20.2 Biogeochemical Cycles

The PCB concentrations are shown in the chart.

The fish in higher trophic levels accumulate more PCBs than the fish in lower trophic levels.

Concerns have been raised about the biomagnification of heavy metals in certain types of seafood.

The EPA recommends that pregnant women and young children not eat swordfish, shark, king mackerel, or tilefish because of their high mercury content.
Salmon, shrimp, pollock, and catfish are low in mercury and should be eaten by these individuals.
A good example of how ecology can affect our lives is biomagnification.

You will be able to discuss the biogeochemical cycles of water, carbon, nitrogen, phosphorus, and sulfur at the end of this section.

The matter that makes up living organisms is recycled.
Carbon, nitrogen, hydrogen, oxygen, phosphorus, and sulfur can be found in a variety of chemical forms and may exist for long periods in the atmosphere, on land, in water, or beneath Earth's surface.
weathering, erosion, water drainage, and the subduction of the continental plates all play a role in the cycling of elements on Earth.

Water is an essential part of living processes.

Carbon is an important component of fossil fuels.
Nitrogen is critical to human agriculture and is a major component of our nucleic acids.
Artificial fertilization used in agriculture has an environmental impact on our surface water.

Burning fossil fuels releases sulfur into the atmosphere, which is critical to the folding of proteins.

The elements are interdependent.

The movement of water is important for the removal of nitrogen and phosphate from the water.
The ocean holds a lot of carbon.
The entire biosphere between the biotic and abiotic world and from one living organisms to another is where mineral nutrients are cycled.

All living processes rely on water.

Human cells are 70 percent water and the human body is half water.
Land animals need fresh water to survive.
Salt water is the majority of the stores of water on Earth.
99 percent of the water is locked up.
Less than one percent of fresh water is found in lakes and rivers.
A lack of surface fresh water supply can have important effects on the dynamics of the environment.
Humans have developed technologies to increase water availability, such as digging wells and using desalination to get water from the ocean.
The supply of fresh water continues to be a major issue in modern times, despite the fact that this pursuit of drinkable water has been ongoing throughout human history.

Less than 1 percent of fresh water is easily accessible to living things, and only 2.5 percent of water on Earth is fresh water.

The water cycle is driven by the Sun's energy as it warms the oceans and other surface waters.

This leads to the movement of large amounts of water into the atmosphere through the process of ice to water Vapor.
Over time, this water vapor condenses into clouds as liquid or frozen droplets and eventually leads to precipitation, which returns water to Earth's surface.
Rain may evaporate, flow over the surface or trickle into the ground.
The This OpenStax book is available for free at http://cnx.org/content/col11487/1.9 flow of fresh water either from rain or melting ice is most easily observed.
Runoff can travel through streams and lakes to the ocean.

Rain occurs before it reaches the soil surface in most natural environments.

The soil begins to move as what is left reaches it.
If the soil becomes saturated with water in a heavy rain, there will be surface runoff.
Plants take up most of the water in the soil.
Some of the water will be used by the plant for its own metabolism, but a lot of it will be lost back to the atmosphere through a process known as evapotranspiration.
The water enters the plant through the roots and leaves and leaves the water in the plant.
Water in the soil that is not taken up by a plant is able to get into the subsoil and bedrock.
It forms here.

There is a large amount of fresh water in the ground.

It can be found in the sand and gravel or in the fissures in the rocks.
Shallow groundwater flows through the fissures and pores and eventually finds its way to a stream or lake where it becomes a part of the surface water again.
There is a constant inflow from the ground and streams do not flow because of it.
It is possible to find some underground in the bedrock for thousands of years.
The source of drinking or irrigation water is usually found in the ground.
Water percolating down from above is being used more to replenish the aquifers than it is to deplete them.

Minerals, including carbon, nitrogen, phosphorus, and sulfur, are cycled from land to water through rain and surface runoff.

As these cycles are described, the environmental effects of runoff will be discussed.

Water from the land and oceans enters the atmosphere when it condenses into clouds and falls as rain or snow.

Precipitated water can enter freshwater bodies.

When the ocean reenters the cycle is complete.

The fourth most abundant element is carbon.

The structure of macromolecules is important to living organisms because of the presence of carbon.
Many of the compounds from plants and algae are stored as carbon, which humans use as fuel.

Fossil fuels have been used faster since the 1800s.

As global demand for Earth's limited fossil fuel supplies has risen since the beginning of the Industrial Revolution, the amount of carbon dioxide in our atmosphere has increased.
Climate change has been associated with an increase in carbon dioxide.

The carbon cycle has two subcycles, one dealing with rapid carbon exchange among living organisms and the other with the long-term cycling of carbon through geologic processes.

Carbon dioxide is dissolved in water.

When matter from living organisms is buried deep underground and becomes fossils, long-term storage of organic carbon occurs.
The carbon cycle has been brought back into action by volcanic activity and human emissions.

There are many ways in which living organisms are connected.

The exchange of carbon between Heterotrophs and autotrophs is an example of this connection.
The basic building block that autotrophs use to build high-energy compounds is carbon dioxide.
These organisms use the Sun's energy to form bonds between carbon atoms.
Most autotrophs get their carbon dioxide from the atmosphere, while marine autotrophs get it in the dissolved form.
Oxygen is a byproduct of fixing carbon in organic compounds.

21 percent of the oxygen content of the atmosphere is maintained by photosynthetic organisms.

The primary consumers of biological carbon exchange are the Heterotrophs.

Heterotrophs acquire the high-energy carbon compounds from the autotrophs by consuming them and breaking them down by respiration to obtain cellular energy.

Aerobic respiration requires oxygen to be obtained from the atmosphere or dissolved in water.
There is a constant exchange of oxygen and carbon dioxide between the autotrophs and the Heterotrophs.
Oxygen and carbon dioxide are released by autotrophs when they respire.
There is excess available for the respiration of other aerobic organisms because they release more oxygen gas as a waste product of photosynthesis.
The carbon cycle is connected by gas exchange through the atmosphere and water.

The movement of carbon through land, water, and air is more complex than the movement between living organisms.

Carbon is stored in a variety of places, including the atmosphere, bodies of liquid water, ocean, soil, rocks, and fossil fuels.

The atmosphere is a major source of carbon in the form of carbon dioxide that is essential to the process of photosynthesis.

The amount of carbon dioxide in the atmosphere is influenced by the amount of carbon in the oceans.

The amount of carbon found in the atmosphere and water depends on the exchange of carbon between the two.

Carbon dioxide from the atmosphere is dissolved in water and reacts with water to form ionic compounds.
A major component of the shells of marine organisms is calcium carbonate, which is formed when some of these ion combine with calcium in the water.
The organisms form on the ocean floor.
The largest carbon repository on Earth is formed by the calcium carbonate.

Carbon is stored in soil as organic carbon as a result of the decay of living organisms or the weathering of rock and minerals.

Fossil fuels are the remains of plants that take millions of years to form.
Fossil fuels are considered non-renewable because of their use.
Land beneath the surface of the ocean can be used as a conduit for carbon to enter the atmosphere.
Carbon dioxide is released when a volcano erupts.

Carbon dioxide is added to the atmosphere by the practices of humans.

Increased carbon-dioxide levels in the atmosphere are caused by the large number of land animals raised to feed Earth's growing human population.
This is an example of how human activity can affect biogeochemical cycles.
Natural processes, such as volcanoes, plant growth, soil carbon levels, and respiration, are taken into account by scientists as they model and predict the future impact of increasing atmospheric carbon on climate change.

Nitrogen is hard to get into the living world.

Even though triple covalent N2 is found in 78 percent of the atmosphere, plants and phytoplankton are not able to incorporate it.
Nitrogen enters the living world via free-living and symbioticbacteria, which incorporate nitrogen into their macromolecules.
Nitrogen fixation is a key role of the cyanobacteria in most aquatic environments.
Nitrogen can be "fix" by the cyanobacteria.

Primary production and decomposition are limited by the available supply of nitrogen, which is why it is important to study organic nitrogen.

The nitrogen that enters living systems by nitrogen fixation is eventually converted into nitrogen gas bybacteria.
Ammonification, nitrification, and denitrification are the three steps in the process.

Similar organisms convert nitrites to nitrates.

Nitrogen enters the living world from the atmosphere.

This nitrogen and nitrogenous waste from animals is then processed back into gaseous nitrogen by soilbacteria, which in turn supplies the land with organic nitrogen they need.

Nitrogen gas is converted into organic compounds by Nitrogen fixingbacteria.

Nitrogen can be released into the environment by two primary means: the burning of fossil fuels, which releases nitrogen oxides, and the use of artificial fertilization, which washes nitrogen into lakes, streams, and rivers.

Acid rain, HNO3 and greenhouse gas effects are all associated with atmospheric nitrogen and could cause climate change.

In the marine nitrogen cycle, the ammonification, nitrification, and denitrification processes are performed by marinebacteria and archaea.

Some of the nitrogen falls to the ocean floor, which can then be moved to land in geologic time by the Earth's surface.

It is an essential component of living processes and makes up the supportive components of our bones.

In aquatic, particularly freshwater, ecosystems, there is often a limit to the amount of Phosphorus that is needed for growth.

There is a substance called thephosphate ion (PO 3 4 ) in nature.

Natural surface runoff is a result of human activity and occurs when it is washed away by weathering.
The rock is from the ocean.
The bodies of ocean organisms and their excretions form the majority of the ocean sediments.
Volcanic ash, aerosols, and mineral dust may be significant sources ofphosphate.
The uplifting of Earth's surface causes the land to be moved over geologic time.

The ocean and marine organisms have the same amount ofPhosphory.

The average time it takes forphosphate to move from the ocean to the land is between 20,000 and 100,000 years.

Weathering of rocks and volcanic activity releasesphosphate into the soil, water, and air, where it becomes available to food webs.

In the oceans,phosphate enters in the form of surface run off, groundwater flow, and river flow.
The ocean water hasphosphate dissolved in it.
The ocean floor is where the marine food webs fall.
The death and decay of these organisms depletes dissolved oxygen, which leads to the death of aquatic organisms.

Dead zones occur when excessive growth of organisms depletes oxygen and kills fauna.

Large dead zones can be found in areas of high population density.

More than 400 dead zones were present as of 2008 and the number of dead zones has increased for several years.

The dead zone off the coast of the United States in the Gulf of Mexico was created by the Mississippi River basin.
Several lake and bay environments, including the Chesapeake Bay in the eastern United States, are negatively affected by nitrates andphosphates fromfertilizers.

The satellite image shows the environment of the bay.

A member of the Army Corps of Engineers is holding a clump of oysters.

Dead zones, which kill many fish and bottomdwelling species such as clams, oysters, and worms, were first identified in the 1970s in the Chesapeake Bay.

Several species have declined in the bay because of excess nitrogen in the water.
The source of thefertilizer is not limited to agricultural practices.
There are more than 150 rivers and streams that are empty into the bay that are carryingfertilizer from lawns and gardens.
The decline of the bay requires the cooperation of industry, agriculture, and individual homeowners.

Between 1982 and 2007, oyster harvesting declined by 88 percent.

The decline was caused by many things, including overharvesting.
Oysters need a certain minimum population density to reproduce.
The oyster population and locations have been altered by human activity.

The restoration of the oyster population in the bay has been a mixed success.

Oysters are good to eat and clean up the bay.

As they eat, they clean the water around them.

In the case of oysters, filter feeders eat by pumping a continuous stream of water over finely divided appendages and capturing plankton and fine organic particles in their mucus.
In the 1700s, it was estimated that it took only a few days for the oyster population to filter the entire bay.
It is estimated that the current population would take nearly a year to do the same job.

Restoration efforts have been ongoing for several years by non-profit organizations.

The oysters can reproduce more efficiently.

The Virginia Institute of Marine Science for the College of William and Mary has developed many disease-resistant varieties that have been used in the construction of oyster reefs.
Efforts by Virginia and Delaware to clean and restore the bay have been hampered because much of the pollution entering the bay comes from other states.

The new oyster strains have spawned a new and economically viable industry which supplies oysters for food and profit, but also has the added benefit of cleaning the bay.

The macromolecules of living things have sulfur as an essential element.

It is a part of the cysteine in the human body.
Sulfur dioxide is found in the form of sulfur dioxide, which enters the atmosphere in three ways: first from the decomposition of organic molecule, second from volcanic activity and third from the burning of fossil fuels by humans.

When sulfur dioxide is dissolved in precipitation as weak sulfuric acid or when it falls directly to Earth, it becomes available to the marine andterrestrial environments.

Sulfates are made available to the ecosystems by weathering of rocks.
Sulfates are returned to the ocean, soil, and atmosphere.

As rain falls through the atmosphere, sulfur is dissolved in the form of weak sulfuric acid, which is found in the form of sulfur dioxide.

Sulfur is released into the soil when rocks weather.
These rocks come from the ocean and are moved to land.
The soil sulfates can enter the food web by being taken up by plant roots.
When these plants die, sulfur is released back into the atmosphere.