Why Do Ecosystems Need Nutrient Cycles?

1. All living organisms need elements like carbon, nitrogen, and phosphorus to build their bodies.
2. Unlike energy, which flows and is eventually lost as heat, matter is recycled.
3. Earth receives constant sunlight, but almost no new matter. Nutrients must therefore move in continuous loops.

Why Don’t Nutrients Run Out?

1. Nutrients are reused through a repeating loop:
   1. Producers absorb minerals from soil, water, or air.
   2. Consumers obtain nutrients by feeding.
   3. Decomposers break down dead organisms and waste, returning nutrients to the environment.
   4. Nutrients re-enter producers, completing the cycle.

What Happens When a Nutrient Cycle Is Disrupted?

1. If a cycle breaks or becomes unbalanced, entire ecosystems shift.
2. The effects of this disruption include:
   1. Nutrient depletion → reduced plant growth, lower productivity.
   2. Nutrient overload → pollution, algal blooms, oxygen loss in water.
   3. Species loss → organisms cannot obtain essential nutrients.
   4. Community changes → fast-growing or opportunistic species dominate.

Example

• Excess phosphorus from fertilizers enters rivers, leading to rapid algal growth.
• This causes water to become turbid and light to become blocked.
• Algal decay depletes dissolved oxygen, creating hypoxic “dead zones.”
• Results include fish kills and biodiversity loss; reduce runoff with buffer strips and smarter fertilizer timing/doses.

How Does Carbon Moves Through Living Systems? (Carbon Cycle)

Carbon is the backbone of organic molecules, moving between the atmosphere and living things through predictable processes.

1. Photosynthesis
   1. Plants and algae take CO₂ from the atmosphere and convert it into glucose.
   2. Carbon moves into living organisms.
2. Respiration
   1. All organisms respire, releasing CO₂ back to the atmosphere.
3. Feeding & Decomposition
   1. Animals obtain carbon by eating plants or other animals.
   2. Decomposers break down dead organisms, releasing CO₂.
4. Combustion
   1. Burning fossil fuels or biomass releases stored carbon into the atmosphere.

How Does Nitrogen Become Usable? (Nitrogen Cycle)

1. Nitrogen is required for proteins and DNA, but most organisms cannot use N₂ gas directly.
2. The nitrogen cycle converts nitrogen into usable forms.
3. Nitrogen Fixation
   1. Nitrogen-fixing bacteria convert atmospheric N₂ into ammonia or nitrates usable by plants.
   2. Locations
      1. Soil bacteria
      2. Root nodules in legumes
4. Nitrification
   1. Nitrifying bacteria convert ammonia → nitrites → nitrates, which plants absorb more easily.
5. Assimilation
   1. Plants absorb nitrates to build amino acids and proteins.
   2. Animals obtain nitrogen by feeding.
6. Ammonification
   1. Decomposers break down dead material, releasing ammonia back into the soil.
7. Denitrification
   1. Denitrifying bacteria convert nitrates back to N₂ gas, returning nitrogen to the atmosphere.

How Does Phosphorus Move Without a Gas Phase? (Phosphorus Cycle)

1. Phosphorus is needed for DNA, RNA, ATP, and cell membranes.
2. It doesn't enter the atmosphere.
3. Weathering: Rock minerals containing phosphate break down, releasing phosphates into soil and water.
4. Absorption: Plants absorb phosphates to build nucleic acids and ATP.
5. Transfer: Animals obtain phosphorus by eating plants or other animals.
6. Decomposition & Sedimentation
   1. Decomposers return phosphates to soil or water.
   2. Some phosphates settle into sediments and may form new rock over millions of years.

Why Are Nutrient Cycles Important?

1. Nutrient cycles keep ecosystems productive and stable by ensuring essential materials are always available.
2. Its key roles are to:
   1. Support growth by supplying producers with essential materials.
   2. Prevent depletion by returning matter to usable forms.
   3. Maintain biodiversity by keeping conditions suitable for many species.
   4. Provide balance by linking producers, consumers, and decomposers.

What Are Some Human Impacts on Nutrient Cycles?

1. Soil Degradation: Deforestation and over-farming reduce soil nutrient content and structure.
   1. Effects
      1. Lower fertility
      2. Erosion
      3. Reduced crop yields
2. Climate Change: Burning fossil fuels increases atmospheric CO₂.
   1. Effects
      1. Altered rainfall patterns
      2. Ocean acidification
      3. Disrupted carbon reservoirs
3. Protecting Nutrient Cycles: Sustainable practices help maintain natural cycles.
   1. Strategies
      1. Crop rotation and reduced fertilizer use
      2. Protecting forests and wetlands
      3. Reducing fossil fuel emissions
      4. Adding compost or organic matter to restore soil nutrients