Solutions for managing cyanobacterial blooms: A scientific summary for policy makers.

Abstract

Algae grow wherever there is water; in oceans, freshwater lakes, rivers, streams and pools. They underpin aquatic food webs, providing nutrition for animals in the system, and along with microbes, are responsible for cycling energy and nutrients throughout the environment. Problems arise when algae bloom, which is often the result of excess nutrients. These nutrients may come from a range of sources, including rainfall and associated runoff from fertilizer application and land erosion, as well as discharge from sewage and other high-nutrient sources. One of the key groups of algae that can bloom in freshwaters, marine and brackish waters is cyanobacteria (also known as blue-green algae). Cyanobacteria are technically not algae, as they are a more ancient lifeform, but they share characteristics in common with algae, including needing sunlight for photosynthesis. They are particularly prolific in calm waterbodies, such as lakes, ponds, weirs and reservoirs, or slow flowing rivers. Cyanobacteria can proliferate in these environments because longer water residence times allow many of them to grow and form blooms. They can also float on the water surface more readily than other algal groups. One of the major problems with cyanobacterial blooms, or cyanoHABs, is that some species can be toxic. Their toxins (cyanotoxins) can have diverse health effects on people and animals, ranging from mild to serious, and impacts on whole ecosystems. Water intended for human and animal consumption generally needs to be treated to remove toxins before drinking, significantly adding to the cost of supply. In many countries, testing methods for cyanotoxins are not available and people may inadvertently be exposed to these health hazards. Even when blooms are not toxic, their use of oxygen at night (= respiration), and bloom decay can result in low-oxygen conditions which kill fish and other animals. They can cause earthy/musty or bad odours via excretory products and decomposing blooms, e.g. rotten egg smells, and can wash up on shores and affect recreational use. They can also cause severe skin irritation for swimmers. There is a wide range of within pond/lake system management and mitigation products, methods and tools available for controlling cyanoHABs blooms. However, it is often difficult to determine which products and approaches may be most effective for a particular waterbody. This provides an overview of the products and and physical, chemical and biological solutions available for control of cyanoHABs, and some detail on their benefits and relative costs. It also points to other publications with more detailed information.