Mangroves' Resilience: Battling Pollution's Impact

Mangroves are a unique ecosystem that is constantly under threat from rising pollution levels. These coastal forests are found in sheltered estuaries and along river banks and lagoons in the tropics and subtropics. Mangroves are affected by various types of pollution, including water pollution from oil spills and herbicides, plastic pollution, and urban development. Oil spills coat the roots of mangroves, limiting oxygen transport to the underground roots, while herbicides and other types of pollutants may also kill them. Plastic waste has been observed to cover up to 50% of the forest floor in some areas, and complete plastic cover of root zones causes tree death. Urban development, such as the construction of buildings and canal systems, can also lead to the destruction of mangrove habitats and alter water quality and runoff. Additionally, activities such as shrimp farming, coastal agriculture, and hotel development can further intensify pollution levels and alter the delicate tidal regimes that mangroves depend on.

Plastic pollution

Mangroves are vital ecosystems that provide many benefits to coastal communities around the world. However, they are under threat from various anthropogenic stressors, including plastic pollution. Plastic waste frequently accumulates in mangrove forests, with plastic debris often covering a significant portion of the forest floor. This waste can smother mangrove roots, impede their growth, and even lead to tree death.

The complex root systems of mangroves make them particularly susceptible to plastic pollution. The roots can trap and accumulate plastic debris, leading to entanglement and physical damage. This accumulation of plastic waste can also create prolonged anoxic conditions, further endangering the health of the mangroves.

The impact of plastic pollution on mangroves has been observed in various regions, including Southeast Asia, where the problem is especially acute. Rivers that discharge large amounts of plastic waste into the ocean are often located near mangrove habitats, leading to the pollution of these fragile ecosystems. For example, the mangroves in the Wouri Estuary in Cameroon are choking on plastic waste due to rapid urbanization and insufficient waste management.

The consequences of plastic pollution in mangroves extend beyond the ecological realm. Mangroves provide essential ecosystem services, such as protecting inland areas from intense weather events like typhoons and strong currents. They also serve as important reproduction sites for many animal species. The loss of mangroves due to plastic pollution can have far-reaching impacts on biodiversity and coastal resilience.

Addressing the issue of plastic pollution in mangroves requires a multi-faceted approach. It involves reducing plastic waste at the source, improving waste management and recycling infrastructure, and promoting low-plastic lifestyles. Additionally, collaboration between communities, industries, and governments is essential to implement effective solutions and protect these vital ecosystems.

Oil spills

Mangroves are highly susceptible to oil exposure. Oil spills can result in initial defoliation, and if the exposure is severe enough, eventual mass mortality and complete loss of the mangrove habitat. Mangrove forests are typically found in coastal intertidal areas in tropical, subtropical, and warm temperate waters. This means that oil entering mangrove forests does so at or near high tide, smothering the aerial roots and leaves. The severity of the oil spill's impact depends on the amount and type of oil, with heavy oils more likely to smother and light oils more toxic to mangroves.

The oil coats and smothers the small plants and aerial root systems, cutting off the transport of oxygen to the underground roots. Mangrove communities, including invertebrates, fishes, and plants, are highly susceptible to damage from petroleum products. A large oil spill can result in the suffocation and death of mangroves within a few weeks to months. A smaller spill may only cause defoliation without tree mortality or ongoing impacts on plant productivity. The type of oil is also a key factor, with heavy oils more likely to smother and light oils more toxic to mangroves. Other factors influencing the impact of oil spills on mangroves include the oil's age and the dispersant used, as well as the species of mangrove and the type of sediment.

The impact of oil spills on mangroves can be long-lasting, with complete recovery of the mangrove ecosystem taking decades. For example, after an oil spill in southern Australia in 1992, it took 10 years for any recovery to be observed in heavily oiled areas, and it is predicted to take 55 years for the mangroves to fully recover. Oil spills can also have sublethal or chronic effects on mangroves, with continuous exposure to high levels of pollution affecting their health and productivity in the long term. For instance, a study of the Baixada Santista pipeline leak in Brazil in 1983 found that, after an initial dieback of trees and an eight-year recolonization period, the canopy cover stabilized but remained 20-30% lower than before the spill.

In addition to oil spills, mangroves are also threatened by water pollution from herbicides, urban development, and the expanding shrimp aquaculture industry.

Urban development

In some regions, however, coastal urbanization has been found to have a positive impact on mangrove growth and carbon stock. This is due to the alteration of local climate conditions, such as temperature, rainfall, and sea levels, which can enhance the growth of mangrove ecosystems. Effective urban planning can play a crucial role in facilitating mangrove conservation and achieving coastal sustainability.

The impact of urban development on mangroves is complex and varies across different regions. It is influenced by various factors, including the degree of urbanization, local climate, and human activities such as conservation efforts and restoration initiatives. While urbanization can have positive effects on mangroves in certain areas, it is important to carefully plan and manage urban development to ensure the sustainability and resilience of mangrove ecosystems.

Overall, while urban development can pose a significant threat to mangroves, there are also opportunities to mitigate its negative impacts and promote the conservation and restoration of these valuable ecosystems.

Shrimp farming

Shrimp farmers dig channels to supply the ponds with enormous quantities of freshwater and seawater, altering the natural flow of water that maintains the health of surrounding mangroves and ecosystems further inland and offshore. Diverting water can harm mangroves by preventing their seeds from being dispersed via seawater, and it can kill the trees by cutting off freshwater supplies. Shrimp farmers also use massive amounts of chemicals, antibiotics, and fertilizers to keep the overcrowded shrimp healthy. This chemical soup, along with enormous quantities of organic waste, contaminates surrounding freshwater and coastal waters.

The expansion of shrimp farming has led to the loss of mangrove forest cover, with some countries showing a closely related decline in mangrove cover with increasing shrimp production. The process of catching wild shrimp larvae to stock the ponds is also hugely wasteful, as it damages the ocean floor and traps many species besides shrimp, leading to depleted marine habitats and local fisheries.

In addition, shrimp farming can have negative social impacts. As shrimp is a cash crop, the profits from shrimp farming are often exported, and the jobs it generates are usually temporary. Local people may be left with a devastated landscape that can no longer support fishing, farming, or wood gathering, and many may be forced to move away.

Climate change

Mangroves are among the most threatened habitats in the world, with less than 50% of the world's mangrove forests remaining intact at the end of the 20th century. Climate change is likely to have a substantial impact on these ecosystems.

Sea Level Rise

Mangroves are sensitive to changes in inundation duration, salinity levels, and flooding duration. Sea level rise is a major threat to mangrove ecosystems as increases in flooding duration can lead to plant death and shifts in species composition, ultimately reducing productivity. Global sea levels have risen by 3.2 mm/yr over recent decades and are likely to rise further by between 0.28 and 0.98 m by 2100. Local factors strongly influence sea level, and rates vary from 1.9 mm/yr in the Caribbean to 7.5 mm/yr in parts of Indonesia and up to 9 mm/yr in the lower Mississippi River Delta.

Storms

The frequency and intensity of storms are expected to increase due to climate change, which will have destructive impacts on mangrove habitats. Intense storm events can cause tree uprooting, branch breaking, and defoliation, leading to the complete removal or large-scale loss of mangrove forests. However, storms can also have constructive impacts by providing rapid inputs of allochthonous sediment, which can increase soil elevation and stimulate productivity and mangrove growth.

Temperature

Global temperatures are predicted to increase by up to 4.8° C by 2081-2100, which will influence mangrove species composition, phenology, productivity, and distribution. Mangroves are currently latitudinally confined by minimum air temperatures, with peak leaf photosynthesis at 28-32° C. Higher temperatures can lead to plant death, and increases in evaporation rates can result in salinity increases, influencing species diversity, size, and productivity.

Precipitation

Frequently asked questions