Algal Toxicology

Algal toxicology and dynamics

Project overview and history

Central Indiana water supply reservoirs have historically experienced and continue to experience taste and odor (T&O) issues. Long-term patterns documented since at least 2002 show that taste-and-odor episodes are highly variable in frequency, intensity and duration among years and within the same reservoir, and very often are associated with the presence of specific species of cyanobacteria, also known as blue-green algae. Understanding the hydrologic and biogeochemical processes that lead to changes in algal metabolite (MIB and geosmin) concentrations in water supply reservoirs is important for improving the quality of water in drinking water reservoirs because it can be an economic burden to water treatment plants to remove these T&O compounds. It is also important to improving our understanding of the possible production of algal toxins that are of concern worldwide.

The Center has provided field and analytical support to the local drinking water utility, collecting data that is used to ensure that production processes are maximized to deliver the highest quality drinking water. We have been assisting in monitoring local reservoirs since summer 2008 through partnerships with local agencies and utilities including previous support from Veolia Water Indianapolis. Citizens Water is continuing and expanding this partnership through funding to support the field, laboratory and analytical research towards developing a better understanding of key chemical, phyisical, and biological processes that drive blooms of specific cyanobacteria and their production of these metabolites in area reservoirs, including Geist, Morse and Eagle Creek Reservoirs. Through continued sampling and through lab and field expeiments, we will work towards improving our understanding of how these complex natural systems respond to changes in deleterious and beneficial directions. This partnership provides significant opportunity for students and faculty in the School of Science to be engaged with the drinking water utility in a way that brings fundamental scientific research and student training to bear on a significant problem with industrial, societial, and private citizen concern.

Project background

The link between blue-green algae and water quality.

Cyanobacteria (blue-green algae) cause a multitude of water-quality concerns, including the potential to produce toxins and taste-and-odor (T&O) compounds. Algal metabolites (toxins and T&O compounds) may cause significant economic and public health concerns, and are of particular interest in lakes, reservoirs, and rivers that are used for drinking-water supply, recreation, or aquaculture. Many cyanobacteria produce intracellular and extracellular metabolites, such as biotoxins (microcystin and cylindrospermopsin) and/or T&O compounds (e.g., 2-methylisoborneol (MIB), trans-1,10-dimethyl-trans-9-decalol (geosmin)) that impact water supplies in reservoirs, rivers, canals, and within water treatment plants. Geosmin and MIB have extremely low odor thresholds to humans and can be detected by consumers at concentrations as low as 5–10 ng/L (part per trillion). These metabolites, particularly in dissolved (extracellular) forms, have been shown to be resistant to conventional water treatment.

Planktothrix is a diverse genus of filamentous cyanobacteria observed to amass in algal blooms in water ecosystems across the globe. - Description from Wikipedia

What are Harmful Algal Blooms (HABs)?

A bloom is a rapid and massive development of algae on the surface of lakes, reservoirs and ponds. Although blooms can occur naturally as part of the yearly cycle of algal dynamics in a water body, some algae, such as Cyanobacteria (blue-green algae), can develop nuisance blooms. Cyanobacteria can sometimes form visible green masses and scums floating on the water surface and which can reach a thickness of a few centimeters along the edges of the water body. Most of the time, algal blooms are simply not visible and form diffuse dense populations right below the water surface.

The definition of a HAB is not so clear since it is a common term and not a scientific term, which describes a diverse array of blooms that can cause detrimental effects, including:

Toxic effects on aquatic life and humans – generally caused by biotoxins:

  • Death of fish, cattle, dogs, and shellfish poisonings
  • Physical impairments: dermatitis, otitis, dizziness, shortness of breath, vomiting, diarrhea

Nuisance conditions affecting:

  • Recreation/tourism (health risk/economic impact);
  • Aesthetics (discoloration) and Taste-and-Odor (T&O) problems in water supplies caused by diverse algal volatile organic compounds (AVOCs), such as MIB and geosmin.

There are a wide range of organisms that can be defined as bloom-forming species. Predominant groups in freshwater ecosystems are Cyanobacteria, some species of Diatoms, Prymnesiophytes and Euglenophytes whereas Dinoflagellates account for more than 75% of coastal blooms (marine). Not all algal blooms produce toxins.


Cyanotoxins can be classified into categories that reflect their biological effects on the systems and organs that they affect most strongly. Each cyanotoxin can be produced by more than one cyanobacterial species; likewise, several toxins can be found within the same species. Toxigenic Cyanobacteria can be found in marine, brackish and freshwaters.

Learn more about cyanotoxins and their producers »

What causes algal blooms?

The development and proliferation of algal blooms likely result from a combination of environmental factors including available nutrients, temperature, sunlight, ecosystem disturbance (stable/mixing conditions, turbidity), hydrology (river flow and water storage levels) and the water chemistry (pH, conductivity, salinity, carbon availability…).

However, the combination of factors that trigger and sustain an algal bloom is not well understood at present and it is not possible to attribute algal blooms to any specific factor.

The development and proliferation of algal blooms likely result from a combination of environmental factors including available nutrients, temperature, sunlight, ecosystem disturbance (stable/mixing conditions, turbidity), hydrology (river flow and water storage levels) and the water chemistry (pH, conductivity, salinity, carbon availabiliy).

However, the combination of factors that trigger and sustain an algal bloom is not well understood at present and it is not possible to attribute algal blooms to any specific factor.


Nutrients promote and support the growth of algae and Cyanobacteria. The eutrophication (nutrient enrichment) of waterways is considered as a major factor. The main nutrients contributing to eutrophication are phosphorus and nitrogen.

In the landscape, runoff and soil erosion from fertilized agricultural areas and lawns, erosion from river banks, river beds, land clearing (deforestation), and sewage effluent are the major sources of phosphorus and nitrogen entering water ways. All of these are considered as external sources.

Internal origin of nutrients comes from the lake/reservoir sediments. Phosphate attaches to sediments. When dissolved oxygen concentration is low in the water (anoxic), sediments release phosphate into the water column. This phenomenon encourages the growth of algae.


Early blue–green algal blooms usually develop during the spring when water temperature is higher and there is increased light. The growth is sustained during the warmer months of the year. Water temperatures above 25°C are optimal for the growth of Cyanobacteria. At these temperatures, blue–green algae have a competitive advantage over other types of algae whose optimal growth temperature is lower (12-15°C).

In temperate regions, blue–green algal blooms generally do not persist through the winter months due to low water temperatures. Higher water temperatures in tropical regions may cause blue–green algal blooms to persist throughout the year.


Blue–green algae populations are diminished when they are exposed to long periods of high light intensity (photo-inhibition) but have optimal growth when intermittently exposed to high light intensities. These conditions are met under the water surface where light environment is fluctuating.

Even under low light conditions, or in turbid water, blue–green algae have higher growth rates than any other group of algae. This ability to adapt to variable light conditions gives cyanobacteria a competitive advantage over other algal species.

Stable conditions

Most of blue–green algae prefer stable water conditions with low flows, long retention times, light winds and minimal turbulence; other prefer mixing conditions and turbid environments.

Drought, water extraction for irrigation, human and stock consumption and the regulation of rivers by weirs and dams all contribute to decreased flows of water in our river systems. Water moves more slowly or becomes ponded, which encourages the growth of algae.

In water bodies, another consequence of stable conditions is thermal stratification. Thermal stratification occurs when the top layer of the water column becomes warmer and the lower layer remains cooler. When the two layers stop mixing, the upper layer becomes more stable (no wind-induced mixing, convection cells)and summer blooms of buoyant blue-green algae are supported.

When a water body is stratified, bottom waters often become depleted with oxygen (anoxia) which may lead to increased nutrient release from the sediments. Pulses of nutrient from the colder bottom layer may fuel up the algal growth in the top layer.


Turbidity is caused by the presence of suspended particles and organic matter (flocs) in the water column. High turbidity occurs when a lot of water is running through the system (high discharge after a rain event). Low turbidity occurs when there is only a small amount of suspended matter present in the water column. Low turbidity can be due to slow moving or stagnant water that allows suspended articles to settle out of the water column. When turbidity is low, more light can penetrate through the water column. This creates optimal conditions for algal growth. In return, growing algae create a turbid environment.

What can be done to reduce blooms?

Watershed management

This is a long–term solution to reduce algal blooms impacting streams and water bodies. Protecting soils from erosion in upstream watersheds, maintaining vegetation cover (cover crops) and no-till agriculture will ultimately lead to better water quality as less sediment and nutrients will be able to enter waterways. Nutrients promote the growth of algae, so reducing the nutrient inputs will reduce the frequency of algal blooms. Measures to improve watershed management will generally not show immediate results, but they will have long term benefits to the environment.

Main ways of reducing the nutrient load are:

  • Avoiding the excessive use of fertilizers and manures on agricultural land within the watershed
  • Protecting soil from erosion
  • Treating sewage to remove nitrogen and phosphorus.
  • Riparian vegetation protection. The riparian zone acts as a buffer and:
    • Filters runoff and prevents pollutants from entering the water body
    • Prevents river bank erosion which can increase turbidity and sedimentation of the water body
    • Shades the water, which reduces the available light and keeps the water temperature lower so algal growth is not encouraged.
  • Managing algal blooms in water storages

Once nutrients enter a water storage they are very hard to remove. Therefore, the most effective strategy is to prevent nutrients from entering the storage in the first place. Algal blooms in water storages such as lakes or dams can be dealt with by using a number of management strategies.


An algaecide is any chemical added to water which is toxic to, and kills algae and/or cyanobacteria (blue–green algae). Examples include copper sulphate or any chelated copper–based products. The use of algaecides to control algal blooms is not recommended and is not an effective long term solution to algal problems. Copper–based algaecides damage and kill algal cells which lead to the release of algal toxins into the surrounding water.

Risks associated with using copper–based algaecides include:

  • Mass release of  algal metabolites (cyanotoxins, T&O compounds) from the algal cells
  • Accumulation of copper in the sediments
  • Growth of nuisance species that are resistant to the algaecide may cause greater water quality problems
  • Copper–based products may kill other aquatic flora and fauna. They can also cause the death of fish through reducing the concentration of oxygen in the water when the algae die.
Water treatment

Algae can be removed from raw water through a number of treatment methods. These include filtration, coagulation using aluminum and ferric iron salts or organic polymers. The most reliable method of algal toxin removal is using activated carbon filtration. This approach uses either powdered activated carbon (PAC), which can be added intermittently whenever the need arises, or granular activated carbon (GAC) absorbers, which are used continuously.

When possible, short–term control techniques for drinking water supplies include changing the position or depth of the water intake to avoid pumping contaminated water with high cell densities.

Resources related to algae

Blue-Green Algal Blooms and Nutrients that Cause Them: Exploring Indiana’s Story One-Day Free Symposium (Updating Page, Webmaster 8.5.14). June 17, 2010

Steuben County No-P fertilizer ordinance waiver denied by State Chemist office, Feb. 9, 2010

Blue-Green Algae in Indiana: An Emerging Threat and the Need for Statewide Monitoring and a Public Information Plan. Presented to the Indiana Environmental Quality Service Council (EQSC), Oct. 26, 2009

State Reports High Levels of Blue-Green Algae in Area Lakes (Kosciusko Lakes and Streams Newsletter), Sept. 2009

2009-07 White River Bloom Information (Updating Page, Webmaster 8.5.14)
The White River is currently experiencing a bloom.  These conditions are being caused by a bloom of single-celled algae in the group of algae known commonly as yellow-brown algae or diatoms. July 2009

CEES research publications

Pascual, D.L., T.H. Johengen, G.M. Filippelli, L.P. Tedesco, and D. Moran. Cultural eutrophication of three Midwest urban reservoirs: The role of nitrogen limitation in determining phytoplankton community structure. Interagency International Symposium on Cyanobacterial Harmful Algal Blooms. September 6-10, 2005. Research Triangle Park, NC. p 68.

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Pascual, D.L., T.H. Johengen, P.G. Meier, G.M. Filippelli, L.P. Tedesco, and D. Moran. 2004. Cultural eutrophication of three Midwest urban reservoirs:  the role of nitrogen and  phosphorus in determining phytoplankton communities.  American Society of Limnology and Oceanography 2004 Summer Meeting Abstract Book, p. 50.

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Indiana resources