Lecture 15: Biogeochemical Cycles Flashcards
What is a source vs. sink?
- Source gives the chemical to the reservoir
- Sink receives the chemical from the reservoir
What are the reservoirs of carbon?
- Atmospheric CO2
- Oceans (CO2, HCO3-, H2CO3, CO32-)
- Rocks and sediment
- Biosphere (terrestrial and aquatic)
- Fossil fuels
Briefly summarize the carbon cycle.
The movement of carbon through the biosphere (atmosphere, ecosphere, hydrosphere, lithosphere)
- Burning fossil fuels puts carbon in the atmosphere
- Atmospheric carbon is absorbed by vegetation, soil, and oceans
How do decomposition rates vary in different conditions?
Decomposition rates are faster at higher temperatures
What is trophic efficiency?
The efficiency of energy flow between trophic levels in a food chain
What is the 10% rule of trophic level transfer?
Each trophic level only give 10% of its energy to the next level
- Uses the other 90% to live, grow, reproduce (lost to the environment as heat)
What is primary production and what limits it?
The amount of CO2 converted into organic molecules
- Limited by nutrients
What is the ocean acidification equation?
CO2 reacts with water creating acid
What are greenhouse gases?
Gases in the earth’s atmosphere that trap heat
Give some examples of greenhouse gases.
- Carbon dioxide (CO2)
- Methane (CH4)
- Nitrous oxide (N2O)
How is methane produced?
How is methane degraded?
Microbial methane production and removal
- Who
- What
- Where
- Production
- Who: methanogens
- What: methanogenesis (type of anaerobic respiration)
- Where: wetlands, guts of ruminants, rice paddies, landfills - Removal
- Who: methanotrophs
- What: methanotrophy (oxidation of methane)
Where: soils, freshwater and marine environments, and atmosphere
Briefly summarize the nitrogen cycle.
- Nitrification produces NO3-
- Nitrosomonas and Nitrobacter - Denitrification produces N2
- Bacillus, Paracoccus, Pseudomonas - Nitrogen fixation produces NH3
- NH3 is oxidized to NO3-
What is the main reservoir of nitrogen?
- Atmospheric N2
- Rocks and sediments (largely unavailable)
What makes nitrogen largely biologically unavailable?
Most of the nitrogen is found in the atmosphere as N2
- The triple bond between the N atoms makes it unreactive
What are the equations of the nitrogen cycle?
What is anamox?
Anaerobic ammonium oxidation
- Oxidation of ammonia to N2
- NH4+ + NO2- –> N2 + 2 H2O
- Responsible for 30–50% of the N2 gas produced in the oceans
- Major sink for fixed nitrogen –> limits oceanic primary productivity
What are the biotic mechanisms for fixing nitrogen?
- Nitrogenase-based reactions
- Low to no oxygen is essential
- Ex. Azotobacter, cyanobacteria
What are the abiotic mechanisms for fixing nitrogen?
- Lightning and electrical discharges can fix N2
- Haber- Bosch process: fertilizer industry
What is Trichodesmium?
Non-heterocyst forming filamentous cyanobacteria
- nifH gene analyses indicates that there are unicellular cyanobacteria that express nitrogenase too
Biological transformations of sulfur
What is anaerobic sulfate reduction?
The reduction of oxidized sulfur compunds (i.e. SO42- or S0 to H2)
Where can we find purple sulfur bacteria and in what conditions?
- Hot springs
- Stagnant water
- Bodies of water with low oxygen concentrations
How have humans influenced the carbon, nitrogen, and sulfur cycles?
Burning fossil fuels puts more carbon/nitrogen/sulfur into the environment, and they come back as things like acid rain, which can harm ecosystems
