Along the lines of bacteria entering the pond through blown
in dust and dirt.
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Out of Africa: bacteria, fungi, viruses
A study confirms that dust crossing the Atlantic carries particles that pose a
health risk.

By DAVID BALLINGRUD
St. Petersburg Times,
published June 14, 2001

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Bacteria, fungi and probably viruses are crossing the Atlantic Ocean to Florida
in clouds of dust from drought-stricken areas of Africa.
Photos taken by NASA satellites and on-the-ground air samples confirm the
trans-Atlantic movement of tiny, potentially hazardous particles, according to
an article published today in the scientific journal Aerobiologia.
The danger posed by the global movement of dust clouds to the United States is
uncertain. Further study is needed, said Eugene Shinn of the U.S. Geological
Survey office in St. Petersburg, one of the article's authors.
"The identification of microbes in transported dust is important. . . . They
may be a source of disease above and beyond that caused by exposure (to dust),"
Shinn said.
Ongoing tests have not identified a particle -- bacteria, fungi or virus --
that by itself is a human disease threat, said Dale Griffin, a USGS
microbiologist and another author of the Aerobiologia article.........
................Garrison, who has gathered dust samples in the Virgin Islands
National Park, said the dust is sometimes visible as a reddish haze as it
approaches from the east. After a sample of air is collected, it is drawn
through a filter and the filter is examined............
..............The dust comes every year during northern Africa's dry season,
when storms in the Sahara Desert and Sahel grassland region generate vast
clouds of dust. These clouds then are pushed westward by the same easterly
"trade winds" that drive hurricanes toward U.S. and Caribbean shorelines every
year. Typically, it takes five to seven days for the dust clouds to cross the
Atlantic.
So much dirt makes the journey that air plants in the Amazon depend on
nutrients derived from the airborne soil. Florida receives more than 50 percent
of all microbe-laden African dust that reaches the United States, according to
a statement released jointly by the USGS and NASA...........
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rest of the article can be found here -
http://www.sptimes.com/News/061401/S...__bacter.shtml


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