Chapter 55 Carbon Cycling Essential Idea: Continued availability of carbon in ecosystems depends on carbon cycling.

Model for Nutrient Cycling As stated in the last section, when we look at nutrient cycling, we have to consider: The main reservoirs for elements. Processes that transfer the elements between reservoirs.

Model for Nutrient Cycling Each reservoir has two questions that need to be answered: Does it contain organic or inorganic materials? Are the materials directly available for use by organisms?

Carbon Cycle Carbon is important because it forms the framework for organic molecules essential to all life.

Carbon Cycle Photosynthesis makes use of CO 2 by converting it into forms used by consumers.

Carbon Cycle Carbon is found in great proportions in fossil fuels, sediments of aquatic ecosystems, the oceans, plants and animal biomass, and the atmosphere. ReservoirCarbon (gigatons) Percent of Total Carbon on Earth Oceans38 x Rocks and Sediments 75 x 10 6 >99.5 Terrestrial Biosphere 2 x Aquatic Biosphere Methane Hydrates1 x Fossil Fuels4.2 x

Carbon Cycle Additionally, aquatic ecosystems contain carbon as dissolved CO 2 and hydrogen carbonate ions.

Carbon Cycle The largest carbon reservoir is found in sedimentary rocks like limestone. Bob Krist/Corbis

Limestone

Animals such as reef-building corals and mollusca have hard parts that are composed of calcium carbonate and can become fossilized in limestone.

Carbon Cycle Key processes concerning the carbon cycle are: The conversion of CO 2 into carbohydrates and other carbon compounds by autotrophs. CO 2 + H 2 O --> C 6 H 12 O 6 + O 2 The return of CO 2 to the atmosphere through cell respiration. C 6 H 12 O 6 + O 2 --> CO 2 + H 2 O

Carbon Cycle When CO 2 is produced by heterotrophs, it diffuses out of the organism and into the water or the atmosphere.

Carbon Cycle The CO 2 in the atmosphere then diffuses into autotrophs in the atmosphere or water. travismulthaupt.com

Carbon Cycle As stated in the last section, volcanoes contribute a lot of CO 2 to the atmosphere over geologic time. The burning of fossil fuels is also adding a lot of CO 2 to the atmosphere.

Methane Methane is produced from organic matter in anaerobic conditions by methanogenic archaeans. It is done so in the absence of O 2. Anthropogenic sources Natural sources.

Methane Some diffuses into the surrounding water, bubbles into the atmosphere, or is trapped and accumulates in the ground.

Methane Natural sources of methane include swamp bottoms, ruminant animals, wets soils where organic decay is occurring in anaerobic conditions. Anthropogenic sources include rice paddies, land fills, sewage treatment plants, etc.

Methane is a potent greenhouse gas and needs to be limited as much as possible to stem global warming/climate change. Methane www3.edp.gov

Methane Methane removal from the atmosphere comes from the chemical reaction of methane with a hydroxyl radical producing water and carbon dioxide. Methane removal in the soil comes from the action of methanotrophs.

Methane Certain microorganisms in the soil are able to use single-carbon compounds such as methane as a fuel. Using a complex pathway, they break methane down into CO 2 and water.

Peat Formation Peat forms when plant material is inhibited from fully decaying by acidic and anaerobic conditions. It is composed mostly of wetland vegetation: principally mosses, sedges and shrubs.

Peat Formation When the soil becomes waterlogged, it often becomes anaerobic, acidic, or both and this contributes to the formation of peat.

Peat Formation Peat formation is the first step in the formation of coal. The formation of coal takes millions of years.

Peat Formation

Peat Formation Partially decomposed organic matter from past geological eras was converted either into coal or into oil and gas that accumulated in porous rocks. serc.carleton.edu

Oil Formation Millions of years ago, plants and animals living in the ocean absorbed energy from the sun and stored this energy in their bodies in the form of carbon.

Oil Formation As these animals died, their bodies sank to the bottom of the ocean where they were covered with layers of sediment deposits.

As these layers of sediment increased the heat and pressure exerted on these remains began to rise. Oil Formation

The degree of heat and the amount of pressure, along with the type of biomass, directly influenced whether oil or natural gas was formed. As heat increases, a lighter gas is formed. If the temperature raises to an even higher heat, or if the biomass is predominantly plant material, natural gas is formed. Oil Formation

As heat increases, a lighter gas is formed. If the temperature raises to an even higher heat, or if the biomass is predominantly plant material, natural gas is formed. Oil Formation

After oil is formed, it travels from the source rocks, where it was formed, through tiny pores in the surrounding rock until it either seeps through the rock onto the surface or is trapped beneath a layer of impermeable rock or clay and forms a reservoir. Oil Formation

Reservoirs range in depth below the surface. Some are only hundreds of feet below, while others have been discovered at depths greater than 30,000 feet. Still others are discovered offshore, and are covered with thousands of feet of water on top of tens of thousands of feet of sediment. Oil Formation

The majority of reservoirs are made up of oil, gas, and water. These fluids are generally separated into layers due to the influence of gravity and differences in density. Gas, being the less dense of the three, migrates to the top, followed by oil and then water. Oil Formation

70% of oil deposits were formed in the Mesozoic age, 20% were formed in the Cenozoic age, and 10% were formed in the Paleozoic age. These differences are the result of many factors, The Mesozoic climate was primarily tropical worldwide, plankton were very abundant in the ocean, the ocean bottoms stagnant and anoxic (preventing the occurrence of decomposition), and organic- rich muds accumulated and formed later source rocks. Oil Formation

Burning of Fossil Fuels When these fossil fuels are burned, CO 2 is produced reentering the carbon cycle. Currently, we are producing far more CO 2 than can be taken out of the atmosphere.

Oil Formation