River drying explains biodiversity

A huge diversity of plants and animals live in and near rivers, and they all get affected by how and when rivers flow. Their abundances can go up and down, they can get moved vast distances downstream and onto floodplains, and sometimes they can even get killed.

“We know that big floods are really important in driving diversity patterns in rivers, but what happens when rivers stop flowing? Are these ‘drying’ events just as important?” asks Dr Catherine Leigh, a freshwater scientist at the Australian Rivers Institute, Griffith University.

dry river bed
A dry river bed in Australia is not that unusual! The Todd River, Alice Springs. Photo: Catherine Leigh

“Rivers that sometimes stop flowing and dry up are found all over the world – most of our rivers in Australia do this– but with drying climate and growing demands on freshwater, many are drying up for longer and more often and we’re seeing some dry up for the first time. We need to know how this is affecting biodiversity.”

Her study, published in the journal Ecography, compared the importance of flooding and drying events – things like how long they lasted, how often they occurred, their seasonality – on river biodiversity using data collected across Australia, France and Spain.

map of study sites
The maps show from where the river flow and aquatic invertebrate data Dr Leigh analysed were collected, either rivers that sometimes stop flowing (red pins) or rivers that flow all year round (blue pins). (Imagery provided by Google Earth, with Image Landsat Data from SIO, NOAA, U.S. Navy, NGA, GEBCO 2015)

Even when including rivers that flow all year round in her analysis, drying-events were the most important predictors of river biodiversity. The number of different families of aquatic invertebrates declined as drying lasted longer, and when it occurred less seasonally (more unpredictably). While long and unpredictable drying events occur naturally in many rivers, climate change and increasingly extreme events might challenge the limits of some species to survive through those dry times.

This also means we need to think just as much (if not more) about the effects of drying on river biodiversity, as we do floods when studying and managing rivers for better biodiversity outcomes.

dry stream
A walk through the beautiful southeast Queensland forest reveals a dry stream channel. While walking I stop, take a moment to enjoy the scenery and appreciate that not all rivers and streams flow all the time. Photo by Catherine Leigh

And if you happen to walk past a river or creek today, one that’s not flowing or has a dry bed, remember that it still contributing to local and global biodiversity and has an important role to play in our environment.


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