We tested tiger snake scales to measure wetland pollution in Perth. The news is worse than expected


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Damian Lettoof, Curtin University; Kai Rankenburg, Curtin University; Monique Gagnon, Curtin University, and Noreen Evans, Curtin University

Australia’s wetlands are home to a huge range of stunning flora and fauna, with large snakes often at the top of the food chain.

Many wetlands are located near urban areas. This makes them particularly susceptible to contamination as stormwater, urban drainage and groundwater can wash metals — such as arsenic, cadmium, lead and mercury — into the delicate ecosystem.

We know many metals can travel up the food chain when they’re present in the environment. So to assess contamination levels, we caught highly venomous tiger snakes across wetlands in Perth, and repurposed laser technology to measure the metals they accumulated.

In our new paper, we show metal contamination in wild wetland tiger snakes is chronic, and highest in human-disturbed wetlands. This suggests all other plants and animals in these wetlands are likely contaminated as well.

34 times more arsenic in wild wetland snakes than captive snakes

Urban growth and landscape modification often introduces metals into the surrounding environment, such as mining, landfill and waste dumps, vehicles and roadworks, and agriculture.

When they reach wetlands, sediments collect and store these metals for hundreds of years. And if a wetland’s natural water levels are lowered, from agricultural draining for example, sediments can become exposed and erode. This releases the metals they’ve been storing into the ecosystem.

A reflective lake, with green vegetation surrounding it
The wetland in Yanchep National Park, Perth, was supposed to be our ‘clean’ comparison site. Its levels of metal contamination was unprecedented.
Shutterstock

This is what we suspect happened in Yanchep National Park’s wetland, which was supposed to be our “clean” comparison site to more urban wetlands. But in a 2020 study looking at sediment contamination, we found this wetland had higher levels of selenium, mercury, chromium and cadmium compared to urban wetlands we tested.

And at Herdsman Lake, our most urban wetland five minutes from the Perth city centre, we found concentrations of arsenic, lead, copper and zinc in sediment up to four times higher than government guidelines.




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In our new study on tiger snake scales, we compared the metal concentrations in wild wetland tiger snakes to the concentrations that naturally occurs in captive-bred tiger snakes, and to the sediment in the previous study.

We found arsenic was 20-34 times higher in wild snakes from Herdsman Lake and Yanchep National Park’s wetland. And snakes from Herdsman Lake had, on average, eight times the amount of uranium in their scales compared to their captive-bred counterparts.

Tiger snake on the ground, near rubbish.
Our research confirmed snake scales are a good indicator of environmental contamination.
Damian Lettoof, Author provided

Tiger snakes usually prey on frogs, so our results suggest frogs at these lakes are equally as contaminated.

We know for many organisms, exposure to a high concentration of metals is fatally toxic. And when contamination is chronic, it can be “neurotoxic”. This can, for example, change an organism’s behaviour so they eat less, or don’t want to breed. It can also interfere with their normal cellular function, compromising immune systems, DNA repair or reproductive processes, to name a few.

Snakes in general appear relatively resistant to the toxic effects of metal contamination, but we’re currently investigating what these levels of contamination are doing to tiger snakes’ health and well-being.

Our method keeps snakes alive

Snakes can be a great indicator of environmental contamination because they generally live for a long time (over 10 years) and don’t travel too far from home. So by measuring metals in older snakes, we can assess the contamination history of the area they were collected from.

Typically, scientists use liver tissue to measure biological contamination since it acts like a filter and retains a substantial amount of the contaminants an animal is exposed to.

But a big problem with testing the liver is the animal usually has to be sacrificed. This is often not possible when studying threatened species, monitoring populations or working with top predators.

Two black swans in a lake, near cut grass
Sediment in Herdsman Lake had four times higher heavy metal levels than what government guidelines allow.
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In more recent years, studies have taken to measuring metals in external “keratin” tissues instead, which include bird feathers, mammal hair and nails, and reptile scales. As it grows, keratin can accumulate metals from inside the body, and scientists can measure this without needing to kill the animal.

Our research used “laser ablation” analysis, which involves firing a focused laser beam at a solid sample to create a small crater or trench. Material is excavated from the crater and sent to a mass spectrometer (analytical machine) where all the elements are measured.

This technology was originally designed for geologists to analyse rocks, but we’re among the first researchers applying it to snake scales.

Laser ablation atomises the keratin of snake scales, and allowed us to accurately measure 19 contaminants from each tiger snake caught over three years around different wetlands.

Wild tiger snake
Snakes generally appear resistant to the toxic effects of heavy metals.
Kristian Bell/Shutterstock

We need to minimise pollution

Our research has confirmed snake scales are a good indicator of environmental contamination, but this is only the first step.

Further research could allow us to better use laser ablation as a cost-effective technology to measure a larger suite of metals in different parts of the ecosystem, such as in different animals at varying levels in the food chain.

This could map how metals move throughout the ecosystem and help determine whether the health of snakes (and other top predators) is actually at risk by these metal levels, or if they just passively record the metal concentrations in their environment.




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It’s difficult to prevent contaminants from washing into urban wetlands, but there are a number of things that can help minimise pollution.

This includes industries developing strict spill management requirements, and local and state governments deploying storm-water filters to catch urban waste. Likewise, thick vegetation buffer zones around the wetlands can filter incoming water.The Conversation

Damian Lettoof, PhD Candidate, Curtin University; Kai Rankenburg, Researcher, Curtin University; Monique Gagnon, Researcher, Curtin University, and Noreen Evans, Professor, Curtin University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Is Perth really running out of water? Well, yes and no


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The future of Perth’s urban wetlands is in doubt.
Orderinchaos/Wikimedia Commons, CC BY-SA

Don McFarlane, University of Western Australia

As Cape Town counts down to “day zero” and the prospect of its taps being turned off, there have inevitably been questions about whether the same fate might befall a major Australian city. The most striking parallels have been drawn with Perth – unsurprisingly, given its drying climate, rising evaporation rates (which increase consumption and reduce water yields) and growing population.

So is Perth really running out of water? The answer depends on what type of water is being considered, and what constitutes “running out”.




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Cape Town is almost out of water. Could Australian cities suffer the same fate?


When faced with this question most people think of drinking water, which is of course essential for household use.

It often ignores non-potable groundwater that is heavily relied upon in Perth to irrigate gardens, lawns, ovals, golf courses and market gardens. This water is also used by light and heavy industry, as well as being crucial to the health of wetlands and vegetation across the coastal plain.

Lake Jualbup in Perth’s western suburbs showing periods of low and high water level. Photos by Geoffrey Dean.
saveourjewel.org, Author provided

Perth’s drinking water supplies are largely safe, thanks to early investment in the use of groundwater and in technologies such as desalination. But somewhat ironically, as this recent book chapter explains, the future supply of lower-quality water for irrigation and to support ecosystems looks far less assured.

A drying climate

Perth’s annual rainfall has been declining by about 3mm per year on average, while the number of months receiving at least 200mm of rain has halved. Meanwhile, the annual mean temperature anomaly has increased by 1℃ in southwest Western Australia in the past 40 years and possibly by more in Perth, given the urban heat island effect.

Perth’s rainfall trend, as measured at Perth Airport’s rain gauge.
Bureau of Meteorology

The overall effect is that soils and vegetation are often dry, meaning that rainfall will be lost to evapotranspiration rather than running off into rivers and dams, or recharging underground aquifers.

At the same time, Perth has made major changes to its drinking water supply. The city now relies chiefly on groundwater and desalination rather than dams. For a variety of reasons, drinking water use per person has declined, most notably since the early 2000s when sprinkler restrictions were introduced. Some have switched to self-supply sources such as backyard bores, so for them total water use may even have increased.

Perth’s trends in runoff, population, and water supply.
Water Corporation

The reduction in per capita use of drinking water is just as well, because inflows into Perth dams have fallen from 300 billion litres a year to less than 50 billion. This disproportionate drop in stream flows, even against the backdrop of declining rainfall, means that evaporation from reservoirs can exceed inflows in very dry years.

Since the late 1970s, Perth has increasingly used groundwater rather than dam water. Seawater desalination has also grown to almost half of total supply. Even more recently Perth began trialling a groundwater replenishment scheme to recharge aquifers with treated wastewater.

With the declines in rainfall and streamflow predicted to continue, water security will continue to be an important policy issue over the next few decades. Although both are much more expensive than dam water, desalination and groundwater replenishment look set to secure Perth’s drinking supply, because seawater is virtually unlimited, and wastewater availability increases in line with the city’s growth.




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Why are non-drinking water supplies less secure?

Boosting drinking water supplies with desalination or groundwater replenishment is unlikely to resolve the pressures on non-potable supplies. To understand why, it is necessary to understand Perth’s unusual hydrology.

Most of Perth is built on permeable sand dunes, which can soak up even the heaviest rainfall. This allows runoff from roofs and roads to be directed into nearby soak wells and absorption basins.

As well as cheap disposal of stormwater, the sands provide Perth with a place to store excess water from winter rains, which is then relied upon for summer irrigation. As a result, local governments have been able to provide many irrigated parks and sports ovals, and more than a quarter of Perth households use a private bore to water their gardens.

This arrangement isn’t as sustainable as it once was. Groundwater levels are falling under many parts of Perth, forcing the state government to reduce allocations and to introduce a range of water-saving measures such as winter sprinkler bans.

Unlike dam inflows, we don’t yet know the full scale of the reduction in natural groundwater recharge rates. But the question still remains: what can we do to halt the decline of this important water store, particularly as Perth’s population is expected to grow to 3.5 million by 2050?

About 70% of local road runoff and half of roof runoff already recharges the shallow unconfined aquifer, because it is the cheapest way to dispose of excess water in areas with sandy soils. As well as reducing discharge costs, this practice helps to ensure that bores do not run dry in summer.

Perth also has large main drains that are designed to lower groundwater levels in swampy areas and prevent inundation. Some of these waters could be redirected into the aquifer where there is a suitable site.

Don’t waste wastewater

About 140 billion litres of treated wastewater are discharged into the ocean every year in the Perth-Peel region. A further 7 billion litres are infiltrated into the sands as a means of disposal where there isn’t an option for ocean outfall. Recent investigations of these land disposal sites have shown them to be effective in protecting wetlands from drying and providing water for public and private irrigation.

Investigations have also shown that the quality of treated wastewater can be greatly improved when infiltrated through the yellow sands into the limestone aquifer in the western part of Perth. It is suitable for irrigation after a few weeks’ residence within the aquifer.




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‘Drought-proofing’ Perth: the long view of Western Australian water


Without these kinds of measures, local governments will struggle to water parks and sports ovals, to protect Perth’s remaining wetlands, and to safeguard the trees that help keep us cool.

The ConversationSo while drinking water supplies for an affluent city like Perth are reasonably secure, our vital non-drinking water supplies need to be augmented using some of the water we currently discharge into the ocean. As Perth gets even hotter and drier, and green spaces and wetlands are needed to provide much-needed cooling, we can no longer afford to let any water go to waste.

Don McFarlane, Adjunct professor, University of Western Australia

This article was originally published on The Conversation. Read the original article.

Squandering riches: can Perth realise the value of its biodiversity?


Julian Bolleter, University of Western Australia

Perth is not known as a model for suburbia and its suburban condition is similar to that of developed cities the world over. However, it does stand out in one respect: it sits in an exceptionally biodiverse natural setting. A strong, informed vision for this setting’s relationship with the city could help Perth become an exemplar for similarly positioned metropolises everywhere.

The greater Perth region has been designated the Southwest Australia Ecoregion (SWAE). This is one of only 35 “biodiversity hotspots” in the world.

Reconciling future growth with biodiversity is a key issue for urban design and planning this century. Indeed, if current trends continue, global urban land cover will increase by 1.2 million square kilometres (equivalent to half the area of Western Australia) by 2030. Much of this will happen in biodiversity hotspots.

This is important because it is estimated we will lose nearly half of all terrestrial species if we fail to protect the hotspots. We will also lose the ecosystem services upon which human populations ultimately depend.

If we fail to protect the world’s 35 biodiversity hotspots we risk losing nearly half of all terrestrial species.
Conservation International, Author provided

“Ecosystem services” may sound like abstract jargon, but it’s actually a term used to describe the services nature provides – such as clean air, water and food, and heatwave and flood mitigation. Without these, human life would be extremely unpleasant, if not unviable.

Perth has a reputedly strong planning system and is comparatively wealthy. If it can’t control its city form to protect biodiversity – compact cities generally being recognised as the best model for protecting land for conservation – then city administrators elsewhere, particularly in the developing world, are likely to struggle.

Misreading the land

The current treatment of the Australian environment has its roots in the European annexation of Australia, which has been characterised by catastrophic misreadings of the land. Governor James Stirling, who was singularly responsible for the European annexation of Perth, was the kind of man who saw what he wanted to see rather than what was there. In The Origins of Australia’s Capital Cities, Geoffrey Bolton writes:

…arriving at the end of … an uncommonly cool, moist summer, [Stirling was] misled by the tallness of the northern jarrah forest and the quality of the alluvial soils close to the river into believing that the coastal plain would offer fertile farming and grazing. It was, Stirling wrote, equal to the plains of Lombardy; and he persuaded himself that the cool easterly land breeze of these early autumn nights must originate from a range of snowy mountains.

Vegetation of Southwest Australia Ecoregion near current-day Perth at the time of European settlement. Based on statewide mapping by John Beard between 1964 and 1981.
DPAW
Remnant vegetation of SWAE near Perth in 2015.
DPAW/WALGA, courtesy of AUDRC, Author provided

The results of such misinterpretations of the land were generally less poetic. Stirling sited the settlement of Perth on a narrow, constrained strip of land between swamps to the north and marshy river edges to the south. These low-lying areas fuelled plagues of mosquitos and, once polluted, deadly typhoid outbreaks.

In time, due to a lingering discomfort with Perth’s “unsanitary” wetlands, more than 200,000 hectares – an area equivalent to 500 Kings Parks – were drained on the Swan Coastal Plain. These biologically productive areas directly or indirectly support most of the coastal plain’s wildlife, so the effects on biodiversity have been catastrophic.

Furthermore, a perception of the Banksia woodland and coastal heath on Perth’s fringes as unattractive and useless has seen much of it cleared for the expansion of the city. Between 2001 and 2009, suburban growth consumed an annual average of 851ha of highly biodiverse land on the urban fringe.

The lesson from this experience is that any future growth in a biodiversity hotspot, or indeed elsewhere, has to be founded on the understanding that we cannot continue to bend nature to our will. We must learn how to work with it.

Within this humbling process, we need to recognise that working with the land is not an entirely pure or noble act; rather, it is imperative for humanity’s survival. As species and ecosystems become threatened and vanish, so too do the ecosystem services that support human wellbeing.

Perth’s Green Growth Plan

The release of the state government’s long-anticipated Perth and Peel Green Growth Plan for 3.5 million may herald a shift in the relationship between the city and the biodiversity hotspot. The plan encapsulates two broad goals:

  • to protect fringe bushland, rivers, wetlands and wildlife in an impressive 170,000 hectares of new and expanded reserves on Perth’s fringe

  • to cut red tape by securing upfront Commonwealth environmental approvals for outer suburban development.

Proposed new and existing reserves – light and dark green respectively – on Perth’s fringe (indicative only).
DOP, courtesy of AUDRDC, Author provided

While ostensibly positive achievements, a question remains as to the implications of clearing a further 45,000ha (3% of the Swan Coastal Plain) of remnant bushland which is not protected by the conservation reserves.

Furthermore, the typically disconnected conservation reserves proposed in the Green Growth Plan lack overall legibility. This stymies the public’s ability to conceptualise the city’s edge, which leads them to care about it (like London’s greenbelt, for instance).

Finally, a question remains about how a plan that places restrictions on outer suburban development will accommodate the powerful local land development industry over time. This is a concern given the frequent “urban break-outs” – where urban development occurs outside nominated growth areas – between 1970 and 2005.

In 2003, the ABC asked revered Western Australian landscape architect Marion Blackwell, “Are we at home now in the land we live in?” She replied, “No, we’re not. We don’t know enough about it, and not enough people know anything about it.”

We still have work to do on our engagement with biodiversity in Western Australia, and Perth specifically, before we can become a model for future cities.


The Conversation is co-publishing articles with Future West (Australian Urbanism), produced by the University of Western Australia’s Faculty of Architecture, Landscape and Visual Arts. These articles look towards the future of urbanism, taking Perth and Western Australia as its reference point. You can read other articles here.

The Conversation

Julian Bolleter, Research Fellow, Australian Urban Design Research Centre, University of Western Australia

This article was originally published on The Conversation. Read the original article.