1. Estuaries are the best cyclers in the world!
Estuarine Cycles
Estuaries are the best cyclers in the world!

2. Sulfur

3. 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)

4. 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

5. The Reduction of Sulfate
Some SO4 reducing bacteria (SRB) are closely related with the rhizophere of Spartina alterniflora (control biogeochemical cycling in marsh sediments)

6. Sulfides in the soil…
Lucinid Bivalves
Lamars et al. 2013

7. SRB Some of the reducing bacteria families include: Desufovibrionaceae
Desulfobacteriaceae
Examples of bacteria….
Desulfovibrio desulfuricans
Desulfobacterium spp.
Image University of Hawaii

8. 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.

9. 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

10. 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!

11. 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 mV to mV

12. Carbon

13. 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).

14. Dissolved Inorganic Carbon
Carbonate Reservoir
Dissolved Inorganic Carbon
DIC – Bicarbonate, carbonate, carbon dioxide
Solid Carbonate Minerals
Calcium carbonate

15. Complex Carbon Cycles
Methane and carbon dioxide are the gases that get attention as they are “greenhouse gases”

16. Methane
Carbon dioxide

18. Inorganic Carbon
The processing of inorganic forms of carbon in phytoplankton are important for short-term process.
CO2 O2

19. Inorganic to Organic Form
Now an organic form for zooplankton to use for energy

20. CO2 The Cycle Continues…
Through heterotrophic functions (respiration), it is now back to the inorganic form

21. Iron was found to be one of the limiting components to “control” phytoplankton populations

23. How about increasing the amount of autotrophic species through iron fertilization? There is a Southern Ocean Iron Enrichment Experiment

24. Ratios of Carbon Terrestrial
Carbon was found to be in ratios with N as follows… C/V
Terrestrial
Leaves Trees Marine Plants Zostera marina 17 – 70 Spartina alterniflora 24 – 45
Marine Macroalgae
Browns 30 (mean) Greens 10 – 60 Reds Microalgae & Microbes Diatoms Greens Bacteria Fungi 10

25. 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.

26. Guess what this is?