Scientists use flooded forests to simulate sea level rise

EDGEWATER, Maryland-Researchers are simulating future floods in dense forests of maple, beech, and poplar trees just a few miles from the Chesapeake Bay.

They used PVC pipes and rubber hose nets to submerge half a football field in woodland to study how trees respond to climate change and its effects-namely, sea level rise and heavy rain.

This is a local experiment, but the researchers said they hope to build a global model to help scientists understand which events led to the earliest stages of tree stress, and when forests near the coast began to transform into wetlands.

“People realize that we are in the midst of huge and rapid changes. As scientists, we want to know in advance how this change will unfold,” said Patrick A., deputy director of research at the Smithsonian Environmental Research Center and the main collaborator on the project. Said Patrick Megonigal.

With rising temperatures and warming waters, the world is preparing for worse weather. Hurricane Ida is just a preview of how the coast and its residents are threatened by climate change. At the same time, wetlands, an important buffer zone against storm damage, are disappearing or forced to retreat inland—taking over forests, fields, and homes.

The Mid-Atlantic is an example of these changes. The water level along the coast here rises by about 5 millimeters per year, which is much higher than the global average.

Part of the problem is that the land is also sinking, mainly due to the effects of the end of the last ice age. During that time, the glacier pressed against the side of the land, raising one end above the Chesapeake Bay. When they retreated, the land under the glacier began to rebound, and the other end began to fall.

At the same time, there is less and less fresh water flowing from the river to stop the salt water moving upstream. As the wetlands were engulfed by the Aral Sea, they had no choice but to retreat to the highlands to take over the forest.

Since the mid-1800s, more than 150 square miles of forest in the Chesapeake Bay area has become swampland, and the rate of retreat of the swampland has almost doubled since then. research shows.

Usually, this transition leaves behind so-called ghost forests, which are bleached and blackened tree trunks killed by salt water.

These changes can be seen in the Chesapeake area. But sea level rise is a global problem, and it also occurs in places with greater population densities and few resources or funds.

Delta regions with large amounts of groundwater pumping, such as New Orleans in the Philippines or areas near Manila, are experiencing some of the most severe sea level rise. But economic engines such as Singapore and New York, as well as small island nations that will lose their entire way of life, are also feeling the impact.

‘The trade-offs people need to consider’

The way the coast changes or develops will have a major impact on the level of damage caused.

A study published in the journal last month Natural disaster review It was discovered that during severe storms of 2100 or later, sea level rise combined with wetland loss could cause US$2.5 billion to US$13 billion in property damage.

Compared with the situation without sea level rise and wetland loss, the area inundated during such storms may be as high as 2.5 times. The study concluded that even low-intensity storms are expected to have a greater impact in the future than today’s high-intensity storms, which is largely due to the reduction of coastal wetlands.

The pace of change does not look good.

A study was published in science It was discovered in June 2020 that the threshold for mangroves and similar coastal ecosystems to rise above the sea level is about 7 millimeters per year.

However, according to a recent report by the Intergovernmental Panel on Climate Change (IPCC), this threshold may be overshadowed by the end of this century. One of its conclusions is that sea levels will inevitably rise, and—in all cases except for minimum warming scenarios—their rate of rise exceeds the rate of coastal ecosystems. In many coastal areas, global sea levels are also rising faster than average, thereby exacerbating risks.

Robert Cope, director of the Institute of Earth, Ocean and Atmospheric Sciences at Rutgers University and author of the latest IPCC report, said that at the current rate of rise in the mid-Atlantic, wetlands and other coastal ecosystems can keep up. “But they can only keep up with it if they have room to do it.”

This means they need space to move inland away from the ocean. This is why it is important to use the forest as a buffer zone. Kopp added that locking things in place with hard infrastructure will prevent natural ecosystems from adapting. “This is a trade-off that people need to consider.”

Land migration

Returning to the Smithsonian Global Change Research Wetlands, where the storm surge project is running, researchers are trying to determine how trees that have not been exposed to salt water respond to increasing salinity. They will look for a threshold that drops rapidly after trees are submerged in sea water.

“We know that mature trees can tolerate occasional exposure to salt water, especially if the salt is washed away by rain, but we don’t know what causes the trees to decrease in frequency, seasonal timing or severity of storm surge events,” Mego Nigal said. “Our research aims to sort out the plant, soil, and microbial processes and mechanisms that started these changes.”

The new experiment is called TEMPEST, which is an appropriate nickname that can effectively measure future tidal surges.

It stems from some of the earliest climate studies here on how higher levels of atmospheric carbon dioxide affect plant life.Located in the wetland, dotted with small rooms for inhaling carbon dioxide₂, The site helps researchers discover that certain plants respond well to elevated carbon dioxide₂, They perform photosynthesis and act as energy expenditure (green Line, July 17, 2018).

Greenhouse gases can also help plants build soil faster so they can rise above the eroding sea. When the wetlands here began to form about 4,000 years ago, the Chesapeake Bay was about 15 feet lower than it is today.

But at a certain point, the sea level rise was too great for this wetland to overcome.

In order to survive, it migrated to the high ground. It is taking over anything that hinders it—including those maple, beech, and poplar trees.

“We know that the forest will eventually succumb,” Meganigal said. “We don’t know how many storm surges it will take to cause damage to the trees.”

Flooded area

To simulate a wetter future marked by more intense rainfall, the researchers will use a complex network of tanks and pipes to flood a forest-covered site with 80,000 gallons of fresh water. This is about 40 times the average daily rainfall of today’s wettest month of the year. At another location, they will be submerged with 80,000 gallons of salt water, and they will be drawn from the mouth of the river and pumped out through a huge bladder.

They will flood these locations once in 10 hours, and then observe and measure the tree’s response to the lack of oxygen at the roots. This means testing how fast the water moves up the trunk and how fast the trees grow.They will take soil samples to measure moisture and microorganisms to see how much carbon dioxide there is₂ The soil is emitting.

As water starts to kill trees, it is assumed that they will stop absorbing and processing carbon dioxide₂ And began to release it, becoming a source of carbon rather than a sink.

They have to measure not only water saturation, but also salinity. They will distinguish between these two stressors and see how they harm trees in different ways.

This is part of a larger project led by the Pacific Northwest National Laboratory and funded by the Department of Energy, which aims to observe the Chesapeake Bay and Lake Erie.

Anya Hopple, a postdoctoral researcher and TEMPEST project leader at the Pacific Northwest National Laboratory, said the idea is to help researchers predict which areas will be at risk of rapid change. They can then use this data to provide information for protection efforts and policies. They may even see that certain species have the ability to adapt and survive quickly, Hopple said.

One step ahead

The efforts of Chesapeake Bay researchers are of practical significance.

According to the National Oceanic and Atmospheric Administration, in the United States, nearly 40% of the population lives in coastal counties. In low-lying deltas like Bangladesh, tidal flooding caused by rising sea levels has become the main driver of displacement.

Knowing what will happen in coastal areas in the future can help planners and local officials determine how much space is left for wetland migration inland, which means limiting the development of infrastructure that connects with forests.

“The way we use land and coasts, we are also encroaching on these areas,” Hopple said.

The benefits of protecting wetlands are huge. They protect wildlife habitats and coastal infrastructure from storms, remove pollutants from the water, and sequester carbon. According to a recent report, more than half of the world’s carbon is captured by plants and animals living in or around the world’s coastlines.Climate line, July 27).

The so-called blue carbon stored in the soil of coastal habitats is of great interest to countries hoping to reduce emissions by restoring swamps and mangroves. Carbon credits may also be used as a way to pay for coastal wetland protection.

Megonigal and Smithsonian researchers are working to create coastal report cards to help governments and conservation organizations determine which coastal ecosystems need protection. They will do this by using data from the Coastal Carbon Atlas, an interactive map containing more than 5,400 carbon profiles.

Although he has seen changes in the wetlands in the past two decades, Megnigar still maintains a positive attitude.

“If you can plan to leave a buffer zone for the swamp to move inland, and you can plan an orderly transition from the forest to the swamp… then there is a lot of room for optimism,” he said. “We just need to focus the conversation not on what may happen, but on what is happening and how we can advance.”