Nutrient Cycles in Ecosystems Overview

Hydrologic (Water) Cycle

Collects, purifies, and distributes the Earth's water supply.

Precipitation

Falls on terrestrial ecosystems.

Surface Runoff

Movement of water over soil after precipitation.

Glaciers

Precipitation converted to ice and stored.

Groundwater

Water that seeps deeper into the soil.

Aquifers

Underground layers of sand and water-bearing rock.

Over-withdrawal of Freshwater

Using water faster than it can be replaced.

Deforestation

Reduces water infiltration into soil.

Wetland Destruction

Affects natural flood control.

Air Pollutants (Aerosols)

May weaken rainfall patterns.

Climate Change

Increases glacial melting and evaporation; alters global water distribution.

Carbon Cycle

Carbon cycles through the biosphere via photosynthesis and aerobic respiration.

Carbon dioxide (CO₂)

Makes up 0.040% of the atmosphere; stored in deeply buried deposits of dead plant matter and algae, which are converted into fossil fuels.

Decomposers

Release stored carbon from insoluble carbonate minerals and rocks in sediment.

Burning Fossil Fuels

Adds CO₂ to the atmosphere faster than natural cycles can absorb.

Nitrogen Cycle

Nitrogen is converted into multiple chemical forms as it circulates among atmospheric, terrestrial, and marine ecosystems.

Essential for

Proteins, vitamins, and DNA.

Five Steps of the Nitrogen Cycle

1. Nitrogen Fixation, 2. Nitrification, 3. Assimilation, 4. Ammonification, 5. Denitrification.

Nitrogen Fixation

Conversion of atmospheric nitrogen into a usable form by nitrogen-fixing bacteria, volcanic activity, lightning, and industrial processes.

Nitrification

Soil bacteria convert ammonia to nitrate, providing energy for nitrifying bacteria.

Assimilation

Plants absorb ammonia or nitrate to create plant compounds; animals assimilate nitrogen by consuming plants or other animals.

Ammonification

Bacteria decompose nitrogen-containing waste, producing ammonia.

Denitrification

Nitrate is converted back to nitrogen gas by denitrifying bacteria in oxygen-poor environments.

Rhizobium

Nitrogen-fixing bacteria found in root nodules of legumes.

Cyanobacteria

Photosynthetic bacteria that fix nitrogen in moist environments.

Key Nitrogen Compounds

Ammonia (NH₃), Ammonium ions (NH₄⁺), Nitrate ions (NO₃⁻).

Phosphorus Cycle

Movement of phosphorus through water, the Earth's crust, and living organisms.

Phosphorus is essential for

DNA and cell membranes; bone and teeth formation.

Phosphate Ions (PO₄³⁻)

Main form of phosphorus available to plants.

Phosphorus cycles slower

Than water, carbon, and nitrogen because it does not have a gaseous phase.

Fertilizer Use

Increases phosphorus runoff, leading to aquatic ecosystem disruptions.

Freshwater Availability

Only 0.024% of Earth's freshwater supply is accessible to humans and other species.