The living environment: Biogeochemical cycles

Many elements have low availability to living organisms. Biogeochemical cycles involve inter-linked processes that allow materials to be recycled and repeatedly re-used. So they don’t build up in wastes and become depleted from where they are relied upon as a resource.

-Photosynthesis. -Aerobic respiration. -Anaerobic respiration. -Combustion. -CO2 dissolving in the sea/exsolving from the sea. -Biomass movements. -Changes in carbon reservoirs. -Increased atmospheric concentration of CO2 . -Less soil dead organic matter. -Increased concentrations of dissolved CO2 , carbonic acid, hydrogen carbonate ions. -Increased atmospheric concentration of methane. -Reduced amount of carbon in plant biomass. -Reduced amount of carbon in fossil fuels.

-Alternatives to fossil fuel use. -Carbon sequestration. -Carbon Capture and Storage (CCS). -Matching afforestation to deforestation. -Increasing soil organic matter. -Conservation of peat bogs.

• atmosphere • hydrosphere • biosphere • lithosphere Human activities alter many of the processes in the carbon cycle. This can alter dynamic equilibria, causing some reservoirs to become depleted while carbon stores increase in other reservoirs.

carbon dioxide 700Gt methane 1.2Gt carbon monoxide Trace

hydrogen carbonate ions dissolved carbon dioxide surface waters 500Gt deep ocean 35,000Gt

carbohydrates, for example, cellulose, lignin, starch, sugars Proteins Lipids, for example, vegetable oils and animal fats Living organisms 470Gt Dead organic matter 3,700Gt

Carbonaceous rocks, for example, limestone, mainly as calcite (calcium carbonate) Fossil fuels: mainly as carbon and hydrocarbons Sedimentary carbonates 20,000,000Gt (twenty million Gt) Fossil fuels 10,000Gt

Photosynthesis captures light energy using pigments such as chlorophyll. It converts low-energy substances such as carbon dioxide and water into high-energy carbohydrates which may be converted into other substances such as proteins and lipids.

Respiration releases the energy that was captured during photosynthesis which is then used to drive metabolic processes. Aerobic respiration returns the carbon to the atmosphere as carbon dioxide. Aerobic respiration breaks down organic compounds more completely and releases much more energy than anaerobic respiration. However, anaerobic respiration allows some organisms to survive and use food sources in oxygen-deficient environments. Anaerobic respiration usually returns the carbon to the atmosphere as methane.

Some of the carbohydrates, proteins, and lipids produced by plants are eaten by herbivores, which may then be eaten by carnivores. These feeding relationships combine to make food webs.

The incomplete decomposition of dead organic matter, often under anaerobic conditions, can produce substances that form long-term carbon stores such as fossil fuels. Some organisms such as molluscs, corals, and many planktonic organisms produce exoskeletons that include calcium carbonate. This may produce rocks such as limestone, which now contain most of the carbon in the lithosphere.

The burning of organic materials releases carbon dioxide. Natural fires in forests and grasslands may be started by lightening.

(they disrupt the natural dynamic equilibria) - deforestation reduces the movement of carbon from the atmosphere into biomass. - Afforestation increases the movement of carbon from the atmosphere into biomass. - marine pollution with toxic materials can reduce phytoplankton populations. This reduces the absorption of dissolved carbon dioxide. Some phytoplankton naturally sinks to the seabed when it dies, increasing the amount of carbon in marine sediments. Carbon dioxide from the atmosphere would have dissolved in the sea to replace this and maintain the equilibrium between carbon dioxide in the atmosphere and in solution in the oceans. So, toxic marine pollution that kills phytoplankton can lead to higher atmospheric CO2 levels - algae live on the underside of sea ice around Antarctica. Some of the carbon they absorb during photosynthesis sinks to the seabed in the faeces of krill that eat the algae. If climate change reduces the area of sea ice then less CO2 may be removed from the sea.

Planting trees to increase the area of forest. (planting trees where they haven’t grown before)

The carbon in dead organic matter in the soil is gradually released as CO2 by the aerobic respiration of soil organisms, especially bacteria and fungi. Ploughing increases the oxygen supply to decomposers living in the soil so aerobic decomposition takes place more rapidly. The amount of carbon in the soil dead organic matter store is reduced and the amount in the atmosphere is increased.

In the absence of oxygen, respiration by anaerobic soil organisms releases methane gas. If the methane is released into the atmosphere, it is gradually oxidised to CO2. Anaerobic environments produced by human activities: - rice Padi fields - landfill sites - anaerobic sediments in reservoirs - livestock intestines Anaerobic environments destroyed by drainage: - waterlogged fields - marshlands - peat bogs

Humans do not directly cause CO2 to dissolve or exsolve but human activities that affect the concentration of CO2 in the atmosphere, will alter these processes to create a new dynamic equilibrium. Dissolved CO2 is in an equilibrium with carbonic acid which dissociates to form hydrogen carbonate and hydrogen ions. The concentration of hydrogen ions affects the pH of the sea so an increase in dissolved CO2 will reduce the pH of the water. So as atmospheric CO2 concentrations rise, dissolved CO2 concentrations increase, which therefore increases hydrogen ion concentrations and makes the sea more acidic.

Methane may be released into the atmosphere during fossil fuel extraction.

The combustion of fossil fuels and wood releases large amounts of CO2 into the atmosphere.

Humans do not directly move large amounts of carbon in biomass between areas, but human activities can produce local changes which have environmental impacts: - the addition of compost/ mulch to improve soil fertility - deforestation and crop harvesting leading to reduced soil organic matter and soil erosion - the movement of biomass into the sea when sewage is discharged - movement of marine biomass into the terrestrial system by fishing/ aquaculture

• conservation of biomass carbon stores • the use of alternatives to fossil fuels • carbon sequestration • Carbon capture and storage (CCS)

Habitats such as peat bogs and forests contain huge amounts of carbon. Protecting these form exploitation, or damaging land-use change, is important to prevent even higher CO2 releases.

Renewable energy resources and nuclear power produce lower CO2 emissions than fossil fuels