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‘Modest’ fine sediment and phosphate pollution in English rivers causes mortality of up to 80% of mayfly eggs

January 12, 2018

Blue-winged Olive. Image: Francisco Welter-Schultes | Wikipedia Creative Commons

Increased levels of fine suspended sediment and phosphate in aquatic ecosystems can have significant negative impacts on the survival of mayfly eggs, according to a new study. Relatively modest levels of pollution can kill up to 80% of eggs, with potentially devastating effects on mayfly populations and wider aquatic food webs.

Writing in the journal Environmental Pollution, a team of researchers led by Nick Everall of the Aquascience Consultancy carried out experiments on the blue-winged olive, a species of mayfly found across Europe, whose populations have fallen in recent decades.

Fine sediments and phosphate pollution from agricultural run-off and untreated sewage have been identified as key causes of this decline. However, until now, research has focused largely on the response of adult and larval mayfly to such multiple stressors.

Supported by the Salmon and Trout Conservation UK, the research team collected eggs of the blue-winged olive to be incubated in laboratory aquariums under different concentrations of fine suspended sediments and phosphate.

In the wild, blue-winged olive eggs are laid on the beds of fast-flowing streams and rivers, and have to survive over winter for up to eight months before hatching into nymphs. As a result, it is important to understand how stressors affect this crucial early stage in the insect’s life cycle. The researchers found that fine sediments cover mayfly eggs, starving them of oxygen and encouraging fungus growth, whilst phosphate can inhibit egg development.

When low levels of fine sediment were added to experiments with raised phosphate levels, the mortality of mayfly eggs increased significantly. However, when phosphate was added to experiments with increased amounts of fine sediment, mortality was not significantly increased.

This finding suggests that fine sediment has a greater impact on mayfly egg mortality than phosphate. As a multiple stressor relationship, it suggests that the run-off of fine sediments into aquatic ecosystems already stressed by phosphate pollution could have significant negative consequences for mayfly populations.


Mayfly egg mortality increases as suspended sediment concentrations rise at a constant level of phosphate concentration. Image: Journal Authors.

Significantly, relatively modest levels of each stressor had damaging effects on mayfly egg survival. The concentrations of fine sediment and phosphate used in this experiment were largely below the Water Framework Directive defined thresholds for river management in England. At levels close to the upper limits for management – 25mg per litre of fine sediment and 0.07 mg per litre of phosphate – the mortality rate of mayfly eggs in the experiment was 80%.

Whilst the experimental conditions don’t fully represent the fluctuating nature of pollutant concentrations found in most rivers, the research team argue that their findings show that the annual mean suspended sediment guideline standard of 25 mg per litre for the UK is not sufficient to conserve mayfly populations.

More broadly, they suggest that increased attention needs to be paid to managing fine sediment into rivers across Europe, particularly as many rivers across the continent have raised phosphate levels. The implementation of effective mitigation strategies for reducing erosion and run-off of fine sediments from agricultural land surrounding rivers is clearly needed.

Everall NC et al (2017) Sensitivity of the early life stages of a mayfly to fine sediment and orthophosphate levels, Environmental Pollution, Online: In Press.

MARS final conference: Managing multiple stress for multiple benefits in aquatic ecosystems

January 5, 2018

Museum of Natural Sciences, Brussels. Image: IRSNB – Thierry Hubin

Over the last four years, the MARS project has investigated the impacts and interactions of multiple stressors in European aquatic ecosystems. Funded under the EU FP7 programme, research within MARS has addressed uncertainties over how to detect, conceptualise and manage multiple stressors in surface waters. MARS was designed to support the implementation and review of the EU Water Framework.

This month MARS will host a conference ‘Managing multiple stress for multiple benefits in aquatic ecosystems’ in Brussels, Belgium to communicate the key results and recommendations from the project. Taking place over two days on 16-17 January, the conference will be have two themes – science, and management/policy.

Conference events on Tuesday 16th will focus on scientific findings, and feature sessions which summarise and review the main MARS outcomes within the context of aquatic multi-stressor research.

On Wednesday, 17th, discussions will turn to the management and policy implications of MARS research. Conference sessions will introduce MARS products for managers and policy makers (such as factsheets, guidance and tools) and discuss effective river basin management and policy under multi-stress conditions.

Hosted by the Museum of Natural Sciences in Brussels, the conference is likely to be of interest to aquatic scientists, water managers and administrators, as well as policy-makers and executives. Conference registration is free.

A conference agenda with full details of speakers and sessions is available as a PDF here.

Top 17 posts of 2017

December 29, 2017

Water outflows from Fewston Reservoir, UK. Image: James Whitesmith | Flickr Creative Commons

As the end of the year approaches, we’ve looked back over 2017 to collect 17 of our most popular posts on freshwater science, policy and conservation.

It’s been the most successful year yet for the Freshwater Blog, with record numbers of visitors. Thanks, as always, for reading. You can keep up to date with our posts, and add your voice to the debate, through our Twitter, Facebook and LinkedIn pages.

The MARS project, which has investigated the interactions and impacts of multiple stressors on aquatic ecosystems since 2014 (and which supports this blog), hosts its final conference in January 2018. You can find out details here.

Happy 2018!


Caddisfly larvae tend remarkable underwater ‘gardens’ (January)


Caddisfly (Tinodes waeneri) larva. Image: Guam Insects | Creative Commons

Caddisflies are found in freshwaters across Europe, with their larvae well-known for their remarkable ability to build cases from organic materials such as vegetation, sand and silt (which can take on beautiful creative forms). In Britain alone, there are around 200 different caddisfly species, making them one of the most diverse groups of pond animals.

New research by a team of ecologists from the UK, Germany and Malaysia has shown how caddisflies are not only resourceful ‘house builders’, but also productive ‘gardeners’ of their habitats. Writing in Freshwater Biology, the researchers, led by Nicola Ings, describe how caddisflies actively encourage food growth in their local environment, through ‘weeding’ and ‘fertilisation’. (read more)


Small birds, big effects: the little auk transforms high Arctic ecosystems (February)


Little Auk colony on the Cape York Peninsula, Greenland. Image: T Davidson

The North Water Polynya is a large area of open sea in Baffin Bay between Greenland and Canada. The area is the largest polynya – an area of sea that remains ice-free year-round, though surrounded by sea ice – in the world, and is one of the most biologically productive marine habitats in the Arctic Ocean.

Ecosystems on the Greenland coastline of the North Water Polynya are transformed – both positively and negatively – by nutrients brought back to land from the open sea by a tiny ‘ecosystem engineer’ bird, the little auk, according to a new study. (read more)


Life in a Drop of Water: an interview with underwater photographer Liam Marsh (February)


Mayfly larvae after moult, in a drop of water. Image: Liam Marsh

Liam Marsh is an award-winning natural history and wildlife photographer based in the Blackdown hills of south Somerset in England. His photographs of aquatic life – both above and below the waterline – are creative, unusual, and often beautiful. We spoke to Liam to find out about his approaches to revealing freshwater worlds through photography. (read more)


Restoration of the Lippe River in Germany doubles fish populations (February)


The restored Lippe River in Germany. Image: Benjamin Kupilas | REFORM

A new study by researchers based in Germany and the USA examined the responses of fish communities to the restoration of the Lippe River in Germany over a 21 year period. The Lippe has been heavily modified by human activity since the early 1800s, with a largely reinforced and straightened channel and bed, highly fragmented flows as a result of numerous weirs, and the widespread destruction of its riparian and floodplain landscapes.

The research team analysed data collected for 4 years before, and 17 years after, restoration at Klostermersch, where two stretches totaling over 3km in length were restored in 1996 and 1997. Restoration involved reconnecting the river’s floodplain with the river, removing bank fixations, widening the river from 18 to 45 metres in width, building a series of small islands, introducing full trees as deadwood, and reintroducing ‘natural’ floodplain drainage systems. In essence, the Lippe River ecosystem was encouraged to become more diverse in structure and dynamic in process. (read more)


Common ground for multiple stressor research (March)


Delegates at the Portugal meeting. Image: Vanessa Bremerich / Markus Venohr

Last week, researchers from three EU aquatic science projects – MARS, GLOBAQUA and SOLUTIONS – met in Sesimbra, Portugal to present their findings, and to discuss opportunities for collaboration. The three projects share a common interest in the effects of multiple stressors on aquatic ecosystems, and their representatives met at a workshop to develop the potential for shared outputs such as policy briefs and water management guidance. (read more)


The rapid evolution of Europe’s newly-discovered first cave fish (March)

Cave loach big Kopie

The newly discovered cave loach from the Danube-Aach system. Image: Jasminca Behrmann-Godel

A diver has made an unusual discovery in an inaccessible underground cave system in Southern Germany: a population of Europe’s first documented cave fish. The pale coloured loach of the genus Barbatula is thought to have diverged from surface fish around 16,000 to 20,000 years ago, following the retreat of ice age glaciers.

“The cave fish was found surprisingly far in the north in Southern Germany,” said project leader Jasminca Behrmann-Godel of the University of Konstanz in Germany, lead author on a newly-published study in Current Biology. “This is spectacular as it was believed before that the Pleistocene glaciations had prevented fish from colonizing subterranean habitats so far north.” (read more)


What is good ecological status and why does it matter? (April)

‘Good ecological status’ is a key term in the EU Water Framework Directive – the policy framework through which European freshwaters are managed. Member states are required to conserve and restore their rivers and lakes to good ecological status by 2027. But what does ‘good ecological status’ mean, and why does it matter?

A new film by the EU MARS project gives an engaging and accessible introduction to the concept. Produced by MARS scientists Christian Feld and Sebastian Birk at the University of Duisburg-Essen, the short film ‘Good ecological status of rivers and lakes’ emphasises the value of healthy aquatic ecosystems to human and non-human life, both now and in the future. (read more)


Multiple pressures and the ecological status of European rivers (May)


Floodplain on the River Ouse, Yorkshire. Image: alh1 | Flickr Creative Commons

The EU Water Framework Directive is the ambitious water policy designed to reduce pressures and achieve a good ecological status for all European water bodies. However, assessing the multiple pressures acting on aquatic ecosystems, and understanding their combined impact on the ecological status of rivers and lakes is challenging, particularly at large scales. Understanding these interactions and impacts is crucial to the planning of effective water policy and management.

In this context, a recently published study provides an assessment of multiple human pressures and their relationships with ecological status for all European rivers. Writing in the (open-access) Nature: Scientific Reports journal, Bruna Grizzetti from the EC Joint Research Centre and colleagues estimate that only 38% of EU rivers reach ‘good’ or ‘high’ ecological status. 20% are rated as ‘bad’ or ‘poor’, whilst 42% are ‘moderate’. (read more)


Environmental restoration prompts widespread water quality increases in China (May)


Lake Taihu on the Yangtze Delta Plain, China: one of the water bodies assessed in the new study. Image: Balázs Andor Zalányi | Flickr Creative Commons

Restoration is a key element of contemporary environmental management, as damaged or degraded ecosystems are guided towards healthier, more resilient and diverse states. As a result, there is widespread interest and attention given to restoration in scientific, management and policy circles globally, particularly about the outcomes and effectiveness of different restoration initiatives.

New insights into restoration management are emerging from China, where many aquatic ecosystems have been highly altered and degraded in recent decades. A new study published in the journal Water Research suggests that water quality in rivers and lakes across China has improved in recent years as a result of significant investment in environmental restoration and water treatment, funded by the Chinese government. (read more)


Protect the Eels (June)

The European eel is one of the continent’s most remarkable and wide-ranging aquatic animals. Young eels (known as elvers) are born in the Sargasso Sea in the West Atlantic Ocean, and migrate back to European watercourses. Here, they mature and grow larger over a number of years, before making the journey back to the Sargasso Sea to spawn themselves.

However, European eel populations are subject to considerable threats. Some eel populations have dropped by over 90% across the continent in recent decades, largely as the result of overfishing and habitat loss. The European eel has been designated as ‘Critically Endangered’ by the IUCN Red List of Threatened Species since 2008 as a result.

A new community-engaged animation has sought to tell the eel’s story, through the voices of children. Protect the Eels is a an animated journey into the hidden ecologies of the River Avon in south-west England, as told by the children of Victoria Park Primary School Bristol, using their drawings, ideas and voices. (read more)


The politics of biodiversity and hydropower on ‘Europe’s last wild river’ (July)

Vjosa No Dams Protest

Local residents and environmental NGOs protest against hydropower development on the Vjosa. Image: Oblak Aljaz

After 20 years of postponement, an unfinished hydropower construction on the Vjosa River in Albania was cancelled earlier this year. The Vjosa is Europe’s last ‘wild’ large river, flowing entirely unobstructed through inaccessible gorges and enormous gravel banks and islands on a course of almost 270 kilometers from the Pindus Mountains to the Adriatic Sea. However, the river system is currently the subject of a number of hydropower constructions, which potentially threaten its rich – but little researched – biodiversity. (read more)


European public want more environmental protections according to new survey (August)

Symbolique 2006

Water is a key element of EU environmental policy. Image: Symbolique 2006

Over half of the European public are in favour of more environmental protections across the continent, according to a new European Parliament survey.

53% of the 27,901 EU citizens interviewed by Kantar Public for the survey thought that existing environmental protections across Europe were ‘insufficient’. 75% of citizens thought that more policy and management interventions were necessary to protect European environments. (read more)


Vulnerable estuary fish populations require stronger conservation management (August)


Gweek estuary, Cornwall. Image: Tony Armstrong | Flickr Creative Commons

Estuaries are transitional ecosystems where freshwater and marine waters meet, and their biodiversity overlaps. As a result of their supporting roles in trade, transport, fishing and tourism, estuaries are often also highly altered and pressurised ecosystems.

According to a new study, European estuaries are home to some of the most vulnerable and least resilient estuarine fish populations in the world. Writing in Nature Scientific Reports, Rita P. Vasconcelos and colleagues outline that European estuaries are particularly pressurised by human activities such as overfishing, habitat alteration and pollution. However, the authors of the newly published study argue that these highly-pressurised European estuaries are often lacking in sufficient protected area coverage to help conserve vulnerable fish species. (read more)


The restoration of large woody debris rapidly increases degraded river biodiversity (September)


The River Wensum in Norfolk, England – one of the rivers used to observe the effects of large woody debris additions in this study. Image: Colinsd40 | Flickr Creative Commons

The reintroduction of large woody debris is a common tool for river restoration schemes which aim to encourage biodiversity and natural flood protection. However, environmental managers have, as yet, been hindered by a lack of scientific evidence on the ecological effects of adding trees and logs to river and stream ecosystems.

A new study by Murray Thompson from the Centre for Environment, Fisheries and Aquaculture Science and colleagues provides valuable new insights to this knowledge gap. Writing in the Journal of Applied Ecology, Thompson and colleagues report on how the presence or absence of large woody debris influences aquatic species and food webs along five rivers in England.

The research team found that populations of aquatic invertebrates and brown trout were higher in the restored and target stretches than in the control stretches. In other words, the presence of large woody debris caused rapid increases in invertebrate and brown trout abundance. (read more)


Freshwater megafauna as conservation flagships? (October)


The arapaima, a fish native to the Amazon Basin, which can grow to over 3 metres in length. Image: Lynn Chan | Flickr Creative Commons

Freshwater megafauna such as sturgeon, river dolphins and turtles could act as valuable ‘flagships’ for freshwater conservation, according to a new open-access study published in the journal BioScience.

In the last decade or so, it has become apparent that freshwater biodiversity is both highly threatened, and is decreasing at a higher rate than its terrestrial or marine counterparts. In part, this awareness can be mapped to an influential – and highly cited – 2006 paper by David Dudgeon and colleagues.

Despite the multiple threats and pressures faced by freshwater ecosystems across the world, they tend to receive less conservation attention, research and investment than their terrestrial and marine equivalents. In their new paper, lead author Dr. Savrina F. Carrizo (IUCN) and Dr. Sonja Jähnig (Leibniz-Institute of Freshwater Ecology and Inland Fisheries, IGB) together with other IGB researchers and a team of international co-authors, suggest that freshwater megafauna could provide a focus for conservation action by acting as flagships for overlooked aquatic ecosystems and biodiversity. (read more)


Sketching another world: Stephen Thackeray’s aquatic art/science drawings (November)


Daphnia and microplastics. Image: Stephen Thackeray

At the start of last month, a succession of drawings of curious organic forms began appearing on our twitter feed. Penned by CEH and MARS freshwater scientist Stephen Thackeray as part of ‘Inktober‘, the images revealed a fascinating underwater world of often-microscopic aquatic life.

Keen to find out more about his interdisciplinary talents, we spoke to Stephen about his art/science practice. (read more)


AQUACROSS interviews address gender equality in research (November)



AQUACROSS seeks to advance the application of ecosystem-based management for aquatic ecosystems in an effort to support the EU 2020 Biodiversity Strategy and other international conservation targets.  The women featured in the AQUACROSS interview blog series will share their common passion for aquatic biodiversity and conservation, their motivations to advance scientific knowledge, and their stellar achievements on this path.

Ultimately, in outstanding research there are no genders. We as researchers share a passion for providing answers and transferring our science to others, with the pledge to leave behind a better world than the one we found. The featured interviews in this blog series will showcase the progress that these AQUACROSS researchers are carrying out towards this goal. (read more)


Thanks for reading, and a very happy 2018 to you!

How do multiple stressors affect food webs in South Wales streams?

December 21, 2017
Welsh stream

A Welsh stream. Image: Kev Lewis | Flickr Creative Commons

Human activities are altering freshwater ecosystems and biodiversity across the world at an unprecedented rate. However, predicting how freshwater species populations are affected by multiple stressors is often difficult, as a result of the complex and interactive ecological processes such as trophic links, competition and mutualism that take place across an ecosystem.

In turn, changes in species composition can have unexpected or emergent effects on ecosystem processes and dynamics. For example, changes in food availability and competition for predator species can lead to ‘trophic cascades’ throughout an ecosystem. As a result, predicting and mitigating the ecosystem-level effects of human stressors requires a detailed understanding of such ‘inter-specific’ interactions between species.

Stream ecosystems are often extremely sensitive to the impacts of human disturbance. The intensification of catchment land use – often agriculture and urbanisation –  is a major driver of biodiversity loss in streams. Bottom-dwelling aquatic insects (or ‘benthic macroinvertebrates’) are often abundant in stream ecosystems, and their communities play key roles in a wide range of ecosystem processes.

However, despite increasing evidence that macroinvertebrate communities are being altered by human pressures, there has been relatively little research on the effects such alterations have on wider freshwater food webs.


Stonefly. Image: Wlodzimierz | Wikipedia Creative Commons

A new open-access study published in Molecular Ecology aims to address this shortfall. A research team led by Caitlin Pearson from the Cardiff School of Biosciences, Cardiff University used a DNA technique called ‘next generation sequencing‘ to investigate the feeding habits of two macroinvertebrates – the Caddisfly, Rhyacophila dorsalis and the Stonefly, Dinocras cephalotesin streams affected by different intensities of livestock farming.

The study – carried out along ten upland streams in South Wales – allowed the research team to analyse how predatory macroinvertebrate diets varied along a land-use intensity gradient. As a result, it offers new insights into how human stressors affect ecological communities in streams.

Lead author of the study, Caitlin Pearson – who is now heavily involved in river conservation with the UK’s West Cumbrian Rivers Trust –  summarises the key findings:

“We know that agricultural land use can affect streams and the organisms that live there, but know less of the consequences for stream food webs.  In part this is because of the difficulties of resolving feeding interactions, particularly among small organisms or where predators eat soft-bodied prey that leave no remains.  We tried to overcome these problem here by probing the guts of predators simultaneously for the DNA of many possible prey types using next generation sequencing.

Both of the predators we investigated were generalists, consuming overall 30 different prey taxa in proportion to their availability.  This included greater use at agricultural sites of the prey that were tolerant of agricultural conditions.  These are important new insights that tell us something of the mechanisms through which how land use affects stream communities, and potentially stream ecosystem functioning.”


Caddisfly. Image: Janet Graham | Flickr Creative Commons

Cardiff University Professor of Ecology and MARS researcher Steve Ormerod continues:

“Modern molecular methods – such as next generation sequencing – are adding very powerful tools to the work of freshwater ecologists.  In this example, we’ve not only gained a wholly new view of the way invertebrate predators feed, but also we have a new perspective of the way in which agricultural intensification affects stream ecosystems.

Predators such as the large and beautiful stonefly Dinocras cepahalotes are being lost from these sites more likely because of physical stressors such as sedimentation rather than because their prey are depleted.  This is in line with similar effects we’ve seen previously (Larsen & Ormerod 2010), and illustrates how classical and modern ecological methods can work together for river management.”

Pearson CE et al (2017) “The effects of pastoral intensification on the feeding interactions of generalist predators in streams” Molecular Ecology, doi: 10.1111/mec.14459. (open-access pre-publication)

Meet the AQUACROSS team: Andrea Funk

December 13, 2017

Dr Andrea Funk on an ecological survey of the Danube River. Image: Andrea Funk

This week we continue our series of interviews with researchers from the AQUACROSS project. AQUACROSS is an EU-funded project which seeks to advance the application of ecosystem-based management for aquatic ecosystems, to help support the EU 2020 Biodiversity Strategy and other international conservation targets.

Dr Andrea Funk is an expert in wetland ecology, with a special focus on  biodiversity, and the restoration and conservation of river-floodplain systems. Her current research focuses on meta-community dynamics in floodplain networks, and species-distribution modelling with an emphasis on floodplain restoration.

We spoke to Andrea to find out more about her work, inspirations and aspirations in freshwater ecology.

What is your focus of your work in AQUACROSS, and why?

My work focuses on the coordination and implementation of the AQUACROSS assessment framework for the Danube basin. More specifically, my focus is on the river-floodplain system along the navigable stretch of the Danube River where we explore trade-offs and synergies of biodiversity targets (especially related to protected areas), ecosystem services (like recreation or tourism) and multiple human activities (like navigation or energy production) related to hydro-morphological alterations based on statistical models.


Riparian silver birch woodland on the Danube floodplain. Image: Andrea Funk

Why is your work important?

Floodplains are key elements for biodiversity protection. They are biodiversity hotspots, they provide a multitude of ecosystem functions and services, but, in turn are also hotspots of multiple human activities. Contributing to our understanding of these highly complex systems provides a basis for a strategic and more integrated management approach, as well as restoration planning.

What are the key challenges for freshwater management in Europe?

Biodiversity is declining rapidly, this is particularly acute for freshwater systems. Freshwaters host rich communities of life including many sensitive and endemic species. In turn, freshwater ecosystems are threatened due to multiple human activities which are also conflicting with multiple ecosystem services and ecosystem functions those systems provide. A main challenge is to balance all these different interests toward a sustainable protection of biodiversity.


Sunset over the Danube. Image: Andrea Funk

Tell us about a memorable experience in your career.

I’m used to having those memorable experiences quite frequently – scientific life is always full of surprises.

What inspired you to become a scientist?

I was always fascinated by water, mud (or call it aquatic sediments) and the life in it.

What are your plans and ambitions for your future scientific work?

With my modelling focus I hope that I can further contribute to the understanding of complex systems and therefore the conservation and restoration of biodiversity hotspots.

Find out more about the AQUACROSS project.

Brass, Three Down: multiple pressures on Arctic Charr populations in Lake Windermere

December 5, 2017

Lake Windermere is the largest natural lake in England. Plummeting to a depth of around 64 metres, its waters support one of Britain’s largest populations of Arctic charr. Charr are cold-water fish, most commonly found in sub-Arctic regions, and their presence in Windermere is often described as a ‘relic’ of the last ice age, as sea-run populations were trapped in the lake when glaciers retreated from the area around 12,000 years ago.

Arctic charr populations in Windermere live on the southern edge of the species’ habitat niche. As a result, they are the least resilient of the salmonid species to warming lake waters due to climate change. There are two distinct populations of charr in Windermere, which live in the deep basins to the north and south of the lake, separated by a shallower ridge.

Populations of charr in both basins have declined in the last 20 years, largely as a result of warmer lake waters which hold less oxygen, eutrophication from agricultural and waste water pollution, and the introduction of invasive species such as roach, which compete with charr for zooplankton prey.

A new film – available to watch in full above – called Brass, Three Down casts a poetic and meditative eye over the place of Arctic charr in the communities local to Windermere, and the multiple pressures their populations face. The film follows a local fishermen, who fishes for charr using traditional techniques (the types of lures used give the film its name), a potter who makes the ceramic pots used traditionally to preserve the fish, and a local chef using charr in his Michelin starred restaurant.

Produced by Henry Iddon and Richard BerryBrass, Three Down also features Dr Ian Winfield from the Centre for Hydrology and Ecology, who are carrying out long-term ecological studies on charr populations in the lake, to inform conservation and restoration strategies.

Brass, Three Down on Vimeo.

Multiple stressor effects on fish assemblages in the Austrian Alps

December 1, 2017

The Drava River at Villach, Austria. Image: Andrey | Flickr Creative Commons

The rivers and stream ecosystems of the mountainous European Alps are under increasing stress as a result of human activities. So-called ’hydromorphological’ alterations – those which change the hydrological regime (or flow) and morphological character (or shape) – are particularly common on Alpine rivers and streams.

Such hydromorphological pressures are often caused by the construction of hydropower plants – which harness the power of fast-flowing streams to generate renewable energy – and flood protection measures along river and stream channels. In addition to alterations to water flows and aquatic habitat, hydromorphological pressures (or stressors) can cause alterations to habitat connectivity for migratory species and – indirectly – to water quality.

Scientists are increasingly documenting the numerous negative ecological impacts of these stressors in Alpine rivers and streams – particularly on fish populations. However, knowledge of stressor impacts remains incomplete, particularly when multiple stressors act in combination.

In this context, a new study investigates the ecological impacts of multiple stressor combinations on fish populations in two river basins in the Austrian Alps – the Drava and the Mura. The open-access study, published in Science of the Total Environment, was supported by the MARS and AQUACROSS projects.

“The river ecosystems of the European Alps are highly under stress through various human activities which are affecting the physico-chemical conditions of running waters and are strongly influencing and impacting their morphological character, hydrological regime and as a consequence, inhabiting aquatic biota and the overall ecological integrity,” explains lead author Rafaela Schinegger, a researcher at the Institute of Hydrobiology and Aquatic Ecosystem Management at the University of Natural Resources and Life Sciences, Vienna (BOKU).

“This is particularly true for many rivers and streams in the European Alps, which constitute the ‘water towers’ of Europe, providing numerous aquatic ecosystem services to their inhabitants and the areas beyond”.

“By analysing an extensive dataset from the 2nd River Basin Management Plan of the EU WFD implementation in Austria, we found a general trend of decreasing ecological integrity with increasing number of stressors and maximum stressor in two Alpine river basins of Southern Austria – the Drava and Mura rivers. Fish metrics based on age structure, fish region index and biological status responded best to single stressors and/or their combinations”, says Schinegger.


A small hydroelectric dam in the Austrian Alps. Such projects can cause multiple stressors on the river ecosystem. Image: Michael Thomas | Flickr Creative Commons

The research team identified seven different stressor categories of single stress or multiple stressor combinations, with up to four stressors acting together at a single site. Just under two-thirds (62%) of stressor-affected ecosystems were impacted by multiple stressor combinations.

Over two-thirds (69%) of the 2590 water bodies investigated across the Drava and Mura basins were impacted by significant human stressors. Connectivity disruptions were the most common stressor found in the basins (1213 water bodies: 47% total), followed by morphological alterations (578 water bodies: 22%), and water abstraction (413 water bodies: 16%).

This analysis provides invaluable information for water managers in the Austrian Alps seeking to prioritise their efforts to mitigate the effects of multiple stressors in rivers and streams. It shows that increases in stressor occurrence reduces overall ecosystem integrity, and that fish assemblages may be negatively affected by such multiple stressor combinations. In terms of biological response, fish metrics based on age structure, fish region index and biological status responded most to single stressors and/or their combinations.

“The knowledge gained in this work provides a basis for advanced investigations in Alpine river basins and beyond, supports WFD implementation and helps prioritizing further actions towards multi-stressor restoration and management.”

One significant finding made by the study is that 37% of headwaters in Austria’s river basins are still in a very good or good ecological state. The authors argue that there is a pressing need for environmental policy and management to protect these headwater reaches from human pressures, particularly from hydropower construction.

Schinegger, R et al (2017) “Configuration of multiple human stressors and their impacts on fish assemblages in Alpine river basins of Austria”, Science of the Total Environment, 

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