Biogeochemical Cycles Nitrogen Phosphorus Carbon Sulfur Basic Components

Biogeochemical Cycles Nitrogen Phosphorus Carbon Sulfur

Basic Components of a Biogeochemical Cycle • Reservoirs – Sources – Sinks • Fluxes • The majority of biogeochemical cycles are microbially mediated.

Nitrogen Cycle

Oxidation States of Nitrogen

Nitrogen Fixation • Atmosphere is major reservoir for nitrogen in the form of nitrogen gas, N 2 • Reduction of nitrogen gas to usable form is extremely difficult – Industrially: Bohr-Haber Process: Elevated temperature and pressure – Microbiologically: Nitrogen fixing microorganisms

Nitrogen Fixation • Limited to prokaryotes • Extremely energy intensive • Overall reaction: N 2 + 8 H+ + 8 e- + 16 ATP = 2 NH 3 + H 2 + 16 ADP + 16 Pi • Nitrogenase is anaerobic

Protection from Oxygen • Heterocysts • Clumping • Rapid metabolism

Measuring Nitrogen Fixation • Heavy (stable) nitrogen • Acetylene reduction

Nitrogen Assimilation and Mineralization • Assimilation: Uptake by prokaryotes and eukaryotes • Possible forms: – Nitrate – Ammonia -- preferred • Mineralization: conversion of organic nitrogen to ammonia • Combined side loop

Nitrification • Overall, conversion of ammonia to nitrate • Step one – Conversion of ammonia to nitrite – Nitrosomonas, Nitrospira, Nitrococcus, Nitrosolobus – Overall chemistry 2 NH 4+ + O 2 -----> 2 NH 2 OH + 2 H+ NH 4+ + 1. 5 O 2 ----> NO 2 - + 2 H+ + H 2 O

• Step 2: – Oxidation of nitrite to nitrate – Nitrobacter, Nitrospira, Nitrococcus – Overall reaction NO 2 - + 0. 5 O 2 ---> NO 3 -

Phosphorus Removal • Chemical precipitation • Biological removal

Microbiology of Acid Mine Drainage