Re-diversifying our waterways, a garden stake at a time

Friday, Jul 7, 2017, 03:59 AM | Source: Pursuit

By Barbara Downes, Jill Lancaster

Re-diversifying our waterways, a garden stake at a time

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Over the last couple of hundred of years, we have drastically altered the Australian landscape.

Huge swaths of land have been cleared for agricultural purposes. Trees have been cut down to make way for roads and developments. Rivers and creeks have been cleared to prevent flooding, and have filled with sand due to erosion. And all of this has had a dramatic impact on the animals native to our waterways, forcing them to move away to find food and a suitable habitat.

But researchers at the University have come up with an amazingly simple solution. They have discovered that by planting garden stakes into river beds they can successfully restore the natural environment and attract back the animals that once lived there.

A typical view of Hughes Creek (Victoria) and many other streams flowing through agricultural landscapes. The stream bed is a sea of sand with almost no visible plant detritus anywhere. Picture: Supplied

Over the years, there has been significant research and work on trying to repair the damage done to Australia's rivers and creeks. But many well-intentioned previous attempts have proved expensive and ineffectual.

"There have been two reviews in the past 10 years showing that most efforts have completely failed to deliver any improvements to species diversity in rivers", says Professor Barbara Downes from the University of Melbourne's School of Geography.

Enter the humble garden stake.

Dr Jill Lancaster, also from the School of Geography, is leading the research project that has made a dramatic improvement to species diversity in a Victorian creek. Dr Lancaster and Professor Downes used the wooden stakes to help recreate environments critical to river animals. And their results have environmental scientists around the world taking notice.

Restoring natural debris

The researchers say their work focuses primarily on testing ecological theories about how dispersal is critical to preventing a loss of species diversity across landscapes.

Thanks to grants from the Australian Research Council's Discovery Programme, they tested the hypothesis that aquatic animals disperse frequently and attempt to colonise streams filled with sand, but are unsuccessful due to the lack of food and shelter. These resources are provided by natural plant debris that drops into channels.

Hammering in stakes to set up a manipulation site on Hughes Creek. Picture: Supplied

In streams degraded by land clearance, such debris is either swallowed by the sand or swept away in winter floods because of the lack of branches and logs that can hold the debris in place in numerous small packs scattered across the stream bed.

Using simple wooden stakes – the kind you can buy at garden nurseries for about a dollar – the researchers, along with a team of student helpers, planted 25-50 pairs of stakes into the bed of a stream in specific locations.

Other areas were left un-staked, to act as controls for the experiment.

The premise is that leaves, branches, bark, twigs and other natural debris that travel downstream are caught or snagged on the stakes. It's this build-up that provides a source of food and shelter for a range of animals – like insects, snails and other invertebrates.

These species account for the majority of diversity in our waterways, but they also attract animals like fish and platypus, which feed on them.

The research was carried out at Hughes Creek, north of Melbourne, an area that is surrounded by cleared agricultural land. Within just four months of staking the creekbed, the researchers began to see an increase in the densities and diversity of invertebrates, including species that are typically found only in more intact and cooler areas upstream.

The researchers say they got an incredibly strong result. Moreover, it was the first landscape-scale field experiment in the world that's been able to demonstrate the role that dispersal plays in creating diversity in degraded environments.

Low-tech, low-cost

Conventional restoration has focused its efforts on returning rivers and creeks to health by replanting trees and undergrowth along the banks, but it's an expensive process and one that requires labour and ongoing maintenance.

"It hasn't translated into any improvements in diversity within the stream itself," Professor Downes says. "There's lots of wonderful effects on the banks – you get increased birds and mammals and plants, but nothing for the streams."

The appeal of the new technique is its low cost, low maintenance approach.

"It is very simple," Dr Lancaster adds. "You don't need expertise, you don't need a lot of money, and the stakes will probably last three to four years."

The research has also focused on a specific layout for the groups of wooden stakes. The distances between the groups need to be short, so animals can treat them as 'stepping stones' within a waterway. If groups of stakes are too far apart, then many animals won't be able to travel between them.

"It's a bit like island hot spots, like Club Med. What we think happened is that they've come as far as the first island, built up numbers and then hopped to the next one," Dr Lancaster explains.

"In terms of restoration, you need to create little islands that are effectively close together so the animals just hop between them and it also ensures there is genetic diversity."

Detritus trap that has collected a sizeable branch along with bark, twigs and leaves, as well as providing a spot for an aquatic plant, Carex, to establish. Aquatic plants were commonly found rooted in the detritus, producing a further but unexpected benefit. Picture: Supplied

The researchers have presented their work at national and international conferences and there has been considerable excitement in the scientific community and environmental agencies, not only because of the strong results but because the technique is simple and easily rolled out.

Thanks to the success of this first experiment, the project is being expanded to test whether successful dispersal can improve species diversity in rivers and creeks in West Gippsland, central Victoria and several streams near Melbourne. The work is being done through a partnership between the Australian Research Council and State Government agencies Melbourne Water and the Department of Environment, Land, Water and Planning.

"It's a bigger scale and wider range of river types. We had a great response in Hughes' Creek; we noticed platypuses in stretches where they had never been before," Dr Lancaster says. "It's entirely possible there will be further effects, but that'll be a whole other study."

Banner image: Supplied