Biogeochemical Cycles – Carbon & Nitrogen (Lecture 2.3)

70 vocabulary flashcards summarizing key terms and definitions from the lecture on biogeochemical cycles, with emphasis on carbon and nitrogen processes, stores, flows, and human impacts.

Biogeochemical Cycle

A closed-system pathway in which chemical elements move through biotic and abiotic components of Earth.

Closed System (Cycles)

A system where matter is recycled internally with negligible input or output to space.

Store (Storage)

A component of a cycle where an element is held in equilibrium with its surroundings, e.g., soil or ocean carbon.

Sink

Part of a cycle where net accumulation occurs; more of an element is absorbed than released.

Source

Location within a cycle that releases more of an element than it absorbs, creating net output.

Transfer (Matter Flow)

Movement of matter without changing its chemical form, e.g., runoff in the water cycle.

Transformation

Process that alters the chemical nature of matter, such as nitrogen fixation converting N₂ to NH₃.

Carbon Cycle

Global movement of carbon between atmosphere, biosphere, lithosphere, and hydrosphere via stores and flows.

Carbon Sink

Any reservoir that absorbs more CO₂ than it releases, e.g., forests or oceans.

Carbon Store

A place where carbon is held for varying times, including biomass, soils, fossil fuels, and carbonate rocks.

Carbon Source

Process or reservoir that emits carbon to the atmosphere, such as combustion of fossil fuels.

Photosynthesis

Process in which autotrophs convert CO₂ and water into glucose and O₂ using sunlight, sequestering carbon.

Cellular Respiration

Metabolic breakdown of organic compounds releasing CO₂ and energy in plants and animals.

Feeding (Carbon Flow)

Transfer of stored carbon through consumption of plants or animals along food chains.

Defecation

Excretion process returning unassimilated carbon to soils or aquatic sediments.

Death & Decomposition

Breakdown of dead biomass by decomposers, releasing CO₂ and nutrients back to the environment.

Sedimentation

Accumulation of organic or inorganic material on ocean or lake floors, potentially forming rock or fossil fuels.

Fossilisation

Long-term conversion of buried organic matter into coal, oil, or natural gas under heat and pressure.

Carbon Sequestration

Capture and long-term storage of atmospheric CO₂ in biomass, soils, oceans, or geological formations.

Residence Time

Average length of time an atom remains in a particular store before moving elsewhere in the cycle.

Dynamic Equilibrium (Carbon)

State where carbon inputs to and outputs from a store are balanced over time.

Fossil Fuel Combustion

Burning coal, oil, or natural gas, rapidly releasing ancient carbon as CO₂ into the atmosphere.

Methanogenesis

Anaerobic microbial production of methane from organic matter in wetlands, rice paddies, or ruminant guts.

Methane (CH₄)

Potent greenhouse gas that traps heat 28× more effectively than CO₂ and persists ~10 years in air.

Ocean Acidification

Decrease in seawater pH caused by uptake of atmospheric CO₂ forming carbonic acid.

Ocean as Carbon Sink

Oceans absorb ~20 % of anthropogenic CO₂ annually, storing it as dissolved inorganic carbon.

Carbonate Rock

Rock such as limestone or dolomite composed largely of CaCO₃, storing vast amounts of carbon.

Limestone

Sedimentary carbonate rock formed from marine skeletons or precipitation, Earth’s largest carbon reservoir.

Reef-Building Corals

Organisms that create CaCO₃ skeletons, contributing to limestone formation and long-term carbon storage.

Carbonate Precipitation

Non-biological formation of CaCO₃ from seawater, removing carbon from the short-term cycle.

Tree Biomass Storage

Accumulation of carbon in trunks, branches, leaves, and roots of forest vegetation.

Soil Organic Carbon

Carbon stored in decomposed plant and animal matter within soils; ~2,500 Gt globally.

Regenerative Agriculture

Farming approach that restores soils, enhancing carbon sequestration and ecosystem health.

Crop Rotation

Alternating crop species each season to reduce nutrient depletion and support soil carbon.

Zero Tillage

Leaving crop residues on fields to decompose naturally, increasing soil organic matter.

Cover Cropping

Planting green manure species between main crops to add nutrients and protect soil.

Composting

Controlled decomposition of organic wastes producing nutrient-rich humus that returns carbon to soil.

Haber Process

Industrial synthesis of ammonia (NH₃) from N₂ and H₂, foundational to synthetic fertiliser production.

Nitrogen Cycle

Transformation and movement of nitrogen through atmosphere, biosphere, lithosphere, and hydrosphere.

Nitrogen Fixation

Conversion of inert N₂ gas into ammonia by lightning or nitrogen-fixing bacteria.

Ammonification

Decomposition process converting organic nitrogen in wastes or corpses into ammonium (NH₄⁺).

Nitrification

Oxidation of NH₄⁺ to nitrite (NO₂⁻) and nitrate (NO₃⁻) by nitrifying bacteria in soils.

Denitrification

Reduction of NO₃⁻ to N₂ gas by bacteria in anaerobic soils, returning nitrogen to the atmosphere.

Assimilation (Nitrogen)

Uptake of NH₄⁺ or NO₃⁻ by plants to build amino acids and nucleic acids.

Nitrogen-Fixing Bacteria

Microorganisms (free-living or symbiotic) that transform N₂ into bioavailable ammonia.

Rhizobium

Genus of bacteria living in legume root nodules, exchanging fixed nitrogen for plant sugars.

Legume Mutualism

Symbiosis where legumes supply carbohydrates to Rhizobium in return for fixed nitrogen.

Organic Nitrogen Store

Nitrogen contained in proteins and nucleic acids of living organisms.

Inorganic Nitrogen Store

Nitrogen held as gaseous N₂ or soil/aqueous nitrates, nitrites, and ammonium.

Eutrophication

Nutrient enrichment of water bodies causing algal blooms, oxygen depletion, and ecosystem decline.

Planetary Boundary – Biogeochemical Flows

Safe operating limit for human alteration of nitrogen and phosphorus cycles, currently exceeded.

Nitrate Pollution

Elevated NO₃⁻ levels in water from fertiliser runoff, linked to health and ecological issues.

Methemoglobinemia (Blue Baby Syndrome)

Condition where high nitrate drinking water impairs oxygen transport in infants.

Energy Efficiency

Using technologies and practices that reduce energy demand and associated CO₂ emissions.

Low-Carbon Technology

Energy sources like solar, wind, hydro, and geothermal that emit little to no CO₂.

Carbon Capture and Storage (CCS)

Technology capturing CO₂ from point sources and injecting it into geological formations for long-term storage.

Reforestation

Planting trees on degraded or deforested land to restore biomass and sequester carbon.

Deforestation

Removal of forest cover, reducing carbon sinks and increasing atmospheric CO₂.

Monoculture

Agricultural practice of growing a single crop species repeatedly, depleting soil nutrients and carbon.

Heavy Tillage

Intense soil ploughing that disrupts structure, increases erosion, and releases stored carbon.

Wetland Drainage

Conversion of wetlands for agriculture or urban use, releasing stored carbon and reducing denitrification.

Livestock Methane Emissions

CH₄ released during ruminant digestion and manure decomposition, contributing to greenhouse forcing.

Aquaculture Nitrogen Impact

Fertiliser and feed inputs in fish farms elevate ammonia and nitrate, disrupting local nitrogen cycles.

Urbanization & Nitrogen

Expansion of cities leading to wetland loss, altered runoff, smog formation, and reduced denitrification.

Nitrogen Boundary Transgression

Human fixation and release of reactive nitrogen far exceeding Earth’s safe operating limit.