Biogeochemical cycles

Biogeochemical Cycles

Flow of chemical elements between the atmosphere, biosphere, hydrosphere, and lithosphere.

Reservoir (in biogeochemical cycles)

A place where an element is stored (e.g., oceans, land, rocks, animals).

Residence Time

The average time an atom or molecule stays in a reservoir.

Flux

The rate of transfer of material between reservoirs.

Photosynthesis

Biochemical reactions by which plants, algae, and cyanobacteria convert light energy into chemical energy, fixing CO₂ into sugars.Equation: 6 CO₂ + 6 H₂O + light → C₆H₁₂O₆ + 6 O₂

Carbon Cycle

The movement of carbon among the atmosphere, oceans, biosphere, and lithosphere.

Types of Carbon in the Carbon Cycle

Organic carbon: from respiration

Anthropogenic carbon:

released from burning fossil fuels and human activities

Major Reservoirs in the Carbon Cycle

Lithosphere (largest), oceans (deep water), terrestrial biosphere, atmosphere (smallest).

Human Impact on the Carbon Cycle

Fossil fuel combustion, cement production, deforestation, land

Nitrogen Cycle

The movement of nitrogen among the atmosphere, biosphere, and soils; conversion between inorganic and organic nitrogen forms.

Why Nitrogen Is Needed

Essential for amino acids, proteins, plant growth, and nutrients.

Nitrogen Fixation

Conversion of atmospheric N₂ into bioavailable organic forms. Done by symbiotic + free

Nitrification

Conversion of ammonia into nitrates by chemoautotrophic bacteria.

Assimilation

Uptake of nitrogen by plants and animals to build organic molecules.

Ammonification

Conversion of organic nitrogen back into ammonium by decomposers.

Denitrification

Conversion of nitrates back into atmospheric N₂ by bacteria.

Major Reservoirs in the Nitrogen Cycle

Atmosphere (largest for inorganic N₂), terrestrial biosphere (organic + inorganic), others insignificant.

Human Impact on the Nitrogen Cycle

Synthetic fertilizers, fossil fuel burning → excess reactive nitrogen → pollution, eutrophication, dead zones.

Environmental Problems from Disturbed Cycles

Climate change, ocean acidification, dead zones, groundwater contamination.

Long term Consequences of Cycle Disturbance

Policies to Reduce Human Impact on Cycles

Reduce carbon emissions, manage fertilizers better, improve wastewater treatment, trap/remove nutrients, redesign food systems, use pricing/regulation/incentives, integrated land–water planning.