Ecosystem Biomass Production and Biogeochemical Cycles

Primary and Secondary Production in Ecosystems

Primary production is the increase in biomass per unit of time by producers. This represents the solar energy that plants (autotrophs) store in the chemical bonds of organic compounds through photosynthesis. Conversely, secondary production is the increase in biomass per unit of time by consumers and decomposers.

Gross and Net Primary Production

Gross Primary Production (GPP) is the total amount of energy fixed by producers through photosynthesis. If we discount the energy consumed for the maintenance of vital functions, such as cell respiration (R), we obtain the Net Primary Production (NPP). The net value represents the amount of biomass available to the next trophic level.

The formula is: NPP = GPP - R

Productivity, Turnover, and Efficiency

Productivity is the ratio of net output (amount of energy per unit of time) to biomass (total organic matter), expressed as a percentage per unit of time; it is essentially the relationship between interest and capital.

• Productivity Formula: (PN / B) * 100
• Turnover Time: This is the time a trophic level needs to double its biomass if it is not consumed by any predator, or the period it takes to renew biomass from one trophic level. It is inversely proportional to productivity: the higher the productivity, the shorter the renewal time.
• Renewal Time Formula: Biomass / Net Production

Efficiency is the percentage of the net output of one level that becomes the net output of the next level. It is expressed as a percentage and usually varies between 6% and 15%. While 10% is often taken as the average, efficiency can be higher in some cases.

Efficiency Formula: (PN level n / PN level n-1) * 100

The Environmental Problem of Bioaccumulation

The process called bioaccumulation is the accumulation of toxic substances, such as heavy metals (cadmium, mercury, lead, and arsenic) or synthetic organic compounds, in living organisms. These substances reach concentrations higher than those recorded in the environment. This occurs when ingested substances cannot be decomposed or excreted effectively.

Limiting Factors in Ecosystems

A limiting factor means that while all factors (light, temperature, and humidity) and elements (phosphorus, nitrogen, calcium, potassium, etc.) are necessary, if one of them is scarce, that specific factor is called the limiting factor. For example, phosphorus is often the limiting factor in water environments.

Biogeochemical Cycles: Carbon, Nitrogen, and Phosphorus

Elements like carbon, oxygen, nitrogen, hydrogen, phosphorus, and sulfur in the biosphere form part of organic matter. Through chemical changes, they may pass into inorganic forms and move through various subsystems. Processes such as dissolution, oxidation, precipitation, and photosynthesis lead these elements from one subsystem to another.

The atmosphere, hydrosphere, crust, and biosphere work as coupled machinery to exchange energy and matter in various ways, transforming the chemical compounds that enter them. A biogeochemical cycle is the set of processes a chemical element experiences as it passes from one subsystem to another as part of different molecules.