Plastics have become an indispensable part of modern life, with global production exceeding 400 million metric tonnes (MT) annually. However, their improper disposal has led to an alarming environmental crisis, particularly concerning microplastics, tiny plastic particles less than five millimetres (mm) in size. These pollutants, which result from the breakdown of larger plastics or originate from synthetic fibres and industrial processes, are now a pressing ecological and health concern worldwide.
Sri Lanka is no exception to this crisis. With our extensive coastline and thriving mangrove ecosystems, the country is facing increasing challenges in managing plastic pollution. Recent studies have highlighted that estuaries and mangroves, often perceived as natural filters for pollutants, may not be as effective in retaining microplastics under extreme weather conditions. Instead, these ecosystems may temporarily trap microplastics only to release them later during storms and floods, significantly increasing marine pollution levels.
Mangroves are unique coastal vegetation that thrive in the intertidal zones of tropical and subtropical regions, including Sri Lanka. They serve as crucial ecological buffers, providing biodiversity support, carbon sequestration, shoreline protection, and serving as nurseries for marine life. We are home to approximately 15,670 hectares (ha) of mangrove forests, primarily found in the coastline.
Mangroves play a significant role in mitigating climate change, as they can store three to five times more carbon per ha than terrestrial forests, with global mangrove carbon storage estimated at 4.19 petagrams (Pg) of carbon. Additionally, they help stabilise coastlines, reduce erosion and protect communities from storm surges, which is crucial given that over 1.5 million Sri Lankans live in coastal areas vulnerable to climate-related disasters.
Beyond their role in climate regulation, mangroves also act as natural filters for pollutants, including microplastics. Their dense root systems, particularly their pneumatophores (aerial roots), trap suspended particles, preventing them from reaching open waters. Studies from the Pearl River Delta in China indicate that mangrove sediments contain up to 17,000 microplastic particles per kilogram (kg) of dry weight, highlighting their efficiency as microplastic sinks. However, this retention capacity is disrupted during extreme weather events, such as monsoons and cyclones, which can resuspend and redistribute accumulated microplastics into marine ecosystems.
Sri Lanka, battered by biannual monsoon seasons and an alarming rise in tropical storms, is grappling with an escalating plastic pollution crisis. With a staggering 1.59 million MT of plastic waste generated annually, vast quantities are funneled through rivers, carrying a relentless tide of debris from urban centres to the ocean. As this deluge of waste fragments into microplastics, our once-thriving coastal ecosystems are turning into toxic dumping grounds. Mangrove forests, the last line of defense for our shorelines, are now suffocating under an onslaught of microscopic pollutants, transforming into alarming microplastic hotspots.
Studies from other parts of the world suggest that urban estuarine mangroves typically store high concentrations of microplastics. In stable conditions, these ecosystems may retain thousands of microplastic particles per kg of sediment. However, extreme hydrological events such as monsoons, cyclones, and floods can disturb these sediments, reducing their retention capacity and flushing microplastics back into the ocean. In Sri Lanka, where monsoonal rains are a dominant climatic feature, the impact of these events on microplastic distribution in mangroves remains underexplored but could be substantial.
The impact of extreme weather
We are highly vulnerable to extreme weather events, including tropical cyclones, heavy monsoonal rains, and flash floods. The World Meteorological Organisation (WMO) has recognised Asia as the region most affected by hydro-meteorological disasters, with Sri Lanka frequently experiencing storm surges and intense flooding. These events significantly influence microplastic transport and deposition.
A recent study in Shenzhen, China, demonstrated that microplastic concentrations in mangrove sediments dropped dramatically after typhoon events, with up to 90% of trapped microplastics being washed away. This suggests that while mangroves function as temporary filters, they may not serve as long-term sinks for microplastics in dynamic coastal environments.
In Sri Lanka, the monsoon season and cyclones in the Bay of Bengal could have a similar effect, reintroducing microplastics into marine ecosystems and exacerbating pollution levels in sensitive coastal habitats. This poses a grave risk to biodiversity, particularly to marine organisms that mistake microplastics for food, leading to bioaccumulation and potential entry into the human food chain through seafood consumption.
Microplastic sources and composition
Microplastics originate from multiple sources, including industrial waste, synthetic textiles, packaging materials, and urban runoff. The composition of microplastics in Sri Lanka’s coastal and mangrove environments is likely diverse, influenced by both local and transboundary pollution.
Studies from other regions have shown that storm-driven transport shifts the composition of microplastics, with an increase in synthetic rubber particles from urban runoff post-storm events. This is particularly concerning for our urban waterways, which receive substantial runoff from roads, industries, and improperly managed waste disposal sites. If similar trends occur in Sri Lanka, microplastic pollution could intensify after heavy rains, affecting both mangrove health and marine biodiversity.
Towards a resilient future
Our mangroves are standing on the frontline of an environmental crisis, yet, they remain overlooked in the fight against plastic pollution and climate change. These ecosystems are more than just picturesque coastal forests; they are nature’s own defense mechanism, absorbing storm surges, sheltering marine life, and filtering pollutants. But, what happens when the very forces that sustain them turn into threats? The evidence is clear: mangroves do not act as permanent microplastic sinks. Instead, under the wrath of monsoons and storms, they release the very pollutants that they once trapped, unleashing a wave of plastic waste back into the ocean.
This is not just a scientific problem; it is a national emergency. With our reliance on fisheries, coastal tourism, and biodiversity, failing to address mangrove degradation and microplastic pollution could devastate both livelihoods and marine ecosystems. Policymakers must step up with aggressive regulations on plastic waste, while conservationists and researchers must push for long-term mangrove monitoring and restoration efforts. But, beyond laws and science, this is also about people - local communities, fishers, activists, and every Sri Lankan citizen. If we do not act now, the very lifelines that protect our coasts will crumble under neglect.
The question is not whether we should take care of our mangroves; it is whether we can afford not to. The tides are shifting, and unless we intervene, we may soon find ourselves drowning in a crisis of our own making.
(The writer is an electronics engineer with a background in information technology and sustainability)
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The views and opinions expressed in this article are those of the author, and do not necessarily reflect those of this publication