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 SO 4 When sulfate is reduced it by phytoplankton, it becomes dimethylsulfoniopropionate (DMSP) to volatile dimethyl sulfide (DMS)

DMS The molecule DMS CH 3 -S-CH 3 Approximately 50% of the global flux of S is derived from the marine environment. Oxidation of DMS leads to production of SO 4 in the atmosphere

Euphotic Zone

The Reduction of Sulfate Some SO 4 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 O 2 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 mV to mV

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.

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 Leaves100 Trees1000 Marine Plants Zostera marina 17 – 70 Spartina alterniflora24 – 45 Marine Macroalgae Browns30 (mean) Greens10 – 60 Reds20 Microalgae & Microbes Diatoms6.5 Greens6 Bacteria5.7 Fungi10

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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