Sheet 5: The collection of Sargassum on land
Types of collection methods
The major problem of Sargassum events is simultaneously environmental, sanitary and economic. Since 2011, the massive strandings weaken beach ecosystems and tourist activities; they are also, however, a serious public health issue. Indeed, after about 72 hours of the seaweed drifting ashore, harmful and corrosive decomposition gases get released (hydrogen sulfide, methane and ammonia gas). There are of course prevention tools, but the removal of the washed up Sargassum still remains unavoidable in most territories.
Green brigades are regularly at work on the beaches, at the initiative of citizens’ associations and institutions. Their environmental impact is quite low but there’s a high health risk due to potential exposure of collector teams to the decomposition gases, not to mention the difficulty of the task. In addition to manual collection, many mechanical collection techniques have been developed.
- Cane Loaders are frequently used. Equipped with a mobile hydraulic arm, they allow the removal of a large quantity of algae. Their collection results are thus high and their wheels allow them to reach many places without risking siltation or sloughing. (See picture 1)
- Mechanical shovels are the most common devices used for land-based collection. They perform well regardless of the amount of beached seaweed and have a long range. On the other hand, they must be combined with skips as these shovels do not have storage capacity. (See picture 2)
- Trailed rakes are machines with good mobility which allow a so-called “clean” collection, with a homogeneous visual rendering. The storage capacity is very limited however, and the seaweed accumulation must be recent. (See picture 3)
- Self-propelled rakes also have a high collection output, with a capacity of up to 150 cubic meters per hour. Their mobility is good and the harvester arm of the machine (similar to a combine harvester) collects little sand. However, the device requires an easy to access and wide beach to be able to operate.
Advantages and disadvantages
In the face of the massive Sargassum events that happen almost every year in the Caribbean, mechanical harvesting is a formidable ally. Tailored to each territory’s specifications, mechanical collections carried out in time, i.e. within three days of the Sargassum washing up on land, allow beach cleans up, and relieve the inhabitants of harmful decomposing heaps, especially tourism professionals.
These devices have two conditions of use: they must be perfectly adapted to the geography of the coastline and to the strandings.
Their major disadvantage is the deterioration of the soil and the acceleration of its erosion. Large machines compact the soil, while others remove astronomical quantities of sand. Combined, these two factors greatly degrade the coastline, especially if they are repeatedly and regularly used. The strandings are not regular but random, as well as generally very intensive, which can also hinder the harvesting methods.
Once harvested, the seaweed is usually spread on a layer about ten centimeters thick on backshore sites. Even if still too few, these dedicated sites are the only safe way to store decomposing Sargassum without any sanitary or environmental damage.
Who sets up the harvest initiatives?
In France, affected municipality mayors are responsible for beach cleanups. . It is part of regular l police powers to make the decision to initiate clean-up actions, in the name of public health. To support them, prefectures and regions regularly inform the mayors and provide technical assistance, as well as financial and human resources to the municipalities. They are working to implement a long-term policy to deal with this recurrent issue.
Aware of the need for a strong response to the Sargassum events, the Minister in charge of Overseas in France announced after his trip to the Antilles last August, the forthcoming creation of a “public anti-sargassum service” which will centralize all the needs, means, measures and responsibilities. This will strongly reinforce the operational response and should be implemented l within 2022.
For example, in Mexico and the Dominican Republic, the collection of Sargassum is mainly managed by hotels undertaking beach cleanups to save tourism, their main resource. But given the magnitude of the phenomenon, Mexico has released nearly 14 million euros from its national fund for natural disasters, to help with cleaning operations. The Mexican government is beginning to invest in larger scale collections carried out by the Secretariat for the Environment and for Natural Resources.
Finally, collaboration with scientific networks is essential, especially since the development of tracking techniques with satellite observation systems, that provide in real time the development stages of Sargassum in the ocean, and thus allow the anticipation of the events. It is truly a collective effort.
Impacts of Sargassum collection
Sargassum must be collected to avoid problems related to its decomposition. However, whichever method is used, it entails risks. The green brigades, regularly at work in a major part of the Caribbean are very exposed to gas emissions. Collection machines can limit this harmful exposure, but other issues arise. When acting on the beaches, the machines remove part of the sand while retrieve the Sargassum at the same time, aggravating beach erosion. Also, the comings and goings can degrade nesting sites of marine turtles, which are very sensitive sites for the reproduction of the concerned species. The recovery techniques must be scrupulously selected according to criteria of protection of surrounding fauna and flora.
Sources
Nationalgeographic.co.uk
Agence Française de Développement (AFD)
Agencia Nacional de Seguridad Industrial y de Protección al Medio Ambiente (Mexique)
Rapport des Directives techniques et de gestion pour la réponse à la contingence
des sargasses dans les Caraïbes et le Golfe du Mexique (gouvernement des États-Unis du Mexique)
www.gob.mx
martinique.gouv.fr
Marine MARIE-CHARLOTTE, Référente entreprise Pôle déchets et économie circulaire
Ingénieure – collecte et valorisation des algues sargasses
ADEME Guadeloupe – Martinique
France 24