Low-Pressure and Sahara Dust from 7/27 to 7/28

For the last two days, a low-pressure zone and a layer of sand (dust) from the Sahara have been interacting in a harmonious dance.

Goes16 image for July 27 at 18:00 UTC
source : https://www.star.nesdis.noaa.gov/GOES/sector.php?sat=G16&sector=taw
Forecast of total Sahara dust in the air column of the SKIRON model for July 27 at 18:00 UTC
source : https://forecast.uoa.gr/en/forecast-maps/dust/north-atlantic

The Sahara dust limits the development of cloud structures in the low-pressure area and its convective movements, with progressive weathering visible on the animation. The depression favours the transport of the layer of dust towards North America.

The presence of Saharan dust in the atmosphere of the North Atlantic has many negative effects on health, in particular by reducing air quality with the presence of fine particles and bacteria. It also impacts the environment with a strong greenhouse effect which favours heat waves and drying of the air which modifies the frequency and the quantity of rainfall.

Conversely, the presence of particles modifies atmospheric dynamics, in particular cyclogenesis. In an atmosphere overloaded with sand, convection is limited or even stopped, cyclones have less favourable conditions to form.

The presence of large quantities of sand from the Sahara modifies our understanding of meteorology in the North Atlantic but also of the current and future climate. Years with large concentrations of Sahara dust disturb our perception of climate change.

Animation of Goes16 satellite images from Wednesday, July 27 to Thursday, July 28, 2022

National French Air Quality Day (9/18/2019)

France is celebrating its National Air Quality Day on 18 September under the auspices of the Ministry of Ecological and Solidarity Transition.

The quality of the air to a minimum of three essential elements :

  • we live permanently in the atmosphere, apart from short passages in liquid media, between 0 and 15km above the surface of the water (atmospheric boundary layer), our skin and most of our mucous membranes are in permanent contact with the air and these compounds;
  • we must inhale at least 10 to 30 thousand litres of air in a day to produce the energy needed for life using available oxygen;
  • High concentration and diversity of fine particles and airborne molecules in air mostly composed by nitrogen (78%), oxygen (21%) and other gas.
Sketch of Atmospheric Boundary Layer

Human activities, geological (volcanism), meteorological (sand haze) and biological (fermentation of wet packed algae) in amount of other can perturb air quality over more or less long period.
In order to qualitatively and quantitatively assess quality of the air in which we move and we breathe, index have been put in place.
It is based on the determination of a value or a colour indicating the quality compared to a normal air or the risk related to particular particles or molecules.

In front of the considerable number of particle, the indices group several sees all the pollutants.
The atmospheric index (ATMO index) used in France takes into account Ozone (O3), Sulphur dioxide (SO2), Nitrogen dioxide NO2 and PM10 (particle up to 10 micrometres in diameter). Future evolutions predict the use of PM25.

Value of pollutants concentration used to compute ATMO Index

The information of the air quality must be correlated with our behaviour.
Placed in a rubbish bin all aware human being will seek to extract itself quickly, except special mission. An atmosphere of poor quality should be avoided.

It is therefore unfortunate that the information on atmospheric indices is not clearly required to avoid immediate risk behaviours such as smoky plumes from charcoal smokers (a large producer of fine particles) or run along roads and motorways at the end of the day at busy times.
Talking about situations that are not palpable enough (i.e., not visible or too far away) does not allow the conceptualization of pollution, makes the notion too abstract and does not allow the acceptance of behaviour that has a strong impact on lifestyles and the economy. But ensures a better, healthier, more peaceful and less violent life.

Information, especially the one which was worked to produce index, means something and must be understood and accepted. TCGNRG participates in this understanding and awareness with the help of adapted training, advices and atmospheric modelling and human behaviour, do not hesitate to contact us for more information.

Atmospheric Index at worldwide scale  : https://waqi.info/fr/

Remarkable Sites and Stranding of Sargassum : the dangerous Door of Hell (Porte d’Enfer)

Sargassum (Sargassum fluitans and natans) have been the main species of visible pelagic floating algae since 2011, stranded on the Caribbean coast. Their stranding are strongly influenced by sea currents and configuration of the coastlines (human making included). Arrival of dense or scattered rafts causes ecological disturbances because of the quantity of organic matter (composed by carbon C, hydrogen H, Oxygen O, Nitrogen N, Phosphorus P and sulphur S) which it brings and the speed of stranding. Rafts of Sargassum move under effects of wind, waves, sea currents and tide. They are home to a wide variety of plankton, fish and shellfish colonies. Sargassum oxygen needs coupled with the poor quality of shallow coastal waters cause asphyxiation and anoxic decomposition -fermentation- generating toxic gases such as hydrogen sulphide (H2S), ammonia (NH3), thiols (R -SH) but also greenhouse gases such as methane (CH4).

These processes of decomposition without oxygen are the subject of many controversies, health, economic and ecological crises. The solutions adopted in the French West Indies are mechanized pickups and emergency dredging, causing extensive destruction of beaches and harbours. The concentrations of two of the most toxic gases (H2S & NH3) are controlled so that populations can be evacuated if there is a risk. Despite measured rates of more than 10ppm H2S (Limit Value-Short-Term Exposure VLCT) no evacuation has been done since 2011.

Remarkable sites

Many beaches are considered to be remarkable sites. They attract many visitors and constitute the tourism potential of our developing countries. The presence of sargassum causes degradation of bathing water quality, landscape potential and air quality. These sites, which are highlighted and exploited by the tourism industry, offer significant profitability due to the lack of maintenance required to date.

The management of these sites is mostly complex and is pooling of many stakeholders, but this can not in any case justify their long-term pollution.

Porte-d-Enfer Beach

Map describing the configuration of Porte-d’Enfer beach and creek

The range of Porte-d-Enfer (16.48 ° N, 61.44 ° W) in Anse-Bertrand (known as the Trou à Man Coco) has been known for the last years of numerous massive sargassum stranding massive (see photo) provoking the fact of its geographical configuration the partial or complete blockage of the creek and a thick layer (more than 15 cm in height) of decomposed compacted algae. Under favourable conditions the production of bio-gases takes place on the whole column of wet Sargassum. It can be observed by the presence of bubbles (under columns shape) or by the dispersion of biofilms of sulpho-reducing bacteria greyish colour on the surface.

In these cases of mass stranding (example September 2018, January and July 2019) swimming is impossible and dangerous for health. The presence in the zone (up to 500m) of the basin is risky because the production of biogas is important, non-homogeneous and highly variable. The temperature of the water favours the production of hydrogen sulphide (H2S) and ammonia (NH3) during the sunniest hours of the day (9am-5pm) and therefore the risk during periods of affluence. Time variations such as wind failure or pressure drops favour high concentrations.

Cleaning – mitigating the effects of stranding

The site is naturally cleaned during the phases of strong increase of swell which warranty a ebb of the organic matter and the re-oxygenation of the basin.

The rainy season lets in the mouth which encourages the ebb and feeding of the sand beach.

The mechanized methods of collection are put in place by the municipality and the services of the French State are only for small quantity stranded algae. An attempt to set up a floating dam was a failure. Collection with crawler excavator help to strongly damaged the beach and nearby roads as well as pollution from petroleum products (see image of a tractor-excavator).

Manual cleaning stay the more efficient and ecologically respectful of the site, but unfortunately it is not set up.

Protection of populations

There have been 22 surveys of H2S and NH3 since 2018 with 15-minute portable measurements. No measures have indicated overtaking of the limit values ​​for exposure, the maximum values ​​recorded are 1.9 ppm for H2S (24/04/2018) and 36 ppm for NH3 (28/05/2018). We can question the validity of these measures when we know that the potential area of ​​biogas production in case of total coverage is 14,000m2 while stranding areas producing biogas is rarely greater than 5,000m2 in Guadeloupe (case of the fishing port of Capesterre-Belle-Eau). Comments made by users in the area confirm this question.

Nevertheless, these measurements are much higher than the chronic and sub-chronic exposure limits of 0.02 ppm for H2S and 0.714 ppm for NH3 [HCSP 08/06/2018]. The sub-chronic exhibition is an exhibition of one to several months which was the case between March and July 2018 according to the statements published by the ARS Guadeloupe (i.e., Regional Health Agency).

Two last values of H2S measured Thursday, July 18, 2019 and Monday, August 12th 2019 reach respectively 5.2 and 4.2 pm which are alert values (>5 ppm) for workers in French Labour Law.

No signboard is visible to alert passers-by (and tourists) of the health risks during periods of beaching and fumes of toxic gas. Without knowledge of the site, many passers-by, children and the elderly, admire the stranding without taking into account the serious health risk.

In the case of the crisis of green algae (Ulva aka sea-lettuce) of Brittany it took nearly ten years, dead wild boars, horses, dogs and several joggers before appearing on the beaches of official information boards.

It is therefore urgent to recognize that human health is worth more than the reputation (or image) of a tourist site. It is essential that the authorities protect people and tourists by intelligently informing about the non-permanent risk of stranding sargassum. This is particularly true for territories that rely on sustainable tourism development.

The Caribbean Geophysics and Numerical Research Group (TCGNRG) remains at your disposal to assist you (communities, collection companies and individuals) to secure the best places taking into account environmental conditions.

Last update (9/07/2019)

Since 20 August 2019 a municipal decree (see photo above) prohibits all nautical activities. This first plain decision of common sense is to be commended. But despite all the poor visibility of the display and the lack of pictogram for people who do not read the French prevents to really warn the risks associated with the presence of anoxic decomposing (fermentation) seaweed for more than two months.

At the moment the photos were taken an under water spear fisherman was coming out of the water without noticing the posters

Guadeloupe Sargassum 2019 : International event


From October 23 to 26, Guadeloupe organizes an event on Sargasso at the regional level (America – Caribbean). At eight (8) weeks of this event let’s make a point of situation.

It should be noted that at least two events have already occurred in 2019 on the subject in the Caribbean area :


The limited information available nevertheless allows to know that there will be a trade fair Sargass’Expo aiming to gather exhibitors around of (in order of importance)

  • remote sensing – prevision;
  • collection;
  • recovery;
  • storage;
  • and health surveillance.

We may be surprised that the sanitary surveillance is thus misplaced, knowing that the main impact of sargassum is first sanitary with olfactory risks (potential complete loss of smell), ocular, cardiac, respiratory, intestinal, etc. In 2018 in Martinique in 31 weeks more than 8500 consultations related to sargassum emanation were counted by the network of sentinel doctors.

The second event is the international scientific conference Sargassum2019. No information is currently available, only the steering committee was presented in April 15, 2019 . The lack of information (i.e. call for communication) and detailed program questions about its progress and the ability to produce useful information for people (residents, schoolchildren, workers, tourists, etc.) and economic actors impacted (fishermen, restaurateur, hotel keeper, sailing sector).

The third event which is Off of sargassum 2019 is a Caribbean Conference, from 19 to 22 October 2019. It is part of the Caribbean Science and Innovation Meeting. It will benefit the presence of some researchers on topics such as Biodiversity, Health, Natural Hazards, Renewable Energy and the Circular Economy. The latter seems much better organized, may produce very interesting results.
Deadline for registration is 16 September 2019 Contact the University of Antilles (Research Office).

TCGNRG wonders about the usefulness of using public funds to communicate on a subject where very little to any has been made since 2014. The methods used at this time are re-employment, most often come from construction industry in opposition with concepts of nature protection and biodiversity. The common sense might have been to wait until 2020 to organize a real cross-cutting conference on the topic on at least a week, giving scientists time to be really prepared.

Nevertheless, TCGNRG offer to individuals, institutions and government our services to assess, analyse or comment on information, methods and equipment will be presented during this event.

Feel free to contact our service : contact@tcgnrg.com

Pollution aux eaux usées à Sarrault Petit-Bourg

Station d’épuration de Sarrault

En Guadeloupe, depuis plusieurs mois, voir années, de nombreuses stations d’épuration (très petites, petites ou grandes) sont en dysfonctionnement voir en panne. Elles sont à l’arrêt ou ne fonctionnent que quelques jours par mois. Les eaux usées (c-a-d égout, eau pluviale) sont rejetées sans traitement sur les côtes. Ces rejets peuvent provoquer des dépassements des seuils de pollution durant plusieurs jours.

Les eaux côtières représentent des quantités peu profonde mais capable de diluer la pollution physique (température, particules), chimique (détergent, antibiotique) et biologique (matière organique, bactérie) à l’aide des courants marins et des vagues. L’absence de grandes marées dans les Petites-Antilles limite la capacité des zones côtières à faire tampon aux rejets.

La pollution provoque la diminution de la quantité d’oxygène dissout avec de l’eutrophisation, particulièrement pendant les périodes chaudes (février-août). Sans oxygène les poissons et les herbes marines meurent asphyxiés et la matière organique c’est-à-dire les feuilles, le bois mort, les algues, la matière fécale vont se décomposer en suivant des filières anaérobiques produisant des gaz tel que le méthane (CH4), l’ammoniaque (NH3), le sulfure d’hydrogène (H2S) ou les mercaptans avec des effets sur la santé humaine et l’environnement. Le méthane est un gaz à effet de serre 25 fois plus stable que le dioxyde de carbone (CO2) et le sulfure d’hydrogène provoque des troubles respiratoires et sensoriels (perte de l’odorat) voir la mort en cas de forte exposition. On parle de décès probable pour des concentrations à plus de 500ppm durant quelques minutes ou des problèmes cardiaques avec une exposition quotidienne de l’ordre de 0,05ppm).

Le cas de la station de la place Sarrault dans la commune de Petit-Bourg (voir carte) est inquiétant car à sa panne est associée à des arrivages de sargasses, la présence des effluents d’une seconde usine de traitement d’eaux usées en dysfonctionnement (depuis la Ravine Onze Heure), la présence de zones de mangrove concentratrices de matière organique et la présence de nombreux herbiers marins qui perdent leurs feuilles à chaque forte houle.

Dans le centre de Petit-Bourg, les effets de la panne de la station d’épuration sont surtout olfactifs avec l’odeur des eaux usées associés à la décomposition accélérée des sargasses bloquées et déchiquetées par les vagues sur la côte, dans les zones de faibles profondeurs.

Station d’épuration de Sarrault

Les taux de gaz comme l’ammoniac et le sulfure d’hydrogène sont fluctuants du fait l’instabilité du vent à la côte et des températures de l’eau de mer et des effluents. Ils dépassent souvent les limites utilisées pour la sécurité au travail.

Les autres effets sont liés à la qualité de l’eau et la présence de bactéries et de toxines. Les bancs sargasse sont des écosystèmes autonomes autour desquelles de nombreuses espèces de poissons prolifèrent attirant les pêcheurs amateurs directement dans le panache des effluents. Le mode de cuisson du poisson aux Antilles généralement à haute température (c-a-d friture, grillade, bouillon) limite les risques d’intoxication mais ne l’annule pas.

Il faut espérer que des mesures seront prises pour assurer la maintenance des équipements environnementaux essentiels et garantir la santé publique. Ou au moins informer les populations, sur les risques et conduites à tenir voir interdit la pêche à la ligne dans cette zone.


#Pollution #Eutrophisation #EauxUsées #Sarrault #PetitBourg #Guadeloupe

Waste water pollution at Sarrault Petit-Bourg

In Guadeloupe, for several months, see years, many treatment plants (micro, small or large) are dysfunctional or broken down. They are stopped or only work a few days a month. Wastewater (i.e., sewer, rainwater) is rejected without treatment at the coast. These discharges can cause pollution , threshold violation can occur for several days.

Coastal waters represent amounts of shallow water that can dilute physical pollution (temperature, particles), chemical (detergent, antibiotic) and biological (organic matter, bacteria) using sea currents and waves motion. The lack of high tides in the Lesser Antilles limits the ability of coastal areas to buffers discards.

Pollution causes a decrease in amount of dissolved oxygen with eutrophication, especially during warm periods (February-August). Without oxygen fish and seagrass die asphyxiated and organic matter that is to say, leaves, dead wood, algae, faecal matter will decompose following anaerobic pathways producing gases such as methane ( CH4), ammonia (NH3), hydrogen sulphide (H2S) or mercaptan with effects on human health and environment.
Methane is a greenhouse gas 25 times more stable than carbon dioxide (CO2) and hydrogen sulphide causes respiratory and sensory disorders (loss of smell) or death in case of high exposure. Probable deaths are reported for concentrations greater than 500 ppm for an exposure of few minutes or heart problems with a daily exposure of around 0.05 ppm.

The case of the station of Sarrault Place at down-town Petit-Bourg (see map) is worrying because its failure is associated with sargassum arrivals, presence of effluents from a second waste water treatment plant malfunctioning (from Ravine Onze Heure), presence of mangrove areas concentrating organic matter and presence of many seagrass beds that lose their leaves with each big swell.

At Petit-Bourg down town , effects of the wastewater treatment plant are mainly olfactory with the smell of wastewater associated with the accelerated decomposition of sargassum blocked and shredded by waves on the coast, in shallow areas.

Gas rates such as ammonia and hydrogen sulphide are fluctuating due to instability of the wind at the coast and seawater and effluent temperatures. They often exceed the limits used by labour law to define safe spaces.

Other effects are related to water quality and the presence of bacteria and toxins. Sargassum raft are autonomous ecosystems around which many species of fish proliferate attracting amateur fishermen directly into the effluent plume. The method of cooking fish in the West Indies generally at high temperature (i.e., frying, grilling, broth) limits the risk of intoxication but does not cancel it.

It is to be hoped that measures will be taken to maintain essential environmental equipment and to ensure public health. Or at least inform the people, about risks and behaviours to hold and if needs ban angling in that area.

#Pollution #Eutrophication #WasteWater #Sarrault #PetitBourg #Guadeloupe


Sargassum on West coast of Martinique

Illustration 1 : Oceanographic and Meteorological data for beginning of June 2019

June 1st and 2nd 2019 beaching of sargassum were observed on the Caribbean coast of Martinique (Fort-de-France, Schoelcher). This type of beaching has been rare since 2011 and the over-abundance of drifting sargassum rafts in the North Atlantic and the Caribbean Sea.

Each year one or two beaching are observed on this coast from Fort-de-France to the Prêcheur. They take place only under favourable oceanographic and meteorological conditions.

The breakdown of the Trade Wind felt after the passage of a tropical wave favoured the action of the Southwest currents. Sargassum beds generally extend northward along the Caribbean coast pushed by the East wind and sea currents. This Sunday June 2nd pelagic algae were trapped by the shallow waters of creeks and bays.

In two days of presence, the decomposition of algae forced their collection on the small artificialized Cove of Batelière at Schoelcher (500 on 200m), due to emanation of di-oxyde of sulphide and ammonia (SO2, NH3). This rapid decomposition can obviously be explained by the age of the rafts that went aground. But also by relatively high water temperatures (27.9-28.5 ° C) which decreases dissolved oxygen concentrations in the water of the order of 1 to 2 mg per litre and therefore anoxic decomposition (i.e., without oxygen ).

The quality of the water is another element to take into account. Only the quality for bathing is continuously monitoring. The last map, published by the Regional Office of Health (ARS), available from (illustration 2) indicates for the beach of Batelière a ‘good’ quality. This measure is misleading because it indicates only the frequency of the presence of certain bacteria of faecal origin but not the capacity of the ecosystem to withstand anthropogenic or natural pollution.

Illustration 2 : Map of Water Quality for Martinique’s bathing of 2018

The runoff water related to this tropical wave (give a name) to degrade the quality of the water, on the biological and physiochemical point, making this area more sensitive to the presence of large amount of living organism.

It is essential to take better account of bathing water quality in the determination of areas exposed to the risk of decomposition pollution of seaweed-type algae. To better prepare the pickup procedures and necessary equipment.

TCGNRG can help you design better risk maps for over-concentration of seaweed based on environmental conditions and better organised your organic matter collection and your recovery procedures. Do not hesitate to contact us

Publication on analyse of Ozone (O3) and Nitrogen Oxide (NOx) concentration in atmosphere

Map of the study area Plocoste et al. 2018

TCGNRG recently published in collaboration with the University of the Antilles (Campus of Guadeloupe) an article on air quality in the center of the archipelago of Guadeloupe

This paper presents a study on ground-level ozone (O3), nitrogen oxides (NOx = NO + NO2) concentrations, and their variabilities in the ambient air of three sites of a tropical archipelago that is moderately urbanized. Statistical analysis was performed on a quite complete (>80%) set of 5 years of measurements (2008–2012). There are few studies on those pollutants and their seasonal behavior in the Caribbean area, where pollution level and cities configuration are different from megacities. Analyses are focused on pollutant variations at the scale of the day, the week, and the seasons, using hourly data.
The observations show that NO x concentrations are more elevated during the wet season, whereas O3 concentrations are higher in the dry season. Amplitudes of ozone cycles are strongly influenced by meteorological conditions (temperature, global radiation, and wind speed) and prevailing levels of NOx.
An ozone weekend effect is detected with the highest amplitude in the city, where anthropogenic activity is the lowest during the weekend. Due to the nature and the origin of pollutants, NO x shows higher variability than O 3 in the time series. Our results evince the need for continuous measurements of volatile organic compounds (VOCs) in order to better quantify their contribution in O3 formation in an insular context where numerous natural sources have been identified.

Statistical analyses of observed NOx and O3 concentrations for 5 years for a typical low industrialized site of the Caribbean area have been done. Air quality for those components is correct based on the standards of the World Health Organization, pollutant source spatial distributions, and level of industrialization. Observations show the same patterns as in megacities but also a strong impact of weather conditions and road traffic. Behaviors of O3 cannot be fully explained without VOCs monitoring. Localization and type of AQS should be reconsidered to improve the accuracy of concentrations of the pollutant and better understand their behaviors.

Where to get it
The article is available on the website of the editor Taylor & Francis
For more information please contact us at : contact@tcgnrg.com

Unprepared sargassum algae collection

Many cities impacted by brown seaweed stranding (Sargassum Fluitans and Sargassum Natans) try to react to the various consequences of this presence of organic matter, living or dead, in large quantity. The effects, although many times reproduced, remain poorly understood and uncontrolled. They range from the simple presence of living floating algae which will modify the landscape, prevent swimming and / or navigation to the decomposition of packed algae on a beach or rip rap in anoxia or anaerobic (lack or total absence of oxygen). This latter case causes multiplication of micro-organisms specialized in usage of nitrogen or sulphur to produce energy. It causes the emission of biogas such as hydrogen sulphide (H2S) and ammonia (NH3).

Figure 1 [english]
Fig. 1: View of the port of Goyave from one of the docks

These two gases are only a small part of the gases emitted during the anaerobic decomposition of these algae, wrongly considered as toxic. This pseudo-toxicity only depends on the fermentation conditions caused by human activities. The risks related to exposure over long periods to concentrations below the alert threshold, 5 ppm for H2S revised to 1 ppm by the High Council for Public Health (HCSP) on 08/06/2018, is undoubtedly dangerous for respiratory tract and general health. This is for people living or working near these emanations from few meters to several kilometres.

Collection, cleaning or bio-redemption of sargassum algae or their waste can’t be imagined using conventional mechanized methods due to the nature of the seaweed: small; charged with sea water and friable in the ageing phase. Beaching area, coastline, mangrove swamp, bay are at the scales of Caribbean island always complex and ecologically sensitive to modifications. Usage of a power shovel on an un-stabilized soils compresses them and modifies water flows rendering these soils at best unusable for a short period and at worst subject to erosion.

There is no point picking up algae that will leave with the next tide or to move sand, rock and concrete to shift algae from an area. The preparation of any cleaning-collection-rehabilitation operations is essential. It must include the adaptation of harvesting methods, the respect of the areas to be treated, the ability to move, store and process the organic or mineral matter collected, while ensuring the safety and health of the people involved and the residents.

The case of the municipality of Goyave (in Guadeloupe, FWI, [16.13N, 61.57W]) is a good example. Subject for several years (2014-2018) to arrivals of seaweed it remains unprepared for pickup operations in its small port . The collection area is a small fisherman port located in a highly anthropized mangrove swamp area which is used as outlet for the wastewater and rainfall water network (Fig. 1). The objective here is not to throw the stone at a particular town, because few communities in the world are truly prepared to respond to non-permanent solicitations such as water, air or soil pollution.

Figure 2 [english]
Fig. 2: Photograph of the mini hydraulic excavator used in the port of Goyave on August 8-9, 2018 with a modified bucket damaged

The recent pickup operations of August 8th & 9th 2018 shows that well. The hydraulic crawler excavator used although its smallness is not adapted to the site and causes damage (Fig. 2). The lack of sargassum on the water surface, in phase of aging these pelagic algae lose their floats (pneumatophore) and sink, pushed to clean the bottom of the port basin. The non-adaptation of the bucket to scratch the rocky bottom damaged it (Fig. 2). The mud a mixture of clay, organic and plastic materials as well as hydrocarbons is stored without precaution on a mangrove swamp area (Fig. 3) and in an unsupervised area initially reserved for sargassum spreading (Fig. 4) . The lack of markup on the building site and the lack of information boards pose questions for the safety of workers and passerby. Presence of biofouling, sargassum decomposition sludge and non-dry mud can emit biogas and locally increase the atmospheric concentrations of H2S or NH3 (Fig. 5).

Figure 3 [english]
Fig. 3: Photograph of a pile of mud stored on old mangrove swamp area near the port of Goyave

This clean-up operation certainly had no effect on air pollution levels, main biogas production areas was not in this area. But it will allow a better quality of the waters of the port and therefore reduce impact of algae decomposition. The environmental cost: degradation of public goods, soil and water pollution is prohibitive compared to the benefits.

Figure 4 [english]
Fig. 4: Photograph of Goyave port mud spreaded on the backside of the beach of Viard

Stranding of sargassum algae should push for better organization and management of environmental work. The complexity of the places and systems concerned, their bio-diversity level imposes a great rigour on the actions that will be conducted there. TCGNRG remains at your disposal to help you set up sustainable devices adapted to the management and treatment of beaching of algae, organic matter or plastic.

Figure 5 [english]
Fig. 5: Photograph showing soiling on one of the docks of the port of Goyave after cleaning operation

La biodégradation des sargasses produit de la boue de décomposition

La biodégradation des algues sargasses est un procédé micro-biologique complexe qui est fortement dépendant des conditions environnementales. La décomposition dans une zone d’activité humaine peut être gênante olfactivement et même devenir toxique en fonction des émissions de sulfure d’hydrogène, d’ammoniaque et de mercaptan entre autres. Les variations de la force et de la direction du vent, de la pression atmosphérique à la surface, des températures de l’air et de l’eau peuvent modifier rapidement et pour des temps plus ou moins longs les concentrations de biogaz. Le transport éolien toujours présent peut advecter les gaz sur de longues distances et intoxiquer un grand nombre de personnes.

Cette biodégradation qui se produit le plus souvent en milieu aquatique (ou fortement humide) peut passer par des phases de fermentation et de putréfaction qui modifient la qualité des eaux avec des effets plus ou moins localisés. Dans un port ou une zone semi-fermée avec de faibles échange de masse d’eau les variations d’acidité et de concentration d’oxygène dissous peuvent impacter le biotop et supprimer toutes traces de vie. Il est donc essentiel de suivre l’évolution de la qualité des eaux et des processus de dégradation.

Photo du port polyvalent de la Vinaigrerie à Petit-Bourg, Guadeloupe, DAF, partiellement recouvert de boue de décomposition des algues sargasses.

TCGNRG peut vous aider à la gestion de ces pollutions atmosphériques et aquatiques en monitorant, simulant et prévoyant les émissions et la propagation des gaz et des déchets associés. Nous proposons aussi de la formation à la gestion et l’entretien des ports, des plages et des eaux côtières. Nécessitez pas à nous contacter!