Half of global methane emissions come from aquatic ecosystems – much of this is human-made


Shutterstock

Judith Rosentreter, Yale University; Alberto Borges, Université de Liège; Ben Poulter, NASA, and Bradley Eyre, Southern Cross UniversityMethane — a greenhouse gas far more potent than carbon dioxide — plays a major role in controlling the Earth’s climate. But methane concentrations in the atmosphere today are 150% higher than before the industrial revolution.

In our paper published today in Nature Geoscience, we show as much as half of global methane emissions come from aquatic ecosystems. This includes natural, human-created and human-impacted aquatic ecosystems — from flooded rice paddies and aquaculture ponds to wetlands, lakes and salt marshes.

Our findings are significant. Scientists had previously underestimated this global methane contribution due to underaccounting human-created and human-impacted aquatic ecosystems.

It’s critical we use this new information to stop rising methane concentrations derailing our attempts to stabilise the Earth’s temperature.

From underwater sediment to the atmosphere

Most of the methane emitted from aquatic ecosystems is produced by micro-organisms living in deep, oxygen-free sediments. These tiny organisms break down organic matter such as dead algae in a process called “methanogenesis”.

Flooded rice paddies
Rice farming releases more methane per year than the entire open ocean.
Shutterstock

This releases methane to the water, where some is consumed by other types of micro-organisms. Some of it also reaches the atmosphere.

Natural systems have always released methane (known as “background” methane). And freshwater ecosystems, such as lakes and wetlands, naturally release more methane than coastal and ocean environments.

Human-made or human-impacted aquatic ecosystems, on the other hand, increase the amount of organic matter available to produce methane, which causes emissions to rise.




Read more:
Emissions of methane – a greenhouse gas far more potent than carbon dioxide – are rising dangerously


Significant global contribution

Between 2000 and 2006, global methane emissions stabilised, and scientists are still unsure why. Emissions began steadily rising again in 2007.

There’s active debate in the scientific community about how much of the renewed increase is caused by emissions or by a decline of “methane sinks” (when methane is eliminated, such as from bacteria in soil, or from chemical reactions in the atmosphere).

We looked at inland, coastal and oceanic ecosystems around the world. While we cannot resolve the debate about what causes the renewed increase of atmospheric methane, we found the combined emissions of natural, impacted and human-made aquatic ecosystems are highly variable, but may contribute 41% to 53% of total methane emissions globally.




Read more:
Feeding cows a few ounces of seaweed daily could sharply reduce their contribution to climate change


In fact, these combined emissions are a larger source of methane than direct anthropogenic methane sources, such as cows, landfill and waste, and coal mining. This knowledge is important because it can help inform new monitoring and measurements to distinguish where and how methane emissions are produced.

Water is a big part of much of our landscape, from mountain rivers to the coastal ocean. This aerial image shows Himalaya rivers, wetlands, lakes and ponds, and the world’s largest mangrove forest (the Sundarbans) at the coast of the tropical Bay of Bengal.
George Allen, Author provided

The alarming human impact

There is an increasing pressure from humans on aquatic ecosystems. This includes increased nutrients (like fertilisers) getting dumped into rivers and lakes, and farm dam building as the climate dries in many places.

In general, we found methane emissions from impacted, polluted and human-made aquatic ecosystems are higher than from more natural sites.

For example, fertiliser runoff from agriculture creates nutrient-rich lakes and reservoirs, which releases more methane than nutrient-poor (oligotrophic) lakes and reservoirs. Similarly, rivers polluted with nutrients also have increased methane emissions.

An aquaculture farm
Coastal aquaculture farms emit up to 430 times more methane per area than coastal habitats.
Shutterstock

What’s particularly alarming is the strong methane release from rice cultivation, reservoirs and aquaculture farms.

Globally, rice cultivation releases more methane per year than all coastal wetlands, the continental shelf and open ocean together.

The fluxes in methane emissions per area of coastal aquaculture farms are 7-430 times higher than from coastal habitats such as mangrove forests, salt marshes or seagrasses. And highly disturbed mangroves and salt marsh sites have significantly higher methane fluxes than more natural sites.

So how do we reduce methane emissions?

For aquatic ecosystems, we can effectively reduce methane emissions and help mitigate climate change with the right land use and management choices.

For example, managing aquaculture farms and rice paddies so they alternate between wet and dry conditions can reduce methane emissions.




Read more:
Climate explained: methane is short-lived in the atmosphere but leaves long-term damage


Restoring salt marsh and mangrove habitats and the flow of seawater from tides is another promising strategy to further reduce methane emissions from degraded coastal wetlands.

We should also reduce the amount of nutrients coming from fertilisers washing into freshwater wetlands, lakes, reservoirs and rivers as it leads to organic matter production, such as toxic algal blooms. This will help curtail methane emissions from inland waters.

These actions will be most effective if we apply them in the aquatic ecosystems that have the greatest contribution of aquatic methane: freshwater wetlands, lakes, reservoirs, rice paddies and aquaculture farms.

This will be no small effort, and will require knowledge across many disciplines. But with the right choices we can create conditions that bring methane fluxes down while also preserving ecosystems and biodiversity.The Conversation

Judith Rosentreter, Postdoctoral Research Fellow, Yale University; Alberto Borges, Research Director FRS-FNRS, Associate Professor at ULiège, Université de Liège; Ben Poulter, Research scientist, NASA, and Bradley Eyre, Professor of Biogeochemistry, Director of the Centre for Coastal Biogeochemistry, Southern Cross University

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

Floodplains aren’t separate to a river — they’re an extension of it. It’s time to change how we connect with them


Melissa Parsons, University of New England and Martin Thoms, University of New EnglandDramatic scenes of flood damage to homes, infrastructure and livelihoods have been with us on the nightly news in recent weeks. Many will be feeling the pain for years to come, as they contend with property damage, financial catastrophe and trauma.

But what if, for a moment, we removed the humans and their structures from these tragic images — what would we see?

We would see a natural process of river expansion and contraction, of rivers doing exactly what they’re supposed to do from time to time. We’d see them exceeding what we humans have deemed to be their boundaries and depositing sediment across their floodplains. We’d see reproductive opportunities for fish, frogs, birds and trees. The floods would also enrich the soils. Floods can be catastrophic for humans, but they are a natural part of an ecosystem from which we benefit.

These scenes clearly depict the intersection of humans and nature, and it’s not working out well for either side.




Read more:
5 ways the government can clean up the Murray-Darling Basin Plan


We must envision a new way of interacting with floodplains – these brilliant social-ecological systems that are not separate to rivers but rather part of the riverine landscape.

Humans can live on and with floodplains — but the way we do that has to change.

What is a floodplain?

Floodplains are relatively flat stretches of land located next to rivers. It helps to think of them as an extension of the river; it is natural and normal for a river to flood their adjacent plains.

Floodplains are composed of sediment the river has transported and then deposited, which makes them incredibly fertile. Flow and sediment regimes interacting over decades — or millennia — determine the physical and ecological character of floodplains, and the way they flood.

There are more than 15 generic floodplain types in Australia. Each harbours a unique set of evolutionary properties, physical features and ecosystems.

These influence the way floodwaters traverse floodplains, how long water remains on a floodplain, the velocity, turbulence and depth of floodwaters, and ecosystem responses to flooding. Floodplains are complex and highly variable.

Floodplains are also dynamic and ever-changing — and we should expect them to change even more in the coming years. Australian rivers have experienced regular periods of increased flood activity in the past 100 years.

And climate change is predicted to increase flood activity.




Read more:
5 ways the government can clean up the Murray-Darling Basin Plan


Humans benefit from floodplains

Floodplains are among the most productive ecosystems on the planet – they are biodiversity hotspots.

That’s in large part due to periodic flooding between different parts of a river-floodplain system; flooding is crucial to the function of floodplains. Without floods, these floodplains wouldn’t “work” — they would not be able to deliver the ecosystem services we benefit from. Those benefits include, but are not limited to:

  • food grown in these fertile soils
  • regulation of a balanced ecosystem
  • cultural heritage
  • transportation (as floodplains are easy to build roads on)
  • the supply of good quality drinking water
  • recreation.

The economic value of floodplain ecosystem services exceed US$25,681 per hectare. Roughly 25% of global terrestrial ecosystem services come from floodplains.

Humans are drawn to live on floodplains because of their productivity. In Australia, the floodplains of the Murray Darling Basin, heavily developed for agriculture, yield more than A$10 billion annually. These floodplain ecosystems provide an estimated A$187 billion per annum from their various ecosystem services.

However, the more we interrupt floodplain processes with development, the more we diminish the supply of ecosystem services.

The perils of living on floodplains

Putting the people back into the news footage reveals a social picture that is costly, traumatic and disruptive. The events of the past weeks have now brought into focus the perils of living on floodplains.

Humans have come up with ways to contend with this peril. Dams and levees. Land use planning. Building codes. Engineered floodscapes. Insurance. Emergency preparation systems and community engagement.

But if floodplains are a social-ecological system, where society gains great benefits but is also periodically placed at risk, which side should get the greatest policy attention? The humans or the ecosystem?

The answer is: both. But they also need to be better integrated.

Balancing the social with the ecological

Balancing the social and ecological aspects of floodplains requires a mindset change. We must combine community participation with research, resilience and adaptation to make long-term decisions about the future of these complex social-ecological systems.

If society wants to continue to derive the billions of dollars of benefits from floodplains, we need to ensure that flooding continues to occur on floodplains, and adapt to risk in imaginative and innovative ways that also protect the benefits.

Business as usual is not an option. The limitations of technocratic controls such as dams and levees should now be obvious. Time and time again, these have increased flood risk and failed to flood-proof the floodplain.

Rarely do such linear solutions solve complex problems in social-ecological systems. Linear solutions often exacerbate a problem or simply move it on to other parts of the system, creating social inequality, environmental decline and future risk.

The Australian government’s 2018 National Disaster Risk Reduction Framework sets the challenge to join up the built, social, economic and natural environments to address disaster risk in Australia.

Accepting the challenge requires a broader focus on balancing the social-ecological sides of Australia’s vast floodplains. Complexity, not linear thinking, must be embedded in the way we reimagine policy about floodplains and floods.

This requires transformative collaborations between government departments, researchers, business, and community stakeholders.


If this article has raised issues for you, or if you’re concerned about someone
you know, call Lifeline on 13 11 14. This story is part of a series The Conversation is running on the nexus between disaster, disadvantage and resilience. You can read the rest of the stories here.
The Conversation

Melissa Parsons, Senior Lecturer, Geography and Planning, University of New England and Martin Thoms, Professor of Physical Geography, University of New England

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

Humpback whales may have bounced back from near-extinction, but it’s too soon to declare them safe


Shutterstock

Olaf Meynecke, Griffith UniversityThe resurgence in humpback whale populations over the past five decades is hailed as one of the great success stories of global conservation. And right now, the federal Department of Agriculture, Water and the Environment is considering removing the species from Australia’s threatened list.

But humpback whales face new and emerging threats, including climate change. Surveying whales is notoriously hard, and the government has not announced monitoring plans to ensure humpback populations remain strong after delisting. We need a plan to keep them safe.

Australia’s whale season is about to begin. Each year between May and November, the mammals migrate north along Australia’s coastline from their feeding grounds in Antarctica to warmer waters. There, they breed before returning south.

So now’s a good time to take a closer look at the status of this iconic, charismatic species.

A pod of humpback whales lunge feeding.
The resurgence of humpback whales is one of conservation’s greatest success stories.
Shutterstock

A host of threats

Humpback whales live in every ocean in the world, and have one of the longest migrations of any mammal.

Humpback whale numbers dwindled as a result of commercial whaling, which in Australia began in the late 18th Century. Whaling and the export of whale products was Australia’s first primary industry. Between 1949 and 1962 Australia’s whalers killed about 8,300 humpback whales off the east coast, until only a few hundred were left.

The International Whaling Commission banned humpback whaling in the Southern Hemisphere in 1963. By then, humpback populations had fallen to about 5% of pre-whaling numbers. In the years since, some whaling continued, but has now largely ceased.

Today humpback whales face new threats. These include:

  • underwater noise which interferes with whale communication
  • pollution
  • vehicle collisions
  • getting caught in fishing gear
  • over-harvesting prey such as krill
  • marine debris
  • habitat degradation
  • climate change.

In particular, the effects of climate change – such as warming waters, shifting currents and ocean acidification – may affect the availability of prey that humpback whales need to survive.

Combined, these worsening threats could disrupt humpback whales’ recent resurgence. Indeed, under one scenario, scientists predict the increase Australia’s humpback numbers could stall — or worse, start declining – in the next five to ten years.




Read more:
Climate change threatens Antarctic krill and the sea life that depends on it


A humpback whale calf caught in a fishing net.
A humpback whale calf caught in a fishing net.
SeaPix, Author provided

The humpback whales’ plight

According to the federal government’s delisting assessment, humpback whales’ strong recovery suggests current threats are not a risk to the population. But this assessment has shortcomings.

It states humpback whales on Australia’s east and west coast have reached, or are exceeding, the original population size – increasing by 10-11% a year over the past decade or longer.

But this information is based on models using data collected prior 2010 for Australia’s west coast, and prior to 2015 for the east coast. This data isn’t readily available to the public and does not include recent population trends.

The predicted population growth from these models doesn’t account for current and future impacts from major threats, including climate change. This is despite recent research and observations suggesting changes in the humpback population.

For example, 2019 research showed potential shifts in calving locations, with newborn humpback whales now frequently spotted outside Australian tropical waters. This — along with the early arrival of migrating humpback whales in Australia in the past years — may be a first sign of changes in breeding and migration habits.

It’s also important to compare humpback whale populations in Australia with those elsewhere, such as in the North Pacific. There, calving rates are declining, and whale abundance and distribution is showing marked shifts. The risk of entanglements with fishing gear is also rising.




Read more:
How climate change is reducing numbers of humpback whale calves in the north-west Atlantic


A whale tail with a fishing line caught in it
Whales can get caught in fishing gear.
Todd Burrows, Author provided

The problem with counting whales

The pre-whaling population size of humpback whales on the east and west coast of Australia is thought to be between 40,000 and 60,000. But information is limited and the actual number may have been much higher

Today, the estimated numbers from population models are similar: roughly 28,000 on the east cost and up to 30,000 on the west coast. But counting humpback whales accurately is very difficult. For example, on the east coast of Australia humpback whales frequently move between populations and during a census may not be attributed to their original population.

What’s more, conditions prior to whaling are not comparable with today’s conditions. Krill is a major food source for whales, and widespread whaling in the Southern Hemisphere caused krill numbers to increase. Research from 2019 suggests humpback whales’ fast recovery after whaling ceased may have been due to widely available krill.

But krill numbers have declined or their availability has shortened in recent years due to threats such as climate change and industrial fishing.




Read more:
Humpback whales have been spotted in a Kakadu river. So in a fight with a crocodile, who would win?


Aerial view of humpback under icy water .
Every year humpback whales migrate from Antarctica where they feed, to breed in Australia.
Shutterstock

Proceed with caution

Humpback whales off Australia’s coast will continue to have some protection under the Environment Protection and Biodiversity Conservation Act, even if they’re taken off the threatened species list.

Generally, all marine mammals are protected in Australian waters. But getting delisted means fewer resources devoted to their protection.

Forecasting the complex interactions of today’s threats, in order to predict tomorrow’s humpback whale populations, is challenging. A cautionary approach should therefore be taken.

In 2016, the US delisted some humpback whale populations. But before doing so, it established a ten-year monitoring plan to track population changes, threats and species abundance.

If Australia proceeds with the delisting, it should follow the US’ lead. Humpback whales should remain listed for another five years so a monitoring plan can be developed. Federal and state governments must invest resources into this process, and react swiftly if changes are detected.

A number of whale researchers and organisations concerned about the humpback whale delisting, including the author, prepared a detailed response to the proposal here.The Conversation

Olaf Meynecke, Research Fellow in Marine Science, Griffith University

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