Biogeochemical Cycles

• The cycling of chemical elements required by life between the living and nonliving parts of the environment. Some examples of these chemical elements are H2O, P, S, N2, O2 and C.

• Gas Cycles:           Sedimentary Cycles:

• Carbon                                   Phosphorus Nitrogen                                 Sulfur Oxygen

Carbon Cycle BasicsAll life is based on the

element carbon. Carbon is the major chemical

constituent of most organic matter, from fossil fuels to the complex molecules (

DNA and RNA) that control genetic

reproduction in organisms. Yet by weight, carbon is

not one of the most abundant elements within

the Earth's crust. 1/12

Egon Schiele (1890-1918)

Autumn Sun 1

Carbon Pools

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Pool Amount in Billions of Metric Tons Atmosphere 578 (as of 1700) - 766 (as of 1999) Terrestrial Plants 540 to 610 Soil Organic matter 1500 to 1600 Ocean 38,000 to 40,000 Fossil Fuel Deposits 4000 Marine Sediments and Sedimentary Rocks 66,000,000 to 100,000,000

Carbon is stored on our planet in the following major pools: • as organic molecules in living and dead organisms found in the

biosphere; • as the gas carbon dioxide in the atmosphere; • as organic matter in soils; • in the lithosphere as fossil fuels and sedimentary rock deposits such as

limestone, dolomite and chalk; • in the oceans as dissolved atmospheric carbon dioxide and as calcium

carbonate shells in marine organisms.

Global Carbon Cycle

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Carbon is exchanged between the active pools due to various processes – photosynthesis and respiration between the land and the atmosphere, and diffusion between the ocean and the atmosphere.

Atmospheric CO2 Concentration-1

4/12Accurate and direct measurements of the concentration of CO2 in the atmosphere began in 1957 at the South Pole and in 1958 at Mauna Loa, Hawaii.

Historical Atmospheric CO2 Concentration

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This figures shows that the concentration of CO2 has never been grater than 300ppmv for the past 400,000 years.

Photoautotrophs

• Ecosystems gain most of their carbon dioxide from the atmosphere. A number of autotrophic organisms have specialized mechanisms that allow for absorption of this gas into their cells. With the addition of water and energy from solar radiation, these organisms use photosynthesis to chemically convert the carbon dioxide to carbon-based sugar molecules.

Photoautotophs

• These molecules can then be chemically modified by these organisms through the metabolic addition of other elements to produce more complex compounds like proteins, cellulose, and amino acids. Some of the organic matter produced in plants is passed down to heterotrophic animals through consumption.

Sea Shells• Carbon dioxide enters the waters of the

ocean by simple diffusion. Once dissolved in seawater, the carbon dioxide can remain as is or can be converted into carbonate (CO3

-2) or bicarbonate (HCO3-).

Certain forms of sea life biologically fix bicarbonate with calcium (Ca+2) to produce calcium carbonate (CaCO3).

Sea Shells• This substance is used to produce shells and

other body parts by organisms such as coral, clams, oysters, some protozoa, and some algae. When these organisms die, their shells and body parts sink to the ocean floor where they accumulate as carbonate-rich deposits. After long periods of time, these deposits are physically and chemically altered into sedimentary rocks. Ocean deposits are by far the biggest sink of carbon on the planet.

Respiration

• Carbon is released from ecosystems as carbon dioxide gas by the process of respiration. Respiration takes place in both plants and animals and involves the breakdown of carbon-based organic molecules into carbon dioxide gas and some other compound by products.

Decomposers

• The detritus food chain contains a number of organisms whose primary ecological role is the decomposition of organic matter into its abiotic components.

Carbon and Life on Earth

• Over the several billion years of geologic history, the quantity of carbon dioxide found in the atmosphere has been steadily decreasing.

• Researchers theorized that this change is in response to an increase in the Sun's output over the same time period. Higher levels of carbon dioxide helped regulate the Earth's temperature to levels slightly higher than what is perceived today.

Carbon and Life on EarthThese moderate temperatures allowed for the

flourishing of plant life despite the lower output of solar radiation. An enhanced greenhouse effect, due to the greater concentration of carbon dioxide gas in the atmosphere, supplemented the production of heat energy through higher levels of longwave counter-radiation. As the Sun grew more intense, several biological mechanisms gradually locked some of the atmospheric carbon dioxide into fossil fuels and sedimentary rock.

Lithosphere

• Carbon is stored in the lithosphere in both inorganic and organic forms. Inorganic deposits of carbon in the lithosphere include fossil fuels like coal, oil, and natural gas, oil shale, and carbonate based sedimentary deposits like limestone. Organic forms of carbon in the lithosphere include litter, organic matter, and humic substances found in soils.

Volcanoes• Some carbon dioxide is released from the interior

of the lithosphere by volcanoes. Carbon dioxide released by volcanoes enters the lower lithosphere when carbon-rich sediments and sedimentary rocks are subducted and partially melted beneath tectonic boundary zones.

Industrial Revolution Since the Industrial Revolution, humans have greatly

increased the quantity of carbon dioxide found in the Earth's atmosphere and oceans. Atmospheric levels have increased by over 30%, from about 275 parts per million (ppm) in the early 1700s to just over 365 PPM today. Scientists estimate that future atmospheric levels of carbon dioxide could reach an amount between 450 to 600 PPM by the year 2100. The major sources of this gas due to human activities include fossil fuel combustion and the modification of natural plant cover found in grassland, woodland, and forested ecosystems.

Other CO2 Sources

• Emissions from fossil fuel combustion account for about 65% of the additional carbon dioxide currently found in the Earth's atmosphere. The other 35% is derived from deforestation and the conversion of natural ecosystems into agricultural systems. Researchers have shown that natural ecosystems can store between 20 to 100 times more carbon dioxide than agricultural land-use types.

http://www.windows.ucar.edu/earth/climate/carbon_cycle.html

N Cycle

Facts

• Ultimate source of nitrogen to organisms is N2 from the atmosphere. Many temperate zone ecosystems limited by availability of Nitrogen

• Nitrogen fixation is the chemical transformation of N2 to NH3

• Nitrogen fixation is energetically costly

• Nitrogen fixation is done by microbes, often in a symbiosis with plants

N’s Role in Life

• The nitrogen cycle represents one of the most important nutrient cycles found in terrestrial ecosystems. Nitrogen is used by living organisms to produce a number of complex organic molecules like amino acids, proteins, and nucleic acids. The store of nitrogen found in the atmosphere, where it exists as a gas (mainly N2), plays an important role for life. This store is about one million times larger than the total nitrogen contained in living organisms.

N Stores• Other major stores of nitrogen include organic

matter in soil and the oceans. Despite its abundance in the atmosphere, nitrogen is often the most limiting nutrient for plant growth. This problem occurs because most plants can only take up nitrogen in two solid forms: ammonium ion (NH4

+ ) and the ion nitrate (NO3

- ). Most plants obtain the nitrogen they need as inorganic nitrate from the soil solution.

Uses of N

• Ammonium is used less by plants for uptake because in large concentrations it is extremely toxic. Animals receive the required nitrogen they need for metabolism, growth, and reproduction by the consumption of living or dead organic matter containing molecules composed partially of nitrogen.

N Cycle

Decomposers

• In most ecosystems nitrogen is primarily stored in living and dead organic matter. This organic nitrogen is converted into inorganic forms when it re-enters the biogeochemical cycle via decomposition. Decomposers, found in the upper soil layer, chemically modify the nitrogen found in organic matter from ammonia (NH3 ) to ammonium salts (NH4

+ ). This process is known as mineralization and it is carried out by a variety of bacteria, actinomycetes, and fungi.

N Cycle ProcessesProcesses involve chemical oxidation and are known as nitrification. However, nitrate is very soluble and it is easily lost from the soil system by leaching. Some of this leached nitrate flows through the hydrologic system until it reaches the oceans where it can be returned to the atmosphere by denitrification. Denitrification is also common in anaerobic soils and is carried out by heterotrophic bacteria. The process of denitrification involves the metabolic reduction of nitrate (NO3

- ) into nitrogen (N2) or nitrous oxide (N2O) gas. Both of these gases then diffuse into the atmosphere.

Nitrogen Fixation

Almost all nitrogen found in any terrestrial ecosystem originally came from the atmosphere. Significant amounts enter the soil in rainfall or through the effects of lightning. The majority, however, is biochemically fixed within the soil by specialized micro-organisms like bacteria, actinomycetes, and cyanobacteria.

Legumes• Members of the bean family (legumes) and

some other kinds of plants form mutualistic symbiotic relationships with nitrogen fixing bacteria. In exchange for some nitrogen, the bacteria receive from the plants carbohydrates and special structures (nodules) in roots where they can exist in a moist environment. Scientists estimate that biological fixation globally adds approximately 140 million metric tons of nitrogen to ecosystems every year.

Nitrogen Fixation

Nodules on plant roots

Human Impact

• The activities of humans have severely altered the nitrogen cycle. Some of the major processes involved in this alteration include:

• The application of nitrogen fertilizers to crops has caused increased rates of denitrification and leaching of nitrate into groundwater. The additional nitrogen entering the groundwater system eventually flows into streams, rivers, lakes, and estuaries. In these systems, the added nitrogen can lead to eutrophication.

Human Impact• Increased deposition of nitrogen from atmospheric

sources because of fossil fuel combustion and forest burning. Both of these processes release a variety of solid forms of nitrogen through combustion.

• Livestock ranching. Livestock release a large amounts of ammonia into the environment from their wastes. This nitrogen enters the soil system and then the hydrologic system through leaching, groundwater flow, and runoff.

• Sewage waste and septic tank leaching.

• A source of energy for some microbes, and a source of N for plants and microbes

Ammonification is the conversion of amino acids to NH3

Nitrification is the oxidation of ammonium:

• ammonium (NH4+) to nitrite (NO2

-)

• nitrite (NO2-) to nitrate (NO3

-)

Denitrification is the reduction of NO3- to nitric oxide (NO), to

nitrous oxide (N2O), and finally to molecular nitrogen (N2)

• NO3- => NO => N2O => N2

The Hydrologic (Water) Cycle

•   The hydrologic cycle is a conceptual model that describes the storage and movement of water between the biosphere, atmosphere, lithosphere, and the hydrosphere (see Figure 8b-1). Water on this planet can be stored in any one of the following reservoirs: atmosphere, oceans, lakes, rivers, soils, glaciers, snowfields, and groundwater.

Hydrologic Cycle

Movement of Water• Water moves from one reservoir to another by way of

processes like evaporation, condensation, precipitation, deposition, runoff, infiltration, sublimation, transpiration, melting, and groundwater flow. The oceans supply most of the evaporated water found in the atmosphere. Of this evaporated water, only 91% of it is returned to the ocean basins by way of precipitation. The remaining 9% is transported to areas over landmasses where climatological factors induce the formation of precipitation.

Movement of Water

• The resulting imbalance between rates of evaporation and precipitation over land and ocean is corrected by runoff and groundwater flow to the oceans.

• The planetary water supply is dominated by the oceans. Approximately 97% of all the water on the Earth is in the oceans. The other 3% is held as freshwater in glaciers and icecaps, groundwater, lakes, soil, the atmosphere, and within life.

Water Reservoirs

ReservoirVolume

(cubic km x 1,000,000)

Percent of Total

Oceans 1370 97.25

Ice Caps and Glaciers 29 2.05

Groundwater 9.5 0.68

Lakes 0.125 0.01

Soil Moisture 0.065 0.005

Atmosphere 0.013 0.001

Streams and Rivers 0.0017 0.0001

Biosphere 0.0006 0.00004

Cycle of Water

• Water is continually cycled between its various reservoirs. This cycling occurs through the processes of evaporation, condensation, precipitation, deposition, runoff, infiltration, sublimation, transpiration, melting, and groundwater flow. Table 8b-2 describes the typical residence times of water in the major reservoirs. On average water is renewed in rivers once every 16 days.

Cycle of Water• Water in the atmosphere is completely

replaced once every 8 days. Slower rates of replacement occur in large lakes, glaciers, ocean bodies and groundwater. Replacement in these reservoirs can take from hundreds to thousands of years. Some of these resources (especially groundwater) are being used by humans at rates that far exceed their renewal times. This type of resource use is making this type of water effectively nonrenewable.

Typical residence times of water found in various reservoirs.

•  Glaciers:  20 to 100 years

•  Seasonal Snow Cover:  2 to 6 months

•  Soil Moisture:  1 to 2 months

•  Groundwater: Shallow  100 to 200 years

•  Groundwater: Deep  10,000 years

•  Lakes:  50 to 100 years

•  Rivers:  2 to 6 months

Evaporation

• Evaporation can be defined as the process where liquid water is transformed into a gaseous state. Evaporation can only occur when water is available. It also requires that the humidity of the atmosphere be less than the evaporating surface (at 100% relative humidity there is no more evaporation). The evaporation process requires large amounts of energy. For example, the evaporation of one gram of water requires 600 calories of heat energy.

Transpiration• Transpiration is the process of water loss from

plants through stomata. Stomata are small openings found on the underside of leaves that are connected to vascular plant tissues. In most plants, transpiration is a passive process largely controlled by the humidity of the atmospheric and the moisture content of the soil. Of the transpired water passing through a plant only 1% is used in the growth process.

Transpiration

• Transpiration also transports nutrients from the soil into the roots and carries them to the various cells of the plant and is used to keep tissues from becoming overheated. Some dry environment plants do have the ability to open and close their stomata. This adaptation is necessary to limit the loss of water from plant tissues. Without this adaptation these plants would not be able to survive under conditions of severe drought.

Infiltration• Infiltration refers to the movement of water into the soil

layer. The rate of this movement is called the infiltration rate. If rainfall intensity is greater than the infiltration rate, water will accumulate on the surface and runoff will begin.

• Movement of water into the soil is controlled by gravity, capillary action, and soil porosity. The burrowing of worms and other organisms and penetration of plant roots can increase the size and number of channels within the soil. The amount of decayed organic matter found at the soil surface can also enhance infiltration.

Runoff

• If the amount of water falling on the ground is greater than the infiltration rate of the surface, runoff or overland flow will occur. Runoff specifically refers to the water leaving an area of drainage and flowing across the land surface to points of lower elevation. It is not the water flowing beneath the surface of the ground. This type of water flow is called throughflow.

Runoff• Runoff involves the following events:

• Rainfall intensity exceeds the soil's infiltration rate.

• A thin water layer forms that begins to move because of the influence of slope and gravity.

• Flowing water accumulates in depressions.

• Depressions overflow and form small rills.

• Rills merge to form larger streams and rivers.

• Streams and rivers then flow into lakes or oceans.

Throughflow and Groundwater Storage

•   Throughflow is the sporadic horizontal flow of water within the soil layer (Figure 8m-1). It normally takes place when the soil is completely saturated with water. This water then flows underground until it reaches a river, lake, or ocean. Rates of water movement via throughflow are usually low. Rates of maximum flow occur on steep slopes and in pervious sediments. The lowest rates of flow occur in soils composed of heavy clays, which can be less than 1 millimeter per day.

Water Movement• Hydrologic movement of water beneath the

Earth's surface. Water usually enters the surface sediments as precipitation. This water then percolates into the soil layer. Some of this water flows horizontally as throughflow. Water continuing to flow downward eventually reaches a permanent store of water known as the groundwater. The movement of groundwater horizontally is called groundwater flow.

Throughflow & Groundwater

Throughflow and Groundwater

• Precipitation that succeeds in moving from the soil layer down into the underlying bedrock will at some point reach an area of permanent saturation that is known as the groundwater zone. The top of this zone is called the water table. Groundwater tends to flow by way of gravity to the point of lowest elevation. Often groundwater flow discharges into a surface body of water like a river channel, lake, or ocean.

Groundwater• Rock formations that store groundwater water are

known as aquifers. Rock formations that cannot store groundwater are called aquicludes.

• Groundwater occurs in two main forms. Unconfined groundwater occurs when the flow of subterranean water is not confined by the presence of relatively impermeable layers. Springs that flow from underground to the Earth's surface are often formed when a perched (impermeable) water table intersects the surface.

Artesian Water• In some cases, groundwater can become confined

between two impermeable layers. This type of enclosed water is sometimes called artesian. If conditions are right, a confined aquifer can produce a pressurized ground to surface flow of water known as an artesian well. In an artesian well, water flows against gravity to the earth's surface because of hydrostatic pressure. Hydrostatic pressure is created from the fact that most of the aquifer's water resides at an elevation greater than the well opening. The overlying weight of this water creates the hydrostatic pressure.

The Oxygen Cycle

Definition of Oxygen

• Oxygen – a colorless, odorless, tasteless gas

• Denser than air• Poor conductor of heat and electricity

Step One of Oxygen Cycle

• Plant release oxygen into the atmosphere as a by-product of photosynthesis.

oxygen

Step Two of Oxygen Cycle

• Animals take in oxygen through the process of respiration.

• Animals then break down sugars and food.

Step Three in Oxygen Cycle

• Carbon dioxide is released by animals and used in plants in photosynthesis.

• Oxygen is balanced between the atmosphere and the ocean.

History of Oxygen

• Early evolution of Earth, oxygen released from H2O vapor by UV radiation and accumulated in the atmosphere as the hydrogen escaped into the earth's atmosphere

• Photosynthesis became a source of oxygen

• Oxygen released as organic carbon and gets buried in sediments.

Photosynthesis

•Definition- process in which green plants use the energy from the sun to make carbohydrates from carbon dioxide and water in the presence of chlorophyll.

How is Photosynthesis Carried Out?

•Photosynthesis only occurs in plants Photosynthesis only occurs in plants containing chlorophyll: containing chlorophyll: •Water is absorbed by the roots and Water is absorbed by the roots and carried to the leaves by the xylemcarried to the leaves by the xylem•Carbon dioxide is obtained from air that Carbon dioxide is obtained from air that enters the leaves through the stomata enters the leaves through the stomata and diffuses to the cells containing and diffuses to the cells containing chlorophyll. chlorophyll. •Chlorophyll is uniquely capable of Chlorophyll is uniquely capable of converting the energy from light into a converting the energy from light into a dormant form that can be stored and dormant form that can be stored and used when needed. used when needed.

Steps in Photosynthesis

• The light energy strikes the leaf, passes into the leaf and hits a chloroplast inside an individual cell

• The light energy, upon entering the chloroplasts, is captured by the chlorophyll inside a grana.

• Inside the grana some of the energy is used to split water into hydrogen and oxygen.

• The oxygen is released into the air. • The hydrogen is taken to the stroma along with

the grana's remaining light energy.

Steps Continued:

• Carbon dioxide enters the leaf and passes into the chloroplast.

• In the stroma the remaining light energy is used to combine hydrogen and carbon dioxide to make carbohydrates.

• The energy rich carbohydrates are carried to the plant's cells.

• The energy rich carbohydrates are used by the cells to drive the plant's life processes.

Respiration• Process by which an organism

exchanges gases with its environment

• Process → oxygen is abstracted from air, transported to cells for the oxidation of organic molecules while CO2 and H2O, the products of oxidation, are returned to the environment

TodayThe Earth’s atmosphere consists

of:• 21% Oxygen

The Earth’s lithosphere consists of:

• 99.5% OxygenThe Earth’s hydrosphere

consists of:• 46.60% Oxygen

The Earth’s biosphere consists of:

• 0.01% Oxygen

Biological Importance of Oxygen

• Humans need it to breathe• Needed for decomposition of

organic waste• Water can dissolve oxygen and it

is this dissolved oxygen that supports aquatic life.

Ecological Importance of Oxygen

• Without oxygen at the bottom of the water body, anaerobic bacteria (those that live without oxygen) produce acids. These acids not only increase acidity, but also cause a massive release of phosphorus and nitrogen, two major fertilizers, from the organic sediment and into the water column.

• These same anaerobic bacteria put toxic gases in the water including hydrogen sulfide (that rotten egg smell), ammonia, carbon dioxide and methane. These gases are all toxic to fish, beneficial bacteria and insects.

• Lack of bottom oxygen is the cause of odors produced by anaerobic bacteria.

Ecological Importance of Oxygen Cont.

• Lack of fish enables disease-hosting mosquitoes to thrive, as mosquitoes are natural food for fish.

• Without oxygen at the bottom at all times, beneficial bacteria and insects cannot biodegrade the organic sediment. Large accumulations of organic sediment follow.