Free the Snake is a short film about the restoration of the Snake River in Washington State, USA. Featuring interviews with Professor David Montgomery from the University of Washington, Bruce Babbitt, former Secretary of the Interior and novelist David James Duncan, the film focuses on the ecological and hydrological impacts of four major dams along the river.
In particular, the dams fragment migration routes of Pacific salmon upstream to spawning grounds, with damaging consequences for the health and size of their populations. But, all hope is not lost. When discussing the possibility of dam removal, David Montgomery suggests that, “The beautiful thing about salmon, if you look at their history, is that they’re resilient. If you give them half a chance then they can come back.”
We live in an age of widespread ecological restoration, in which centuries of human impacts on the environment are being addressed, under guiding principles such as rewilding, biodiversity conservation and ecosystem service provision. Restoration projects are particularly common on rivers and streams, partly because these ecosystems have often been particularly impacted by pollution, fragmentation and so on; but also because restoration approaches such as weir removal, ‘daylighting’ and riparian zone planting have become widely adopted. However, despite the increasing number of river restoration projects implemented across the world, there is still sparse scientific evidence on the long-term effects of such projects, and the factors affecting their success or failure.
A new study by MARS project leader Daniel Hering and colleagues addresses this shortfall in knowledge by studying the effects of the restoration of river hydromorphology on aquatic habitats and biodiversity. Hydromorphology is the term used to bring together the interactions of hydrology (e.g. water flows), geomorphology (e.g. bedrock) and ecology (e.g. plant and animal communities) in river or stream. Hydromorphological processes include the formation of meanders, riffles and pools: all of which contribute to a diverse set of habitat niches for freshwater life.
As reports such as the 2012 European Environment Agency ‘European Waters: assessment of status and pressures‘ outline, there is increasing evidence that river hydromorphology often has a strong impact on the health and diversity of aquatic ecosystems. However, projects which restore river hydromorphology often have limited effects on freshwater biodiversity. One common explanation for this effect is that river restoration often takes place over short sections of river, which are insufficient to allow ecological communities to develop, and geomorphological processes to take place.
To investigate this phenomenon, Hering and colleagues undertook experiments on rivers in ten regions across Northern Europe, as part of the EU REFORM project. For each region, they studied the impacts of two restoration projects: one on a short section of river; one on a longer section. At each section of restored river, the team sampled habitat composition in the river and its floodplain, three aquatic organism groups (aquatic plants, insects and fish), two floodplain-inhabiting organism groups (floodplain vegetation, ground beetles), and food web composition and land–water interactions. These findings were then compared to samples taken upstream at non-restored sections of river of roughly equal length.
After accounting for regional variations in river size and restoration approaches, the team, publishing in the Journal of Applied Ecology, found that the length of the restored river made no significant difference to its ecological health and diversity, as sampled by the range of indicators above. Instead, they found that what mattered was the substrate composition of the river bed: in other words, the aquatic habitat it provides for organisms.
Where habitat had been created in restoration, populations of fish, aquatic insects, aquatic plants and floodplain vegetation increased, regardless of the length of the restored river section. Substrate habitat restoration might include measures such as increasing the number of boulders or presence of wood (for example tree trunks) to diversify water flows and depths, and habitat niches for different aquatic organisms.
Whilst in-stream habitat restoration was important for aquatic biodiversity, restoration projects also had pronounced impacts on floodplain ecology. The authors suggest that this is because hydromorphological restoration, even at relatively small scales, tends to create habitat types close to the river bank (such as gravel and sand bars), which are often completely lacking in degraded sites. Such habitat types are rapidly colonized by ground beetles and, to a lesser degree, by specialised floodplain vegetation. Both organism groups have comparatively high dispersal abilities and are less affected by barriers such as weirs when compared to aquatic organism groups.
Overall, the study suggests that the ecological success of river restoration for aquatic organisms doesn’t depend on the length of restored river, but rather the quality and diversity of habitats on the river’s bed. However, for floodplain organisms, relatively small-scale restoration projects may yield significant positive effects.
Stressors are environmental changes that place stress on the health and functioning of an ecosystem. There is increasing evidence – largely from marine environments – that multiple stressors may interact to produce unexpected effects on aquatic ecosystems. However, there is a pressing need to better understand the ‘ecological surprises’ caused by multiple stressors in freshwater ecosystems (a point made in papers by MARS scientists Steve Ormerod in 2010 and Daniel Hering and colleagues in 2015).
Existing scientific literature from marine environments show that multiple stressors can have effects that are greater than the sum of those caused by individual stressors. This ‘synergistic’ interaction poses important questions for environmental managers and policy makers. In short, it is difficult enough to manage individual stressors such as pollution, habitat destruction and overfishing, without the unexpected and, as yet, largely unpredictable interactions and effects these stressors might have.
In the light of this uncertainty, a team of researchers from the University of Pretoria in South Africa and the University of Alberta in Canada analysed data from 88 existing scientific studies that show the responses of freshwater ecosystems to pairs of stressors. The team, led by Michelle Jackson from the University of Pretoria, brought together the findings of these studies to investigate the characteristics and effects of different stressor interactions; and the extent to which interactions vary between different stressor pairs and response measurements.
Freshwater stressors may cancel each other out
Recently published in Global Change Biology, the team’s findings are perhaps surprising, at least initially: the environmental effects caused by pairs of stressors in freshwater was most often less than the sum of their single effects. This is known as an antagonistic interaction, where two or more stressors interact to cancel out some or all of their individual effects.
Across the 88 surveyed studies, stressors included acidification, increased water temperatures, ultraviolet radiation, contamination, nutrification, habitat alteration and invasive species. Antagonistic interactions were found in the majority (41%) of surveyed studies, affecting animal abundance, biomass, condition, growth/size and survival and plant diversity. The authors suggest that this widespread antagonism could be due to the effects of the stronger stressor overriding and negating those of the weaker one. Here, environmental managers might seek to rank the effects of the strongest stressor in an antagonistic interaction in order to forecast the cumulative impacts of multiple stress.
Another suggestion is that exposure to one stressor can result in greater tolerance to another. An important point made here is that there may exist a potential for co-adaption within freshwater ecosystems to minimise the net effects of multiple stressors. However, despite the predominantly antagonistic interactions, net effects of multiple stressors were still mostly negative, underlining the widespread threats faced by freshwater ecosystems.
Multiple stressors in freshwaters: the overall picture
Overall, the net effects of stressor pairs were frequently more antagonistic (41%) than synergistic (where the overall effect is more than the sum of individual stressors: 28%), additive (overall effect is equal than the sum of individual stressors: 16%) or reversed (overall effect is opposite to the positive / negative effect of individual stressors: 15%).
Synergistic interactions between multiple stressors such as increasing sea temperatures, species invasions and habitat destruction have been observed in a number of studies of marine ecosystems. Why is the picture different for freshwaters? The authors suggest that this is due to greater inherent environmental variability in smaller aquatic ecosystems, which fosters higher potential for ecological acclimation and co-adaptation to multiple stressors.
Antagonistic interactions were most frequently observed in affecting animal condition; synergies and reversals with plant growth and size; and additive effects with plant diversity. This variability shows that it is important to consider the ecological metrics used to measure the impacts of multiple stressors.
Different effects on ecosystem diversity and function
Interestingly, multiple stressors had different effects on the diversity and function of ecosystems. Multiple stressor interactions affecting species diversity were most often additive. This suggests that the species eliminated by one stressor were often not the same as those eliminated by the second, and additional stress causes additional species loss.
On the other hand, the most common interaction affecting the functional performance of an ecosystem was antagonism. This may be a result of a process known as compensatory species dynamics. Here, the remaining species in the stressed ecosystem may compensate functionally (e.g. in nutrient cycling) for species loss. This in turn points to the idea that an ecosystem’s functional resilience to stress is not simply dependent on biodiversity, but instead determined by species identity and traits. In short, the findings here suggest that freshwater biodiversity is more sensitive than ecosystem function to the impacts of multiple stressors.
The authors identified that 15% of studies showed reversal effects from multiple stressors. These reversals are termed ‘ecological surprises’, in that they reverse the environmental impacts – negative to positive (or vice versa) – caused by the individual stressors. Whilst reversals were the least common type of interaction observed, their existence has potentially important effects for environmental management.
The stressor most commonly associated with reversal interactions was climate warming. For example, a study by Patrick Thompson and colleagues in 2008 found that warming reversed the negative effects of excess nitrogen supply on phytoplankton growth, possibly as a result of increased conversion of nitrates and ammonia by enzymes as a result of increased temperatures. Ecological responses to temperature change are complex, but the evidence here on multiple stressors causing reversals suggests that there may be ever more ‘ecological surprises’ in a warming world.
Lessons for freshwater conservation management
The paper contains potentially important lessons for freshwater conservation management. For multiple stressors that generate additive or synergistic interactions, management that focuses on a single stressor should cause a positive outcome. However, in ecosystems affected by antagonistic stressor interactions, both stressors may need to be removed in order to foster any significant ecological recovery.
The MARS project has now been running for well over a year, and many of the project experiments are beginning to yield results. Today we’re happy to share a short new documentary about the project, which you can watch above.
The film explains the problems posed by multiple stresses such as nutrient pollution and climate change on freshwater ecosystems, and the ways in which the MARS project is implementing innovative scientific research to better understand and manage their effects.
The new documentary features interviews with MARS scientists Anne Lyche Solheim from NIVA in Norway and Steve Ormerod from Cardiff University in Wales, and Anders Iversen, Water Framework Directive Co-ordinator at the Norwegian Environment Protection Agency. It shows fascinating new footage of MARS stream experiments in the Austrian Alps, and deep lake experiments at the IGB LakeLab research station on Lake Stechlin in Northern Germany.
The piece was predominantly filmed on two heavily stressed and modified rivers: the Emscher in Germany and the Calder in West Yorkshire, England. Additional footage was shot on the upland River Hodder in Lancashire, England. The footage of the underwater char was shot by Jack Perks (who we’ve featured on the blog before), and the footage of the blue-green algal bloom was filmed by Scott Nelson (whose Rivière des chutes film will be featured here soon).
We hope you enjoy the film.
For a while now, we’ve been enjoying fantastic wildlife photographs taken by Neil Phillips and posted on his @UK_Wildlife twitter page. Many of Neil’s photographs capture otherwise unseen views of underwater life, providing a window into this diverse and often beautiful submerged world.
We contacted Neil to find out more about his process and rationale for taking photographs of freshwater life. His response is posted below, alongside a number of his stunning photographs.
I did try a few time to photograph the fish and other creatures in my tropical freshwater aquarium at home, which were mostly failures due to reflection from the onboard flash, though I did manage a couple of photos of my pet caecilians (a type of legless amphibian)
It was not until I started my job in environmental education I really tried again, this time using flash off camera and putting a dragonfly nymph in an old small display aquarium. The shots I got were OK but I still had a way to go.
Soon after this I came across another book with a triangular design for a photographic aquarium and set about building my own (with some help from my dad) from small bits of glass I bought from a local glazier. With this new aquarium, I started getting images that I was happy with.
The setup I use now is a small triangular or rectangular tank with something natural coloured for the background, filled with filtered clean water, and using my Pentax K-3 and the DFA 100mm macro lens, with the flash (with a diffuser) on the off camera flash cable.
The IUCN Freshwater Plant Specialist Group is a global network of scientists and researchers with an interest in the conservation of wetland plants. It was formed initially with the support of the Fondation Tour du Valat and Plantlife under the umbrella of the Species Survival Commission (SSC) of the International Union for Conservation of Nature (IUCN).
The Freshwater Plant Specialist Group is one of around 120 Specialist Groups coordinated by the IUCN Species Survival Commission. These are communication networks of people with a common interest, which exist to support and further the conservation of the organisms for which they are responsible. Each Group has a Chair (responsible for the overall coordination of the Group), a Red List Authority (responsible for the coordination of IUCN Red List assessments of extinction risk) and members.
The Chair of the Group, Richard Lansdown (whose fantastic photographs illustrate this piece) explains more:
“The Freshwater Plant Specialist Group was initiated after discussion between Will Darwall of the IUCN Freshwater Biodiversity Unit and me around a meeting of the IUCN Freshwater Conservation Steering Committee on which we both serve in June 2011. IUCN had long been looking to establish a freshwater plant specialist group but was looking for the right chair.
My proposal to establish the group, supported by the Fondation Tour du Valat and PlantLife was unanimously agreed at a meeting of the IUCN Council in June 2011. I was initially reluctant to commit to establishing the group but was convinced by the people I met at the second meeting of the IUCN SSC Specialist Group Chairs in 2012. I formally signed the papers establishing the group in 2013. The Freshwater Plant Specialist Group now has over 140 members in more the 60 countries, with many organisation represented among the members.”
The Freshwater Plant Specialist Group exists to promote and further the conservation of wetland plant species and the habitats upon which they depend. Its aim is to achieve this through a combination of:
- Establishing a database of all aquatic and wetland plants, including vascular plants, bryophytes, lichens and algae that are dependent upon wetlands. The database will store information on the taxonomy, nomenclature and distribution of each species, with the aim that it be improved through review by FPSG members. The foundation of the database has been established with funding from EU Biofresh (Biodiversity of Freshwater Ecosystems) project and work by Nur Ritter.
- Assessment of the conservation status of all wetland-dependent plants using the IUCN Red List categories and criteria.
- Preparation of action plans for the conservation of wetland-dependent plants, initially concentrating on specific regions for which a regional Red List assessment of freshwater-dependent plants has been completed.
- Support for individual projects proposed by the members. This support will mainly take the form of providing information and links to contacts, as well as assistance with preparation of funding proposals.
Richard further outlines the collaborative nature of the Group:
“Although specifically aimed at conservation of wetland-dependent plants, wetland conservation cannot be successful without information on the environment on which the plants depend, or on methods of managing this environment. Therefore, whilst the membership of the group will be dominated by botanists, people with an interest in plants but their main knowledge and experience in other disciplines such as hydrology, geology, geomorphology and water management will also be welcomed as members.”