estuarine cycles estuaries are the best cyclers in the world!
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Estuarine Cycles
Estuaries are the best cyclers in the world!
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Sulfur
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• 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)
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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
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The Reduction of Sulfate• Some SO4 reducing bacteria (SRB) are closely
related with the rhizophere of Spartina alterniflora (control biogeochemical cycling in marsh sediments)
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Sulfides in the soil…
Lucinid Bivalves
Lamars et al. 2013
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SRB
• Some of the reducing bacteria families include:
Desufovibrionaceae Desulfobacteriaceae
Examples of bacteria….Desulfovibrio desulfuricansDesulfobacterium spp.
Image University of Hawaii
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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.
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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
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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!
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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
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Carbon
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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).
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Carbonate Reservoir
Dissolved Inorganic Carbon• DIC – Bicarbonate, carbonate,
carbon dioxide
Solid Carbonate Minerals• Calcium carbonate
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Complex Carbon Cycles
• Methane and carbon dioxide are the gases that get attention as they are “greenhouse gases”
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Inorganic Carbon
• The processing of inorganic forms of carbon in phytoplankton are important for short-term process. CO2O2
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Inorganic to Organic Form
CNow an organic form for zooplankton to use for energy
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The Cycle Continues…
CO2
Through heterotrophic functions (respiration), it is now back to the inorganic form
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Iron was found to be one of the limiting components to “control” phytoplankton populations
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How about increasing the amount of autotrophic species through iron fertilization? There is a Southern Ocean Iron Enrichment Experiment
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Ratios of CarbonCarbon was found to be in ratios with N as follows… C/V
TerrestrialLeaves 100Trees 1000
Marine PlantsZostera marina 17 – 70Spartina alterniflora 24 – 45
Marine MacroalgaeBrowns 30 (mean)Greens 10 – 60Reds 20
Microalgae & MicrobesDiatoms 6.5Greens 6Bacteria 5.7Fungi 10
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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.
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Guess what this is?