Biogeochemistry is the study of how biological, geological, and chemical factors influence the cycling of elements like carbon, nitrogen, phosphorus, and sulfur through ecosystems. The interplay between these elemental cycles is critical, particularly the role of microorganisms in processes such as carbon cycling and nitrogen fixation. Isotopic analysis serves as a vital tool in this research, helping to trace changes in elemental ratios and identify sources of new carbon in the environment.

1. BIOGEOCHEMISTRY

2. What is Biogeochemistry?
• The study of the biological, geological and chemical factors that influence the
movement of chemical elements through living systems across space and
time.
• Processes can be studies at the microbial, ecosystem and global scales
• Scales are becoming increasingly integrated.
• Ex: The role of microorganisms in carbon cycling and global climate change
• Elements “cycle” through reservoirs often termed as source or sink
• Matter of perspective and what is being measured
• Ex. Plant biomass is a sink of atmospheric carbon (CO2) via photosynthesis
Burning of fossil fuels (i.e. dead plants) is a source of carbon to the atmosphere

4. Four main elemental cycles
• Carbon (C)
• Nitrogen (N)
• Phosphorous (P)
• Sulfur (S)
• Elements do not cycle independently.
• Ex: Denitrification (N03  N2) requires C that is easily consumed by microbes

5. Carbon Cycle
Short Term
Storage
Long Term Storage
Significant Microbial
Component
Notice: natural processes
of photosynthesis and
respiration are nearly
equal if not slightly in
favor of storage in biota,
soils, and ocean surface
water
UNITS!
Gigatons C/Year

6. Nitrogen Cycle
Critical microbial components
at all stages.
Highly abundant form of
N. Inaccessible to most
organisms due to the
triple bond between N
atoms. Primarily rely on
nitrogen fixing bacteria to
introduce bioavailable N
to ecosystems. (Note:
Some trees can fix N due
to symbiotic relationship
with bacteria.)
Main mechanism in which
nitrogen is removed from
ecosystems
DON

7. Sulfur Cycle
Important microbial
component
Concern of acid rain
via Industrial
Processes

8. Phosphorous Cycle
No gaseous phase
Weathering of rock is the
original source of P
Important microbial
component

9. Isotopes: a powerful technique in Biogeochemistry
• Isotopes: atoms of the same element that vary in atomic mass due to different
number of neutrons
• Two most common in Biogeochemistry research
• Carbon: 12C, 13C Nitrogen: 14N, 15N
• Different reservoirs have isotopic signatures
• Plants: higher 13C:12C than the atmosphere
• Nitrogen in the ocean: higher 15N:14N signature than terrestrial bound nitrogen
• Organisms higher on the food chain have higher 15N values
• Vegetarian/vegans have lower 15N values
}Research implications?

10. Two main isotopic techniques
• Relative Abundance: measure isotopic ratios to determine if
something is changing
• Ex: The ratio of atmospheric 13C:12C is increasing indicating more plant-based
carbon is entering the atmosphere
• What is the source of this new plant-based carbon?
• Stable Isotopes: Raise the amount of the rarer isotope way above
background levels and follow it through a system
• Ex:15N can be added to a stream and measured downstream to determine
the demand for N by microorganisms.