Biogeochemical Cycles

First, let’s look at this word and define its parts!

Bio-geo-chemical

Bio=life

Geo=earth

Cycle=move around and around (like the hand on a clock-face)

In ecology, we examine the movement of important abiotic items with cycles.

• A biogeochemical cycle is the movement of a particular chemical through the biological (biotic) and geological (abiotic) parts of an ecosystem.

• A substance can change forms at different phases of a cycle (as we will see with each different cycle).

• Cycles don’t necessarily have a beginning or end.

3 Main Abiotic items studied in the biogeochemical cycles

Water

Carbon

Nitrogen

The Water Cycle• … is also known as the hydrologic cycle

The Water Cycle

• Precipitation (water) falls to earth. Some of it goes in the ground, some into waterways, or in temporary pools.

• Percolation allows water to infiltrate (go down through) the soil (causing ground water).

The Water Cycle

• Runoff occurs when water on the surface flows in to the ocean.

The Water Cycle

• Evaporation occurs when liquid water becomes a gas and moves up into the atmosphere.

• Transpiration is when water gas is released from plant leaves.

• When all this water gas forms clouds, it is called condensation.

Think, Pair, Share

After condensation, what step in the cycle is next? Why is this important?

The Water Cycle• … is also known as the hydrologic cycle

The Carbon-Oxygen Cycle• … we’ll probably just refer to it as the carbon cycle.

The Carbon-Oxygen Cycle

• Carbon and Oxygen often travel together in the form of CO2 (carbon dioxide).

• We’ll start in the atmosphere, but remember that matter and energy flows in a cyclical pattern in an ecosystem.

The Carbon-Oxygen Cycle

• Gaseous CO2 is pumped in to the atmosphere from multiple sources like heterotrophs exhaling and burning fuels.

The Carbon-Oxygen Cycle

• The atmospheric CO2 is taken in by plants, which are then eaten by primary consumers.

• Primary consumers are preyed upon by secondary consumers.

The Carbon-Oxygen Cycle

• From secondary consumers, CO2 is returned to the environment in two ways:

– Death (decay/fossil fuel)

– Exhaling during Cellular Respiration

Where to next?

So remind me, where does the carbon and oxygen go after death and cell respiration?

The Carbon-Oxygen Cycle• … we’ll probably just refer to it as the carbon cycle.

The Nitrogen Cycle

The Nitrogen Cycle

• Just like in the other two cycles, nitrogen travels in the atmosphere. Nitrogen, unlike carbon and water, must take different chemical forms in order to travel.

The Nitrogen Cycle

• In the air, nitrogen takes the form of N2. It is then “fixed” by bacteria & fungi in the soil, to become ammonium, NH4

+.

The Nitrogen Cycle

• Once fixed by bacteria, it can then be assimilated(taken in and used) by plants, which are then consumed by primary consumers.

The Nitrogen Cycle

• Once those animals are dead, the decomposition (breaking down) process by way of fungi and bacteria can then return the nitrogen to the soil, starting the whole process over again.

The Nitrogen Cycle

• Nitrogen can also be denitrified and released back into the atmosphere by bacteria.

The Nitrogen Cycle

• It should also be noted that lightning plays a role in bringing in the original N2 into the atmosphere!