Why a wetland might not be wet


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Wetlands can have decades-long dry periods.
Felicity Burke/The Conversation, CC BY-SA

Deborah Bower, University of New England; Ben Vincent, University of New England; Darren Ryder, University of New England; John Thomas Hunter, University of New England; Lindsey Frost, University of New England; Manu Saunders, University of New England, and Sarah Mika, University of New England

Lake Eyre is one of Australia’s most iconic wetlands, home to thousands of waterbirds that migrate from all over Australia and the world. But it is often dry for decades between floods.

Many people think wetlands are swamps or ponds that die when dry. But unlike many places worldwide, most Australian wetlands have natural wet-dry cycles, with dry spells that can last for decades. Dry phases are necessary for the life cycle of the wetland itself, as well as for many of the plants and animals that live there.




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So, if wetlands are still wetlands when they’re dry, how do you spot one? And what do we need to know about these unique places to protect their wonderful and unique biodiversity?

Fogg Dam wetlands in the Northern Territory are a riot of colour during monsoon season.
Geoff Whalan/Flickr, CC BY-NC

When the rains come

Floods are vital for a wetland. As one fills, water depth can increase rapidly, the temperature falls, and dissolved oxygen is high as turbulent raindrops or floodwaters fill the basin. Within a few hours of wetting, animals and plants that can tolerate the dry periods will hatch, sprout or resume life, and a new aquatic food web begins.

Algae begin blooming, the soil releases nutrients, and tiny aquatic animals like rotifers hatch from dried eggs. Within a week, copepods and other small crustaceans hatch and adult insects like dragonflies arrive to lay their eggs. Huge numbers of waterbirds may flock to the wetland to enjoy the abundant algae and crustaceans. Other critters emerge from hideouts in crayfish burrows, beneath leaf litter or buried in shallow sediment.

When wetlands flood they fill rapidly with life.
Felicity Burke/The Conversation, CC BY

After filling, new plants emerge in distinct zones depending on water depth and how often and long they are wet. Wetland plants produce oxygen and store carbon, two services essential for life on earth. They have evolved many ways to survive through dry times and thrive during the wet.

Some plants, like pondweed, are so adapted to aquatic life that a single stem can grow thin branching leaves underwater and thicker broader leaves above water. This helps the plant to access oxygen underwater while simultaneously maximising the sunlight it receives above water. Both are necessary for growth and survival.




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As the wetland dries, water temperatures increase, dissolved oxygen drops and aquatic animals either leave or prepare to survive the dry times.

Some, like mosquito larvae, have adapted to stagnant water. They breath through siphons on their tail to survive this final drying stage. Once the wetland is completely dry, microbes take over to start breaking down any remaining organic matter and the cycle starts again.

Macquarie Marshes in NSW moves between wet and dry.
Margaret Donald/Flickr, CC BY-ND

Many plants and animals in the wetland die and decompose, enriching the earth. These very fertile soils are the reason why wetlands are so often drained for cropping and grazing. If undisturbed, these nutrients are stored in the soil until the next flood. When completely dry, the wetland may only be evident as a depression of fine soil with a perimeter of sedges or reeds.

Wetlands may stay dry for many decades, while eggs and seeds wait and rest until the next flood. Some eggs (such as shield shrimp) are small enough to be dispersed by the wind, or hitch a ride on waterbirds leaving the area.

The plants, animals and microbes occupying wetlands improve the surrounding landscape, providing pollination, pest control, carbon and nutrient storage, and waste removal. Wetlands store 35% of carbon in only 9% of the earth’s surface, reducing floods and recharging groundwater. Understanding how plants and animals will adapt to the extended dry periods predicted with climate change is increasingly important.

Under dry earth, many plants and creatures wait for the rains to come again.
Felicity Burke/The Conversation, CC BY

A drying climate is particularly concerning for high altitude wetlands that are very restricted in the Australian landscape. They occur on the New England Tablelands and Monaro Plateau and can be rapidly degraded by grazing, cropping, diverting or storing water, or fires that can each destroy thousands of years of peat growth in a few days. Losing these wetlands brings us a step closer to losing threatened species such as the Giant dragonfly and Latham’s snipe that rely on these unique upland wetlands.




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Wetlands are largely threatened by lack of understanding that the quiet dry periods fuel the booming wet periods. It is critical that we know where wetlands are in the landscape, so we can protect them during wet and dry phases. Protecting wetlands even when they’re not wet sustains vital seed and egg banks that kickstart complex food webs linking land and water across Australia’s iconic wetland ecosystems.The Conversation

Deborah Bower, Lecturer in Ecosystem Rehabilitation, University of New England; Ben Vincent, Research officer, University of New England; Darren Ryder, Professor of Aquatic Ecology and Restoration, University of New England; John Thomas Hunter, Adjunct Associate Professor in Landscape Ecology, University of New England; Lindsey Frost, Technical Officer, University of New England; Manu Saunders, Research fellow, University of New England, and Sarah Mika, Research fellow, University of New England

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

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EcoCheck: Australia’s Wet Tropics are worth billions, if we can keep out the invading ants


Steve Turton, James Cook University

Our EcoCheck series takes the pulse of some of Australia’s most important ecosystems to find out if they’re in good health or on the wane.

The largest area of tropical rainforest in Australia – the so-called Wet Tropics – is a narrow strip along the northeast coast of the continent, totalling about 2 million hectares.

It represents just 0.26% of the continent, but is crammed with hugely diverse landscapes: rainforests, sclerophyll forests, mangrove forests and shrublands, as well as areas of intensive agriculture and expanding urban rural population centres.

The Wet Tropics bioregion and World Heritage Area.
Peter Bannink/Australian Tropical Herbarium, Author provided

The Wet Tropics are home to a dizzying array of plants and animals. These include at least 663 vertebrate species, 230 butterflies, 135 different dung beetles and a remarkable 222 types of land snail. The area is teeming with more than 4,000 plant species, including 16 of the world’s 28 lineages of primitive flowering plant families.

In all, the Wet Tropics bioregion contains 185 distinct ecosystems. Of these, 18 are officially listed as endangered and 134 are of conservation concern.

Wild riches

Just under half of the region is covered by the Wet Tropics of Queensland World Heritage Area, the world’s second-most-irreplaceable natural world heritage area. A recent analysis listed it as the planet’s sixth-most-irreplaceable protected area in terms of species conservation, and its eighth-most-irreplaceable when considering only threatened species.

Yet despite its global conservation significance, the Wet Tropics was recently described by the International Union for the Conservation of Nature (IUCN) as a World Heritage Area of “significant concern”.

This is due to the threat posed to the area’s biodiversity and endemic plants and animals by invasive species, diseases and predicted climate change impacts. Only two other Australian world heritage properties are listed as “of concern”: the Great Barrier Reef and Kakadu National Park.

Given these concerns, one might expect research dollars to be flowing towards the Wet Tropics. In fact, the opposite is happening: the new National Environmental Science Program has pledged a paltry A$10,000.

Commonwealth funding for Wet Tropics research under successive programs: the CRC for Rainforest Research; the Marine and Tropical Sciences Research Facility (MTSRF); and the National Environmental Research Program (NERP). Under the National Environmental Science Program, only $10,000 has been allocated (not shown).
Rainforest CRC; MTSRF; NERP; CRC Reef Synthesis Report; Reef & Rainforest Research Centre, Author provided

While we’re talking money, it’s worth pointing out that the Wet Tropics are a goldmine. In its 2014-15 report, the Wet Tropics Management Authority calculated that this natural global asset is worth a whopping A$5.2 billion each year – roughly half of it from tourism.

A 2008 report found that the Wet Tropics create the greatest economic benefit of any of Australia’s natural world heritage properties, excluding the Great Barrier Reef. It found that every dollar spent on management costs earned an A$85 return in tourism spending. Even in purely economic terms that makes a pretty compelling case for conservation.

Climate and conservation

But there are question marks over the Wet Tropics’ future, not least because it is considered a hotspot for impacts from climate change. This is primarily due to the very large predicted declines in range size for almost all of the vertebrates that are unique to this part of the world, such as the iconic lemuroid ringtail possum. Climate change is likely to force some species to shift their geographic ranges, or face extinction.

Many of the species at greatest risk of extinction from climate change are confined to higher elevations and thus have very limited scope for dispersal. Of all the rainforest vertebrate species in the Wet Tropics, 30% live within the coolest 25% of rainforest. This gives them nowhere to go if things warm up. For unique species, that figure is even higher, with 45% living in these cooler areas.

Nor is the future too bright for many mountaintop plants, according to a study that modelled the future of suitable climate conditions for 19 species found only above 1,000 m elevation.

The study predicted that, by 2080, 84% of these species would have no suitable habitat anywhere in the Wet Tropics, and so would no longer be able to survive there.

Cat-ants-trophe

Watch out for these crazy guys.
John Tann/Wikimedia Commons, CC BY

The climate isn’t the only problem. Another is the accidental introduction of one of the world’s worst invasive species, yellow crazy ants, into two locations in the Wet Tropics.

Judging by the ants’ impacts elsewhere, this is an impending natural catastrophe. Based on the small amounts of research in the region so far, ecologists Lori Lach and Conrad Hoskin predict that a large invasion of yellow crazy ants could affect most of the animal species in the Wet Tropics.

These impacts could be direct – through predation and harassment – or indirect, such as by the removal of invertebrate prey or disruption of processes such as decomposition, pollination and seed dispersal. The potential for knock-on effects in a system as complex and interconnected as the Wet Tropics rainforest is very high.

We have only a small window of opportunity – perhaps five years at most – to keep the Wet Tropics safe from yellow crazy ants. The cost of failure by the Australian and Queensland governments is unimaginable. Yellow crazy ants are also a threat to agriculture and urban areas, so we should anticipate a successful and properly funded eradication campaign — mirroring the papaya fruitfly eradication efforts in the same region back in the mid-1990s.

If the siege can be repelled, we can hopefully go on enjoying the Wet Tropics – not to mention the money it generates – for many years to come.

Are you a researcher who studies an iconic Australian ecosystem and would like to give it an EcoCheck? Get in touch.

The Conversation

Steve Turton, Professor of Environmental Geography, James Cook University

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