Scientists Identify Important Source
of Nutrients to Florida's Coral Reefs
(entered 07/30/03)
FOR IMMEDIATE RELEASE
July 24, 2003
CONTACT INFORMATION
Dr. James Leichter
Scripps Institution of Oceanography
(858) 822-5330 jleichter@ucsd.edu
Dr. Steven Miller
NOAA's National Undersea Research Center
University of North Carolina at Wilmington
(305) 451-0233 millers@uncw.edu
UNCW professor teams with Scripps and UC-Berkeley scientists
to identify important source of nutrients to Florida's coral reefs
Key Largo, Florida -- Coral reef scientists were surprised
to learn that the deep ocean is the source of 20-40 times more nitrogen
and phosphorus on the outer coral reef than nutrient pollution from
sewage and storm water runoff.
A new study published this month documents a large and
not previously quantified source of nutrients to the coral reefs
of the Florida Keys - the deep ocean. Lead author Dr. James Leichter,
Scripps Institution of Oceanography, said, "We studied upwelling
of cool, subsurface water at multiple sites along the Florida Keys
reef tract. Our results show that this natural source of nutrients
can deliver as much as 20-40 times more nitrogen and phosphorus
to the outer reef tract than estimates of nutrient pollution from
sewage and storm water runoff."
While these numbers are remarkable it's important to
provide context. Co-author Dr. Steven Miller, University of North
Carolina at Wilmington, added, "I'm sure some people will try
to use these numbers to claim that changing sewage disposal practices
in the Keys is unnecessary, but they would be wrong. What our results
show is that a major nutrient pump exists offshore. However, nothing
in our study contradicts the fact that we also have a nearshore
pollution problem."
The study was published this month in the journal Limnology
and Oceanography and was a collaboration among scientists from Scripps
Institution of Oceanography, the University of California at Berkeley,
and the University of North Carolina at Wilmington (UNCW). Much
of the work conducted during this study utilized saturation diving
and the NOAA Aquarius underwater laboratory in Key Largo.
"What I like about this study is that it provides
a balanced approach to a complicated issue. They acknowledge that
while upwelling is a significant source of nutrients to the offshore
reefs, they don't dismiss the need to better understand the dynamics
of nearshore nutrient pollution making its way offshore," said
Dr. Brian Keller, science coordinator for the Florida Keys National
Marine Sanctuary.
The large amounts of nitrogen and phosphorus are brought
to the reef by an oceanographic process called upwelling, in this
case a specific, high frequency form of upwelling caused by internal
tidal bores. Leichter explained, "It's a little like waves
sloshing back and forth in a bathtub, but in the ocean at much grander
scales and in ways that sometimes cause surges of deep water to
move into much shallower areas. When this happens in the Keys, nutrients
brought to the reef can increase 10 to 100 times over background
levels."
The upwelled water is rich in nutrients due to natural
processes. When plankton and other organisms produced or living
in surface waters die, they often sink to the bottom. Leichter further
explained, "As these materials sink, they start to break down,
they get eaten and excreted, and the end result is the slow and
continuous addition of nitrogen and phosphorus to waters with increasing
depth."
Interestingly, the upwelled water makes it to the reef
a lot more often than people realize, sometimes several times a
day. "The presence of this water on the reef for extended periods
of time has the potential to significantly affect the biology of
corals, sponges, and algae," added Leichter.
"This study illustrates the importance of assessing
water quality over different time scales," said Dr. Joe Boyer
of Florida International University. Boyer manages the largest and
longest running water quality monitoring program in south Florida.
"Our sanctuary-wide, quarterly monitoring efforts occasionally
pick up these events, but are not designed to quantify this type
of detail," he added.
Another important result of the study documents that
a special form of nitrogen in the upwelled water is also present
in samples of algae collected from the reef. This part of the work,
led by Hannah Stewart, University of California - Berkeley, suggests
that the algae are directly using nitrogen from the upwelled water.
"This is particularly interesting because some scientists believe
that this special form of nitrogen is a sewage signal - a smoking
gun - for pollution, while our work clearly suggests otherwise for
the offshore reefs," added Miller.
These results are the culmination of work first started
in the early 1990s, initially with single deployments of oceanographic
equipment that detected the surprising frequency and intensity of
the upwelling events, and later with equipment deployments throughout
the Keys to document the regional significance of these events.
"While our study focused on a large natural source of nutrients
for the Florida Keys reef tract, things like coral disease, global
warming, and overfishing are also important. The impacts of humans
in this system are clearly dramatic and complex. That's why it's
important to accurately assess variability in this system that is
a normal part of the system," added Leichter.
The paper by James Leichter, Hannah Stewart, and Steven
Miller, is titled "Episodic nutrient transport to Florida coral
reefs" (Limnology and Oceanography Vol 48:1394-1407) and is
available free at http://aslo.org/lo/toc/vol_48/issue_4/1394.pdf.
This research was funded by NOAA's National Undersea
Research Center at the University of North Carolina at Wilmington
(UNCW). The Aquarius underwater laboratory is owned by NOAA and
is managed by UNCW (www.uncw.edu/aquarius).
Person interviewed: Dr. Steven Miller and Dr. James
Leichter
News organization: Environmental News Network
Air time: Thu, July 24 2003 at 12:00 AM Time zone
Contact information
Name: Steven Miller
Tel: (305) 451-233
smiller@gate.net
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