Biogeochemical Cycle

Gunjan Mehta

VSC, Rajkot

Outline

Fundamentals of Biogeochemical cycles Definition Types of Biogeochemical cycles Sedimentary cycles Gaseous cycles Hydrological cycle

‘Fundamentals’ of biogeochemical cycles

Biogeochemical cycles are cycling of chemical elements or nutrients from the abiotic environment to organism and then back to the abiotic environment.

The pathway by which chemical circulate through ecosystem involve both living (biotic) and nonliving (geological) components.

Involved organism (bio), environmental geology (geo) & chemical changes (chemical)

They enable a specific chemical element or nutrient to be taken and reused through various forms.

They also cause the circulation of these elements in the atmosphere, hydrosphere, litosphere and biosphere

Definition BIO: Biology. Life. Living things. These cycles all

play a role in the lives of living things.

GEO: Earth. Rocks. Land. This refers to the non-living processes at work.

CHEMICAL: Molecules. Reactions. Atoms. All cycles include these small pathways. Complete molecules are not always passed from one point to the next.

The overall movement of nutrients from the physical environment, through organism, and back to the environment constitutes a

biogeochemical cycle.

i. A large reservoir pool of elements – Chemical elements in inorganic forms in the abiotic

components of biosphere.- From where the element are absorbed by autotrophic

organism and converted into complex organic form- Eg: fossil fuels, minerals, sediments.

Divided into 2 components:

ii. An exchange/cycling pool – Chemical elements or nutrients in complex organic forms in

the biotic components of biosphere.- The element is passed along food chain and ultimately

converted back into inorganic form to be released into the environment

- Eg: atmosphere, soil, water

Biogeochemical Cycles Components

Definition BIO: Biology. Life. Living things. These cycles all

play a role in the lives of living things.

GEO: Earth. Rocks. Land. This refers to the non-living processes at work.

CHEMICAL: Molecules. Reactions. Atoms. All cycles include these small pathways. Complete molecules are not always passed from one point to the next.

There are two types of biological cycles:-

1.Gaseous cycle: element returns to and is withdrawn from the atmosphere as a gas. Eg; Carbon, Nitrogen, Oxygen

2.Sedimentary: the element is absorbed from the sediment by plant roots passed to heterotrophs and eventually returned to the soil by decomposers, usually in the same area. Eg. Phosphorus, Sulphur

3.Hydrological cycle: Separate cycle

The N cycle

The N cycle over land

Nitrogen is essential to all living systems: Eighty percent of Earth's atmosphere is made up of nitrogen in its gas phase.

Atmospheric nitrogen becomes part of living organisms in two ways:

1. through bacteria in the soil that form nitrates out of nitrogen in the air.

2. through lightning. During electrical storms, large amounts of nitrogen are oxidized and united with water to produce an acid that falls to Earth in rainfall and deposits nitrates in the soil.

Plants take up the nitrates and convert them to proteins that travel up the food chain through herbivores and carnivores.

When organisms excrete waste, the nitrogen is released back into the environment. When they die and decompose, the nitrogen is broken down and converted to ammonia.

Nitrates may also be converted to gaseous nitrogen through a process called denitrification and returned to the atmosphere, continuing the cycle.

Human impacts:

1. by artificial nitrogen fertilization (through the Haber Process, using energy from fossil fuels to convert N2 to ammonia gas (NH3) and planting of nitrogen fixing crops (Vitousek et al., 1997).

2. transfer of nitrogen trace gases (N2O) to the atmosphere via agricultural fertilization, biomass burning, cattle and feedlots, and other industrial sources (Chapin et al. 2002). N2O in the stratosphere breaks down and acts as a catalyst in the destruction of atmospheric ozone.

3. NH3 in the atmosphere has tripled as the result of human activities. It acts as an aerosol, decreasing air quality and clinging on to water droplets (acid rain).

4. Fossil fuel combustion has contributed to a 6 or 7 fold increase in NOx flux to the atmosphere. NO alters atmospheric chemistry, and is a precursor of tropospheric (lower atmosphere) ozone production, which contributes to smog, acid rain, and increases nitrogen inputs to ecosystems (Smil, 2000).

5. Ecosystem processes can increase with nitrogen fertilization, but anthropogenic input can also result in nitrogen saturation, which weakens productivity and can kill plants (Vitousek et al., 1997) → algae blooms.

6. Decreases in biodiversity both over land and in the ocean can result if higher nitrogen availability increases nitrogen-demanding species (Aerts and Berendse 1988).

The Oxygen cycle

Plants use the energy of sunlight to convert carbon dioxide and water into carbohydrates and oxygen via photosynthesis.

6CO2 + 6H2O + energy → C6H12O6 + 6O2 Photosynthesizing organisms include the plant life of the land areas as well as the phytoplankton of the oceans. The tiny marine cyanobacteria Prochlorococcus was discovered in 1986 and accounts for more than half of the photosynthesis of the open ocean.

Animals form the other half of the oxygen cycle breathing in oxygen used to break carbohydrates down into energy

in a process called respiration.  O2 + carbohydrates → CO2 + H2O + energy

Carbon moves from the atmosphere to plants.In the atmosphere, carbon is attached to oxygen in a gas called carbon dioxide (CO2). Through the process of photosynthesis, carbon dioxide is pulled from the air to produce food made from carbon for plant growth. Carbon moves from plants to animals.Through food chains, the carbon that is in plants moves to the animals that eat them. Animals that eat other animals get the carbon from their food too.

Carbon moves from plants and animals to soils.When plants and animals die, their bodies, wood and leaves decays bringing the carbon into the ground. Some is buried and will become fossil fuels in millions and millions of years.

CARBON CYCLE

Carbon moves from the atmosphere to the oceans. In aquatic ecosystems, CO2 from the air combines with water to produce bicarbonate ion (HCO3), a source of carbon for photosynthetic protists. When aquatic organisms respire, the CO2 they give off becomes bicarbonate ion

Carbon moves from living things to the atmosphere.Each time you exhale, you are releasing carbon dioxide gas (CO2) into the atmosphere. Animals and plants get rid of carbon dioxide gas through a process called respiration.

Carbon moves from fossil fuels to the atmosphere when fuels are burned.When humans burn fossil fuels to power factories, power plants, cars and trucks, most of the carbon quickly enters the atmosphere as carbon dioxide gas. Each year, five and a half billion tons of carbon is released by burning fossil fuels. That’s the weight of 100 million adult African elephants! Of the huge amount of carbon that is released from fuels, 3.3 billion tons enters the atmosphere and most of the rest becomes dissolved in seawater.

Cell respirationEach time you exhale, you are releasing carbon dioxide gas (CO2) into the atmosphere. Animals and plants need to get rid of carbon dioxide gas through a process called respiration.

CombustionWhen humans burn fossil fuels to power factories, power plants, cars and trucks, most of the carbon quickly enters the atmosphere as carbon dioxide gas.

Chemical weatheringChemical weathering of inorganic deposits, such as limestone and marble from the skeletal remains of shell animals such as corals and gastropods.

The carbon fixed into complex organic compounds is returned to the atmosphere by the counterbalancing release of carbon dioxide mainly through:

Carbon Cycle CO2 - fixation

Photosynthetic autotrophs

Aerobic respiration ------> CO2

Fossil fuel burning ------> CO2

Volcanic eruptions ------> CO2

Atmosphere, soils, plant biomass

Largest holding stations for Carbon

PHOSPHORUS CYCLE

in the ocean

and just over land

The phosphorus cycle describes the movement of phosphorus through the lithosphere, hydrosphere, and biosphere. The atmosphere does not play a significant role, because phosphorus and phosphorus-based compounds are usually solids at the typical ranges of temperature and pressure found on Earth.

Phosphorus normally occurs in nature as part of a phosphate ion, consisting of a phosphorus atom and some number of oxygen atoms, the most abundant form (called orthophosphate) having four oxygens: PO43-. Most phosphates are found as salts in ocean sediments or in rocks. Over time, geologic processes can bring ocean sediments to land, and weathering will carry terrestrial phosphates back to the ocean.

Plants absorb phosphates from the soil and phosphate enters the food chain. After death, the animal or plant decays, and the phosphates are returned to the soil. Runoff may carry them back to the ocean or they may be reincorporated into rock.

The primary biological importance of phosphates is as a component of nucleotides, which serve as energy storage within cells (ATP) or when linked together, form the nucleic acids DNA and RNA. Phosphorus is also found in bones, and in phospholipids (found in all biological membranes).

Phosphates move quickly through plants and animals; however, the processes that move them through the soil or ocean are very slow, making the phosphorus cycle overall one of the slowest biogeochemical cycles.

Human influence:

Artificial fertilizers and other wastes not absorbed by plants mostly enter the groundwater and collect in streams, lakes and ponds. The extra phosphates are a major contributor to the process called eutrophication, which causes excessive growth of water plants and algae populations and subsequent depletion of dissolved oxygen potentially suffocating fish and other aquatic fauna.

The carbon cycle

Sulphur cycle

Introduction

Flow of a chemical through certain subdivisionsAtmosphereLithosphereHydrosphereBiosphere

Usually of Elements(Institute)

Introduction

Sulfur- S, it is an elementNaturally found in earthAt room temp., it is a solidPresent in proteins, amino acids, vitamins, and

enzymes, necessary for plants and animalsOften reacts with hydrogen creating hydrogen

sulfide Can dissolve in water With metals in water, forms metal sulfides;sulfates in air

(“Sulfur”)

Sulfur Cycle

(“Part IV”)

Sulfur Cycle

In ground: most found in rocks, or salt in earth, or as sediment at bottom of oceanFound as S, H2S, SO4

-2, (NH4)2SO4

Enter ground: Plants absorb, or left by acid deposition (fog or precipitation)

As SO4-2, (NH4)2SO4, and then turn H2S by

bacteria, decay, and plant useStored: Ground, rock, ocean, somewhat in air

(“Oxygen”)

Sulfur Cycle

Sulfur is transferred into biosphere then back into ground, or from ground to atmosphereMicroorganisms turn it into H2S (gas)

Oxidized in atmosphere to SO2, and then to H2SO4 (an acid) with water contact

Mined ores released to atmosphere in factories as H2S and SO2

Volcanoes and hot springs

Sulfur Cycle

Deposited next in water Through precipitation, dry deposition, leaching

Rainfall= deposited 73E12 grams sulfur in 1960 SO4

-2 leaches from soil into ocean as sediment H2SO4 falls into ocean Dimethyl Sulfide, carbonyl sulfide (biogenic gases),

released by plankton returns back into atmosphere (turns into SO2)

Either re-evaporated, left as sediment for long time, or deposited on land

High amount of sulfur is deposited on land by sea When back on land, cycle repeats

Driving Force

Driven by: constant addition of sulfur to environment by

earths interior (geosphere)Human disturbance, addition of sulfur to

atmosphere, (also dug up from environment)Natural processes (incl. Biological, hydrological,

due to sun’s energy)Plant uptake, microbes (Desulfovibrio sp. or

Desulfotomaculum sp.)

(“A Black Smoker”)

Percentages of Sulfur

Common in ground as FeS2

Reservoirs Oceanic Rocks Sediment Freshwater Ice Atmosphere Sea

(“Sulfur Cycle”)

Percentages of Sulfur

Most sulfur in particulate formTherefore it is a sedimentary cycleVery short residence time in atmosphere (1-2

days)Even in atmosphere, found as aerosols (<1

micrometer), not gas usually In atmosphere, way less than 1% Its around .000314 percent90-95% SO2 from power plants and factories

Human Effect

When mine ores, sulfur/sulfides released into soil Combustion of fossil fuels

Release of SO2, causes acid rain, increases amount already present

28% of sulfur in rivers from pollution, mining, erosion, etc.

Help move cycle but also upset balance- too much S means acid rain

Hydrodesulphurization (refine hydrocarbons)- surplus of S in Alberta Canada

(“Arial”)

(“Sulfur Mining”)

Phosphorus Cycle

No gaseous phase

Slow rate of transfer

Released by erosion of exposed rock

Absorbed by plants, algae, and some bacteria

Exported from terrestrial ecosystems by runoff to oceans

May be returned through seabird guano