Novel Freshwater Ecosystems: A River Management Perspective

A NextGen Blog post by Becca Jordan, University of Nottingham.

Photos © Alison M. Jones, unless otherwise noted.

Rebecca Jordan is a postgraduate student studying Environmental Leadership and Management at the University of Nottingham in the UK. This blog explores the “novel ecosystems concept” as a river management tool.

Recently, I wrote an essay for one of my postgraduate modules about the “novel ecosystems concept” and the debate surrounding its validity and usefulness. Novel ecosystems are those that have been so dramatically changed from their historical state that they have become entirely new systems with unique species interactions and the ability to self-sustain.1Hobbs, R.J. et al. I noticed that novel ecosystems in a freshwater context were scarcely mentioned in the primary literature, so today I am exploring freshwater novel ecosystems, and what they may mean for river management and conservation.

To be categorized as a novel ecosystem, the changes that have occurred have to have been caused by human actions, such as human-introduced invasive species, landscape degradation or climate change. The reason to recognize these novel ecosystems is to ensure that resources are not wasted in trying to restore severely-degraded ecosystems to unrealistic states. Instead the focus should be on flexible management practices tailored to the new ecosystem that exists today.2Hobbs, R.J., Higgs, E. et al In my studies, I found examples of novel ecosystems from the woodlands of Australia to the reefs of the Caribbean – but very little mention of freshwater examples.3Lindenmayer, D.B et al.,4Graham, N.A. et al. However, there are freshwater novel ecosystems. The lack of references to these freshwater novel ecosystems may just mean that they have been under-studied within this particular ecological management concept.

Salmon River Basin sign on weed management and invasive identification, Idaho

One fascinating element of novel ecosystems in a freshwater context, is how they interlink with societal uses of rivers. Urban rivers are relied upon by towns and cities for transportation, recreation, tourism, waste disposal, water provision, cultural significance and so much more.5Francis, Robert A This onging, multi-use approach has led to significant degradation of urban rivers, to the point where many have a reputation for having poor water quality and little ecological excellence. It has been argued that with such high levels of degradation, in addition to the use of hard engineering for river management, many urban rivers are now novel ecosystems, created by the cities that have grown up around them. Here are just a few examples of changes that have led to such urban novel ecosystems:6Francis, Robert A

  • Channelization simplification has led to more homogenous assemblages of vegetation around rivers, resulting in a lack of natural biodiversity.
  • Large waste and machinery in and around rivers have created new habitats for wildlife,
  • Chemicals from surrounding industries cause water-quality decline and species extirpation.
  • Non-native species invasions and loss of species diversity produce entirely new trophic webs and species assemblages.
Cuyahoga River passing through urban Cleveland, Ohio

On the surface, all of these may seem to be conditions that must be corrected. But the perspective of the novel ecosystems approach is that instead of spending huge amounts of money and putting in decades of efforts to restore these rivers, we should embrace them. The key focus of river managers should become that of ensuring resilience in the ecosystem, while allowing it to continue to support human needs. Recognizing the value of novel freshwater species interactions and their ecological roles in our urban rivers could change the way we think of these places and how we manage them. This would result in rivers that may not be very similar to their historic state; but that become resilient with biodiversity that supports stable ecosystem functioning – at a much lower cost than restoration.

Although, the shores of the  NY-NJ Harbor have been overrun by phragmites, ecologists have realized that they were quite effective in saving NY and NJ shorelines from even further damage by Superstorm Sandy. So, plans to eradicate phragmites were abandoned, since it would be devastating if another superstorm came through when phragmites were gone, and before replacement native species had taken hold.

Monocultures of phragmites that have overtaken saltmarsh ecosystems in NJ’s Lower Raritan River

Sometimes novel ecosystems can mimic ecosystems of the past, but occur in new areas. For example, in the Missouri River, a novel delta has formed as a result of the ageing shifts in the Lewis and Clark Reservoir. This delta mimics the perfect conditions for sauger (Sander canadensis) spawning, which historically would have happened in other reaches of the river.7Graeb, Brian D. S et al. There have been years of sauger decline in the Great Lakes caused by channel engineering and migration barriers, but those populations where the novel delta formed have remained stable. In fact, researchers determined that every single sauger they tagged and tracked has spawned at the novel delta.8Graeb, Brian D. S et al. Given this evidence, novelty could be what saves native species.

However, native species are not always protected by novel ecosystems formation. Often invasive species thrive in their place. Most temporary streams in California are now so altered – having been converted into permanent streams for dams or drainage. It would be incredibly difficult to return these streams to their historical state.9Moyle, P. B et al This change has opened up niches for invasive species such as the green sunfish (Lepomis cyanellus) to enter the ecosystems and create new species interactions, solidifying the state of these streams as novel ecosystems and making it more difficult for endemic species like the California roach (Hesperoleucus symmetricus) – a fish native to Western North America – to persist.10Moyle, P. B et al. This process is expected to be replicated across many more streams in such Mediterranean climates.

Central Valley’s Friant Dam and stream below, California

The scale of management that would have to take place to return these streams back to their historical state would be huge, involving the widespread removal of dams and a lot of time and money spent on habitat re-connectivity. Thus, some argue that these novel ecosystems should be allowed to exist, with some minimal management to ensure the best possible outcome both ecologically and socially. The bulk of the resources could then be redirected to freshwater conservation and restoration projects that have a higher chance of success.

Freshwater fish all over the world are now at risk of extinction; and we only have finite resources to save them.11Harvey, F. It is vitally important that we assess river management from all possible angles, including that of a novel ecosystem approach where population stability and diversity are valued over historic composition. One thing to note is that nobody is saying that the novel ecosystems approach should be heralded as the new way to deal with every single degraded river. Rather, this approach should be one branch of the decision tree used by ecologists and river managers to reach the most effective solution for each individual case.12Miller, James R & Bestelmeyer, Brandon T.

Green Sunfish, courtesy of Creative Commons

I personally think that seeing the value of a self-sustaining novel ecosystem will open up new opportunities for managing rivers that have been heavily impacted by human activity and invite a more deliberate and reasoned way of allocating conservation and restoration resources. This allows space for greater creativity in how we interact with rivers, as well as a test of how willing we are to accept that the consequences of our actions are not always going to be reversible.


Francis, Robert A, 2014. Urban rivers: novel ecosystems, new challenges. Wiley interdisciplinary reviews. Water, 1(1), pp.19–29.

Graeb, Brian D. S, Willis, David W & Spindler, Bryan D, 2009. Shifts in sauger spawning locations after 40 years of reservoir ageing: influence of a novel delta ecosystem in the Missouri River, USA. River research and applications, 25(2), pp.153–159.

Graham, N.A., Cinner, J.E., Norström, A.V. and Nyström, M., (2014). Coral reefs as novel ecosystems: embracing new futures. Current Opinion in Environmental Sustainability, 7, pp.9-14.

Harvey, F., 2021. Global freshwater fish populations at risk of extinction, study finds. The Guardian.

Hobbs, R.J., Arico, S., Aronson, J., Baron, J.S., Bridgewater, P., Cramer, V.A., Epstein, P.R., Ewel, J.J., Klink, C.A., Lugo, A.E. and Norton, D., (2006). Novel ecosystems: theoretical and management aspects of the new ecological world order. Global ecology and biogeography, 15(1), pp.1-7.

Hobbs, R.J., Higgs, E., Hall, C.M., Bridgewater, P., Chapin III, F.S., Ellis, E.C., Ewel, J.J., Hallett, L.M., Harris, J., Hulvey, K.B. and Jackson, S.T., (2014). Managing the whole landscape: historical, hybrid, and novel ecosystems. Frontiers in Ecology and the Environment, 12(10), pp.557-564.

Lindenmayer, D.B., Fischer, J., Felton, A., Crane, M., Michael, D., Macgregor, C., Montague‐Drake, R., Manning, A. and Hobbs, R.J., (2008). Novel ecosystems resulting from landscape transformation create dilemmas for modern conservation practice. Conservation Letters, 1(3), pp.129-135.

Miller, James R & Bestelmeyer, Brandon T, (2016). What’s wrong with novel ecosystems, really? Restoration ecology, 24(5), pp.577–582.

Moyle, P. B, 2014. Novel Aquatic Ecosystems: The New Reality For Streams In California And Other Mediterranean Climate Regions. River research and applications, 30(10), pp.1335–1344.

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