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Harmful algal blooms (HABs) are caused by a complex set of physical, chemical, biological, hydrological, and meteorological conditions. Many unanswered questions remain about occurrence, environmental triggers for toxicity, and the ability to predict the timing, duration, and toxicity of HABs.
Emerald-green harmful algal blooms (HABs) have become an all-too-familiar summertime sight in many U.S. lakes and reservoirs. A new USGS study reports that the cyanobacteria that cause HABs also occur in large rivers.
A new study successfully predicts when mixtures of the toxins produced by these blooms in Kabetogama Lake, Voyageurs National Park, will exceed drinking-water guidelines.
Freshwater and marine algal blooms can be called harmful because they lower dissolved oxygen concentrations, alter aquatic food webs, leave ugly scums along shorelines, produce taste-and-odor compounds that cause drinking water and fish flesh to taste bad, or produce toxins so potent they poison organisms in the water and on the land.
Many different types of algae can cause harmful algal blooms (HABs) in freshwater ecosystems. The most frequent and severe blooms typically are caused by cyanobacteria, the only known freshwater algae with the potential for production of toxins potent enough to harm human health. Cyanobacterial harmful algal blooms (cyanoHABs) are of increasing global concern. CyanoHABs can threaten human and aquatic ecosystem health. Economic damages related to cyanoHABs include the loss of recreational revenue, decreased property values, and increased drinking-water treatment costs.
Nationwide, toxic freshwater cyanobacterial harmful algal blooms have been implicated in human and animal illness and death in at least 43 states. In August 2016, at least 19 states had public health advisories because of cyanoHABs.
Cyanobacteria are naturally occurring microscopic organisms. Although they are true bacteria, they function more like algae in aquatic ecosystems. For that reason, they typically are considered to be part of algal communities, which is why they often are called "blue-green algae". Cyanobacterial blooms can appear as discolorations in the water or paint-like scums at the water surface. Typically, the blooms are blue-green in color, but they also can be yellow, red, or brown.
Cyanobacteria are notorious for producing a variety of compounds with water-quality concerns. Cyanobacteria produce taste-and-odor compounds that people are sensitive to at very low concentrations (even parts per trillion) in drinking water. Taste-and-odor compounds can accumulate in fish flesh making taste bad, an important concern for the aquaculture industry.
Of greater concern than unpleasant taste and odor is the production of toxins that affect human health. Human ingestion, inhalation, or contact with water containing elevated concentrations of cyanotoxins can cause allergic reactions, dermatitis, gastroenteritis, and seizures.
USGS National Water-Quality Program scientists are leading a diverse range of studies to address cyanoHAB issues in water bodies throughout the United States, using a combination of traditional methods and emerging technologies in collaboration with numerous partners. However, despite advances in scientific understanding of cyanobacteria and associated compounds, many questions remain unanswered about the occurrence of cyanoHABs, the environmental triggers for toxicity, and the ability to predict the timing and toxicity of cyanoHABs.
Advanced warnings at time scales relevant to cyanoHAB management (hours to days) would allow proactive, rather than reactive, responses to potential events. Sensors that measure cyanobacteria in near real-time show promise for use in early warning systems.
The ability for cyanobacteria to produce cyanotoxins as well as taste-and-odor compounds is caused by genetic distinctions. By analyzing those distinctions, we can gain a greater understanding of the world of cyanoHABs, an understanding that may lead us to new ways to combat this threat. USGS is developing field and laboratory methods to quantify cyanobacteria and associated compounds that include field protocols, field guides, sample preparation techniques, development of assays, and molecular tools.
Nutrient enrichment: A key factor in occurrences of cyanoHABs
One of the key causes of cyanoHABs is nutrient enrichment. When nutrients from agricultural and urban areas are transported downstream, they can cause cyanoHABs that can impair drinking-water quality and require closure of recreational areas.
The USGS, in cooperation with local, state, federal, tribal, and university partners, is pioneering new monitoring, assessment, and modeling approaches to better understand nutrient sources, their transport, and their role in cyanoHABs development.
Tracking the water quality of the nation’s streams and rivers
The USGS monitors nutrient concentrations and flux at key sites nationwide. Annual data are featured at the website, Tracking Water Quality of the Nation's Rivers and Streams.
In addition, the USGS uses advanced optical sensor technology to track nitrate levels in real time at more than 140 sites nationwide. These data provide real-time information, improve load calculations, and advance our understanding of processes controlling nutrient variability. The data are publicly available at the website, WaterQuality Watch.
Identifying Nutrient Sources and Hotspots
USGS models of nutrient concentrations and loads in streams provide an important tool for identifying nutrient sources. Estimates derived from these models provide insights into which areas and sources are contributing the largest amounts of nutrients to local streams, lakes, and reservoirs. The models also enable the tracking of nutrients and their sources from local streams to the Nation’s estuaries and the Great Lakes. See website, Tracking the Source and Quantity of Nutrients to the Nation's Estuaries.
U.S. Geological Survey - Environmental Health Algal and Other Environmental Toxins Laboratory — Lawrence, Kansas
U.S. Geological Survey Environmental Health Toxins and Harmful Algal Blooms Research Team
Follow the links below to find additional web pages on HABs.
Follow the links below to access data or web applications associated with harmful algal blooms, cyanotoxins, and cyanobacteria.
Below are multimedia items associated with this Harmful Algal Blooms.
Find links to publications on harmful algal blooms, cyanotoxins, and cyanobacteria below.
Below are news stories associated with this project.
Building knowledge to protect ecological and human health
First-of-its-kind survey shows that algal toxins are found nationwide