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Acoustic monitoring of freshwater ecosystems: Costa Rica study reveals diverse underwater soundscapes

April 26, 2019

The study site – Cantanara Swamp at La Selva Biological Station in Costa Rica. Image: Ben Gottesman.

Freshwater ecosystems across the world are disproportionately threatened by human activity, causing ongoing losses of aquatic biodiversity globally. Many freshwater conservationists highlight the need for more comprehensive ecological monitoring and assessment programmes to better understand ecosystem changes, and to strengthen conservation initiatives accordingly.

An innovative new study seeks to address this need using an unusual approach: acoustic monitoring of freshwater soundscapes. A soundscape is the aural equivalent of a visual landscape: all the sounds we hear in a space (whether through our ears, or through recording devices), emitted by both human and non-human sources. Soundscapes are never static, often varying with the time of day, weather conditions and human activity.

Researchers from Purdue University, USA and Nanjing University of Science and Technology, China recorded the aquatic soundscape of a Neotropical freshwater swamp in Costa Rica for 23 days in 2015. They used special underwater microphones – known as hydrophones – to delve into the acoustic world of the freshwater wetland. They wanted to better understand how soundscape recording might enhance existing freshwater ecosystem monitoring and assessment initiatives.

The promise of soundscape ecology

Soundscape ecology is a growing inter-discipline, popularised by the sound recordist Bernie Krause and the ecologist Bryan Pijanowski (Director of the Center for Global Soundscapes who led this study), amongst others. By recording soundscapes, it may be possible to gain a picture of the biological community present in an area, and to assess animal activity patterns. Such approaches have numerous benefits to ecologists: being non-invasive, offering high temporal resolution, facilitating long-term sampling strategies in remote areas, and providing an archive of detailed digital data for long-term analyses.

However, soundscape recording approaches have – as yet – been largely confined to terrestrial (e.g. bats and birds) and marine ecosystems (e.g. whales and dolphins). The research team behind the new study – published in Freshwater Biology – suggest that soundscape recording can provide a valuable tool in difficult-to-access aquatic environments where visibility is limited, and sound is a principle means of animal communication.

Lead author Ben Gottesman, a PhD Candidate at Purdue University’s Center for Global Soundscapes, explains, “The sounds of freshwater habitats are still mostly a mystery, especially in the tropics. Rainforests are noisy places, filled with sounds of birds, bugs and amphibians. But what about underwater? Is there a similar sort of cacophony in the forested wetlands?”

Such sonic explorations aren’t solely driven by curiosity, but could also yield valuable environmental data, Gottesman suggests, “If you are like my skeptical grandpa, you may be wondering why we would care about aquatic soundscapes? The reason is because these sounds could unlock an efficient and effective way to monitor freshwater biodiversity, which is rapidly declining and can be difficult and costly to measure.”

The paper is part of a special issue of Freshwater Biology exploring the potential of acoustic methods for freshwater ecology. Other papers cover topics including acoustic monitoring of piranhas in Peru, lesser water boatmen in a Mediterranean pond, and toads in Northern France; and the possibility of ‘acoustic refuges’ in fish habitats.

Exploring the underwater sounds of a Costa Rica wetland

The research team submerged a hydrophone connected to an automated acoustic recorder in the Cantanara Swamp in Costa Rica – known for its richness of amphibian, bird, mammal and invertebrate species. Their equipment recorded 10 minutes of underwater sound each hour, and 1 minute each 15 minutes. This sampling strategy created 2,121 sound recording ‘snapshots’ from the swamp over the 23 day fieldwork period.

Ben Gottesman outlines the aims of the study, “Our goals were to assess the diversity of sounds within this wetland and also the temporal dynamics. We found rich diversity in sound types – eighteen in all.

“We were surprised by the daily soundscape dynamics. Whereas the day-time and night-time soundscapes were filled with the clicks, stridulations and buzzes of aquatic insects, dusk and dawn were notably quiet. We posited several explanations for these crepuscular lulls, but still do not have a definitive answer.”

spectogram costa rica

Spectrograms and oscillograms (below the spectrograms) of eight sound types from the study. Time (seconds) is on the x-axis and Frequency (kHz) is on the y-axis of spectrograms. See all eighteen sound types here.

Classifying underwater ‘sound types’ from the wetland soundscape

The eighteen sound types – creatively termed ‘Cyclops’, ‘Geiger’, and ‘Highchair’ amongst others – were classified based on their audible differences, and the visual patterns they generated in a spectogram. Spectograms are a visual representation of the spectrum of frequencies of an audio signal over time. The frequencies of the recorded sound types spanned a huge audio spectrum: from below 100 Hz (sub harmonic frequencies below human hearing) to above 22 kHz (higher than the sounds made by most mosquitoes).

Whilst the sound types have yet to be identified to their animal sources, the study shows that there was a rich diversity of underwater sounds emitted in the Cantarana Swamp, forming a soundscape with distinct daily dynamics.

“We are still in the early stages of classifying freshwater sounds and identifying the ecological factors that influence soundscape diversity and dynamics. Both of these are basic steps necessary for acoustic monitoring to become useful as a freshwater habitat assessment tool,” says Gottesman. “This study illustrates that healthy tropical wetlands like this one can contain rich soundscapes, and are therefore promising sites for acoustic monitoring.”

Acoustic monitoring: a valuable new method for freshwater science and conservation?

The study authors suggest that there are a number of necessary steps for freshwater acoustic monitoring and assessment techniques to become more widely used. These include ‘ground-truthing’ soundscape data with in situ field samples of biological and environmental conditions, and creating ‘field guides’ of the sounds emitted by individual species.

The authors state that for soundscape methods to be effective in freshwater environments, their measurements must have a strong positive correlation with at least one measure of biodiversity, such as species richness or abundance. Clearly, this is an emerging approach with significant potential for the monitoring and assessment of freshwater ecosystems globally.

“I hope that this work will inspire other freshwater ecologists working in the tropics to drop in a hydrophone. There is so much left to learn,” says Gottesman.


Gottesman, B. et al (2018) “Acoustic monitoring reveals diversity and surprising dynamics in tropical freshwater soundscapes”, Freshwater Biology,

100 Plastic Rivers – tracking the sources of plastic pollution from river to sea

April 9, 2019

Microplastic fragments. Image: Wolfram Burner | Flickr Creative Commons

Plastic pollution is increasingly recognised as a major global environmental challenge, particularly in the world’s oceans. However, recent evidence shows that plastics are increasingly present in freshwater river systems, not only affecting the health and status of aquatic life, but also providing another source of plastics to marine environments.

A global initiative called the 100 Plastic Rivers Project investigates how plastics are transported and transformed in rivers and how they accumulate in river and estuary sediments, where they can leave a long-lasting pollution legacy.

The project has been working with scientists in more than 60 locations across the world to sample water and sediment in rivers for both primary microplastics (such as cosmetic microbeads) and secondary microplastics (from larger plastic items which have broken down, or clothing fibres).

By assessing freshwater and oceanic systems as interlinked, the aim of the project is to better understand how we might manage the global plastic crisis. 100 Plastic Rivers Project researchers suggest that our ability to assess global risks from microplastic impacts on environmental and public health is limited by a lack of knowledge of their transport, deposition and uptake through aquatic ecosystems. A key question here concerns the toxicological effects microplastics can have on aquatic food webs.

Project lead Professor Stefan Krause, of the School of Geography, Earth and Environmental Sciences at the University of Birmingham, UK, explains, “Even if we all stopped using plastic right now, there would still be decades, if not centuries-worth of plastics being washed down rivers and into our seas.

We’re getting more and more aware of the problems this is causing in our oceans, but we are now only starting to look at where these plastics are coming from, and how they’re accumulating in our river systems. We need to understand this before we can really begin to understand the scale of the risk that we’re facing.”

The 100 Plastic Rivers Project aims to provide an overview of the global distribution of microplastics in freshwater ecosystems, using newly-developed standardised sampling protocols and extraction methods. All of the data collected will be GPS and date tagged and uploaded into an open-access database for researchers to use. One of the key advances made by the project – funded by the Leverhulme Trust, the EU Horizon 2020 Framework, the Royal Society and the Clean Seas Odyssey – is a ‘toolkit’ of approaches for assessing microplastic pollution in river systems.

The initial results of the project are being presented this week at the General Assembly of the European Geosciences Union (EGU), in Vienna, Austria. They show a huge diversity in the types and sources of plastic found in selected river estuaries in the UK and France.

In a recent pilot study, the 100 Plastic Rivers team at the University of Birmingham collaborated with the Clean Seas Odyssey citizen science project to ‘field-test’ their sampling methods. Working with members of the public in river estuaries around the UK and France coast, the team gained an insight into the different types of microplastic accumulating in estuary sediment. This initial picture suggests that even in countries bound by strict EU water pollution policies, there are numerous sources of plastic contributing to high concentrations of microplastics in river systems.

The project is looking for more partners, so if you are currently working on microplastics or already work in a freshwater system and can collect sediment and water samples, the 100 Plastic Rivers team can send you a sample kit and standardised protocol. Samples can then be sent back to the University of Birmingham for analysis. We will follow the progress of the 100 Plastic Rivers Project, and report back on the findings of their important work in the future.

100 Plastic Rivers Project

Mining sewage for fertilisers and energy to prevent water shortages

April 5, 2019

To meet the world’s growing water needs, we need to squeeze the most out of every drop, which means seeing wastewater as a valuable resource. Image Credit – Danilo Pinzon / World Bank (CC BY-NC-ND 2.0)


Re-published from our partners at Horizon: the EU Research & Innovation magazine.


Currently, water use risks leaving half the world facing severe scarcity by 2030 as demand outstrips supply. The linear way our societies and industries think about water – constantly extracting it for use and then dumping it back into oceans and rivers – is unsustainable in a world facing the challenges of a growing population and climate change.

“Natural water resources are not endless,” says Dr Christos Makropoulos, Associate Professor at the National Technical University of Athens, Greece, and the Chief Information Officer of KWR, a water research institute in the Netherlands. “They are very dependent on a stable climate, which is currently changing – and we’ve based our entire economy and livelihoods on them just being available whenever we need them.”

The United Nations believes there could be enough water to meet the world’s growing needs, but only if we find a better way to make the most of every drop. One way to do this is to think about water in terms of the circular economy – keeping water within social or industrial systems for as long as possible and simultaneously extracting additional value from it.

“If you manage to treat and reuse wastewater, and extract useful materials and energy, like nutrients that could become fertilisers for agriculture, or added-value compounds for the chemical industry – you are both protecting the environment and shielding your cities and industries from water scarcity,” says Dr Makropoulos.

In the Netherlands, researchers are re-using wastewater from a brewery by treating it through an engineered ecosystem. Image credit - Christos Makropoulos

In the Netherlands, researchers are re-using wastewater from a brewery by treating it through an engineered ecosystem. Image credit – Christos Makropoulos

Water mining

He is the co-coordinator of NextGen, a project demonstrating different circular water technologies across ten different sites in Europe. In the Netherlands they are using engineered ecosystems to treat and reuse wastewater from a brewery. In the United Kingdom, they are developing technologies to extract methane gas from wastewater treatment plants so that it can be used as an energy source.

They even have a portable wastewater mining unit in Greece that extracts sewage, cleans it using tiny membranes, disinfects it and then irrigates public parks.

The technologies at all ten sites use water in ways that reduce the amount that needs to be extracted and therefore enhances regional resilience against water scarcity. Most of these solutions were developed prior to NextGen’s inception, but the project is helping to refine and advance the technology while also showcasing their potential on a bigger, more commercial stage.

“In each site we demonstrate a different set up that closes the cycle in terms of energy, water or resources, or sometimes a combination of all three,” says Dr Makropoulos. “Part of the ambition here is to use these sites as living labs, in other words as spaces where people – like schools, regional authorities or municipalities, or businesses – can visit and understand how they work.”

This is a crucial step in convincing local governments and businesses to change how they think about water – that it is a renewable resource rather than a commodity to be exploited. In the past, circular technologies struggled to scale up because regulators and the market did not appreciate their potential and failed to create the commercial environment needed to drive demand.

These ‘living labs’ are also a tool to help regulators see the need to change legislation, added Dr Makropoulos. Outdated definitions and regulations of waste are currently standing in the way of some resources extracted from wastewater entering the market or becoming cost-competitive.

According to Ilaria Schiavi, a resource management expert at IRIS, an Italian sustainable technology business, many European countries struggle to grasp how the circular economy works in practice.

“Not many countries have circular economy strategies and the ones that do are still figuring out how actions can trickle down to planning on the ground,” she says.

This could mean that opportunities to create systems that reduce a region’s water demand are missed in major development projects, which can lock areas into the current use-and-discard water culture.

“The approach to water has been that it will always be there and we don’t need to think about it when enlarging a city,” says Schiavi, who is also the project coordinator of Project Ô, which aims to demonstrate different technologies and approaches to circular water management. “But that’s not true anymore.”

Lower bills

The researchers are developing software to help local authorities and businesses analyse and understand the economic benefits of sustainable water strategies, such as the amount of money saved by rewarding those who use less water with lower bills. They are also demonstrating wastewater recycling technologies that ease the pressure on existing sewage treatment sites alongside strategies for using alternative sources of local water, like rain or from industrial sources.

Water stress happens when demand for water exceeds the amount available of acceptable quality, and varies from region to region. Image credit - Horizon

Water stress happens when demand for water exceeds the amount available of acceptable quality, and varies from region to region. Image credit – Horizon

Most existing water treatment plants were built to deal with domestic sewage, but with growing pollutants from nearby industry and changing habits in society, like the increased use of antibiotics, plants now have to cope with contaminants that they were not initially designed for. This cocktail of pollutants makes it more expensive to clean the water, but also harder to extract any resources that could be reused.

“We are trying to act on the contaminants close to the source of the contamination because they are concentrated enough to be effectively treated,” says Schiavi.

The project team has already helped install a treatment plant at an Israeli aquaculture research centre that would enable 100% recycling of the water, thus eliminating the need to take more out of the ocean.

The plant uses algae to treat the wastewater, which pulls nutrients out and these are then used for feeding locally farmed fish or as a feedstock for nutraceutical (dietary supplements) or other industrial applications. This circular approach also prevents the wastewater being dumped back into the environment, where it can trigger huge blooms of toxic algae that can suffocate other marine life.

“The best way to prevent waste is not to generate it, and that’s the same approach we want to create with wastewater,” said Schiavi.


This post Mining sewage for fertilisers and energy to prevent water shortages was originally published on Horizon: the EU Research & Innovation magazine | European Commission.

Insect declines in Germany: can insect-friendly farming practices help reverse the trend?

March 29, 2019
dragonfly wind

A dragonfly holds tight to vegetation in strong wind. Dragonfly populations are declining across Europe. Image: Jean François Bonachera | Flickr Creative Commons

Insect conservation is currently a hot topic in Germany. A succession of scientific studies have documented insect population declines across species and habitats in recent years, a trend which is gaining increasing public and political attention. As is the case with global concerns over insect declines, the big question is: what can be done to reverse these negative trends?

Scientists document insect declines across Germany

A 2017 study found that flying insect biomass in Germany has dropped by 76% over the last 27 years. Researchers collected flying insects across different habitats within protected areas in lowland western Germany using mesh tent traps. They noticed a steep decline in insect biomass (the total weight of insects caught) in recent years, particularly around midsummer, where biomass has dropped by 82%. Writing in the journal PLOS ONE, Caspar Hallmann and colleagues attribute the declines (in part) to agricultural intensification, particularly intensive fertiliser and pesticide use, and habitat loss. Another PLOS ONE study in 2013 documented how the leaching of neonicotinoids (a common agricultural insecticide, linked to insect declines globally) led to significant declines in aquatic insect abundance. Many flying insects (such as dragonflies and damselflies) have significant aquatic phases in their life cycles, and water pollution is thus a key stressor on wider insect populations.

Another German study found that light pollution can be a cause of insect declines. Scientists from the Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB) suggest that climate change, pesticides and land use changes alone cannot fully explain the decline in insect populations in Germany. “Half of all insect species are nocturnal. As such, they depend on darkness and natural light from the moon and stars for orientation and movement or to escape from predators, and to go about their nightly tasks of seeking food and reproducing,” explains Dr. Maja Grubisic, lead author of the 2018 study in Annals of Applied Biology. “An artificially lit night disturbs this natural behaviour – and has a negative impact on their chances of survival.” The researchers identify light pollution as an emerging stressor for insect populations, particularly in agricultural landscapes. They argue that light pollution should thus be considered as part of environmental conservation approaches designed to protect insect populations.

Earlier this month, a study found that over half of the c.500 wild bee species found in Germany are at risk of extinction, or already locally extinct – a trend driven by intensive agricultural practices. Researchers from the Ludwig-Maximilians-Universitaet (LMU) found that bee species which emerge in late summer struggle to find sufficient food in intensive agricultural landscapes. “According to our analysis, late-emerging species – Melitta tricincta, for instance – are increasingly at risk in agricultural areas, because they can no longer find sufficient food,” says Prof. Susanne Renner, lead author of the study. “In regions where the land is intensively farmed, the fields are virtually devoid of flowers at that time of the year. Bees that emerge in the spring can at least count on the availability of plants such as oilseed rape and the presence of blooming orchards.”

save the bees

Supporters of the ‘Save the Bees’ campaign in Bavaria, Germany. Image: Friends of the Earth

Public and political appetite for positive change

Awareness of such insect declines has reached public and political realms recently. Last month, environmental groups behind the ‘Save the Bees’ campaign in Bavaria, southern Germany secured the signatures of around 1.75 million people (nearly 20% of eligible Bavarian voters) in a petition to radically improve the environmental impacts of farming methods in the state. The petition asks that 20% of land is made ‘bee-friendly’ by 2025, and 30% by 2030. This shift could be made possible by a shift to more organic farming approaches, campaigners suggest. The petition states that 10% of green spaces in Bavaria should be turned into insect-friendly flowering meadows, and that rivers and streams should be buffered from pesticides and fertilisers through the protection of riparian strips of natural vegetation along their banks.

The ‘Save the Bees’ campaign – which involved a series of high-profile, carnival-like protests in the run-up to the petition deadline – is designed to change and strengthen the existing Bavarian Nature Conservation Act. But the ‘Save the Bees’ campaign is not just about bees. Last month, Agnes Becker, the leader of the Bavarian Ecological Democratic Party (ÖDP), which backed the petition, told a television debate, “It’s not so much about the honey bee as it is about a very long and ever-growing list of threatened species of animals and plants, but the bee is our mascot, our symbol.”

The referendum result has prompted a series of round-table meetings between the environmental groups behind the petition, and the Bavarian Farmers Association which contests some of the proposed measures. The Association argues that the petition’s demands of de-intensified farming methods are restrictive and unworkable. The latest round-table, held last week, prompted four working groups – ‘agricultural landscapes’, ‘forest’, ‘waters’ and ‘settlements/urban areas’ – to be established whilst the state parliament decides whether to enforce the petition demands in law.

Meanwhile, the Social Democrat (SPD) Minister for the Environment Svenja Schulze has proposed an ‘action plan for insect protection’ across the whole of Germany. The action plan, which was originally proposed to the German cabinet in October 2018, is under consultation, and could mobilise €100 million of funding each year for insect conservation in Germany. Schulze says, “Stopping the decline of insects is a key political task of our time.” Depending on the progression of negotiations, the action plan could be adopted by the government as early as next month.


Bees are important pollinators of flowers and crops. Image: BrambleJungle | Flickr Creative Commons

Could ‘insect-friendly’ agriculture halt insect population declines?

What these scientific findings and political debates have in common is a concern with making German agricultural practices more ‘insect-friendly’. Insects, of course, provide important ecosystem services, particularly pollination, in many agricultural landscapes. The German Association for Environmental Protection and Conservation (BUND) estimates that the economic value of the pollination services provided annually by insects in Europe is more than 14 billion euros.

A key question, then, is how to balance insect conservation (and that of biodiversity more widely) with the economic and food security concerns of modern agricultural production? Are shifts to lower-intensity, organic-led farming approaches – as advocated by the ’Save the Bees’ campaign – realistic in practice?

A recent policy report from the Ten Years For Agroecology (TYFA) project suggests that they might – but that such a shift requires significant changes to public eating habits. Published in September 2018, the TYFA report uses computer modelling to explore the possibilities of ana Europe ‘agro-ecological’ food system for 2050. An agro-ecological system is based on “abandoning pesticides and synthetic fertilisers and redeploying extensive grasslands and landscape infrastructures,” in order to protect biodiversity and mitigate climate change effects, whilst still providing sustainable food sources for European populations.

Authors Xavier Poux and Pierre-Marie Aubert report that whilst such agro-ecological measures would likely lead to a decline in agricultural production of around 35% across Europe, this would not be an issue if public eating habits shifted away from meat towards plant-based diets. They suggest that whilst such a scenario represents a ‘utopia’, their study shows that it is possible to reduce agricultural carbon footprints and restore healthy natural environments, whilst feeding European people healthily. In other words, whilst their vision is unlikely to be played out in practice, perhaps alternative approaches to European agricultural practices are realistic, if there is sufficient public and political will.

dragonfly flight

Sympetrum dragonfly in flight: aquatic ecosystems are important for many flying insect populations. Image: Artur Rydzewski | Flickr Creative Commons

The wider landscape: what about aquatic environments?

What do these issues and debates have to do with aquatic environments? In short: a lot. As noted before, many flying insects have significant aquatic stages (e.g. as larvae), and often require high water quality to successfully hatch. More broadly, terrestrial and aquatic environments are inherently linked across wider landscapes, and biodiversity losses on land are often accompanied by parallel losses in water, which can happen at a great rate and magnitude. The EU MARS project found that the impacts of intensive agriculture – pollution, habitat loss and fragmentation, water abstraction – can are often some of the most important stressors on aquatic ecosystems.

As aquatic scientist Dr Sebastian Birk from the University of Duisburg-Essen puts it, “The bigger issue is ‘how do we want to live in the future’?’ Insect declines and aquatic ecosystem degradation are just indicators of how we treat our natural environments. Ultimately, pollutants often end up in the gutter, and then our rivers and lakes. So what you do on the land will affect the waters, too.”

We will continue to follow the developments in Germany and report back over the coming months.

What does the future hold for European rivers and lakes?

March 15, 2019

Lake Beyşehir, one of the study locations for future environmental storylines in the study. Image: Pixabay | Creative Commons

Can we predict what the future holds for European rivers and lakes? How might changes to socio-economic conditions alter future trajectories for the health and status of surface waters across the continent? These are the questions at the centre of a new study led by Leoni Mack, from the University of Duisburg-Essen in Germany.

Funded by the EU MARS project, Mack and colleagues developed computer models to project how European surface waters are likely be impacted by different climatic, land use, management and development trends in the future. Their results suggest that stronger environmental policy and management are needed to achieve good ecological status in European surface waters under future conditions.

However, if such measures are not implemented, the linked pressures of human activity and climate change are likely to cause ongoing reductions in ecological status across the continent. Their results suggest that the impacts of pressures across Europe are likely to be more severe in rivers than lakes.

Key pressures in the future are likely to be similar to today: nutrient inputs from agriculture, land use changes (e.g. riparian zone development), poorly managed water abstraction, and growing climate change effects (e.g. water temperature increases; changes to flood and drought patterns).

There is likely to be geographical variation in how these pressures affect freshwaters, the study suggests. In Continental and Atlantic regions of Europe, land use changes are likely to be the key driver of environmental pressures, whilst in Mediterranean regions, the effects of climate change are predicted to dominate. In more northerly Boreal regions, the combined impacts of land use and climate change are predicted to drive environmental pressures, reflecting a likely trend of agricultural activities shifting northward with a warming climate.


Graphical abstract of the study showing: methods, map of study basins, and results (TN= nitrogen, TP = phosphorous, Chl-a= algae growth). Image: Mack et al 2019.

Three lake and four river basins were modelled in the study, representing a number of typical European environmental conditions and human pressures. Nitrogen, phosphorous and chlorophyll a (a proxy for algae growth) dynamics were modelled to two time horizons – 2030 and 2060. These dates were chosen to give a picture of how alterations to current environmental policy (e.g. the Water Framework Directive) could have short-term impacts in the next decade (2030), and how climate change effects might be experienced over a longer term (2060).

Three storylines describing land use, management and development were assessed: ‘Consensus’, ‘Techno’, and ‘Fragmented’. Each storyline describes possible political, economic and cultural trends which to different combinations of drivers and pressures across Europe, using Shared Socio-Economic Pathway projections of socio-economic trends and IPCC Representative Concentration Pathway projections of climate change. The storylines are thus broad-brush forecasts of possible future trends across the continent, developed to help guide environmental policy and management decisions.

In Consensus World, future development in Europe follows similar patterns to the recent past, and environmental conservation and policy is supported. The world tends towards being relatively politically stable (Shared Socio-Economic Pathway 2), alongside a stablising and relatively low level of climatic change (Representative Concentration Pathway 4.5).

In Techno World, economic growth is strong, led by technological innovation, and human resource consumption is high. Ecosystems are valued largely for the benefits they provide to humans, and environmental protections are gradually rolled back over time in favour of promoting economic growth. High greenhouse gas emissions and rising global temperatures (Representative Concentration Pathway 8.5) are present, and there is a strong, carbon-based global economy (Shared Socio-Economic Pathway 5).

Fragmented World envisions a future with rising carbon emissions and significant climatic change (Representative Concentration Pathway 8.5). Technological developments are slow, and fossil fuel dependence is high; international cooperation is poor and significant pockets of poverty persist (Shared Socio-Economic Pathway 3). There is poor trans-national co-operation on environmental protections. Current environmental policy commitments are not met, or rolled back over time.

The authors highlight that different management approaches could have positive ecological impacts in each storyline. In Consensus World, present-day measures such as riparian shading had a positive impact on ecological status, whilst in Techno World, technological improvements such as increasing wastewater treatment efficiency were predicted to be key. In Fragmented World, agricultural extensification (i.e. the reduction in fertilisers and pesticide use per land area) was highlighted as a means of reducing nutrient pollution and habitat change.

The study, published in Science of the Total Environment, is rich in detail of how these potential political, economic, climatic and environmental trajectories might interact with freshwater ecosystems in the future. Overall, the results highlight the need for continued high ambitions for freshwater policy and management, and the political and public will to implement it for decades to come. The study emphasises the need for locally-appropriate targeted freshwater management measures to mitigate the effects of environmental pressures, whichever storyline(s) might develop in the future.

Mack, L et al (2019), “The future depends on what we do today – Projecting Europe’s surface water quality into three different future scenarios”, Science of The Total Environment, Volume 668, 10 June 2019, Pages 470-484


Microplastics from the 1950s found in London lake sediments

March 1, 2019
Hampstead Pond No.1 in North London.

Hampstead Pond No.1 in North London. Image: Paul Robertson | Flickr Creative Commons

Microplastics dating back to the 1950s have been found in a sediment core taken from the lake bed of Hampstead Pond No.1 in London, UK. Plastic pollution is frequently featured in the news as a contemporary, oceanic environmental problem. However, a new open-access study by Dr. Simon Turner from University College London and colleagues provides evidence of long-term plastic accumulation in urban freshwater environments.

Hampstead Pond No.1 is one of thirty ponds on Hampstead Heath in North London, dug in the 17th and 18th centuries as reservoirs. Other ponds on the Heath are open to outdoor swimmers, anglers and model boating enthusiasts. However, despite their location in a cherished area of urban green space, the new study demonstrates that the ponds have been receiving plastic pollution for more than 60 years.

Plastic in UK lakes: a growing issue of concern

The impetus for the study, published in the Journal of Paleolimnology, arose from previous research carried out between 2008-2012 on other UK lakes. Dr. Turner explains, “At Edgbaston Lake, Birmingham we observed a lot of litter in the reed-filled margins but less in the deep water – and like some of the beach clean ups, some of the plastic waste, including crisp packets, drinks bottles, especially noticeable by their packaging design and best-before dates, had clearly been hanging around for a considerable period of time.

“What we realised was the amount and type of litter accumulating in lakes, especially plastic waste, had not really been assessed, especially when compared to marine habitats and simple questions like ‘how long has plastic been accumulating in lakes’ and ‘has plastic litter in lakes changed over time’ remained largely unanswered.”

In 2015, Rebecca Vaughan – at the time a UCL undergraduate – carried out a study of Edgbaston Lake to quantify just how much plastic waste was present in the lake sediment. Dr. Turner then built on this study to explore whether it was possible to identify microplastics (less than 5mm in diameter) in a dated lake sediment core. He and his research team chose an archived sediment core from Hampstead Pond No. 1, as it was accurately dated, large in volume, and surrounded by urban spaces which could provide sources of plastic pollutants.

As there is no long-term monitoring of plastic waste, such historical cores can provide a picture of plastic pollution through time. Plastics generally degrade very slowly –  a process which has been estimated to take hundreds of years – and so are likely to have built up in sediments in many freshwater environments. However, historical lake sediment cores had not been analysed for plastic pollutants prior to this study.


Selected microplastic particles and fibres found in HAMP1 sediment core from Hampstead Pond No.1. Image: Turner et al (2019)

Microplastics in Hampstead Pond No.1

Dr. Turner and colleagues found a range of microplastic fibres and fragments in the Hampstead Pond No.1 sediment core. The fibres – of varying colours – are likely to be derived from the breakdown of synthetic textiles, and released into the lake from wastewater and sewage (although these inputs are relatively low in the pond), or via clothing, textiles, swimwear or fishing line. Microplastic fragments in the core were all orange foam polystyrene particles, ranging from 0.2–2mm in size.

Whilst there are some fibres in the core which may date from the late 19th and early 20th centuries, the majority of the microplastics found in the study date from the 1950s onwards. The accumulation rate of microplastics in the lake sediment was at its highest in the decade before 2009, when the core was taken.

Dr. Turner explains, “Like other contaminants released into aquatic systems, the composition and abundance of microplastics looks to have varied over time, as a result of changing industrial and domestic sources. We only have really started to quantify the inputs, transport and burial processes of microplastics in lakes, but this paper and others similar, are a step in understanding the global movement and accumulation of plastic waste in aquatic systems.”


Reflections from neighbouring houses on Hampstead Pond No.1 after dark. Image: Chris Guy | Flickr Creative Commons

Microplastics and freshwater conservation

Microplastics can be ingested by freshwater organisms, as this recent paper by Dr. Fred Windsor and colleagues shows, potentially leaching harmful contaminants and additives into their bodies, or altering their physiology. As a result, understanding the transmission of microplastics through freshwater food webs – and their subsequent burial in sediments or transport elsewhere – is a key topic for research.

Dr. Turner says, “To get low density microplastic waste into benthic sediments we have to have a mechanism for accumulation and sinking – be it biofouling or ingestion and burial with organisms. Considering how resilient to degradation plastics were designed to be, my thoughts are that once in a lake, microplastics probably go through quite a few organisms before ultimate burial.”

Microplastic research in freshwaters is a growing area of scientific interest, and this paper contributes significantly to the field by showing that historical patterns of plastic pollution can be found in lake bed sediment cores. Clearly, plastic pollution is a key – if under-communicated – topic for freshwater conservation and policy. As Dr. Turner puts it, “Plastic waste in the environment – it’s not all about the oceans.”

Read the journal article

Turner, S., Horton, A.A., Rose, N.L. et al. (2019) “A temporal sediment record of microplastics in an urban lake, London, UK”, J Paleolimnol.

Global insect declines: 33% of aquatic species threatened with extinction

February 15, 2019

68% of caddisfly species populations are declining – more than any other order of insects. Image: Katja Schulz | Flickr Creative Commons

Global insect biodiversity is in dramatic decline according to a new review of existing scientific evidence. Aquatic insects are particularly threatened, with mayfly, dragonfly, stonefly and caddisfly species all showing significant declines over recent years.

Population declines of terrestrial and aquatic insects – in 41% of all species – are roughly twice those estimated for other vertebrates (mammals, birds and amphibians – 22% of species). The total global mass of insects is falling by an average of 2.5% each year, the study suggests, with potentially severe impacts on ecosystems and their services – such as pollination – globally.

“As insects comprise about two thirds of all terrestrial species on Earth, the trends confirm that the sixth major extinction event is profoundly impacting life forms on our planet,” say study authors Francisco Sánchez-Bayo and Kris Wyckhuys.

Writing in the journal Biological Conservation, the authors reviewed 73 historical scientific reports of long-term insect population dynamics from across the world. They selected studies which considered all species in a taxon (e.g. family or order) within a large area (i.e. a region or country), or smaller areas intensively studied for more than 10 years.

freshwater insect declines 2019

Percentage of insect species in decline or extinct in four aquatic orders. Graphic redrawn from Sánchez-Bayo and Wyckhuys (2019: Fig 3b)

Freshwater species

Four orders of freshwater insects are addressed in the paper: mayflies (Ephemeroptera), dragonflies and damselflies (Odonata), stoneflies (Plecoptera) and caddisflies (Trichoptera). As most freshwater insect species have relatively inflexible life cycles, which makes them particularly sensitive to environmental pressures, the authors say. As a result, insects are vulnerable to pressures such as flow alterations, habitat fragmentation, pollution and invasive species.

The study suggests that – like for vertebrates – declines of aquatic insects are higher than those of their terrestrial counterparts (see graphics above and below). The authors estimate that 33% of aquatic insects are threatened with extinction, compared to 28% of terrestrial taxa.

Habitat generalist’ aquatic insects – which can occupy a number of different habitats – have been particularly affected, with major losses in all four orders of insects in large river systems across Europe and North America. However, insect communities have generally remained stable – or shown lesser declines – in near-natural mountain streams and lakes.

freshwater insect declines and extinctions 2019

Annual species declines and extinction rate for four aquatic insect orders. Extinction rate denotes the percentage of species not observed in >50 years. Graphic redrawn from Sánchez-Bayo and Wyckhuys (2019: Table 1)

Drivers of insect decline

Dr Sánchez-Bayo and Dr Wyckhuys identify four key drivers of global insect population decline: habitat loss, pollution, biological factors and climate change. For aquatic species, they highlight pollution as the main driver of population declines. Common sources of aquatic pollution include fertilisers and synthetic agricultural fertilisers, sewage and landfill leaching from urban areas, and industrial chemicals from factories and mining sites. The authors highlight the damaging impact of pyrethroid, neonicotinoid and fipronil insecticides on aquatic insects, due to their acute and chronic toxicity in water bodies.

As insects are crucial parts of food webs from the tropics to the tundra, the authors suggest that urgent conservation and restoration schemes are necessary to safeguard their populations and the ecosystem services they support. In particular, they highlight the need to reduce the runoff and leaching of toxic chemicals – particularly from industrial agriculture – into water bodies, in order to support the persistence and re-colonisation of aquatic insect populations.

Speaking to ABC television in Australia, Dr Sanchez-Bayo said, “We are not alarmists, we are realists. We are experiencing the sixth mass extinction on Earth. If we destroy the basis of the ecosystem, which are the insects, then we destroy all the other animals that rely on them for a food source. It will collapse altogether and that’s why we think it’s not dramatic, it’s a reality.”

The authors state that immediate global conservation action is required, chiefly through rethinking, “current agricultural practices, in particular a serious reduction in pesticide usage and its substitution with more sustainable, ecologically based practices.”


Spraying pesticides on a lettuce field in Arizona, USA. Pesticide pollution is one of the key pressures on aquatic insect populations, according to the new study. Image: Jeff Vanuga | Creative Commons Public Domain Files

What about the tropics? Geographic variations and data deficits

The study reveals the geographic variation in detailed, long-term insect research across the world. The majority of the 73 studies selected for this meta-analysis are located in Europe and the USA, with only a handful from Central America, Brazil, South Africa, China, Australia and New Zealand. In fact, the data for China and Australia refers to managed honey bees only.

Whilst this reflects the distribution of funding and support for long-term ecological monitoring, it also restricts the certainty of making broad statements about the global health and status of insect populations. The insect declines reported here are primarily from temperate, northern hemisphere ecosystems. This isn’t to underplay the significance of the dramatic trends reported in the paper, but instead to caution about drawing global trends from the reviewed studies.

If anything, this study suggests that in addition to conserving the populations we know about, there is significant work to be done in studying (and mostly likely, protecting) those for which there are currently data deficits. Such work is unlikely to provide any good news, according to Georgina Mace, who told the New Scientist recently that Sánchez-Bayo and Wyckhuys’s review could in fact underestimate the declines in insect populations across the tropics.

So, in short, the picture of global insect declines painted by Dr Sánchez-Bayo and Dr Wyckhuys is alarming, but may not show the full extent of global declines. What is clear is that insect conservation must become a key focus for environmental policy with immediate effect if species declines – both documented and undocumented – are to be halted.

F. Sánchez-Bayo, K.A.G. Wyckhuys, (2019), “Worldwide decline of the entomofauna: A review of its drivers”, Biological Conservation, 232, pp. 8-27

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