DESSIN is a European Union project (featured on the blog last year) which aims to specifically address water scarcity and water quality issues in urban areas, partnering scientists with water management organisations and technology companies to design new and innovative solutions for water management.
DESSIN has two broad aims: first to explore new technology and management approaches to address some of the world’s most pressing water issues; and second to use the ecosystem services concept to provide evidence of the benefit of new approaches in economic, social and environmental terms, in order to encourage their widespread adoption. DESSIN’s work is carried out at five urban study areas across Europe.
DESSIN has recently released details of their new Ecosystem Service Evaluation Framework designed to show how innovative technologies can help support and promote the services provided to humans by freshwater ecosystems.
The DESSIN Framework uses the Common International Classification of Ecosystem Services developed by the European Union to standardise assessments. It feeds the resulting classifications into the DPSIR adaptive management framework.
The DPSIR framework (Driving forces, Pressures, States, Impacts, Responses) has been adopted by the European Environment Agency to help understand society-environment interactions, and to assess related issues of governance and sustainability.
As this diagram shows, innovative technologies (Responses) are trialled in the framework to assess their impacts on ecosystem Drivers (human alterations to the environment), Pressures (the effects of human activity) and States (the conditions of the ecosystem under study).
As a result, the changes to ecosystem service provision (Impact I) can be estimated, and valued (Impact II). This estimated change in ecosystem service availability and value, and the resulting effects on human well-being, can then feedback into policy and decision making, as further Responses.
The above diagram shows a case study example of the DESSIN Framework applied to the River Emscher in Northern Germany. Responding to decades of urban alteration and pollution of the river, the DESSIN team are trialling three innovative approaches in the catchment: sewer networks, waste-water free streams and ecological restoration.
Each response aims to address the pressures from different drivers which result in changes to the ecosystem’s state, with the intention of promoting ecosystem services such as water purification, flood protection and biodiversity conservation (Impact I). The economic value of such services is calculated on the basis of factors such as avoided costs for technological water treatment and ecological restoration, compensated instead by the functioning of the ecosystem (Impact II).
You can keep up to date with the progress of the DESSIN project on their website.
Every two years, the European Federation for Freshwater Sciences organises a symposium to bring together more than 500 people including aquatic researchers, water managers and policy makers from across Europe and the world.
Earlier this month, the 9th Symposium for European Freshwater Sciences was held in Geneva, Switzerland on the banks of Lake Geneva. The symposium provided a platform for researchers to present and discuss key issues and new research on freshwater science and management.
This year, the theme of the symposium was ‘Water for a thirsty planet in the 21st century‘, which reflects a growing awareness about the impacts of multiple stressors on freshwater ecosystems in an increasingly developed and pressured world. As such, the symposium was attended by a number of scientists from the MARS project, many of whom presented their work.
We spoke to two MARS scientists, Sebastian Birk and Stephen Thackeray, to get their reflections and responses to this intensive, but obviously inspiring, week of presentations and discussions in Geneva. The Centre for Hydrology and Ecology also compiled a Storify timeline of tweets from the symposium using the #SEFS9 hashtag, through which you can follow the week’s workshops and talks.
Sebastian Birk, University of Duisburg-Essen, Germany (website)
A key strength of the symposium is that you meet the people around Europe working on similar issues. This is great for maintaining and enchanting the contacts in your research network, and for fostering common spirit for the topics that we’re all working on. There were a lot of young scientists – PhDs and postdocs – presenting their work at the symposium, and it was great to see a new generation of researchers with new ideas.
In addition to networking with other researchers, I predominantly attended to listen to talks related to the MARS topics on aquatic multiple stresses, and I particularly wanted to see what other work on the topic is going on in Europe. Many talks addressed the effects (and even the mitigation) of multiple stressors, and this was related to satellite topics like ecosystem services.
One fascinating body of research was presented by a working group on multiple stressors from the University of Otago in New Zealand. Their work has been going on for more than a decade, and it was inspiring to see how far they have already got in researching the impacts of multiple stressors at different spatial scales, and their research may well be useful for us in MARS.
There was a special session on aquatic multiple stressors, and the MARS project was represented and discussed in three different talks. I gave an overview of the status of our project; our colleagues from Cardiff University talked about multiple stress modelling in the Welsh catchments; and then our Danish colleagues presented on the river channel experiments where they carry out work on the effects on multiple stress.
Multiple stressors pose new challenges for environmental management. Instead of stressor effects being only additive, we are increasingly seeing synergistic and antagonistic interactions between stressors, which means that you cannot simply ‘add up’ the effects of individual stressors on the environment to understand their total effect.
Synergism and antagonism are key terms in multiple stressor discussions. Synergism means that the interaction of multiple stressors produces an effect stronger than just adding up the single stressor effects. On the other hand, antagonism produces an effect that is weaker than the additive sum of individual stressors. Both of these interactions are challenging our predictive capacity for understanding the effects of anthropogenic stress which is so relevant for successful water body management.
Multiple stresses are increasingly being seen as an important issue by policy makers and environmental managers, and we have a huge opportunity with the MARS project to contribute valuable work to understanding and managing their effects. It was great to present this work to a community of like-minded researchers at the symposium.
Stephen Thackeray, Centre for Hydrology and Ecology, UK (website)
Along with four colleagues I recently joined hundreds of researchers from around the world at the Symposium for European Freshwater Sciences (SEFS9) in Geneva, as a representative of the UK Centre for Ecology & Hydrology (CEH). As always, we found SEFS to be an interesting and fun meeting, with many opportunities to make new contacts, catch up with colleagues, and learn something new. I presented on the subject of seasonality within lake ecosystems, and future directions for freshwater phenology, using material from my recently completed shifting seasons project, and from the current GloboLakes project
Overall, SEFS9 was an outlet for a great diversity of freshwater science but, for me, some of the strongest emerging themes were the ecology of urban freshwaters, methane cycling within lakes, the use of environmental DNA (eDNA) as a biodiversity monitoring tool and the assessment of impacts of multiple environmental stressors. It is this last topic that is most relevant to work being conducted within the MARS project.
However, one of my other lasting impressions from the meeting was that there was a thriving young researcher community (and I do mean community) present, all of whom are already making excellent contributions to their fields. We were also privileged to see a series of excellent plenaries, demonstrating how theory, experimentation and observation can be blended in order to provide new insights. For me, the talks given by Jef Huisman, Elena Litchman and Núria Bonada were all exceptional in this respect.
Based upon the SEFS9 experience, I am also left with the definite impression that scientific communication has itself evolved. There was a whole other dialogue on the presentations occurring throughout the meeting via Twitter, and blog posts such as this one only add to the expanding reach of the research community.
The thought of taking a dip in an outdoor swimming pool on a construction site in the middle of London isn’t necessarily everyone’s idea of a good time. However, a new initiative called “Of Soil and Water: King’s Cross Pond Club” has recently opened just such a pool on the site of one of London’s most extensive redevelopment schemes. And the most innovative part of this scheme? The new pool is filtered entirely by natural processes, using an array of planted vegetation both above and below the waterline to keep the pool clean enough to safely swim.
Part-public amenity, part-land art and part-open air natural experiment, Of Soil and Water is a small, self-enclosed ecosystem in a new 40 metre pool, which is designed to be self-purifying, despite the multiple stresses and pollutants emitted from the urban environment. The pool is the result of a collaboration between the Ooze architects (Eva Pfannes and Sylvain Hartenberg) and artist/architect Marjetica Potrč, as part of a series of art events commissioned by King’s Cross Central Limited Partnership. Recently opened, the pool provides a small beacon of urban freshwater nature, nestled amongst cranes and concrete footprints of high-rise buildings in construction close to Kings Cross station, and will remain open to the public until 2017.
Describing the project’s concept, artist Marjetica Potrč said of the work “We have to rethink how we live with the city and with nature. Here, we are collaborating with nature, and the artwork encourages the viewer to participate in that experience. Water is a source of life but it is also a metaphor for regeneration. We want to understand people’s influence upon nature but also our balance with nature.”
Speaking recently to the Guardian, the Ooze architects suggest that visitors can swim in “a living laboratory where they are aware of their relationship with nature, and about consequences of their interactions with nature”. This emphasis on a ‘living landscape’ (however small in scale), is designed to allow the natural features of the pool to change over time. This relatively open process-based ecology that underpins the design was chosen the architects to “show a micro-landscape in the becoming; the succession of the different stages of natures related to different soils and waters. The experience of visitors will change continuously within the 18 months.”
Whilst this idea is laudable in many ways (and chimes with many of the non-linear and process-based approaches currently dominating ecology and restoration), there will doubtless be a tension between allowing for the trajectories the pool ecosystem can take over time, whilst ensuring the ecosystem services it provides, namely the naturally purified water. It’ll also be interesting to watch how the biodiversity of the pool changes over time.
Located close to a network of canals, and within a few miles of a number of lakes, ponds and rivers, the pool will likely be colonised by mobile invertebrates like damselflies and water boatmen before too long. One question might be: if outside plants and animals begin to colonise the pool – lets say even birds and small mammals start to nest (and feed, and leave faeces etc) there – how far does this ‘living landscape’ allow for their presence, whilst still maintaining water quality?
In all probability, given the pool’s short lifespan, this is unlikely to be a major issue, but it does flag up the idea that whilst we might undertake environmental management that emphasises natural processes and uncertainty, there is still the need for managers to choose which processes to prioritise, and to what ends. In this way, we see further parallels with the pool and wider questions that environmental restorationists are asking in their work.
Plant filtration systems for freshwaters are not new (indeed, you could argue that they’re the original water treatment works…), but are being increasingly adopted in environmental management which tackles multiple stressors. Put simply, many aquatic and marshland plants can take up excess nutrients, chemicals and toxins from the water in which they grow, removing these dissolved pollutants from being available in (and harming) the wider ecosystem.
For example, in 2009 Alan Berger, a landscape architect at MIT in the USA, proposed an initiative to use vegetation planting to help improve water quality in 2600km of polluted canals and waterways that thread through the Pontine Marshes, south of Rome in Italy. Using a large grant from the European Union’s LIFE+ project, Berger and colleagues designed a landscape-scale ‘Wetland Machine’, filtering all the water in the marshes through a 2.3 km² area of wetland built-in winding channels and planted with vegetation that is particularly efficient at taking up and storing pollutants and toxins such as marsh grass.
Berger’s winding design ensures that the water flows through the wetland at a sufficiently low-speed for the pollutants and toxins to be taken up by the plants. Berger’s work in Italy is still ongoing, but represents one of the largest and most ambitious examples of natural water filtration management in the world (see more information here).
To loop back to the (comparatively small) Of Soil and Water pool at Kings Cross: how have the designers used natural processes to filter the pool’s water, so that it is safe to swim in? The pool is split into three zones: a swimming zone; a regeneration zone; and a filter zone. In the regeneration zone, largely free-floating plants including water lilies and mare’s tail absorb nutrients from the water, and pondweeds oxygenate the pool. Algal growth is limited by allowing microorganisms and zooplankton to flourish, which in turn graze on the algae.
In the filter zone, a layer of gravel collects a growing biofilm of microorganisms, fed by nutrients brought into the pool by the bathers and the urban environment and oxygen in the water. The biofilm mineralises any organic matter in the pool, and helps reduce pathogenic germs, whilst the limestone gravel releases calcium into the water which binds to dissolved phosphates. Here too, plants which filter nutrients and toxins from the water are grown, including flag irises, water mint, marsh marigold and various rush species.
On close inspection, whilst Kings Cross pool does not rely entirely on natural processes to filter the bathing water. Instead, a series of pumps and water skimmers circulate the water and help remove floating impurities, and a phosphate filter keeps phosphorous concentrations low in the pool, preventing algal growth.
Despite this, when viewed as a whole, the Of Soil and Water pool is clearly ambitious, environmentally minded, and perhaps above all, fun. Engaging people with urban nature and ecosystems that are otherwise unnoticed or taken for granted is an important step in helping foster responsibility and care for the environment. And here, at a small pool of water amongst the high-rises, bulldozers and cranes, is an example of natural processes being able to thrive, both for the enjoyment and appreciation of people, and – hopefully – for the health and biodiversity of the wider urban environment.
Freshwater ecosystems are incredibly diverse yet increasingly threatened environments. A study by David Dudgeon and colleagues in 2006 found that freshwater ecosystems were far richer in species than land or marine ecosystems, when compared to the respective areas of the Earth’s surface that they cover.
However, Dudgeon also suggested that freshwater biodiversity was decreasing at a faster rate than land or marine based biodiversity, as a result of a multitude of freshwater stressors such as pollution, overexploitation, habitat destruction, invasive species and the impacts of climate change. The interactions and cumulative effects of this ‘cocktail’ of multiple and emerging freshwater stressors is far from clear, which is why multiple stressors are the key focus for research in the MARS project.
In recent years, numerous European environmental policies have been implemented to protect, conserve and restore the continent’s freshwater ecosystems. Two key pieces of European legislation, the Habitats Directive and the Water Framework Directive, have a strong focus on biodiversity. In the Water Framework Directive (first implemented in 2000), analyses of different “biological quality elements” are used to assess the ecological health and status of water bodies (predominantly using data on biological traits and ecological preferences of freshwater species), which in turn guides funding for conservation and restoration work.
As a result, to properly implement such environmental policy requires comprehensive and detailed information on freshwater species. However, until now, such data has largely been scattered, incomplete and not comprehensive: varying widely in quality and precision. To address this shortfall, the freshwaterecology.info database has been set up to provide comprehensive and harmonised data on the ecological characteristics of European freshwater species, which can be used by scientists, policy makers, environmental managers, students and the public.
The online database categorises organisms by their ‘ecological parameters’ – an amalgamation of biological information and ecological preferences in other categorisations – which include: 1) distribution (e.g., per ecoregion or per catchment); 2) spatial preferences (e.g., stream zonation or altitudinal preferences); 3) habitat preferences (e.g.,hydrological, temperature or salinity preferences); 4) pollution, trophy and saprobity (e.g., different saprobic and trophic indices); and 5) life history (e.g., life span, fecundity, feeding types).
The freshwaterecology.info online database currently holds data on around 20,000 freshwater species across five different organism groups: fish, macroinvertebrates (insects), macrophytes (plants), diatoms and phytoplankton. Much of the data brought together in the portal has been collected and classified by successive, complementary European Union projects, including Euro-limpacs, Refresh, WISER, FAME, EFI+ and BioFresh. The development of the freshwaterecology.info database has been led by Astrid Schmidt-Kloiber and Daniel Hering and now forms a key part of the integrated Freshwater Information Platform.
The integrated freshwaterecology.info database allows users to search by species and ecological parameters, giving comprehensive citations to the authors who supplied the data as well as to the literature references the classifications were based upon. Similarly, it includes taxa entry and validation tools, to allow users to enter and create standardised taxa lists using the database’s taxonomy. All the data accessed through the portal can be exported and downloaded to allow further quantitative analyses.
How might the freshwaterecology.info database be used to help further freshwater science, policy and conservation across Europe? In a recently published journal article in Ecological Indicators, Schmidt-Kloiber and Hering outline a number of examples of how the database could be (and already is) important for freshwater research.
First, presenting species data within ecoregions – an area of land and/or water with a geographically distinct assemblage of species, natural communities, and environmental conditions – rather than within national state boundaries, has allowed for targeted biodiversity analyses such as those of Conti et al 2014 and Hering et al 2009 at appropriate ecoregional scales, using data from freshwaterecology.info.
Second, knowledge on the ecological preferences of freshwater species is a key element of biomonitoring and assessment systems within European policies like the Water Framework Directive. Most ecological assessment strategies require numerically coded biological information on individual species: indeed in a 2012 paper, MARS scientist Sebastian Birk and colleagues found that two-thirds of European river assessment and almost half of lake assessment approaches required such data.
Third, ecological restoration is an increasingly common form of environmental management in a world subject to ongoing human alterations. A key question is how to evaluate the success (or failure) of restoration measures. A review by Verdonschot et al. 2012 on freshwater restoration evaluation highlights the value of biological indicators and ecological preferences in tracking the recovery of a degraded ecosystem following restoration work.
Finally, species traits are commonly used in computer models built by scientists to attempt to forecast how species and ecosystems might respond to climate change in the future. Here, a key focus for research is the ‘sensitivity’ of species to climate altered environmental factors such as water temperature, flow and quantity. Studies such as Hering et al. 2009, Sandin et al. 2014 and Conti et al. 2014 have used data on ecological preferences from the online database to reveal that freshwater species in Mediterranean and high mountain ecosystems are particularly vulnerable to projected changes in climate.
The formation of the freshwaterecology.info database provides a significant step forward in the comprehensiveness, accessibility and use of freshwater biodiversity data in Europe. As Schmidt-Kloiber and Hering write in their new paper, “A sound understanding of ecological functioning is a prerequisite for the implementation of biological approaches into European aquatic ecosystem management.”
Depending on funding, the database will continue to grow in both content and use in the future. Data is continually being added, filling species gaps, and providing new information for scientists to undertake new research and analysis to respond to both existing and emerging trends and threats in European freshwater ecology. As such, freshwaterecology.info is an invaluable tool.
Astrid Schmidt-Kloiber describes the potential and challenges offered by the freshwaterecology.info database, “We are grateful to all contributing experts and acknowledge the balancing act they had to manage when codifying their comprehensive ecological knowledge and translating it into numerical values. Finally, we have achieved a great and important goal and moved harmonised assessments throughout Europe a big step forward. Still, the database also shows us the knowledge gaps and the urgent need for more basic research, for example regarding the general distribution of some species or the temperature preferences and dispersal capacities often called for in global change modelling.”
The interactions and impacts of multiple stressors on aquatic ecosystems is one of the key challenges for current environmental research, policy and conservation. Whilst there are many success stories of pollution being reduced on rivers and lakes across the continent, and aquatic life returning (see for example salmon in the River Mersey and River Tyne in England), Europe’s freshwaters are still subject to multiple stresses, many of which are subtle, complex and poorly understood.
New scientific research suggests that these stresses – chemical pollution, drought, floods, habitat destruction amongst many others – can interact in complex and dynamic ‘cocktails’. A key point here is that these interactions may intensify their individual effects on freshwaters: in other words, the combined damage multiple stressors cause to ecosystems may be more than the sum of the individual parts (known as a synergistic effect).
As studies such as this one by Daniel Hering and colleagues from earlier in the year suggest, multiple stressors pose a series of new, complex and non-linear challenges for aquatic ecosystem conservation and, increasingly, restoration. But despite this emerging awareness of the challenges multiple stressors pose to the health of freshwater ecosystems, there are comparatively few scientific studies which provide quantitative evidence on their effects, making it difficult to inform suitable management and mitigation strategies.
Responding to this shortfall in knowledge, a team of MARS scientists led by Peeter Nõges from the Estonian University of Life Sciences, reviewed 219 existing scientific papers, published since 1986, which quantify the prevalence and effects of multiple stresses on river, lake, groundwater and estuary environments. Nõges and colleagues suggest that whilst there is a pressing ongoing need for quantitative evidence on multiple stressors, this is hampered by a lack of suitable and coordinated sampling techniques and analyses amongst researchers.
Publishing in Science of the Total Environment, a key finding of their study is that nutrient stress (e.g. from fertiliser or sewage pollution) was a key element of most (71-98%) multiple stress combinations in surface waters (rivers, lakes and estuaries). Hydrological stress (e.g. water scarcity, flooding) was found to be a key factor in rivers (74% of studies) and groundwater (83%) environments.
Together, combined hydrological and nutrient stresses were found in over half the studied rivers, and around a quarter of lakes. This finding tallies with reports submitted by European Member States under the Water Framework Directive, describing the pressures (a slightly different, and inherently anthropocentric, meaning to stressor) faced by Europe’s freshwaters. Here, again, member states reported diffuse pollution and hydromorphological alteration (i.e. the alteration of river and lake courses and flows).
Across all the biological groups analysed in the reviewed studies, multiple stressors had most impact on lake ecosystems compared to single stressor conditions. However, the effect of multiple stressors was generally lower in estuarine waters.
The review outlines how different retention times for nutrients (i.e. the amount of time spent in an environment) in rivers and lakes, influenced by water movement and flow, causes different effects. Specifically, where in flowing rivers the retention time of nutrient pollution is low, it is much higher in still or slow-moving lake and estuary environments.
This has a couple of important implications for ecosystem health and functioning. First, high levels of nutrient pollution may be carried through river systems without significant impact, yet when they reach the brackish, slow estuary environment (and switch to an increased residence time) become a likely cause of eutrophication. This means that issues of scale must be taken into account when studying the causes and effects of multiple stressors: and that pollutants may be carried many miles before having harmful impacts.
Second, this finding suggests that the environmental impacts of other hydrological stresses which reduce the speed of river flows (e.g. droughts, dam construction and water abstraction) may intensify the effect of nutrient pollution. This is because river environments where nutrients would generally be washed through become slow or still, increasing the nutrient residence time, and potentially causing harmful environmental impacts such as eutrophication and algal blooms.
Another important finding made by Nõges and colleagues is that the response of freshwater species to multiple stressors reported in the 219 studies is largely ambiguous. Across all the varied aquatic conditions in studies analysed in the review, only fish populations were significantly more impacted when the effects of multiple stressors were increased. This is described as being a result of the mobile lifecycle of many fish species, acting as consumers at different levels of the food chain, across a variety of habitats. For the authors of this study, it is this niche diversity that makes fish particularly susceptible to the impacts of multiple stressors, and also, therefore a potentially important group of bioindicators to detect their effects.
Nõges and colleagues conclude by suggesting that their efforts to provide a first comprehensive assessment of existing scientific research on multiple stressors in aquatic environments were complicated by the seemingly unlimited number of potential stressor combinations and numerous sampling strategies and scales in the papers reviewed. Given that increasingly technological and innovative industries across the world are continually developing new chemicals and plastics, a proportion of which are likely to end up in aquatic environments eventually, this almost-unmanageable diversity of potential multiple stressors makes research and management tricky.
However, EU projects like MARS, SOLUTIONS and GLOBAQUA are specifically targeting this shortfall in scientific knowledge on the interactions and impacts of multiple stressors, as a means of helping manage and mitigate their effects on aquatic ecosystems, both now and in the future.
In recent years, microplastic pollution has been identified as an increasingly pervasive and damaging environmental stressor in the world’s seas, found even in remote locations in the Arctic ocean and deep sea trenches, far from human settlements.
Microplastics are, as the name suggests, tiny particles of plastic (less than 5mm in size in this study) which enter aquatic environments either directly as manufactured pellets from industrial and farming processes and microbeads from cleaning and cosmetic products; or indirectly through the erosion and breakdown of larger plastic items such as fishing nets and household waste. When ingested by fish and marine mammals, microplastics can obstruct or damage internal processes, cause bodily stress, and potentially lead to the uptake of harmful chemicals.
Global plastic production has increased exponentially since the 1960s, to around 299 million tonnes in 2013 alone, meaning there is a huge amount of plastic currently being used and thrown away around the world, a proportion of which is ending up in entering aquatic systems as pollution, and taking many years, if not centuries, to break down. So in short, microplastics are one of the most widespread and potentially damaging aquatic stressors emerging from the growth of consumer society in recent decades.
But as yet, most of the scientific and conservation work on microplastic pollution has focused on seas and oceans. But what about microplastic pollution in freshwaters?
A paper published earlier this year in the journal Water Research, led by Dafne Eerkes-Medrano at the Aquatic Ecology Group, Department of Zoology at the University of Cambridge provides a timely overview of research on the impacts of microplastics on freshwater systems.
Whilst there is still only a small body of research on freshwater microplastics, the review work by Eerkes-Medrano and colleagues suggests that microplastic presence and impact may be equally as far-ranging in freshwaters as it is in marine habitats. Their study documented evidence of microplastics in freshwater environments as widely spread as Lake Hovsgol in Mongolia, Lake Geneva and the River Danube in Europe, and Lake Superior, Lake Huron and Lake Erie in Canada and the USA.
However, whilst there are a growing number of studies documenting microplastic pollution around the world, our knowledge of this emerging environmental stressor remains patchy. As such, Eerkes-Medrano and colleagues suggest a number of key areas requiring further research to help develop and strengthen freshwater conservation and policy on microplastics.
First, we need to better understand how microplastics reach freshwater ecosystems, and how they disperse and degrade over long periods of time. This is largely a question of understanding and mapping plastic pollution from household, industrial and agricultural sources, and studying how it is gradually broken down. The movement and potential deposition of microplastics is shown to depend largely on river flow, wave action and releases of water from dams and hydropower plants. As such, microplastic concentrations are likely to be high in areas where water velocity is low, and the sediment it carries is suspended and deposited.
A key question for the management of microplastic pollution is how to prevent it entering freshwaters at source. A recent UN report on marine microplastics advocated more widespread and effective plastic recycling processes to reduce waste. Here, it might be the case that creative and effective science communication work which engages the public with microscopic images of micoplastic pollution (as shown here from a study by the Chesapeake Bay Program in the USA) could help bring this otherwise largely invisible issue to life, and help foster more environmentally concious plastic use and disposal.
Second, we need better monitoring systems to detect microplastics in freshwaters. This is a challenging process, because microplastics are so small and easily transported by the movement of water. Similarly, when a sample of sediment is taken from the bed of a freshwater, it is difficult to separate the microplastics from other organic particles in the sediment. Finally, without any historical data on microplastics in freshwaters, it is difficult to define any baselines for what might be ‘safe’ concentrations in an aquatic ecosystem, nor which particular plastics and sizes cause the most harm to aquatic life.
Third, and perhaps crucially, we need to better understand the impacts of microplastic pollution on freshwater biota. Again, scientific studies of the effects of microplastics on freshwater life is relatively sparse, but tellingly in almost all surveyed studies, microplastics were ingested by freshwater species including catfish, freshwater snails, clitellate worms Japanese medaka and gudgeon. Perhaps surprisingly, in one of these studies, tiny plastic particles between 20 and 1000nm were shown to accumulate in the tissues of the minuscule freshwater water flea Daphnia magna.
Whilst there is variation in the ecological effects observed in the available studies, microplastics can have harmful effects on freshwater life by blocking internal digestion processes, causing physiological stress, and causing the uptake of potentially damaging chemicals. Both the microplastics themselves, and the chemicals they leach, have the potential to bioaccumulate in larger animals such as predatory birds and fish, with harmful effects potentially cascading through an ecosystem’s trophic layers. Here, microplastic concentrations and residence time (i.e. the amount of time they stay in the ecosystem without degrading) are suggested to be important in determining how much impact pollution is likely to have on freshwater life.
Fourth, there are many unanswered questions about the potential impacts of freshwater microplastic pollution on humans. Eerkes-Medrano and colleagues ask, if microplastic pollution is increasingly recognised as a freshwater issue, what might its effects be on the freshwater resources used by humans, such as drinking and bathing water? How might microplastics contaminate food production, both in freshwater, and potentially in the surrounding landscape where they might be deposited?
Whilst there are numerous unanswered questions about the presence, dynamics and effects of microplastic pollution, the key point of this new review by Eerkes-Medrano and colleagues is that microplastics are an important area for freshwater scientific research and policy development. Greater knowledge and awareness of microplastics in marine environments mean that marine policy is slowly beginning to address their impacts, for example in the European Commissions Marine Strategy Framework Directive, which explicitly lists microplastics as an important and damaging source of ‘marine litter’ to be managed.
But forming new and effective environmental policy and conservation strategies requires a strong scientific evidence base, which in turn needs appropriate funding sources and monitoring systems. This review shows that there is still much work to be done on surveying, monitoring and researching freshwater microplastic pollution, in order to support the formation of appropriate policies and strategies to manage this emergent and potentially widespread freshwater stressor.
Many of us know about the familiar sources of water pollution: fertilisers running off agricultural fields, sewage leaking from underground pipes and oil and fuel leaking from boats, amongst many others. But what if the pollutants and stresses on aquatic environments weren’t chemical and visible, but sonic and audible? How might noise pollution affect underwater life, and how might we manage it? How, in fact, in a crowded, noisy world do we even define what noise pollution might be?
A recent study published by Stephen Simpson and colleagues at the Universities of Exeter and Bristol in England investigated how the noise made by ships affects the behaviour of juvenile European eels. They found that underwater sound pollution significantly affects the behaviour of juvenile eels in ‘life or death’ scenarios when ambushed or pursued by a predator. Their findings suggest that sound may need to be increasingly taken into account when assessing the multiple pollutants and stressors that aquatic life is exposed to, both in oceanic and freshwater ecosystems.
The European eel’s life-story is fascinating, and (perhaps surprisingly for such a well-studied species) still has an element of scientific uncertainty. Eels spawn in the Sargasso Sea in the Western Atlantic Ocean, and larvae are carried along ocean currents back to rivers in Western Europe. When the larvae approach river estuaries they metamorphosise into ‘glass eels’ with almost transparent bodies measuring around 10cm in length. The glass eels go through subsequent growth cycles into elvers and finally adult eels as they migrate upstream, sometimes living for over 20 years in rivers and lakes (they have been known to travel across wet ground like snakes in order to find suitable habitat) before migrating downstream and out to the Sargasso Sea to begin the cycle again.
Unfortunately, European eel populations are critically endangered. Studies by the Zoological Society of London suggest that eel numbers in the River Thames have dropped by around 95% in the last 30 years, due to a combination of overfishing (particularly at the glass eel stage – these are a delicacy), habitat loss, barriers to migration (such as weirs), chemical pollution (particularly by this chemical) and climate-related shifts in Atlantic ocean currents. In short, eel populations are struggling, and it is important to understand what factors are threatening the species, and how they might be managed. And in this context, the study by Simpson and colleagues reminds us to consider sound as an important, if not always considered, source of aquatic pollution that may affect their populations.
In their study conducted, glass eels were collected in the River Severn and transferred to laboratory aquariums. There, the eels were exposed to recordings of large ferries, tankers and container ships moving around three UK harbours, along with ambient recordings of the harbours with no ship noise, which acted as a control, both in laboratory and open-water conditions. The recordings were made with a special microphone known as a hydrophone, which is dropped under the water’s surface and records the otherwise inaudible (to humans, at least) underwater soundscape.
A hydrophone recording of a dredger boat at the confluence of the River Lea and River Thames in East London. Taken as part of the Surface Tension project. This recording is for reference to show how loud underwater sound pollution can be, and was not used in the study by Simpson and colleagues.
The glass eels in the laboratory study were then subjected to two simulated ‘predator attacks’. In the first ‘ambush’ simulation, a single eel was acclimatised to a new tank with a ‘predator window’ where a model fish on a pendulum arm was swung. When the eel passed the small glass window, the model predator was swung (in an admirable adherence to control conditions, the researcher doing the ‘swinging’ listened to loud music on headphones so as not to know which soundscape was being played to the eel). In the second ‘pursuit’ simulation, eels were chased with a handnet through an experimental tank arranged as a maze with Perspex blocks. In both simulations, the response of the eels to ‘predation’ was carefully noted, under both ship noise and ambient soundscape conditions.
The results were significant: when the ship noise was played, eels were 50% less likely to startle to an ‘ambush’ predator compared to the ambient, control soundscape, and when they did startle, this reaction was 25% slower. Similarly, eels in the ‘pursuit’ simulation were caught more than twice as quickly when exposed to the ship noise soundscape. Additionally, the eels exposed to ship noise altered their spatial behaviour and movement, and heightened their stress (as observed by the ventilation and metabolic rate).
Lead author Dr Steve Simpson, Senior Lecturer in Marine Biology & Global Change at the University of Exeter, said: “Our findings demonstrate that acute acoustic events, such as the noise of a passing ship, may have serious impacts on animals with direct consequences for life-or-death behavioural responses. If these impacts affect whole populations then the endangered eel, which has seen a 90 per cent crash in abundance over the past 20 years due to climate change, may have one more problem to deal with as they cross busy coastal areas.”
Co-author Dr Andy Radford, Reader in Behavioural Ecology at the University of Bristol, outlined that: “The fact that eels were affected physiologically and spatially suggests that other important functions may also be affected. We focused on anti-predator responses as, unlike impacts on movement or feeding, there is no way to compensate for being eaten after the disturbance goes away.”
The findings remind us that documenting the multiple stressors that affect freshwater life is not a simple process. Here, the pollutants affecting the eels behaviour and possible survival rates are not chemical but sonic. Sound pollution is a commonly observed problem in oceanic environments, but less so in freshwaters. So the question here is: how can aquatic sound pollution be monitored and managed, if at all?
The management of anthropogenic noise is already included in the US National Environment Policy Act and the European Commission Marine Strategy Framework Directive, and as a permanent item on the International Maritime Organisation Marine Environmental Protection Committee agenda, but given the thousands of busy, interconnected shipping lanes that criss-cross the world, how effective can these policies be? And given that the findings of this study may be replicated in other fish species, we might ask what about the management of sound pollution in freshwater environments?
This leads to another complication in understanding the full suite of multiple stressors impacting eel populations: spatial and temporal scale. In other words, the eels move through different environments (oceanic, estuarine, freshwater) at different points in their life cycles, covering thousands of miles from birth to death. Sound pollution stressors that affect freshwater populations of eels may occur hundreds, or even thousands, of miles away in the ocean or in river estuaries. These are dynamic populations with complex life cycles affected by different stressors at each stage of growth. So the second issue here is how to foster co-operative, interlinked management strategies for such migratory species, which help mitigate and manage the effects of stressors in oceanic, estuarine and freshwater environments?