Benthic Nutrient Cycling in Coastal Ecosystems

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Benthic Nutrient Cycling in Coastal Ecosystems
The Kostka Lab Department of Oceanography,
Florida State University
Microbes are the hidden heroes of coastal
marine ecosystems because they break down or
degrade dead plant and animal bodies, thereby
releasing nutrients to be reused by plants. When
microbes on the sea bottom regenerate nutrients
to be used as food for phytoplankton, scientists
call this benthic-pelagic coupling. In the
past, it was thought that because muddy sediments
on the bottom of the ocean contain a lot of
organic matter, these parts of the seafloor were
the most important to benthic-pelagic coupling.
However, recently, scientists have found evidence
that sandy sediments are just as important or
perhaps more important than mud. Therefore, we
are studying the microbiology of marine sands for
their role in replenishing nutrients for
phytoplankton. Nutrients carried into the
oceans by rivers are vital to the health and
productivity of estuaries. However, surplus
nutrient supply from human sources is known to
cause excessive growth of algae leading to fish
kills and habitat degradation. Rivers commonly
flow through a system of estuarine marshes before
reaching the ocean. These marshes act as enormous
biological reactors in which nutrient loads are
altered. Studying the fate and balance of
nutrients in coastal marshes is therefore also
essential to understanding the function of
estuaries.

• Estuaries are where its at!
• Estuaries, where rivers meet the sea, are unique
  and important environments, serving as storm
  barriers, critical wildlife habitat, and
  economically valuable fisheries
• Nutrients carried to the ocean by rivers are
  vital to the health of estuarine plants and fish
• However, excess nutrients from human sources
  cause harmful algal blooms such as Red Tides
  and fish kills
• Estuarine ecosystems such as marshes and sand
  flats act to remove harmful excess nutrients,
  thereby protecting fisheries
• As more people move to the Gulf coast, FSU
  researchers are studying how estuaries can be
  managed to serve humanity in the best way possible

Collecting cores of sandy sediment from the Gulf
of Mexico at St. George Island. ?

• Kidneys of the Coast
• Clean water is the lifes blood of coastal marine
  ecosystems
• Tidal marshes and subtidal sand flats act as
  giant filters, removing harmful nutrient
  pollution from excess fertilizers deposited on
  land, thereby keeping the water clean
• FSU researchers in our lab use cutting-edge
  technologies to determine how this giant filter
  works, providing vital information for
  environmental managers

Experiments for measuring nitrogen fluxes at the
sediment-water interface. Cores are incubated in
the FSUCML controlled environment chamber ?
? Sampling a sediment profile from a fiddler
crab burrow.
? Processing sediment cores for DNA
analysis. Apalachicola Bay at St. George Island
? Sediment core collected from Apalachicola Bay
Model of nitrogen cycling in marsh sediments. ?
Sandy Sediments In a NSF project with Dr.
Markus Huettel, the Kostka laboratory is
investigating the concept that coastal marine
sands act as giant filters, filtering out dead
plant or animal bodies, and releasing inorganic
nutrients to be used as food for plants. Our
research closely couples chemistry and
microbiology to determine what controls nutrient
release from the sandy seafloor at two
contrasting sites near St. George Island,
Florida. One site represents conditions found in
Apalachicola Bay, while the other is more typical
of conditions found in the northeastern Gulf of
Mexico. We have determined how fast organic
matter is processed by microbial activities in
the giant filter using radiotracers and flux
chambers. Using the latest genetic methods, we
have documented whos there or which microbe
groups are present to degrade organic matter in
the sands. By combining our estimates of
microbial activity along with genetic
identification of microbe groups, we will find
out how the giant filter works in the Bay vs. the
Gulf.
Estuarine Marshes The goal of this
project is to study nitrogen cycling in marsh
sediments of the Apalachicola National Estuarine
Research Reserve (ANERR), Florida. The ANERR
encompasses a productive and pristine ecosystem
where the Apalachicola River reaches the Gulf of
Mexico. Pristine beaches, beautiful scenery,
abundant oysters, fish, manatees, dolphins, and
migratory birds make the Apalachicola Bay a
valuable resource and attractive recreation
destination. Prior to reaching the ocean, the
Apalachicola River forms a network of
distributaries and flows through an extensive
system of low-salinity marshes at the boundary
between the River and the Apalachicola Bay.
Our work at the FSU Coastal and Marine Laboratory
involves the study of long-term nitrogen loss via
denitrification (nitrogen gas production by
microorganisms) and nitrogen burial in ANERR
marsh sediments. Controlled environment chambers
at the FSUML are used to incubate sediment cores
during denitrification rate measurements. This
research is being conducted with financial
support from the NOAA Estuarine Reserves
Division, graduate fellowship program for Tom
Gihring, a graduate student in Dr. Kostka's
laboratory.