harmful algae bloom
Chaohu Lake, the fifth largest freshwater lake in the country, is frequently hit by blue
algae outbreaks in the summer. An outbreak last year suffocated 110 square km of the lake area.

Scientists Celebrate Algal Bloom After Australian Dust Storm, but Could It Be Trouble?

October 08, 2009 03:00 PM
by Haley A. Lovett
The number of microorganisms in Sydney Harbor tripled in the days following the dust storm. Phytoplankton is a key part of the ocean ecosystem, but too much of it can have dire consequences.

Nitrogen-Rich Dust Stirs Up Life in Oceans Near Australia

In the midst of a drought this September, Australia was hit by a dust storm that dumped thousands of tons of red dust onto cities in New South Wales and Queensland. When the storm blew out to the Tasmanian Sea, it took with it an estimated 3 million tons of dust, sprinkling it in the ocean.

Ian Jones, a professor at the University of Sydney, told ABC Science that the ocean water near Australia normally lacks nutrients such as nitrogen and phosphate, which help ocean-dwelling microorganisms such as phytoplankton grow. After the storm littered the ocean with soil, phytoplankton thrived, tripling in number in the samples taken from Sydney Harbor.

Some researchers see this bloom in microorganisms as validation for those who would like to “fertilize” the ocean with nutrients to increase fish populations and CO2 absorption.

But in the past, the ocean’s delicate ecosystems have shown that there can be too much of a good thing.

Harmful Algae Blooms Can Suffocate Ocean Life, Create “Dead Zones”

Although algae and other phytoplankton are always present in ocean water, these tiny organisms can experience periods of dramatic population growth, known as “blooms,” usually due to increases in water temperature or available nutrients.

Algal blooms can be harmful in two ways: the algae itself can be toxic to marine life or humans (or emit waste gasses that are irritating to eyes and skin), or the sheer mass of the algal bloom can cause harm to the ocean ecosystem.

Larges masses of algae quickly consume the available nutrients in the water and die off simultaneously. The bacterial process that breaks down the dead algae uses an immense amount of oxygen, making the water uninhabitable for other creatures, and creating a “dead zone.”

One such dead zone exists near the delta of the Mississippi river in the Gulf of Mexico. During the summer time when temperatures rise, this area (which varies in size by year, but can grow to approximately the size of Massachusetts) is almost entirely devoid of marine life due to mass algal blooms and the subsequent depletion of oxygen in the water.

Lake Erie also suffers from a dead zone (also called a hypoxic zone).

What Causes Algal Blooms and Creates Dead Zones?

Algal blooms do occur naturally. A NASA article explains that if a large amount of cold water moves to the surface from the ocean floor, it can carry with it nutrients that will fuel an increase in the number of microorganisms presents. The Australian dust storm is another case where an algal bloom resulted from a natural cause.

Fertilizers used in farming that make their way to the ocean through runoff have also been linked to algal blooms. In 2004 scientists observed the first direct link between farming runoff and algal blooms, when over five years, four major irrigation events annually in the Yaqui River Valley led to algal blooms in the nearby Sea of Cortez. 

In the case of the dead zone in the Gulf of Mexico, pollution such as fertilizer and sewage runoff that enters the ocean through the Mississippi river brings with it phosphates and nitrogen, both nutrients that help algae thrive.

Why Does the Ocean Need Algae and Other Phytoplankton?

When it appears in normal amounts, algae and other phytoplankton are an integral part of the marine food chain. Many small species feed on algae and are then consumed by larger species. When there is more phytoplankton present, there is more food available.

Algae also helps process CO2 and produces much of the Earth’s oxygen. The increase in phytoplankton in the Tasmanian Sea following the dust storm is thought to have helped absorb more CO2 than normal. Some researchers hope that if nutrients are artificially introduced into the ocean to promote algae growth, that more CO2 can be processed and absorbed by algae. 

Although the absorption of CO2 by algae can be good for air pollution in the short term, other studies have found that CO2 absorbed by microscopic organisms in the ocean stays in the ocean environment and contributes to the ocean’s rising acidity.

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