18.2 The Carbon and nitrogen cycle What are ecosystems made of? Our Biosphere

Learning Targets Describe the short term cycling of carbon through the processes of photosynthesis and respiration Identify carbon sinks and carbon sources Describe short term and long term storage of carbon Describe how human actions interfere with the natural carbon cycle Describe the nitrogen cycle

Carbon Cycle All life on earth is built around carbon atoms Carbon is found in many forms: Atmosphere (Carbon Dioxide) Biosphere (Carbohydrates) Hydrosphere (Calcium carbonate) Geosphere (Carbon arrangement) Carbon is provided by the environment, moves through organisms and then returns to the environment again.

Short term cycle Atmospheric Carbon Dioxide Photosynthesis Cellular Carbon Dioxide Respiration, decay, or consumption Short term cycling of carbon begins with carbon dioxide and the process of photosynthesis. Plants and algae have the ability to take the inorganic carbon in carbon dioxide and transformed into organic carbon, which is food. Plants and animals engage in reverse of photosynthesis, which is respiration

Photosynthesis

Long term cycles Organic materials are buried AKA – Fossil Fuels Peat, coal, tar, oil, soil Carbon stored in the ocean Many ocean creatures use calcium carbonate (CaCO3) to make their shells or to make the reef material where coral animals live. Carbon might also be stored as chemical energy in the cells of the plant or the animal. If this happens, the carbon will stay stored as part of the organic material that makes up the plant or animal until it dies. it decomposes and the carbon is released back into the environment. Other times, the organic material of the organism is buried and transformed over millions of years into coal, oil, or natural gas. When this happens, it can take millions of years before the carbon becomes available again. When algae die, their organic material becomes part of the ocean sediments, which may stay at the bottom of the ocean for many, many years. Over millions of years, those same ocean sediments can be forced down into the mantle when oceanic crust is consumed in deep ocean trenches. As the ocean sediments melt and form magma, carbon dioxide is eventually released when volcanoes erupt.

Carbon Sinks and Carbon Sources Carbon sources (add carbon) Fossil fuel use, deforestation, animals, decaying plant remains Carbon sinks (store carbon) Healthy living forests and our oceans act as carbon sinks. Reservoirs can change from a sink to source and vice-versa Carbon sources are places where carbon enters into the environment and is available to be used by organisms. Carbon sinks are places where carbon is stored because more carbon dioxide is absorbed than is emitted. Places in ecosystem that store carbon are reservoirs. Average time that carbon stays in a reservoir is residence time. Amount of CO2 in the atmosphere is very low – 0.03%, therefore some increase or decrease have large effect.

Scientists can use data from air bubbles trapped in the ice of glaciers to determine what the natural level of carbon dioxide was before the Industrial Revolution, when humans began to use lots of fossil fuels. Measurements of the different gases in the air bubbles tell us that the natural level of carbon dioxide was about 280 parts per million. Today the amount of carbon dioxide in our atmosphere is 388 parts per million and that amount continues to rise every year.

Human Actions Impact Carbon Cycle Largest source of atmospheric CO2 is burning fossil fuels When we burn coal, oil, or natural gas, we release the stored carbon in the process of combustion. That means that combustion of fossil fuels is also a carbon source.

Human Actions Impact Carbon Cycle Second largest source of atmospheric CO2 is deforestation Carbon sink – Trees absorb CO2 When trees are cut, lose ability to absorb CO2 Carbon source- If tree is burned or decomposes When we cut down trees, we lose their ability to absorb carbon dioxide and we also add the carbon that was stored in the tree into the environment. Healthy living forests act as a carbon sink, but when we cut them down, they are a carbon source

Why Carbon Cycle is Important Why small amounts of CO2 important? CO2 absorbs infrared energy from Sun Greenhouse gases trap heat that should radiate out into space Greenhouse gas levels increase, global temperatures increase = Global Warming

The Nitrogen Cycle Most abundant gas in atmosphere Essential component of organic materials Amino Acids Proteins DNA and RNA Chlorophyll molecules used for photosynthesis

The Nitrogen Cycle Must be “fixed” or converted to a usable form “Fixed” in 3 ways Lightning Blue-green algae Mainly “fixed” by bacteria in soil Nitrogen fixing bacteria combine nitrogen with oxygen = nitrates or ammonia Just like how photosynthesis converts sunlight to a useable energy

Symbiotic relationship with legumes (peas, beans, peanuts) Symbiotic relationship with legumes (peas, beans, peanuts). Use carbohydrates from plant to produce ammonia. When plant dies, the fixed nitrogen fertilizes the soil Animals eat plant tissue and create animal tissue.

Excess fertilizers run off the land, and causing nitrification in ponds and rivers, ending up in the ocean causing a “Dead Zone”. Nitrogen “fertilizes” ponds causing bacteria to grow. When bacteria die, their decomposition uses up all the available oxygen killing everything else. Dead Zone