Toxicity and Algae

Algae as Indicator

Algae are indicator species; their wellbeing is like a window into the overall health of the system in which they grow. Toxic algae blooms are caused by physiographic and anthropogenic factors and indicate systemic imbalance at the edges between land and water. Harmful algae blooms occur within fresh water and saltwater ecologies, producing excess microalgae or macroalgae growth.


Sargassum bloom in The Caribbean (Robert Scribbler)

Algae Blooms and Climate Change

Coastal algal blooms, dead zones, and episodes of eutrophication are an increasingly common global phenomenon in the context of climate change. Climatic shifts cause warming waters, which hold less oxygen and are more susceptible to blooms.

Algal blooms generally occur in response to excessive nutrient inputs from on-farm fertilizer, manure, or sewage runoff. The nitrogen and phosphorus-rich pollutants cause rapid algae reproduction; the microalgae photosynthesize prolifically and settle on the bottom of aquatic systems when they die. Microbial populations explode while they decompose the algae, which de-oxygenates the water, causing many other aquatic species to suffocate. These algal blooms emit airborne toxins—harming human and nonhuman health and interrupting economic and social function. The USGS has partnered with other governmental organizations to survey and report on localized toxic algae counts, which can be found here.



Runoff Reduction: 

Measures to reduce runoff include: improved water systems infrastructure, reduced applications of excessive fertilizers, improved soil health and water retention, responsible and appropriately scaled technology and inputs for farming systems, implementation of field margins or boundary zones between productive fields and waterways to reduce runoff.

Towards the Establishment of an International Nitrogen Management System provides a global assessment of reactive nitrogen and its environmental and social impacts. It also aims to provide recommendations on strategies to reduce emissions of reactive nitrogen, including measures to make production systems, especially farms, more efficient in their use of fertilizer.

Freshwater bloom in Walla Walla, WA

Dead Zones

Global dead zones, or areas with damagingly-low levels of dissolved oxygen, are rapidly increasing. The dead zone in the Gulf of Mexico is roughly the size of New Jersey, an accumulation of Mississippi River-bound fertilizer runoff from massive export-oriented agriculture projects of the midwest. Financial interests fueled by the mega-economy blatantly disregard consequences downstream--those that support life, people, and ecosystems.

Cyanobacteria or blue-green algae are particularly toxic to human and ecosystem health. Freshwater cyanobacterial blooms produce highly potent cyanotoxins which are known as cyanobacterial HABs (cyanoHABs). The release of these toxins in an algal bloom occurs during cell death (EPA).



Global Aquatic Dead Zone Map

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