What the world needs now to fight climate change: More swamps

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Freshwater cypress swamp, First Landing State Park, Va.
VA State Parks, CC BY

William Moomaw, Tufts University; Gillian Davies, Tufts University, and Max Finlayson, Charles Sturt University

“Drain the swamp” has long meant getting rid of something distasteful. Actually, the world needs more swamps – and bogs, fens, marshes and other types of wetlands.

These are some of the most diverse and productive ecosystems on Earth. They also are underrated but irreplaceable tools for slowing the pace of climate change and protecting our communities from storms and flooding.

Scientists widely recognize that wetlands are extremely efficient at pulling carbon dioxide out of the atmosphere and converting it into living plants and carbon-rich soil. As part of a transdisciplinary team of nine wetland and climate scientists, we published a paper earlier this year that documents the multiple climate benefits provided by all types of wetlands, and their need for protection.

Saltwater wetland, Waquoit Bay Estuarine Research Reserve, Mass.
Ariana Sutton-Grier, CC BY-ND

A vanishing resource

For centuries human societies have viewed wetlands as wastelands to be “reclaimed” for higher uses. China began large-scale alteration of rivers and wetlands in 486 B.C. when it started constructing the Grand Canal, still the longest canal in the world. The Dutch drained wetlands on a large scale beginning about 1,000 years ago, but more recently have restored many of them. As a surveyor and land developer, George Washington led failed efforts to drain the Great Dismal Swamp on the border between Virginia and North Carolina.

Today many modern cities around the world are built on filled wetlands. Large-scale drainage continues, particularly in parts of Asia. Based on available data, total cumulative loss of natural wetlands is estimated to be 54 to 57 percent – an astounding transformation of our natural endowment.

Vast stores of carbon have accumulated in wetlands, in some cases over thousands of years. This has reduced atmospheric levels of carbon dioxide and methane – two key greenhouse gases that are changing Earth’s climate. If ecosystems, particularly forests and wetlands, did not remove atmospheric carbon, concentrations of carbon dioxide from human activities would increase by 28 percent more each year.

Wetland soil core taken from Todd Gulch Fen at 10,000 feet in the Colorado Rockies. The dark, carbon-rich core is about 3 feet long. Living plants at its top provide thermal insulation, keeping the soil cold enough that decomposition by microbes is very slow.
William Moomaw, Tufts University, CC BY-ND

From carbon sinks to carbon sources

Wetlands continuously remove and store atmospheric carbon. Plants take it out of the atmosphere and convert it into plant tissue, and ultimately into soil when they die and decompose. At the same time, microbes in wetland soils release greenhouse gases into the atmosphere as they consume organic matter.

Natural wetlands typically absorb more carbon than they release. But as the climate warms wetland soils, microbial metabolism increases, releasing additional greenhouse gases. In addition, draining or disturbing wetlands can release soil carbon very rapidly.

For these reasons, it is essential to protect natural, undisturbed wetlands. Wetland soil carbon, accumulated over millennia and now being released to the atmosphere at an accelerating pace, cannot be regained within the next few decades, which are a critical window for addressing climate change. In some types of wetlands, it can take decades to millennia to develop soil conditions that support net carbon accumulation. Other types, such as new saltwater wetlands, can rapidly start accumulating carbon.

Arctic permafrost, which is wetland soil that remains frozen for two consecutive years, stores nearly twice as much carbon as the current amount in the atmosphere. Because it is frozen, microbes cannot consume it. But today, permafrost is thawing rapidly, and Arctic regions that removed large amounts of carbon from the atmosphere as recently as 40 years ago are now releasing significant quantities of greenhouse gases. If current trends continue, thawing permafrost will release as much carbon by 2100 as all U.S. sources, including power plants, industry and transportation.

Kuujjuarapik is a region underlain by permafrost in Northern Canada.
Nigel Roulet, McGill University., CC BY-ND

Climate services from wetlands

In addition to capturing greenhouse gases, wetlands make ecosystems and human communities more resilient in the face of climate change. For example, they store flood waters from increasingly intense rainstorms. Freshwater wetlands provide water during droughts and help cool surrounding areas when temperatures are elevated.

Salt marshes and mangrove forests protect coasts from hurricanes and storms. Coastal wetlands can even grow in height as sea level rises, protecting communities further inland.

Saltwater mangrove forest along the coast of the Biosphere Reserve in Sian Ka’an, Mexico.
Ariana Sutton-Grier, CC BY-ND

But wetlands have received little attention from climate scientists and policymakers. Moreover, climate considerations are often not integrated into wetland management. This is a critical omission, as we pointed out in a recent paper with 6 colleagues that places wetlands within the context of the Scientists’ Second Warning to Humanity, a statement endorsed by an unprecedented 20,000 scientists.

The most important international treaty for the protection of wetlands is the Ramsar Convention, which does not include provisions to conserve wetlands as a climate change strategy. While some national and subnational governments effectively protect wetlands, few do this within the context of climate change.

Forests rate their own section (Article 5) in the Paris climate agreement that calls for protecting and restoring tropical forests in developing countries. A United Nations process called Reducing Emissions from Deforestation and Degraded Forests, or REDD+ promises funding for developing countries to protect existing forests, avoid deforestation and restore degraded forests. While this covers forested wetlands and mangroves, it was not until 2016 that a voluntary provision for reporting emissions from wetlands was introduced into the U.N. climate accounting system, and only a small number of governments have taken advantage of it.

Models for wetland protection

Although global climate agreements have been slow to protect wetland carbon, promising steps are starting to occur at lower levels.

Ontario, Canada has passed legislation that is among the most protective of undeveloped lands by any government. Some of the province’s most northern peatlands, which contain minerals and potential hydroelectric resources, are underlain by permafrost that could release greenhouse gases if disturbed. The Ontario Far North Act specifically states that more than 50 percent of the land north of 51 degrees latitude is to be protected from development, and the remainder can only be developed if the cultural, ecological (diversity and carbon sequestration) and social values are not degraded.

Also in Canada, a recent study reports large increases in carbon storage from a project that restored tidal flooding to a saltmarsh near Aulac, New Brunswick, on Canada’s Bay of Fundy. The marsh had been drained by a dike for 300 years, causing loss of soil and carbon. But just six years after the dike was breached, rates of carbon accumulation in the restored marsh averaged more than five times the rate reported for a nearby mature marsh.

Ten feet (3 meters) of carbon-rich soil accumulation along Dipper Harbour, Bay of Fundy, New Brunswick, Canada, has been radiocarbon dated to have accumulated over 3,000 years.
Gail Chmura, McGill University, CC BY-ND

In our view, instead of draining swamps and weakening protections, governments at all levels should take action immediately to conserve and restore wetlands as a climate strategy. Protecting the climate and avoiding climate-associated damage from storms, flooding and drought is a much higher use for wetlands than altering them for short-term economic gains.

This article has been updated to add a link to the Scientists’ Second Warning to Humanity.The Conversation

William Moomaw, Professor Emeritus of International Environmental Policy, Tufts University; Gillian Davies, Visiting Scholar, Global Development and Environment Institute, Tufts University, and Max Finlayson, Director, Institute for Land, Water and Society, Charles Sturt University

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


How did the fish cross the road? Our invention helps them get to the other side of a culvert

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When a stream enters a culvert, the flow can be concentrated so much that water flows incredibly fast. So fast, in fact, that small and juvenile fish are unable to swim against the flow and are prevented from reaching where they need to go to eat, reproduce or find safety.

Jabin Watson, The University of Queensland; Craig E. Franklin, The University of Queensland; Harriet Goodrich, University of Exeter; Jaana Dielenberg, The University of Queensland, and Rebecca L. Cramp, The University of Queensland

Fish need to move to find food, escape predators and reach suitable habitat for reproduction. Too often, however, human activities get in the way. Dams, weirs and culverts (the tunnels and drains often found under roads) can create barriers that fragment habitats, isolating fish populations.

An Australian innovation, however, promises to help dwindling fish populations in Australia and worldwide. Our solution, recently described in Ecological Engineering, tackles one of the greatest impediments to fish migration in Australia: culverts.

A culvert crisis in our waterways

Freshwater ecosystems are one of the most heavily impacted by human activities.

Many freshwater species, such as the iconic barramundi, start their life as larvae in estuaries, then as small juveniles they make mammoth upstream migrations to freshwater habitats. In fact, about half of the freshwater fish species in southeast Australia need to migrate as part of their life cycle.

When fish are unable to pass human-made barriers, the decline in populations can be huge. For example, in the Murray-Darling Basin where there are thousands of barriers and flows are highly regulated, fish numbers are estimated to be at only 10% of pre-European numbers.

In New South Wales alone, there are more than 4,000 human-made barriers to fish passage. Over half of these are culverts. Culverts are most often installed to allow roads to cross waterways. They are designed to move water under the road, which they do quite efficiently, but often with no consideration of the requirements of the animals that live there.

When a stream enters a culvert, the flow can be concentrated so much that water flows incredibly fast. So fast, in fact, that small and juvenile fish are unable to swim against the flow and are prevented from reaching where they need to go to eat, reproduce or find safety.

A map of human-made barriers to fish passage in NSW. Image: Fisheries NSW.

Many current design ‘fixes’ come with problems

The problem culverts pose for fish is now well acknowledged by fisheries managers, and as a result efforts to make culverts fish-friendly are now widespread.

Where space allows, these new fish passage solutions can resemble a natural stream, where rocks of various sizes are added to break up the flow. Alternatively, artificial baffles (barriers to break up and slow the flow) are also commonly attached to the walls of the tunnel.

These designs do have some drawbacks. They may suit some fish sizes and species, but not all. They can be expensive to install. They also tend to catch debris, which increases maintenance costs and the risk of flooding upstream during high flow events.

A box culvert running under a road.

Using physics to find a new solution

We took a new approach that harnesses a property of fluid mechanics that scientists call the “boundary layer”. When a fluid moves over a solid surface, friction causes the water to slow down next to the surface. This thin layer of slower-moving water is called the boundary layer.

Where two surfaces meet, such as in the corner of a square culvert, the boundary layers of the bed and wall merge. This creates a small area of slower-moving water – the “reduced velocity zone” – right in the corner. This is quite small, but little fish can still use it and are very good at finding it.

We wanted to expand this zone (to accommodate a wider range of fish sizes) and slow the water in it further.

So, we added a third surface, generating three boundary layers that then joined. This was done by adding a square beam running the length of the channel wall, close to the floor. The boundary layers of the floor, wall and bottom surface of the beam merged to create a reduced velocity channel along the side of the main flow.

In this GIF to the right hand side, the reduced velocity zone is revealed by adding a fluorescent dye, which lingers in the slower flowing water under the square beam we added to the channel.

Testing our design in a 12 metre channel (or flume) found that water velocity in the zone below the beam was slowed by up to 30%. For small fish, this is a huge reduction.

In tests, we focused on small-bodied species, or juveniles of larger growing species, because these are considered the weakest swimming size class and most vulnerable to high water velocities created within culverts. Every species tested saw significant improvements in their ability to swim and traverse up the channel.

All of the species benefited, regardless of their body shape or swimming style.

The GIF on the right hand side here shows a juvenile Murray cod swimming upstream using the reduced velocity zone we created by adding the beam.

Creating a slower-flowing zone

Our novel fish passage design is highly effective, yet very simple. It’s a square beam installed along the length of a culvert wall, so it’s easy to incorporate into new structures and cheap to retrofit into existing culverts.

It is also much less likely to trap debris than baffles or rocks embedded in the floor of a culvert.

This is a totally new approach that has the potential for widespread application, helping to restore the connectivity of freshwater fish populations here in Australia, and overseas.

A Crimson-spotted rainbowfish navigates the fast flow by swimming under the beam we added to channel.
Harriet Goodrich, Author provided
You can see the beam more clearly here. A Crimson-spotted rainbowfish swims under the beam we added to slow the water flow in that area.
Harriet Goodrich, Author provided

More research lies ahead. We’re hoping that by optimising the dimensions of the beam we can get even more fish through the channels, with even greater ease. We’re also planning field testing to check our laboratory findings work in the real world.

Freshwater biodiversity is greatest in the tropics. Here, developing countries are having drastic impacts on their freshwater ecosystems. The simplicity of this design may make it an affordable approach to help maintain and restore habitat connectivity in developing regions.

Matthew Gordos from NSW Fisheries contributed to this article.The Conversation

Jabin Watson, Postdoctoral researcher, The University of Queensland; Craig E. Franklin, Professor in Zoology, The University of Queensland; Harriet Goodrich, PhD student, University of Exeter; Jaana Dielenberg, Science Communication Manager, The University of Queensland, and Rebecca L. Cramp, Senior Research Fellow, The University of Queensland

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