Introduction to Biogeochemical

Introduction to Biogeochemical
Cycles

Jean
-
Marc Mayotte

jean_marc.mayotte@geo.uu.se

Matter cannot be created or destroyed...


...but it can be moved around

What is a biogeochemical cycle?



The movement of matter through a closed
system (Earth) such that there is no beginning or
end of the movement; the matter simply moves
between reservoirs.

Earth is a closed system

(
almost... there is some very small gain/loss from space
)


We can divide the system into four parts:


Atmosphere

Hydroshpere

Lithosphere

Biosphere

The processes in the biosphere can have very large impacts the ”balance” of the cycles
and are very important to sustaining life on Earth... hence the emphasis on
bio

in
bio
geochemical cycles

Atmosphere

The layer of gasses held close to Earth by the
force of gravity

Hydrosphere

The total mass of all
liquid

water on Earth

Lithosphere

The outermost ”shell” of the Earth

This one!

Biosphere








Global sum of all ecosystems on Earth

General cycle

Movement through the
atmosphere is
generally rapid

Movement through
soils and rocks is
generally slow

Movement to/from
influences the fluxes
to/from other
reservoirs

What is the ”matter”?...
(sorry)

•
Carbon (C)

•
Oxygen (O)

•
Nitrogen (N)

•
Sulfur (S)

•
Phosphorus (P)

•
Water

(H₂O)

•
Methane (CH₄)

•
Silica (Si)

•
Hydrogen (H)

•
Potassium (K)

•
Calcium (Ca)

•
Iron (Fe)

•
Magnesium (Mg)
…

There are about 30 chemical elements and compounds important to life...

Why is this important?

Living organisms depend on chemical inputs to
sustain their energy needs and well
-
being. The
speed, location and efficiency with which these
chemicals are moved, changed and recycled is
directly related with the diversity and scale of
life on Earth. The cycles can also help explain
the accumulation of greenhouse gasses and
illustrate the impacts of human interactions with
the environment.

Where is the matter moving?

Reservoirs

Ocean floor

S
oil

Deep sediments/rocks

Ocean surface

Coastal ocean

Plants

Deep ocean

Atmosphere

Terrestrial

Ocean

How is the matter moving?

Fluxes

•
Dissolution out of and dissolving into water

•
Plant life and bacteria are major drivers of
chemical cycling

•
Geologic events (volcanos, subduction,
abduction)

•
Precipitation, errosion, freeze/thaw,
evaporation

•
Sedimentation and burying


Sources

and
sinks

•
A
source

is a reservoir with a large outward
flux of the chemical in question

•
A
sink

is a reservoir with a relatively low
outward flux of the chemical in question. A
deposited chemical will remain in the sink for
a very long period of time (almost permanent
on a human timescale)

The Nitrogen cycle

Nitrogen cycle in the biosphere

Nitrogen is a very important part of many
biological processes but it cannot be used in its
elemental (N) form by ”higher order” plants and
animals as it does not react with other
chemicals easily. Processes which convert free
nitrogen into more accesable forms are fixation
and nitrification. Mineralization and
denitrification then move it back to molecular
nitrogen. All of these processes are an integral
part of the biosphere.

Nitrogen cycle in the biosphere

The Nitrogen cycle

Fluxes

The Nitrogen cycle

Sinks

The Nitrogen cycle

Human Influence

Discussion:

•
Artificial nitrogen fixation (ex: man
-
made
fertilizers) has introduced a vast amount of
fixed nitrogen into the nitrogen cycle. What
consequences does this have on the
surrounding ecosystems, most notably the
aquatic ecosystems?

Eutrophication

The addition of artificial nutrients (fixed
nitrogen) to natural waters can cause a dramatic
increase in population of nutrient demanding
organisms (ex: cyanobacteria (algae) and
phytoplankton) which can cause a dramatic
decline in oxygen levels in the water (hypoxia)
thus making the water uninhabitable by many
marine animals.

Eutrophication

Conclusions

•
The cycling of chemicals on Earth has been greatly altered
by human interaction.

–
Knowledge of how cycles have been altered is important for
many numeric models of the environment and must be
accounted for (ex: the global climate models have sub
-
models
of these cycles imbedded in them)

•
Understanding these cycles is essential to understanding
global climate change

•
Many of the cycles are coupled (one chemical affects
another); the cycles are way, way more complex than
shown above.

•
The figures presented here are not complete or absolutely
accurate and should only be used to give an idea of the
general behavior of the cycling.