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Lake temperature ‘regimes’ will shift under future climate change

March 27, 2020
The Spiegelsee – or ‘Mirror Lake’ – in the Austrian Alps. A new study predicts that climate change will warm lake water temperatures over the coming century. Image: Hannes Flo | Flickr Creative Commons

Water temperature is an important variable in lake ecosystems across the world. Variations in water temperature influence a wide range of environmental patterns and processes, including species distributions, growth rate, phenology, food webs, and greenhouse gas emissions.

Predictions of future climate change suggest that lake temperatures are likely to warm in many places, altering ecosystem health and functioning. Understanding and modelling lake water temperatures is thus a key step for freshwater scientists working on climate change resilience and adaptation.

However, until now, there has been no global classification of water temperature into ‘lake thermal regions’ to support this work. A newly published study in Nature Communications addresses this shortfall.

Professor Stephen Maberly from the Centre for Ecology & Hydrology, UK and colleagues used satellite data to identify nine different lake thermal regions across the world. They grouped global lakes based on seasonal patterns of their surface water temperatures. The coldest thermal region includes lakes in Alaska, Canada, Siberia and China, and the warmest covers lakes in equatorial South America, Africa, India and south-east Asia.

“Thanks to cutting-edge analysis using satellite images of more than 700 lakes, taken twice a month over 16 years, we produced the first global lake temperature classification scheme,” says Prof. Maberly. “By combining this with a lake model and climate change scenarios we were able to identify that northern lakes, such as those in the UK, will be particularly sensitive to climate change.”

The study is the result of a collaboration between researchers from the Universities of Dundee, Glasgow, Reading and Stirling and the Dundalk Institute of Technology.

Global map of the studied lakes by thermal region. Image: Maberly et al 2020

The research team used climate change models to predict that under the most extreme climate change scenario (Representative Concentration Pathway 8.5), global lakes would be on average 4°C warmer, and 66% would be classified in a warmer thermal regime. Under low (RCP 2.6) and medium (RCP 6.0) future climate change scenarios, 12% and 27% of lakes would be shifted into warmer thermal regimes.

Under the most extreme climate change scenario, the research team predict that there will be a 79% reduction in the number of lakes in the coldest and northern-most thermal regime by 2100. In other words, warmer waters due to extreme climate change could cause the disappearance of over three-quarters of unique sub-polar lake ecosystems over the next century.

Even if climate change is less extreme than this scenario, there are still likely to be negative effects on cold-water species and ecosystems. “Cold-water fish species in particular can be stressed by warmer temperatures,” explains Prof. Maberly. “The potential negative impact on salmonids such as salmon, trout and Arctic charr, for example, is concerning because they play a central ecological role within food webs and also have great economic importance.”

Professor Andrew Tyler of the University of Stirling, who led the overall project, GloboLakes, says, “This is an example of pioneering UK-led research that has delivered the capability to monitor our inland waters at the global scale from satellite based platforms. This is not only yielding new insights into the impacts of climate change, but also the evidence base from which to better manage these ecologically sensitive environments and mitigate against the effects of change.”

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Stephen C. Maberly, Ruth A. O’Donnell, R. Iestyn Woolway, Mark E. J. Cutler, Mengyi Gong, Ian D. Jones, Christopher J. Merchant, Claire A. Miller, Eirini Politi, E. Marian Scott, Stephen J. Thackeray, Andrew N. Tyler. 2020. Global lake thermal regions shift under climate change. Nature Communications. DOI: 10.1038/s41467-020-15108-z

An app to classify lakes into the nine thermal regions is available in the R programming language at GitHub.

Stormy waters: the effects of extreme weather on lake ecosystems

March 13, 2020
Lightning storm over Lake Titicaca, Peru. Image: Tomas de Castro | Flickr Creative Commons

Climate change is increasing the frequency and intensity of extreme weather across the world. High winds and heavy rain during storm events can significantly affect freshwater systems. However, what is not yet fully understood is how extreme weather affects the health of lake ecosystems.

Freshwater scientists know that storms can alter physical processes in lakes such as water flows from tributaries, mixing in the water column, sediment disturbance and water temperature. At the moment though, scientists only have a limited understanding of how ecological processes – particularly those involving algae at the base of food webs – are affected by storms.

A new study from a global team of scientists warns that lakes around the world may undergo significant ecological shifts in response to extreme storms as a result of ongoing climate change. They state that there is a pressing need for research to inform adaptive conservation strategies.

“Though it is clear that storm events can affect water quality and wildlife in lake ecosystems, we need to develop a clearer understanding of where and when the impacts of these events might be most and least severe,” said co-author Dr. Stephen Thackeray from the Centre for Ecology and Hydrology, UK.

“If extreme weather events significantly change carbon, nutrient, or energy cycling in lakes, we better figure it out quickly,” said lead author Dr. Jason Stockwell, from the University of Vermont, USA, “because lakes can flip, like a lightbulb, from one healthy state to an unhealthy one – and it can be hard or impossible to flip them back again.”

Extreme weather and algae communities in lakes

The new open-access study, written by Dr. Stockwell and 38 co-authors, is published in the Global Change Biology journal. It focuses on algae – or phytoplankton – the microscopic organisms which support virtually every freshwater food web. Phytoplankton are vital in lake ecosystems as they take up carbon dioxide, make carbohydrates, and release oxygen using sunlight through photosynthesis. Phytoplankton are also a valuable food source for many aquatic animals.

So how might we better understand how phytoplankton – and by extension, wider lake ecosystems – respond to extreme storms?

The study authors reviewed and collated evidence from thousands of existing scientific studies. They found that only 31 studies have ever investigated the effects of storms on phytoplankton communities, and that their results provide no clear picture of the relationship. Similarly, there appeared to be no clear trends in how phytoplankton responses differ by storm types, in different lake ecosystem types, or at different times of year.

A framework for understanding the effects of storms on lake ecosystems

In response, the authors develop a framework for understanding the effects of storms on lake ecosystems, in an effort to encourage and guide future research. The framework shows that the impact of storm events on lakes is not simply the result of storm strength at one point in time and space. Instead, a watershed-scale approach is required to map the different relationships between storm, lake and watershed attributes.

A framework for understanding the effects of storms on lake ecosystems. Image: Stockwell et al (2020)

As the paper’s conceptual framework (above) shows, the extent to which a lake ecosystem is affected by storm events depends on the characteristics of the storm, lake and watershed. These in turn influence lake conditions such as nutrient pollution and sediment movement during the storm event.

These altered lake conditions can then influence the dynamics of phytoplankton and zooplankton at the base of the food web, which can then cascade through higher trophic levels of the ecosystem, potentially altering its health and functioning.

“This paper provides a compelling framework on understanding both direct and indirect effects of storms on lake ecosystems,” said co-author Dr. Lisette de Senerpont Domis from the Netherlands Institute of Ecology. “In a wind exposed delta area such as the Netherlands with a lot of shallow lakes impacted by agriculture we will likely experience some of the negative impacts of storms, such as algal blooms.”

New research collaborations and lake monitoring

The authors call for major new interdisciplinary collaborations to research storm impacts on lake ecosystems through networks such as the Global Lake Ecological Observatory Network. They outline the value of integrating watershed and lake physical models with biological models to better predict lake ecosystem responses to storms. They also highlight the importance of expanding long-term lake monitoring schemes, and using sensors that provide detailed data on ecological parameters during storm events.

“The framework we outline provides exciting opportunities for researchers from different disciplines to work as teams to identify the conditions and mechanisms by which storms are likely to have negative impacts on lake ecosystems,” said Dr. Stockwell. “We must quickly learn more—so we can better respond to the very real and pressing threat of climate change on lakes around the world. Without healthy lakes, we are sunk,” he said.

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Jason D. Stockwell, Jonathan P. Doubek, Rita Adrian, Orlane Anneville, Cayelan C. Carey, Laurence Carvalho, Lisette N. De Senerpont Domis, Gaël Dur, Marieke A. Frassl, Hans‐Peter Grossart, Bas W. Ibelings, Marc J. Lajeunesse, Aleksandra M. Lewandowska, María E. Llames, Shin‐Ichiro S. Matsuzaki, Emily R. Nodine, Peeter Nõges, Vijay P. Patil, Francesco Pomati, Karsten Rinke, Lars G. Rudstam, James A. Rusak, Nico Salmaso, Christian T. Seltmann, Dietmar Straile, Stephen J. Thackeray, Wim Thiery, Pablo Urrutia‐Cordero, Patrick Venail, Piet Verburg, R. Iestyn Woolway, Tamar Zohary, Mikkel R. Andersen, Ruchi Bhattacharya, Josef Hejzlar, Nasime Janatian, Alfred T. N. K. Kpodonu, Tanner J. Williamson, Harriet L. Wilson, (2020) Storm impacts on phytoplankton community dynamics in lakes. Glob Change Biol.; 00: 1– 29. https://doi.org/10.1111/gcb.15033

An Emergency Recovery Plan for global freshwater biodiversity

February 27, 2020

2020 could be a pivotal year for the future of Earth’s biodiversity. In November, the world’s governments will meet at the Convention on Biological Diversity (CBD) conference to agree a new global deal to conserve and restore biodiversity.

Global freshwater biodiversity is in particular need of stronger and more effective policy and conservation action. Despite covering less than 1% of the Earth’s surface, freshwater ecosystems support around 10% of all known species, including one-third of all vertebrate species.

However, freshwater biodiversity has collapsed in recent decades. Freshwater species populations have declined by 83% globally since 1970, according to the 2018 WWF Living Planet Report, and now 27% of the freshwater species assessed for the IUCN Red List are threatened with extinction. It is estimated that freshwater habitats host more species per square kilometre than their land or oceans counterparts: yet freshwaters are suffering biodiversity declines two-to-three times faster.

WWF estimates that around 30% of global freshwater ecosystems have been lost since 1970. It’s not just plants and animals that rely on freshwaters – they’re vital for humans too, variously providing water, food, livelihoods, and flood and drought protection.

Percentage of global freshwater species threatened with extinction. Image: WWF

A major new scientific paper published in BioScience last week outlines an Emergency Recovery Plan for freshwater biodiversity declines, designed to influence discussions at the CBD conference in November. Developed through collaborations between scientists from WWF, International Union for Conservation of Nature (IUCN), Conservation International, Cardiff University and other institutions, the paper outlines a six-point plan to ‘bend the curve’ of global freshwater declines.

Based on contemporary scientific research and conservation strategies, the six key themes of the paper emphasise solutions for positive environmental change. They provide explicit recommendations for improving freshwater conservation and restoration in international agreements, particularly the CBD and the UN Sustainable Development Goals.

“Nowhere is the biodiversity crisis more acute than in the world’s rivers, lakes and wetlands – with over a quarter of freshwater species now heading for extinction. The Emergency Recovery Plan can halt this decades-long decline and restore life to our dying freshwater ecosystems, which underpin all of our societies and economies,” said Dave Tickner, WWF-UK Chief Freshwater Advisor and lead author on the paper.

The six themes of the Emergency Recovery Plan are: letting rivers flow more naturally, reducing pollution, protecting critical wetland habitats, ending overfishing and unsustainable sand mining in rivers and lakes, controlling invasive species, and safeguarding and restoring river connectivity through better planning of dams and hydropower.

“The causes of the global collapse in freshwater biodiversity are no secret, yet the world has consistently failed to act, turning a blind eye to the worsening crisis even though healthy freshwater ecosystems are central to our survival. The Emergency Recovery Plan provides an ambitious roadmap to safeguarding freshwater biodiversity – and all the benefits it provides to people across the world,” said co-author, Professor Steven Cooke of Carleton University in Canada.

The Emergency Recovery Plan aims to influence global environmental policy in three ways. First, it recommends maintaining existing elements of agreements that are already aligned to the Recovery Plan, such as CBD Aichi target 9 on invasive species and SDG 6 on clean water and sanitation.

Second, it recommends amending or extending existing targets or indicators so that they better align with the Recovery Plan. For example, CBD Aichi target 11 and SDG 15.1 both aim to increase the extent of conserved and restored habitat, but the geographic scale of their designations don’t always suit the wide range of freshwater habitats – from vast river catchments to tiny ponds. Improving these designations could help improve how freshwaters are managed and protected by global policy.

Third, the Recovery Plan identifies major gaps in policies where key freshwater issues are overlooked or underrepresented. For example, there is currently no recognition of alterations to water flows and levels in the CBD Aichi targets.

Hippopotamus surfacing in the Mana Pools National Park, Zimbabwe. Image: naturepl.com/Tony Heald/ WWF

Cutting-edge freshwater research is increasingly untangling the multiple pressures that affect the health of aquatic ecosystems, and it is vital that this knowledge is translated into policy. To achieve this globally, the authors highlight the need for better collaborations between policy makers, governments, NGOs, researchers, managers and wider stakeholders, all driven by the common desire to halt freshwater biodiversity declines.

“It would be easy to interpret this work as a further message of freshwater doom but it is in fact the opposite. It is a forward-looking plan, with specific areas of action, for how to address the 21st century challenges that our freshwater ecosystems face. It presents an opportunity for us to change the trajectory of biodiversity decline in turn supporting the health of the planet and the livelihoods of people,” said co-author, Ian Harrison, from the Moore Center for Science.

“We have the last opportunity to create a world with rivers and lakes that once again teem with wildlife, and with wetlands that are healthy enough to sustain our communities and cities, but only if we stop treating them like sewers and wastelands,” said Tickner. “This decade will be critical for freshwater biodiversity: countries must seize the chance to keep our life support systems running by ensuring freshwater conservation and restoration are central to a New Deal for Nature and People.”

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David Tickner, Jeffrey J Opperman, Robin Abell, Mike Acreman, Angela H Arthington, Stuart E Bunn, Steven J Cooke, James Dalton, Will Darwall, Gavin Edwards, Ian Harrison, Kathy Hughes, Tim Jones, David Leclère, Abigail J Lynch, Philip Leonard, Michael E McClain, Dean Muruven, Julian D Olden, Steve J Ormerod, James Robinson, Rebecca E Tharme, Michele Thieme, Klement Tockner, Mark Wright, Lucy Young, (2020) “Bending the Curve of Global Freshwater Biodiversity Loss: An Emergency Recovery Plan”, BioScience, https://doi.org/10.1093/biosci/biaa002

Insect populations on German stream have declined by 81% since 1960s due to climate change

February 14, 2020
The blue-winged olive (Serratella ignita), one of the aquatic insects monitored in the new study, which found that insect populations declined by 81.6% between 1969 and 2010 on the Breitenbach stream, Germany. Image: Francisco Welter-Schultes, Wikipedia Creative Commons

Insect populations are in big trouble. A number of recent scientific studies have documented insect declines across the world, prompting a 2019 meta-analysis of the evidence by Dr. Francisco Sánchez-Bayo and Dr. Kris Wyckhuys to conclude that “almost half of [insect] species are rapidly declining and a third are being threatened with extinction.”

Aquatic insects – which number more than 55,000 species – are important in many freshwater food webs, with species found everywhere from tiny puddles to large rivers and lakes. However, like their terrestrial counterparts, aquatic insect populations are in decline, largely due to the effects of intensive agriculture, water pollution and, increasingly, climate change.

However, researchers have often found it hard to disentangle the effects of climate change on insect populations from those of other stressors. In this context, a new study uses a unique long-term dataset from a German stream located in a nature reserve to isolate the effects of a changing climate on the stream’s insect communities since the 1960s.

Their findings are startling. Writing in Conservation Biology, the research team state that insect abundance on the Breitenbach stream declined by 81.6% between 1969 and 2010. Over this period, water temperature in the stream increased by 1.88°C, and there was a general shift towards low water flows in increasingly dry years. Their study suggests that climate change has already significantly impacted freshwater ecosystems, even in protected areas where agricultural and urban stressors are minimal.

Historical images of the Schlitz river station and Breitenbach river in flood (bottom left) and summer drought (bottom right). Images provided by Dr. Viktor Baranov.

Lead author Dr. Viktor Baranov explains, “Our analysis is based on a unique long term dataset collected by the scientists at the Schlitz river station on the Breitenbach stream from early 1960 – though our particular dataset only starts in 1969 – until 2010. This dataset is uniquely detailed and based on the weekly collection of the aquatic insects from the large, greenhouse like emergence-traps installed over the stream and parts of the riparian zone.

“The Breitenbach is a tiny stream: 6.3km in length, with a catchment area of 8.3 km². It flows to the Fulda river, with entirety of the catchment sitting in the Breitenbach valley nature conservancy area. The site was therefore sheltered from direct anthropogenic impacts such as agricultural development and industrial pollution during the period of observation. Therefore, the dataset offered us a disentangled view of the climate change impacts on this freshwater ecosystem.”

The study is the result of a collaboration at the Department of River Ecology and Conservation, Senckenberg Research Institute and Natural History Museum Frankfurt, Germany between Dr. Baranov, Dr. Jonas Jourdan, Dr. Francesca Pilotto and Dr. Peter Haase, alongside Prof. Rüdiger Wagner from the University of Kassel, Germany.

Historical images of insect collection at the Schlitz river station. Images provided by Dr. Viktor Baranov.

Dr. Baranov outlines the importance of studying insects as a means of understanding wider environmental change, “Aquatic insects are providers of crucial ecosystem services such as river water purification, fertilisation of flood plains, and food sources for many other animals. They are therefore generally an ‘engine’ of lowland and riverine ecosystems. We can thus learn a lot about the state and health of the environment by observing changes in insect diversity and numbers.

“Environmental changes have led to the decrease of the aquatic insects by 81.6% in the Breitenbach stream. But we also observed an increase in richness (+8.5%), Shannon diversity (+22.7%), evenness (+22.4%) and inter-annual turnover (+34%). Moreover, the community’s trophic structure and phenology has changed: the duration of emergence increased by 15.2 days while the peak of emergence moved 13.4 days earlier.

Additionally, the trophic structure of the community has altered drastically: grazer, scraper and gatherer–collector species have decreased significantly in their relative abundance, while passive filter feeders and predators have increased. Increased temperatures and increasingly dry years appear to be the chief drivers of change in the insect community.”

Insects from the Breitenbach stream in a collection jar. Image: Dr. Viktor Baranov.

Decades of intensive study at the Schlitz river station generated the rich datasets which allowed the researchers to analyse the environmental effects of climate change in the stream over time.

Dr. Baranov emphasises the importance of such ongoing long-term studies, stating, “Our findings would have been missed in shorter datasets, as most of the observed effects span decades. This study illustrates the value of the long term datasets in the study of the climate change effects on the freshwater communities, and the complex – and often non-linear – nature of community responses to the global climate crisis.”

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Baranov, V., Jourdan, J., Pilotto, F., Wagner, R. and Haase, P. (2020), Complex and nonlinear climate‐driven changes in freshwater insect communities over 42 years. Conservation Biology. Accepted Author Manuscript. doi:10.1111/cobi.13477

9th European Pond Conservation Network Conference announced

February 7, 2020
Shooting Close: a restored pond. Image: Richard Walton

A note from Dr. Richard Walton:

We are thrilled to announce the 9th European Pond Conservation Network Conference which will be held at University College London over 18-22 May, 2020.

Responding to the considerable need to conserve European ponds, the conference will combine pond biology, hydrology and landscape ecology with pond conservation practice. We welcome and encourage both scientists and conservation practitioners to attend and present their observations.

Please visit the conference website for further information, registration details and to submit an abstract. The deadline for abstracts is 28th February 2020 and the Early Bird deadline for registration is 20th March.

We hope to see you at the meeting – a four-day celebration of ponds and pond people!

Kind regards,

The EPCN 2020 Organising Committee

Eavesdropping on underwater worlds: the potential of aquatic ecoacoustics

January 30, 2020
Acoustic Ecologist Dr Simon Linke, who co-edited the special journal issue on aquatic ecoacoustics. Image: Griffith University

Could listening to the underwater sounds made by freshwater life help us better document and protect aquatic ecosystems? A new special issue of the Freshwater Biology provides intriguing evidence to suggest that it could.

Acoustic monitoring has emerged as a key tool for ecologists and conservationists in recent years. Bioacoustics (the study of sounds produced by or affecting living things) and ecoacoustics (the study of environmental sounds relating to ecosystem processes) continue to grow in popularity as approaches to ecological monitoring.

These approaches centre on the idea of passive acoustic monitoring, or PAM, where researchers place autonomous acoustic sensors (aka microphones) in study sites to capture sound recordings of the environment over time.

The recordings – whether transcribed by human researchers listening back, or by computer algorithms – can then be used to calculate biodiversity metrics such as species abundance, behaviour and phenology. Technological advances increasingly make PAM an affordable, long-term and non-invasive ecological sampling approach for researchers: a ‘listening ear’ on a changing world.

Ecoacoustics can detect and monitor water birds and amphibians, aquatic insects, fish, processes of sediment transport and gas exchange, and human activities. Image: Linke et. al. (2020)

However, the use of such acoustic monitoring techniques has yet to be fully explored or adopted in freshwater systems. The new special issue, edited by Dr Simon Linke, Dr Camille Desjonqueres and Dr Toby Gifford, outlines the opportunities acoustic monitoring offers to freshwater researchers and conservationists, in an effort to raise awareness of its potential.

“Monitoring freshwater ecosystems is time consuming and costly. Using acoustics enables us to observe what is going on 24/7,” says Dr Desjonqueres. “We took over the editorial desk of Freshwater Biology for an issue,” Dr Linke continues. “We invited the biggest names in the field to help us tackle some of the key steps towards operationalising acoustics in the freshwater realm.”

The special issue contains nine studies that investigate underwater acoustics (including the work by Ben Gottesman and colleagues which we covered last year), and three studies on water birds and frogs. Tracing a lineage of describing underwater sound back to Aristotle, the editors identify six key challenges for the widespread uptake of freshwater ecoacoustic monitoring.

1. Characterising sounds and linking them to organisms and ecosystem processes

Four main groups of freshwater organisms are known to produce sounds: amphibians, crustaceans, fish and insects. However, it is rare that researchers can visually identify the source of different sounds in underwater environments. Lowering a hydrophone beneath the water’s surface can be a surprising and disconcerting experience: the listener becomes immersed in the invisible soundworlds created by aquatic life. How might such soundscapes be translated into useful ecological metrics?

The editors highlight the need for more comprehensive catalogues of the sounds of freshwater life, which could offer researchers ‘reference recordings’ to compare to their own studies. In this issue, two studies develop such ‘soundtype references’ in Costa Rica and Northern Australia.

Underwater recordings of Cantarana Swamp, Costa Rica made by Ben Gottesman and colleagues.

2. Improving automatic sound detection and analysis techniques

In addition to better identifying and cataloguing freshwater sounds, the editors highlight the need to improve how recordings are processed and analysed. Autonomous sound recorders have the potential to generate a lot of data, particularly if multiple recorders are used over an extended period.

Manual transcription of these recordings – whether through listening, or the use of visual spectrograms – is thus time-consuming. As such, automatic sound recognition technologies – which can identify organisms based on their sonic signatures – are needed.

In this special issue, two papers develop the basis of what editor Dr Gifford calls a “Shazam for fish” by documenting the calls of different species of piranhas in Peru, and the spawning calls of ‘love-sick’ burbot in northern Canada. Another study develops an automated detection algorithm for the underwater vocalisations of the spadefoot toad, whilst another uses a deep learning algorithm to acoustically detect the highly-endangered white-bellied heron in Bhutan.

3. Archiving and sharing freshwater acoustic data

As researchers make advances in identifying aquatic life through sound, it is important that their data is archived and shared amongst the global scientific community, the editors state. They write that, “While the Cornell Lab of Ornithology’s Macaulay Library contains some fish sounds (982, which represents 0.25% of all calls), these are mainly marine and from the 60s and 70s.”

Initiatives such as the Freshwater Information Platform are driving forward open-access sharing of datasets, and perhaps there is scope to develop their sound libraries in the future.

4. Understanding acoustic patterns across landscapes

The way that ecosystems and biodiversity vary across landscapes is called spatial heterogeneity by ecologists. Traditional ecological surveys account for spatial heterogeneity in their design, often by replicating study methods in different areas of a landscape.

The editors suggest that ecoacoustic methods have yet to adopt similar approaches. They suggest that this is due to the volume of data generated by ecoacoustic methods and the demands it places on computer analysis systems. In this issue, one paper uses a regular spaced set of hydrophones to show that acoustic activity of aquatic insects (Hempitera sp.) is higher in open water than vegetated areas.

5. Understanding acoustic patterns over time

Ecoacoustic methods offer researchers the potential to monitor ecosystems over long timescales, offering an insight into the diurnal and seasonal patterns of life that occur in them.

Two studies in the issue (here and here) highlight nightly aquatic insect activity patterns. The editors suggest that studies which seek to identify aquatic animals by their calls should focus on such times of day when activity is highest.

6. Making links between sound and ecological health

The end goal of all ecological assessments is to understand the ecological health and condition of a landscape. Whilst there are limits to the scope of this in freshwater environments (e.g. only 20% of fish are soniferous), the editors highlight three useful approaches.

First, changes in aquatic sound can indicate changes to the wider ecological community. Second, ecoacoustics can help us understand the effects of noise on aquatic ecosystems. Third, ecoacoustics could help the automatic detection of invasive species – such as the round goby – reaching an ecosystem.

Clearly, ecoacoustic techniques offer new opportunities for freshwater scientists and conservationists seeking to understand and protect aquatic ecosystems, and the wide-ranging and innovative studies in this special issue highlight their rich potential.

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Linke, S., Gifford, T., Desjonqueres, C., (2020) “Special Issue: Passive acoustics: a new addition to the freshwater monitoring toolbox”, Freshwater Biology, Volume 65, Issue 1

Microplastic pollution could inhibit stream ecosystem functioning

January 17, 2020
Microplastic fragments. Image: Wolfram Burner | Flickr Creative Commons

Could plastic pollution affect how a stream ecosystem functions? According to a newly published study, the answer is yes.

Plastic pollution is rapidly growing in visibility as one of the key environmental concerns of this ‘Anthropocene’ age. Researchers around the world are increasingly focusing their efforts on understanding the effects that plastics – and particularly microplastics – might have on aquatic ecosystems.

As yet, however, this work has been largely focused on seas and oceans. Whilst there is a growing body of research on the effects of plastic pollution on freshwater ecosystems, there are still many unanswered questions.

The new study, led by Naiara López-Rojo, shows that microplastic pollution may cause significant effects on how stream ecosystems function. The research team used microcosm experiments (essentially glass jars filled with stream water) to study how different concentrations of microplastic pollution affected the growth of caddisflies, and the rates at which they decomposed leaf litter.

Leaf litter decomposition is a vital component of many stream ecosystems. Leaf litter – the leaves that fall into a stream from surrounding vegetation – is a key energy source for many invertebrates at the heart of stream food webs. Its decomposition – accelerated by invertebrates such as caddisflies – helps release carbon and nutrients to the wider ecosystem.

Recent studies show that microplastics are being found even in remote sites, carried on atmospheric currents. How might their presence affect stream ecosystems?

Caddisfly survival and leaf litter decomposition decreased with increasing microplastic concentrations in the study. Image: Naiara López-Rojo et al (2020)

López-Rojo, from the University of the Basque Country, Spain, and colleagues, exposed caddisflies and leaf litter to different concentrations of microplastics in water. They found that microplastics were rapidly ingested into the bodies of the caddisflies – most likely through the ingestion of particles attached to leaf litter – and then excreted.

This finding is consistent with recent studies, such as that by Fred Windsor and colleagues in rivers in South Wales, UK, which show evidence of microplastic uptake by invertebrates.

López-Rojo and colleagues found that higher concentrations of microplastics caused increased caddisfly mortality – which increased 9-fold at the highest concentration. However, they found that altering microplastic concentrations did not significantly affect caddisfly growth.

The researchers observed that increasing the concentration of microplastics in the microcosms caused leaf litter decomposition rates by the caddisflies to decline.

A Sericostoma sp. caddisfly larvae. Image: Wlodzimierz | Wiki Creative Commons

The study, published in the journal Environmental Pollution, is short in length and based on a relatively small sample size (32 microcosms, observed over a number of weeks). So why are its findings significant?

First, it provides more evidence to show that microplastics can be rapidly ingested into the bodies of freshwater organisms, and thus potentially accumulate and move through the food web into larger animals. Second, it suggests that the functioning of stream ecosystems – in this case through the key process of leaf litter decomposition – could be inhibited by the presence of high concentrations of microplastics.

The authors highlight the need for better monitoring of microplastic pollution in stream ecosystems to understand the extent of the pressures it might exert. In particular, they suggest that more research is needed to understand how microplastic pollution might affect ecosystems already influenced by multiple contaminants and stressors.

What is clear is that microplastic pollution is a growing issue for freshwater conservation and policy. López-Rojo and colleagues’ study is likely to be only the latest advance in the ongoing scientific effort to document and unravel its effects on freshwater ecosystems.

López-Rojo, N. et al (2020, “Microplastics have lethal and sublethal effects on stream invertebrates and affect stream ecosystem functioning,” Environmental Pollution, Volume 259, April 2020, 113898

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