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 desulfuricansDesulfobacterium 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”

Carbon dioxide

Methane

Inorganic Carbon

• The processing of inorganic forms of carbon in phytoplankton are important for short-term process. CO2O2

Inorganic to Organic Form

CNow an organic form for zooplankton to use for energy

The Cycle Continues…

CO2

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 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

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?