Could a million freshwater turtles help clean up some of Australia's polluted rivers? A team of scientists believes, they could!

by Larry Powell

The freshwater turtle, Emydura macquarii. Credit: Claudia Santori.

For well over a century, invasive freshwater fish from Europe - carp (originally from China) - have been released, either deliberately or accidentally from fish farms, into Australian waterways. The fish, now widely regarded as pests, are thriving. 

Their habitat includes rivers flowing through the Murray-Darling Basin of New South Wales. Those vast waterways support, through irrigation and other means, about 40% of agricultural production for the entire country - not to mention vital aquatic eco-systems and drinking water for about three million people. 

Baby Emydura macquarii. Credit: Tom Burd.

By contrast, the clock is ticking for Australia's native freshwater turtles. The new study says the most common species has declined by up to 91 percent in the past 40 years. It blames urbanization, which damages their habitat and makes the turtles more vulnerable to mass die-offs from disease. They're also being run over by vehicles on roadways. And foxes, like the carp, also introduced from elsewhere, are destroying their nests. 

Ironically, the scientists have now discovered that the turtles could play a vital role in any plan to rid the rivers of the nuisance carp. As carp die, they decompose and give off ammonia, which is toxic to other creatures.

An experiment the researchers carried out showed, convincingly, that the turtles could act as an effective "clean-up crew." Turns out, they have a huge appetite for the carcasses of the fish, a trait which would improve water quality, to everyone's benefit.

Day nine of the experiments - with turtles present in the water, 

the carp carcass has been completely devoured. 

Credit: Ricky Spencer and Claudia Santori.

The researchers built "artificial wetlands" made up of several large tanks like the one above. They placed dead carp in all of them. Then they put the turtles, in groups of four, in some. The tanks were monitored, either until the carcasses had fully decomposed or been completely eaten by the turtles.

The results, as documented in a study, now published in the journal, Nature,  are striking.

The turtles stripped carp carcasses to skeletons within five days, whereas, without turtles present, the carcasses took more than 27 days - more than five times longer - to decompose. In the tanks with the turtles, ammonia levels fell and dissolved oxygen levels - which aquatic animals need to survive, recovered. Without turtles, the water progressively deteriorated and became very dirty. While crayfish, prawns, and shrimp act similarly, none are as effective as the turtles. 

The leader of the research team, Ricky Spencer of Western Sydney University, believes, a plan by the Australian Government to use a biological agent to get rid of the carp, could be devastating. That's because, without lots of turtles doing the scavenging, mounds of dead fish rotting in the rivers would only emit more ammonia and compound problems of water pollution.

“We’re not just talking about the health of our rivers here," Prof. Spencer adds.  "We’re talking about human health. These are river systems that supply our drinking water and irrigate the fruit and vegetables we eat. So turtles are critical to sustaining the health of humans, as well as our rivers.”

But, with turtle populations on the decline, finding enough to do an effective job, will be daunting. So, the research team is proposing what it calls "Australia's largest, community-empowered conservation program. Local communities will lead 'expansionary conservation,' where we aim to release more than one million extra turtles throughout southeastern Australia each year." A crowd-funding program has been launched to pay for the effort.

Kiss the Ground (Official Movie Trailer 2020)

The Arctic is burning like never before — and that’s bad news for climate change

Nature

Wildfire smoke at the Arctic Circle.  MIKOFOX ⌘ 2020 Vision

Fires are releasing record levels of carbon dioxide, partly because they are burning ancient peatlands that have been a carbon sink. Story here.

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Ecology: Conservation and food system changes needed to bolster biodiversity

Trees, shrubs and debris are burned on the Canadian prairies to make  way

for more cropland. A PinP photo.

Nature

Declines in terrestrial biodiversity from habitat conversion could be reversed by adopting a combination of bold conservation methods and increases in the sustainability of the food system, a modelling study published in Nature suggests.

Human pressures, such as the destruction of natural habitats to make way for agriculture and forestry, are causing rapid declines in biodiversity, and placing at risk the ecosystem services upon which we depend. Ambitious targets for biodiversity have been proposed, but it is unclear how these targets can be achieved whilst retaining the ability to feed a growing population. Using land-use and biodiversity models, David Leclère and colleagues show how this is possible. 

Conservationists need to increase the amount of actively managed land, restore degraded land and adopt generalized landscape-level conservation planning. Meanwhile, we need to eat fewer animal-derived calories, waste less food and find ways to intensify food production sustainably.

If this double-pronged strategy is followed, more than two thirds of future biodiversity losses from habitat conversion could be avoided, the authors suggest. However, they caution that other threats, such as climate change, must also be addressed to truly reverse biodiversity declines.

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Nature Communications

Faster growth leads to a shorter lifespan in trees, according to a paper published in Nature Communications. The findings could have implications for predictions of how much carbon forests can store under climate change.

A black spruce (Picea mariana) forest.
Photo credit - Western Arctic National Parklands

A relationship between faster tree growth rates and shorter tree lifespan has been shown in some trees, particularly in cold-adapted conifers, but whether this applies across species and climates has been disputed. Such a trade-off would be at odds with the use of tree growth rates as a proxy for carbon storage, and cast doubt on Earth system model predictions of global forest carbon storage.

Roel Brienen and colleagues analysed a large dataset of tree-ring data representing 110 tree species across all continents except Africa and Antarctica. They report that faster growth is linked to reduced tree lifespan both across and within tree species, and show that this is not due to covariance with climate or soil variables. Using model forest simulations based on data about the black spruce (Picea mariana), they further show that this trade-off has the potential to slow down or even reverse the global forest carbon sink in the future.

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Science Daily

A table iceberg in the Norwegian Arctic. Such icebergs are rare
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The eastern Arctic Ocean's winter ice grew less than half as much as normal during the past decade, due to the growing influence of heat from the ocean's interior, researchers have found. Story here.

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The Narwhal
Conservation and agriculture have often been at odds. But as Ottawa develops the first federal carbon offset standard, farming techniques that reduce greenhouse gas emissions are having a moment. Story here.

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Zack Koscielny is a fifth generation farmer located near Strathclair,
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