Give river ecosystems a chance

Four ideas for river management in a rapidly changing world

The Yangtze River, China upstream of the Three Gorges Dam. We visited here back in 2013 and saw just how major the Three Gorges Dam operation is and how much it has modified the river upstream and downstream. Photo: J. Tonkin.

Freshwater makes up somewhere in the order of 1% of the Earth's surface. Despite this, freshwaters harbour around a third of all vertebrates and nearly half of all fish species globally.

That is quite remarkable.

What’s concerning though is that freshwater ecosystems are among the most threatened in the world. This is no exaggeration — according to the International Union for the Conservation of Nature (IUCN) Red List, a third of all classified freshwater species are threatened with extinction.

Given their relative rarity and their disproportionate biodiversity, freshwater ecosystems deserve to be a primary focus of conservation and restoration efforts globally. Healthy functioning freshwaters provide countless benefits to people from clean water for drinking to fisheries and medicinal benefits. Yet, despite many important efforts, unfortunately, freshwaters are severely under protected.

Freshwaters are impacted by widespread persistent and emerging threats, including land-use change, pollution, invasive species, flow modification, over-exploitation, salinisation, emerging contaminants and so on. This is not stopping any time soon.

Rivers, in particular, are under immense pressure. For instance, there are several thousand large hydropower dams planned or in progress around the world as we speak. Unfortunately, many of these new ventures are in hyperdiverse river basins like the Amazon, Congo and Mekong, threatening thousands of species of fish, not to mention all the other biodiversity these systems harbour.

Climate change is making all this worse. Climate change is a threat multiplier. All the existing stressors on freshwaters are intensifying with the coupled climate change threat.

It’s clear that rivers need our help, but our societal myopia is not doing much to help. Short-term gains come at the cost of healthy, functioning, sustainable ecosystems. And short-term thinking tends to be the focus of management efforts.

As a result our river ecosystems are all too regularly not in a state that is resilient to what is coming down the pike with climate change.

There are countless things we can and need to do to help build resilience in rivers but here I’m providing four broad, high-level ideas of things I think are needed among all the others.¹

1. Manage for variability

2. Build resilience

3. Anticipate and adapt

4. Prioritise nature-based solutions

Manage for variability

Rivers are rhythmic systems that fluctuate in cycles of peaks (floods) and troughs (droughts). Depending on where you are and how predictable the climate is, these can be extremely predictable or chaotic. Sometimes, where most of the precipitation falls as snow like in Colorado, rivers can be so cyclic that these rhythms can be turned into music!²

This natural variability is fundamentally important for biodiversity. Species have evolved over thousands of years to capitalise on it for things like spawning and migration cues. When natural variability is modified or removed, native biodiversity suffers, often at the expense of invasive species.

Look at all that beautiful variability that was removed when the Flaming Gorge Dam was completed in 1963! Source: Lytle and Poff (2004).

Rivers are also spatially diverse in their physical conditions. This diversity of habitats results in a diversity of species: diversity begets diversity. As habitats are removed when channelise rivers or convert their margins into farms, we begin to lose species. It’s as simple as that.

Tasman River, New Zealand. Several different habitats are present across this wide braided river, including various combinations of aquatic habitat and diverse terrestrial habitats. Each of these comprise different species. Source: Google Earth.

However, standard river management approaches have prioritised the optimisation of systems towards static, simplified states, for instance, to mitigate flood risk and water supply provision. Obviously, we need to protect human infrastructure and lives from flood risk but there are ways to do it that don't involve channelising rivers into featureless drains. This simplification of systems has led to large-scale ecological destruction, and puts them in a fragile state.

Managing for variability is a required alternative. But what does variability look like?

It looks like allowing the natural cycle of floods and droughts to persist, rather than damming and removing all of this inherent, beautiful variability. It looks like letting a river flow free to create a range of diverse habitats, which each support unique species. It looks like optimising for messiness rather than efficiency.

Build resilience

A shift in the focus of river ecosystem management from restoration of historical conditions to resilience of ecosystems under future change is needed. What we have experienced in the past may no longer exist in the future.

Promoting variability both spatially and through time can promote the resilience of river ecosystems by helping to provide diverse resources, refuges from disturbances, and habitat variability that promotes species diversity and thus bolsters the ability for a system to respond to disturbances. Species diversity in itself is a mechanism of resilience by providing a so-called portfolio effect: the more species a system comprises, the more likely it will remain stable in its system properties. Just like a sensible investor likes to build up a diverse portfolio of stocks and shares to buffer them from market shocks, an ecosystem with more diversity will be more resilient to unexpected climate shocks.

Nature-based solutions build natural variability into a system and provide a system with the room, both physically and metaphorically, to adjust in response to future changes. Locking a system into narrow channels bounded by stop-banks/levees means the system has very little capacity to adjust and adapt to future conditions.

Anticipate and adapt

Working with massive uncertainties requires embracing flexible and adaptable approaches to river management. Adaptive management involves experimenting, monitoring, and adjusting approaches as needed. In particular, adaptive management allows for managers and policymakers to make decisions flexibly and dynamically in response to information that arises. Adaptive management is often used in environmental flow programmes where dammed river flows are adjusted to better suit the needs of the environment downstream of dams. Flow releases can be experimented and learned from and adapted as needed for greater benefits for the environment.

More importantly to me, as the world continues to rapidly change, is to be anticipatory in our approach to managing rivers. This requires better statistical and mathematical modelling to anticipate the outcome of future events. A few years back, we wrote a paper calling for more mechanistic approaches to forecasting future river states into uncertain future conditions to enable better decision making. Doing so will alert decision makers about what is coming long before trends can be detected using typical approaches. By then, it is usually too late to implement any fixes.

Prioritise nature-based solutions

As I outlined last week, nature-based solutions are a key tool in our arsenal for mitigating climate change and restoring ecosystems. These are becoming more widespread in their application to address climate and socio-ecological issues. In rivers, this may look like giving rivers room to move, restoring floodplains or riparian forests, or connecting rivers to floodplain habitats.

Nature-based solutions are a harder sell for policymakers and many members of the public because of their perceived risk. Widening a river’s boundaries, creating retention ponds, or connecting a river to its floodplain have the perception of greater risk and uncertainty compared to hard infrastructure. However, grey solutions, such as increasing stop-bank/levee size and reinforcing bank protection are in many cases providing a false sense of security. Flood magnitudes are extremely uncertain over the next century given the rate at which climate change is unfolding and the uncertainties with modelling. At the same time grey infrastructure or hard infrastructure provide singular benefits: flood risk mitigation. By contrast, nature-based solutions provide many co-benefits from ecological to social to financial.

From short-term to long-term thinking

Many of the approaches I outlined represent a shift from short-term to long-term thinking. The shifting risks of climate change-driven extreme floods requires a rethink of how rivers are managed. Providing nature-based approaches to river management helps mitigate flood risk under uncertain climatic futures while providing important ecological and societal co-benefits. More generally, there is a need to balance the protection of human infrastructure and livelihoods with the need to protect the ecological values of rivers and the benefits flooding provides to floodplains. A general shift towards living with rivers is needed for both flood risk management and ecological health. Rivers need to be treated as the dynamic entities they are.

What do you think? I’m hosting a workshop in two weeks on a related topic to this post. I’d love to hear your thoughts. Do you have strong feelings about what we need to do to protect rivers or freshwaters more generally?

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A couple of relevant recent posts

1. Note, I’m overlooking many, many things here, but these are four current themes on my mind. There’ll be plenty more posts on related topics. A large chunk of my research focus is on the ecology and management of rivers.

2. A friend of mine from the US who is passionate about rivers started making music out of river flow regimes. Check out the article here.