often highest (Baffoe et al., Reference Baffoe, Zhou, Moinuddin, Somanje, Kuriyama, Mohan, Saito and Takeuchi2021). But without successful progress in SDG 9, many SDGs related to human well-being and economic advancement become limited. Progress of SDG 14 has shown that without appropriate infrastructure, developing countries have greater difficulty to (1) increase economic benefits from domestic fishery products, (2) transition to greener technology throughout the fishery supply chain (i.e. aquaculture facilities) and (3) increase scientific capacity to ensure sustainable fisheries production. Recognizing the scale most appropriate for SDG implementation will be critical for future progress.
5.1 Evaluating SDG 14 indicators and identifying mutual opportunities
We argue that a key theme for embracing environmental flows thinking in the current political landscape is to enact long-term monitoring programmes as soon as possible to reduce uncertainty in our understanding of flow dynamics and their potential changes as climate change progresses and as society continues to develop. Additionally, this data-driven basis has the capacity to inform design and implementation of policies regardless of which scale is considered (e.g. transnational, national/regional, local/urban/rural). Prioritizing environmental flow data can provide more holistic understandings of the proposed SDG indexes and a better ability to predict management scenarios influenced by flow. This is in contrast to today's approach, where the current SDGs focus on budgets towards marine technology and maritime laws put the responsibility on coastal countries, despite the contributions of upstream countries to the variety of issues reported in this article.
A number of conceptual frameworks exist to aid investigations of river ecosystem dynamics, implementation of restoration approaches, assessment of tradeoffs and decision-making guidance that could also inform issues in marine systems. A non-exhaustive list includes the ecological limits of hydrologic alteration framework, the restoring rivers for effective catchment management framework and the motivation and ability (MOTA) framework (Friberg et al., Reference Friberg, Angelopoulos, Buijse, Cowx, Kail, Moe, Moir, O'Hare, Verdonschot, Wolter, Dumbrell, Kordas and Woodward2016; Nguyen et al., Reference Nguyen, Korbee, Luan, Tran, Loc and Hermans2019; Poff et al., Reference Poff, Richter, Arthington, Bunn, Naiman, Kendy, Acreman, Apse, Bledsoe and Freeman2010). The source-to-sea conceptual framework emphasizes scale-based interconnectivity of various flows: water, sediment, pollutants, materials, biota and ecosystem services (Granit et al., Reference Granit, Liss Lymer, Olsen, Tengberg, Nõmmann and Clausen2017). Inclusion of social components into frameworks or policy has the opportunity to include local values and cultures into the decision-making and prioritization processes. However, greater framework development is needed to demonstrate clear biophysical and socio-economic connections between rivers, estuaries and marine ecosystems so resilience can be systematically linked and quantified.
In addition to conceptual frameworks, there exists partnership-driven approaches that encompass the interconnections of land, water and coastal systems as a central guiding theme (Silvestri et al., Reference Silvestri and Kershaw2010), often to protect biodiversity with an ecosystem services focus (Reuter et al., Reference Reuter, Juhn and Grantham2016). The ridge-to-reef approach encourages joint public–private partnerships among terrestrial and marine stakeholders, which has been primarily adopted for island countries and states near the equator (Carlson et al., Reference Carlson, Foo and Asner2019). Locally collected spatial data of multiple stressors are critical to develop a synergistic modelling framework (i.e. terrestrial drivers, anthropogenic drivers, marine drivers, groundwater/nutrient models, coastal discharge models, coral reef predictive model) (Comeros-Raynal et al., Reference Comeros-Raynal, Lawrence, Sudek, Vaeoso, McGuire, Regis and Houk2019; Delevaux et al., Reference Delevaux, Whittier, Stamoulis, Bremer, Jupiter, Friedlander, Poti, Guannel, Kurashima, Winter, Toonen, Conklin, Wiggins, Knudby, Goodell, Burnett, Yee, Htun, Oleson and Ticktin2018; Rude et al., Reference Rude, Minks, Doheny, Tyner, Maher, Huffard, Hidayat and Grantham2016) or landscape indicators (Rodgers et al., Reference Rodgers, Kido, Jokiel, Edmonds and Brown2012) necessary to inform ridge-to-reef decision making. The white water to blue water initiative was a Caribbean-focused ancillary that attempted to develop public, private and non-profit partnerships that could jointly improve management of watershed and marine ecosystems in support of sustainable development (Laughlin et al., Reference Laughlin, Dionne, Colmenares, McDonald and Smith2006). More recently, a wholescape approach to marine management has been proposed that intends to expand upon the pre-existing catchment-based approach in England and Wales (Catchment Based Approach: Improving the Quality of Our Water Environment, 2013; Maltby et al., Reference Maltby, Acreman, Maltby, Bryson and Bradshaw2019; Stojanovic & Barker, Reference Stojanovic and Barker2008). Expanding the scope of these strategies to other river systems and marine environments offers an opportunity to identify efficient pathways to mutual sustainability success.
6. Conclusions
Global fisheries sustainability concerns and a global water crisis put the sustainability of rivers and other freshwater ecosystems in jeopardy. Many costly lessons have been learned from American and European efforts to utilize river systems to the fullest extent, and this has left a legacy of persistent environmental issues that have no short-term solutions and contentious long-term prospects. Stewardship of rivers seems to come after development needs instead of in tandem when rivers are contributing to human enterprise and delivery of multiple ecosystem services. Society in general can learn from these many ecological mistakes and adopt, prevent, maintain and restore strategies based on those experiences.
As a way to provide researchers, managers and policy makers with recommendations to improve both marine and freshwater environments and make cross-system conservation more accessible (Álvarez-Romero et al., Reference Álvarez-Romero, Pressey, Ban, Vance-Borland, Willer, Klein and Gaines2012; Reuter et al., Reference Reuter, Juhn and Grantham2016), we present 10 areas that relate this review to the land–marine interface and SDG 14 (Figure 3). In select places below, we have mentioned ongoing SDG acceleration actions (in italics) that provide management agencies and practitioners approaches that can be considered for implementation.
(1) Regulation of river flows supports multiple SDGs, but often negatively affects migratory fishes (critical for both freshwater and marine ecosystems) and fishes that depend on natural flow regimes. Developing incentives or mitigation measures to allow fish passage and restore natural flow regimes can support the SDGs jointly, especially if subsidies are used to support such development. Similarly, identifying ‘focused flows’ can support estuarine nursery habitats for fish during dry periods (Montagna et al., Reference Montagna, McKinney and Yoskowitz2021). A data-driven approach directed at decision makers may be an effective means to build technical capacity and enable restoration particularly for freshwater systems and their estuaries.
(2) Freshwater aquaculture has the potential to boost food production from inland waters that cannot enhance capture-based production (Cooke et al., Reference Cooke, Bartley, Beard, Cowx, Goddard, Fuentevilla, Leonard, Lynch, Lorenzen and Taylor2016; Gephart et al., Reference Gephart, Golden, Asche, Belton, Brugere, Froehlich, Fry, Halpern, Hicks, Jones, Klinger, Little, McCauley, Thilsted, Troell and Allison2021). Identifying hydrologic connectivity and flood dynamics to reduce escapement of non-native species and poor water quality spillover, particularly for pond-based aquaculture (Boyd et al., Reference Boyd, D'Abramo, Glencross, Huyben, Juarez, Lockwood, McNevin, Tacon, Teletchea, Tomasso, Tucker and Valenti2020), may help maintain river and estuary ecosystem health while also supporting food security.
(3) Developing long-term gauging systems and water-monitoring programmes in rivers provides a crucial data prerequisite to understanding key estuarine and coastal ecosystem processes (Chilton et al., Reference Chilton, Hamilton, Nagelkerken, Cook, Hipsey, Reid, Sheaves, Waltham and Brookes2021). These can include hydrodynamics, salinity, regulation, sediment dynamics, nutrient cycling and trophic transfer and connectivity. For example, identifying critical time periods and discharges of nutrient runoff from non-point source polluters and other future rural development requires modelling of environmental flows when implementing preventative and reactive management actions (e.g. riparian buffers) (Lind et al., Reference Lind, Hasselquist and Laudon2019; Van Niekerk et al., Reference Van Niekerk, Taljaard, Adams, Lamberth, Huizinga, Turpie and Wooldridge2019).
(4) Understanding flow relationships to hypoxic dead zone areas may better inform impact radii and synergistic effects with ocean currents. Predicted relationships may help inform fishing production for both capture fisheries and aquaculture. This is particularly relevant for aquaculture located in protected bays and deltas that rely on flow conditions and/or coastal currents. One idea to capitalize on this problem is to install seaweed or mollusc aquaculture to assimilate nutrients causing dead zones (Racine et al., Reference Racine, Marley, Froehlich, Gaines, Ladner, MacAdam-Somer and Bradley2021).
(5) Identifying the relationship between freshwater-dependent ecosystems and groundwater-dependent ecosystems may help delineate saltwater intrusion for coastal cities and water resource management for land-based agriculture. Monitoring and mapping water-chemistry parameters (e.g. chloride) in wells can detect saltwater intrusion and inform water-use practices (Cherry & Peck, Reference Cherry and Peck2017).
(6) Uncovering flow relationships with plastic types and sizes may improve capture efficiency and pollution reduction before it reaches marine environments. A transboundary diagnostic analysis/strategic action programme methodology could be deployed in tandem with river basin management to link flow regimes to land-based sources of pollution.
(7) Quantifying flow relationships from rivers to sensitive habitats can improve conservation outcomes, but can also reveal how pollution from rivers can disperse among regions using ocean currents (Carlson et al., Reference Carlson, Evans, Foo, Grady, Li, Seeley, Xu and Asner2021). Developing ecosystem-based adaptation measures such as managed-access and reserves can provide pathways for economic and ecological resilience.
(8) Assess tradeoffs between river development (e.g. sand mining), historic water quality and sediment dynamics as functions of environmental flows. Many other forms of rural development (e.g. logging, ranching) occur adjacent or near to rivers with direct influence on environmental flows and downstream water quality. Analysing either modern high-resolution imagery or historical imagery can provide a cost-effective means to quantifying changes in the landscape and its impact on adjacent freshwater–marine systems (Hackney et al., Reference Hackney, Vasilopoulos, Heng, Darbari, Walker and Parsons2021; Nita et al., Reference Nita, Munteanu, Gutman, Abrudan and Radeloff2018).
(9) Engage stakeholders throughout the development chain to uncover cultural heritage values and generate awareness of sustainable marine commodity platforms that allow for policy dialogue from a bottom-up approach. For systems with small-scale fishing communities that may be data poor we recommend the small-scale fisheries resource and collaboration hub and their guide on community-based resource management.
(10) Build equal participation capacity and empower local knowledge production to inform management practices, governance approaches and co-development best practices. One way to implement this in practice is the source-to-sea approach which is a collaborative and participatory-oriented framework to embed projects and programmes into the source-to-sea continuum (Mathews et al., Reference Mathews and Stretz2019).
Figure 3. Graphical depiction of how marine ecosystem health is tightly linked with riverine ecosystem health and environmental flows. Within this river–marine landscape, we highlight 10 areas where environmental flow opportunities can mutually benefit both systems and achieve SDG targets. Specific details of each point can be found in the main text but an overview for each point is provided as follows: (1) regulation of rivers, (2) freshwater aquaculture, (3) nutrient runoff, (4) flow relationships to hypoxic dead zone areas, (5) freshwater-dependent ecosystems and groundwater-dependent ecosystems, (6) environmental flow relationships with plastic types and sizes, (7) flow relationships from rivers to sensitive habitats, (8) tradeoffs of river development, (9) engage stakeholders and (10) equal participation and knowledge production.
We recognize that watersheds and estuaries have unique circumstances but the challenges that they face are globally prevalent. It is our goal to encourage policy makers, researchers and managers to build metaphorical bridges to their marine counterparts where appropriate. Through these partnerships, we expect innovative methodologies, practices and policies will yield greater progress towards maintaining resilient ecosystems, recovering resilience in altered ones and achieving SDG 14 targets.
In summary, freshwater and marine systems alike are physically and ecologically connected so it is ideal that the policies that govern these systems follow suit. While this review only focused on SDG 14, further work examining other SDG topics such as energy development, food production and drinking water would be particularly valuable. Addressing these issues from a global scale, such as the hydrological cycle, would be the ideal means to connect ecosystems to bring about collaboration at larger spatial scales. This paper, instead, serves to link the two most critical ecosystems needed to support SDG 14 – marine ecosystems and the rivers that feed them.
Supplementary material
The supplementary material for this article can be found at https://doi.org/10.1017/sus.2022.19.
Acknowledgements
A diverse array of stakeholders interested in fisheries, rivers and oceans have collectively shaped our thoughts on this topic but particular thanks is given to the course leader of the Bergen Summer School's Life Below Water Course, Katja Enberg, who encouraged this manuscript and provided feedback on early development of the manuscript. Thanks also go to the students of the course who presented many lovely personal insights on fish, fisheries and oceans. Special thanks go to Jennifer Clausen at jacdraws.com for help in designing and drawing Figure 3.
Author contributions
H. H. H. conceptualized the manuscript, coordinated the improvements, designed the figures and assisted in writing. K. A. W. and V. H. P. wrote Section 1 of the paper and edited the manuscript. H. H. H. wrote Section 2 of the paper and edited the manuscript. L. L. and E. B. wrote Section 3 of the paper and edited the manuscript. I. G. C. and H. H. H. wrote the case study section of the paper and edited the manuscript.
Financial support
This project has received funding from the European Union Horizon 2020 Research and Innovation Programme under the Marie Sklodowska-Curie Actions, Grant Agreement No. 860800: RIBES ‘River flow regulation, fish Behaviour and Status’. K. A. W. is supported by the Australian-American Fulbright Commission. V. H. P.'s contribution to this work is funded by NORSUS basic funding from the Research Council of Norway.
Conflict of interest
None.
Data
The associated data can be found at: https://doi.org/10.5281/zenodo.7251395.
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