Estuarine Cycles
Estuaries are the best cyclers in the world!
Sulfur
• There are many forms of sulfur in estuaries
• Sulfur is a good oxidation-reduction element
(redox)
• Seawater contains high amounts of SO4
• When sulfate is reduced it by phytoplankton,
it becomes dimethylsulfoniopropionate
(DMSP) to volatile dimethyl sulfide (DMS)
DMS
• The molecule DMS
CH3-S-CH3
• Approximately 50% of the global flux of S is
derived from the marine environment.
• Oxidation of DMS leads to production of SO4
in the atmosphere
The Reduction of Sulfate
• Some SO4 reducing bacteria (SRB) are closely
related with the rhizophere of Spartina
alterniflora (control biogeochemical cycling in
marsh sediments)
Sulfides in the soil…
Lucinid
Bivalves
Lamars et al. 2013
SRB
• Some of the reducing bacteria families
include:
Desufovibrionaceae
Desulfobacteriaceae
Examples of bacteria….
Desulfovibrio desulfuricans
Desulfobacterium spp.
Image University of Hawaii
Back to Sulfates?
• A significant fraction of sulfides by SR are
reoxidized to sulfates at the “oxic-anoxic”
sediment interface
• Dissolved Sulfides can diffuse into bottom
sediments and can contribute to further O2
depletion in estuaries through oxidation.
Sulfides
• They are not retained in sediments in
estuaries
• Are variable based on location, depth and
temperatures
• Can also vary if there is iron
present
Pyrite is a crystal form
of Iron sulfide
Oxidation Reduction Potential
• Measures the amount of oxidizers, those
wanting to take oxygen from the environment.
Some include: Chlorides, Bromides, Ozone
Because these oxidizers steal electrons, there is
a higher ORP reading! Higher voltage!
ORP
• The less available oxidizers, the lower the
potential and lower the ORP reading which
means there are more chances for a reducing
environment
• In short the more negative – reducing
conditions, the more positive – oxidizing
• Ranges -1200 mV to +1200 mV
Carbon
Carbon
• It is necessary for biological functions and is
the key element on earth (over 1,000,000
compounds)
• Oxidation states from +4 to -4
• Has both long-term and short-term cycles
• We will focus on the “carbonate reservoir”
(Holmen, 2000).
Carbonate Reservoir
Dissolved Inorganic Carbon
•DIC – Bicarbonate, carbonate,
carbon dioxide
Solid Carbonate Minerals
•Calcium carbonate
Complex Carbon Cycles
• Methane and carbon dioxide are the gases
that get attention as they are “greenhouse
gases”
Methane
Carbon dioxide
Inorganic Carbon
• The processing of inorganic forms of carbon in
phytoplankton are important for short-term
process.
Inorganic to Organic Form
Now an
organic form
for
zooplankton to
use for energy
The Cycle Continues…
Through
heterotrophic
functions
(respiration), it is
now back to the
inorganic form
Iron was found to be one of the limiting components
to “control” phytoplankton populations
How about increasing the amount of autotrophic species
through iron fertilization?
There is a Southern Ocean Iron Enrichment Experiment
Ratios of Carbon
Carbon was found to be in ratios with N as follows… C/V
Terrestrial
Leaves
Trees
Marine Plants
Zostera marina
Spartina alterniflora
Marine Macroalgae
Browns
Greens
Reds
Microalgae & Microbes
Diatoms
Greens
Bacteria
Fungi
100
1000
17 – 70
24 – 45
30 (mean)
10 – 60
20
6.5
6
5.7
10
Carbon emissions?
• Marshes, inner waters and tidal flats are
thought to be the largest producers of carbon
dioxide in terms of ecosystems.
• Reasons, types of biota in estuaries, thus
produce carbon dioxide.
• Estuaries are thought to be net heterotrophic.
Guess what this is?