Nutrient Cycles and Biogeochemistry

Key Definitions

• Nutrients encompass elements and compounds essential for survival, acquired through consumption.
  • Macronutrients are needed in larger quantities, like nitrogen, carbon, and phosphorus.
  • Micronutrients are needed in smaller quantities.
• Nutrient cycles, also known as biogeochemical cycles, involve the movement of nutrients through ecosystems, including the atmosphere, hydrosphere, lithosphere, and biosphere.
• Pools or reservoirs are locations where nutrients reside for different durations, defining the residence time.
• Flux defines the rate at which materials move between pools.

Biogeochemistry

• Biogeochemistry studies chemical processes within pools and the movement of elements between them, which are influenced by biological processes.
• Reservoirs include the atmosphere, hydrosphere, lithosphere, and biosphere.
• Nutrients can be found in inorganic forms, such as in the lithosphere; or in organic forms like living organisms and dissolved organic matter (DOM).
• Biological processes such as photosynthesis, respiration, nitrogen fixation, and denitrification play a role.
• Other processes include weathering (physical, chemical), solution, sedimentation, streamflow, and upwelling.

Biogeochemical Cycle Components

• A source pool releases more nutrients than it receives.
• A sink pool receives more nutrients than it releases.

Global Biogeochemical Cycles

• Gaseous cycles primarily source atmospheric gases.
  • Nitrogen is an example.
• Sedimentary cycles primarily source sediments.
  • Phosphorus is an example.

Carbon Cycle

• Photosynthesis enables plants, algae, and cyanobacteria to remove carbon dioxide from the air and water.
• Respiration returns carbon to the atmosphere and oceans.
• Terrestrial plants use atmospheric carbon dioxide.
• Aquatic plants use dissolved carbonates sourced from the hydrosphere.
• Sedimentary rock is a major reservoir.

Nitrogen Cycle

• Nitrogen Fixation converts nitrogen with hydrogen to form ammonium, and occurs through lightning or nitrogen-fixing bacteria.
• Nitrification converts ammonium ions into nitrite and then nitrate ions by bacteria.
• Denitrifying bacteria convert nitrates back into gaseous nitrogen, releasing it back to the atmosphere.
• A significant portion of nitrogen in the environment comes from human activities.
• The atmosphere is a major reservoir.

Phosphorus Cycle

• Sediment and sedimentary rock are major reservoirs.

Human Impacts on Nutrient Cycles

• Human activities like burning fossil fuels, deforestation, and crop tillage disrupt nutrient cycles.
• Methane from livestock also contributes to such disruptions.
• The increased amounts of Nitrogen Oxides (NOx), Ammonia, Nitrous Oxide, and Phosphates in the environment influence the disruption.
• These activities lead to eutrophication and the creation of "dead zones."
• Observed impacts include:
  • Anthropogenic climate change
  • Ocean acidification
  • Sea level rise
  • Ice melt
  • Coral mortality
  • Range shifts
  • Biome changes

Ecosystem Services

• Provisioning provides goods produced by ecosystems.
• Regulating benefits from regulation of ecosystem processes.
• Cultural aspects are non-material benefits from ecosystems.
• Supporting services enable other services.