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The Organic Chemistryof Water

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Biogeochemical Cycles

Organic chemistry deals mainly with chemical compounds consisting primarily of carbon and hydrogen.

Inorganic compounds such as dissolved sea salts account for the majority of dissolved solids in seawater.

Dissolved organic elements also interact with organisms on a significant scale.These elements are crucial to life and differ from the sea salts in

several ways.

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Biogeochemical Cycles

Proportions of organic elements in seawater differ from the proportions of sea salts because:The principle of constant proportions does not apply to these

elements.These nonconservative constituents have concentrations and

proportions that vary independently of salinity due to biological and geological activity.

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Biogeochemical Cycles

All life depends on material from the nonliving part of the Earth.The continuous flow of elements and compounds between organisms

(biological form) and the Earth (geological form) is the biogeochemical cycle.

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Biogeochemical Cycles

Organisms require specific elements and compounds to stay alive.Aside from gases used in respiration or photosynthesis, those

substances required for life are called nutrients. The primary nutrient elements related to seawater chemistry are carbon,

nitrogen, phosphorus, silicon, iron, and a few other trace metals. Not all elements and compounds cycle at the same rate. The biogeochemical cycle of the various nutrients affects the nature of

organisms and where they live in the sea.

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Carbon

Carbon is the fundamental element of life. Carbon compounds form the basis for chemical energy and for

building tissues. The seas have plenty of carbon in several forms. It comes from:

Carbon dioxide in the air.Natural mineral sources - such as carbonate rocks.Organisms - excretion and decomposition.

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Carbon

Carbon cycle.The movement ofcarbon betweenthe biosphereand the nonlivingworld is described

by the carbon cycle.

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Nitrogen

Nitrogen is another element crucial to life on Earth. Organisms require nitrogen for organic compounds such as

protein, chlorophyll, and nucleic acids. Nitrogen makes up about 78% of the air and 48% of the gases dissolved

in seawater.

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Nitrogen

Gaseous nitrogen must be converted to a chemically usable form before it can be used by living organisms.

Bacteria “fixes” nitrogen from the air into usable compounds - nitrate, nitrite and ammonium.

In these forms, autotrophs take up the nitrogen and incorporate it into their systems as protein.

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Nitrogen

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r The nitrogen cycle.

Bacteria and humanscarry out many of theimportant steps of thenitrogen cycle.The cycle has fourstages: Assimilation,Decomposition,Nitrification,Denitrification.

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Phosphorus and Silicon

Phosphorus is another element important to life because it is used in the ADP/ATP cycle, by which cells convert chemical energy into the energy required for life.Phosphorus combined with calcium carbonate is a primary

component of bones and teeth.

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Phosphorus and Silicon

The phosphorus cycle.Dissolved phosphorous iscarried to the sea byrunoff and leaching fromland. Phosphorus is usedby plants, then recycledthrough animals until it isreleased from wasteand decay.

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Phosphorus and Silicon

Silicon is used similarly by some organismsin the marine environment (including diatomsand radiolarians) for their shells and skeletons.Silicon exists in these organisms

as silicon dioxide, called silica.

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Iron and Trace Metals

Iron and other trace metals fit into the definition of a micronutrient.Micronutrients are substances essential to organisms in very small

amounts.These are essential to organisms for constructing specialized

proteins, including hemoglobin and enzymes. Plants need iron to produce chlorophyll.

Other trace metals used in enzymes include manganese, copper, and zinc.

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