‘Good ecological status’ is a key term in the EU Water Framework Directive – the policy framework through which European freshwaters are managed. Member states are required to conserve and restore their rivers and lakes to good ecological status by 2027. But what does ‘good ecological status’ mean, and why does it matter?
A new film by the EU MARS project gives an engaging and accessible introduction to the concept. Produced by MARS scientist Christian Feld and colleagues at the University of Duisburg-Essen, the short film ‘Good ecological status of rivers and lakes’ emphasises the value of healthy aquatic ecosystems to human and non-human life, both now and in the future.
A guest post by Werner Brack of the SOLUTIONS project
Mutagenicity – where chemicals interact with our genes, resulting in harmful mutations, potentially causing cancer and damaging our offspring – is a major environmental concern. Mutagenicity in drinking water resources – including many European rivers, lakes and reservoirs – is a particular problem. Although rarely investigated, similar mutation effects can be observed in wildlife, and it is still under debate whether mutagens can damage whole populations.
Mutagenic effects can be detected in water and other samples using biotests such as the Ames test, which uses different strains of Salmonella bacteria. In the River Rhine and other rivers and lakes mutagenicity has been frequently detected, however there has been no success in identifying the compounds causing this effect.
New research by the SOLUTIONS project is providing new insights into these problems. Investigations on the River Rhine and the Rivers Mulde and Holtemme from the Elbe catchment provide evidence on possible drivers of mutagenicity and of its effects on wild populations of freshwater shrimps (Gammarus pulex).
The River Mulde is impacted by historical pressures from Bitterfeld-Wolfen, one of the oldest chemical industrial sites in Germany, which still supports multiple chemical production processes today. Wastewater is discharged after treatment in a large mixed industrial and municipal treatment plant to the river.
Two years ago, scientists from the Helmholtz Centre for Environmental Research found mutagenic effects downstream from the wastewater discharge (Hug et al., 2015). Now they are able to identify causes. Two potent mutagenic aromatic amines (2,3- and 2,8-phenazindiamine) were emitted into the river; compounds that probably stem from dye production, and explain up to 80 % of the observed mutagenic effects (Muz et al., 2017a) In short, chemical pollution on the river is causing mutations in aquatic organisms, causing significant stress to the ecosystem health and status.
In the River Rhine the situation is more complex. As there are multiple water inputs from tributaries and treated wastewater from industries and households, it is not one or a couple of chemicals causing mutagenicity: instead a mixture effect. However, the latest investigations show that it is not just the poorly-defined and complex mixture of ten thousands of chemicals and effects adding up (Muz et al., 2017b). There are clear drivers of mixture mutagenicity. Aromatic amines from industry meet carboline alkaloids such as norharman known from coffee, tobacco smoke and well-cooked food.
Interestingly, these drivers are not (or only very weakly) mutagenic as individual compounds. However, when taken up by organism together as a mixture they react to highly potent mutagens. Although this effect explained only a part of the found mutagenicity in the Rhine River it may provide a key for better understanding environmental mutagenicity.
And what about new indications that mutagenicity is affecting wildlife populations? To demonstrate these effects SOLUTIONS scientists investigated another water body, the River Holtemme in Saxony-Anhalt, Germany. There are indications that mutagenic wastewater components may impact on the genetic diversity of freshwater shrimps. Downstream of a wastewater effluent discharge which caused mutagenic effects in the Ames test, genetic diversity of freshwater shrimps dropped. At the same time, so-called private alleles were occurring, exotic pieces of DNA that are an indication of mutations.
The evidence is increasingly clear: chemical pollution can cause mutations to aquatic organisms which damage their health and diversity. The question, then, is how to find policy and management solutions to limit chemical pollution wherever possible.
If you would like to read more:
C. Hug, M. Sievers, R. Ottermanns, H. Hollert, W. Brack, M. Krauss (2015) Linking mutagenic activity to micropollutant concentrations in wastewater samples by partial least square regression und subsequent identification of variables. Chemosphere 138:176-182
P.A. Inostroza, I. Vera-Escalona, A.-J. Wicht, M. Krauss, W. Brack, H. Norf (2016) Anthropogenic stressors shape genetic structure: Insights from a model freshwater population along a land use gradient. Environ. Sci. Technol. 50:11346-11356
M. Muz, J.P.Dann, F. Jäger, W. Brack, M. Krauss (2017a) Identification of mutagenic aromatic amines in river samples with industrial wastewater impact. Environ. Sci. Technol. accepted
M. Muz, M. Krauss, S. Kutsarova, T. Schulze, W. Brack (2017b) Mutagenicity in surface waters: Synergistic effects of carboline alkaloids and aromatic amines. Environ. Sci. Technol. 51:1830-1839
Water connects lives at all scales, supporting human and non-human populations alike, through networks that link Earth’s most remote areas with some of its biggest cities. The ecological inter-connectedness of freshwater and marine habitats – lakes, rivers, estuaries and oceans – is increasingly acknowledged by scientists and water managers. However there is the need for large-scale experimental research in order to better understand the dynamics and threats of these connected aquatic systems.
Scientists from 19 leading research institutes and universities, and two enterprises from 12 countries, across Europe are collaborating on a new project AQUACOSM, a “Network of Leading European AQUAtic MesoCOSM Facilities Connecting Mountains to Oceans from the Arctic to the Mediterranean”. AQUACOSM will support the first systematic large-scale ecological experiments in linked freshwater and marine ecosystems. The project is coordinated and led by Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB) in Germany.
“For more than 100 years, inland water and marine research have largely developed in parallel to each other. Now it’s time to reunite both”, says IGB researcher Jens Nejstgaard, who leads the new EU-funded project. In AQUACOSM, scientists from both marine and freshwater realms are joining up an integrated, international network of experimental infrastructures. Their aim is to significantly improve the quality of experimental data for all types of water. “We want to better coordinate international large-scale experimental research projects, develop good practices together, and open up the freshwater and marine mesocosm research infrastructures for a broader international, interdisciplinary collaboration,” outlines Nejstgaard.
The project uses a network of experimental mesocosms across Europe. Mesocosms are structures used to recreate variables from the natural environment within controlled, observable conditions. In other words, mesocosms create an ‘ecosystem in minature’, bridging the gap between laboratory work and field studies, where the effects of different climatic and human pressures on the environment can be simulated.
AQUACOSM researchers will examine how different aquatic ecosystems react to environmental impacts caused by global climate change and population growth. “The impact of these stress factors can vary widely within different ecosystems and seasons”, emphasises Nejstgaard. As a result, they have to be investigated in different climatic and geographic regions, using comparable mesocosm experiments and measurement methods. AQUACOSM connects the infrastructures needed to do such experimental research across a range of different European water types, through climatic and geographic zones stretching from the Arctic to the Mediterranean.
The AQUACOSM experimental infrastructures include tank systems and flow channels on land such as in Lunz am See in Austria, and large free-floating open-ocean facilities such as the Kiel Offshore Mesocosms (KOSMOS) off Svalbard in the Arctic. The IGB-LakeLab in Lake Stechlin, Germany is one of the largest facilities in the world, providing 24 mesocosms, each containing 1,270 m³ of water, supporting research into the impacts of climate change on deep water lakes.
AQUACOSM will offer researchers, both from Europe and further afield, the opportunity to access and use this connected network of mesocosms, as a means of fostering new collaborations and large-scale ecological insights across biomes. This research is intended to feed into networks of stakeholders – water managers and policy makers, for example – as a means of strengthening the protection and restoration of aquatic habitats, both freshwater and marine.
A diver has made an unusual discovery in an inaccessible underground cave system in Southern Germany: a population of Europe’s first documented cave fish. The pale coloured loach of the genus Barbatula is thought to have diverged from surface fish around 16,000 to 20,000 years ago, following the retreat of ice age glaciers.
“The cave fish was found surprisingly far in the north in Southern Germany,” said project leader Jasminca Behrmann-Godel of the University of Konstanz in Germany, lead author on a newly-published study in Current Biology. “This is spectacular as it was believed before that the Pleistocene glaciations had prevented fish from colonizing subterranean habitats so far north.”
The loach is Europe’s first reported cave fish, discovered in 2015 by diver Joachim Kreiselmaier in the hard-to-reach Danube-Aach karst cave system, which drains into the River Rhine. “It was only when the glaciers retreated that the system first became a suitable habitat for fish. They must have moved there at some point following the end of the Würm glacial period, no more than 20,000 years ago and seemingly from the Danube.” said Arne Nolte from the University of Oldenburg/Max-Planck Institute for Evolutionary Biology in Plön, Germany.
In evolutionary terms, the loaches’ adaptation to pitch-black underground cave life has been extremely rapid, occurring over the course of a few thousand years. “Their eyes are much smaller than in other fish, almost as if they were curved inwards and their colouring has almost disappeared. The fish have elongated barbels on their heads, and their nostrils are larger than those of their cousins who live closer to the surface,” explains Jörg Freyhof from the Leibniz Institute for Freshwater Ecology and Inland Fisheries (IGB) Berlin.
The cave system where loach populations were found was sealed for hundreds of thousands of years until the end of the last ice age, when glaciers retreated northwards to leave a new opening, known as the Aach Spring. It is through this spring that a loach population is likely to have entered the underground cave system from surface waters, becoming isolated and taking on new evolutionary paths.
The caves are notoriously difficult for divers to access, requiring dry spells which make the underground water system calm and clear enough for exploration. “No more than 30 divers have ever reached the place where the fish have been found,” diver Joachim Kreiselmaier said. “Due to the usually bad visibility, strong current, cold temperature, a labyrinth at the entrance most divers do not come back again for diving.”
Over 2015 and 2016, Kreiselmaier brought back five live loach specimens for Behrmann-Godel to analyse. Based on morphological and genetic comparisons to surface fish caught upstream and downstream of the cave, the researchers report that the cave loaches are indeed an isolated population and the first known European cave fish.
North America and China are known hotspots for cave dwelling fish, but the discovery of the underground loach populations in Southern Germany suggests that cave fish distributions may be wider than previously thought. For project leader Jasminca Behrmann-Godel, the loaches’ rapid evolutionary adaptation suggests that similar populations may be found in Europe in the future, “Cavefish could exist virtually everywhere in principle, and there’s no good reason to expect long evolution times for them to adapt to cave environments.”
The discovery indicates that some underground cave ecosystems may be more complex and nutrient-rich than previously thought, allowing them to support such permanent fish populations. It is also a reminder that the conservation of underground aquatic ecosystems – for example through reducing diffuse pollution and water abstraction – is of crucial importance, not only for species we already know about, but potentially those that are yet to be discovered.
Research will continue into the loaches’ genetic, genomic and behavioural characteristics, which may provide unique insights into the traits of a species in the ‘early’ stages of evolution. For Jörg Freyhof, the discovery is a reminder that “the wonders of nature can turn up anywhere, even in your own backyard.”
Human alterations to the physical characteristics of water bodies – their shape, course, bed and banks – are common across Europe. Such ‘hydromorphological’ alterations may be the result of flood protection needs, navigation, urban development, abstraction demands or water storage.
Hydromorphological alterations due to water storage – for example, hydroelectricity generation, agricultural irrigation and public water supplies – are particularly widespread, and many of the affected water bodies have been designated as ‘heavily modified‘ by the Water Framework Directive (WFD). As a result, effective management and mitigation strategies are clearly needed to improve the ecological health and status of affected water bodies.
Since 2013, the ECOSTAT project – an European Commission Working Group for the implementation of the WFD – has been researching the effectiveness of mitigation measures for the effects of water storage on water bodies in 23 European countries. ECOSTAT recently published a report on this research, based on engagements with stakeholders across Europe. Framed as a ‘knowledge exchange’ tool for water managers, the report highlights how mitigation measures for water storage across Europe are commonly focused on maintaining minimum ‘environmental flows’ along river courses, particularly of water and migratory fish.
Their report centres on the idea of ‘good ecological potential‘ in heavily modified water bodies. EU member states are required to undertake management to guide most of their water bodies towards ‘good ecological status’, which is measured by a range of biological and chemical indicators. However, heavily modified water bodies (for example, a hydropower dam on a river) are instead required to be managed towards ‘good ecological potential’.
In effect, this is a measure of progress towards a lowered baseline of ecological status, which is limited by human modifications. Implicit in the measure of ‘good ecological potential’ is an awareness that highly modified water bodies are unlikely to ever reach the ecological status of their less modified equivalents, and so the task for water managers is to improve their status as far as possible, given the multiple pressures they face.
The recent ECOSTAT report compared the effectiveness of mitigation measures for water storage pressures across Europe in achieving good ecological potential. Mitigation measures – for example, maintenance of water flows and temperature below a dam, or the installation of fish passes – are aimed to improve the ecological potential of heavily modified water bodies. However, there is a need across Europe for managers to share information on ‘what works’ when implementing mitigation measures under multiple pressures.
Water storage in reservoirs, dams and canals for water supply, power generation, irrigation and recreation can have a number of harmful ecological effects. Flows of water, nutrients and sediments are often altered, and migration routes and breeding grounds for aquatic animals such as salmon are cut off. Habitats are often altered, both upstream and downstream of water storage constructions, potentially altering erosion dynamics and water temperature, depth and oxygen levels. A range of common measures – largely targeted at maintaining or restoring environmental flows – are outlined in the report.
Connectivity of fish migration routes
The free passage of migratory fish is a key requirement of the WFD, and may be used as an indicator for assessing whether water bodies are meeting good ecological potential or status. As a result, ensuring connectivity in migration routes was a key priority for most countries, with in-channel fish passes and bypass channels (which circumvent small obstructions) the most common measures.
Bypass channels are reported as being most effective at helping migratory species navigate small dams and weirs. Both bypass channels and in-channel fish passes require ongoing maintenance, and a wider conservation of habitats involved in other life stages (e.g. spawning) to be successful. In hydropower plants, the installation of ‘fish friendly’ turbines which have fewer blades and slower rotation speeds may increase the downstream migration success rate for some fish species. The most common reason for not implementing such measures is due to high costs and technological requirements.
Water flows play a key part in shaping the physical and ecological characteristics of a water body, and as such its sustainability and productivity. As with connectivity, the WFD explicitly acknowledges the importance of the flow regime for the status of aquatic ecosystems and includes it as one of the key quality elements supporting biological elements in the classification of ecological status.
Most European counties implement mitigation measures for flow alterations, although these vary depending on geography and human pressures. Where low flows are a problem, measures may include increasing flows from dam outflows, reducing abstraction rates and altering river morphology to maximise habitat availability under low flows. Where rapidly changing flows (for example, from ‘hydropeaks’) are the issue, dam outflows may be regulated or rerouted, and river morphology may be altered to provide refuge habitats for variable flows, in order to minimise the effects on downstream ecosystems. As with connectivity, technical challenges and high installation costs were commonly cited as reasons not to implement such measures.
Closely tied to hydrological flows, sediment transport plays a fundamental role in determining and maintaining river channel morphology and ecosystem habitats. Water storage reservoirs can fundamentally alter sediment dynamics: causing upstream deposition where flows are low, and downstream erosion and transport where flows are higher, and/or more variable.
A focus on mitigating sediment alteration is less of a priority in European countries than for connectivity and water flows. Where practiced, the two most effective techniques are reported to be mobilising flows and restoring lateral erosion processes. Where the first measure is dependent on managing water flows, the second is practiced largely where river banks have been reinforced with rock or concrete. Lateral erosion measures aim to remove such fortifications to allow natural erosion processes to return along the river’s banks, thus increasing sediment supply to areas where there is presently little, due to such modifications.
Dams and weirs create stretches of ‘impounded’ flows on rivers, where upstream flows are often reduced, water depth increased, and sediment deposition increased. Impounded flows may extend out over former flood plains. Some rivers may alternate between impounded and free-flowing stretches, creating a fragmented course, often with low connectivity between habitats. Impounded areas may be at increased risk of stagnation and eutrophication linked to water pollution.
Measures to mitigate the impacts of impoundments are not yet widespread in Europe, according to the ECOSTAT report. Where practiced, the measures with highest ecological impact are the restoration of tributary and floodplain features in impounded stretches, in order to encourage a more ‘natural’ flow regime; the reduction of water storage levels above a dam or weir; and the construction of free-flowing channels which bypass the impoundments, in order to create appropriate aquatic habitats. Following inputs from water managers across Europe, improvements to impounded channel habitats and reconnecting tributaries and floodplain features are the most realistic measures for implementation.
Lake level alterations
Large dams with reservoirs may be built for multiple water uses including hydropower, water supply (e.g. drinking water), flood protection and water regulation. Depending on the different requirements of these uses, the water level in reservoirs can vary over time and use. For example, for flood protection water levels are relatively high during wet periods and lower during dry periods. For hydropower use, rapidly changing energy production (hydropeaking), can cause high water level fluctuations, particularly in smaller reservoirs. Such fluctuations can cause widespread ecological stress, particularly to the communities of plants, fish (often juveniles) and insects which live in shallow lake margins, and may find their habitat periodically flooded or dried out.
Most of the European countries reporting to the ECOSTAT study implement measures to mitigate the effects of lake level fluctuations. These include better management of abstraction rates and timing, and ensuring lakes are properly connected to tributaries, to allow mobile species to migrate to suitable habitats when lake levels fluctuate. Both measures are ranked as having high ecological and practical effectiveness by the contributing water managers. However, reductions to abstraction may be difficult to achieve given the high economic value (e.g. hydropower, agriculture) of the abstracted water.
Physical and chemical alterations
Large dams and weirs can alter water temperature, nutrient concentrations and patterns of winter ice formation, both upstream and downstream, through the alterations to hydrological regimes outlined above. These impacts can reduce habitat quality and spawning success for many aquatic species, particularly fish.
Of these impacts, mitigation measures for water temperature alterations are most common, and were reported by around half of the ECOSTAT stakeholders. Flexible and multiple intakes of water, which allow for the controlled intake of water from different depths (and thus, temperature) from a reservoir to a downstream river, are the key implemented measure. However, at present, there is too little practical experience to give a clear indication of the ecological effectiveness of such measures.
The report helpfully brings together information on the use and effectiveness of mitigation measures for water storage pressures across Europe. However, there were variations in the scale at which measures were applied on rivers and lakes (e.g. 100m to 10km on rivers), which limited direct comparisons between sites. Similarly, there were variations in how ‘good ecological potential’ was calculated in different countries, reflecting its highly site- and pressure- specific nature as a metric. As a result, the report advocates more harmonisation in calculation techniques.
More broadly, the maintenance of regular and interconnected water flows is a key theme in all the pressures explored above. Free-flowing rivers allow species to migrate, regulate temperatures, foster natural sediment dynamics, and create diverse habitats. The challenge, as highlighted by this report, is to attempt to simulate and restore such conditions, even when faced with the multiple pressures (and challenges) present in heavily modified water bodies.
Halleraker et al, (2016) Working Group ECOSTAT report on common understanding of using mitigation measures for reaching Good Ecological Potential for heavily modified water bodies – Part 1: Impacted by water storage; EUR 28413; doi: 10.2760/649695
Last week, researchers from three EU aquatic science projects – MARS, GLOBAQUA and SOLUTIONS – met in Sesimbra, Portugal to present their findings, and to discuss opportunities for collaboration. The three projects share a common interest in the effects of multiple stressors on aquatic ecosystems, and their representatives met at a workshop to develop the potential for shared outputs such as policy briefs and water management guidance.
The workshop was structured in seven parts where researchers from the different projects presented their findings together. In the first, Teresa Ferreira (MARS), Ralf Ludwig (GLOBAQUA) and Tobias Schulze (SOLUTIONS) presented findings of analyses on the impacts of multiple stressors on river basins across Europe. Their work was based on the establishment of links from pressures/states to indicators of ecosystem services, which can help better identify the impact of multiple stressors on aquatic ecosystems. The findings of the MARS basin studies will be published in the coming months.
In the second session, Laurence Carvalho (MARS), Vicenç Acuña (GLOBAQUA) and Paul van den Brink (SOLUTIONS) reviewed the ecological effects of multiple stressors across ecosystem types (rivers, lakes and transitional waters), and across spatial scales (laboratory, mesocosm and flume experiments; individual water bodies and river basins and Europe-wide). Their collaborations sought to outline common stressor combinations (and their effects), which could be presented in a joint water policy and management briefing in the future.
In the third session, Markus Venohr (MARS), Philippe Ker-Rault and Ralf Ludwig (GLOBAQUA) discussed the potentials and pitfalls of downscaling climate and socioeconomic scenarios of the future at the river basin scale. In MARS, the scenarios are based on a set of ‘storylines‘, which are variously refined to specific river basins through stakeholder engagement. Whilst each scenario is a broad-scale approximation, their use in modelling provides a range of possible future trajectories to inform management and policy decisions. The session will lead to a joint publication and a white paper on downscaling scenario forecasts to the river basin scale, which is most useful for management.
The fourth session involved a discussion of how to link chemical and ecological status, led by Antoni Ginebreda (GLOBAQUA) and Andreas Focks (SOLUTIONS). The ‘good status’ of European water bodies according to Water Framework Directive requirements depends on them fulfilling both good ‘ecological’ and ‘chemical’ status. However, the complex interactions between different pressures – chemical and nutrient pollution, hydrological and hydromorphological alterations, land use changes – makes untangling their joint impacts on ecosystem status challenging. This session synthesised knowledge from across projects to scope the potential of strategies including: multi-pollution characterisation and effects; ecotoxicological risk assessment; modes of action of pollutants; compound prioritisation and identification of River Basin Specific Pollutants, the use of sensitive traits as indicators of ecological quality, and the links between biological and chemical monitoring data.
In the fifth session, Lidija Globevnik and Yiannis Panagopoulos (MARS), Alberto Pistocchi (GLOBAQUA) and Jos van Gils (SOLUTIONS), discussed approaches taken in the three projects to model the interactions of multiple pressures driving the status of European water bodies. In this session, particular focus was placed on hydrological pressures and chemicals interacting with other stressors, as well as the regional variability of interactions.
The sixth session focused on the science-policy dialogues and impacts prompted by the three projects. Discussions led by Daniel Hering and Erik Jeppesen (MARS), Ebun Akinsete and Nick Voulvoulis (GLOBAQUA) and David López Herráez (SOLUTIONS) focused on the translation of the projects’ scientific results into recommendations for improving the European regulatory frameworks on freshwater, with particular emphasis on the Water Framework Directive. The discussions developed themes for a number of joint policy briefs, which will be published in the future.
Wider public, policy and academic communication of results (of which this blog is one channel) was the topic of the final session. Sebastian Birk (MARS), Damià Barceló and Gabriele Sacchettini (GLOBAQUA) led discussions of how the databases, scientific reports and papers, policy-briefs and water management tools produced by the projects might be best presented to different audiences.
The workshop was deemed a real success by all who took part, as it sparked many new discussions and opportunities for collaboration between the three projects.
Three attendee reflections can be read below:
“This was a very useful occasion to find synergies between our projects, and was especially important for our policy and dissemination activities. The workshop has offered several possibilities for the coming months, and some useful tools. MARS is a complementary project finishing reasonably soon, whilst GLOBAQUA will have a couple more years; the idea is to work together and build on the results that MARS is providing.”
Gabriele Sacchettini, GLOBAQUA
“This was a very relevant meeting because two projects – MARS and GLOBAQUA – have been funded by the same EU FP7 fund, so it’s important to come together and streamline messages that are useful for water management.”
Tom Buijse, MARS
“I came here to find synergies between the three projects, and particularly to discuss how this might be communicated in policy briefs. The workshop has been a success – a very nice location and great organisation – and very useful in terms of the timing of the three projects. MARS is finishing soon, and it’s time to catch up with the results, and the themes SOLUTIONS and GLOBAQUA can develop and continue.”
David López Herráez, SOLUTIONS
Lakes across the world are increasingly impacted by human activities, which can cause ‘cocktails’ of multiple stressors to affect their ecological health and status. Nutrient pollution and rising water temperatures are causing eutrophic blooms of toxic cyanobacteria in many shallow lakes, whilst abstraction pressures for drinking and irrigation is lowering water levels (or even drying out) on others.
As a result, there is a growing need for effective lake conservation and restoration strategies that help mitigate the effects of an increasingly pressurised world. A new open-access special issue of the journal Water compiled by MARS scientist Erik Jeppesen and colleagues brings together a set of papers on this theme. The research profiled in the special issue is largely focused on the restoration of eutrophic lakes under climate change, and has been undertaken by scientists across the world.
A key theme running the studies is how nutrient loading into lakes interacts with climate change in affecting aquatic ecosystems. Nutrient loading and climate change is a common multiple stressor combination in aquatic environments. Climate change can increase concentrations of nutrients (e.g. through evaporating water bodies), increase water temperatures (which can increase the risk of eutrophication), and cause an increase in extreme events such as flood and drought, which can alter nutrient loading patterns (e.g. through soil erosion). However, multiple stressor interactions are rarely entirely predictable or fully understood, which is why there is significant ongoing research on the topic in aquatic science and management.
The collected studies in the new special issue suggest that it is important to note variations in the dynamics of eutrophic lakes across different climate zones. Many past studies on the restoration of eutrophic lakes have been carried out in northern temperate regions. However, the papers in this special issue broaden the global coverage to include warm lakes, with studies from Denmark, Turkey, USA, Brazil, Russia, The Netherlands, Poland and China.
As a result, whilst reducing nutrient pollution is presented as the key factor for lake restoration under climate change across all studies, it is suggested that different methods to those applied in northern temperate region are needed for warm lakes. For example, the thresholds for achieving ‘clear water’ (i.e. non-eutrophic) conditions through nutrient reductions are likely to be lower in warm lakes than cold; however there still remains significant uncertainty.