Lecture 14 - Nitrogen Sulfur Phosphorous and other Nutrients

• photosynthesis is not limited by the availability of carbon
• nitrogen and phosphorus most common in freshwater systems
• sulfur, silicon, and iron can be important in certain situations
• N2 gas is the most form of nitrogen
• in aquatic ecosystems N can be in inorganic and organic forms
• most important inorganic forms of N in aquatic ecosystems are Nitrate and ammonium
• nitrite and and nitrous oxide can also be present in significant quantities
• nitrogen has many organic forms such as:

  Amino acids, nucleic acids, proteins and urea
• organic forms of nitrogen can be dissolved or particluate
• nitrogen is required for life
• many consumers can only assimilate organic nitrogen, such as, fish, insects and mammals
• use enzymes to breakdown complex organic molecules
• primary producers and bacteria can take dissolved inorganic nitrogen from the water
• ammonium is preferred as it takes less energy to use
• the enzyme nitrogenase is inactivated by oxygen and so specialized cells called heterocyst are used to protect it from oxygen