Coastal Habitat Restoration and Coastal Erosion Mitigation: Good for Wildlife, Resiliency, and Storing Carbon

 

Coastal Habitat Restoration

     Coastal environments offer many ecosystem services, extreme weather resilience services, carbon sink services, and unique and sometimes delicate habitats. An important ecosystem service that coastal environments offer is prevention and limiting of coastal erosion which can result in loss of valuable coastal land and destruction of property. An article for Phys.org observes:

“Pollution, coastal development, climate change and many other human impacts have degraded or destroyed swathes of mangrove forests, saltmarshes, seagrass meadows, macroalgae (seaweed) forests and coral and shellfish reefs.”

Researchers studied the results of coastal ecosystem restoration and recently published in One Earth. They found that most coastal restoration projects resulted in the return of animal species to population and diversity levels matching natural coastal ecosystems. Their review found that animal populations in restored coastal habitats were 61% larger and 35% more diverse than in unrestored, degraded sites. They did note, however:

“Although restoration generally helped animals, good outcomes are not guaranteed. We found many projects where animal numbers or diversity barely increased. It was not clear why some projects were great for animals and others had lackluster results.”

They note that more consistent restoration outcomes are needed. I think this is especially important since many carbon offsetting projects these days involve coastal restoration of mangrove habitat and other so-called ‘blue carbon’ goals of storing carbon in marine and coastal ecosystems.

     Researchers at the University of Gothenburg discovered this year that mangroves and salt marshes store far more carbon than previously thought:

 

“… much of the carbon is exported to the ocean-bound as bicarbonate as the tide recedes and remains dissolved in the ocean for thousands of years. Bicarbonate stabilizes the pH and can reduce ocean acidification.”

 

Carbon is stored as CO2 in the biomass and muddy soils. The study involved intertidal carbon transport in 45 mangrove swamps and 16 salt marshes around the world. Carbon accounting through fate and transport was measured and it was found that inorganic carbon export, or outwelling, is a major fate of CO2. The study also noted possible effects on the local pH of near-shelf waters:

 

“…intertidal wetlands might modify the pH of nearshore shelf waters, but the magnitude and scale of the impact on seawater pH are highly site-specific, depending on the climate, geomorphology, hydrology, and size of the system.”

 

     A 2022 study in Current Biology explored global targets for mangrove and seagrass recovery, emphasizing both protection and restoration. Protection is of course useful for stemming the continued loss of these ecosystems, but restoration is required for desirable increases in these ecosystems. Net changes are shown in the graphics below for both mangroves and seagrass ecosystems.

 

     Seagrass restoration is ongoing in the Indian River Lagoon in Florida with over 70 projects making positive impacts. One issue is the proliferation of sewage spills and septic system effluent, which damage these environments.

     New methods of modeling coastal flooding events, known as compound flooding, can help untangle the complex interactions between river flows, ocean tides, and storm surges. A new framework called the Energy Exascale Earth System Model (E3SM) has been developed to do this. Atmosphere, land, river, and ocean models are combined into a single framework that is thought to be an accurate means of analysis.

     Seagrass also has the ability to filter human pathogens. A recent study found that it does so very effectively:

“The findings were nothing short of astounding. Mussels thriving in regions enriched with seagrass demonstrated a remarkable 65% reduction in bacterial pathogens compared to their counterparts from areas devoid of seagrass.”

This means that seagrass can help ensure the safety of seafood. This is important since seagrass environments are habitats and feeding grounds for many aquatic species and sea birds.

     Reef restoration is another very important endeavor needed throughout the world. We hear much about coral reefs being damaged by climate change, reacting to warmer and more acidic ocean waters by bleaching and dying off. However, we hear much less about other very serious threats to reefs. One is blast fishing, now illegal in many parts of the world, but this kind of fishing with dynamite has damaged reefs in many places in Southeast Asia that are now being restored, many through carbon offsetting projects.

     Below are some slides from the One Earth study mentioned above and referenced below.

 

Blue Carbon Ecosystems

     As the graphic below says, “Coastal blue carbon ecosystems can store two to five times more carbon per unit area than tropical rainforests.” For this reason, these ecosystems are desirable for restoration due to the potential carbon credits alone. Of course, there are other benefits to restoring these habitats. These ecosystems include mangrove swamps, seagrass meadows, and coastal shell reefs. They sequester carbon through good old-fashioned photosynthesis.

 

Monitoring and Verification is Important

     While the study in One Earth mentioned above shows that ecosystem restoration works most of the time, we still need a better understanding of the projects that have not worked. Monitoring can be a key to that understanding and point to the best solutions. However, monitoring can be challenging since these environments can be impenetrable, hard to navigate, and dangerous.

     Animal surveying via underwater cameras processed with AI can improve monitoring:

 

“New technologies, such as artificial intelligence (AI) and environmental DNA (eDNA), allow us to collect more and better data on which animals are present and how they use these habitats. We're rapidly becoming less reliant on hauling in nets or diving down to count animals.”

 

This tech can enable more monitoring over larger areas, and it is much cheaper than other forms of counting. The ‘eDNA metabarcoding’ approach identifies taxa living in a given area from environmental DNA samples collected on-site. DNA fragments are targeted, sequenced, and compared with reference databases. This allows for documenting species by water and sediment samples rather than by collecting specimens.

 

“eDNA biomonitoring approaches allows to characterize and study virtually all communities (e.g. bacteria, plants, fish, crustacea etc.) in a comprehensive, standardised, relatively rapid and cost-efficient way. It is also more easily implementable over large spatial scale, and allows to study habitats traditionally difficult to access (e.g. seafloor).”

 

     There are other important verification mechanisms such as the Mangrove Restoration Tracker Tool which tracks pre-restoration site baselines, restoration interventions, and post-restoration monitoring efforts.

     The researchers note that coastal restoration projects are challenged by a rigorous and chaotic permitting process that involves several government agencies. This can no doubt slow down project deployment and increase the cost of restoration. It is perhaps another reason to seek permit reform.

    

 

Blue Carbon Credits

     According to CarbonCredits.com:

“Coastal habitats cover 2% of the ocean’s surface but store 50% of the carbon in their sediment. They’re a 75-gigaton carbon sink, which is equal to 8 years of carbon emissions from fossil fuel.”

     The UN estimates that between 25% and 50% of coastal ecosystems have been damaged or destroyed over the last 100 years. Also destroyed was their ability to store carbon, their ability to mitigate coastal erosion, and their ability to provide habitat.

     Blue carbon credits, like other carbon credits, must have demonstrable and measurable carbon sequestration capabilities. They must meet established standards for carbon accounting and verification, such as the Verified Carbon Standard or the Gold Standard. Restoring mangrove swamps are the most popular blue carbon projects since they have other positive effects like decreasing erosion and mitigating flooding. Coastal marshes, seagrass meadows, and kelp forest restorations make up other blue carbon projects. CarbonCredits.com lists three ways to invest in blue carbon credits: 1) direct investment, 2) investing in blue carbon funds, and 3) buying blue carbon credits on the voluntary carbon market (VCM).

 

 

 

Coastal Erosion

     Coastal erosion can have many causes such as severe storm events. Other issues can make the problem more likely to occur and events more severe when it does. On the U.S. West Coast, there is an issue of coastal erosion enabled by inland dams, including hydropower dams, that hold back sediment that would have otherwise been available to be deposited along the coast near the mouths of those dammed rivers. Starved of sediment the coast is more easily eroded. Waves, tides, and storm surges may erode vulnerable sections of the coast, and higher sea levels in general support such erosion.

          Coastlines are dynamic areas that change according to seasons and other cyclic processes. Causes of coastal erosion include hydraulic action, abrasion, impact and corrosion by wind and water, other natural forces, or human actions and development. How a particular shoreline gets eroded is dependent on the forces acting on it as well as the composition and the corresponding erodibility of the material such as sand, soil, or rock. Hydraulic action involves strong waves pushing compressed air into cracks in the rock and forming caves that then break. Attrition happens when loose pieces of rock (scree) collide, and gradually make each other smaller, smoother, and rounder. Abrasion, or corrasion, happens when waves carrying scree hit cliff faces and wear them down. Chemical weathering, or corrosion, is another major cause of coastal erosion. This occurs when acids in the water dissolve limestone or chalk.

     The hardness of the rock is important as are the consolidation of the rock and the presence of fractures. The bathymetry or shape of the seafloor influences wave strength hitting the coast. Thus, rates of erosion can vary significantly. Offshore shoals and bars can act as wave breaks, dissipating the energy that hits the coast. Both the seafloor and the configuration of shoals and bars can change over time, also affecting the erosion rate of the coast.

     Global sea level rise has increased coastal erosion. In Louisiana and Florida, these higher sea levels are also influenced by geological seafloor changes so the effect is amplified. In addition, the coastal areas there are highly developed, which enables a lot more coastal erosion. Beach erosion is common, and sand is always in demand. One company uses unrecyclable glass to be crushed and distributed as beach sand.  

     Coastal erosion rates can be as much as 25ft per year in the U.S. Southern Atlantic Coast and 50ft per year in some places in the Great Lakes. Human activities have increased the rates of erosion. One study estimated that nearly 26% of the world’s beaches may disappear by the end of this century. According to climate.gov:

 

“In the United States, coastal erosion is responsible for roughly $500 million per year in coastal property loss, including damage to structures and loss of land. To mitigate coastal erosion, the federal government spends an average of $150 million every year on beach nourishment and other shoreline erosion control measures.1 In addition to beach erosion, more than 80,000 acres of coastal wetlands are lost annually—the equivalent of seven football fields disappearing every hour of every day.”

 

     The state of Louisiana has proposed a $50 billion project to restore the Mississippi River and the coastal areas it affects by more or less unleashing the river to its natural processes. Years of construction have changed sediment and erosion patterns. The French built the first levee on the Mississippi River in 1717. Now there are 3,787 miles of levees and floodwalls along the Mississippi. Louisiana’s coastlines are disappearing at a rate of 24 square miles per year. This Mississippi River Conservation Plan project has been called "one of the great engineering challenges of the 21st century". The project also involves pumping sediment into marshes and barrier islands. The project still needs full state approval and federal government assistance.

 

 

 

Erosion Control Methods

 

     Erosion control methods are divided into hard-control methods and soft-control methods. Hard-control methods include sea walls and groynes. Groynes are structures built perpendicular to the shoreline to impede the flow of sediment, presumably including longshore currents. Seawalls are expensive to build but provide very good protection. They are expected to have a lifespan of 50-100 years. Groynes are expected to last about 30-40 years. Both need to be maintained and both should be custom-built for the conditions encountered on that particular section of coast. Soft-control methods include sandbags, beach nourishment, and dynamic revetments. Sandbags are a known flood control solution. Beach nourishment is practiced where wave erosion and longshore drift, which is caused by currents that run nearly parallel but slightly oblique to the shoreline. Dynamic revetments, also known as cobble berms, are man-made storm beaches with gravel and cobble-sized stones that limit beach erosion from storms while still allowing all the normal beach processes.

     In the past, the solutions to coastal erosion were dominated by hard-control methods. However, many view their results as a net negative as they can cause problems by interfering with natural currents and natural sand-shifting processes. They can also divert stormwater into undesirable places and lead to increased beach erosion along adjacent shorelines.

     Extreme storms, sea level rise, and shoreline change mean that coastal environments can be quite dynamic. The USGS has developed a Coastal Vulnerability Index (CVI) and a Coastal Change Hazards Portal. Below is a snapshot of the CVI for the US coasts.

 

Electrodeposition: Small Electric Currents in Coastal Seawater Soils Can Increase Reactivity, Calcium Carbonate Precipitation, and Precipitation of Other Mineral Salts That Can Cement Sand

     A fascinating recent study shows that small electric currents, just 2 to 3 volts, can increase the formation of calcium carbonate and 4 volts can increase the formation of magnesium hydroxide and hydromagnesite. These voltages are too low to be felt by sea life. These components can help hold the sand together, acting as a natural cement.

“By applying a mild electric stimulation to marine soils, we systematically and mechanistically proved that it is possible to cement them by turning naturally dissolved minerals in seawater into solid mineral binders — a natural cement,” lead author Loria noted in the press release. Below is a picture of the more consolidated and better-cemented sand. Estimated costs are about $3-6 per cubic meter. Current methods of coastal restoration are 20 times that. It was also noted that electrically conductive geotextiles could be deployed over unstable marine soil masses for stabilization purposes. The abstract of the paper explains the process:

“Here we demonstrate the application of mild electrical stimulations to precipitate calcareous mineral binders from seawater in the pores of marine soils via electrodeposition, an alternative approach to mitigating coastal erosion. Results of electrochemical laboratory experiments unveil that the polymorphs, precipitation sites, intrusion mechanisms, and effects of electrodeposited minerals in marine sands vary as a function of the magnitude and duration of applied voltage, soil relative density, and electrolyte ionic concentration. Surprisingly, in addition to the precipitation of calcium carbonate and magnesium hydroxide, the formation of hydromagnesite is also observed due to electrically driven fluctuations in the local pH. These electrodeposits lead to enhanced mechanical and hydraulic properties of the marine sands, indicating that electrodeposition routes could be developed to reinforce marine soils in coastal areas that more closely mimic natural systems.”

Hydromagnesite is a component of stalagmites and stalactites. All of these mineral precipitates can contribute to the formation of a natural cement for sand grains that can potentially make the result stronger than the concrete of sea walls. If necessary, the process could be reversed by switching the cathode and anode to change the local pH and re-dissolve the minerals. The goal of the main process is to cement the marine substrate without using actual cement. The method is known as electrodeposition and is already used to protect exposed metal structures from seawater corrosion. The technique works at a laboratory scale, so the next step is to scale up the process with some pilot projects.

 

References:

Restoring coastal habitat boosts wildlife numbers by 61%—but puzzling failures mean we can still do better. Michael Sievers, Christopher Brown, and Rod Connolly. Phys.org. April 22, 2024. Restoring coastal habitat boosts wildlife numbers by 61%—but puzzling failures mean we can still do better (msn.com)

‘Natural cement’: Scientists electrocute sand to stop coastline erosion. Mrigakshi Dixit. Interesting Engineering. August 22, 2024. ‘Natural cement’: Scientists electrocute sand to stop coastline erosion (msn.com)

The $50 Billion Plan to Unleash the Mississippi River And Save Louisiana’s Coast. Hannah Crawford. AZ Animals. August 22, 2024. The $50 Billion Plan to Unleash the Mississippi River And Save Louisiana’s Coast (msn.com)

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Zap Of Electricity Could Save Coastlines From Climate Change Driven Erosion. Stephen Luntz. IFL Science. August 22, 2024. Zap Of Electricity Could Save Coastlines From Climate Change Driven Erosion (msn.com)

Enhanced but highly variable biodiversity outcomes from coastal restoration: A global synthesis. Michael Sievers, Rod M. Connolly, Kimberly A. Finlayson, Stephen E. Swearer, Stephanie R. Valdez, and Christopher J. Brown. One Earth. Volume 7, ISSUE 4, P623-634, April 19, 2024. Enhanced but highly variable biodiversity outcomes from coastal restoration: A global synthesis: One Earth (cell.com)

See the unexpected material being used to rebuild the Louisiana coast. CNN. May 29, 2024. See the unexpected material being used to rebuild the Louisiana coast (msn.com)

Scientists make optimistic discovery while studying mangroves and salt marshes: 'This contribution has previously been overlooked'. Jeremiah Budin. The Cool Down. April 12, 2024. Scientists make optimistic discovery while studying mangroves and salt marshes: 'This contribution has previously been overlooked' (msn.com)

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The Mangrove Restoration Tracker Tool. Global Mangrove Alliance. The Mangrove Alliance

Ambitious global targets for mangrove and seagrass recovery. Christina A. Buelow, Rod M. Connolly, Mischa P. Turschwell, Maria F. Adame, Gabby N. Ahmadia, Dominic A. Andradi-Brown, Pete Bunting, Steven W.J. Canty, Jillian C. Dunic, Daniel A. Friess, Shing Yip Lee, Catherine E. Lovelock, Eva C. McClure, Ryan M. Pearson, Michael Sievers, Ana I. Sousa, Thomas A. Worthington, Christopher J. Brown. Current Biology. Volume 32, Issue 7. April 11, 2022, Pages 1641-1649.e3. Ambitious global targets for mangrove and seagrass recovery - ScienceDirect

Reef restoration program backed by major corporation sees rapid success: 'It makes a huge difference'. Susan Elizabeth Turek. The Cool Down. August 24, 2024. Reef restoration program backed by major corporation sees rapid success: 'It makes a huge difference' (msn.com)

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