The Importance of Biogeochemical Cycles in Ecosystems
Nutrient Cycling in Ecosystems
A nutrient is a chemical that is essential to living things and is cycled through ecosystems.
• Matter and nutrients are cycled through the biotic and abiotic environment. This process is known as a biogeochemical cycle.
The Water Cycle (the Hydrologic Cycle)
What is it and how does it work?
Common Terms
- Evaporation: Water turning to gas due to increased temperatures.
- Condensation: Gaseous water (vapor) turns into a liquid due to decreased temperatures.
- Precipitation: Any waterfall from the sky (rain, snow, sleet, etc.).
- Runoff: Water that flows from dry land to a body of water.
- Infiltration: Filtering of water through a porous substance.
Forms of Water on Earth
- Liquid
- Gas
- Solid
Sources of Water
- Oceans
- Surface and Ground Water
- Lakes
- Rivers
- Streams
Processes of the Water Cycle
• There are 6 processes in the water cycle:
- Evaporation
- Transpiration
- Condensation
- Precipitation
- Infiltration
- Runoff
Evaporation
- Evaporation is the change of liquid water into a vapor (gaseous form).
- Sunlight helps this process because it raises the temperature of liquid water in oceans and lakes.
- Warm air rises up into the atmosphere and becomes the vapor involved in condensation.
Transpiration
- Evaporation of water from plant leaves.
- About 10% of the moisture found in the atmosphere is released by plants through transpiration.
- One leaf will transpire many more times water than its own weight.
- A large oak tree can transpire 151,000 liters of water in one year!
Factors that affect transpiration:
- Temperature
- Humidity
- Wind and air movement
- Soil moisture
- The type of plant it is!
Condensation
- When water vapor condenses in the atmosphere, it forms clouds.
- Water molecules combine with tiny particles of dust, salt, and smoke in the air to form cloud droplets, which grow and develop into clouds.
Precipitation
- When the warm vapor reaches the atmosphere, it cools and falls back to Earth.
- Water droplets grow when particles of water collide.
- If enough water collisions occur, it will produce a droplet large enough to fall out of a cloud as precipitation.
- This can occur as rain, snow, sleet, and hail.
Infiltration
- Infiltration occurs when precipitation seeps into the ground.
- This depends a lot on the permeability of the ground.
- The more permeable – the more precipitation seeps into the ground.
- This water then enters into soil levels or groundwater storage.
Runoff
- If precipitation occurs faster than it can infiltrate the ground, it becomes runoff.
- Runoff remains on the surface and flows into streams, rivers, and eventually large bodies of water such as lakes or the ocean.
- Infiltrated groundwater moves similarly as it recharges rivers and heads towards larger waters.
Runoff: An example of what can happen if it precipitates faster than the ground can infiltrate!!
The Carbon Cycle!
What is Carbon?
- Carbon is the key element for all living things.
- Autotrophs use carbon in the process of photosynthesis.
- Consumers eat plants/animals so the carbon (in the things they eat!) is transferred to them.
Photosynthesis
Recall: Photosynthesis is a process used by plants (producers) to remove CO2 from the atmosphere to make sugars (carbohydrates).
carbon dioxide + water + light energy → carbohydrate + oxygen
CO2 + H2O → C6H12O6 + O2
This is the chemical formula for glucose (which is a sugar!)
6CO2 + 6H2O → C6H12O6 + 6O2
Because matter is not created or destroyed the number of atoms on one side must equal the number of atoms on the other side (we will learn more about this in Grade 10!)
Cellular Respiration
A process used by animals to release CO2 and produce usable energy.
carbohydrate + oxygen → carbon dioxide + water + ENERGY!
C6H12O6 + O2 → CO2 + H2O
C6H12O6 + 6O2 → 6CO2 + 6H2O
Steps in the Carbon Cycle
- Carbon is found in the atmosphere.
- CO2 is absorbed by the autotrophs during photosynthesis.
- Autotrophs are consumed by heterotrophs and carbon enters the food web.
- CO2 enters the atmosphere through cellular respiration.
- After extended time and extreme heat/pressure, the carbon in the ground becomes fossil fuels (Ex – coal, oil, gasoline).
- Factories burn fossil fuels and add CO2 back into the atmosphere.
- Decomposers break down all organisms and CO2 is returned to the atmosphere.
Detritus is non-living organic material, including the bodies of dead organisms.
Inorganic Carbon
There are three main storage types of inorganic carbon:
- Atmosphere
- Oceans
- Earth’s crust
- Carbon in the ocean is used by plants for photosynthesis.
- Some can combine with calcium to make calcium carbonate (which is used to make shells).
- Most is crushed over time as sediment and becomes rocks.
Organic Carbon
- Carbon is also held in the bodies of living things.
- Decomposition of things when they die means carbon is returned to the cycle in the inorganic form (CO2).
EXCEPTION!: Bogs
- A bog is an environment that has very little oxygen – and decomposition is very slow.
- The ground is wet and spongy with dead and decomposing vegetation and the carbon in dead plants can stay in that form (peat).
The Nitrogen Cycle
What is Nitrogen?
- Nitrogen is the most abundant element in the Earth’s atmosphere.
- It makes up close to 79% of the Earth’s atmosphere.
- It is required for making DNA and proteins!
- It cannot be absorbed directly by plants and animals until it is converted into compounds that can be used.
- The usable form of nitrogen is called a nitrate ion (NO3-).
The Nitrogen Cycle: How does the Nitrogen Cycle Work?
STEP 1 – Nitrogen Fixation (*We need to get Nitrogen in a usable form*)
In order to use Nitrogen for making DNA and proteins, we need it to be in a usable form.
There are two ways of doing this:
- Atmospheric Nitrogen Fixation
- Nitrogen-Fixing Bacteria
1) Atmospheric nitrogen fixation
Small amounts of Nitrogen can be fixed by lightning.
- Nitrogen gas reacts with oxygen in the air, producing nitrates.
- These nitrates dissolve in rain or surface water – where it enters the soil!
Nitrogen Fixation (cont’d)
2) Nitrogen-Fixing Bacteria
Special nitrogen-fixing bacteria can convert the nitrogen into a form that plants can use.
- These bacteria are found either in the soil or roots of special plants (Example – soybeans, peas, clovers).
- These plants have root nodules.
- A nodule is a lump in the roots that contains the nitrogen-fixing bacteria.
Nitrification
- All organisms produce wastes and all organisms eventually die.
- Decomposers break down the nitrogen-containing compounds in the waste or dead bodies of organisms into ammonia.
- So…. Through the process of nitrification, ammonia NH3 (from the decomposition of waste/bodies) is converted into nitrite ions (NO2-).
- BUT– the usable form of nitrogen is nitrate – NO3-
Nitrite NO2-
So…. We need to convert nitrites into nitrates.
How does all of this happen?
→ BACTERIA!
Nitrogen in waste/dead body tissue → Ammonia → Nitrates (USABLE FORM!) NO3-
Decomposers → Nitrite Bacteria → Nitrate Bacteria
Denitrification
Step 3- Denitrification (The opposite of nitrification!)
- Just like we had bacteria and lightning converting nitrogen into usable nitrates, the opposite can also occur!
- Denitrifying bacteria convert the simple nitrogen compounds back into nitrogen gas (N2), which is then released back into the atmosphere.
Nitrates ———> nitrites ———–> nitrogen gas
NO3- NO2- N2
Why do plants need Nitrogen?
Too Much Nitrog