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Looking for ‘needles in a haystack’: using eDNA to detect endangered sturgeon populations

November 30, 2022
A sturgeon is sampled by scientists on the Danube. New eDNA techniques can help track the size and location of sturgeon populations along the river. Image: BOKU-IHG

Sturgeons are some of the most iconic fish species in the Danube River. However, their populations are in significant decline as a result of decades of pollution, habitat loss, overfishing and the fragmentation of migratory routes.

Often termed ‘living fossils’ due to their ancient lineages, sturgeons are often large and long-lived. Their migratory lifespans between freshwater and saltwater environments makes sturgeons particularly vulnerable to human pressures. The Danube River supports six native species of sturgeons, all of which are threatened by human activities.

Given the Danube’s vast length – spanning more than 2800km – it is vital that conservationists can monitor the size and location of sturgeon populations along the river in order to protect them. Two recently-published studies suggest that new environmental DNA (or eDNA) techniques offer significant potential for detecting sturgeon populations across large rivers like the Danube.

When an organism moves through an environment it constantly sheds tiny pieces of organic material such as dead skin cells, mucus and faeces. Scientists can test water samples for the DNA in this organic material. Such environmental DNA can point to the recent presence of a species, even if it cannot be otherwise detected or seen. As a result, eDNA approaches are increasingly valuable to scientists seeking to detect a host of elusive and tiny species across different ecosystems.

“Despite the need for a better understanding of the distribution and population status for many fish species in large rivers, the use of traditional sampling methods failed in the past, thereby hampering reliable assessments,” says Dr. Paul Meulenbroek, senior author of both studies, based at BOKU, Vienna. “Water samples can be used to identify those species that have recently been present in a local environment, with genetic material such as skin cells, intestinal cells, scales, or mucus being obtained directly from environmental samples.”

eDNA techniques allow scientists to look for sturgeons in large and murky water bodies. Image: BOKUIHG

One study, published in Biodiversity and Conservation, developed an eDNA reference database for five native Danube sturgeons, and two non-native species. This allowed researchers to use eDNA techniques to search for the “needles in a haystack” sturgeon populations along the entire length of the Danube. This work provided the first large-scale snapshot of threatened sterlet populations along the river, with the species found in around half of all surveyed sites.

The partner study, published in Molecular Ecology Resources, explored the potential of eDNA techniques to estimate the abundance of sturgeon species. Researchers found that total fish eDNA concentrations and total fish abundance were highly correlated.

Together, the two studies suggest that sifting river water for microscopic pieces of organic eDNA material can help scientists determine both the location and abundance of sturgeon species along the vast Danube catchment.

“An in-depth understanding of species distribution and population dynamics is essential for developing adaptive conservation management plans, and in this regard, the benefits of an eDNA approach for conservation efforts, fisheries management, and scientific studies are numerous,” outlines Dr. Meulenbroek.

“eDNA metabarcoding is potentially more sensitive than traditional survey methods, as well as being more cost effective and non-invasive,” Dr. Meulenbroek continues. “It facilitates time-limited coverage of large geographical areas, thereby enabling the implementation of conservation measures within an ecologically and politically-actionable time scale.”

As the new studies suggest, eDNA approaches hold significant promise for conservationists seeking to strengthen their existing attempts to protect sturgeon populations across the Danube basin. “To facilitate sustainable conservation initiatives, it is of the utmost importance to gain a reliable understanding of the present status and development of remnant populations and sound study results providing evidence-based data for making water management decisions,” concludes Dr. Meulenbroek.

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This post is supported by the MEASURES project.

Restoring Europe’s ecosystems to reverse biodiversity loss and build resilience to climate change

November 17, 2022
A partnership of four major EU funded projects aim to restore European ecosystems. Image: WaterLANDS

Recent major reports on the state of the world’s climate and biodiversity clearly show the need for urgent, large-scale ecosystem restoration. Across the world, ecosystems are being degraded at rates faster than efforts to protect them, whilst ongoing climate change places increasing pressures on their health and functioning.

An awareness of the need to urgently restore healthy, resilient ecosystems underpins a partnership of major EU funded projects: WaterLANDS, SUPERB, REST-COAST, and MERLIN. Addressing the restoration of wetlands, forests, coastlines and freshwaters respectively, the projects have been funded to support the European Green Deal’s aspirations of a low-carbon, climate resilient future.

Each project aims to demonstrate how best-practice approaches for ecosystem restoration can be applied and upscaled across the continent. They are each developing innovative ways of implementing nature-based solutions in restoration to benefit ecosystems, societies, and even economies. Central to this work is the need to effectively monitor and share the results of ecosystem restoration to help wider global communities plan effective restoration strategies.

The four projects aim to restore four interlinked ecosystem types: forests, wetlands, coastlines and freshwaters. Image: SUPERB

Together, the four projects address the overarching restoration of Europe’s varied ecosystems. “Rivers, forests and coasts are complementary environments to wetlands through ecosystem services, linked biodiversity and water flow and quality,” explains Craig Bullock, project coordinator of wetland restoration project WaterLANDS. “This means their enhancement and restoration has a direct connection with wetland functioning and restoration potential.”

WaterLANDS focuses on the restoration of six wetland sites across Europe, learning from existing sites where successful restoration has been undertaken. The project encourages community-led practices to design and implement restoration projects.

“Communities should remain part of the landscapes we are trying to protect and restore,” says Shane McGuinness, deputy project coordinator of WaterLANDS. “In many cases they have been using these areas for generations and it is unreasonable of us to presume that this will suddenly cease. We need to support communities to move away from the practices of the past and towards more sustainable practices of the future.”

The partnership of projects focused on interlinked ecosystems holds significant promise. “I see the potential for better landscape level planning of restoration activities,” says Elisabeth Pötzelsberger, project coordinator of SUPERB, which focuses on forest restoration. “For example, focus areas and restoration targets for specific ecosystems could create synergies across different ecosystem types.”

Drawing on projects across twelve countries, SUPERB aims to restore thousands of hectares of forest landscape across Europe. “We want to particularly highlight the importance of considering adaptation requirements in choosing restoration approaches and targets because climate change does already, or will soon, have dramatic impacts on the suitability and resilience of specific forest types,” explains Dr. Pötzelsberger. “We call this prestoration or forward-looking restoration.”

The projects aim to use innovative nature-based solutions in restoration to help tackle biodiversity loss and build resilience to climate change. Image: REST-COAST

The restoration of ecosystems across land and freshwater is inherently linked to those along Europe’s coastlines. “River-delta-coast connectivity is an essential element to enhance the natural resilience of sediment starved coastal systems,” says Agustín Sánchez-Arcilla, project coordinator of REST-COAST, which focuses on the restoration of the continent’s coastal ecosystems.

Europe’s coastlines are some of the continent’s biodiverse environments, but are often subject to numerous human and climatic pressures, whilst poorly protected by environmental policy. REST-COAST focuses on nine case studies, from the eastern Mediterranean to the North Sea. “We hope to increase the scale and the speed of coastal restoration interventions, particularly for vulnerable hot spot locations,” outlines Prof. Sánchez-Arcilla.

The partnership of projects has the potential to develop how restoration projects interact with industry, policy and financiers. “Aside from the physical links between these ecosystems, there are also connections through commercial land uses such as agriculture and forestry and through governance to support restoration,” says WaterLANDS coordinator Craig Bullock. “There are also connections through landscape finance given that these biophysical linkages and ecosystem service outputs provide for a package of financial investment at a landscape level.”

The projects aim to support major European environmental policies through engagements with policy makers, industry and financiers. Image: MERLIN

The governance structures Dr. Bullock mentions are crucial to this project partnership. The four projects were funded to support European Green Deal objectives to foster climate resilience and nature recovery across the continent, alongside the aim of becoming net carbon-neutral by 2050. By promoting the widespread and innovative scaling-up of ecosystem restoration across Europe, the partnership offers a significant opportunity to amplify scientists’ voices in the development of the proposed European Nature Restoration Law.

“The four projects gather substantial expertise on nature restoration in Europe,” says Sebastian Birk, project coordinator at MERLIN. “All projects have a focus on specific ecosystems like forests, freshwaters and the coast. These specific views are now integrated by the clustering activity to find solutions at landscape-scale.

“This is indispensable when moving towards achieving the European Green Deal ambitions,” Dr. Birk continues. “Our activities affect all parts of the environment, and our remedies need to be integrative. This perspective allows the four projects to jointly act on the European Nature Restoration Law.”

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Major new awards seek innovative solutions to restore Europe’s rivers, lakes and wetlands

November 4, 2022

As we regularly document on this blog, freshwaters are among the most globally threatened ecosystems. And, as the latest MERLIN podcast explored, while restoration projects are increasingly popular across the continent, there is an urgent need for new approaches which both benefit nature and are financially sustainable.

The new MERLIN Innovation Awards (MIA) 2023 aims to showcase cutting-edge products and services which help protect and restore increasingly threatened freshwater ecosystems. The awards seek submissions of innovative, widely applicable, and market-ready solutions from companies and organisations across the world.

Applications are open for companies across the world in two categories: MIA Product of the Year and MIA Service of the Year.

The MERLIN Innovation Awards offer companies a unique opportunity to pitch their innovative products and services to seventeen European freshwater restoration project managers, as well as other key decision makers and stakeholders. Selected companies will automatically be included in the MERLIN Marketplace, an online portal which features best-practice approaches to freshwater restoration, due for launch in 2023.

“Innovative solutions for inland water restoration are increasingly sought after. The MERLIN Innovation Awards will reach out to the vibrant community of solution providers and allow them to showcase their products and services to restoration practitioners across Europe. Let us grow together with this initiative,” says Dr. Sebastian Birk, co-coordinator of the MERLIN project at the University of Duisburg-Essen.

The MERLIN Innovation Awards aim to connect companies developing state-of-the-art approaches for ecosystem restoration to potential buyer organisations. The Awards provide a unique opportunity for companies to join the rapidly-growing global freshwater ecosystem restoration community, and to offer innovative solutions to help address pressing environmental issues and benefit nature and society.

The MERLIN Innovation Awards 2023 application deadline is 22nd December 2022 (17:00 CET). The independent MIA jury will comprise freshwater restoration managers from the MERLIN project and other related stakeholders with backgrounds in business, NGOs or administration.

For any additional questions, you can consult the Awards webpage and FAQs or contact info@connectology.eu.

MERLIN Podcast Episode 2 – Freshwater Restoration in Europe: Transformation, Disruption and Inspiration

October 26, 2022

This week we’re delighted to bring you the second episode of the MERLIN podcast.

The podcast follows the MERLIN project in its journey to mainstream freshwater restoration in Europe. It offers a behind the scenes look at some of the continent’s most ambitious freshwater restoration projects carried out through cutting-edge aquatic science and conservation.

This episode explores the big ideas that are shaping how major freshwater restoration projects are being carried out across Europe. From dam removal to floodplain restoration, the European Union funded MERLIN project is investing millions of euros to disrupt and transform existing ways of carrying out freshwater restoration.

But what do these keywords – transformation and disruption – actually mean in practice? And what are the underlying inspirations that motivate scientists and environmentalists to help bring Europe’s freshwaters back to life?

In September 2022 podcast host Rob St John travelled to Fulda, just outside Frankfurt in Germany, to attend the first MERLIN all-partner meeting. At the meeting Rob spoke to project partners from all over Europe to find out about how they’re working together to research, plan, finance and implement major freshwater restoration projects. The aim of this work is to encourage healthier European rivers, streams, peatlands and wetlands, which aren’t only good for nature, but also bring many social and economic benefits.

You can also listen and subscribe to the podcast on Spotify, Amazon, and Apple Podcasts. Stay tuned for the next episode soon!

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This article is supported by the MERLIN project.

Dambusters: new film documents dam removal across Europe

October 10, 2022

Dam removal has become one of the most important tools in modern river restoration. Removing dams and other barriers such as weirs is a vital step in shifting river systems back towards more natural states, allowing the free flow of water and migratory species such as salmon.

A major new film released this weekend documents dam removal projects across five European countries. Dambusters tells the stories of so-called ‘river heroes’ who are taking action to restore free-flowing rivers in Spain, France, Estonia, Lithuania and Finland. Presented by Pao Fernández Garrido from the World Fish Migration Foundation, Dambusters was supported by a range of environmental organisations including WWF, Wetlands International and The Nature Conservancy, and produced by Francisco Campos-Lopez Benyunes at Magen Entertainment.

In Estonia, the film focuses on the Pärnu River, where seven weir removals have opened up over 3,000km of river after 150 years of fragmentation. The film highlights the importance of public communication and support, stating that over 75% of Finnish citizens support dam removal, compared to around 10% of the public in other European countries.

“When I filmed the explosion, the moment it blew up was incredible,” Robert Epple says in the film. Epple, a pioneer of dam removal, and founder of the European Rivers Network, adds, “I understood in that moment it blew up, that there was not only a dam that disappeared, but that there were thousands of barriers also in people’s mind, so to say, which blew up simultaneously. Because I knew that if people see these images, they’d understand that a dam is not eternal, that we can undo what was done in the past, if it no longer serves its purpose and give it back to nature.”

Dambusters film poster

“The ecosystem is functioning and the ecosystem’s resilience is getting back,” reflects Saija Koljonen, a researcher at SYKE, Finland, following a dam removal project. “The whole ecosystem, it’s a complex system from the catchment area and the riparian forest, and the species in the water. The whole complexity is working naturally afterwards. So, that is the aim of these kind of big restoration projects. I see the river continuity and connectivity is the key to the ecosystem resilience. So the ecosystems function normally or naturally if connectivity is taken care of. So, dam removal is the best option for connectivity.”

“I spoke with the construction guys and they said that there’s been tour buses with people, full of people just coming here to check out this dam removal site,” says Finnish actor and environmentalist Jasper Pääkkönen. “We’re actually reviving this local community, local economy, and everybody benefits. People benefit, nature benefits, the fishery, other animals, they all benefit from it.”

Dambusters was premiered at the recent European Rivers Summit in Brussels. It is released at a time when there is a renewed focus on river restoration. The proposed EU Nature Restoration Law strengthens the ambition to restore 25,000 kilometres of European rivers through the removal of obsolete barriers alongside the restoration of floodplains and wetlands. Recent research suggests that there are more than 1.2 million barriers fragmenting European rivers, and around 150,000 are obsolete.

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Dambusters website.
Watch the film online.

MERLIN: Bringing Europe’s freshwaters back to life

September 23, 2022

The MERLIN project held its first all-partner meeting last week in Fulda, Germany. Scientists, restoration managers and industry stakeholders all took part in valuable discussions over how best to mainstream freshwater restoration in Europe.

A new video exploring the key issues around the project was premiered at the meeting. A collaboration between the Schneeaufmoss creative agency and MERLIN partners, the video outlines five key challenges for contemporary freshwater restoration, and how the project is tackling them. Packed with beautiful footage of the continent’s waterways, the video is narrated by Christian Cummins of FM4 Radio.

The new video follows the recent launch of the first MERLIN podcast. A second podcast was recorded at the meeting, exploring ideas around transformation, disruption and inspiration as drivers of freshwater restoration. This second podcast will be released in the coming weeks.

MERLIN researchers in Fulda, Germany. Image: MERLIN

MERLIN Questionnaire

MERLIN researchers also launched a new questionnaire seeking to better understand shared goals around river restoration.

“We want to identify landscape and policy interventions that can help practitioners across agriculture, hydropower, insurance, navigation, peat extraction and water supply sectors tackle their own challenges, while contributing to achieve EU Green Deal objectives,” says Dr. Alhassan Ibrahim from the James Hutton Institute. “These objectives include climate resilience, improved biodiversity, zero pollution, sustainable food systems, health and wellbeing.”

“The responses to the questionnaire will help us to understand Europe’s environmental and policy needs and opportunities for mainstreaming nature-based solutions in the sectors,” continues Dr. Ibrahim. “We will draw from the results and other data sources – such as policy interviews and roundtables – to develop strategies and a route map to overcome the challenges in the economic sectors and harness the opportunities for win-win solutions.”

You can complete the questionnaire here (updated 17.10.22: questionnaire now closed).

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This article is supported by the MERLIN project.

MERLIN Podcast Episode 1: introduction and floodplain restoration on the Rhine Delta

September 9, 2022

This week we’re delighted to bring you Episode 1 of the new MERLIN podcast. As we’ve covered in recent months, MERLIN is a major European Union funded project which is investing millions of Euros to help mainstream freshwater restoration across the continent over the coming years.

This podcast follows the MERLIN project in this journey. It offers a behind the scenes look at some of the continent’s most ambitious freshwater restoration projects carried out through cutting-edge aquatic science and conservation.

In July 2022 podcast host Rob St John travelled to the Netherlands to meet MERLIN practitioners working on the project’s large river restoration sites.

Over a number of hot, sunny days the team explored floodplains across the Rhine Delta which had been restored through a major project called Room for the River. Started in 1995, Room for the River worked to reconnect the Rhine with its floodplains, which had become isolated through the construction of dikes and levees. By making room for the river to periodically inundate its floodplains, new spaces for biodiversity habitat, carbon storage and recreation have been brought back to the Rhine catchment.

Walking along the banks of the Rhine, Rob speaks to restoration practitioners about their work, and catches up with MERLIN coordinator Sebastian Birk to hear about what the project hopes to achieve.

You can also listen and subscribe to the podcast on Spotify, Amazon, and Apple Podcasts. Stay tuned for Episode 2 in the coming weeks.

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This article is supported by the MERLIN project.

Freshwater Fact Cards: drawing attention to special freshwater species

August 31, 2022
Freshwater Fact Cards highlight key information about species which deserve special conservation attention. Image: Studio Adén

Freshwaters are some of the most biodiverse yet highly threatened ecosystems in the world. As conservationists have repeatedly highlighted recently, the freshwater biodiversity crisis receives significantly less attention and support than that on land, or in the seas.

Part of this shortfall in attention is due to the nature of freshwater environments. Rivers, lakes, streams and wetlands can often obscure the wildlife they support below the water’s surface. This can make it hard not only to notice their richness, but also any ecological declines.

As a result, highlighting important – but often overlooked – freshwater species has become a key advocacy approach for many conservationists in recent years. In some cases, this approach tallies with ecological theory, which suggests that the conservation of particular ‘umbrella species’ can benefit the health of the wider ecosystem.

A new series of illustrated cards highlights twenty freshwater species that deserve special conservation attention. Scientists from IGB, Berlin and the Alliance for Freshwater Life have curated the project to spotlight species which are often inconspicuous, or found in remote regions, but are vital for freshwater conservation efforts.

The European Sturgeon fact card. Image: Studio Adén

“We chose the twenty species for two reasons,” says project curator Dr. Fengzhi He from IGB. “First, some are considered charismatic and hold the potential to function as flagship umbrella species to enhance freshwater conservation. The selected freshwater megafauna species such as European sturgeon, arapaima, Amazon river dolphin, common hippopotamus, gharial, Chinese giant salamander fall under this category. These are also species targeted in the Freshwater Megafauna Futures project.

“Most of these freshwater megafauna species are threatened, and the Chinese paddlefish has been officially listed as Extinct by the IUCN Red List,” continues Dr. He. “Second, we included species that are closely studied by IGB researchers. Some of these species may be smaller but have important ecological roles in local ecosystems or are key model organisms in freshwater research.”

The Freshwater Fact Cards highlight fascinating information about each of the featured species. For example: How do arapaima breathe? How deep can Baikal seals dive? How fast are hippos? How long can freshwater pearl mussels live? And how do water fleas reproduce?

Baikal seal fact card. Image: Studio Adén
Freshwater pearl mussel fact card. Image: Studio Adén

“We really hope that these fact cards will raise the fascination of people about freshwater life,” says project curator Prof. Sonja Jähnig from IGB. “We are very happy about the nice visualisations and illustrations done by Studio Adén. The cards not only show interesting facts on freshwater species and the research conducted at IGB, but they can be used as postcards or decorations.”

“Freshwater biodiversity is underrepresented in the information presented to the general public, often being out of sight, out of mind. We would like to use the Freshwater Fact Cards to highlight amazing freshwater life and promote public awareness and conservation actions for freshwater biodiversity,” says Dr. He.

“We will distribute the cards widely at outreach events, where visitors can take them as small souvenirs,” says Prof. Jähnig. “The fact cards also support the Alliance for Freshwater Life in their ambition to raise the profile of freshwater biodiversity and make people better understand, value, and safeguard freshwater biodiversity.”

The Freshwater Fact Cards project is still growing. “If you have an idea for which species we should add, or if there is an idea for a new set of species from a certain region, or including other artists, please reach out to us,” says Prof. Jähnig.

MERLIN restoration case studies: large transboundary rivers

August 18, 2022
The five large transboundary river sites in the MERLIN project: (4) Room for the Rhine branches, Netherlands; (7) Upper-Mid-Danube floodplain, Austria and Hungary; (8) Lower Danube floodplain, Romania; (9) Tisza River, Hungary; (10) Germany’s Blue Belt.

The MERLIN project focuses on 17 freshwater restoration case studies located across Europe.

These diverse sites and projects – including large rivers, small streams, peatlands and wetlands – offer researchers the opportunity to learn about best-practice approaches for restoration in contemporary landscapes. The project will explore how the impact of these projects contributes to the targets of the EU Green Deal.

Moreover, MERLIN is investing more than €10 million in these projects to help upscale their management through the use of nature-based solutions. It is intended that the progress made in bringing freshwaters back to life at these sites will help strengthen arguments for mainstreaming freshwater restoration across the continent.

This is the third of three articles introducing the 17 restoration case studies. This week, we focus on the five large transboundary rivers.


Floodplain rewetting along the Rhine Valley at Noordwaard, Netherlands. Image: MERLIN

Room for the Rhine Branches, Netherlands

Restoration of a resilient large river system for biodiversity, flood protection and navigation

Ongoing restoration work will be carried out across a 300km network of River Rhine branches throughout the Netherlands. These stretches of river – from the German border to the North Sea – have been heavily modified for centuries, with widespread weirs, embankments and groynes alongside intensive agriculture, mining and urban development.

This restoration of the Rhine branches follows decades of work through the Room for the River programme, which finished in 2018. Whilst significant progress has been made, climate change and channel erosion pose new challenges for restoration, which will be managed in the future through the Integrated River Basin Management programme.

Restoration measures, tailored to local conditions, include: floodplain restoration (e.g. through the removal of artificial channels and dikes); river channel restoration (e.g. the removal of polluted sediments); and connectivity restoration (e.g. the removal of barriers to the movement of water, sediment and fish). The overall aim is to create a more resilient large river system which balances conservation, flood protection, freshwater supply, navigation and recreation needs.

“A lot has been already been achieved by the Room for the River programme, but there are new challenges due to climate change, resulting in more extreme discharge patterns, and incised river beds requiring sediment management,” says Tom Buijse from restoration managers DELTARES. “Its successor is IRM for which the visionary plan should be ready by 2023. This will result in a follow-up programme for the coming decades.”

Find out more.


Floodplain reconnection at Liberty Island, Hungary. Image: MERLIN

Upper-Mid-Danube floodplain, Austria and Hungary

Reconnecting floodplains and tributaries to foster multifunctional landscapes

Two stretches of the Mid-Danube River in Austria and Hungary are being restored through a range of measures across its floodplains and tributaries. Whilst the sites are geographically independent, the upscaling of their restoration will be developed together.

In Austria, a stretch of the Danube in the Donau-Auen National Park will be managed towards more natural conditions by reconnecting floodplains to the main river, restoring riparian areas and removing artificial bank structures. It is intended that this range of adaptive restoration measures will help address multiple pressures such as riverbed deepening, the impacts of navigation, flood protection and land-use alterations.

In Hungary, a side branch of the Danube has been reconnected to the main river around the 4km-long Liberty Island. A key goal for this initiative has been to create a long-term, sustainable conservation model for white willow alluvial forests around the river. Restoration work has cleared invasive and non-native tree species around riparian areas, restoring water flows in the river side arm to allow the forest to flourish, even in times of drought.

“This case study represents the systematic process-orientated restoration of a whole large river stretch through adaptive management processes, to address multiple pressures,” say restoration managers from viadonau. “These are multifunctional floodplains, where restoration design should address the maintenance of a variety of ecosystem services and trade-offs including fishing, shipping, flood protection, forestry, agriculture and recreation,” add project partners from BOKU, Vienna.

Find out more.


Reconnecting floodplains along the Lower Danube in Romania. Image: MERLIN

Lower Danube floodplain, Romania

Reconnecting floodplains to boost biodiversity and buffer floods

Floodplain restoration is being upscaled at a series of sites along the Lower Danube River in Romania. As with much of the basin, the Lower Danube is highly regulated and altered by human construction, and as a result its huge former floodplain is largely disconnected from the main river. Intensive land use around the river has caused further habitat degradation, water and soil pollution, and water supply issues.

Restoration work seeks to reconnect the Lower Danube River with its floodplains as a means of boosting ecosystem health and mitigating flood risks. It is intended that more natural hydrological cycles will be created across wide areas of floodplain, wetland and polder, fostering a biodiverse mosaic of landscapes linked to the river. It is hoped that restoration work will, in turn, encourage sustainable grazing, fishery and aquaculture activities, alongside increased recreational and tourism use.

“The entire Danube river is regulated and long dike system protects the largest former floodplain area in the continent,” say restoration managers from WWF Romania. “The implemented measures use nature-based solutions to reconnect a part of the former floodplain with the Danube River.”

Find out more.


Wildflowers on the banks of the Tisza River, Hungary. Image: Györgyfi | Wikimedia Creative Commons

Tisza River, Hungary

Rewetting floodplains for sustainable farming practices

Floodplains on the Tisza River – a major tributary of the Danube – will be reconnected to the river and transitioned to sustainable farming systems. Like much of the Danube basin, the Tisza has been heavily modified by humans, and many of its former floodplains are dominated by intensive arable farming, which has dried out these formerly-wet landscapes.

Two floodplains in the middle Tisza River will be ‘rewetted’ through a series of floodways and flood risk reduction reservoirs. Initially implemented over 1,800 ha of floodplains, this work will increase water retention in the landscape, and create the conditions for sustainable floodplain farming practices.

It is intended that floodplain restoration will not only increase biodiversity and buffer flood waters, but also help foster economically-viable land-use systems around the Tisza. It is hoped that this work could be upscaled to over 150,000 ha of former floodplain landscapes along the Tisza basin.

“This case study presents real integrated solutions for flood risk management, water scarcity in agriculture, biodiversity loss, and climate adaptation,” say restoration managers from WWF Hungary. “It offers new economic and social opportunities for local communities, and for the cooperation of stakeholders.”

Find out more.


Historic buildings on the River Lahn, part of the national Blue Belt restoration project. Image: Living Lahn project

Germany’s Blue Belt

Renaturalising a major network of German rivers and floodplains

This ambitious national project seeks to restore around 4350km of rivers and 240,000 ha of their floodplains across Germany. The Blue Belt initiative began in 2019, and aims to renaturalise a huge network of federally-managed waterways, whilst at the same time maintaining their commercial navigability for boat traffic.

Most of the Blue Belt network – which includes major rivers such as the Rhine, Elbe and Weser – is heavily modified, with altered water flows, channel structure and degraded water quality. Floodplains across the network are often subject to intensive urban and industrial land use.

It is intended that renaturalisation of the banks and floodplains of this national river network will create significant new biodiversity habitat and offer new opportunities for tourism and recreation. Restoration work in the Blue Belt initiative seeks to foster a major new biotope network along Germany’s waterways.

“This project aims to ecologically restore functional river landscapes throughout Germany, but at the same time not to set aside commercial navigability,” say restoration managers from the Federal Institute of Hydrology, Koblenz. “Renaturalised federal waterways and their floodplains will form an important part of a biotope network and help to preserve water and floodplain species and their habitats. As a result of this a significant number of ecosystem services are generated, sustained or even enhanced.”

Find out more.

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This article is supported by the MERLIN project.

MERLIN restoration case studies: small streams and basins

August 4, 2022
The six small streams and basin sites in the MERLIN project: (2) Basque streams; (11) Emscher catchment; (13) Sorraia catchment; (15) Tzipori catchment; (16) Scheldt catchment; (17) Forth catchment.

The MERLIN project focuses on 17 freshwater restoration case studies located across Europe.

These diverse sites and projects – including large rivers, small streams, peatlands and wetlands – offer researchers the opportunity to explore best-practice approaches for restoration in contemporary landscapes. The project will document how the impact of these projects contributes to the targets of the EU Green Deal.

Moreover, MERLIN is investing more than €10 million in these restoration projects to help upscale their management through the use of nature-based solutions. It is intended that the progress made in bringing freshwaters back to life at these sites will help strengthen arguments for mainstreaming freshwater restoration across the continent.

This is the second of three articles introducing the 17 restoration case studies. This week, we focus on the six small streams and basin sites.


River barriers on the Deba River, Spain. Image: MERLIN

Basque streams, Spain

Reconnecting a heavily altered river through barrier removal.

A series of dams on the 60km-long Deba River in Spain will be removed to allow water, fish and sediment to move freely along its course. The local region of Gipuzkoa has a long history of industrial and urban development, and as a result the Deba’s channel is heavily altered. Many of the built obstacles along the Deba are now either obsolete or disused, yet they continue to block the free movement of water and fish.

Restoration work aims to reconnect the Deba River by removing ten dams along its course. It is intended that this work will restore more natural flow conditions in the river basin, whilst also supporting populations of migratory fish such as trout and eels, which migrate upstream to spawning grounds. It is also hoped that dam removal along the Deba will help restore habitat for wildlife.

“A key objective is to promote environmental education and nature-based solutions as restoration policies,” say restoration scientists from the University of the Basque Country. “Stakeholder interaction is being promoted, connecting local communities, institutions and governments.”

Find out more.


Wildflowers blooming on artificial dikes along the Emscher River. Image: MERLIN

Emscher catchment, Germany

Restoring riverbank habitats for biodiversity and recreation.

The Emscher River and its tributaries in Northern Germany have been heavily altered over many years. Urban and industrial development in the Emscher catchment has left much of the river flowing through concrete channels fragmented by weirs, culverts and artificial pumping stations. Cut off from its natural floodplains, the Emscher has been heavily polluted for decades as a result of sewage overflows and industrial run-off.

The MERLIN project will help restore meadow grasslands along riverbanks throughout the Emscher catchment to provide new habitat and recreation areas. These activities will help boost urban biodiversity in the catchment, and will complement wider river restoration measures being undertaken in the region. The MERLIN project will also help foster more participatory water management – for example through citizen science initiatives – and explore synergies between water management and environmental restoration.

“The Emscher restoration is, among other drivers, triggering the structural change in the region with the aim of ecological, social and economic sustainability,” say restoration managers from Emschergenossenschaft. “Nature-based solutions are being implemented in the urban areas to enhance climate regulation and adaptation, improving urban climate and the attractiveness of the cities, and thus, enhancing quality of life.”

Find out more.


Removing invasive water hyacinth in the Sorraia catchment. Image: MERLIN

Sorraia catchment, Portugal

Reconnection of floodplains and water flows through ‘blue-green’ restoration.

Rivers and floodplains across the Sorraia catchment in Southern Portugal will be restored using measures which improve water quality, boost biodiversity and encourage natural water flows. The Sorraia River and its tributaries are vulnerable to drought, as a result of a Mediterranean climate compounded by irrigation, flow regulation and damming. There are many permanent barriers such as weirs throughout the basin, which provide obstacles to fish migration. In the lower basin, much of the river system has been deepened and connected to irrigation channels. Agricultural activity also brings water quality issues due to nutrient and pesticide pollution.

Restoration in the Sorraia basin seeks to improve ‘blue-green’ connectivity between the river and its floodplains. Strategies include restoring riparian vegetation along river banks and the removal of exotic invasive plants such as water hyacinth and Brazilian milfoil. Other innovative nature-based solutions to be applied in the catchment include the creation of farm ponds, forest islands and ‘pollinator hotels’ to help boost floodplain biodiversity. It is intended that this ‘blue-green’ landscape restoration will also help reduce nutrient and sediment runoff and reintroduce natural water flow dynamics. Fish passes will also be constructed at weirs and river crossings to reconnect migration corridors.

“The case study has the ambition to quantify the importance of greening in the landscape, especially in agricultural landscapes,” say restoration managers from the University of Lisbon. “Both the National Environmental Authority APA and the National Agriculture Authority are part of the Advisory Committee of the Project, and The Farmers Association is a partner. The results are expected to have impacts that could feedback at the international policy level.”

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Multiple land uses across the Tzipori catchment. Image: MERLIN

Tzipori catchment, Israel

Floodplain restoration and sustainable agriculture across an entire river basin.

The Tzipori River in Israel is fed by natural springs in the Nazareth Hills, and flows 32km through an intensively cultivated catchment to the Mediterranean Sea. The river is subject to a number of ecological stressors including water abstraction for agriculture, channel modification for flood protection, effluent and sewage pollution, and heavily agricultural land-use.

Restoration of the Tzipori catchment – which covers around 300km2 – centres on floodplain restoration, the creation of natural flood retention basins, and the transition to sustainable agricultural practices. It is intended that restored wetlands, floodplains and riparian vegetation will help naturally reduce flood risks, boost biodiversity, improve water quality and provide new opportunities for ecotourism.

“The restoration plan for the Tzipori takes a broad and in-depth ecological and hydrological perspective, accounting for the interfaces of the river with agriculture, urban spaces, and the open, natural landscapes along its entire length,” say restoration managers from Tel Aviv University. “The implementation of this plan, leading to rehabilitation of the entire river through a holistic river-basin approach, is considered a breakthrough in the field of river rehabilitation in Israel.”

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Small stream in the Scheldt catchment. Image: MERLIN

Scheldt catchment, Belgium

Stream restoration for biodiversity habitat and flood protection.

An area of the upper Scheldt River basin around Zwalm in Belgium will be restored through a range of measures aimed at improving biodiversity habitat and water quality and reconnecting fish migration routes. The 355km long Scheldt River flows through France, Belgium and The Netherlands to the North Sea. Its upper reaches consist largely of small brooks, which are heavily impacted by untreated urban wastewater and agricultural pollution.

Restoration work through MERLIN seeks to restore riparian and fish spawning habitat along the upper catchment. Barriers to fish migration will be removed, and fish passes equipped with new online monitoring technologies will be installed to improve the connectivity of the catchment. Advanced new wastewater treatment plan and sewerage systems will be installed to help reduce the environmental impacts of pollution on the upper catchment streams. Water buffer basins along catchment floodplains will help reduce flood risks by slowing the flow of heavily rainfall.

“This project shows that ecological, economic and social aspects of restoration can be optimised in a smart manner, even over large spatial areas in densely populated areas with very high industrial and agricultural activities,” say restoration managers from Ghent University.

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Stream dynamics in the Forth catchment. Image: MERLIN

Forth catchment, Scotland

River restoration in a post-industrial landscape for flood risk, biodiversity and socio-economic benefits.

Restoration work across the Forth catchment in Central Scotland includes both peatland and stream environments. Stream restoration in the catchment will include upscaling work being undertaken on the Allan Water, a tributary of the Forth. Allan Water (like other rivers within the Forth basin) is liable to cause flooding in downstream urban areas as a result of physical modifications to the river and its disconnection with floodplains.

Restoration work through MERLIN seeks to restore connections between the rivers and their floodplains on the Allan, Forth and Teith, to contribute to natural flood management and the restoration of valuable wetland habitats. Measures include placing large woody debris in the river channel and removing sections of engineered bank protection. Rivers will be reconnected to their floodplains through the removal of embankments and the restoration of stream channels, together with riparian tree planting. Through these works, restoration managers hope to create a more natural meandering river course surrounded by biodiversity-rich habitats. It is also intended that this work will help buffer flood risks, store carbon, and help boost local communities.

Restoration of these rivers in MERLIN is undertaken in partnership with The Allan Water Project Steering Group and others, which engages with landowners to support sustainable land management practices.

“The Forth Valley provides a rich and diverse landscape with a wide range of ecosystem services that have been impacted by centuries of mining, industry and urban expansion that along with poor management has compromised the natural assets of soil, water and air and includes areas of significant economic deprivation,” say restoration managers from the University of Stirling. “Despite this, the diverse landscape, interconnected with rivers, lakes, estuary and coastal environments presents many of the solutions required to support a smooth inclusive and just transition to a net zero economy, whilst mitigating against the extremes of climate change.”

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This article is supported by the MERLIN project.