Sargassum: environmental issues and impact monitoring

The first Europeans who explored the coasts of America were already crossing the Atlantic, keeping an eye on these large concentrations of floating seagrass meadows in which their vessels could become entangled and alter their course. However, it has only been in the last decade that the concentration of this planktonic macroalgae has increased excessively, affecting coastal areas in 13 countries. In fact, in 2018, more than 1.1 million tonnes of sargassum invaded the Mexican Caribbean coast, marking a turning point in the environmental history of the region. In the 2025 tourist season, a 40% increase compared to last year is expected along Mexico’s Caribbean coast. This Atlantic shoreline of postcard-perfect paradises has turned into a scene of crisis: beaches buried under mountains of decomposing algae, tourists staying away, and coastal communities facing a threat that goes far beyond the visual.

Sargassum is abundant in the Sargasso Sea, but a recurring Atlantic sargassum belt (GASB) has been observed in satellite imagery since 2011, often extending from West Africa to the Gulf of Mexico. In June 2018, the 8,850-kilometre GASB contained over 20 million metric tonnes of this macroalgae’s biomass. Mengqiu Wang et al. The great Atlantic Sargassum belt.

When sargassum arrives en masse, it doesn’t just ruin the landscape’s aesthetics: it triggers a chain of devastating environmental impacts. The decomposition of this biomass releases toxic gaseous compounds, generates nauseating odours and pollutes the water, causing the feared “brown tides”. Furthermore, it accelerates coastal erosion and alters entire ecosystems, threatening biodiversity and public health.

Next, we will analyse the ecology and proliferation of sargassum, as well as the factors that favour its growth and expansion across the Atlantic. We will examine the effects of its decomposition and the impacts it has on water quality, air qualityAir quality refers to the state of the air we breathe and its composition in terms of pollutants present in the atmosphere. It is considered good when poll...
Read more and human health. Finally, we will discuss the importance of measuring its emissions, source of foul odours, because monitoring the volatile compounds they emit is key to ensuring air quality and protecting coastal communities.

Definition and context of sargassum

Sargassum isn’t just any seaweed: it’s a nomadic brown macroalgae, an oceanic wanderer that floats freely thanks to small gas-filled vesicles, as if wearing its own natural life jacket. It drifts through the warm waters of the western Atlantic, forming vast floating patches that, seen from above, resemble golden moving islands.

But these islands aren’t empty: they’re genuine floating oases that harbour a vibrant marine community. Among their brown fronds hide juvenile fish, crabs, shrimp and even sea turtles, which find there food, shelter and a safe place to grow away from predators.

Ecology and proliferation of sargassum

The most surprising aspect is its expansion speed: sargassum can double its biomass in less than 20 days. Fueled by excess nutrients (many from human activities) and favoured by changes in ocean currents, this marine traveller can quickly transform into a coastal threat.

“Under Florida and Caribbean sunshine, sargassum can decompose in 1-2 days, then release foul-smelling gases (hydrogen sulphide and ammonia), attract insects and promote bacterial growth, thus posing threats to humans.” Optical Oceanography Laboratory. College of Marine Science. University of South Florida.

When it reaches dry land, the charm fades. What was once a floating ecosystem becomes a foul-smelling mass of decomposing matter. It releases gases like hydrogen sulphide (H₂S) and ammonia (NH₃), pollutes water and air, and accelerates the erosion of white sand beaches and crystal-clear waters. What floats giving life in the ocean becomes a major environmental problem on the coast.

Sargassum and climate change

The exceptional increase in sargassum in recent decades is not an isolated phenomenon: it reflects global climate imbalance. Rising ocean temperatures, changing wind patterns and marine currents, and nutrient overload (largely from agricultural runoff and untreated wastewater) have created the perfect breeding ground for its massive proliferation.

This “sargassum belt” stretching from Africa to the Caribbean has grown year after year, fueled by a warmer and more polluted ocean. Thus, sargassum becomes a biological thermometer of climate change: a floating signal that marine systems are under pressure, and that the consequences of global warming are literally washing ashore.

That’s why studying and monitoring sargassum isn’t just a scientific matter: it’s an urgent environmental need to protect both the ocean’s wealth and the health and wellbeing of communities living alongside it. Because this golden traveller, when unchecked, can become an unwelcome visitor.

Effects of sargassum decomposition

The decomposition of sargassum in coastal areas is a complex process involving the degradation of large volumes of organic matter under varying environmental conditions. When sargassum accumulates on beaches and begins to decompose, it triggers microbiological and chemical processes that transform the compounds present in the seaweed. This phenomenon not only alters the physico-chemical composition of the environment but also has direct impacts on public health and local ecological balance.

During decomposition, the macroalgae releases nutrients such as nitrogen and phosphorus, which can promote the eutrophication of nearby water bodies. Furthermore, the accumulation of decomposing sargassum reduces sunlight penetration and decreases dissolved oxygen concentration, affecting marine fauna and flora. Another significant effect is the generation of leachates, liquids rich in organic matter and toxic compounds that can infiltrate the subsoil and contaminate groundwater.

Hydrogen sulphide (H₂S) and ammonia (NH₃) emissions

One of the most noticeable and concerning aspects of sargassum decomposition is the release of foul-smelling gases into the air, mainly hydrogen sulphide (H₂S) and ammonia (NH₃), which not only deteriorate environmental quality but also pose a risk to human health for those living in or visiting affected areas.

During the anaerobic decomposition process of sargassum, bacteria break down organic matter and release H₂S: a colourless gas characterised by its rotten egg smell that is toxic even at low concentrations, potentially causing eye irritation, respiratory problems and, with prolonged exposure, neurological effects. NH₃, on the other hand, is an irritant gas that can affect the respiratory tract and cause discomfort in eyes and throat.

Emissions of these compounds not only create discomfort due to their odour, but can also reach dangerous levels in poorly ventilated areas. The presence of H₂S and NH₃ is one of the main indicators of advanced sargassum decomposition and represents an environmental management challenge and a public health protection issue in affected coastal regions.

Air quality and odour control

The release of gases like H₂S and NH₃ during sargassum decomposition directly impacts coastal air quality. The accumulation of these volatile compounds can exceed recommended limits set by national and international organisations, affecting both residents and tourists. Beyond health risks, the perception of foul odours reduces quality of life and negatively impacts the tourist appeal of Caribbean beaches.

Facing this situation, continuous monitoring of air quality becomes essential to identify critical zones and implement preventive measures. Odour control strategies include sargassum collection, proper waste management, and application of gas neutralisation technologies during decomposition. Comprehensive management of these impacts is crucial to minimise risks and ensure healthy environments for coastal communities.

Kunak projects

At Kunak Technologies we have developed advanced environmental monitoring systems that we implement to measure air quality in areas affected by sargassum decomposition, such as in Guadeloupe, a French Caribbean archipelago, and the coast of Cancún in Mexico. On the ground, our Kunak AIR Pro and AIR Lite devices provide real-time detection of key pollutants, including hydrogen sulphide and ammonia, associated with organic matter decomposition processes on beaches impacted by massive sargassum arrivals. These systems feature high-precision sensors mounted on intelligent cartridges that enable simultaneous measurement of various gases and particles in the atmosphere. The result is reliable and comparable data to reference stations.

The information generated by Kunak sensors becomes a fundamental tool to identify critical areas, define pollution patterns and evaluate the effectiveness of sargassum management and collection strategies. Furthermore, with the obtained data, authorities and environmental managers can implement specific corrective measures, optimise waste management and communicate transparently about specific risks to both permanent and temporary residents. Similarly, the integration of consultation platforms and control panels facilitates advanced data analysis and evidence-based decision making.

Guadeloupe

The sargassum proliferation in the Caribbean archipelago of Guadeloupe has increased concerns about emissions of gases like hydrogen sulphide (H₂S) and ammonia (NH₃), responsible for foul odours and potential public health impacts. To address this challenge, in collaboration with Gwad’Air (Guadeloupe’s ATMO), we have deployed Kunak’s technology as an advanced environmental monitoring solution. The Kunak AIR systems enable precise, real-time measurement of these gases, thanks to their specific H₂S and NH₃ sensors, capable of detecting low concentrations and rapid variations in ambient air.

These devices, equipped with intelligent cartridges and featuring simple calibration, guarantee reliable data even under adverse weather conditions and in remote locations like the Guadeloupe archipelago. The continuous data transmission to the Kunak AIR Cloud platform facilitates analysis and rapid decision-making during high emission episodes, allowing authorities and environmental managers to anticipate risks and implement effective mitigation measures to protect both the population and local ecosystems.

Cancún Coast (Mexico)

In the Cancún area, massive sargassum arrivals have generated recurrent episodes of foul odours associated with seaweed decomposition, primarily due to the release of H₂S and NH₃. The monitoring we conduct with Kunak AIR Pro equipment, in collaboration with our distributor Repmex, has become an essential tool for environmental control and protection of air quality in tourist and residential areas. These systems enable continuous tracking of harmful gas concentrations, thanks to their ability to simultaneously measure up to five pollutants and suspended particles.

The integration of H₂S and NH₃ sensors, combined with remote data management and real-time alerts through Kunak AIR Cloud software, enables a swift response to critical pollution levels. Moreover, the easy deployment, low maintenance and autonomous operation of Kunak devices make them ideal for use in hard-to-reach coastal areas, ensuring constant and precise monitoring. Thus, Kunak monitoring effectively contributes to minimising negative impacts of sargassum on human health, tourism and the natural environment.

Biogas production from sargassum

The production of biogas from sargassum represents a promising biotechnological alternative to utilise this macroalgae, whose massive proliferation is creating significant environmental, economic and public health challenges in tropical and subtropical regions.

“Sargassum is considered a potential resource for biogas production due to its composition, low operating costs and its ability to generate co-products and by-products.” López-González, I.E. 2024.

Sargassum is particularly attractive as raw material due to its high carbohydrate content and low proportion of hard-to-decompose compounds like lignin, which facilitates its degradation and conversion into biogas. The biological process is based on the anaerobic digestion of sargassum, where microorganisms break down the biomass in the absence of oxygen, generating a gas mixture composed mainly of methane (CH₄) and carbon dioxide (CO₂).

Management and treatment strategies

The processing of sargassum for biogas production requires several steps:

Collection and mechanical treatment

To utilise sargassum for biogas production, an efficient collection strategy is required. This step is crucial to prevent its accumulation and decomposition on beaches, where it causes environmental impacts and public health issues. Collection can be carried out both at sea, using specialised barges equipped with capture and shredding systems, and on the coast, using adapted machinery to separate the seaweed from sand and other solid waste. This first step is key to preserving biomass quality and reducing contaminant content before processing.

Drying and stabilisation solutions

Once salt and sand have been removed from the collected sargassum, the process continues with sargassum pre-treatment, which includes drying, shredding and, in some cases, removal of contaminants such as heavy metals, to ensure biogas and by-product quality. Subsequently, the biomass is introduced into biodigesters, where anaerobic digestion produces biogas and a solid residue known as digestate, which can be valorised as biofertiliser, thus promoting a circular economy approach. The generated biogas can be purified through techniques like water scrubbing or selective membranes, obtaining biomethane suitable for injection into natural gas networks or for direct use in energy generation and transport.

The drying and stabilisation of sargassum are crucial stages for its energy valorisation, particularly in processes like biogas production, where excessive moisture can affect anaerobic digestion efficiency and stability. Since sargassum arrives on coasts with high water content, pre-drying significantly reduces biomass weight and volume, facilitating handling, transport and storage, while also improving calorific value and the quality of produced biogas.

Similarly, sargassum stabilisation involves processes to prevent rapid decomposition and release of foul-smelling gases (H₂S, NH₃), thereby facilitating its subsequent use.

Sustainable coastal management plans

At laboratory scale, the process viability has been demonstrated, and there are operational prototypes in Mexico and various Caribbean areas that are producing biogas used as a heat or electricity source. However, its industrial scale-up still faces technical and economic challenges, such as the need for process integration, energy efficiency optimisation, and handling large biomass volumes. The system’s sustainability depends not only on economic and environmental viability, but also on its social integration and the generation of multiple co-products, like biohydrogen, biomethanol and fertilisers, which increase the process’s added value.

In summary, collection and mechanical treatment allow adding value to sargassum as a bioenergy resource, while also being a procedure that contributes to mitigating the negative effects of its massive arrival, integrating sustainable and technologically viable solutions for affected regions. Meanwhile, drying and stabilisation enhance its potential for energy utilisation as renewable energy and biofertilisers.

Frequently asked questions about sargassum

How does sargassum affect air quality?

When sargassum reaches coastal areas, it decomposes releasing compounds such as hydrogen sulphide (H₂S) and ammonia (NH₃), gases that negatively affect air quality. Initially, these emissions produce unpleasant odours but, at high concentrations, they can cause eye, nose and throat irritation, as well as respiratory problems, particularly in vulnerable individuals. Furthermore, prolonged exposure to high levels of H₂S may pose risks to public health and wellbeing in coastal communities.

In summary, sargassum decomposition on beaches represents not only an environmental and tourism issue that affects quality of life, but also a public health challenge due to the release of harmful gases that deteriorate air quality.

What sensors are needed on sargassum-affected beaches?

For efficient and sustainable management of coastal sargassum, it’s necessary to timely detect emissions produced during its aerobic decomposition. This requires implementing a sensor network to accurately monitor in real-time environmental variables affecting air quality. The most relevant sensors include: suspended particulate matter (PM1, PM2.5, PM10) and pollutant gases like ammonia (NH₃) and hydrogen sulphide (H₂S), key parameters to assess environmental impact and user exposure near sargassum accumulations.

How are H₂S emissions from sargassum quantified?

Quantification of hydrogen sulphide (H₂S) emissions in air is performed using standardised techniques ensuring precision and traceability. The most common methods are:

• Electrochemical sensors: real-time measurement with high sensitivity of H₂S adsorbed on the sensor surface, generating an electrical current proportional to gas concentration.
• Passive samplers: method requiring prior planning, based on adsorbent cartridges impregnated with zinc acetate or other suitable reagent. H₂S from air is fixed on the cartridge and later extracted in laboratory for analysis. The resulting compound is quantified through visible spectrophotometry.
• Solution absorption systems: Air is passed through an alkaline solution (cadmium hydroxide or zinc acetate), where H₂S is retained as a precipitate. The captured sulphide is determined by spectrophotometry or iodometric titration.

In all cases, H₂S concentration is calculated considering the sampled air volume, environmental conditions and analytical system calibration. These methods are regulated by specific technical standards to ensure result reliability.

Can biogas from sargassum mitigate odours?

Utilising sargassum for biogas production can significantly contribute to mitigating unpleasant odours associated with its beach decomposition. The anaerobic digestion process transforms sargassum biomass into biogas within closed reactors, preventing direct release of volatile compounds like hydrogen sulphide (H₂S) and ammonia (NH₃), main culprits of the malodour escaping into air.

By processing sargassum before it decomposes on sand, emission of foul-smelling gases to the environment is reduced. Moreover, biogas plants typically incorporate odour control systems like biofiltration, minimising odours during organic waste treatment. This not only improves environmental quality of the area, but also transforms a problematic waste into a renewable energy source and biofertilisers.

When floating in the ocean, sargassum is a source of food, shelter and reproduction for marine life, but on the shoreline it poses a threat to coastal ecosystems.

What role does sargassum play in climate change?

The massive proliferation of sargassum is closely linked to climate change due to rising ocean temperatures, changes in marine currents and increased nutrient levels in water (from human activities and pollution).

In turn, the excessive accumulation of sargassum invading coastal regions like the Caribbean creates negative effects that exacerbate climate change:

• Disruption of marine ecosystem dynamics: by covering reefs and seagrass beds, sargassum prevents photosynthesis, reduces dissolved oxygen and affects biodiversity.
• Greenhouse gas emissions: during beach decomposition, sargassum releases gases like ammonia (NH₃), methane (CH₄) and hydrogen sulphide (H₂S), contributing to global warming and affecting air quality.
• Ecological cycle disruption: excess biomass modifies trophic chains and can cause anoxia (oxygen depletion) in coastal ecosystems.
• Climate feedback loop: massive sargassum proliferation is a phenomenon worsened by climate change that in turn can intensify some of its negative effects on ecosystems and atmosphere.

In summary, sargassum serves both as an indicator of climate change effects on oceans and as a new environmental challenge, whose sustainable management and utilisation are key to mitigating its impact on climate and coastal ecosystems.

Conclusion

The sargassum phenomenon, far from being solely an environmental challenge, also represents an opportunity for innovation and the promotion of sustainability in affected coastal regions. The transformation of sargassum into biogas and other valuable products demonstrates how science and technology can turn a problem into a source of renewable energy and local development. However, for these solutions to be truly effective and safe, continuous monitoring of air quality becomes essential.

Detection of gases and foul odours enables risk anticipation, public health protection and ensures that management and valorisation processes of sargassum are conducted responsibly. Real-time environmental monitoring not only helps mitigate negative impacts of sargassum decomposition but also strengthens resilience of coastal communities and preserves quality of life and tourist appeal of these areas.

Ultimately, the comprehensive approach to sargassum, combining efficient management, energy valorisation and environmental monitoring, charts the course towards a cleaner, safer and more sustainable future for affected coastlines. Investing in innovation and environmental vigilance is undoubtedly the best strategy to transform the sargassum challenge into a progress opportunity grounded in sustainability.

References

• Mengqiu Wang et al.,The great Atlantic Sargassum belt. Science365, 83-87(2019). https://www.science.org/doi/full/10.1126/science.aaw7912
• Martínez-González, G. Sargazo: la irrupción atípica de un ecosistema milenario. Salud pública Méx vol.61 no.5 Cuernavaca sep./oct. 2019 Epub 07-Ago-2020. https://doi.org/10.21149/10838
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• López González, I. E., Lucho Constantino , C. A. ., & López Pérez, P. A. (2023). La invasión de sargazo: de un problema ambiental a un área de oportunidad. Tópicos De Investigación En Ciencias De La Tierra Y Materiales, 10(10), 18–26. https://doi.org/10.29057/aactm.v10i10.11236
• Araiza, M. J., Balandrano, A. L. y Hernández, J. P. (2019). Alga Sargazo como posible fuente de materias primas para la extracción de carotenoides. Memorias del Concurso Lasallista de Investigación, Desarrollo e Innovación, 6(2), 25-28. https://repositorio.lasalle.mx/handle/lasalle/1994