Global freshwater species populations decline by 83% since 1970
The Zambezi River in Africa: home to diverse populations of wildlife, but increasingly pressured by water pollution and dam construction. Image: Ninara | Flickr Creative Commons
Global freshwater species populations have dropped by 83% since 1970, according to a new report published by the World Wildlife Fund. The Living Planet Report 2018 assessed the populations of 880 representative freshwater species across the world between 1970-2014 to calculate the Living Planet Index.
The WWF report states that freshwaters – including lakes, rivers and wetlands – are the most threatened of all global habitats. Freshwater ecosystems provide habitat for over 100,000 known species of fishes, molluscs, reptiles, insects, plants and mammals, despite covering less than 1% of the Earth’s surface.
Overall, freshwater habitats are home to more than 10% of known animals and about one-third of all known vertebrate species. However, as the new figures show, freshwaters are experiencing significant biodiversity loss. The report identifies multiple pressures driving biodiversity loss including habitat modification, fragmentation and destruction; invasive species; overfishing; pollution; disease; and climate change.
Image: WWF
The report highlights the importance of ‘connected and free-flowing’ rivers in supporting healthy freshwater ecosystems, and the human populations which rely on them. When reservoir or hydropower dams are built, rivers straightened and their banks reinforced, or floodplains built on, the natural processes that take place throughout a river system are often damaged. Such processes often include fish migration, the dynamics, temperature and volume of water flows, seasonal flooding (and floodplain fertilisation) and sediment movement.
A recent scientific paper estimates that around half of global rivers are significantly impacted by flow regulation and/or fragmentation. As the report highlights, this means more than a quarter of the sediment which was naturally transported by global rivers to the ocean each year is now being trapped behind dam walls in reservoirs. Assuming the completion of all dams planned and under construction, it is predicted that the global percentage of rivers which are fragmented or regulated would nearly double to 93%, largely due to major dam construction in the Amazon Basin.
Increasing demands on water have also significantly reduced the global number of permanent rivers and lakes in recent decades, the report highlights. Based on over three million satellite images analysed using the Water Explorer, it is estimated that more than 90,000km2 of previously permanent freshwaters have been lost or become intermittent. In other words, rivers and lakes which previously existed all year round are now either gone or dry for periods of each year, as a result of water abstraction, dam construction and flow diversions. Over 70% of this loss of surface waters is concentrated in just five countries in Central and Western Asia.
Dry river channel on the Rio Grande, USA where water abstraction and dam construction have caused sections of the river to temporarily dry out. Image: JN Stuart | Flickr Creative Commons
In short, the regulation and disconnection of water flows through river catchments can throw complex and dynamic freshwater systems off kilter, and significantly alter the habitats they provide. This has contributed not only to the significant declines in freshwater biodiversity, but often also has negative effects on human communities who rely on freshwaters for food, water, and fertile agricultural land.
More widely, across all terrestrial, freshwater and oceanic ecosystems, the Living Planet Index calculates that global populations of mammals, birds, fish, reptiles, and amphibians have declined, on average, by 60% between 1970 and 2014, the most recent year with available data. This figure is based on data on 16,704 populations of 4,005 vertebrate species globally.
“This report sounds a warning shot across our bow,” says Carter Roberts, president and CEO of WWF-US. “Natural systems essential to our survival—forests, oceans, and rivers—remain in decline. Wildlife around the world continue to dwindle. It reminds us we need to change course. It’s time to balance our consumption with the needs of nature, and to protect the only planet that is our home.”
“In the next years, we need to urgently transition to a net carbon-neutral society and halt and reverse nature loss through green finance and shifting to clean energy and environmentally friendly food production,” says Marco Lambertini, Director General of WWF International. “In addition, we must preserve and restore enough land and ocean in a natural state to sustain all life.
But we have two main problems. First, and perhaps the greatest, is the cultural challenge. For too long we have taken nature for granted, and this needs to stop. The second is economic. We can no longer ignore the impact of current unsustainable production models and wasteful lifestyles. These must be accounted for and addressed.”
The Mekong giant catfish, a critically endangered species native to the Mekong basin in South-East Asia. Image: Lynn Chan | Flickr Creative Commons
The report develops short-term and long-term imperatives for policy and management which can ‘bend the curve of biodiversity loss’ (a phrase from a related recent Nature Sustainability paper). First, it highlights a ‘window of opportunity’ between now and 2020 to strengthen environmental policy as new goals and targets are currently being set for the Convention on Biological Diversity (CBD).
Secondly, it develops a ‘roadmap for 2020 to 2050’ to halt biodiversity loss, calling for the ambitious goals of the CBD – “By 2050, biodiversity is valued, conserved, restored and wisely used, maintaining ecosystem services, sustaining a healthy planet and delivering benefits essential for all people” – to continue to provide the basis of global environmental policy and management. This goal can be supported by the ongoing development of more effective biodiversity indicators, and scenario models which predict biodiversity trends in the future, the report argues.
Overall, the message is one that ‘business as usual’ approaches to managing biodiversity loss are not enough, and that the debate needs to be reframed from one in which ‘nature is nice to have’ to one in which ‘nature is a need to have’. This is a process in which the political and social relevance of nature is radically escalated, in order to galvanise cohesive movements which drive positive environmental change. As the report concludes, “We are the first generation that has a clear picture of the value of nature and the enormous impact we have on it. We may also be the last that can act to reverse this trend.”
The Freshwater Blog 
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