Ecological Cycles & Nutrient Recycling

• Understanding ecological cycles is crucial for comprehending how Earth's closed systems sustain life through the recycling of nutrients, water, and essential elements like carbon and nitrogen.
• Key materials are constantly recycled and reused by living things, maintaining ecological balance.

Cycling of Important Nutrients

• Nutrients, found in food, are essential to build and operate an organism's body.
• These are made of elements like carbon, oxygen, hydrogen, and nitrogen and are pure substances and cannot be broken down into simpler substances.
• Nutrients include carbohydrates, fats, and proteins, among others.

Water Cycle

• It involves the continuous movement of water on, above, and below the surface of the Earth.
• The main processes include evaporation, transpiration, condensation, precipitation, and run-off.
• Evaporation: heat from the sun warms bodies of water and converts it into water vapour.
• Transpiration: Water vapour is released into the atmosphere through plants' leaves.
• Condensation: As water vapor cools, it changes into liquid forming clouds.
• Precipitation: Water falls back to earth in the form of rain, snow or hail.
• Water that falls on the ground is called run-off, which flows off the surface into streams or rivers.
• Aquifers: Some water seeps into the ground into underground lakes.
• Some ground water is taken up by plants through their roots.

Carbon Cycle

• A critical process for all life on Earth, involving the continuous recycling of carbon atoms.
• Photosynthesis and cellular respiration are two natural processes, impacting the carbon cycle, performed by living things.
• Photosynthesis: Producers (plants) use the sun's energy to create sugar.
  • The word equation is: carbon dioxide + water + light yields glucose + oxygen
  • The chemical equation is: 6CO2 + 6H2O + light yields C6H12O6 + 6O2
• Cellular Respiration: Performed by consumers to break down food and create energy.
  • It releases carbon dioxide back into the atmosphere.
  • The word equation is: glucose + oxygen yields carbon dioxide + water + energy
  • The chemical equation is: C6H12O6 + 6O2 yields 6CO2 + 6H2O + energy
• Combustion: This releases carbon dioxide into the atmosphere.
• Decomposition: Most of the carbon that forms living organisms is returned to the atmosphere by decomposers.

Impact of Human Activities on the Carbon Cycle

• Mining releases previously stored carbon.
• Burning fossil fuels, such as coal, oil, and gas, increases carbon dioxide levels.
• Deforestation also increases CO2 levels.
• Oceans are known as carbon sinks because they can absorb large amounts of CO2 from the atmosphere.
• An excess of carbon dioxide can lead to ocean acidification and disrupt aquatic ecosystems.
• High levels of CO2 in the atmosphere have been linked to climate change.
• Climate change leads to shrinking glaciers, rising ocean levels, and affects many other environmental factors.

Nitrogen Cycle

• This cycle is essential because nitrogen is required for DNA and producing essential proteins.
• Nitrogen constitutes 79% of the earth's atmosphere.
• Nitrogen is constantly recycled and reused in different forms.
• Nitrogen cycle is composed of many smaller cycles.
• Producers cannot directly use nitrogen gas (N2) but absorb it as nitrate ions (NO3-)
• Nitrogen fixation occurs by nitrogen-fixing bacteria in root nodules of legumes, peas, beans, and soil.
• Decomposers: Bacteria and fungi decompose organisms and release nitrogen as ammonium.
  • They add to the process of ammonification.
• Most plants cannot use ammonium as is and rely on nitrifying bacteria.
  • Nitrifying bacteria convert ammonium into nitrites (NO2-) and then nitrates (NO3), which plants can absorb.
• Denitrifying bacteria live in soil and convert nitrates back into nitrogen gas, returning it to the atmosphere.
• Consumers get usable nitrogen by eating producers.
  • When they digest proteins, animals produce a toxic by-product, which must be excreted in the form of urea.

Impact of Human Activities on the Nitrogen Cycle

• Human activities have increased the movement of nitrogen through the environment by about 140 million tonnes annually.
• Farming: Nitrogen is a main ingredient in many fertilizers, excess nitrates wash from the soil into streams
  • This results in more nitrogen that the natural processes of the cycle can handle.
  • This can lead to eutrophication.
• Burning of Fossil Fuels: Emissions contain pollutants entering the atmosphere. Nitrogen or sulfur-containing gas mixes with water vapor to make acids fall back to Earth in acid precipitation.
• The effects of acid rain: Soil quality, aquatic environments and plant and animal health.
• Responses include some countries limiting emissions, reducing acid rain greatly.
• Since wind can carry emissions across borders, acid rain is still an international problem.