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High levels of pesticide pollution found in streams in German agricultural landscapes

June 17, 2021
Pesticides from intensive agriculture are present at high concentrations in streams across Germany. Image: amberandclint | Flickr Creative Commons

The use of pesticides to control insects, fungi and plants which threaten agricultural production has soared globally in recent decades. One recent study suggests that that around one-third of the planet’s agricultural land is at ‘high risk’ of pesticide pollution, and that aquatic ecosystems are particularly vulnerable to the harmful effects of pesticide run-off.

The 2019 UN Global Environment Outlook states that food production is a major driver of global biodiversity loss, and a significant pollution source for aquatic environments. This is particularly the case where intensified agricultural practices are heavily reliant on chemical pesticides and fertilisers.

A newly-published study suggests that small streams in agricultural landscapes across Germany are heavily polluted with pesticides, causing significant effects on aquatic biodiversity. Over two years, a team of scientists led by the Helmholtz Centre for Environmental Research (UFZ) studied pesticide contamination at more than 100 monitoring sites on streams flowing through agricultural lowland regions across Germany.

The research team found that government ‘safe’ thresholds for pesticides were exceeded in over 80% of the streams. In 18% of the streams, these thresholds were exceeded by more than ten different pesticides, showing the ‘cocktail’ of chemical stressors the small stream ecosystems are subject to.

“We have detected a significantly higher pesticide load in small water bodies than we originally expected,” says Professor Matthias Liess, ecotoxicologist at the UFZ and coordinator of the small water monitoring project.

In some streams the pesticide loads were significantly higher than government thresholds. In three water bodies, the insecticide thiacloprid was detected at concentrations over one hundred times the threshold. In twenty-seven streams, the insecticides clothianidin, methiocarb, and fipronil, as well as herbicides such as terbuthylazine, nicosulfuron, and lenacil, exceeded the threshold 10 to 100-fold.

Researchers studied pesticide contamination in streams in German agricultural landscapes for two years.
Image: André Künzelmann / UFZ

The researchers’ detailed datasets revealed that pesticides negatively impact stream insect communities at much lower concentrations than previously assumed in government risk assessments. “For sensitive insect species, the pesticide concentration in the small lowland streams is the most relevant factor that determines their survival,” says Professor Liess. “In contrast, other environmental problems such as watercourse expansion, oxygen deficiency, and excessive nutrient content are less important. For the first time this study allows a ranking of environmental problems.”

The study suggests that German government thresholds for the management of aquatic pesticide pollution are insufficient for protecting invertebrate communities. The researchers suggest that this is because, until now, the ecological risk posed by pesticides has been predicted using laboratory studies, artificial ecosystems and computer simulations.

“In addition to pesticides, many other stressors act on organisms in the ecosystem,” states Professor Liess. “These make them much more sensitive to pesticides. Natural stressors such as predation pressure or competition between species are not sufficiently taken into account in the risk assessment. But these obvious problems often go unnoticed because the degree of pesticide contamination and the effect of this have not been validated in the field – neither in Germany nor in other countries.”

The scientists found that the type of sampling method use significantly influenced their measurements of pesticide concentrations. Scoop samples of water are standard for water quality monitoring under the EU Water Framework Directive. However, the scientists found that ‘event samples’, which automatically collect water samples after rainfall, provide much higher concentrations of pesticides entering the stream ecosystems.

“The event sample provides much more realistic results because the pesticides enter the water bodies as a result of the increased surface run-off from the field, especially during rain,” says Professor Liess. “In order to realistically depict the water pollution, samples must therefore be taken after rainfall events. That’s why we need an official regular environmental monitoring to be able to assess the amount and the effects of pesticides.”

The study has significant implications for the management of aquatic ecosystems within agricultural landscapes in Germany. ”We are still using pesticides that were approved many years ago based on an outdated risk assessment,” argues Professor Liess. “This must therefore change as soon as possible. Only in this way can we preserve the biodiversity in our waters and with it the services that these biotic communities provide for our ecosystems.”


Liess, M., Liebmann, L., Vormeier, P., Weisner, O., Altenburger, R., Borchardt, D., Brack, W., Chatzinotas, A., Escher, B., Foit, K. and Gunold, R., (2021). “Pesticides are the dominant stressors for vulnerable insects in lowland streams.” Water Research, (open-access until 29 July 2021)

PONDERFUL is launched: pond ecosystems for resilient landscapes in a changing climate

June 4, 2021
The new PONDERFUL project aims to champion and support the value of pond ecosystems. Image: PONDERFUL

Next week marks the launch of the new PONDERFUL project. The EU Horizon 2020 funded project will explore the role of ponds in protecting freshwater biodiversity, delivering ecosystem services, and helping mitigate climate change impacts.

Ponds are increasingly recognised as vital habitats for freshwater biodiversity, and important biogeochemical hotspots. As a result, they are responsible for providing a range of vital ecosystem services. However, ponds and other small freshwaters have long been overlooked in aquatic research.

This means that they are largely under-valued in environmental management and policy. In Europe, for example, the Water Framework Directive almost completely ignores ponds in its freshwater policy guidance.

“PONDERFUL is the largest EU-funded project to date on the role of ponds in protecting biodiversity and delivering ecosystem services, specifically to mitigate and adapt to the impacts of climate change,” says Professor Sandra Brucet, who leads the PONDERFUL project.

”We expect to create unique new datasets linking freshwater biodiversity to the delivery of ecosystem services, to help us give better advice to land and water managers working to protect freshwater biodiversity and deliver vital ecosystem services,” continues Professor Brucet. “This fundamental new data will particularly help us better define the relationship between aquatic biodiversity and the production of greenhouse gases, a major concern in the management of aquatic habitats.”

Ponds have long been overlooked in scientific research and undervalued in environmental policy. Image: PONDERFUL

The PONDERFUL project involves 18 partners from 11 states – including Uruguay in South America – forming what is likely to be the largest-ever pond research project. The project is designed to support IPBES and other biodiversity strategies and conventions to better protect freshwater biodiversity, which, as this blog has documented, is a severely threatened component of global biodiversity.

“We’ve brought together a strong international team of aquatic ecologists, geochemists, modellers, landscape conservationists and social scientists, and will collaborate closely with relevant stakeholders,” says Professor Brucet. “This will help provide new guidance to policy makers and practitioners to help them maximise the enormous practical benefits to be gained from working with ponds.”

Ponds are known to be freshwater hotspots, but new research shows they can help landscape-wide recovery too. Many of the existing pond ecosystem studies have taken place in Europe, and there is a significant need for additional research, both across the continent and globally.

“We think PONDERFUL could create a step change in interest amongst both researchers and practitioners in the role of these small, but critical, habitats,” says Dr Jeremy Biggs, from the UK Freshwater Habitats Trust, which has championed the importance of ponds for 30 years. “There may be as many as 3 billion ponds on the planet, and their importance is out of all proportion to their size. Although often regarded as ‘the humble pond’, we regard them as frankly miraculous, hence our adoption of the neat acronym ‘PONDERFUL!’”

PONDERFUL will bring together researchers both from across Europe, and globally. Image: PONDERFUL

The PONDERFUL online launch will mark the start of collaborations between over 500 researchers and practitioners from 39 countries in Europe. The launch, which will introduce the value and importance of pond ecosystems, will also promote the Ramsar Convention’s 2018 Resolution XIII.21 on the ‘conservation and management of small wetlands’.

“In the UN Decade on Ecosystem Restoration, with the protection, creation and management of ponds we have perhaps the most achievable, deliverable and impactful single water management programme we find to protect freshwater biodiversity,” says Dr Biggs. “We just need to make people aware of the enormous benefits to be associated with these ancient, natural and rich freshwater ecosystems.”

The PONDERFUL online launch takes place from 1500hrs (CEST) on Thursday 10th June 2021. Attendance is free, sign up here.

Developing MEASURES for reconnecting migratory fish habitats in the Danube basin

May 28, 2021
The Danube at Mitterhaufen, Austria. The MEASURES project aimed to restore ecological river corridors across the Danube basin. Image: MEASURES

In 2019 we featured a major new freshwater project, MEASURES, founded to manage and restore ecological riverine corridors in the Danube River basins. Funded by the EU as part of the Danube Transnational Programme, MEASURES aimed to improve habitat quality and connectivity along the Danube in order to support populations of six threatened sturgeon species, as well as other migratory fish and wider aquatic biodiversity in the basin.

Earlier this month, the project held its final conference, bringing together participants from diverse fields interested in the conservation and restoration of the Danube basin.

“The MEASURES final conference was held to disseminate the key results of the project, and to present linkages with other initiatives dealing with revitalisation and ecological continuity of the Danube and its tributaries,” says project manager Silke Drexler. “Although the conference took place virtually, it was of high interest to a broad group of stakeholders. The participants included scientists, experts from NGOs, practitioners from private companies, and from governmental agencies. The vibrant discussions addressed topics such as eDNA, broodstock collection, science-policy implementation and future projects for a vital eco-corridor along the Danube.”

The MEASURES project had four key areas of activity, each accompanied by a fact-sheet. First, the project created a series of ‘Infosystem Eco-Corridors’, based on the establishment of a network of Danube stakeholders across 8 partner countries. A new MEASURES Information System (MIS) was developed, hosting online information on migratory fish and habitats in the Danube basin, linked to the Freshwater Information Platform and the Danube Future Knowledge Base. (fact-sheet)

Second, project researchers undertook fieldwork and data collection to map potential sturgeon habitats along the Danube and its tributaries. This resulted in a publication, the Danube Migratory Fish Habitat Manual, which detailed key sturgeon habitats in the basin, and the methods used to map them. The habitat mapping activities in MEASURES have already contributed to the latest draft of the Danube River Basin Management Plan (fact-sheet)

Third, the project undertook a series of activities to strengthen populations of migratory fish populations in the Danube basin. These included restocking programmes for Russian sturgeon and sterlet, alongside the development of an eDNA sampling method to monitor their populations (activities featured in a recent issue of the World Wildlife Magazine). Project researchers collected gene stocks of sturgeon populations from broodstock and ex-situ samples for future stocking, which is hoped to be undertaken through a follow-up project, LIFE–Boat 4 Sturgeons. (fact-sheet)

Fourth, MEASURES published a new Strategy for the Danube Ecological Corridor, which built on project findings to outline how migratory fish habitats can be restored and reconnected through the Danube basin. The MEASURES Strategy is designed to help support and improve environmental management plans and legislation at different scales throughout the basin, providing suggestions for specific conservation and restoration activities. Details of the Strategy, and the MEASURES eDNA monitoring methods, will be explored in further blog posts over the coming months. (fact-sheet)

Attendees at the virtual MEASURES final conference.

A policy brief entitled Solutions and Barriers – Conservation of Migratory Fish Species and Their Habitats synthesises these activities, and calls for the establishment of a Regional Water Council on the Mura and Sava rivers in order to better support local, national and international cooperation. The MEASURES website features a wealth of information about the Danube basin and its migratory fish species, including an archive of newsletters, images and a 2021 calendar.

“The MEASURES project involved 24 partners from 13 countries cooperating to secure threatened riverine fish species,” says project co-ordinator Thomas Hein. “Our three year cooperation allowed major steps in gaining new knowledge on migratory fish in the Danube River Basin and transferring these insights into practice. MEASURES is an excellent example of cross-sectoral international collaboration to address an important aspect of freshwater biodiversity.”


MEASURES website
MEASURES Information System (MIS)

Lake heatwaves to become ‘hotter and longer’ by the end of the century

May 20, 2021
Lake Isabella, California, under drought conditions. New research suggests that heatwaves will become increasingly common influences on global lake ecosystems in coming decades. Image: Don Barrett | Flickr Creative Commons

Lake ecosystems across the world are increasingly vulnerable to water temperature increases caused by ongoing climatic change. Species of plants, fish and animals that live in lakes are particularly susceptible to the effects of climate change, because they have often adapted to local conditions and lack the ability to migrate away from a changing habitat.

As recent research has shown, warming water temperatures can interact with other environmental stressors such as nutrient pollution to cause significant ecological issues like eutrophic algal blooms. However, until recently, little was known about lake heatwaves, particularly how and where they will occur in the future.

IntEL, a newly-completed EU-funded research project, has recently provided the first detailed study of lake ecosystem responses to warming temperatures under predicted future climate change. “Quantifying and understanding these changes is crucial if we are to try to mitigate these impacts,” says Prof. Eleanor Jennings, IntEL project coordinator. “In addition, the ability to describe and quantify these effects can contribute to the weight of evidence that the global population must reduce their output of greenhouse gases”

Writing in the Nature journal, IntEL researchers provide a new metric to quantify lake heatwaves, produced through computer modelling work across hundreds of sites globally. The research team show that lake heatwaves are likely to become “longer and hotter” by the end of the 21st Century. Significantly, they suggest that some lakes will reach a permanent heatwave state extended over multiple years.

“Lake heatwaves are defined as periods of anomalous lake surface temperatures, when temperatures exceed historical average conditions for that time of year,” says IntEL research fellow Dr. Iestyn Woolway. “The metric developed can be applied to any lake on Earth but, in this study, we focused solely on lakes using satellite observations.”

The researchers suggest that by the end of the 21st Century, many global lakes will have increased water temperatures as a result of more regular heatwave events. Heatwaves, in many lakes, will thus cease to be extreme events, and instead become part of ‘normal’ ecosystem conditions.

The project findings have significant implications for freshwater life in lakes. The researchers highlight the potential for ecosystem shifts as a result of decreased ice cover, decreased water oxygen levels, and increased cyanobacteria blooms in different lakes.

Similarly, they note the potential for warming water temperatures to alter the mixing and cycling of thermal layers and nutrients in some lakes. The likely result is the alteration, or loss, of habitat for biodiversity in many lakes, potentially causing the breakdown of food webs. Species already at the upper limit of their temperature tolerance, and those unable to migrate to more favourable habitats, may become locally extinct.

The researchers write, “These complex inter-actions are hard to forecast, but the extreme heatwave in the summer of 2003 in central Europe illustrated the range of effects that might be expected, including increased thermal stability and hypolimnetic oxygen depletion, production of cyanobacterial blooms and a regime shift from pelagic to benthic productivity.”

In other words, whilst we can expect lake heatwaves to increase in intensity and duration across the world in the coming decades, it is difficult to accurately forecast the resulting ecological impacts. This uncertainty provides a convincing argument both for transitioning to low-carbon economies to minimise future climatic change, and in building climate resilience into freshwater systems through habitat conservation and restoration work.

The IntEL researchers are not finished with their work, however. “Future work will investigate the influence of climate change on a host of other essential lake properties, including the phenology of lake stratification – the vertical layering that exists in many lakes in summer – and the influence of warming on greenhouse gas production in lakes,” says Prof. Jennings.


Woolway, R.I., Jennings, E., Shatwell, T. et al. Lake heatwaves under climate change. Nature 589, 402–407 (2021).

‘Plastic is everywhere’: microplastics found in 1950s freshwater fish specimens

May 7, 2021
Specimens of sand shiner fish in the Field Museum’s collections collected in 1972, 1953, and 1907. Image: Kate Golembiewski, Field Museum

Freshwater fish have been swallowing microplastics since at least the 1950s, according to a newly published study. Microplastics – tiny threads and fragments of plastic resulting from the breakdown of waste, clothing and cosmetics – are an increasingly important topic of environmental concern, having been found in deep oceans, on high mountain tops, and even in the atmosphere.

A team of researchers examined preserved freshwater fish specimens from the Chicagoland region, USA, kept in the Field Museum collection. Four species in the museum collection – largemouth bass, channel catfish, sand shiners, and round gobies – had specimen records dating back to 1900. The team’s analysis shows that once plastic manufacturing became industrialised in the 1950s, microplastics began to significantly accumulate in the fishes’ bodies.

“For the last 10 or 15 years it’s kind of been in the public consciousness that there’s a problem with plastic in the water. But really, organisms have probably been exposed to plastic litter since plastic was invented, and we don’t know what that historical context looks like,” says Dr. Tim Hoellein, associate professor of biology at Loyola University Chicago and the corresponding author of the new study, published in the Ecological Applications journal. “Looking at museum specimens is essentially a way we can go back in time.”

Working with Dr. Caleb McMahan, an ichthylogist at the Field Museum, Hoellein and graduate student Loren Hou examined the preserved fish specimens for evidence of microplastics. “We would take these jars full of fish and find specimens that were sort of average, not the biggest or the smallest, and then we used scalpels and tweezers to dissect out the digestive tracts,” says Hou, lead author of the new study. “We tried to get at least five specimens per decade.”

Hou used hydrogen peroxide to look for microplastics in the preserved fishes’ digestive tracts. “It bubbles and fizzes and breaks up all the organic matter, but plastic is resistant to the process,” she says. Under the microscope, microplastics more than half-a-century old were revealed. ”We look at the shape of these little pieces. If the edges are frayed, it’s often organic material, but if it’s really smooth, then it’s most likely microplastic,” says Hou.

“We found that the load of microplastics in the guts of these fishes have basically gone up with the levels of plastic production,” says McMahan. “It’s the same pattern of what they’re finding in marine sediments, it follows the general trend that plastic is everywhere.”

The research team point to a key cause of microplastics discovered in the fish specimens: fabrics. Many of the microplastics they discovered were thread-like and likely to have been washed out of clothing. “It’s plastic on your back, and that’s just not the way that we’ve been thinking about it,” says Hoellein. “So even just thinking about it is a step forward in addressing our purchases and our responsibility.”

A portion of the Field Museum’s fish collections, which contain two million specimens and are primarily housed in underground storage in the museum’s Collection Resource Center. Image: Kate Golembiewski, Field Museum

The researchers cannot say for sure how microplastic ingestion affected the fish specimens studies, but it is likely to have caused physiological effects. “When you look at the effects of microplastic ingestion, especially long term effects, for organisms such as fish, it causes digestive tract changes, and it also causes increased stress in these organisms,” says Hou.

Their study is published on the heels of the claim that scientific breakthroughs could facilitate the use of bacterial biofilms to trap and recover microplastics from rivers, lakes and seas. Speaking to the Microbiology Society’s Annual Conference at the end of April, Yang Liu, a researcher at Hong Kong Polytechnic University, and colleagues are hopeful that a naturally occurring bacteria can be used to colonise and aggregate microplastics in the environment, causing them to sink for removal.

Liu outlines why microplastic is such an important environmental issue, “Microplastics are not easily bio-degradable, where they retain in the ecosystems for prolonged durations. This results in the uptake of microplastics by organisms, leading to transfer and retention of microplastics down the food chain.

“Due to their huge surface area and adsorption capacity, microplastics can adsorb toxic pollutants, such as pesticides, heavy metals, and drug residues at high concentrations. This leads to biological and chemical toxicity to organisms in the ecosystems and humans after prolonged unintended consumption of such microplastics. Moreover, microplastics are also difficult to remove in wastewater plants, resulting in their undesired release into the environment,” Liu states. Liu and colleagues hope that their nascent technique will eventually be used in wastewater treatment plants to stop microplastics travelling into the wider environment.

For now, the museum specimen study by Hou and colleagues reminds us that for all its contemporary interest, microplastic pollution is nothing new. Hou and colleagues hope their study will act as a ‘wake-up call’ for the public and politicians to take notice of the widespread and pervasive nature of microplastic pollution in our aquatic environments.


Loren Hou et al (2021), A fish tale: a century of museum specimens reveal increasing microplastic concentrations in freshwater fish, Ecological Applications. DOI: 10.1002/eap.2320

One of Europe’s last wild rivers: biodiversity and hydropower on the Vjosa River

April 23, 2021
Braided river channel on the Vjosa River, Albania. Image: Gregor Subic

The Vjosa River in Albania is often termed one of ‘Europe’s last wild rivers’. It flows unobstructed by dams and hydropower plants along its 270km course through deep canyons, braided channels and wide meanders to the Adriatic Sea. The fact that the Vjosa River’s course – and that of its tributaries – is intact makes it a unique river system in Europe.

In recent years, scientists and campaign groups have undertaken a series of research projects and public events in order to highlight the Vjosa’s diverse ecosystems, and the biodiversity they support. This work has been carried out in response to the increasing threat of hydropower construction in the Vjosa catchment. Whilst the Vjosa is bordered by a number of protected areas, it has little environmental protection, and as a result there are currently 38 hydropower plants planned for construction within its catchment. However, up until recently, there has been very little data available on the Vjosa’s ecological and fluvial diversity, meaning environmental campaigners have had scant scientific evidence available to support their work.

A newly released report provides the first ‘baseline’ study of the Vjosa’s ecosystems and biodiversity, stating that the river is an extremely rare site with valuable habitats supporting numerous protected and endangered species. A team of scientists – co-ordinated by Dr. Paul Meulenbroek at the University of Natural Resources and Life Sciences, Institute of Hydrobiology and Aquatic Ecosystem Management (IHG) in Vienna – documented over 1100 plant and animal species, many of which are protected under national and international law. Their study suggests that the Vjosa is thus one of the few remaining ‘reference’ sites for dynamic floodplains in Europe, characterised by its ‘near-natural’ status.

The report authors use their findings to make a series of objections to the proposed Kalivaç hydropower plant. The Kalivaç project was originally approved in 1997, but its construction – close to the town of Tepelena – has never been finished, and the river still flows uninterrupted. However, plans for the project’s construction continue, with a proposed 43 metre-high rockfill dam across the river which would create a 16km² reservoir as a means of generating hydropower electricity.

The authors make three main objections to construction. First, they argue that the Kalivaç project would lead to the complete and irretrievable loss of more than 1000 hectares of natural and near-natural river and floodplain landscape. They suggest that such “destruction of one of the greatest wild river landscapes in Europe” would cause local decreases in around 40% of all species, and block over 800km of the river network to migratory fish.

Second, the authors suggest that the Kalivaç project poses a significant local biodiversity extinction risk, and it is expected to destroy around 870 hectares of habitat listed by the EU Habitat Directive. As such, the authors state that the project poses a contravention of a number of European and international laws and conventions, also including the IUCN Red List, the Bern Convention, and Birds Directive.

Third, the report states that the Kalivaç reservoir would fill with sediment within 60 years, leading to an ongoing loss in energy potential each year, and requiring significant dredging management. The authors suggest that such sedimentation would pose high economic costs to hydropower managers, cause ongoing ecological losses, and limit the potential of the Vjosa catchment to attract eco-tourists.

Image: Sébastien Champeaux

The report is released only weeks after environmental activists staged public interventions in Paris, Brussels, Berlin and Tirana, where fabric spelling out ‘Vjosa National Park Now’ was draped in the foreground of heritage monuments. The interventions were coordinated by the Save the Blue Heart of Europe campaign as a means of highlighting the need to designate the Vjosa as Europe’s first Wild River National Park. In September 2020, Albanian Prime Minister Edi Rama stated his intention to protect the Vjosa, but there has been little subsequent progress, and the current environmental protection designations offer only minimal protection from future hydropower construction.

The authors of the new report conclude by outlining the urgent need for significant new environmental protections for the Vjosa catchment. They write, “The fauna and flora of this highly dynamic river represent the last inhabitants of a dwindling river refuge. Their survival depends on well-planned management of both the catchment and the surrounding areas. As a model for restoration measures, and a cradle of biodiversity and natural heritage, this river and its community are too important to be lost.”


Meulenbroek, P., Egger, G., Trautner, J., Drescher, A., Randl, M., Hammerschmied, U., Wilfling O., Schabuss, M., Zornig, H., Graf, W. (2020) The river Vjosa – A baseline survey on biodiversity, potential impacts, and legal framework for hydropower development. pp. 180. DOI: 10.5281/zenodo.4139640

Catch the drift: river fish and birds rely on mobile invertebrate prey

April 9, 2021
Dipper. Image: Charles Tyler

New research shows how salmon, trout and river birds in Welsh upland rivers rely on invertebrate prey with specific ‘drifting’ behaviours for their food sources.

The open-access study, led by Cardiff University, found that iconic predatory fishes, such as the brown trout and Atlantic salmon, and birds, such as the Eurasian dipper and grey wagtail, are most abundant where invertebrate prey have certain characteristics. Specifically, all the predators were most numerous where mobile ‘drifting’ prey such as mayflies occurred abundantly in fast flowing habitats. These traits also predicted predator populations more effectively than overall prey variety or abundance.

The team from Cardiff, Cambridge and Roehampton Universities, the British Trust for Ornithology and Imperial College of London assessed predator numbers along Welsh upland rivers in relation to invertebrate numbers and trait composition. Researchers were also interested in assessing whether these specific aspects of biodiversity were important elements in river ecosystem services such as economic gains from angling or cultural values.

“Our work demonstrates the importance of river invertebrates – the ‘hidden biodiversity’ that is often underappreciated by society – in sustaining well-known and iconic river predators” said Dr Cayetano Gutiérrez-Cánovas, lead author of the study. “Roughly half of European rivers currently fail against EU targets for ecological status which is likely to reduce invertebrate numbers and prey availability for freshwater predators – yet this link is seldom made or recognised by those charged with managing river ecosystems”, states Gutiérrez.

Grey wagtail. Image: Charles Tyler

Co-author of the study, Prof Steve Ormerod added:

“We’ve known for some time that predators specialise on certain prey types – for example invertebrates of the correct size for adult birds to feed their young, or prey rich in calcium for egg formation. But this new study shows us how several river predators converge on accessible, drifting prey in faster flows. This raises intriguing questions about how they divide up these prey resources, but also how we can manage and restore rivers to ensure that these and other predators can co-exist in numbers.”

The findings of this study might go some way to explaining dramatic declines of freshwater vertebrates by showing how reliance on river invertebrates can make aquatic predators vulnerable to ongoing river degradation or the transfer of toxicants to apex predators.

Amidst growing concerns about the plight of freshwater vertebrates, the study illustrates how healthy invertebrate populations benefit predators while also helping society. Invertebrate-dependent salmonids, such as trout and salmon, are highly ranked in recreational fishing that boosts visitor numbers, employment and local economies. In addition, greater invertebrate availability also benefits bird conservation, with all its associated cultural value and opportunities for ecotourism.

This research was funded by the NERC DURESS investigation into the benefits that upland rivers provide to society as well as the EU MARS study of multiple stressors on freshwater ecosystems.


Gutiérrez‐Cánovas, C., Worthington, T. A., Jâms, I. B., Noble, D. G., Perkins, D. M., Vaughan, I. P., Woodward, G., Ormerod, S.J. & Durance, I. (2021). Populations of high‐value predators reflect the traits of their prey. Ecography. (open-access)

Leaky sewers cause hidden nutrient pollution in German urban waters

March 26, 2021
Sewers under Berlin, Germany. Image: SnaPsi | Flickr Creative Commons

A growing body of research suggests that untreated wastewater leaking from damaged or badly designed sewer systems is a key source of urban water pollution. However, data on sewer leaks and pollution is often missing from large-scale environmental assessments of urban areas.

A new study by Dr. Hong Hanh Nguyen and Dr. Markus Venohr from the Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB) in Berlin responds to this deficit. The authors propose the first German national estimation of wastewater losses from defective sewer systems by bringing calculations of sewer leaks into urban catchment models.

“Sewer systems are hidden in the ground and perform an important – but often unrecognised – job to collect wastewater ahead of its subsequent treatment,” says co-author Dr. Markus Venohr. “Damage to sewer systems, and any potential leaks into surrounding ground, are often hard to detect and quantify,” Dr. Venohr explains. “As a result, these aspects are usually neglected in large-scale nutrient emission modelling.”

The researchers upscaled local calculations of sewer leaks to both pipe, city and municipality scales using a combination of datasets and expert knowledge. They found that pollution from sewer leaks is found across both public and private sewers, but is particularly common in ageing pipes more than 40 years old.

“In our new paper, we calculate the contribution of losses from leaking sewer systems to overall Germany-wide nutrient emissions,” Dr. Venohr continues. “We discuss these nutrient losses within the framework of the LAWA-funded project AGRUM-DE, to which our work makes an important contribution.”

“Our study shows that sewer age and type, together with human population density, are key factors influencing the potential for sewer losses from public and private sewers,” says Dr. Venohr.

One key finding from the study is that water pollution from leaking sewers might account for between 10–20% more nutrient loads entering groundwater from urban areas across Germany than previously calculated.

“Overall, sewer leaks were estimated to locally add a substantial share of nutrient emissions from urban systems to groundwater, and thus to surface waters,” Dr. Venohr outlines.

The study stresses the importance of addressing leaky sewer systems as a potentially significant source of water pollution in urban environments. The authors suggest that their study framework will allow environment managers to better target pollution sources and incorporate leaky sewers as part of the long-term nutrient water management of agricultural and urban emissions.


Nguyen, H.H., Venohr, M. Harmonized assessment of nutrient pollution from urban systems including losses from sewer exfiltration: a case study in Germany. Environ Sci Pollut Res (2021).

Towards a freshwater ethic: lessons from Aldo Leopold for contemporary aquatic conservation

March 10, 2021
Aldo Leopold on a trip to the Rio Gavilan watershed in Mexico’s northern Sierra Madre Occidental. It was here that some of his key ideas about land and water conservation were formed in the 1930s. Image: Pacific Southwest Forest Service, USDA | Flickr Creative Commons

“All ethics so far evolved rest upon a single premise: that the individual is a member of a community of interdependent parts. The land ethic simply enlarges the boundaries of the community to include soils, waters, plants and animals, or collectively the land.” This is the core of early-20th Century American conservationist Aldo Leopold’s outlook on environmental management, or as it his commonly known, his ‘land ethic’.

Writing in his seminal A Sand County Almanac, published in 1949, Leopold outlines a gently-radical ecosystem-orientated approach to natural resource management, in which humans are encouraged to foster a responsible and sustainable relationship with the biotic communities with whom they share a landscape. The book, which in a series of essays documents the ecosystems on Leopold’s farm in Wisconsin, and more widely in the USA, Canada and Mexico, is a landmark text in the development of the American (and arguably, global) conservation movement. In no small part due to its lyrical tone, A Sand County Almanac is also widely cited as popularising public debates in both ecology and environmental ethics.

The ‘land’ in Leopold’s land ethic leads a casual reader to assume that he was solely interested in terrestrial ecosystems. However, as the quote above shows, Leopold’s land ethic explicitly includes a responsibility towards the conservation of aquatic ecosystems. Indeed, Leopold was a keen angler, and wrote about the sustainable management of rivers and streams, particularly in terms of the impact of soil erosion and run-off as a result of poor land management.

More than half a century later, then, could Leopold’s work be used to develop a ‘freshwater ethic’ which could strengthen contemporary aquatic conservation? According to a team of freshwater researchers writing in the Aquatic Conservation journal, there is rich potential to rediscover Leopold’s work in this way.

The team, led by Prof. Steven J Cooke from Carleton University, Canada, reflect on Leopold’s scholarship to identify a set of ‘Aldo-inspired’ recommendations for protecting and restoring freshwater ecosystems in an Anthropocene era. These include: adopting an ecosystem approach; managing freshwaters as coupled social-ecological systems; acknowledging the limits to human dominance over freshwater systems; and addressing the underlying causes of environmental issues rather than their symptoms.

“2020 was the 70th anniversary of Aldo Leopold’s land ethic,” says Prof. Cooke. “That seemed like an opportune time to take a pause and reflect on what the land ethic has meant in terms of aquatic conservation and consider how it could be used to explicitly define a freshwater ethic.”

“There are few ecologists and nature conservationists whose thinking has not been touched, or even inspired, by Aldo Leopold: the ethical notions that love and respect for the natural environment stem from a perspective in which ‘land is a community to which we belong’; that our action is ‘right when it tends to preserve the integrity, stability and beauty of the biotic community,’” says co-author Prof. Steve Ormerod from Cardiff University. “Although stated often as a ‘land ethic’, Leopold’s boundaries embraced soil and water as much as they embraced plants and animals: an environmental whole of which we are citizens.”

“One of Leopold’s first peer reviewed papers was in Transactions of the American Fisheries Society and he was responsible for the management of aquatic resources at various times in his career. It is easy to think of Leopold as being concerned about land and terrestrial wildlife but his definition of both was inclusive in many ways and he certainly understood the interconnections between land and water,” Prof. Cooke says.

Aldo, Carl, and Estella Leopold beside the Wisconsin River. Image: Aldo Leopold Archives.

The journal authors argue that Leopold’s outlook has significant value for contemporary freshwater management. This is reflected in their ‘Aldo-inspired’ recommendations, which also include: acting now to address the biodiversity crisis, even when faced with uncertainty; identifying ‘win-win-win’ scenarios in which the value of clean water is shown to have wide societal benefits; and the vital nature of ‘wild’ or barely-modified rivers.

Moreover, the authors look to Leopold to remind us that freshwaters are a core element of diverse human-nature relationships, and a sense of ‘freshwater optimism’ is necessary to make positive conservation progress. On this point, the authors quote Leopold on his conservation philosophy, writing in 1938 that, “We shall never achieve harmony with the land, anymore than we shall achieve absolute justice or liberty for people. In these higher aspirations the important thing is not to achieve but to strive.”

“The plight of freshwater ecosystems – now some of the most threatened on earth – motivated us to re-emphasise Leopold’s holistic view in our paper,” states Prof. Ormerod. “Human actions around freshwaters so often reflect a careless assumption that rivers and lakes exist for drinking water, for waste disposal or for hydropower. Or that wetlands can be drained for development without thought for the consequences. Freshwater ecosystems are critical to our survival – and Leopold reminds us not only of our ethical responsibility towards them, but that our own fate will be tied to theirs.”

“Today A Sand County Almanac remains on the reading list in many natural resource management programs,” says Prof. Cooke. “It is our hope that our essay will help to inspire the next generation of aquatic biologists and managers to consider Leopold’s wisdom and apply his principles to contemporary conservation problems.”


Cooke, SJ, Lynch, AJ, Piccolo, JJ, Olden, JD, Reid, AJ, Ormerod, SJ. Stewardship and management of freshwater ecosystems: From Leopold’s land ethic to a freshwater ethic. Aquatic Conserv: Mar Freshw Ecosyst. 2021; 1– 13.

World’s ‘forgotten fishes’ in catastrophic decline

February 23, 2021
Snorkelling in a river in Western Cape, South Africa. Image: Jeremy Shelton

Nearly a third of global freshwater fish species are threatened by extinction, according to a major new report compiled by 16 conservation groups.

Released today, The World’s Forgotten Fishes report states that 80 species of freshwater fish are known to have gone extinct, with 16 of these extinctions occurring in the last year alone. Since 1970, populations of migratory freshwater fish have fallen by 76%, and large ‘megafauna’ fish species by a startling 94%.

The report, published by a coalition of groups including WWF, IUCN, and the Alliance for Freshwater Life, highlights the rich variety of global freshwater fish species: the current known total of 18,075 species accounts for over half of all the world’s fish species, and a quarter of its vertebrate species.

However, despite the vital role these fish species play in human health, food security, livelihoods and culture for communities across the world, many of their populations are in critical decline. Common threats to freshwater fish include habitat destruction, hydropower dam construction, agricultural and industrial pollution, and climate change. In some regions, overfishing, poaching and invasive species are also key pressures.

The Iznajar hydropower dam in Spain. Dam construction is one of the key threats to freshwater fish populations in global rivers. Image: Global Warming Images / WWF

“Nowhere is the world’s nature crisis more acute than in our rivers, lakes and wetlands, and the clearest indicator of the damage we are doing is the rapid decline in freshwater fish populations. They are the aquatic version of the canary in the coalmine, and we must heed the warning,” says Stuart Orr, WWF Global Freshwater Lead.

“Despite their importance to local communities and indigenous people across the globe, freshwater fish are invariably forgotten and not factored into development decisions about hydropower dams or water use or building on floodplains. Freshwater fish matter to the health of people and the freshwater ecosystems that all people and all life on land depend on. It’s time we remembered that,” Orr argues.

The report is published only days after a paper in the journal Science shows that half of all global river systems have been significantly impacted by human activities, with only very large tropical basins subject to lower levels of alteration. The study, by Dr. Guohuan Su and colleagues, states that freshwater fish biodiversity has become homogenised in many river basins due to human alterations, primarily river fragmentation and the introduction of non-native species.

Freshwater fish are part of vital aquatic ecosystems, providing prey for predators such as this giant otter in the Pantanal, Brazil – the world’s largest tropical wetland. Image: R.Isotti, A.Cambone / Homo Ambiens / WWF

However, despite the declining trends in freshwater fish populations across the world, The World’s Forgotten Fishes ends on a hopeful note. It argues that 2021 is a crucial year to address the freshwater biodiversity crisis, through implementing the tenets of the WWF-led Emergency Recovery Plan into a New Deal for Nature and People ahead of the UN Convention on Biological Diversity (CBD) conference held in Kunming, China in May.

“The good news is that we know what needs to be done to safeguard freshwater fishes. Securing a New Deal for the world’s freshwater ecosystems will bring life back to our dying rivers, lakes and wetlands. It will bring freshwater fish species back from the brink too – securing food and jobs for hundreds of millions, safeguarding cultural icons, boosting biodiversity and enhancing the health of the freshwater ecosystems that underpin our well-being and prosperity,” states Orr.

“What we need now is to recognise the value of freshwater fish and fisheries, and for governments to commit to new targets and solutions implementation, as well as prioritising which freshwater ecosystems need protection and restoration. We also need to see partnerships and innovation through collective action involving governments, businesses, investors, civil society and communities,” concludes Orr.

Freshwater fish populations are crucial sources of food and livelihood to many communities across the world, including this fisherman on the Luangwa River, Zambia. Image: James Suter / Black Bean Productions / WWF-US


Read The World’s Forgotten Fishes report.