Carbon and Nitrogen Cycle
Learner Outcomes
• You should be able to describe the sinks
sources and exchange for carbon
• You should be able to describe the impact of
different types of fossil fuel and their relation
to atmospheric carbon dioxide concentrations
• Your should be able to describe the basic
nitrogen cycle and which component of it
humans have had the most impact
Carbon Dioxide
• Sources
• Sinks
• exchange
Trends in Atmospheric Concentrations and
Anthropogenic Emissions of Carbon Dioxide
Carbon Cycle
• Major storage or sink is
ocean
• Other sources are biomass,
soil, rock/sediment
• Transferred/released to
atmosphere
Units Gigatons
Fluxes are Gigatons/year
Practices that release/uptake Carbon
Dioxide
Release
• Burning of fossil fuels
• Deforestation
• Cement manufacturing
• Volcanic gases
Uptake
• Reforestation
• Absorption into ocean
• Uptake by biological
processes (corals,
shells)
How is organic carbon stored in sediments and rocks?
• Fossil fuels are
concentrations of peat,
coal, oil, and natural gas.
• 1 unit of coal produces
approximately
• 1.5- 2X amount of CO2 as
petroleum,
• and 2X CO2 as natural
gas
A peat bog in western Ireland
World Carbon Dioxide Emissions by Region, 2001-2025
(Million Metric Tons of Carbon Equivalent)
Nitrogen Cycling
•
•
•
•
Fixation
Decay
Nitrification
denitrification
Nitrogen Cycle: Source and Fixation
• Air is major reservoir (source)
• Most organisms cannot use N2 so they have to
“fix” it
– Nitrate ions (NO3-)
– Ammonia (NH4 )
– Urea (NH2 ) 2CO
Nitrogen Cycle: Fixation
• Atmospheric fixation (lightening strikes) 5-8%
of total nitrogen fixed
• Biological fixation-certain microbes or
symbiotic relationship with some plants and
animals
• Industrial-make ammonia, urea and
ammonium nitrate. Nearly 50% of total
nitrogen fixed
Nitrogen Cycle: Decay
• Following biological fixation: nitrogen passes
through the food chain
• Waste product decays and is broken down into
ammonia
Nitrogen Cycle: Nitrification
• Remember ammonia?
• Taken up by plants directly or converted into
nitrates/nitrites by nitrifying bacteria
• Nitrites (NO2-)
• Nitrates (NO3-)
Nitrogen Cycle: Denitrification
• Bacteria reduces nitrates to nitrogen gas
• Replenishes the atmosphere
• Question: Can denitrifiers keep up with
agricultural impact on nitrogen fixation?
Nitrogen Cycle