1.2.6 Biogeochemical cycles

Helpful prior knowledge and learning objectives:

Helpful prior learning:



Learning objectives:

The Whanganui River in New Zealand

Figure 1. The Whanganui River in New Zealand, the first river to be granted legal personhood (Activity at the end refers to this)

(Credit: James Shook CC BY 2.5)

The water in your body is just visiting. 

It was a thunderstorm a week ago. 

It will be the ocean soon enough. 

Most of your cells come and go like morning dew. 

We are more weather pattern than stone monument. 

Sunlight on mist. Summer lightning. 

Your choices outweigh your substance.


-- “Naming the River” from Field Guide to the Haunted Forest 

by ©Jarod K. Anderson, with permission

Jarod Anderson’s poem beautifully highlights the connection between humans and nature. Like all living things, our bodies are about 70% water, which comes from and returns to our ecosystems, through vital biogeochemical cycles.

What are biogeochemical cycles?

Biogeochemical cycles move essential elements between abiotic (nonliving) and biotic (living) parts of ecosystems. Elements like water, carbon, oxygen, nitrogen and phosphorus cycle through the air, land, water, and organisms, link all Earth systems. However, human activities often disrupt these cycles, risking collapse of the Earth systems on which we depend.


This section explores the water and carbon cycles, showing their importance to Earth's life-support systems.

How does the water cycle work?

The water cycle, or  hydrosphere, is the stocks and flows of all water on Earth. Stocks, or storages, of water include oceans, glaciers and ice caps, groundwater, surface water, the atmosphere and living organisms. Figure 2 shows that the salty oceans hold most water (97.2%), while a tiny fraction of freshwater exists mainly as ice in glaciers and ice sheets.

Figure 2. The composition of water in Earth’s hydrosphere in pie charts

Figure 2. The composition of water in Earth’s hydrosphere

(Credit: Woudloper CC BY-SA 4.0)


Water moves between stocks, driven by solar radiation and gravity. Water is  transferred from one place to another, or it is transformed into different states. 

Figure 2 shows these movements between water stocks.

The water cycle

Figure 3. The water cycle

(Credit: NASA)

Why is the water cycle important for life on Earth?

The water cycle is crucial for ecosystem function. It stabilises Earth's temperature, cooling areas through evaporation, transpiration and sublimation. Glaciers and ice sheets also reflect warming solar radiation back into the atmosphere. Oceans absorb carbon dioxide (CO2) from the atmosphere, reducing global warming. Ocean currents distribute heat globally. In addition to regulating temperature, the water cycle also distributes matter like nutrients vital for life and also supplies fresh water for organisms' survival.

How does human economic activity disrupt the water cycle?

Human economic activities disrupt the water cycle, including:


Human disruptions to the water cycle damage the ecosystems on which we depend, and are depleting water stocks for human agricultural systems. Protecting and supporting the water cycle is critical to all life on Earth.

How does the carbon cycle work?

Carbon is an element found in all life forms, making up nearly 50% of organisms’ dry biomass. The carbon cycle is how carbon moves between Earth's atmosphere, hydrosphere, biosphere, and lithosphere. Carbon stocks include the atmosphere, oceans, living organisms, rocks and soil. Carbon is transferred and transformed between these stocks, shown in Figure 5.

The carbon cycle

Figure 5. The carbon cycle

(Credit: Met Office)

Why is the carbon cycle important for life on Earth?

The carbon cycle moves carbon from the atmosphere, hydrosphere and lithosphere to living organisms in the biosphere, which is essential for life and climate regulation. Carbon dioxide, a greenhouse gas, warms Earth which supports life. However, excessive carbon dioxide in the atmosphere causes overheating and acidifies oceans, both of which threaten life. Balanced carbon levels in Earth’s various stocks are crucial to functioning ecosystems on which humans depend.

How does human economic activity disrupt the carbon cycle?

Human economic activities significantly alter the carbon cycle:

These activities increase atmospheric carbon dioxide (Figure 6) beyond the levels that natural processes can remove. As a result, Earth’s average temperature is increasing, causing climate change, higher sea levels, ocean acidification, and altered habitats for plants and animals.


Figure 6: Annual CO2 emissions

(Credit: Our World in Data)

Human agriculture and civilizations developed around 10,000 years ago under stable climates with less than 1°C temperature variation, a period called the Holocene. Currently, global temperatures are almost 1.5°C warmer than the pre-Industrial time period because burning fossil fuels has increased concentrations of carbon dioxide in the atmosphere (Figure 6). The climate is changing so rapidly that it will likely be difficult for our societies and economies to adapt.

Our current economies disrupt the carbon cycle and destabilise the conditions for human life on Earth. To restore balance in the carbon cycle, we must dramatically reduce our CO2 emissions and regenerate ecosystems.

Activity 1.2.6

Concept: Systems

Skills: Thinking skills (creative and critical thinking, transfer)

Time: Depends on the option - see below

Type: Individuals, pairs or group - depends on the option


Option 1 - Creative thinking

40+ minutes

Imagine that you are a water molecule or a carbon atom. From that perspective, write a short poem (story, or some other format) that reflects your experience in some part of the water or carbon cycle, or that reflects how human activities have disrupted your movement in the water or carbon cycle. 



Option 2 - Discussion: Does it make sense to distinguish between living and nonliving parts of nature?

20-25 minutes


E rere kau mai te Āwanui, Mai i te Kāhui maunga ki Tangaroa. Kō au te Āwa, kō te Āwa kō au.

“The great river flows from the mountains to the sea. I am the river, the river is me.”

--Ngāti Hau, the indigenous communities along the Whanganui River, New Zealand


Questions to think about / discuss in small groups or as a class:



Option 3 - Legal personhood for nature

40-50 minutes

Some countries and regions are giving legal personhood to abiotic parts of nature, like rivers, to increase their protection under the law. Alone or with some partners, do some quick research on legal personhood to find answers to these questions or others that come up:


Discuss what you found out with a few other students or as a whole class.



Option 4 - Annotating diagrams

The illustrations in this section show the water and carbon cycles. However, the human disruptions to these cycles are only described in words. Make those disruptions visible by adding them to the cycle diagrams. You may want to work alone to test your understanding, or work with a partner to support each other’s understanding.




Ideas for longer activities, deeper engagement, and projects are listed in Subtopic 1.5 Taking action

Further exploration

Sources

Anderson, J. (2020, November 27). “Naming the River”. Field Guide to the Haunted Forest. Amazon Digital Services.

Daly, H., Farley, J. (2011). Ecological Economics (2nd ed.). Washington, D.C.: Island Press.

Encyclopedia Britannica (2024, January 24). Māori. https://www.britannica.com/topic/Maori.

Freid, D. (Director). (2018). The River is Me [Film].

Met Office (n.d.). Carbon cycle. https://www.metoffice.gov.uk/weather/climate/climate-explained/carbon-cycle.

NASA (n.d.). Classroom Activity: Modelling the Water BudgetJet Propulsion Laboratory, California Institute of Technology. https://www.jpl.nasa.gov/edu/teach/activity/modeling-the-water-budget/.

Rutherford, J., Williams, G. (2015). Environmental Systems and Societies. Oxford: Oxford University Press.

Terminology

Link to Quizlet interactive flashcards and terminology games for Section 1.2.6 Biogeochemical cycles


ecosystem: the interaction of groups of organisms with each other and their physical environment

biogeochemical cycle: Earth system cycles that move essential elements like water, carbon and nitrogen between living and nonliving parts of ecosystems

abiotic: nonliving

biotic: living

water cycle: the stocks and flows of all water on Earth

hydrosphere: all the waters on Earth

stock: an accumulation of something, such as energy, matter, information, or money

flow: movement of something such as energy, matter, information or money between stocks

glacier: a mass of dense ice that constantly moves under its own weight, found in high altitudes and at the poles

groundwater: water that collects underground in soil or in rock crevices and pores

surface water: water that collects on the surface of the ground, like lakes and rivers; also known as blue water

atmosphere: the gases surrounding the Earth

freshwater: a water body with very low or no salt content

solar radiation: energy emitted by the sun

gravity: the force that attracts a body towards the centre of the earth, or towards any other physical body having mass

transfer: to move something from one place to another

transform: a change in the state, energy or chemical nature of something

evaporation: the transformation of a substance like water from a liquid into a gas

transpiration: the transformation of water from a plant's leaves, stem, or flowers to a gas

sublimation: transformation of a substance like water from a solid to a gas without first becoming a liquid

water vapour: the gaseous state of water

condensation: the transformation of water vapour into water droplets and clouds due to cooling in the atmosphere

precipitation: the transfer of water from clouds to the Earth as rain, snow or hail

infiltration: the transfer of water through soils, collecting as groundwater

runoff: the draining away (transfer) of water and the substances carried in it from the surface of land, or structure

carbon dioxide (CO2): gas produced by burning carbon or organic compounds and through respiration, naturally present in the atmosphere and absorbed by plants in photosynthesis

ocean currents: the predictable movement of ocean water in a direction

overextraction: taking too much of something away from somewhere else, especially using effort or force

pollution: the presence of a substance that has harmful effects on the environment

organic waste: any material that easily breaks down in nature and comes from either a plant or an animal

deforestation: removing a wide area of trees, often for farming, mining, or urbanisation

reinforcing feedback: a situation where change in a system causes further changes that amplify the original change which can lead to tipping points in a system

fossil fuel: a non renewable energy source including coal, oil, and natural gas, formed over millions of years in the Earth's crust from decomposed plants and animals

climate change: a change in the temperature and precipitation patterns in an area, in recent times due to human economic activities

economy: all the human-made systems that transfer and transform energy and matter to meet human needs and wants

biomass: organic matter

carbon cycle: the movement of carbon between Earth's atmosphere, hydrosphere, biosphere, and lithosphere

biosphere: all the living organisms on Earth

lithosphere: the solid, outer part of Earth

photosynthesis: the process by which green plants and some other organisms use sunlight to transform carbon dioxide and water into food

cellular respiration: the transformation of food (carbohydrates) into energy within cells

consumption: using resources and products to meet needs, or in food chains, eating another organism

decomposition: breaking something into smaller parts, especially organic materials

oceanic gas exchange: the process where gases like CO2 move between the atmosphere and the oceans

fossilisation: the process that occurs when plant and animal remains are preserved in sedimentary rock

sedimentation: process in which rock is formed from small pieces of sand, stone, etc. that have been left by water, ice, or wind

extraction: taking something away from somewhere else, especially using effort or force

combustion: a chemical process in which a substance reacts rapidly with oxygen and gives off heat

greenhouse effect: a process that occurs when gases in Earth's atmosphere trap the Sun's heat

built environment: human-made structures or conditions in an area

urbanisation: the increase in the proportion of people living in towns and cities, along with the built environment

livestock: a population of animals kept by humans for their use

ocean acidification: a reduction in the pH of the ocean over time, caused primarily by absorption of carbon dioxide

habitat: the natural home or environment of an animal, plant, or other organism

Holocene: the current geological epoch, beginning approximately 11,700 years ago, noted for its stable climate

legal personhood: a legal concept where a person or a thing has legal rights and/or duties