Ghost Forests - Sea Level Rise

Introduction


Sea Level Rise

Sea-level rise already causes an increasing amount of flooding, which is predicted to continue as our planet warms. Melting ice caps, mountain tops and glaciers that have been icy for thousands of years, are continuing to lose mass at an alarming rate. This loss of ice not only causes sea-level rise, but also puts communities at risk who have historically relied on ice melt for their survival.

Managed Retreat

Ghosts forest can be used as indicators while considering managed retreat. Specifically we can weigh the costs of trying to protect and reverse the phenomenon, vs the costs and benefits of allowing those forests to die and transition to new biomes.

Since there appear to be benefits to allowing forests to transform into wetlands, communities might relinquish these areas to nature as wetlands such as mangroves when flooding will be fairly mild, or the community might want to get started in building oyster or even coral reefs if sea level rise and flooding are expected to be more extreme.

"Climate change is affecting people all over the world, and everyone is trying to figure out what to do about it. One potential strategy, moving away from hazards, could be very effective, but it often gets overlooked," said Siders, assistant professor in the Joseph R. Biden, Jr. School of Public Policy and Administration and the Department of Geography and Spatial Sciences. "We are looking at the different ways society can dream bigger when planning for climate change and how community values and priorities play a role in that."

"Managed retreat has been happening for decades all over the United States at a very small scale with state and/or federal support. Siders pointed to Hurricanes Harvey and Florence as weather events that caused homeowners near the Gulf of Mexico to seek government support for relocation. Locally, towns such as Bowers Beach, near the Delaware coast, have used buyouts to remove homes and families from flood-prone areas, an idea that Southbridge in Wilmington is also exploring.

People often oppose the idea of leaving their homes, but Siders said thinking seriously about managed retreat sooner and in context with other available tools can reinforce decisions by prompting difficult conversations. Even if communities decide to stay in place, identifying the things community members value can help them decide what they want to maintain and what they purposely want to change.


"If the only tools you think about are beach nourishment and building walls, you're limiting what you can do, but if you start adding in the whole toolkit and combining the options in different ways, you can create a much wider range of futures," she said."


It is argues that "... long-term adaptation will involve retreat. Even traditionally accepted visions of the future, like building flood walls and elevating threatened structures, will involve small-scale retreat to make space for levees and drainage. Larger-scale retreat may be needed for more ambitious transformations, such as building floating neighborhoods or cities, turning roads into canals in an effort to live with the water, or building more dense, more compact cities on higher ground.


Some, but not all these futures currently exist.


In the Netherlands, the municipality of Rotterdam has installed floating homes in Nassau harbor that move with the tides, providing a sustainable waterfront view for homeowners while making room for public-friendly green space along the water. In New York City, one idea under consideration is building into the East River to accommodate a floodwall. Both cities are using combination strategies that leverage more than one adaptation tool.

Adaptation decisions don't have to be either/or decisions. However, it is important to remember that these efforts take time, so planning should begin now.


"Communities, towns, and cities are making decisions now that affect the future," said Siders. "Locally, Delaware is building faster inside the floodplain than outside of it. We are making plans for beach nourishment and where to build seawalls. We're making these decisions now, so we should be considering all the options on the table now, not just the ones that keep people in place."


According to Siders, the paper is a conversation starter for researchers, policymakers, communities and residents that are invested in helping communities thrive amid changing climate. These discussions... shouldn't focus solely on where we need to move from, but also where we should avoid building, where new building should be encouraged, and how we should build differently.


"Managed retreat can be more effective in reducing risk, in ways that are socially equitable and economically efficient, if it is a proactive component of climate-driven transformations," said Mach. "It can be used to address climate risks, along with other types of responses like building seawalls or limiting new development in hazard-prone regions."

Coastal Overtopping

"Low-lying coastal regions host nearly 10% of the world's population. In addition to ongoing erosion and rising sea levels, these areas and their unique ecosystems are facing destructive hazards, including episodic flooding due to overtopping of natural/artificial protection, as in the case of Hurricane Katrina, which hit the United States in 2005, Cyclone Xynthia in Europe in 2010, and Typhoon Haiyan in Asia in 2013 (the largest tropical cyclone ever measured). These episodic events are expected to become more severe and more frequent due to global warming, while the consequences will also increase due to increased anthropogenic pressure, such as coastal and infrastructure development, rapid urbanization. Although the magnitude and frequency of these events remain uncertain, scientists believe that countries in the tropics will be particularly affected."

"The combination of tides and episodes of large waves is the main contributor to episodes of coastal overflow," says Rafaël Almar, a researcher in coastal dynamics at IRD, and the coordinator of the study. "We identified hot-spots, where the increase in risks of overtopping is higher, such as in the Gulf of Mexico, the Southern Mediterranean, West Africa, Madagascar and the Baltic Sea."

"The scientists also performed an initial global assessment of the potential coastal overtopping over the 21st century, by taking into account different sea-level rise scenarios. Results show that the number of overtopping hours could increase with a faster pace than the average rate of sea-level rise. "The frequency of overtopping is accelerating exponentially and will be clearly perceptible as early as 2050, regardless of the climate scenario. By the end of the century, the intensity of the acceleration will depend on the future trajectories of greenhouse gas emissions and therefore the rise in sea-level. In the case of a high emissions scenario, the number of overtopping hours globally could increase fifty-fold compared with current levels," Rafaël Almar warns. "As we go along the 21st century, more and more regions will be exposed to overtopping and consequent coastal flooding, especially in the tropics, north-western United States, Scandinavia, and the Far East of Russia."

Further studies will be needed on the local and regional levels to flesh out these global projections, which provide a solid basis for proposing effective adaptation measures in the hotspots identified." - An Acceleration of Coastal Overtopping Around the World

Sea Water Intrusion

This happens with waterways, as tides bring seawater further past the mouth of these waterways, killing freshwater species, and causing other problems. Thanks to sea level rise, this problem is getting worse, and to the point that some coastal communities which traditionally relied on their local waterways for freshwater, are now finding their drinking water contaminated by sea salt.

Seawater intrusion is also an issue when seawater makes its way into aquifers. This can happen via waterways, or via coastal overtopping.

Ghost Forests

These are caused by sea level rise bringing salt water into forest that are not adapted for the salinity. The forests die, releasing methane and other green house gasses as they turn to marshlands. "Drowned trees in what scientists call "ghost forests" increased the amount of carbon dioxide released by these ecosystems by about 25%, according to a study."


"Before conducting the new study, Martinez said some researchers thought the dead trees were acting as straws to suck up greenhouses gases from the soil. When the tree dies, remaining water is flushed out of the leaves, which they thought would allow greenhouse gases to diffuse up the tree.

But their research showed that higher tree stems hold less greenhouse gases than they thought.

She added that they are still unsure how greenhouse gas emissions differ between tree species and how to advise land managers on mitigation efforts. Some researchers have suggested implementing "living shorelines" made from plants and rocks to buffer saltwater surges.

"It's a hard question to answer because snags can become a new habitat for other animals," Martinez said. "We're hoping to get a better idea of how greenhouse gases change as the trees are dying and also get better estimates of live tree stem emissions." 

" In the United States, ghost forests are most common along the Atlantic coast, from Canada to North Carolina, as well as in Louisiana.

Yet as ominous as these eerie ecosystems appear, Kirwan’s research has shown that they are not a sign of impending doom. Instead, ghost forests actually offer evidence that the natural world is responding to climate change, and resiliently transforming to survive sea level rise. By sacrificing a strand of trees along the coast, the newly-formed marshland can protect the forest and other land further inland.

Salt marshes are one of the most productive ecosystems on the planet, and they are effective buffers, protecting inland regions from storm surge. “This creation of ghost forests is a sign that marshes are being preserved,” Kirwan says. “They are migrating.”

It’s unclear when ghost forests were first scientifically described, but research started ramping up in the 1980s. And yet, scientists are only just now beginning to understand the complex effects they have on the environment. According to the Virginia Institute research, for instance, carbon sequestration rates may be higher in ghost forests than in the original forest, because the wet soil and healthy marsh ecology replaces the dry forest floor.

However, other research has shown that among the most likely plant species to colonize marshlands are the phragmites, a group of perennial grasses. Phragmites sequester less carbon than trees, meaning coastal deforestation could instead lead to more carbon dioxide in the atmosphere.

There are many questions begging for answers: how plants and animals are affected by ghost forests, the impacts of coastal deforestation and how long these types of marshlands will be able to protect inland areas from flooding."

"...New marshland should be able to buffer against some sea level rise, but may not be able to keep this up for long." 



"Ghost forests are expanding along the East Coast due to a combination of drought conditions and tropical storms. Trees in wetland areas are dying at increasing rates because they are exposed to saltwater more often; a flood or storm surge that may have occurred once in 100 years in the past may now occur once every 20 years or more. This consistent exposure to saltwater can damage the roots of trees, keeping them from absorbing the freshwater and nutrients they need to grow and thrive."


"... Runoff from agriculture and wastewater ditches can also create pathways for saltwater to intrude upon wetlands and forests, contributing to their decline. This information is key for changing how agricultural workers, environmental managers, regional climate mitigation planners and others interact with one another and the environment that supports us all."

Benefits of Ghost Forests

Guiding Managed Retreat

Communities will need to decide which areas they allow to become ghost forests and which will need to be protected by seawalls or other options. Communities may choose to allow ghost forests to turn into salt marshes, while picking new places for replacement trees to be planted. Strategic tree planting, especially along water ways can help recreate riparian buffers that will minimize erosion, sedimentation, pollution, and flooding higher in the watershed, which could allow for better protection along new coastlines.

Solutions

Salination of Soil and Aquifers

"Sea-level rise, in combination with increased groundwater pumping can increase saltwater intrusion in groundwater aquifers. Saltwater intrusion into groundwater aquifers can increase treatment costs for drinking water facilities or render groundwater wells unusable.


As the sea levels rise, the “salt front” (location of the freshwater-saltwater line) may progress further upstream. This encroachment may be further exacerbated by drought, reduced rainfall or changes in water use and demand. Saltwater intrusion can result in the need for water utilities to increase treatment, relocate water intakes, or development of alternate sources of fresh water.


Saltwater intrusion, through surface or ground water sources, may diminish the availability or quality of source waters for drinking water utilities."

Pollution 


Major storms and floods can damage buildings, overload sewers, farms, and chemical storage facilities. Waste is picked up from damaged buildings, road ways, and tipped bins sending a huge array of unknown chemicals, bacteria, and other microbes into people's drinking water, soil, and air.


Some parts of the world have waste sites including hazardous waste stored at low altitudes, and these are now under threat from sea level rise and increasingly intense flooding. Managed retreat should take into consideration how to ensure both that these sites won't leek into the environment, and won't be a source continued danger to communities.

Sustainable Drainage Systems (SUDS)

SUDs passively reduce flooding down stream by slowing the flow of water, letting it spread out in safe places so that it can better infiltrate the soil. This has many benefits from reducing erosion and siltation, to recharging ground water and making the landscape more resilient against droughts, fires and heatwaves. 

Recharging ground water also means salt water intrusion can be reduced along coastal areas, while guaranteeing safe ground water for future generations.

Click the SUDs button to learn more about these systems.

Green Space Expansion

Green space is our greatest natural defense against flooding. These green spaces can be renovated to de-compact the soil and build flood mitigation infrastructure including reservoirs and swales. Ecologically these areas increase biodiversity, and can help expand our range of wildlife corridors which will further protect wildlife against the threats of extinction caused by fractured habitats. Keystone species, particularly beavers should be allowed to colonize these areas, providing flood protection in areas where human/animal interactions can be minimized.

Examples of Green Spaces

Green spaces can perform a number of services, and incorporating green spaces in flood prevention plans can even boost their success and biodiversity.

Greenbelts and greenways are strips of green areas connecting communities while tamping down excessive urban sprawl. These spaces reduce air pollution, provide connectivity for wildlife, and if properly designed can provide connectivity to humans instead of forcing everyone to drive in private vehicles. Greenbelts can absorb flood water, but this may result in people having to take alternative routes such as roads until the waters recede.

Wetlands are vital for many migratory and stationary species. Seasonal rains can turn deserts, grasslands, and other biomes into vibrant space for pollinators as well as other species who feed on them. Flooding may negatively impact tourism, but should be less likely to destroy homes unless indigenous communities or park rangers live in the area.

Wetlands

Wetlands are natures sponges, and have been under threat from farmers and urban developers draining these natural resources. By restoring wetlands we both buffer land and communities from storms and floods, but we'll also restore biodiversity for millions of species who rely on wetlands to reproduce, eat, and find refuge year round or on their migration routes.

Pollution Sites Must be Maintained and kept far from Places that are expected to experience Flooding based on history or the proposed flood/sea level rise forecasts.


Sewage Facilities Need to be Revamped to Withstand or Work with Nature


Illegal sewage releases are becoming more common thanks to more frequent flooding and larger populations than some of these sewage facilities were designed to serve. Sewage releases during floods threatens water safety, and can spread deadly diseases to rescue workers, flood victims, wildlife, and domestic animals.



Eliminate Feed Lots, Factory Farms, and Manure Lagoons in Flood Prone Areas

Along water ways or in flood prone areas, these facilities endanger water safety. During major storms, farmers were unable to drain manure lagoons ahead of major storms which caused fecal mater and other contagious materials to flood into people's homes. Factory farm buildings filled with thousands of chickens and pigs were left to flood with the animals un-evacuated, meaning that after the flood waters receded, they were filled with rotting animal corpses, presenting further threat of dangerous diseases to nearby communities. - https://www.npr.org/sections/thesalt/2016/11/04/500701098/manure-happens-especially-when-hog-farms-flood

At the absolute least, any farmers already in these areas or applying for building approval should be required to submit their plan for full animal evacuation in the event of these storms as well as infrastructure to eliminate the risk of flooding manure into waterways or nearby communities. Similarly zoos, dog boarders, and other such facilities should be discouraged in flood-prone areas or areas that may contaminate waterways.

Tools & Apps

Water Pumping

The pumping of water takes a larger amount than many people realize. Pumping ground water for agricultural, industry, or public use, moving it between facilities, etc. all require energy since water is a fairly heavy substance.

Maps & Tools

Maps by Region Check specific State and Country pages to see if there are more specific maps, tools, projects, and groups for specific areas. If you have suggestions, we would love to hear what else we can include. Some states and countries have more detailed watershed, county, and city level maps. Other topic sections such as plastic, agriculture may be worth checking to understand how pollution enters our water ways, and how industries might endanger water sources without proper regulation, mitigation, or clean up systems to protect communities from these threats.

North America

USA

Cambodia

Madagascar

United Kingdom

North America

USA

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