Bending the Curve of Global Freshwater Biodiversity Loss: An Emergency Recovery Plan
Feb 19, 2020 at 4:40pm
Despite their limited spatial extent, freshwater ecosystems host remarkable biodiversity, including one-third of all vertebrate species. This biodiversity is declining dramatically: Globally, wetlands are vanishing three times faster than forests, and freshwater vertebrate populations have fallen more than twice as steeply as terrestrial or marine populations. Threats to freshwater biodiversity are well documented but coordinated action to reverse the decline is lacking. We present an Emergency Recovery Plan to bend the curve of freshwater biodiversity loss. Priority actions include accelerating implementation of environmental flows; improving water quality; protecting and restoring critical habitats; managing the exploitation of freshwater ecosystem resources, especially species and riverine aggregates; preventing and controlling nonnative species invasions; and safeguarding and restoring river connectivity. We recommend adjustments to targets and indicators for the Convention on Biological Diversity and the Sustainable Development Goals and roles for national and international state and nonstate actors.
Intro: Humans have caused widespread planetary change, ushering in a new geological era, the Anthropocene (a term first coined in the 1980s by Eugene F. Stoermer, a freshwater biologist). Among many consequences, biodiversity has declined to the extent that we are witnessing a sixth mass extinction (Ceballos et al. 2017). Recent discourse has emphasised the triple challenge of bending the curve of biodiversity loss (Mace et al. 2018) while also reducing climate change risks and improving lives for a growing human population. In 2020, governments will review international agreements relevant to this challenge, including the Convention on Biological Diversity (CBD) and the Sustainable Development Goals (SDGs). There is a brief window of opportunity now to set out recommendations that can inform these agreements and guide future policy responses.
Nowhere is the biodiversity crisis more acute than in freshwater ecosystems. Rivers, lakes, and inland wetlands (such as deltas, peatlands, swamps, fens, and springs) are home to an extraordinary diversity of life. Covering less than 1% of Earth's surface, these habitats host approximately one-third of vertebrate species and 10% of all species (Strayer and Dudgeon 2010), including an estimated 70 species of freshwater-adapted mammals, 5700 dragonflies, 250 turtles (Balian et al. 2008), 700 birds (IUCN 2019), 17,800 fishes (Fricke et al. 2019), and 1600 crabs (Neil Cumberlidge, Northern Michigan University, 4th June 2019). The levels of endemism among freshwater species are remarkably high. For instance, of the fish species assessed for the freshwater ecoregions of the world, over half were confined to a single ecoregion (Abell et al. 2008).
Freshwater ecosystems also provide services to billions of people, including impoverished and vulnerable communities (Lynch et al. 2016). However, the management of freshwater ecosystems worldwide has frequently prioritized a narrow range of services for macroeconomic benefit at the expense of habitats, flora and fauna, and the diverse benefits they provide to communities. Consequently, the current rate of wetland loss is three times that of forest loss (Gardner and Finlayson 2018), and populations of freshwater vertebrate species have fallen at more than twice the rate of land or ocean vertebrates (Grooten and Almond 2018). Of the 29,500 freshwater dependent species so far assessed for the IUCN Red List, 27% are threatened with extinction. Among these, an estimated 62% of turtle species, 47% of gastropods, 42% of mammals, 33% of amphibians, 30% of decapod crustaceans (crabs, crayfish, and shrimps), 28% of fishes, and 20% of birds are at risk (figure 1; IUCN 2019). Populations of freshwater megafauna, defined as animals that reach a body mass of 30 kilograms, declined by 88% from 1970 to 2012, with the highest declines in the Indomalaya and Palearctic realms (−99% and −97%, respectively; He et al. 2019).
The causes of these declines have been comprehensively synthesised (e.g., Dudgeon et al. 2006, Reid et al. 2019), but no global framework exists to guide policy responses commensurate with the scale and urgency of the situation, and actions to safeguard freshwater biodiversity have been “grossly inadequate” (Harrison et al. 2018). Recommendations to address immediate threats to and underlying drivers of global biodiversity loss have focused mainly on terrestrial ecosystems, such as forests and grasslands (e.g., Kok et al. 2018) or have emphasised particular conservation strategies, such as enhancing protected area coverage and condition (e.g., Dinerstein et al. 2019, Visconti et al. 2019). Although they are valuable, these proposals have either assumed, simplistically, that measures designed to improve land management will inevitably benefit freshwater ecosystems, or they have neglected to consider freshwater biodiversity at all. Anthropogenic threats distinct to freshwater ecosystems, especially those linked to hydrological regimes and loss of connectivity, have been insufficiently considered in international conservation agreements and conventional conservation strategies, impeding investment in appropriate policy and management measures and contributing inadvertently to the disproportionately high losses of freshwater species and habitats.
In this article, we present an Emergency Recovery Plan to reverse the rapid worldwide decline in freshwater biodiversity. This plan extends the concept of species recovery plans established in legislation such as the US Endangered Species Act 1973 and the Australian Environment Protection and Biodiversity Conservation Act 1999. Given the speed and extent of collapse in freshwater biodiversity, parallels can be drawn with postdisaster recovery situations, and we have deliberately used the word emergency to convey the urgency with which conservationists, water managers, stakeholders, and policymakers must act to avoid further deterioration of habitats and to promote recovery of biodiversity. The plan is novel in this conceptual foundation, in its focus on solutions (rather than documentation of threats) and in its explicit recommendations for international agreements, especially the CBD and the SDGs.
The Emergency Recovery Plan: Priorities for action
The plan is structured around six priority actions (figure 2). Five of these focus on the major causes of freshwater biodiversity loss described by Dudgeon and colleagues (2006): flow alteration, pollution, habitat degradation and loss, overexploitation of species, and invasive nonnative species (INNs). In the priority action on overexploitation we have considered exploitation of abiotic substrates, such as sand and gravel, alongside biota, reflecting rising concerns about the damage to freshwater ecosystems caused by rapid expansion of riverine aggregate mining (UNEP 2019). We have also defined a sixth priority action on connectivity because of the distinct and pervasive role of dams and other infrastructure in fragmenting freshwater ecosystems and disrupting movements of water, species, sediments, and nutrients (Grill et al. 2019). Just as threats to freshwater biodiversity loss often act synergistically (Craig et al. 2017), so these priority actions should be considered and planned coherently for maximum efficiency and impact. Measures to address one cause of biodiversity loss can, in many contexts, help address other causes too.
Given the scale of the crisis, the plan must be ambitious. But it must also be technically feasible and pragmatic in political and socioeconomic terms. As we outline in box 1, each priority action has already been implemented successfully in one or more situations across the globe, providing proof of concept and lessons that can inform how to scale up efforts.
Below, for each priority action, we briefly review the problem, potential policy and management solutions, and the current implementation status of these solutions.
Action 1: Accelerate implementation of environmental flows
Water management for power generation, for flood risk reduction, or to store and deliver water for agricultural, industrial, or domestic uses changes the quantity, timing, and variability of water flows and levels. In doing so, it directly alters the physical availability of freshwater habitats, their ambient conditions, connectivity between habitats, and ecosystem processes such as sediment flow. These alterations, in turn, affect functional links between hydrological regimes and the life histories of freshwater species (Bunn and Arthington 2002) and therefore contribute substantially to losses of freshwater biodiversity. Climate change exacerbates flow alteration in many situations (Döll and Bunn 2014).
Maintaining or restoring ecologically important attributes of hydrological regimes improves biodiversity outcomes (Poff et al. 1997, Bunn and Arthington 2002, Olden et al. 2014). The science and practice of environmental flow assessment enables identification and quantification of these attributes. A sophisticated methodological toolbox now exists for developing environmental flow scenarios and recommendations in a wide range of water resource management contexts, from minimally altered to heavily managed freshwater ecosystems (Acreman et al. 2014, Poff et al. 2017). Many environmental flow assessment tools consider desired socioeconomic and cultural objectives alongside biodiversity goals, aiding incorporation of recommendations into river basin plans, water allocation regimes, and design and operation of water infrastructure. The 2018 Brisbane Declaration and Global Action Agenda on Environmental Flows set out 35 recommendations to accelerate implementation (Arthington et al. 2018).
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