Nutrient Supply and Cycling

Biogeochemistry

The study of the physical, chemical, and biological factors that influence the movement and transformation of elements.

Nutrient Requirements

All organisms require specific chemical elements (nutrients) for metabolism and growth, which they absorb from the environment or obtain through food.

Examples of required elements include Zn, Ca, Cl, Se, Cu, P, Fe, Na, Mn, K, and Mg .

Source of Nutrients

The ultimate source of mineral nutrients is the Earth's crust (minerals in rocks), while the atmosphere is the source of gases like carbon and nitrogen.

Nutrient Cycling

There are two broad processes involved in nutrient cycling:

• Fixation: The transformation of abiotic nutrients into forms that can be used or assimilated by organisms.

Carbon fixation: Occurs via photosynthesis.

Nitrogen fixation: Accomplished by bacteria or lightning.

• Mineralization: The release of nutrients from complex organic forms into simpler inorganic forms.

Decomposition: Organic compounds are broken down into CO2​.

Denitrification: Conversion of NH3​ to N2​, primarily by bacteria.

Autotrophs (Producers)

Organisms that produce their own food (e.g., plants, algae, phytoplankton, some bacteria).

Heterotrophs (Consumers):

Organisms that must consume other organic matter for food (e.g., animals, fungi, most protozoa and bacteria).

C:N Ratios:

These ratios reflect the biochemistry of organisms.

Plants: Have higher C:N ratios because carbon is the main component of their structural compounds, while nitrogen is mostly in enzymes.

Animals/Microorganisms: Have lower C:N ratios.

Digestive Adaptations

Herbivores: Have longer intestines and larger cecums to process complex plant matter.

Carnivores: Have shorter intestines

Soil Development and Fertility

Weathering: The process of releasing elements from rock minerals, which is essential for soil development.

Soil Composition: A mixture of mineral particles, organic matter, water, and organisms.

Factors Influencing Fertility

Texture: Determined by particle sizes (sand, silt, clay). It affects water-holding capacity and nutrient movement.

Parent Material: The type of rock (e.g., limestone vs. granite) determines the minerals released and the soil's pH.

Leaching: The movement of dissolved particles from upper to lower soil layers. High leaching in tropical forests leads to nutrient-poor soils.

Global and Aquatic Patterns

Mean Residence Time (Turnover Rate): The average time a molecule spends in a specific pool (e.g., soil or living biomass).

Turnover is much faster in tropical rainforests (0.4 years for soil organic matter) than in boreal forests (353 years) due to temperature and moisture.

Aquatic Systems

Nutrient Status: Lakes are classified as Oligotrophic (nutrient-poor), Mesotrophic (intermediate), or Eutrophic(nutrient-rich).

Upwelling: Brings deep, nutrient-rich waters to the surface, creating highly productive zones for fisheries.

Nutrient Spiraling: In moving waters (rivers/streams), nutrients cycle as they are transported downstream.