The Danube River and its Delta: well-known, but threatened by multiple pressures | WWF
The Danube River and its Delta: well-known, but threatened by multiple pressures

Posted on 30 October 2018

Hydropower and regulation have introduced significant changes
The last few decades have seen a significant loss of habitats and species in the Danube River basin, reflecting the dire picture of biodiversity worldwide that is painted in the WWF 2018 Living Planet Report, released on 30 October.

This year’s edition of WWF’s every-two-year report on the state of life on our planet makes for grim reading. Humans have wiped out 60% of wildlife populations in just 40 years. Species population declines have been especially dramatic in the tropics of Central and South America and the Caribbean, dropping by 89% since 1970. Meanwhile, the Palearctic realm that includes Europe has experienced a population drop of 31%.
  
The global situation is reflected in the Danube River basin, one of Europe’s biodiversity hotspots. The river and its adjacent floodplains are inhabited by about 2,000 plant and 5,000 animal species. The approximately 6,000 km2 large Danube delta is one of the largest remaining natural wetlands in Europe.

It is a biodiversity hotspot, home to some 5,000 plant and animal species and where both boreal species and species typical of Central and Western Europe occur. Among the approximately 3,500 animal species, a total of 473 vertebrates (74 fish, 9 amphibians, 12 reptiles and 325 birds) have been reported. About 60% of the world population of Pygmy cormorant can be found here beside 5% of the Paleo-arctic population of White pelicans and 90% of the world population of Red-breasted goose.

“The high biological diversity of the riverine network of the Danube River and its Delta is well-known, but threatened by multiple pressures”, said Dr Thomas Hein, a hydro-biologist at the University of Natural Resources and Life Sciences (BOKU) in Vienna and a member of the International Association for Danube Research (IAD).

At basin level, still various forms of pollution are a key issue as well as hydro-morphologic alterations for the riverine landscape of the Danube River and its main tributaries. As in many large rivers worldwide, hydropower production, regulation measures for navigation as well as flood protection have introduced significant changes to the river system.”

Hein continues: “The changes to the river system have for example introduced massive alterations of longitudinal connectivity patterns of the Danube tributaries and along the course of the Danube River; and a massive reduction of lateral connectivity between the river channel and the former extensive floodplains. These alterations affect aquatic biodiversity and the provision of a variety of ecosystem services such as nutrient cycling and retention, aquatic productivity, sediment fixation, water purification, and many others. Furthermore, future drivers of change such as climate change will affect the riverine network locally as well as at basin scale with implications for the riverine ecosystem and related human uses.”

The research of many IAD members underlines some of the drivers and impacts of biodiversity loss in the Danube river basin:   
  • The number of dams has increased in the last 60 years significantly (more than 60 in the Danube main channel) with massive impacts on riverine biodiversity.
  • The area of floodplains has decreased by more than 60-90% in the different Danube reaches compared to historic conditions with far-reaching effects on biodiversity and ecosystem services such as floodwater retention, nutrient retention and a variety of provisioning services.
     
  • While the floodplain areas have been reduced, most of the remaining sites have been declared protected areas of key importance for the remaining biodiversity of floodplain habitats, forming an important part of the EU’s Natura 2000 network of specially protected sites.
     
  • Umbrella species such as sturgeon have experienced serious declines, with possible cascading effects at food web and ecosystem level. Multiple anthropogenic impacts have driven many species to near extinction: e.g. in the case of sturgeons, the flagship species of the Danube Basin, urgent measures are needed to ensure their revival.
     
  • While efforts in the last 30 years have led to significant improvements of water quality in the Upper Danube, the lower reaches are still affected by point sources of pollution, while diffuse pollution is widespread across the whole basin. Emerging pollutants pose additional problems to water quality in the whole catchment area.
     
  • Climate change projections highlight the different regional effects, with an increase of winter precipitation in the Upper and Middle Danube and a significant reduction of precipitation in the lower basin regions. Overall, a significant increase of air and water temperatures is expected, leading for example to a reduction of the oxygen content in the river.
     
  • Invasive species are a further threat to biodiversity. River surveys have shown a massive increase especially of the benthic invertebrates and fish fauna.
     
  • Protection of ecological corridors along the riverine network facilitating species migrations can help to mitigate some climate change vulnerabilities.
     
  • The ecological status is threatened by the important role the Danube plays in developing a climate-friendly trans-European transportation network. The Danube is furthermore a major part of the Rhine-Danube transport Corridor. Enhancing transportation capacity must respect ecological requirements. Joint solutions serving ecological and societal needs have to be sought.
     
  • Hydropower production will remain a major function of the Danube and its tributaries and is an important part of renewable energy regimes, but side effects such as altered hydrology, temperature, habitats and biota have to be taken into account and at least mitigated.
These developments, the historical situation as well as potential future trends for biodiversity and ecosystems are confirmed, Dr Hein emphasises, by a long list of publications of IAD members.

The threats to nature in the Danube basin and beyond are also a direct threat to human welfare, livelihoods and well-being. The Danube basin is home to 80 million people. Many depend on the natural resources of the region for their livelihoods and well-being. 20 million people depend on the basin’s rivers for their drinking water. More significantly perhaps, the region and its natural resources are significant for providing a host of ecosystem services, including climate regulation, water purification and flood management.

In the Danube basin as worldwide, we are facing an existential challenge on par and related to that posed by climate change. We need to radically escalate the political relevance of nature and galvanize a cohesive movement across state and non-state actors to drive change, to ensure that public and private decision-makers understand that business as usual is not an option.
 
The Living Planet Report documents the state of the planet—including biodiversity, ecosystems, and demand on natural resources—and what it means for humans and wildlife. Published by WWF every two years, the report brings together a variety of research to provide a comprehensive view of the health of the Earth.

International Association for Danube Research (IAD): Established in 1956, IAD is the oldest association of an active network of scientists in the Danube River Basin of Europe.

WWF Danube-Carpathian Programme (WWF-DCP) is responsible for leading and to a significant extent implementing WWF’s efforts to preserve, restore and sustainably manage the natural values of the Danube-Carpathian ecoregion, which we call the Green Heart of Europe.
Fishermen on a boat carrying wood. Danube Delta, Romania
© Michel Gunther / WWF