Biomass, Productivity, and Key Biogeochemical Cycles

Understanding Biomass and Ecosystem Productivity

Biomass is the total amount of organic matter contained in living beings. It is usually expressed in units of mass per surface area (e.g., g/m², kg/m²) or mass per volume (e.g., g/cm³, kg/m³).

Ecosystem Productivity

Biomass production, or productivity, is the increase in biomass in an ecosystem over a determined period of time. It can be measured in different units, for example, kg/m² per year.

Key Production Definitions

• Gross Production: The total solar energy converted into organic matter per unit time.
• Net Production: The difference between gross production and respiration (energy used) across all trophic levels.

Ecological Pyramids and Trophic Relationships

Ecological pyramids are graphical representations used to interpret the trophic relationships of individuals within an ecosystem.

Types of Ecological Pyramids

1. Pyramids of Numbers: The area of each level is proportional to the number of individuals in the ecosystem at that trophic level.
2. Pyramids of Biomass: The area of each level is proportional to the biomass of that trophic level, often providing a better representation of ecosystem reality.
3. Pyramids of Production: The area of each trophic level is proportional to its production (gross or net).

The Cycles of Matter: Biogeochemical Processes

The Cycle of Matter: The organic chemical elements that form organisms are constantly reused. Matter in nature describes a cycle that begins when producers incorporate these elements into their bodies and ends when decomposition returns them to the environment.

Biogeochemical Cycle: This term describes the specific path an element takes in nature, starting when producers incorporate it and ending when it returns to the environment.

Major Biogeochemical Cycles

The Carbon Cycle

The Carbon Cycle begins when photosynthetic organisms absorb CO₂ from the air or water.

The Nitrogen Cycle

1. Plants absorb and utilize soil nitrate nitrogen in the synthesis of biomolecules.
2. Nitrogen content in the biomolecules flows through the trophic chain.
3. Decaying organisms release nitrogen from biomolecules, which is converted into ammonia and released into the soil.
4. Nitrifying bacteria transform ammonia into nitrates.

The Phosphorus Cycle

1. Producers absorb phosphates and use them for the synthesis of biomolecules.
2. Phosphorus content in the biomolecules passes to other trophic chains as organisms decay.
3. Free phosphorus molecules and the skeletons of animals release phosphates, making them available again in the soil for plants.