Nutrients are essential chemical elements that organisms need to survive and reproduce (Smith & Smith 1998). Macronutrients, needed in large quantities, include carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, sulphur, magnesium, and calcium, while micronutrients like iron, copper and zinc are needed in lesser quantities (Smith & Smith 1998). In aquatic systems, nitrogen and phosphorus are the two nutrients that most commonly limit maximum biomass of algae and aquatic plants (primary producers) (UNEP & Gems Water 2006). Since the availability of these elements is often less than biological demand, environmental sources can regulate or limit the productivity of organisms in aquatic ecosystems (UNEP & Gems Water 2006). The micronutrients are also required for metabolism and growth of organisms, but for the most part, cellular demands for these nutrients do not exceed supply (UNEP & Gems Water 2006).

Different forms of nitrogen and phosphorus include nitrate, nitrite, ammonia, organic nitrogen (in the form of plant material or other organic compounds), and phosphates (orthophosphate and others). Nitrate is the most common form of nitrogen and phosphates are the most common forms of phosphorus found in natural waters (

Land-based activities resulting in agricultural runoff, sewage and industrial discharges, and atmospheric releases from fossil fuel combustion are the main anthropogenic sources of nutrients to the marine environment (GESAMP 2001).



An imbalance in the nutrient ratio of the aquatic ecosystem changes its structure and functions.  This produces several negative impacting that include:(UNEP/GPA 2006,, UNEP 2005,, UNEP DEWA/GRID-Europe 2008):

  • Eutrophication or the increased loading of nutrients (especially nitrogen and phosphorus) to freshwater or marine systems, which in turn leads to increases in plant growth and often to undesirable changes in ecosystem structure and function;
  • Increased primary production;
  • Toxic algal blooms often called “red tides” Sometimes the algae are diluted to the point of being invisible but although the water seems clear, it may still contain dangerous levels of highly potent toxins;
  • Toxins may also be carried by the wind causing eye irritation, and respiratory problems to persons on land;
  • Oxygen depletion. Low oxygen conditions in coastal marine waters are primarily the result of increased phytoplankton that sink to the sea floor when they die. When this happens, the organic matter is regenerated by bacterial activity consuming oxygen. This leads to low oxygen concentrations and most marine life is unable to survive. These areas are often called marine dead zones;
  • Degradation of marine habitats, including coral reefs and sea-grass beds;
  • Alteration of marine food-webs, including damage to larval or other life stages;
  • Death of fish, shellfish, mammals, sea birds and other animals;
  • Coral mortality through the reduction of light penetration, and by depleting the oxygen in the environment;
  • Humans are exposed to toxins through the consumption of contaminated seafood products in particular shellfish which causes gastrointestinal problems.  These problems include nausea, vomiting, diarrhea, dizziness, disorientation, amnesia and permanent memory loss, and paralysis or even death in severe cases of poisoning.
  • Decreased tourism revenues from marine-based activities and damage to aquaculture leading to lost income generating opportunities.


According to GESAMP (1991), eutrophication is one of the most damaging effects that humans have on the oceans, both in its scale and its consequences. Coastal areas with relatively little water circulation are particularly vulnerable (UNEP/GPA 2006).


Global versus Caribbean Studies on Nutrients

During the last two centuries, human activities have resulted in large-scale changes in the nutrient cycle, with an increase since about 1950 (UNEP 2005). The global annual nitrogen and phosphorus input to ecosystems has more than doubled during this time. This increase is caused by the higher demand for food, fuel, and fiber (UNEP 2005). Before the industrialization of the western world, the annual flux of nitrogen from the atmosphere to land and aquatic environments was 90-130 million tons per year and phosphorus 1-6 million tons per year. Anthropogenic sources have created an additional flux of 200 million tons of nitrogen and 10.5-15.2 million tons of phosphorus per year (UNEP 2005). According to UNEP/GPA (2006), the global nitrogen input from rivers to the oceans is expected to continue to rise and projections for 2030 show an increase of 14% compared to 1995. According to UNEP (2000), inorganic nitrogen fertilizers used in agriculture represent 60% of the total anthropogenic nitrogen released. The same study states that less than half of the nitrogen applied is taken up by plants - the rest is lost to the air, or dissolved in surface waters and groundwater. To sustain a growing global population the total amount of fertilizer use, will, according to UNEP (2005), have to increase from the present level of 140 million tons to 167-199 million tons per year by 2030. This is an increase of 0.7-1.3% annually. According to FAO (2000), the annual increase over the last 30 year has been 2.4%. Without improvement in, for example land management, many of these nutrients will end up in the oceans. However, up to now their efforts to control  nutrient enrichment of the marine environment from human sources has met with varied success (UNEP/GPA 2006).

Coastal waters around the world account for only 10-15% of total sea area, but they support approximately 50% of global marine primary production (Paerl 1997). Eutrophication mainly influences coastal zones but according to UNEP/GPA (2006), it is also apparent over larger areas of semi-enclosed seas including the Gulf of Mexico. This area of hypoxic conditions or “dead zone” in the Gulf of Mexico was estimated to be 9 500 km2 in the early 1990s and by 2008 it had grown to 22 000 km2 (UNEP/GPA 2006) ( According to UNEP/GPA (2006), human activities have increased nitrogen influx in the Mississippi River basin four-fold. The reason for the increase includes over–fertilization of the Mississippi’s waters from farms, towns and factories often as much as 1 000 miles upstream (

According to UNEP DEWA/GRID-Europe (2008), harmful algal blooms and hypoxia have always existed and is a natural phenomena but the increase in the last decades is, in some cases, clearly related to human development. The number of dead zones globally have, according to Larsen (2004), doubled every decade since 1960 – with 146 dead zones being reported in 2004 and according to NOAA this number had reached 200 in 2006 ( Another study done by UNEP & GRID Europe (2008) stated that 350 dead zones were spotted in 2006, 175 were of concern, 161 were documented and only 13 had shown improvement. Many of the hypoxic areas are seasonal but some persist year around (UNEP DEWA/GRID-Europe 2008).

The economic impact of algal blooms can be extensive and in European marine waters, the annual socio-economic impact is estimated at around 850 million Euros, affecting mainly commercial fisheries (158 million Euros) and tourism (687 million Euros) (ECOHARM 2003). Harmful algal blooms in the USA is, estimated to cost at least $50 million dollars per year (Anderson, 2004).

Nutrients have been ranked as the second most important pollutant source category in the Wider Caribbean Region (GESAMP 2001). Siung-Chang (1997) suggests that organic and nutrient pollution is the most serious pollution problem in the Caribbean and that it is widespread. The total estimated nutrient load from land-based sources in the Caribbean Sea is 13 000 tonnes/yr of nitrogen and 5 800 tonnes/yr of phosphorus (UNEP 2000). The predominant source of nutrients in the Caribbean region is discharge of untreated sewage, and non-point agricultural run-off. Other sources include aquaculture facilities, industrial facilities and atmospheric deposition. According to GESAMP (2001), atmospheric deposition of nitrogen between 1980-2020 may increase by 2 - 4 times over large areas of the Caribbean Sea.

Nutrients loads to the sea are constant during the winter months at the northeast Venezuelan coast (Gaspar 1996). Large rivers, such as the Orinoco are believed to enrich the coastal waters with nutrients, resulting in eutrophication between May and November. Data suggest that during the rainy season the increased nutrients from the Orinoco River in Venezuela result in a net increase in phytoplankton carbon biomass (Corredor & Morell 2001). Severe phytoplankton blooms occurred between 1991 and 1996 due to climatic abnormalities and nutrient enrichment, which resulted in oxygen depletion and reduction of coral reef cover from 43% to less than 5% in Morrocoy National Park, Venezuela (Garzón-Ferreira et al. 2000). In Cartagena Bay and the Ciénaga de Tesca in Colombia, mass fish mortalities were observed due to the oxygen deficiency created (UNEP et al 2006). Algal growth has increased on the coral reefs of Belize due to the discharge of sewage in the Hondo River (between Mexico and Belize) and in the Chetumal Bay Basin.

Other places in the Wider Caribbean Region reported to have problems with eutrophication include San Juan Bay (Puerto Rico), Havana Bay (Cuba), and Kingston Harbour (Jamaica) among others (CEDI 2000, UNEP et al 2004). In Havana Bay, eutrophication is particularly severe, as the Bay receives approximately 300 000 m3 of urban-industrial non-treated sewage per day (González et al 1997, Valdés et al 2002). In The Bahamas, red tides have occurred where large quantities of nutrients are found in the surface waters (UNEP et al 2006).  Cyanobacterial blooms, have also been observed to completely cover large areas of reefs in the Florida Keys, leading to the eventual death of the benthic cover, especially the soft corals and gorgonians (Linton & Werner 2003).


Laws, Regulations, and Policy Responses on Nutrient pollution

The most important regional legal framework for the prevention, reduction and control of pollution from excess nutrients is the Convention for the Protection and Development of the Marine Environment of the Wider Caribbean Region (Cartagena Convention). The Convention entered into force in 1986 and is a legally binding, regional multilateral environmental agreement for the protection and development of the WCR. The Protocol Concerning Pollution from Land-Based Sources and Activities (LBS Protocol) of the Cartagena Convention sets forward general obligations and a legal framework for regional co-operation, provides a list of priority source categories, activities and associated pollutants of concern and promotes the establishment of pollution standards and schedules for implementation. The Convention deals with nutrients through its LBS Protocol. In this LBS Protocol:


  • Annex I lists Primary Pollutants of Concern, which include nitrogen and phosphorous compounds;
  • Annex III establishes specific regional effluent limitations for domestic sewage; and
  • Annex IV refers to Agricultural Non-point Sources of Pollution.


Regarding nutrients, Annex IV of the LBS Protocol refers to Agricultural Non-point Sources of Pollution and states that the Parties shall develop plans for the prevention, reduction and control of agricultural non-point sources of pollution.  These plans should include:


  1. An evaluation and assessment of agricultural non-point sources of pollution that may affect the Convention Area, which may include:
  • an estimation of loadings;
  • an identification of associated environmental impacts and potential risks to human health;
  • the evaluation of the existing administrative frameworks to manage agricultural non-point sources of pollution;
  • an evaluation of existing best management practices and their effectiveness, and
  • the establishment of monitoring programmes.


  • Education, training and awareness programmes, which may include: 
    • the establishment and implementation of programmes for the agricultural sector and the general public to raise awareness of agricultural non-point sources of pollution and their impacts on the marine environment, public health and the economy;
    • the establishment and implementation of programmes at all levels of education on the importance of the marine environment and the impact of pollution from agricultural activities.


    There is currently no international convention dealing solely with nutrient pollution and no agreement or regulation on fertilizer use, use of manure, or release of sewage from land into the sea. However, Annex IV of the International Convention for the Prevention of Pollution from Ships MARPOL73/78 is one of the most important Conventions on the regulation on sewage discharges from ships. According to Annex IV discharge of sewage into the sea is allowed if the ship is discharging comminuted and disinfected sewage at a distance of more than 3 nautical miles from the nearest land, or sewage which is not comminuted or disinfected at a distance of more than 12 nautical miles from the nearest land, provided that in any case, the sewage that has been stored in holding tanks shall not be discharged instantaneously but at a moderate rate when the ship is en route and proceeding at not less than 4 knots ( However, the nutrient load caused by nitrogen and phosphorus from ships treated sewage is currently not regulated. Hence, the treated sewage containing some nitrogen and phosphorus that is discharged into the sea increases the nutrient load of the marine environment.

    What is the Caribbean Environment Programme (CEP) doing?

    Examples of on-going activities on the reduction of pollution by excess nutrients in coastal waters include:


    • CEP continuously promotes the LBS Protocol through National LBS Promotional Workshops, meetings and capacity building activities.
    • A regional capacity building activity on Annex IV or the LBS Protocol dealing with Agricultural Non-Point Sources of Pollution was held in Panama City 18-20 Feb. 2008. The training entitled “Modelling Non-Point Sources of Marin Pollution and Sediment Discharges using Geographical Information Systems (GIS)” offered the participants tools to identify areas of high erosion risk and to quantity the loads from non-point sources of pollution. A similar activity is to be held in July 2008 in Cuba within the GEF-IWCAM project.
    • The Integrating Watersheds and Coastal Areas Management (IWCAM) Project in the Small Developing States (SIDS) of the Caribbean was approved by the Global Environment Facility (GEF) in May 2004. The project is five (5) years in duration and it commenced in the last quarter of 2005. The overall objective of this Project is to strengthen the commitment and capacity of the participating countries to implement an integrated approach to the management of watersheds and coastal areas. The 13 Caribbean SIDS participating in this project are Antigua & Barbuda, The Bahamas, Barbados, Cuba, Dominica, Dominican Republic, Grenada, Haiti, Jamaica, Saint Kitts & Nevis, Saint Lucia, Saint Vincent & the Grenadines and Trinidad and Tobago. The main issues to be addressed under the IWCAM Project are: Diminishing freshwater supplies, degraded freshwater and coastal water quality, Inappropriate land use, and hygiene and sanitation. Additional information on the Project may be found on the Project website:
    • With financing provided by the Global Environment Facility (GEF), a project entitled "Reducing Pesticide Runoff to the Caribbean Sea" is currently on-going in Colombia, Costa Rica and Nicaragua. The project is a cooperative effort of national, regional and local stakeholders.  As Secretariat to the Cartagena Convention, UNEP-CAR/RCU is responsible for overall carrying out of the project and co-ordination at the regional level. LINK project web site.
    • In collaboration with Earth University in Costa Rica, the CEP has supported activities under the project “Best Management Practices in Agriculture”. These include pilot projects in Guatemala and Costa Rica demonstrating best practices in organic farming techniques and dairy farming, sustainable farming practices including proper fertilization and the use of environmentally friendly techniques and alternatives in pest control. LINKS to reports Agreed.  The report from Costa Rica has been received and under review while we are still awaiting report from Guatemala.
    • The CEP in collaboration with the UNEP GPA facilitates the development and implementation of National Programmes of Action (NPAs) for the prevention of pollution from land based sources and activities. In 2007, direct support was provided to Jamaica, Saint Lucia, Trinidad and Tobago and Barbados for completion of these plans. Ongoing efforts are focused on strategic planning and sustainable financing to enable these NPAs to be mainstreamed into development planning processes and implemented
    • Following the preparation of a Sewage Needs Assessment Guidance document for implementing Annex III of the LBS Protocol, relating to Wastewater Management, pilot projects were initiated in Saint Lucia and Jamaica to develop national planning mechanisms to control marine pollution from domestic sewage. Detailed project plans for improving infrastructure for sewage and wastewater management were also developed. Similar sewage needs assessments are ongoing in Tobago and Panama and once finalized efforts will focus on the sharing of experiences from these national assessments. LINKS to Saint Lucia, Jamaica and Tobago are completed and available.
    • A regional workshop to promote Environmentally Sound Technologies (EST) in the provision of sanitation and water at the community level was conducted in Kingston, Jamaica in collaboration with the International Environmental Technology Center, Division of Technology, Industry & Economics (UNEP-DTIE-IETC). Wastewater management professionals and community members from across the WCR reviewed available ESTs and discussed regional opportunities for funding for further action. One of the proposed initiatives highlighted at the workshop is the establishment of a Caribbean Revolving fund for Regional wastewater investment and management.
    • We can also include reference to the GEF Contaminated Bays Project training that has been carried out related to Nutrient Removal Technologies.


    What can you do?

    Simple ways of taking action;

    • Use non-phosphate soaps and detergents.
    • Use fertilizers sparingly.
    • Practice landscaping to reduce surface run-off from bare spots in your yard.
    • Ensure proper collection of sewage from domestic pets.
    • Avoid discharge of untreated sewage directly at sea, rivers or water bodies.
    • Choose cruise ships with sound environmental practices.
    • Do not bath or fish near an outfall discharging domestic or industrial wastewater effluent.
    • Don’t flush household products such as cleansers, beauty products, medicines, paints, tampons, diapers down the toilet.
    • When you wash your car use biodegradable soaps over grass or gravel or go to a car wash.
    • Join environmental groups that protect the environment.
    • Teach children and adults with less knowledge that nutrient pollution is harmful to the Caribbean sea.



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