Download The Phosphorus Cycle

Name:
NATURAL BIOGEOCHEMICAL CYCLES
Carbon Cycle

The carbon cycle is the set of biogeochemical processes by which carbon undergoes chemical
reactions, changes form, and moves through different reservoirs on earth, including living
organisms.

The geological component of the carbon cycle is driven by plate tectonics and includes processes
like volcanic eruptions and burial of carbon-rich sediments on the ocean floor.

The biological component of the carbon cycle is driven by respiration and photosynthesis by living
organisms.

Humans influence the global carbon cycle in several ways, but primarily through burning fossil
fuels.
Nitrogen Cycle
The nitrogen cycle is the process by which nitrogen is converted between its various chemical forms. This
transformation can be carried out by both biological and non-biological processes. Important processes in the
nitrogen cycle include fixation, mineralization, nitrification, and denitrification. The majority of Earth's atmosphere
(approximately 78%) is nitrogen, making it the largest pool of nitrogen. However, atmospheric nitrogen has limited
availability for biological use, leading to a scarcity of usable nitrogen in many types of ecosystems. The nitrogen
cycle is of particular interest to ecologists because nitrogen availability can affect the rate of key ecosystem
processes, including primary production and decomposition. Human activities such as fossil fuel combustion, use of
artificial nitrogen fertilizers, and release of nitrogen in wastewater have dramatically altered the global nitrogen
cycle
Sulfur Cycle
Sulfur, most commonly identified by its variation of yellow colorings, is an abundant element in the Earth's crust, mostly
in minerals, but also in a variety of substances including water, the atmosphere, and certain other organisms. The
storage of sulfur in the various compartments of Earth and its biosphere, and the many transfers occurring among them,
is referred to as the sulfur cycle. The Sulfur cycle includes both atmospheric and terrestrial processes. Sulfur is an
important nutrient for organisms, being a key to certain amino acids, proteins, and other biochemical’s. Plants satisfy
their nutritional needs for sulfur by bringing in simple mineral compounds from the environment. This mostly occurs as
sulfate dissolved in soil water that is taken up by roots also when sulfur dioxide is absorbed by environments where the
atmosphere is somewhat polluted with gas. Animals obtain the sulfur they need by eating plants or other animals, and
digesting their organic forms of sulfur, which are then used to “synthesize” necessary sulfur-containing biochemical’s.
Oxygen Cycle
The oxygen cycle is the continual exchange of oxygen between the atmosphere and the water, the plants and animals and
mineral matter. The oxygen cycle is a complex series of processes in which all of the oxygen atoms present in the earth
circulate. It all starts with plants. Plants use the energy from the sun to use carbon dioxide from the atmosphere and
release oxygen back into the atmosphere through a process called photosynthesis. During the day, plants use little amounts
of oxygen to break down carbohydrates and take in large amounts of carbon dioxide to create sugars. But in the night,
because of the lack of sunlight, plants only use oxygen and release carbon dioxide just like animals. The next step of the
oxygen cycle is in the water. Oxygen within the hydrosphere is known as dissolved oxygen (DO). Oxygen enters the
water in areas with rapid movement and high surface area, and then it is collected in small pools or ponds where
microorganisms break down organic matter and consume the DO in the water. The balanced rates of Oxygen uptake (how
fast oxygen is consumed in the hydrosphere) and Oxygen transfer (how much oxygen is being used up) help keep lakes
and ponds healthy and lively. The last step of the oxygen cycle deals with the organisms of the earth. The beginning of
their roles starts with carbon dioxide in the atmosphere. Plants take in the CO2 and release oxygen and sugars
which organisms consume and use for energy. After the oxygen and sugars are consumed, the organisms then release any
leftover CO2 and the cycle begins again.
Water Cycle
The water cycle has no starting point. But, we'll begin in the oceans, since that is where most of Earth's water
exists. The sun, which drives the water cycle, heats water in the oceans. Some of it evaporates as vapor into the air.
Ice and snow can sublimate directly into water vapor. Rising air currents take the vapor up into the atmosphere,
along with water from evapotranspiration, which is water given off through the leaves of plants and evaporated
from the soil. The vapor rises into the air where cooler temperatures cause it to condense into clouds. Air currents
move clouds around the globe; cloud particles collide, grow, and fall out of the sky as precipitation. Some
precipitation falls as snow and can accumulate as ice caps and glaciers, which can store frozen water for thousands
of years. Snowpack in warmer climates often thaw and melt when spring arrives, and the melted water flows
overland as snowmelt. Most precipitation falls back into the oceans or onto land, where, due to gravity, the
precipitation flows over the ground as surface runoff. A portion of runoff enters rivers in valleys in the landscape,
with stream flow moving water towards the oceans. Runoff, and ground-water seepage, accumulate and are stored
as freshwater in lakes. Not all runoff flows into rivers, though. Much of it soaks into the ground as infiltration. Some
water infiltrates deep into the ground and replenishes aquifers (saturated subsurface rock), which store huge
amounts of freshwater for long periods of time. Some infiltration stays close to the land surface and can seep back
into surface-water bodies (and the ocean) as ground-water discharge, and some ground water finds openings in
the land surface and emerges as freshwater springs. Over time, though, all of this water keeps moving, some to
reenter the ocean, where the water cycle "ends" ... and "begins."
The Phosphorus Cycle
The phosphorus cycle is a sedimentary cycle (unlike carbon, oxygen, and nitrogen), the atmosphere is not a
reservoir for phosphorous nor do microorganisms fix phosphorus as they do nitrogen. Phosphorus enters the
biosphere almost entirely from the soil through absorption by plant roots. Weathering of rocks containing
phosphate minerals, chiefly apatite [Ca5(PO4)3OH], results in the relatively small pool of inorganic phosphorus
available for organismal use. In most soils the major amount of phosphorus absorbed by plants comes from organic
molecules that undergo decomposition releasing phosphorus in plant-available inorganic forms. The release of
organically bound nutrients to plant-available forms is termed mineralization, a process important in the release
to the soil of sulfur and nitrogen as well as phosphorus. Phosphorus is used by organisms in energy transfers (ATP,
NAPD), as a component of nucleic acids (RNA, DNA), and as a structural element of membranes (phospholipids).
The phosphorus cycle has fewer compartments than the other major nutrient cycles and also has a significant
“leak” of phosphorus back to its lithosphere reservoir from which it is returned to active cycling only after long
intervals of geologic time. The combination of three factors makes phosphorus a nutrient of concern in most
ecosystems:
 Most soils have only small amounts from the weathering of disjunctly distributed rocks.
 Phosphorus is more insoluble than other nutrients and less mobile, hence less phosphorus travels in the
soil solution; roots generally must grow into a zone of phosphorus availability.
 Phosphorus that drains from the land to the ocean is used by organisms in the surface waters, but a
considerable amount is lost to the sediments in the shells and bones of marine organisms and by
precipitation and settling of phosphates.
Human activities alter the phosphorus cycle chiefly by adding more available phosphorus where little was
available previously. Phosphate-containing detergents used in the 1960s were carried by sewage systems into
rivers and lakes and were a boon to algae and microorganisms, which responded with exuberant flushes of growth.
Widespread eutrophication resulted and detergent-makers were obliged to remove phosphates from their
products. Eutrophication—the enrichment of fresh waters with nutrients—results in blooms of plankton and
algae. Death of these organisms increases the populations of aerobic bacteria of decay which, in turn, deplete the
dissolved oxygen in the waters, thereby killing fish and other aerobic organisms. The anaerobic microorganisms
move in, and the fresh water becomes an unpleasant, smelly soup of decay.
Agricultural use of phosphate-containing fertilizers has increased as the acreage of farmlands has expanded over
time. At first, guano (the dung of seabirds) was collected from deposits on seashore rocks and added to the fields,
but demand by inland farmers for phosphate fertilizer stimulated the mining of phosphate deposits (ocean
sediments of past geologic ages). These applications, too, wash out of the fields into the world's waters and also can
cause eutrophication.