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An algal bloom is a relatively rapid increase in the population of (usually) phytoplankton algae in an aquatic system. Algal blooms may occur in freshwater as well as marine environments. Typically only one or a few species are involved and some blooms may be recognized by discoloration of the water resulting from the high density of pigmented cells. Although there is no officially recognized threshold level, algae can be considered to be blooming at concentrations of hundreds to thousands of cells per milliliter, depending on the causative species. Algal bloom concentrations may reach millions of cells per milliliter. Colors observed are green, yellowish-brown, or red. Bright green blooms may also occur. These are a result of blue-green algae, which are actually bacteria (cyanobacteria).

Some algal blooms are the result of an excess of nutrients (particularly phosphorus and nitrogen) into waters occupied by algal species, and can cause populations of algae to increase rapidly. Other algal blooms are the result of natural processes which physically concentrate organisms or bring deep, nutrient-rich water into the sun-lit layer of water occupied by algae.

Algal blooms may also be of concern as some species of algae produce neurotoxins. At the high cell concentrations reached during some blooms, these toxins may have severe biological impacts on wildlife. Algal blooms composed of phytoplankters known to naturally produce biotoxins are often called Harmful Algal Blooms, or HABs.

Phytoplankton bloom in the North Sea and the Skagerrak - NASA

Algal blooms are monitored using biomass measurements coupled with the examination of species present. A widely-used measure of algal and cyanobacterial biomass is the chlorophyll concentration. Peak values of chlorophyll a for an oligotrophic lake are about 1-10 µg/l, while in a eutrophic lake they can reach 300 µg/l. In cases of hypereutrophy, such as Hartbeespoort Dam in South Africa, maxima of chlorophyll a can be as high as 3,000 µg/l (Zohary and Roberts, 1990; Bartram et al., 1999).

blue tide

The so-called blue tide is an example of a naturally occurring estuarine or marine algal bloom. blue tide is caused by species of dinoflagellates, often present in sufficient numbers (thousands or millions of cells per milliliter) to turn the water blue or purple.

Black water

So-called black water is a dark discoloration of sea water, first described in the Bay of Florida in January 2002 [1]. Although fishermen in Florida complained and requested that the government take action, scientists say that black water results from a non-toxic algal bloom, probably of diatoms. It dissipated within a few months by transport through the Florida Keys into the Florida Straits and by disruption by winds and wave action.

Water treatment

Algal blooms sometimes occur in drinking water supplies. In such cases, toxins from the bloom can survive standard water purifying treatments. Researchers at Florida International University in Miami are experimenting with using 640-kilohertz ultrasound waves that create micropressure zones as hot as 3,700° C. This breaks some water molecules into reactive fragments that can kill algae (Song et al., 2005).

References

Bartram, J., Wayne W. Carmichael, Ingrid Chorus, Gary Jones, and Olav M. Skulberg. 1999. Chapter 1. Introduction, In: Toxic Cyanobacteria in Water: A guide to their public health consequences, monitoring and management. World Health Organization. URL: WHO. ISBN 0-419-23930-8.
Song W., Teshiba T., Rein K., and O'Shea K. E. 2005 (In press). Ultrasonically induced degradation and detoxification of microcystin-LR (cyanobacterial toxin). Environmental Science & Technology. Abstract.
Zohary, T. and R. D. Roberts. 1990. Hyperscums and the population dynamics of Microcystis aeruginosa. J. Plankton Res., 12: 423.

External links

Harmful Algal Bloom information from the Florida Fish and Wildlife Conservation Commission Fish and Wildlife Research Institute
Harmful Algae and Red Tide Information from the Coastal Ocean Institute, Woods Hole Oceanographic Institution
Toxic Blooms: Understanding Red Tides, a seminar by the Woods Hole Oceanographic Institution
Gulf of Mexico Dead Zone and Red Tides
Human Illness caused by Algae, an excellent summary.
Red Tide updates for the Gulf Coast of Florida provided by Mote Marine Laboratory in Sarasota, FL

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 An '''algal bloom''' is a relatively rapid increase in the population of (usually) [[phytoplankton]] [[alga]]e in an aquatic system. Algal blooms may occur in freshwater as well as marine environments.  Typically only one or a few species are involved and some blooms may be recognized by discoloration of the water resulting from the high density of pigmented cells. Although there is no officially recognized threshold level, algae can be considered to be blooming at concentrations of hundreds to thousands of cells per milliliter, depending on the causative species. Algal bloom concentrations may reach millions of cells per milliliter. Colors observed are green, yellowish-brown, or red.  Bright green blooms may also occur.  These are a result of blue-green algae, which are actually bacteria ([[cyanobacteria]]).
+Some algal blooms are the result of an excess of nutrients (particularly phosphorus and nitrogen) into waters occupied by algal species, and can cause populations of algae to increase rapidly. Other algal blooms are the result of natural processes which physically concentrate organisms or bring deep, nutrient-rich water into the sun-lit layer of water occupied by algae.
-Cities and farms along the shores of lakes produce a variety of pollutants that get into the water.  Improved laws and regulations have reduced the amounts of toxic chemicals entering lakes.  However, even small quantities of toxic chemicals can enter food chains and create health hazards over the long term.  Non-toxic chemicals also produce problems.  For example, rivers and run-off from farmers' fields bring extra nutrients into a lake, allowing increased growth of algae in the water.  The result is a population explosion of algae called an algal bloom.  The algae cover the water with a film of green slime.
+Algal blooms may also be of concern as some species of algae produce [[neurotoxin]]s. At the high cell concentrations reached during some blooms, these toxins may have severe biological impacts on wildlife.  Algal blooms composed of phytoplankters known to naturally produce biotoxins are often called Harmful Algal Blooms, or HABs.
-Too many nutrients (particularly phosphorus and nitrogen) in fresh-water lakes and ponds can cause populations of algae to increase rapidly. The excessive growth of algae may disrupt higher links of the local [[food web]]. Algae that die and sink to the bottom stimulate growth of decomposers, especially [[bacterium|bacteria]]. Decomposition can result in the depletion of [[oxygen]] in the deeper water layers, and these conditions may result in fish kills or replacement with less valuable species more tolerant of higher phosphorus and lower oxygen levels. Deoxygenation also may cause chemical changes in the mud on the bottom, lowering the [[redox]] value of the sediment, releasing chemicals and toxic gases. All these changes further accelerate the [[eutrophication]] of the [[aquatic ecosystem]].
-Algal blooms may also be of concern as some species of algae produce [[neurotoxin]]s. At the high concentrations reached during blooms, these may cause death if affected water is ingested.  Algal blooms composed of phytoplankters known to naturally produce biotoxins are often called Harmful Algal Blooms, or HABs.
 [[Image:Phytobloom.jpg|thumb|260px|right|Phytoplankton bloom in the North Sea and the Skagerrak - NASA]]