Download Biogeochemical Cycles - Willoughby

Biogeochemistry and
Biogeochemical Cycles
Definitions:
“…the more or less circular transfer of chemical
elements from the (abiotic) environment to the
organisms and from organisms back to the (abiotic)
environment.” Odum, 1971.
“the study of the controls on the concentrations and
cycling of elements in and above the earth’s crust by
the synthesis, death and decomposition of
organisms.” Gorham, 1991.
Examples:
carbon, nitrogen, sulfur, Fe, Mn, etc.
Big Picture
• Over the ‘long term’, biogeochemical
cycling has played a fundamental role in
planetary evolution on Earth (especially
the atmosphere and hydrosphere).
Example: rise of O2 in Earth’s atmosphere.
• At present, many biogeochemical cycles
are effectively treated as dynamic
equilibria among cycled materials.
• Anthropogenic effects are measurable.
Orbital Variations
Eccentricity
100,000 yr
Tilt
41,000 yr
Precession
23,000 yr
From Albarede, 2003
Residence Time (steady state)
Response Time (non steady-state)
•
Definition: Average time the substance spends in the reservoir. It is the
time required to double the concentration in a reservoir (if output ceased).
•
Ri = amti in reservoir/fluxi
Example residence times:
water in atmosphere: 11 days
water in ocean: 3550 yr
•
Materials can be imported and exported
from ecosystems and long-term storage pools.
Basic Biogeochemical Cycle
System boundary
Inorganic Storage Pool
Available Abiotic Pool
Decomposition
(Mineralization)
Biosynthesis
Living Organic Matter
Death
Dead Organic Matter
Uplift, mining, etc.
Organic Storage Pool
Major, Minor, and Trace Elements in
Biogeochemical Cycles
• Major elemental components of living organisms (C,
H, O, N, P, S)
– Carbohydrates, proteins, lipids, nucleic acids
• Minor elements: Ca, K, Mg, Na, Si
• Trace elements: B, Co, Cr, Cu, Fe, Mn, Mo, Ni, Se,
Sn, V, Zn, REEs
• Ca and Si are only minor components of protoplasm,
but are major components of exo and endoskeletons
of microorgs and macroorgs
• Fe, Mn, N, S are also cycled rapidly via redox
processes which may not be directly coupled to the
production and decay of organic matter
(students run screaming from the room)
A Partially Open Biogeochemical
Cycle: The Oceanic Carbon System
Atmosphere
Shallow Sea
EXCHANGE
OF WATER
CO2
Dissolved Inorganic Carbon
Organically-Bound Carbon
Organic carbon
Deep Sea
Carbonate particles
Long-term removal
EXCHANGE
OF WATER