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Harmful algal bloom
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Harmful algal bloom
A harmful algal bloom (HAB), or excessive algae growth, sometimes called a red tide in marine environments, is an algal bloom that causes negative impacts to other organisms by production of natural algae-produced toxins, water deoxygenation, mechanical damage to other organisms, or by other means. HABs are sometimes defined as only those algal blooms that produce toxins, and sometimes as any algal bloom that can result in severely lower oxygen levels in natural waters, killing organisms in marine or fresh waters. Blooms can last from a few days to many months. After the bloom dies, the microbes that decompose the dead algae use up more of the oxygen, generating a "dead zone" which can cause fish die-offs. When these zones cover a large area for an extended period of time, neither fish nor plants are able to survive.
It is sometimes unclear what causes specific HABs as their occurrence in some locations appears to be entirely natural, while in others they appear to be a result of human activities. In certain locations there are links to particular drivers like nutrients, but HABs have also been occurring since before humans started to affect the environment. HABs are induced by eutrophication, which is an overabundance of nutrients in the water. The two most common nutrients are fixed nitrogen (nitrates, ammonia, and urea) and phosphate. The excess nutrients are emitted by agriculture, industrial pollution, excessive fertilizer use in urban/suburban areas, and associated urban runoff. Higher water temperature and low circulation also contribute.[citation needed]
HABs can cause significant harm to animals, the environment and economies. They have been increasing in size and frequency worldwide, a fact that many experts attribute to global climate change. The U.S. National Oceanic and Atmospheric Administration (NOAA) predicts more harmful blooms in the Pacific Ocean. Potential remedies include chemical treatment, additional reservoirs, sensors and monitoring devices, reducing nutrient runoff, research and management as well as monitoring and reporting.
Terrestrial runoff, containing fertilizer, sewage and livestock wastes, transports abundant nutrients to the seawater and stimulates bloom events. Natural causes, such as river floods or upwelling of nutrients from the sea floor, often following massive storms, provide nutrients and trigger bloom events as well. Increasing coastal developments and aquaculture also contribute to the occurrence of coastal HABs. Effects of HABs can worsen locally due to wind driven Langmuir circulation and their biological effects.
HABs from cyanobacteria (blue-green algae) can appear as a foam, scum, or mat on or just below the surface of water and can take on various colors depending on their pigments. Cyanobacteria blooms in freshwater lakes or rivers may appear bright green, often with surface streaks that look like floating paint. Cyanobacterial blooms are a global problem.
Most blooms occur in warm waters with excessive nutrients. The harmful effects from such blooms are due to the toxins they produce or from using up oxygen in the water which can lead to fish die-offs. Not all algal blooms produce toxins, however, with some only discoloring water, producing a smelly odor, or adding a bad taste to the water. Unfortunately, it is not possible to tell if a bloom is harmful from just appearances, since sampling and microscopic examination is required. In many cases microscopy is not sufficient to tell the difference between toxic and non-toxic populations. In these cases, tools can be employed to measure the toxin level or to determine if the toxin-production genes are present.
In a narrow definition, harmful algal blooms are only those blooms that release toxins that affect other species. On the other hand, any algal bloom can cause dead zones due to low oxygen levels, and could therefore be called "harmful" in that sense. The usage of the term "harmful algal blooms" in the media and scientific literature is varied. In a broader definition, all "organisms and events are considered to be HABs if they negatively impact human health or socioeconomic interests or are detrimental to aquatic systems". A harmful algal bloom is "a societal concept rather than a scientific definition".
A similarly broad definition of HABs was adopted by the US Environmental Protection Agency in 2008 who stated that HABs include "potentially toxic (auxotrophic, heterotrophic) species and high-biomass producers that can cause hypoxia and anoxia and indiscriminate mortalities of marine life after reaching dense concentrations, whether or not toxins are produced".
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Harmful algal bloom
A harmful algal bloom (HAB), or excessive algae growth, sometimes called a red tide in marine environments, is an algal bloom that causes negative impacts to other organisms by production of natural algae-produced toxins, water deoxygenation, mechanical damage to other organisms, or by other means. HABs are sometimes defined as only those algal blooms that produce toxins, and sometimes as any algal bloom that can result in severely lower oxygen levels in natural waters, killing organisms in marine or fresh waters. Blooms can last from a few days to many months. After the bloom dies, the microbes that decompose the dead algae use up more of the oxygen, generating a "dead zone" which can cause fish die-offs. When these zones cover a large area for an extended period of time, neither fish nor plants are able to survive.
It is sometimes unclear what causes specific HABs as their occurrence in some locations appears to be entirely natural, while in others they appear to be a result of human activities. In certain locations there are links to particular drivers like nutrients, but HABs have also been occurring since before humans started to affect the environment. HABs are induced by eutrophication, which is an overabundance of nutrients in the water. The two most common nutrients are fixed nitrogen (nitrates, ammonia, and urea) and phosphate. The excess nutrients are emitted by agriculture, industrial pollution, excessive fertilizer use in urban/suburban areas, and associated urban runoff. Higher water temperature and low circulation also contribute.[citation needed]
HABs can cause significant harm to animals, the environment and economies. They have been increasing in size and frequency worldwide, a fact that many experts attribute to global climate change. The U.S. National Oceanic and Atmospheric Administration (NOAA) predicts more harmful blooms in the Pacific Ocean. Potential remedies include chemical treatment, additional reservoirs, sensors and monitoring devices, reducing nutrient runoff, research and management as well as monitoring and reporting.
Terrestrial runoff, containing fertilizer, sewage and livestock wastes, transports abundant nutrients to the seawater and stimulates bloom events. Natural causes, such as river floods or upwelling of nutrients from the sea floor, often following massive storms, provide nutrients and trigger bloom events as well. Increasing coastal developments and aquaculture also contribute to the occurrence of coastal HABs. Effects of HABs can worsen locally due to wind driven Langmuir circulation and their biological effects.
HABs from cyanobacteria (blue-green algae) can appear as a foam, scum, or mat on or just below the surface of water and can take on various colors depending on their pigments. Cyanobacteria blooms in freshwater lakes or rivers may appear bright green, often with surface streaks that look like floating paint. Cyanobacterial blooms are a global problem.
Most blooms occur in warm waters with excessive nutrients. The harmful effects from such blooms are due to the toxins they produce or from using up oxygen in the water which can lead to fish die-offs. Not all algal blooms produce toxins, however, with some only discoloring water, producing a smelly odor, or adding a bad taste to the water. Unfortunately, it is not possible to tell if a bloom is harmful from just appearances, since sampling and microscopic examination is required. In many cases microscopy is not sufficient to tell the difference between toxic and non-toxic populations. In these cases, tools can be employed to measure the toxin level or to determine if the toxin-production genes are present.
In a narrow definition, harmful algal blooms are only those blooms that release toxins that affect other species. On the other hand, any algal bloom can cause dead zones due to low oxygen levels, and could therefore be called "harmful" in that sense. The usage of the term "harmful algal blooms" in the media and scientific literature is varied. In a broader definition, all "organisms and events are considered to be HABs if they negatively impact human health or socioeconomic interests or are detrimental to aquatic systems". A harmful algal bloom is "a societal concept rather than a scientific definition".
A similarly broad definition of HABs was adopted by the US Environmental Protection Agency in 2008 who stated that HABs include "potentially toxic (auxotrophic, heterotrophic) species and high-biomass producers that can cause hypoxia and anoxia and indiscriminate mortalities of marine life after reaching dense concentrations, whether or not toxins are produced".
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