Nutrient Cycles Notes

Within ecosystems, chemical elements required by living organisms are constantly recycled.
Water and air penetrate the soil.
Nutrients are used by organisms for growth.
Decomposers break down organic matter.
Soil stores nutrients, which plants absorb.
Autotrophs obtain inorganic nutrients from the environment.
Nutrients are used to synthesize carbon compounds, which are then transferred by feeding.
Saprotrophs (decomposers) break down organic material and return nutrients to the environment.

Common examples of matter and nutrients include carbon, nitrogen, and water.
1. Water Cycle
2. Carbon Cycle
3. Nitrogen Cycle

The carbon cycle demonstrates the exchange (transfer) of carbon between sources and sinks.
The total amount of carbon does not change as the Earth represents a closed ecosystem.
Carbon is either sequestered or transferred between the Earth’s four environmental spheres:
- Biosphere – Carbon is stored within organic compounds (carbohydrates, lipids, etc.).
- Hydrosphere – The carbon is stored as either dissolved $\text{CO}_2$ or as bicarbonate ions.
- Lithosphere – Carbon compounds are found in detritus or fossil fuels (coal, oil, gas).
- Atmosphere – Carbon mainly accumulates as carbon dioxide {CO}2) or methane ($$ \text{CH}4).

Respiration: $\text{CO}_2$ released from animals into the air.
Photosynthesis: $\text{CO}_2$ trapped by plants and turned into Oxygen.
Combustion: Organic carbon in the form of fossil fuels (gas, oil, coal) is burned and turned into $\text{CO}_2$ .
Decomposition: Decomposers break down dead material (organic carbon) from plants and other organisms and release $\text{CO}_2$ into the air, soil, and water.

The diagram illustrates the flow of carbon between:
- Animals
- Plants
- Fossil Fuels
- Oceans
- Limestone
- Atmosphere ( $\text{CO}_2$ )
Key processes include respiration, photosynthesis, fossilization, feeding, sedimentation, extraction, pollution, decomposition, and dissolution.

The process of carbon transfer between a source and a sink is referred to as a carbon flux.
Global carbon fluxes are large and are measured in gigatonnes (1 billion metric tonnes).
Two of the main carbon fluxes within ecosystems are photosynthesis and cell respiration.
Photosynthesis takes up $\text{CO}2$ from the atmosphere, while cell respiration releases $\text{CO}2$ .
The equation for Photosynthesis is: $H2O + CO2 \rightarrow C6H{12}O6 + O2$
The equation for Cellular Respiration is: $C6H{12}O6 + O2 \rightarrow H2O + CO2 + ATP$

The carbon in living organisms can be released via decomposition.
Saprotrophs will break down decaying organic matter into $\text{CO}_2$ .
Decomposition requires oxygen (aerobic respiration) and cannot occur effectively in anaerobic or acidic conditions (e.g., waterlogged soil).
Partially decomposed organic matter gradually forms fossil fuels.
Different types of fossil fuels may form depending on conditions:
- Peat forms from plant material in wetlands, before forming coal.
- Oil forms from organic material that has settled on the sea bed.
The transformation follows: Plant Material $\rightarrow$ Peat $\rightarrow$ Coal, using Heat and Pressure

Peat, coal, oil, and natural gas are fossil fuels, which function as major carbon sinks within the lithosphere (earth).
These carbon deposits can be released into the atmosphere (as $\text{CO}_2$ ) via combustion.
Combustion reactions involve the production of energy (heat) in the presence of oxygen gas.
Combustion reactions can occur naturally following lightning strikes (acts as an ignitor).
Human activity is greatly increasing combustion rates of fossil fuels (as an energy source).
The general equation for Combustion is: Fossil Fuel + Oxygen $\rightarrow$ Carbon Dioxide + Water + Energy.

The Keeling curve is a daily record of the global atmospheric $\text{CO}_2$ concentrations.
This record demonstrates the following:
- Carbon dioxide levels are increasing due to human activity (combustion).
- There are annual fluctuations due to photosynthesis and cell respiration (levels lower in northern hemisphere summers).
- The data from 1960 to 2020 shows a rise from approximately 320 ppm to over 400 ppm.

The majority of the Earth’s atmosphere is composed of nitrogen gas ( $\text{N}_2$ = ~79%); however, it is chemically inert in this form.
Atmospheric nitrogen must be chemically processed by nitrogen-fixing bacteria in order to be used by plants. This is known as Nitrogen Fixation.
Plants absorb nitrogen from the soil as nitrite ions, nitrate ions, or ammonium, while animals consume these products from plants.
When organisms die, nitrogen is in an organic form (proteins) and must be converted back into inorganic form (ammonification).
Nitrogen in the soil is converted back into inert nitrogen gas by denitrifying bacteria.

The water (hydrologic) cycle describes the continuous movement of water on, above, and below the surface of the Earth.
This movement of water involves several different processes, including:
- Evaporation – Water is converted to vapour by the sun and transferred from the Earth’s surface to the atmosphere.
- Transpiration – Water vapour is released by plants and soil into the atmosphere.
- Condensation – Water vapour is transformed into liquid water droplets in the air (creating clouds and fog).
- Precipitation – Water vapour in the atmosphere condenses into liquid (rain) or solid (snow) and returns to the Earth.
- Infiltration – The flow of water from the ground surface into the soil.
- Runoff – The variety of ways water moves along the ground.
- Subsurface Flow – The flow of water underground (will eventually drain into oceans or return to the surface via springs).