Algal bloom
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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.
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).
See also
- ciguatera
- dead zone (ecology)
- dinoflagellate (see "neurotoxins" and "red tide" under Ecology and fossils and see "phosphate" under Cautions)
- domoic acid
- red tide
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