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August 31, 2004
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.
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Contacts:
Gretchen Cook-Anderson
Headquarters, Washington
Phone: 202/358-0836
Rob Gutro
Goddard Space Flight Center, Greenbelt, Md.
Phone: 301/286-4044
Randy Filmore
University of South Florida
Phone: 813-974-9051
Jana Goldman
NOAA/NWS Climate Services Division
Phone: 301/713-2483 x181
Harvey Leifert
American Geophysical Union
Phone: 202-777-7507
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Florida Red Tide Bloom of Karenia Brevis, Karenia Brevis Under a Microscope (inset)
Credit: Woods Hole Oceanographic Instititute/NOAA and NOAA/CHBR
Dark Water Plume and MODIS Chlorophyll Flourescence Image
The left image was captured by the MODIS instrument on Oct. 19, 2003. Overlaid were the locations where water samples were collected to determine
their Karenia brevis (toxic phytoplankton) abundance between Sept. 19 and Oct. 19, 2003. Large circles mean higher abundance. Smallest circles mean
“not present.” The dark plume flows from the central Florida coast to the Dry Tortugas.
The image on the right is from the same time period. The fluorescence increases from dark blue to green, yellow and red. Credit: NASA/USF
Dark Water Near Charlotte Harbor, Fl and Everglades River Areas of Low Salinity
The left image is a MODIS image which shows dark water on Oct. 9, 2003. The arrows show the average wind speed and direction (day and night) from
the QuikScat scatterometer. Oct 8-14 is in black, Oct. 15-19 is in red.
Areas of low salinity or salt usually occur near the mouths of rivers. In the image on the right, the white lines on this color enhanced image depict
the approximate locations of Everglades rivers. Credit: NASA/USF/NOAA/UM
What the Red Tide and black Water Affects
This model illustrates different aspects of the food chain that are affected by red tide and blackwater events. Low oxygen levels in bottom water
caused by non-toxic algae may also have adverse effects on the ecosystem. (Modified from Smayda, 1992) Credit: Woods Hole Oceanographic
Instititute/NOAA
SeaWiFS Sees Blackwater Feb. 4, 2002
This image from Orbimage’s SeaWiFS shows blackwater patches off the coast of Florida on Feb. 4, 2002. Credit: Orbimage/NASA/USF
Charlotte Harbor, Florida
The researchers estimated the total amount of nitrogen and phosphorus needed for the satellite-detected phytoplankton bloom in the upstream near
Charlotte Harbor, where some moderate concentrations of Florida’s red tide species, Karenia brevis, were found from water samples. Credit: MOTE
Marine Laboratory
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