NASA Satellites Detect Glow of Plankton in Black Waters

For the first time, scientists may now detect a
phytoplankton bloom in its early stages by looking at its red
“glow” under sunlight, due to the unique data from two NASA
satellites. According to a study conducted in the Gulf of
Mexico, this phenomenon can forewarn fishermen and swimmers
about developing cases of red tides that occur within plumes
of dark-colored runoff from river and wetlands, sometimes
causing “black water” events.

Dark-colored river runoff includes nitrogen and phosphorus,
which are used as fertilizers in agriculture. These nutrients
cause blooms of marine algae called phytoplankton. During
extremely large phytoplankton blooms where the algae is so
concentrated the water may appear black, some phytoplankton
die, sink to the ocean bottom and are eaten by bacteria. The
bacteria consume the algae and deplete oxygen from the water
that leads to fish kills.

Chuanmin Hu and Frank Muller-Karger, oceanographers at the
College of Marine Science of University of South Florida, St.
Petersburg, Fla., used fluorescence data from NASA’s Moderate
Resolution Imaging Spectroradiometer (MODIS) instruments
aboard both NASA’s Terra and Aqua satellites. MODIS detects
the glow or phytoplankton fluorescence, from the plant’s
chlorophyll. The human eye cannot detect the red
fluorescence.

The ability to detect glowing areas of water helps
researchers identify whether phytoplankton are present in
large dark water patches that form off the coast of Florida.
Without these data, it is impossible to differentiate
phytoplankton blooms from plumes of dark river runoff that
contain few individual phytoplankton cells.

Because colored dissolved organic matter that originates in
rivers can absorb similar amounts of blue and green color
signals as plants do, traditional satellites that simply
measure ocean color cannot distinguish phytoplankton blooms
within such patches.

Although satellites cannot directly measure nutrients in
lakes, rivers, wetlands and oceans, remote sensing technology
measure the quantities of plankton. Scientists can then
calculate how much nutrient might be needed to grow those
amounts of plankton.

Hu and others used this technique to study the nature and
origin of a dark plume event in the fall of 2003 near
Charlotte Harbor, off the south Florida coast. Moderate
concentrations of one of Florida’s red tide species, were
found from water samples.

“Our study traces the black water patches near the Florida
Keys to some 200 kilometers (124 miles) away upstream,” said
Hu. “These results suggest that the delicate Florida Keys
ecosystem is connected to what happens on land and in two
remote rivers, the Peace and Caloosahatchee, as they drain
into the ocean. Extreme climate conditions, such as
abnormally high rainfall in spring and summer 2003, may
accelerate such connections,” he added.

These findings are based on scientific analyses of several
things. Data used include satellite ocean color from MODIS
and Sea-viewing Wide Field-of-view Sensor (SeaWiFS), and wind
data from NASA’s QuikSCAT satellite. U.S. Geological Survey,
National Oceanic and Atmospheric Administration (NOAA),
Florida’s Fish and Wildlife Research Institute, and other
organizations provided rain, river discharge, and field
survey information.

By knowing which way the winds blow and the currents flow, Hu
and colleagues can predict where black water may move.

Red tides occur every year off Florida and are known to cause
fish kills, coral stress and mortality, and skin and
respiratory problems in humans. Previous studies show that
prolonged “black water” patches cause water quality
degradation and may cause coral death. The use of remote
sensing satellites provides effective means for monitoring
and predicting such events.

The link between coastal runoff and black water events is an
example of how land and ocean ecosystems are linked together.
“Coastal and land managers over large areas need to work
together, to alleviate more black water events from taking
place in the future,” said Muller-Karger.

This study appeared in a recent issue of the American
Geophysical Union’s Geophysical Research Letters. Coauthors
of the article include Gabriel Vargo and Merrie Beth Neely
from University of South Florida and Elizabeth Johns from
NOAA’s Atlantic Oceanographic and Meteorological Laboratory.

NASA’s Science Directorate works to improve the lives of all
humans through the exploration and study of Earth’s system,
the solar system and the Universe.

For more information and images on the Internet, visit:

http://www.gsfc.nasa.gov/topstory/2004/0826planktonglow.html