Estuary nitrogen cycle
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Nitrogen is one of several elements essential to the survival
of marine organisms. Bacteria consume nitrogen in specific compunds that
they can use and later excrete it, frequently in a different compund. Nitrogen
cycles through the ecosystem by being absorbed and excreted by bacteria,
plankton, and other marine life.
In a normal cycle, nitrifying bacteria transform nitrogen in ammonia ions
into nitrate and nitrite ions. Denitrifying bacteria breathe nitrates and
nitrites and convert the nitrogen to pure gas that bubbles out of the sediment.
Joye's research shows that when sulfide is present, nitrifying bacteria
curtail their activity.
Because less nitrogen is available to denitrifying bacteria, less exits
the system as nitrogen gas. Enough ammonia ions build up in sediment and
water to feed an exploding population of phytoplankton. Phytoplankton add
organic material to semiment, creating conditions that favor production
of even more sulfide.
Ultimately the phytoplankton consume all of one of the other elements in
their diet and die all at once. This mass mortlaity not only eliminates
the food supply for fish and crustaceans but also depletes dissolved oxygen
in the water; it is used up by decaying plankton corpses.
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Last updated January 31, 1997