Impacts of Mangroves on Coastline Stability

Impacts of Mangroves on Coastline Stability

Mangroves occupy the endless shorelines of many Middle Eastern countries, including the UAE, KSA, Oman, and Bahrain. Climate change is increasing the severity and frequency of threats and causing global sea levels to rise. Acting as ‘green lungs’ mangroves significantly improve the quality of life for wildlife and humans and reduce the risk of erosion, tsunamis, storms, and floods in coastal areas. These hazards can potentially put shorelines at risk, yet something as simple as the presence of mangrove forests can make a substantial difference.

This article debates the importance of mangroves and highlights the impacts of mangroves on coastline stability. It aims to summarize the role of mangrove ecosystems in coastal protection from erosion, wind, swell waves, storm surges, and tsunamis.

Mangroves are built up of a group of 73 species of trees and shrubs. These species can be found in 123 countries and territories, which are estimated to cover 15.2 million hectares of land, or 0.4% of all forests and 1% of tropical forests (FAO 2007). Asia has the most incredible abundance (39% of the world’s population), then followed by Africa (21%), North and Central America (15%), South America (12.6%), and Oceania (Australia, Papua New Guinea, New Zealand, and South Pacific islands) (12.4%).

These halophytic (tolerant to saline waters) evergreen forests are found in the intertidal zones of sheltered shores, estuaries, tidal creeks, backwaters, lagoons, marshes, and mudflats of the tropical and subtropical latitudes. These plants are of great ecological importance and socio-economic significance. Mangroves are a vital hub for tropical marine biotopes as they are a critical component of coastal environmental development. These plants form highly productive ecosystems, providing habitat for marine and terrestrial species, protecting coastal areas from storms and sea level rises, and acting as intense carbon sinks. Mangroves provide defense against water inundation and protect against coastal erosion.

They provide the following benefits for coastal protection.

Reduction of Coastal Erosion

The waves and currents impact the coastline, sometimes carrying sediments to the coast and causing erosion and land loss. The sturdy root systems of mangrove trees help form a natural barrier against violent storm surges and floods. These above-ground roots slow water flow, enhance sediment deposition, and prevent erosion. These plants prevent corrosion and improve sedimentation by reducing wave energy and water over the soil surface, reducing the water’s capacity to dislodge sediments and carry them out of the mangrove area. In addition, mangrove forests stabilize the coastline by reducing erosion caused by storm surges, currents, waves, and tides by limiting erosion and shielding coastal communities from the destructive forces of tropical storms.

Protection against wind and wave damage

The thickets of mangroves that buttress tidal mudflats also provide a buffer zone that protects the land from wind and wave damage. The dense mangrove forest canopies reduce wind speeds locally. This prevents further development of wind and swell waves in and immediately behind the mangroves. This can potentially reduce damage to nearby infrastructure. In the most severe storms, mangroves may be damaged or torn up by the high winds and waves, although the breakage or uprooting of mangrove trees is relatively rare.

Protection against Tropical cyclones

Tropical cyclones (also called hurricanes and typhoons) can cause loss of life and damage property and infrastructure. Mangroves can rapidly reduce wave energy as they pass through the trees. The effectiveness of this barrier in reducing the height of relatively small waves is anywhere between 13% to 66% over a 100 m wide mangrove belt. The effectiveness largely depends on the density of the mangrove vegetation, and waves passing through dense aerial roots and tree canopies will be reduced most effectively.

Protection against Tropical cyclones

Hurricanes and typhoons can cause loss of life and damage to property and infrastructure. Mangroves can rapidly reduce wave energy as they pass through the trees. The effectiveness of this barrier in reducing the height of relatively small waves is anywhere between 13% to 66% over a 100 m wide mangrove belt. The effectiveness largely depends on the density of the mangrove vegetation, and waves passing through dense aerial roots and tree canopies will be reduced most effectively.

Protection against storm surges

Storm surges are seawater flows onto the land, driven by high winds and low pressure. They can reach several meters in depth, occasionally causing massive loss of life and destruction of property. A few studies suggest that mangroves can reduce storm surge levels by up to 50 cm per km width of mangroves.
Protection against Tsunamis: Coastal forests such as mangroves cannot completely stop a tsunami, but they can absorb some of the energy of the flowing water and so reduce the force of the impact, saving lives and reducing property damage. Mangrove trees also disrupt the massive water flows as the wave recedes and blocks property and people from being swept back to sea.

Act as Carbon sinks by storing Carbon:

Mangrove forests are carbon-rich habitats; growing mangrove forests allows more carbon to be sequestered by photosynthesis in habitats where other trees would not thrive. Mangrove forests contribute to global warming mitigation by absorbing carbon dioxide from the atmosphere, most of which is stored inside the plant. When mangrove tree roots, branches, and leaves die, they are often buried in soil, which is subsequently immersed in tidal water, reducing material decomposition and increasing carbon storage. According to research, coastal mangroves exceed most other forests regarding carbon storage capability. For example, mangrove forests in the Indo-Pacific region were the subject of a study that showed they could store about four times per hectare more than the other tropical rainforests and store up to 10 times more carbon per hectare than terrestrial forests. Typical mangrove soils are rich in organic matter and composed of living roots, dead leaves, and woody materials. The dense network of acceptable sources helps to armor the soil from erosive forces and trap and bind soil particles. Because mangrove soils are often saturated and have shallow oxygen content (anaerobic conditions), much of this organic matter accumulates, forming a layer of peat that increases in thickness over time. The peat absorbs water during heavy rains and storm surges, reducing the chances of coastal flooding.

Mangroves to increase soil level

Mangrove root growth pushes the soil upward. These processes can allow mangroves to keep pace with rising sea levels. The mangrove root networks can also reduce debris movement and enhance sedimentation. The roots stabilize current soils and trap sediment inland and localized litterfall from the mangroves, encouraging active soil build-up to minimize erosion. The building of soil and the ability of mangrove roots to push soil upwards can result in a high soil level, which can be helpful defense day-to-day for low-lying regions that are becoming affected by rising sea levels.

In conclusion, mangrove trees serve as a natural barrier to reducing tsunamis’ destructive effects. Even if mangrove forests do not provide perfect protection against tsunamis over specific wave depths, they may contribute to protecting the environment and its inhabitants. Over relatively short distances, mangrove forests may be able to minimize the height of wind and surge waves; however, the protection depends much on the structure, depth, and composition of the forest. Mangrove breadth, density, topography, size, and forward storm speed affect how well mangrove forests defend against frequent, lower-intensity, and more catastrophic storms.

Additionally, mangrove trees defend against coastal erosion by lowering wave energy and current speed, which reduces the water’s ability to push silt out of mangrove areas. Mangroves naturally provide wave dissipation and serve to contribute to coastal defense positively. The dissipation also fosters a positive feedback loop that facilitates mangrove colony growth. Mud banks and their dense mangrove forests generate efficient wave-energy dissipation. Closer inshore, the remaining energy is gently dissipated by mangroves, with a positive effect on flocculation and sediment trapping (Furukawa et al., 1997)

In areas where mangroves have been cleared, coastal damage from hurricanes and typhoons is much more severe. As a result, maintaining healthy mangrove forests can be seen as an adaptive strategy for reducing risk and providing long-term coastal protection. By filtering out sediments, the forests protect coral reefs and seagrass meadows from smothered in sediment. It is significant to highlight that the degree of protection provided by mangrove forests depends on the quality of the surrounding trees. Therefore, compared to tiny and dispersed mangrove forests, the mangrove forest with good structure, composition, depth, width, and high density might become the protective layers against any catastrophic environmental hazards and damages.

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