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
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
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
NASA's Science Directorate works to improve the lives of all humans
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and the Universe.
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