SUBTOPIC 2.

3: BIOGEOCHEMICAL CYCLES

https://eduinput.com/introduction-to-biogeochemical-cycles/
Biogeochemical cycles play a crucial role in maintaining the availability of essential chemical elements for
living organisms. These cycles involve the movement and transformation of elements like carbon,
nitrogen, and phosphorus between different environmental compartments such as the atmosphere,
hydrosphere, lithosphere, and biosphere.

​Human activities, such as burning fossil fuels, deforestation, and agriculture, significantly impact these
natural cycles, often leading to imbalances that can affect the sustainability of ecosystems. Understanding
and managing human impacts on biogeochemical cycles is vital for ensuring the health and stability of our
environment

This unit is a minimum of 4 hours.

Guiding Questions

●​ How do human activities affect nutrient cycling, and what impact does this have on the
sustainability​
of environmental systems?
●​ What are the key processes involved in the carbon, nitrogen, and phosphorus cycles, and how do
they interact within ecosystems?
●​ How do changes in biogeochemical cycles influence ecosystem services and biodiversity?

Understandings

INTRODUCTION TO BIOGEOCHEMICAL CYLES

​2.3.1 Biogeochemical cycles ensure chemical elements continue to be available to living
organisms.

●​ Define the term "biogeochemical cycle"

 BIOGEOCHEMICAL CYCLE COMPONENTS by
Anton Antonio April 3, 2015
Biogeochemical Cycles: Key Concepts

●​ Closed Systems for Nutrient Recycling:​

●​ Biogeochemical cycles recycle essential nutrients, ensuring their availability to living

organisms.
●​ Major cycles include the carbon, nitrogen, and phosphorus cycles, which sustain
ecosystems by maintaining balanced nutrient flows.
●​ Components of Biogeochemical Cycles:​

●​ These cycles involve complex interactions between the atmosphere, hydrosphere,

lithosphere, and biosphere, creating a network of nutrient exchanges that support life.
●​ Human Impacts on Biogeochemical Cycles:​

●​ Carbon Cycle: Activities like fossil fuel burning, deforestation, and industrial processes
elevate atmospheric CO₂ levels, driving climate change.
●​ Nitrogen and Phosphorus Cycles: Excessive fertilizer use in agriculture raises nitrogen
and phosphorus levels in soils and water bodies, causing eutrophication and nutrient
pollution in aquatic ecosystems.
●​ Environmental Consequences: Disruptions to these cycles can lead to ecosystem
imbalances, biodiversity loss, and decreased ecosystem resilience.
●​ Importance of Cycles for Ecosystem Health:​

●​ Continuous nutrient cycling is vital for ecosystem productivity, supporting food webs and
maintaining biodiversity.
●​ Effective nutrient management and reducing anthropogenic impacts are essential for
ecosystem stability and sustainability.

2.3.2 Biogeochemical cycles have stores, sinks and sources.

●​ Define the terms "stores," "sinks," and "sources" in the context of biogeochemical cycles
●​ Discuss the roles of stores, sinks, and sources in maintaining the balance of biogeochemical
cycles.
Biogeochemical Cycles: Core Concepts

●​ Essential Processes for Nutrient Recycling:

●​ Biogeochemical cycles, like the carbon, nitrogen, and phosphorus cycles, ensure
continuous nutrient availability through Earth’s atmosphere, hydrosphere, lithosphere,
and biosphere.
●​ These cycles consist of stores, sinks, and sources where elements are held,
accumulated, or released.
●​ Key Components:
●​ Stores (Storages):
●​ Elements are held for varying durations in reservoirs such as oceans, soil,
atmosphere, or organisms.
●​ Examples: Carbon in fossil fuels, nitrogen in soil, and phosphorus in sediments.
●​ Sinks:
●​ Areas of net accumulation where elements are absorbed faster than they are
released.
●​ Examples: Forests (carbon sinks) absorb more CO₂ than they release, and
oceans capture atmospheric CO₂.
●​ Sources:
●​ Areas of net release where elements are discharged faster than absorbed.
●​ Examples: Fossil fuel combustion emits CO₂, and agriculture releases nitrogen
as N₂O.
●​ Matter Movement in Ecosystems:
●​ Transfers:
●​ Movement of matter without altering its form. Example: Water cycling from
precipitation to runoff.
●​ Transformations:
●​ Changes in the chemical form of matter. Example: Nitrogen fixation by bacteria
converts atmospheric nitrogen (N₂) to ammonia (NH₃), making nitrogen usable for
plants.

2.3.3 Organisms, crude oil and natural gas contain organic stores of carbon. Inorganic stores can
be found in the atmosphere, soils and oceans.

●​ Explain what is meant by the term "residence time" in the context of the carbon cycle
●​ Outline the differences between carbon stored in living organisms and carbon stored in the
atmosphere.
​Carbon Cycle and Carbon Stores

●​ Carbon’s Role:​

●​ Carbon is essential for all life and is central to energy production through fossil fuel
combustion (oil, coal, natural gas), which releases CO₂ into the environment.
●​ Carbon Sinks:​

●​ Places where carbon is stored, such as oceans (largest sink), forests, soil, fossil
fuels, and the atmosphere.
 ●​ Oceans hold much more carbon than all forests combined, but climate change affects
their capacity to absorb CO₂.

Organic and Inorganic Carbon Stores

●​ Organic Carbon:
●​ Organisms: Store carbon in molecules like carbohydrates, proteins, and lipids, cycling it
through photosynthesis and respiration.
●​ Fossil Fuels: Crude oil and natural gas hold ancient organic carbon, releasing CO₂ when
burned.
●​ Soil Organic Matter: Dead organic material decomposes, storing carbon in soil.
●​
●​ Inorganic Carbon:
●​ Atmosphere: Contains CO₂, a greenhouse gas that influences climate.
●​ Soils: Store carbonates (e.g., calcium carbonate) formed through weathering, which are
stable over long periods.
●​ Oceans: Contain dissolved CO₂, bicarbonate, and carbonate ions, absorbing about 20%
of annual atmospheric CO₂ emissions.

Processes in Oceans:

●​ Physical Dissolution: CO₂ dissolves in seawater, forming carbonic acid.

●​ Biological Uptake: Marine organisms (e.g., phytoplankton) use CO₂ for photosynthesis,
incorporating it into their biomass.

Equilibrium and Residence Time

●​ Equilibrium: When carbon input matches output, maintaining stable levels in reservoirs.
●​ Residence Time:
●​ Short: Atmosphere, plants, and soils have short carbon cycles (days to years).
●​ Long: Fossil fuels have long residence times (millions of years), only disturbed by human
activities like mining and combustion.

https://www.geomon.co.uk/carbon-storage-in-ecosystems/
 https://www.geomon.co.uk/carbon-storage-in-ecosystems/

THE CARBON CYCLE

​2.3.4 Carbon flows between stores in ecosystems by photosynthesis, feeding, defecation, cellular
respiration, death and decomposition.

●​ Outline the different flows in the carbon cycles

●​ ​Identify where carbon is stored
●​ Define carbon fixation
●​ Define carbon budget

Key Processes in the Carbon Cycle

●​ Photosynthesis:​

●​ Plants and photosynthetic organisms absorb CO₂ from the atmosphere, converting it into
glucose and other organic compounds using sunlight energy.
●​ Produces oxygen as a byproduct, essential for aerobic respiration in plants and animals.
●​ Major source of atmospheric oxygen, initially contributed by early algae and bacteria.
●​ Feeding:​

●​ Animals ingest plants and other organisms, transferring carbon through the food chain as
it supports growth, energy, and reproduction.
●​ Defecation:​

●​ Not all carbon is assimilated; some is excreted, returning carbon to the soil and
supporting decomposers or becoming part of soil organic matter.
●​ Cellular Respiration:​

●​ Plants and animals release CO₂ through respiration by breaking down organic
compounds for energy, returning carbon to the atmosphere.
●​ Combustion:​

●​ Burning fossil fuels (coal, oil, natural gas) releases CO₂ into the atmosphere, a significant
human contribution to atmospheric carbon.
●​ Fossilization:​

●​ Organic matter under prolonged pressure transforms into coal, oil, and natural gas
deposits, storing carbon over geological timescales.
●​ Sedimentation:​
 ●​ Organic material settles in aquatic environments and, under pressure, forms fossil fuel
deposits (coal, oil, natural gas).
●​ Death and Decomposition:​

●​ Decomposers break down dead organisms, releasing CO₂ and nutrients back into the soil
and atmosphere, recycling carbon.

Carbon Balance:

●​ Net Uptake: If photosynthesis > respiration, the ecosystem absorbs more CO₂, acting as a
carbon sink.
●​ Net Release: If respiration > photosynthesis, the ecosystem releases more CO₂, contributing to
atmospheric carbon levels.

The Global Carbon Cycle

●​ Dynamic Equilibrium: The carbon cycle is a balanced system where carbon moves continuously
between different reservoirs, including the atmosphere, oceans, soil, plants, and fossil fuels. The
equilibrium is maintained by a balance between carbon absorption and release.
●​ Natural Carbon Flows and Stores:​

●​ Carbon is stored in reservoirs like forests, soils, oceans, and fossil fuels.
●​ It flows through processes like photosynthesis, respiration, decomposition, and
sedimentation.
●​ Human Impact on Residence Time:​

●​ Human activities, especially fossil fuel combustion, have accelerated the release of
stored carbon.
●​ Burning fossil fuels like oil, coal, and gas releases carbon that was locked away for
millions of years, significantly increasing atmospheric CO₂ levels.
●​ This rapid release alters the residence time in natural stores, disrupting the balance of
the carbon cycle.
●​ Environmental Implications:​

●​ Increased atmospheric CO₂ contributes to global warming and climate change, as carbon
is a major greenhouse gas.
●​ Shifts in carbon storage impact ecosystems, biodiversity, and global climate patterns.
 https://www.e-education.psu.edu/earth103/node/1019
Carbon Cycle Animation

Application of skills: Create a systems diagram of the carbon cycle.

​Systems Diagrams of the Carbon Cycle:

Understanding the carbon cycle involves visualizing how carbon flows between different stores in
ecosystems. Systems diagrams are useful tools for representing these flows and highlighting the
distinctions between transfers and transformations.

●​ Transfers:
●​ Transfers involve the movement of carbon from one store to another without changing its
form. For example, the transfer of carbon from plants to herbivores through feeding is a
direct movement of organic carbon.
●​ Another example is the movement of carbon from the atmosphere to the ocean through
the process of CO₂ dissolution.
●​ Transformations:
●​ Transformations involve changes in the chemical form of carbon as it moves between
stores. Photosynthesis and cellular respiration are key transformations in the carbon
cycle.
●​ During photosynthesis, CO₂ is transformed into organic compounds like glucose. In
cellular respiration, these organic compounds are broken down, releasing CO₂ back into
the atmosphere.
A systems diagram of the carbon cycle typically includes the following components:

●​ Atmospheric CO₂: The primary inorganic store of carbon in the atmosphere.

●​ Plant Biomass: A major organic store of carbon, representing carbon fixed through
photosynthesis.
●​ Animals: Representing carbon transfers through feeding.
●​ Soil Organic Matter: Including carbon from defecation, death, and decomposition.
●​ Decomposers: Organisms that transform dead organic matter into inorganic forms.

2.3.5 Carbon sequestration is the process of capturing gaseous and atmospheric carbon dioxide
and storing it in a solid or liquid form.

●​ Define carbon sequestration

●​ Describe how trees naturally sequester carbon through the process of photosynthesis.
●​ Identify and describe two human-enhanced methods of carbon sequestration.
Carbon Sequestration: The process of capturing and storing atmospheric CO₂ in solid or liquid forms,
reducing greenhouse gases in the atmosphere and helping mitigate climate change.
https://en.wikipedia.org/wiki/File:Carbon_sequestration-2009-10-07.svg
Tree Growth and Forest Ecosystems:

●​ Photosynthesis:
●​ Trees and other vegetation absorb CO₂ from the atmosphere during photosynthesis.
●​ CO₂ is converted into organic compounds, such as glucose, which are used to build plant
tissues.
●​ Biomass Storage:
●​ ​The carbon absorbed by trees is stored in their biomass, including trunks, branches,
leaves, and roots.
●​ Forests act as significant carbon sinks, sequestering large amounts of CO₂ over their
lifetimes.
●​ Soil Carbon:
●​ ​Dead plant material, such as leaves and branches, decomposes and contributes to soil
organic matter.
●​ Soil stores carbon as organic matter, which can remain in the soil for long periods.

Formation of Fossil Fuels:

●​ Organic Matter Burial:

●​ ​Over millions of years, dead plants and microorganisms accumulate in sediment layers.
●​ These organic materials are buried under sediments, where they are subjected to high
pressure and temperature.
●​ Fossilization:
●​ The buried organic matter gradually transforms into fossil fuels, such as coal, oil, and
natural gas.
●​ This process effectively locks away carbon in a stable, long-term form.

Importance of Natural Carbon Sequestration

●​ Climate Regulation:
 ●​ Natural carbon sequestration helps regulate the global climate by reducing atmospheric
CO₂ levels.
●​ Forests and other ecosystems play a vital role in balancing the carbon cycle and
mitigating the effects of climate change.
●​ Biodiversity and Ecosystem Health:
●​ Healthy, carbon-sequestering ecosystems support diverse plant and animal species.
●​ Maintaining and restoring these ecosystems contributes to overall ecological health and
resilience.

Case Study: Carbon Sequestration Capabilities of Various Forest Types in the Pacific
Northwest

https://databasin.org/datasets/5e106e515eaf4b7f87053455fd7eb197/

https://www.climatehubs.usda.gov/hubs/northwest/topic/northwest-forests-and-woodlands
​Introduction

Forests in the Pacific Northwest are renowned for their rich biodiversity and significant carbon
sequestration capabilities. This case study assesses the carbon sequestration potential of different forest
types in this temperate region, focusing on their role in capturing and storing atmospheric carbon dioxide
(CO₂).

​Forest Types Studied

●​ Deciduous Forests:
●​ Dominated by broadleaf trees such as maple, alder, and oak.
●​ Known for high species diversity and seasonal leaf shedding.

Coniferous Forests:

●​ Composed mainly of evergreen trees like Douglas fir, Western hemlock, and Sitka spruce.
●​ Characterized by large, long-lived trees with high biomass.

Mixed Forests:

●​ Contain a combination of deciduous and coniferous species.

●​ Provide structural complexity and varied carbon sequestration dynamics.
​2.3.6 Ecosystems can act as stores, sinks or sources of carbon.

●​ Define the terms "carbon sink," "carbon store," and "carbon source"
●​ Describe the role of a mature forest as a carbon store and explain how it maintains equilibrium
●​ Compare and contrast the carbon dynamics in a young forest and a forest destroyed by fire.
Roles as Carbon Stores, Sinks, and Sources:

●​ Stores: Ecosystems with balanced carbon inputs (photosynthesis) and outputs (respiration) act
as stable carbon stores, holding carbon in biomass and soil without net accumulation or release.
●​ Sinks: Ecosystems absorb more CO₂ than they release, typically when photosynthesis outpaces
respiration. Carbon sinks are vital for lowering atmospheric CO₂, aiding in climate change
mitigation.
●​ Sources: Ecosystems that release more CO₂ than they absorb act as carbon sources, which
occurs when respiration and decomposition exceed photosynthesis, contributing to climate
change.
Carbon Dynamics Across Ecosystem Types:

●​ Young Forests as Carbon Sinks: High photosynthetic activity in young forests due to rapid
growth leads to significant CO₂ uptake, making them robust carbon sinks.
●​ Mature Forests as Carbon Stores: Balanced rates of photosynthesis and respiration in mature
forests result in stable carbon storage, with minimal net carbon gain or loss.
 ●​ Forests Affected by Fire or Deforestation as Carbon Sources: When forests are burned or
cleared, the rapid release of CO₂ from decomposing or burning biomass and reduced
photosynthesis make these areas significant carbon sources.
Factors Affecting Carbon Balance in Ecosystems:

●​ Climate: Temperature and rainfall patterns influence photosynthesis and respiration, impacting an
ecosystem's role as a carbon sink, store, or source.
●​ Disturbances: Events like fires, storms, and human activities (e.g., deforestation) shift
ecosystems from sinks or stores to sources.
●​ Ecosystem Type: Forests, grasslands, and wetlands each differ in carbon storage and
sequestration potential, depending on their unique biological and physical properties.

​2.3.7 Fossil fuels are stores of carbon with unlimited residence times. They were formed when
ecosystems acted as carbon sinks in past eras and become carbon sources when burned.

●​ Outline the process by which fossil fuels become carbon sources when burned.
●​ ​Explain the role of fossil fuels as carbon stores.
●​ Explain the concept of residence time and discuss why the residence time of carbon in fossil fuels
is considered unlimited.
Fossil Fuels as Long-Term Carbon Stores

●​ Nature and Composition:​

●​ Fossil fuels (coal, oil, and natural gas) consist of carbon-rich organic materials from
ancient plants and microorganisms.
●​ Stored deep within Earth’s crust, these fuels have remained isolated from the
atmosphere, effectively sequestering carbon for millions of years.
●​ Residence Time:​

●​ Carbon in fossil fuels has an extremely long residence time, often spanning hundreds of
millions of years.
●​ Unlike carbon in living organisms or the atmosphere, fossil fuels act as long-term carbon
reservoirs due to their deep burial and stable geological preservation.
●​ Formation Process:​

●​ Fossil fuels formed in past geological periods when vast amounts of organic matter were
buried and subjected to intense heat and pressure.
●​ These ancient ecosystems acted as significant carbon sinks, absorbing CO₂ from the
atmosphere, which was then stored in organic matter and locked away in fossil deposits
over time.
 https://serc.carleton.edu/details/images/65244.html
Fossil Fuels as Carbon Sources

●​ Burning Fossil Fuels:​

●​ When fossil fuels are extracted and combusted, the stored carbon is released back into
the atmosphere as CO₂.
●​ This process converts fossil fuels from long-term carbon stores to immediate and
substantial carbon sources.
●​ Fossil fuel combustion is a major driver of increased atmospheric CO₂ levels, contributing
significantly to global warming and climate change.
●​ Impact on the Carbon Cycle:​

●​ The large-scale burning of fossil fuels disrupts the natural carbon cycle by rapidly
reintroducing CO₂ that was sequestered over millions of years.
●​ This surge in atmospheric CO₂ overwhelms natural carbon sinks, like forests and oceans,
which cannot absorb the excess quickly enough.
●​ The resulting imbalance amplifies the greenhouse effect, leading to rising global
temperatures and climate-related impacts.
EFFECTS OF HUMAN ACTIVITY ON CARBON
CYCLE
2.3.8 Agricultural systems can act as carbon stores, sources and sinks, depending on the
techniques
used.

●​ Explain how crop rotation can enhance the role of soil as a carbon sink.
●​ Outline the benefits of cover cropping for soil carbon sequestration.
●​ Describe the impact of heavy tillage on soil carbon storage and CO₂ emissions.
Agricultural systems play a complex role in the carbon cycle and can function as carbon stores, sources,
or sinks based on the farming practices and techniques employed:

●​ Carbon Store:​

●​ Soil Organic Matter: With sustainable practices, agricultural soils can store carbon in the
form of organic matter, helping to sequester CO₂ from the atmosphere.
●​ Crop Biomass: Crops absorb CO₂ during photosynthesis and store it temporarily in their
biomass until harvested or decomposed.
●​ Carbon Source:​

●​ Soil Disturbance: Conventional tilling and land-clearing practices disturb the soil,
releasing stored carbon as CO₂.
●​ Livestock Farming: Animal farming generates methane (CH₄) through enteric
fermentation and manure management, making it a potent source of greenhouse gases.
●​ Fertilizer Use: Nitrogen-based fertilizers can lead to the release of nitrous oxide (N₂O), a
greenhouse gas, into the atmosphere.
●​ Carbon Sink:​

●​ Conservation Tillage and Cover Crops: Reduced or no-till farming, along with the use
of cover crops, helps to sequester carbon by maintaining soil structure and encouraging
carbon storage.
●​ Agroforestry: Integrating trees and shrubs into agricultural lands allows farms to act as
carbon sinks, as trees absorb and store CO₂ over time.
No-Till Farming

●​ Definition: No-till farming is an agricultural method where crops are planted directly into
undisturbed soil, without the use of tillage implements. This practice minimizes soil disturbance,
allowing organic matter to accumulate naturally.
●​ Benefits:
●​ Soil Structure Preservation: By avoiding tillage, soil structure is maintained, promoting
healthier root systems and soil ecosystems.
●​ Reduced Soil Erosion: No-till farming protects soil from erosion caused by wind and
water, especially in vulnerable areas.
●​ Enhanced Water Retention: The undisturbed soil surface improves water infiltration and
retention, reducing runoff and supporting crop growth in dry conditions.
●​ Increased Carbon Storage: Organic matter from previous crop residues accumulates on
the soil surface, sequestering carbon and contributing to long-term soil fertility.
●​ Example: An image of soybeans growing in wheat residue effectively illustrates no-till farming.
The previous crop's residue remains on the soil surface, retaining nutrients and carbon for the
current crop and demonstrating the method's sustainability benefits.

https://www.agri-pulse.com/articles/16869-cover-crops-can-benefit-farmers-earth-in-many-ways
Cover Cropping:

●​ Cover cropping involves planting specific crops, such as radishes, clover, or rye, between main
cash crops to protect and enrich the soil during off-seasons. These plants cover the soil surface,
preventing erosion and maintaining soil health.
●​ Benefits:​

●​ Soil Erosion Prevention: Cover crops shield soil from wind and water erosion,
especially in periods between main crop harvests.
●​ Weed Suppression: They outcompete weeds, reducing the need for herbicides and
preserving soil ecosystems.
●​ Enhanced Soil Fertility and Structure: The root systems of cover crops improve soil
structure and aeration, which benefits subsequent cash crops.
●​ Carbon Sequestration: As cover crops decompose, they add organic matter and carbon
to the soil, increasing carbon storage over time and enhancing soil fertility.
 ●​ Example: An image of radishes as a cover crop illustrates their protective role for soil and their
contribution to organic matter. The decaying radishes provide nutrients to the soil, demonstrating
how cover cropping supports sustainable, carbon-rich farming practices.

Crop Rotation:

●​ Definition: Crop rotation is the practice of planting different crops in the same field across
successive seasons. Rotating crops with varied root structures and nutrient requirements
prevents soil compaction and maintains soil fertility.
●​ Benefits:
●​ Enhanced Soil Structure: Different crops contribute diverse root structures, which
improve soil aeration and reduce compaction.
●​ Biodiversity Boost: Crop rotation fosters a more diverse soil microbiome and pest
resistance by interrupting pest and disease cycles.
●​ Nutrient Cycling: Rotating nitrogen-fixing plants like legumes with other crops enriches
soil nitrogen levels, reducing the need for synthetic fertilizers.
●​ Carbon Sequestration: Improved soil health through rotation allows soil to retain more
organic matter, effectively storing carbon and acting as a carbon sink.
●​ Example: An example of rotating legumes with grains shows the benefits of nitrogen enrichment
and enhanced organic matter content in the soil, supporting sustainable and productive
agriculture.

https://canadianfoodfocus.org/on-the-farm/crop-rotations-ensure-a-sustainable-future-for-agriculture/
Agroforestry:

●​ Agroforestry is a land management approach that incorporates trees and shrubs into agricultural
systems, combining elements of agriculture and forestry to create a more diverse and sustainable
landscape.
●​ Benefits:​

●​ Carbon Sequestration: Trees and shrubs capture and store carbon in their biomass and
root systems, helping mitigate climate change.
●​ Soil Health Improvement: The roots of trees and shrubs stabilize soil, enhance soil
structure, and increase water retention.
●​ Biodiversity: Agroforestry creates habitats for a wide range of species, boosting
ecosystem diversity and resilience.
●​ Climate Resilience: Integrating trees can protect crops from extreme weather and
increase farm resilience to climate impacts.
 ●​ Additional Organic Matter: Leaf litter and pruned branches enrich the soil with organic
matter, improving its fertility over time.
●​ Example: Planting fruit or nut trees alongside traditional crops provides dual benefits—carbon
storage and an alternative income source for farmers, promoting both ecological and economic
sustainability.

https://www.usda.gov/media/blog/2020/08/21/promoting-pollinators-agroforestry
Impact on Soil Health and Carbon Sequestration:

These sustainable agricultural practices not only sequester carbon but also improve overall soil health.
Increased organic matter in the soil enhances soil fertility, water retention, and resilience to environmental
stresses. By adopting these practices, farmers can contribute to climate change mitigation while
maintaining productive and sustainable agricultural systems.

​2.3.9 Carbon dioxide is absorbed into the oceans by dissolving and is released as a gas when it
comes out of a solution.

●​ Describe the process by which carbon dioxide is absorbed into the oceans.
●​ Outline the role of oceans as a carbon sink and discuss the factors that influence the rate of CO₂
absorption
●​ Describe the process by which carbon dioxide is absorbed into the oceans.
https://nautil.us/how-seawater-might-soak-up-more-carbon-261446/
Oceans in the Carbon Cycle

●​ Role as a Major Carbon Sink: Oceans absorb about 20% of CO₂ emissions from human
activities each year, playing a critical role in mitigating climate change by reducing atmospheric
CO₂ levels.
CO₂ Absorption and Release Mechanisms

●​ CO₂ Absorption:​

●​ Dissolution Process:
●​ CO₂ from the atmosphere dissolves in seawater, forming carbonic acid (H₂CO₃).
●​ Dissolved CO₂ converts into stable bicarbonate (HCO₃⁻) and carbonate ions
(CO₃²⁻) in seawater.
●​ Biological Uptake:
●​ Photosynthesis: Marine organisms like phytoplankton absorb CO₂ for
photosynthesis, incorporating it into their biomass, which enables more CO₂ to
dissolve from the atmosphere.
●​ CO₂ Release:​

●​ Outgassing:
●​ When CO₂ concentration in seawater surpasses atmospheric levels, CO₂ is
released back into the atmosphere through oceanic circulation and warming.

Limitations as a Carbon Sink

●​ Absorption Capacity Constraints:

●​ Warmer water holds less CO₂, reducing oceanic absorption efficiency in a warming
climate.
●​ Factors such as ocean circulation and ecosystem capacity further limit CO₂ uptake.

​2.3.10 Increases in concentrations of dissolved carbon dioxide cause ocean acidification, harming
marine animals.

●​ Explain the chemical process of ocean acidification

 ●​ Describe how increased concentrations of dissolved CO₂ affect the pH of seawater..
●​ Explain the impact of ocean acidification on the ability of marine organisms to form calcium
carbonate shells and skeletons.

https://www.researchgate.net/figure/Schematic-diagram-of-ocean-acidification-The-reaction-between-dissolved-carbo
n-dioxide_fig1_319405916
​

●​ Ocean acidification results from the absorption of increased atmospheric CO₂ by the oceans,
leading to a drop in seawater pH and making it more acidic. This process particularly threatens
organisms that depend on calcium carbonate (CaCO₃) for their shells and skeletons, like mollusks
and corals.

Process of Ocean Acidification

●​ CO₂ Dissolution:
●​ CO₂ dissolves in seawater, forming carbonic acid (H₂CO₃).
●​ Carbonic acid dissociates into bicarbonate ions (HCO₃⁻) and hydrogen ions (H⁺).
●​ Increased H⁺ ions decrease seawater pH, resulting in acidification.
●​ Chemical Reactions:
●​ The increase in H⁺ ions reduces carbonate ion (CO₃²⁻) availability, which is needed for
calcium carbonate formation.
 ●​ Calcium Carbonate Dependence: Reduced carbonate ions make it harder for
organisms to build and maintain their shells and skeletons, impacting marine biodiversity.

Impacts of Ocean Acidification

●​ Marine Life:
●​ Species reliant on CaCO₃ for structural integrity, such as coral reefs, shellfish, and some
plankton, are particularly vulnerable.
●​ Acidification weakens these organisms, affecting their growth, reproduction, and survival,
which disrupts marine food webs and ecosystem stability.

https://ugc.berkeley.edu/background-content/ocean-acidification/

https://mindthegraph.com/blog/ocean-acidification-consequences/
Impact on Marine Life

●​ Harm to Molluscs:​

●​ Species like clams, oysters, and snails depend on calcium carbonate for shell formation.
●​ Ocean acidification reduces carbonate ion availability, leading to thinner, weaker shells.
●​ Thinner shells make molluscs more vulnerable to predation and environmental stresses.
●​ Harm to Corals:​

●​ Corals rely on calcium carbonate to build reef structures.

●​ Acidified waters slow coral growth and compromise their skeletons’ integrity.
●​ Weakened coral structures are more susceptible to damage, disease, and reduced reef
resilience.

Broader Ecosystem Effects:

●​ Many marine organisms, including some species of plankton and fish, are affected by changes in
pH and carbonate ion availability.
●​ The disruption of shell and skeleton formation can lead to declines in populations of key species,
affecting the entire marine food web.
●​ Coral reefs, which provide habitat and protection for numerous marine species, face degradation
and loss, impacting biodiversity and coastal ecosystems.
​Case Study: Effects of Ocean Acidification on Coral Reefs in the Great Barrier Reef

https://www.cruisemapper.com/ports/great-barrier-reef-port-646#google_vignette
​Introduction

The Great Barrier Reef (GBR), located off the coast of Queensland, Australia, is the world's largest coral
reef system and a UNESCO World Heritage site. It spans over 2,300 kilometers and is home to
thousands of marine species, making it a critical habitat for marine biodiversity. However, this iconic
ecosystem faces significant threats from ocean acidification, driven by increased atmospheric CO₂ levels.

Sources: Ocean pH and Atmospheric CO₂ Levels: Doney, S. C., Fabry, V. J., Feely, R. A., & Kleypas, J. A. (2009).
Ocean Acidification: The Other CO2 Problem. Annual Review of Marine Science, 1, 169-192. Feely, R. A., Doney, S.
C., & Cooley, S. R. (2009). Ocean acidification: Present conditions and future changes in a high-CO2 world.
Oceanography, 22(4), 36-47. Coral Calcification Rates: De'ath, G., Lough, J. M., & Fabricius, K. E. (2009). Declining
Coral Calcification on the Great Barrier Reef. Science, 323(5910), 116-119. Coral Bleaching Events: Hughes, T. P.,
Kerry, J. T., Álvarez-Noriega, M., Álvarez-Romero, J. G., Anderson, K. D., Baird, A. H., ... & Wilson, S. K. (2017).
Global warming and recurrent mass bleaching of corals. Nature, 543(7645), 373-377.
​Impact of Acidification:

●​ Calcification:
●​ Lower pH levels reduce the availability of carbonate ions, which are essential for coral
calcification. This weakens coral skeletons and hampers growth.
●​ Bleaching:
●​ Acidification, combined with rising sea temperatures, stresses corals, leading to more
frequent and severe bleaching events.
●​ Biodiversity Loss:
●​ As corals struggle to maintain their skeletons, the structure of the reef deteriorates,
leading to habitat loss for many marine species.

Ecosystem Services at Risk:

●​ Coastal Protection:
●​ Coral reefs act as natural barriers against storms and erosion. Degraded reefs are less
effective, increasing vulnerability for coastal communities.
●​ Fisheries:
●​ Many fish species depend on healthy coral reefs for spawning and feeding. A decline in
reef health can reduce fish populations and impact local fisheries.
●​ Tourism:
●​ The Great Barrier Reef is a major tourist attraction. Coral degradation can reduce its
appeal, affecting tourism revenue.

​2.3.11 Measures are required to alleviate the effects of human activities on the carbon cycle.

●​ Define low-carbon technologies and explain how they contribute to mitigating the effects of
human activities on the carbon cycle
●​ Explain the process of carbon capture and storage (CCS) and its role in reducing atmospheric
CO₂ levels.
●​ Outline the environmental benefits of reforestation in terms of carbon sequestration.
Human Activities Impacting the Carbon Cycle and Mitigation Strategies
Human activities like fossil fuel combustion, deforestation, and soil disruption have disrupted the carbon
cycle, raising CO₂ levels and intensifying climate change. Key strategies to mitigate these effects include
adopting low-carbon technologies, reducing fossil fuel dependence, and enhancing carbon sequestration.
Low-Carbon Technologies

●​ Renewable Energy:​

●​ Description: Transitioning to solar, wind, hydro, and geothermal energy reduces CO₂
emissions.
●​ Benefits: These technologies produce electricity without burning fossil fuels, thus
lowering greenhouse gases and preserving non-renewable resources.
 ●​ Example: Solar panels and wind turbines generate power with minimal environmental
impact.
●​ Energy Efficiency:​

●​ Description: Energy-efficient technologies in industry, transport, and buildings lower

energy demand and CO₂ emissions.
●​ Benefits: Reducing energy demand cuts emissions and energy costs.
●​ Example: LED lighting, efficient appliances, and better building insulation save significant
energy.

Reducing Fossil Fuel Use

●​ Fossil Fuel Reduction:​

●​ Description: Cutting back on fossil fuel use in energy and transport reduces CO₂
emissions.
●​ Benefits: Decreasing fossil fuel dependency lowers greenhouse gases.
●​ Example: Electric vehicles and public transport reduce the need for gasoline and diesel.
●​ Minimizing Soil Disruption:​

●​ Description: Sustainable agriculture, such as no-till farming and cover cropping, protects
soil carbon stores.
●​ Benefits: These practices prevent soil erosion, improve soil health, and boost carbon
sequestration.
●​ Example: No-till farming keeps soil structure intact, conserving organic matter and
carbon.
●​ Deforestation Reduction:​

●​ Description: Protecting forests and managing them sustainably conserves carbon

stores.
●​ Benefits: Forests act as carbon sinks; conserving them preserves this function.
●​ Example: Policies curbing illegal logging and promoting sustainable forestry protect
forests' CO₂ absorption capacity.

Carbon Capture Initiatives

●​ Reforestation:
●​ Description: Reforesting degraded lands restores forest cover and increases carbon
sequestration.
●​ Benefits: Trees absorb atmospheric CO₂, storing it in biomass, aiding ecosystem
restoration.
●​ Example: The Bonn Challenge seeks to restore 350 million hectares of forests by 2030.
●​ Artificial Carbon Sequestration:
●​ Description: Artificial carbon sequestration technologies capture CO₂ emissions from
industrial sources and store them underground in geological formations.
●​ Benefits: This process prevents CO₂ from entering the atmosphere and contributes to
reducing greenhouse gas concentrations.
●​ Example: Carbon capture and storage (CCS) involves capturing CO₂ from power plants
and industrial facilities and injecting it into
Biochar:
Biochar is a stable form of carbon created from organic matter through a process called pyrolysis, which
involves heating the material in the absence of oxygen. This process not only converts organic matter into
a carbon-rich, porous substance but also has significant benefits for soil fertility and carbon storage.
Biochar is increasingly recognized as a valuable tool for sustainable agriculture and climate change
mitigation.

●​ Benefits of Biochar:
●​ Enhanced Nutrient Retention: Biochar’s porous structure improves the soil’s ability to
retain nutrients and water, making them more available to plants. This reduces the need
for chemical fertilizers and enhances plant growth.
●​ Increased Microbial Activity: The porous nature of biochar provides habitats for soil
microorganisms, which play crucial roles in nutrient cycling and soil health.
●​ pH Regulation: Biochar can help neutralize acidic soils, improving growing conditions for
many crops.
●​ Long-Term Sequestration: By converting organic waste into biochar, carbon is locked
into a stable form that resists degradation. This prevents the carbon from being released
back into the atmosphere as CO₂, contributing to long-term carbon sequestration.
●​ Climate Change Mitigation: The use of biochar in soils not only sequesters carbon but
also reduces greenhouse gas emissions from soils, such as nitrous oxide (N₂O) and
methane (CH₄), which are potent greenhouse gases.

●​ Environmental Benefits:
●​ Waste Management: Biochar production provides a sustainable way to manage
agricultural and forestry waste, converting it into a valuable resource.
●​ Soil Health: Improved soil structure and fertility contribute to enhanced crop yields and
resilience against environmental stressors such as drought and erosion.

●​ Applications of Biochar:
●​ Agricultural Use: Biochar is widely used in farming to improve soil fertility, enhance crop
yields, and reduce the need for chemical inputs. It is particularly beneficial in degraded
soils and regions facing soil fertility challenges.
●​ Reclamation Projects: Biochar is used in land reclamation projects to restore soil health
and productivity in degraded lands, such as former mining sites and deforested areas.
●​ Gardening and Landscaping: Home gardeners and landscapers use biochar to improve
soil quality, increase plant growth, and enhance the aesthetic value of gardens and green
spaces.

HL ONLY
CARBON STORES IN THE LITHOSPHERE
​2.3.12 The lithosphere contains carbon stores in fossil fuels and in rocks, such as limestone, that
contain calcium carbonate.

●​ Define the term 'lithosphere'

●​ Explain the significance of the lithosphere in the carbon cycle.
The lithosphere, Earth’s outer layer, is a major long-term carbon reservoir, storing carbon for hundreds of
millions of years in fossil fuels and carbonate rocks.

Key Carbon Stores in the Lithosphere

●​ Fossil Fuels:
●​ Types: Includes coal, oil, and natural gas.
●​ Formation: Created from ancient plant and microorganism remains, buried and
compressed over millions of years under heat and pressure.
●​ Carbon Content: Fossil fuels are carbon-rich, releasing CO₂ when burned for energy.
●​ Residence Time: Carbon in fossil fuels remains stored for geological timescales, only
entering the carbon cycle when extracted and combusted.
●​ Carbonate Rocks:
●​ Types: Limestone and dolomite, containing calcium carbonate (CaCO₃).
●​ Formation: Formed from marine debris (e.g., shells, coral) or precipitated directly from
seawater.
●​ Carbon Storage: Carbonate rocks represent one of Earth’s largest carbon reservoirs,
storing carbon in a stable, long-term form.
●​ Residence Time: Carbon in these rocks remains sequestered for hundreds of millions of
years, acting as a durable carbon sink.

Importance of Lithospheric Carbon Stores

●​ Climate Regulation: Carbon stored in the lithosphere plays a significant role in regulating Earth’s
climate over geological timescales.
●​ Slow Carbon Release: Through processes like weathering and volcanic activity, carbon is
gradually reintroduced into the atmosphere, helping to maintain a natural carbon cycle balance.
​2.3.13 Reef-building corals and molluscs have hard parts that contain calcium carbonate that can
become fossilized in limestone.

●​ Explain how reef-building corals contribute to carbon storage in the lithosphere.

●​ Describe the role of molluscs in the formation of limestone.
●​ Outline the process of fossilization of calcium carbonate structures in corals and molluscs
●​ Discuss the significance of limestone as the largest carbon store in Earth systems.
Reef-building corals and molluscs are crucial marine organisms that contribute to the global carbon cycle
through their calcium carbonate (CaCO₃) structures, which can fossilize and form limestone—the largest
carbon store on Earth.

Calcium Carbonate Structures

 ●​ Corals:
●​ Reef-building corals secrete CaCO₃ to build their skeletons, forming extensive reef
systems.
●​ These reefs provide essential habitats for diverse marine species.
●​ Molluscs:
●​ Molluscs like clams, oysters, and snails produce CaCO₃ shells.
●​ When these shells accumulate on the ocean floor, they contribute to sediment layers and
carbon storage.

Fossilization Process

●​ Calcium carbonate structures from corals and molluscs can become buried by sediment over
time.
●​ Through compression and cementation, these sediments transform into limestone, preserving
fossilized remains of marine organisms within the rock layers.

Limestone as a Carbon Store

●​ Largest Carbon Store: Limestone holds a vast amount of carbon in a stable, solid form, serving
as Earth’s largest carbon reservoir.
●​ Climate Regulation: By storing carbon long-term, limestone helps maintain stable atmospheric
CO₂ levels, influencing climate regulation.

Limestone Formation Processes

●​ Biological: Fossilization of corals and molluscs is a primary biological pathway for limestone
formation.
●​ Non-Biological: Limestone also forms through chemical precipitation from seawater, without
biological involvement, contributing further to carbon sequestration.

Importance of Limestone Carbon Storage

●​ Long-Term Climate Regulation: Carbon in limestone is sequestered for millions of years,

reducing its presence in the carbon cycle and stabilizing Earth’s climate.
●​ Geological Carbon Cycle: Limestone participates in the geological carbon cycle. Weathering of
limestone releases carbon slowly, balancing CO₂ levels over extended timescales.
​2.3.14 In past geological eras, organic matter from partially decomposed plants became fossilized
in coal, and partially decomposed marine organisms became fossilized in oil and natural gas held
in porous rocks.

●​ Describe the process of coal formation from partially decomposed plant matter.
●​ Explain the conditions necessary for the formation of oil and natural gas from marine organisms.
●​ Identify two geological periods when significant coal formation occurred and explain why these
periods were conducive to coal formation
https://lms-leicester.libguides.com/c.php?g=807815
​Fossil fuels are carbon-rich energy sources formed from ancient plants and marine organisms over tens
of millions of years. These fuels—coal, oil, and natural gas—are critical carbon stores shaped during
specific geological periods under ideal conditions.

Coal Formation

●​ Source Material: Partially decomposed plant matter from ancient forests and swamps.
●​ Process:
●​ Plant debris accumulated in wetlands and was buried under sediments.
●​ Increased pressure and temperature transformed plant material into peat, then lignite,
bituminous coal, and finally anthracite (hard coal).
●​ Key Geological Periods:
●​ Carboniferous Period (359–299 million years ago): Known for vast coal-forming
forests and swamps, leading to major coal deposits.
●​ Permian Period (299–252 million years ago): Continued coal formation in a
high-organic productivity environment.

Oil and Natural Gas Formation

●​ Source Material: Decomposed marine organisms, including plankton and algae.

●​ Process:
●​ Organic matter from marine organisms mixed with sediments on the ocean floor.
●​ Burial under additional sediments increased pressure and temperature, converting
organic material into kerogen, then into oil and gaseous hydrocarbons (natural gas).
●​ Oil and gas migrated until trapped in reservoirs by impermeable rock layers.
●​ Key Geological Periods:
●​ Mesozoic Era (252–66 million years ago): High sea levels and warm climates promoted
plankton growth, leading to significant oil and gas formation.
●​ Cenozoic Era (66 million years ago–present): Continued formation in newer
sedimentary basins due to active tectonic processes.

Conditions Favorable for Fossil Fuel Formation

 ●​ High Organic Productivity: Warm, humid climates and abundant vegetation increased organic
matter accumulation. Marine environments rich in plankton also contributed to substantial
deposits.
●​ Anaerobic Conditions: Low-oxygen environments, like swamps and deep ocean floors, slowed
decomposition, allowing organic material to accumulate.
●​ High Sedimentation Rates: Rapid burial by sediments protected organic matter from full
decomposition, facilitating fossilization.

Geological Significance

●​ Carboniferous Period: Ideal for extensive coal formation due to dense, swampy forests and high
organic accumulation.
●​ Mesozoic and Cenozoic Eras: Marine conditions promoted plankton growth, creating large
sedimentary basins that yielded substantial oil and gas reserves.

2.3.15 Methane is produced from dead organic matter in anaerobic conditions by methanogenic
bacteria.

●​ Define methanogenesis and explain the role of methanogenic bacteria in this process.
●​ Describe the conditions necessary for methanogenesis to occur
●​ Discuss the significance of wetlands as natural sources of methane emissions
Methane is a powerful greenhouse gas produced under anaerobic (oxygen-free) conditions by
methanogenic bacteria. These conditions are found in environments like swamps, rice paddies, and the
stomachs of ruminant animals such as cattle.

Key Aspects of Methane in the Carbon Cycle

●​ Methanogenesis:
●​ Methanogenic bacteria decompose organic matter in oxygen-free conditions, releasing
methane as a byproduct.
●​ This process occurs in various anaerobic environments, including wetlands, flooded rice
fields, and the digestive systems of ruminants.
●​ Greenhouse Gas Impact:
●​ Methane is a potent greenhouse gas with a global warming potential 25 times greater
than CO₂ over a 100-year period, making it a significant contributor to the enhanced
greenhouse effect.
●​ Due to its high warming potential, even small methane emissions have a large impact on
climate.
●​ Methane Oxidation:
●​ Methane in the atmosphere is gradually oxidized to CO₂ and water vapor, returning to the
carbon cycle in a less potent form.
●​ It has a relatively short atmospheric residence time of about 12 years, compared to CO₂,
which remains in the atmosphere for centuries.

Importance of Methane in Climate Regulation

 ●​ Short-Term Warming Potential: Despite its short lifespan, methane’s immediate warming effect
is substantial, impacting near-term climate scenarios.
●​ Carbon Cycle Completion: Through oxidation, methane transitions to CO₂, linking it back to the
broader carbon cycle and contributing to long-term atmospheric carbon levels.

Methanogenic Bacteria:

●​ Role: These bacteria are responsible for breaking down organic matter in the absence of oxygen,
producing methane as a byproduct.
●​ Types: There are different types of methanogenic bacteria, each adapted to specific anaerobic
environments.
●​ Anaerobic Conditions: Methanogenesis occurs in environments where oxygen is absent or
extremely limited. These conditions prevent the complete decomposition of organic matter,
allowing methanogenic bacteria to thrive
Swamps and Wetlands:

●​ Description: Swamps, wetlands, and marshes are waterlogged areas where organic matter
accumulates.
●​ Process: Dead plant material and other organic matter settle in the waterlogged soil, where
anaerobic conditions prevent full decomposition. Methanogenic bacteria break down the organic
matter, releasing methane into the atmosphere.
●​ Impact: Wetlands are significant natural sources of methane emissions
Rice Paddies:

●​ Description: Rice paddies are flooded agricultural fields where rice is grown.
 ●​ Process: The standing water in rice paddies creates anaerobic conditions in the soil. As rice
plants grow and decay, methanogenic bacteria decompose the organic matter, producing
methane.
●​ Impact: Rice cultivation is a major agricultural source of methane emissions.

https://water.unl.edu/article/manure-nutrient-management/reducing-carbon-footprint-cattle-operations-through-diet
Stomachs of Ruminants:

●​ Description: Ruminants, such as cattle, sheep, and goats, have specialized stomachs (rumens)
that allow them to digest fibrous plant material.
●​ Process: In the rumen, anaerobic conditions enable methanogenic bacteria to break down
cellulose and other complex carbohydrates, producing methane as a byproduct.
●​ Impact: Livestock farming contributes significantly to global methane emissions due to enteric
fermentation in ruminants.

​2.3.16 Methane has a residence time of about 10 years in the atmosphere and is eventually
oxidized to carbon dioxide

●​ Define the term 'residence time' and explain its significance for methane in the atmosphere
●​ Describe the oxidation process of methane in the atmosphere
●​ Explain why methane is considered a potent greenhouse gas.
Methane, although present in smaller concentrations than carbon dioxide (CO₂), has a powerful impact on
global warming due to its high global warming potential (GWP) and unique atmospheric properties. Its
role in the atmosphere and sources are crucial in understanding climate dynamics.

Key Characteristics of Methane

●​ Global Warming Potential (GWP):​

●​ Methane’s GWP is about 25 times that of CO₂ over a 100-year period, making it a potent
greenhouse gas despite its lower atmospheric concentration.
●​ This high GWP means even small amounts of methane significantly influence global
temperatures.
 ●​ Residence Time in the Atmosphere:​

●​ Methane remains in the atmosphere for approximately 10 years, during which it absorbs
infrared radiation and contributes to the greenhouse effect.
●​ After its residence time, methane is oxidized into CO₂ and water vapor, completing its
cycle in the carbon system.

Methane Sources

●​ Natural Sources:
●​ Wetlands, termite activity, and oceanic processes contribute to methane emissions.
●​ Anthropogenic Sources:
●​ Agriculture (notably from rice paddies and livestock), fossil fuel extraction and use,
landfills, and biomass burning are major human-driven sources of methane.

Oxidation of Methane

●​ Role of Hydroxyl Radicals (OH):

●​ Methane is primarily removed from the atmosphere through its reaction with hydroxyl
radicals, highly reactive molecules that are produced by sunlight acting on water vapor
and ozone.
●​ This oxidation process is essential for converting methane to less potent greenhouse
gases (CO₂ and water vapor), though the CO₂ contributes to the long-term greenhouse
effect.

Climate Implications

●​ Short-Term Warming Impact: Methane's potent warming effect, albeit over a shorter time span,
makes it critical in near-term climate considerations.
●​ Importance of Reducing Methane Emissions: Mitigating methane emissions, particularly from
anthropogenic sources, is an effective strategy for reducing short-term global warming impacts
and managing overall greenhouse gas emissions.

​Oxidation Reaction:

●​ CH₄ + OH → CH₃ + H₂O

●​ CH₃ + OH → CH₃O
●​ CH₃O + O₂ → HCHO + HO₂
●​ HO₂ + NO → NO₂ + OH
●​ NO₂ + sunlight → NO + O
●​ O + O₂ → O₃ (ozone)
●​ HCHO (formaldehyde) eventually breaks down to CO₂ and H₂O

NITROGEN CYCLE
2.3.17 The nitrogen cycle contains organic and inorganic stores.
 ●​ Outline the organic and inorganic stores in the nitrogen cycle.

The nitrogen cycle is essential for distributing nitrogen—a vital element for all living organisms—through
the atmosphere, soil, water, and biological systems. This cycle ensures nitrogen is available in forms that
organisms can use to produce proteins, nucleic acids, and other key molecules necessary for life.

Organic Nitrogen Stores

●​ In Living Organisms:
●​ Proteins: Nitrogen is essential for amino acids, the building blocks of proteins needed for
growth and cellular functions.
●​ Nucleic Acids: DNA and RNA contain nitrogen within their nucleotide structures, critical
for storing and transmitting genetic information.
●​ Other Compounds: Nitrogen is also a component of chlorophyll for photosynthesis and
certain hormones.
●​ In Dead Organic Matter:
●​ Decomposition: After organisms die, decomposers like bacteria and fungi break down
organic nitrogen into simpler forms.
●​ Humus: This decomposed organic matter in soil contains nitrogen that can be
transformed into inorganic nitrogen, accessible to plants.

Inorganic Nitrogen Stores

●​ Atmospheric Nitrogen (N₂):
●​ Nitrogen Gas: About 78% of Earth's atmosphere is nitrogen gas, which is inert and
cannot be directly used by most organisms.
●​ Nitrogen Fixation: Certain bacteria and industrial processes (e.g., Haber-Bosch) convert
atmospheric nitrogen into usable forms like ammonia (NH₃).
●​ Soil and Water Nitrogen Compounds:
●​ Ammonia (NH₃) and Ammonium (NH₄⁺): Produced by nitrogen-fixing bacteria,
decomposers, and industrial processes. Plants can absorb these forms directly or
through further conversion.
●​ Nitrites (NO₂⁻) and Nitrates (NO₃⁻):
●​ Nitrification: Nitrifying bacteria convert ammonia into nitrites and then into
nitrates.
●​ Assimilation: Plants absorb nitrates to form organic molecules.
●​ Denitrification: Denitrifying bacteria convert nitrates back into nitrogen gas,
releasing it into the atmosphere and completing the nitrogen cycle.
 https://www.geeksforgeeks.org/diagram-of-nitrogen-cycle/

​2.3.18 Bacteria have essential roles in the nitrogen cycle.

●​ Describe the process of nitrification and explain the role of bacteria in this process.
●​ Outline the process of denitrification and discuss its significance in the nitrogen cycle.
Bacteria are essential for driving the nitrogen cycle, transforming nitrogen into various forms usable by
plants, animals, and other organisms. Without bacterial activity, the nitrogen cycle would be disrupted,
impacting all life.

Key Processes Facilitated by Bacteria

●​ Nitrogen Fixation: Converts atmospheric nitrogen (N₂) into ammonia (NH₃), making nitrogen
accessible to plants.
●​ Bacteria Involved:
●​ Free-Living Nitrogen-Fixing Bacteria: Examples include Azotobacter and
Clostridium in soil.
●​ Symbiotic Nitrogen-Fixing Bacteria: Examples include Rhizobium, which form
nodules on legume roots.
●​ Process:
●​ Nitrogen gas (N₂) is converted to ammonia (NH₃) by the enzyme nitrogenase,
allowing plants to absorb and use nitrogen in organic compounds.
●​ Nitrification: Converts ammonia (NH₃) into nitrites (NO₂⁻) and then into nitrates (NO₃⁻), which
plants readily absorb.
●​ Bacteria Involved:
●​ Ammonia-Oxidizing Bacteria: Nitrosomonas converts ammonia into nitrite.
●​ Nitrite-Oxidizing Bacteria: Nitrobacter converts nitrite into nitrate.
●​ Process:
●​ Ammonia is first oxidized to nitrite by Nitrosomonas, then nitrite is converted to
nitrate by Nitrobacter.
●​ Assimilation: Plants absorb nitrates (NO₃⁻) and use them to build proteins and other organic
molecules.
●​ Role of Bacteria: While assimilation mainly happens in plants and animals, bacteria
maintain a steady supply of nitrates in the soil.
●​ Ammonification: Decomposes organic nitrogen from dead organisms and waste back into
ammonia, replenishing nitrogen in the soil.
●​ Bacteria Involved:
●​ Decomposers: Bacillus and Pseudomonas break down nitrogen-containing
organic matter into ammonia.
●​ Process:
●​ Organic nitrogen is decomposed into ammonia by decomposing bacteria,
returning it to the soil for plants to reuse.
●​ Denitrification: Converts nitrates (NO₃⁻) back into nitrogen gas (N₂), releasing it into the
atmosphere and completing the nitrogen cycle.
●​ Bacteria Involved:
●​ Denitrifying Bacteria: Pseudomonas and Clostridium, especially in anaerobic
(oxygen-free) conditions.
●​ Process:
●​ Nitrate (NO₃⁻) is reduced to nitrogen gas (N₂), allowing nitrogen to return to the
atmosphere and keeping the nitrogen cycle balanced.

2.3.19 Denitrification only happens in anaerobic conditions, such as soils that are waterlogged.
 ●​ Define denitrification
●​ Describe the conditions under which denitrification occurs.
●​ Explain how insectivorous plants obtain nitrogen in anaerobic conditions

Denitrification is an essential anaerobic process in the nitrogen cycle, converting nitrates (NO₃⁻) back into
nitrogen gas (N₂), which then re-enters the atmosphere. This process typically occurs in waterlogged
soils, where the absence of oxygen creates anaerobic conditions.

Key Impacts on Soil and Plant Growth

●​ Reduced Soil Nitrates: Denitrification decreases the nitrate content in soil, thereby limiting the
amount of nitrogen available for plant uptake. This can hinder the growth of plants that rely on
nitrogen for essential functions like protein synthesis.
●​ Challenges in Waterlogged Soils:​

●​ Anaerobic conditions in waterlogged soils reduce oxygen availability, affecting root

respiration and making it difficult for plants to absorb necessary nutrients.
●​ Root systems may struggle to access oxygen, leading to slower growth or even plant
death if the conditions persist.

Adaptations of Insectivorous Plants

●​ Some plants have evolved specific adaptations to survive in waterlogged environments, including:

https://www.ft.com/content/6b71cd84-4ff5-11e9-8f44-fe4a86c48b33

●​ Pitcher Plants (genus Nepenthes and Sarracenia): Have modified leaves forming
pitcher-shaped structures filled with digestive enzymes and fluids. Insects are attracted to the
pitchers, fall in, and are digested.
​

●​ Sundews (genus Drosera): Have glandular hairs on their leaves that secrete sticky substances
to trap insects. The leaves then curl around the prey, secreting digestive enzymes to break it
down.

https://www.mdpi.com/2075-4450/4/3/413

​2.3.20 Plants cannot fix nitrogen so atmospheric dinitrogen is unavailable to them unless they
form mutualistic associations with nitrogen-fixing bacteria.
 ●​ Explain why plants cannot fix atmospheric nitrogen on their own.
●​ Describe the mutualistic relationship between Rhizobium bacteria and leguminous plants

https://news.illinois.edu/view/6367/204407
Nitrogen is an essential nutrient for plant growth, but atmospheric dinitrogen (N₂) is unavailable to plants
because they cannot fix nitrogen on their own. To overcome this limitation, some plants form mutualistic
associations with nitrogen-fixing bacteria. These associations allow plants to access nitrogen in a usable
form, providing them with a competitive advantage in ecosystems where nitrogen is a limiting factor.

Key Process: Nitrogen Fixation

●​ Nitrogen Fixation: Nitrogen-fixing bacteria convert atmospheric nitrogen (N₂) into ammonia
(NH₃), a form plants can absorb and use to create essential organic compounds like amino acids
and proteins.
●​ Enzyme: Nitrogenase, found in these bacteria, catalyzes the conversion of N₂ into NH₃.

Types of Nitrogen-Fixing Bacteria

1.​ Free-Living Bacteria: e.g., Azotobacter, which fix nitrogen independently in soil.
2.​ Symbiotic Bacteria: e.g., Rhizobium and Frankia, which form mutualistic relationships with
specific plants.

Mutualistic Relationships in Plants

●​ Leguminous Plants:
●​ Form root nodules that house Rhizobium bacteria, which convert N₂ into ammonia.
●​ Examples: Peas (Pisum sativum), beans (Phaseolus vulgaris), clover (Trifolium spp.),
and soybeans (Glycine max).
 ●​ Mechanism:
●​ Plant roots secrete flavonoids, attracting Rhizobium.
●​ Bacteria infect the root hairs, leading to nodule formation.
●​ Within nodules, bacteria convert N₂ into ammonia for plant use.
●​ Non-Leguminous Plants:
●​ Form nodules with Frankia bacteria to access fixed nitrogen.
●​ Examples: Alder (Alnus spp.), sweetfern (Comptonia peregrina), and bayberry (Myrica
spp.).
●​ Mechanism:
●​ Frankia bacteria colonize the plant roots, forming nodules and fixing atmospheric
nitrogen similarly to Rhizobium in legumes.

Ecological SignificanceThese mutualistic associations allow plants to overcome nitrogen limitations in

soils, giving them a competitive advantage and enhancing nitrogen availability in the ecosystem, which
benefits overall plant growth and productivity.

2.3.21 Flows in the nitrogen cycle include mineral uptake by producers, photosynthesis,
consumption, excretion, death, decomposition and ammonification.

●​ Describe the process of mineral uptake by producers

The nitrogen cycle includes several key processes that move nitrogen through ecosystems, involving both
transformations and transfers:

Key Processes in the Nitrogen Cycle

1.​ Mineral Uptake​

1.​ Plants absorb inorganic nitrogen compounds, such as nitrates (NO₃⁻) and ammonium
(NH₄⁺), from the soil.
2.​ This uptake is crucial for synthesizing proteins, nucleic acids, and other nitrogen-based
compounds essential for plant growth.
2.​ Photosynthesis​

1.​ Plants convert CO₂ and H₂O into glucose and oxygen using sunlight.
2.​ This carbon fixation process supports nitrogen assimilation by providing energy and
organic molecules necessary for plant growth.
3.​ Consumption​

1.​ Herbivores consume plants to obtain nitrogen, which is then transferred to carnivores
through the food web.
2.​ Nitrogen flows from plants to herbivores, then up the food web to higher trophic levels.
4.​ Excretion​
 1.​ Animals excrete nitrogenous wastes, such as urea, uric acid, and ammonia, returning
nitrogen to soil and water.
5.​ Death​

1.​ Upon death, plants and animals add nitrogen to the ecosystem’s organic matter.
6.​ Decomposition​

1.​ Decomposers (bacteria and fungi) break down dead organic matter into simpler nitrogen
compounds.
2.​ Decomposition transforms complex nitrogen compounds into simpler forms, such as
ammonia.
7.​ Ammonification​

1.​ Decomposers convert organic nitrogen in dead matter and waste into ammonia (NH₃),
which can further convert to ammonium (NH₄⁺) in the soil.
2.​ This process returns nitrogen to a form usable by plants.

Transformation Flows

●​ Photosynthesis: Converts light energy to chemical energy, indirectly supporting nitrogen

assimilation.
●​ Decomposition: Breaks down organic nitrogen compounds into simpler, usable forms.
●​ Ammonification: Converts organic nitrogen into inorganic ammonia.

Transfer Flows

●​ Mineral Uptake: Moves inorganic nitrogen from soil to plants.

●​ Consumption: Passes nitrogen through the food web.
●​ Excretion: Returns nitrogen to the environment.
●​ Death: Adds nitrogen from organisms to the ecosystem’s organic matter.
Application of skills: Create a systems diagram of the nitrogen cycle.

HUMAN ACTIVITY ON NITROGEN CYCLE

2.3.22 Human activities such as deforestation, agriculture, aquaculture and urbanization change
the nitrogen cycle.

●​ Discuss the impacts of human activity on the nitrogen cycles.

 image from www.drmonline.ne
​Human activities significantly disrupt biogeochemical cycles, affecting the natural balance and posing
threats to ecosystems. These disruptions impact the cycles of elements that regulate Earth's climate.
Here’s a summary of key human-induced disruptions to biogeochemical cycles:

Key Human Impacts on Biogeochemical Cycles

●​ Burning Fossil Fuels:

●​ Increases CO₂ levels in the atmosphere, enhancing the greenhouse effect and
contributing to global warming.
●​ Reduces Arctic Sea ice, decreasing reflected sunlight and increasing Earth's heat
absorption.
●​ Pollution from combustion increases atmospheric particles, scattering and reflecting
sunlight, altering energy distribution.
●​ Deforestation:
●​ Disrupts nutrient cycling, particularly in tropical rainforests where nutrients cycle within
leaf litter and tree biomass.
●​ Without tree canopies to intercept rainfall, soils and leaf litter wash away, leading to soil
degradation and nutrient loss.
●​ Aquaculture:
 ●​ Fish farms use fertilizers and antibiotics that can leach into surrounding water bodies,
disrupting the nitrogen cycle and potentially causing pollution.
●​ Urbanization:
●​ Drains wetlands, which are vital sites for denitrification, a process that removes nitrogen
from water and releases it into the atmosphere.
●​ Reducing wetlands limits denitrification, increasing nitrogen in water systems.
●​ Agriculture:
●​ Extensive nitrogen fertilizer use accelerates nitrogen transfer to soil and water, causing
leaching and groundwater contamination.
●​ Nitrogen from fertilizers and fossil fuel combustion contributes to eutrophication in aquatic
systems, degrading water quality and harming aquatic life.
●​ Forest burning and combustion increase atmospheric nitrogen deposition.
●​ Mining of Fossil Fuels:
●​ Extracts fossil fuels that would otherwise remain in Earth’s crust, releasing stored carbon
into the atmosphere as CO₂.
●​ Clearing vegetation for mining reduces natural carbon sinks, exacerbating CO₂
concentration and accelerating climate change.
●​ Livestock Ranching:
●​ Livestock waste releases ammonia, contributing nitrogen to soils, which leaches into
water systems, impacting groundwater and surface water quality.

2.3.23 The Haber process is an industrial process that produces ammonia from nitrogen and
hydrogen for use as fertilizer.​

●​ Describethe Haber process

●​ Outline the advantages and disadvantages of using the Haber process for fertilizer production.
​The Haber process, also known as the Haber-Bosch process, is an industrial method for synthesizing
ammonia (NH₃) from nitrogen (N₂) and hydrogen (H₂) gases. This process is fundamental for producing
fertilizers, which significantly enhance agricultural productivity. However, the use of the Haber process
also comes with both advantages and disadvantages.

Chemical Reaction:

●​ Equation: N₂ (g) + 3H₂ (g) ⇌ 2NH₃ (g)

●​ Conditions: The reaction typically occurs at high temperatures (around 450-500°C) and high
pressures (150-200 atmospheres) in the presence of an iron catalyst.

Raw Materials:

●​ Nitrogen (N₂): Sourced from the air, which is composed of approximately 78% nitrogen.
●​ Hydrogen (H₂): Usually derived from natural gas (methane) through a process called steam
reforming, where methane reacts with water to produce hydrogen and carbon dioxide (CO₂).
●​ Output: The ammonia produced is used primarily to manufacture fertilizers such as ammonium
nitrate (NH₄NO₃) and urea (CO(NH₂)₂), which provide essential nitrogen for plant growth.
https://chemistrytalk.org/haber-process/
​2.3.24 Increases in nitrates in the biosphere from human activities have led to the planetary
boundary for the nitrogen cycle being crossed, making irreversible changes to Earth systems
likely.

●​ Explain the significance of the 'planetary boundary' in the context of the nitrogen cycle.
●​ Discuss two major environmental impacts of crossing the nitrogen cycle planetary boundary.

https://www.researchgate.net/figure/Proposed-new-planetary-boundaries-framework-Updated-version-of-the-planetar
y-boundaries_fig2_356855403
Human activities, particularly the extensive use of inorganic fertilizers, have pushed the nitrogen cycle
beyond its sustainable limits, leading to potentially irreversible changes in Earth's ecosystems. The
Stockholm Resilience Centre has identified critical indicators that show this planetary boundary has been
crossed, with severe implications for environmental and human health.
Key Indicators of Nitrogen Cycle Disruption

●​ Increased Nitrate Levels:

●​ Rising nitrate concentrations in rivers, lakes, and groundwater due to fertilizers and
manure.
●​ Leads to water pollution, unsafe drinking water, and harm to aquatic organisms.
●​ Eutrophication:
●​ Nutrient overload, especially from nitrogen and phosphorus, promotes excessive algae
growth in water bodies.
●​ Results in oxygen-depleted "dead zones," habitat loss, and fish kills, disrupting aquatic
ecosystems.
●​ Decreased Biodiversity:
●​ Excess nitrogen favors certain species, causing imbalances and reducing overall species
diversity.
●​ Loss of biodiversity weakens ecosystem resilience, impacting services like water
purification and habitat stability.

Causes of Planetary Boundary Breach

●​ Inorganic Fertilizer Use:

●​ Fertilizers produced via the Haber-Bosch process have drastically increased bioavailable
nitrogen in ecosystems.
●​ The drive for high crop yields has led to over-reliance on nitrogen-rich fertilizers, pushing
nitrogen levels beyond natural limits.

Impacts of Irreversible Changes

●​ Water Quality Degradation:

●​ Eutrophication and nitrate contamination degrade water quality, endangering human and
aquatic health.
●​ Contaminated water can lead to health issues, especially in infants and vulnerable
populations.
●​ Reduced Food Security:
●​ Excess nitrogen can harm soil and crop health, potentially reducing yields and impacting
food security.
●​ Lower crop productivity threatens farmers' livelihoods and global food supplies.
●​ Human Health Risks:
●​ High nitrate levels in drinking water are linked to health problems like
methemoglobinemia (blue baby syndrome) in infants.
●​ Nitrogen compounds in the atmosphere can contribute to respiratory issues due to fine
particulate matter.

​2.3.25 Global collaboration is needed to address the uncontrolled use of nitrogen in industrial and
agricultural processes and bring the nitrogen cycle back within planetary boundaries.
 ●​ Explain why global collaboration is necessary to manage the nitrogen cycle
●​ Discuss the role of international agreements and policies in regulating nitrogen emissions from
industrial processes.
The excessive use of nitrogen in agriculture and industry has pushed the nitrogen cycle beyond safe
planetary limits, causing significant environmental and health issues. Tackling this issue requires a
coordinated global approach and actionable measures to bring the nitrogen cycle back into balance.

The Need for Global Collaboration

●​ Shared Responsibility:
●​ Nitrogen pollution is a global problem affecting ecosystems and health, calling for joint
international efforts.
●​ The nitrogen cycle is interlinked with other biogeochemical cycles, requiring cooperation
across multiple environmental sectors.
●​ International Agreements and Policies:
●​ Frameworks like the Paris Agreement and Sustainable Development Goals (SDGs)
provide collaborative platforms to address nitrogen management.
●​ Developing and enforcing global regulations can standardize practices and mitigate
nitrogen pollution worldwide.

Key Measures to Restore Planetary Boundaries

●​ Efficient Fertilizer Use:

●​ Precision farming and optimized fertilizer application reduce nitrogen runoff and minimize
pollution.
●​ Providing farmers with training and tools enhances efficient fertilizer use, reducing waste
and environmental impact.
●​ Promoting Sustainable Agriculture:
●​ Cover crops can improve soil health, decrease reliance on synthetic fertilizers, and
enhance soil organic matter.
●​ Crop rotation helps maintain soil fertility, reduces pest and disease pressures, and
balances nutrient levels.
●​ Reducing Nitrogen Emissions:
●​ Stricter regulations on nitrogen emissions from industrial sources help lower nitrogen
levels entering ecosystems.
●​ Enforcement of compliance with emission standards is essential to achieve sustainable
nitrogen management.
●​ Promoting Alternative Nitrogen Sources:
●​ Legumes and nitrogen-fixing plants naturally enrich soils, reducing the need for synthetic
fertilizers.
●​ Investment in alternative nitrogen sources and sustainable agriculture fosters long-term
solutions for nitrogen cycle restoration.