LANDSCAPE DESIGN –BIOGEOCHEMICAL CYCLE

Implications of Water Cycle

•The water cycle has a tremendous impact on the climate. For instance, the
greenhouse effect will cause a rise in temperature. Without the evaporative cooling
effect of the water cycle, the temperature on earth would rise drastically.
•The water cycle is also an integral part of other biogeochemical cycles.
•Water cycle affects all life processes on earth.
•The water cycle is also known the clean the air. For instance, during the process of
precipitation, water vapours have to attach themselves on to particles of dust. In
polluted cities, the raindrops, apart from picking up dust, also pick up water-soluble
gas and pollutants as they fall from the clouds. Raindrops are also known to pick up
biological agents such as bacteria and industrial soot particles and smoke.
Water changes its state through a variety of processes from evaporation, melting
and freezing, to sublimation, condensation, and deposition. All these changes
require the application of energy.

Stages of Water Cycle

There are many processes involved in the movement of water apart from the major
steps given in the above water cycle diagram. Listed below are different stages of
the water cycle.
1. Evaporation
The sun is the ultimate source of energy, and it powers most of the evaporation that
occurs on earth. Evaporation generally happens when water molecules at the
surface of water bodies become excited and rise into the air. These molecules with
the highest kinetic energy accumulate into water vapour clouds. Evaporation usually
takes place below the boiling point of water. Another process
called evapotranspiration occurs when evaporation occurs through the leaves of
plants. This process contributes to a large percentage of water in the atmosphere.
2. Sublimation
Sublimation occurs when snow or ice changes directly into water vapour without
becoming water. It usually occurs as a result of dry winds and low humidity.
Sublimation can be observed on mountain peaks, where the air pressure is quite low.
The low air pressure helps to sublimate the snow into water vapour as less energy is
utilised in the process. Another example of sublimation is the phase where fog
bellows from dry ice. On earth, the primary source of sublimation is from the ice
sheets covering the poles of the earth.
3. Condensation
The water vapour that accumulated in the atmosphere eventually cools down due
to the low temperatures found at high altitudes. These vapours become tiny droplets
of water and ice, eventually coming together to form clouds.
4. Precipitation
Above 0 degrees centigrade, the vapours will condense into water droplets.
However, it cannot condense without dust or other impurities. Hence, water vapours
attach itself on to the particle’s surface. When enough droplets merge, it falls out of
the clouds and on to the ground below. This process is called precipitation (or
rainfall). In particularly cold weather or extremely low air pressure, the water droplets
freeze and fall as snow or hail.

5. Infiltration
Rainwater gets absorbed into the ground through the process of infiltration. The level
of absorption varies based on the material the water has seeped into. For instance,
rocks will retain comparatively less water than soil. Groundwater can either follows
streams or rivers. But sometimes, it might just sink deeper, forming aquifers.

6. Runoff
If the water from rainfall does not form aquifers, it follows gravity, often flowing down
the sides of mountains and hills; eventually forming rivers. This process is called
runoff. In colder regions, icecaps form when the amount of snowfall is faster than the
rate of evaporation or sublimation. The biggest icecaps on earth are found at the
poles.
Oxygen cycle, along with the carbon cycle and nitrogen cycle plays an essential role in
the existence of life on the earth. The oxygen cycle is a biological process which helps
in maintaining the oxygen level by moving through three main spheres of the earth
which are:
•Atmosphere
•Lithosphere
•Biosphere
This biogeochemical cycle explains the movement of oxygen gas within the
atmosphere, the ecosystem, biosphere and the lithosphere. The oxygen cycle is
interconnected with the carbon cycle.
The atmosphere is the layer of gases presents above the earth’s surface. The sum of
Earth’s ecosystems makes a biosphere. Lithosphere is the solid outer section along with
the earth’s crust and it is the largest reservoir of oxygen.
Stages of the Oxygen Cycle
The steps involved in the oxygen cycle are:
Stage-1: All green plants during the process of photosynthesis, release oxygen back
into the atmosphere as a by-product.
Stage-2: All aerobic organisms use free oxygen for respiration.
Stage-3: Animals exhale Carbon dioxide back into the atmosphere which is again
used by the plants during photosynthesis. Now oxygen is balanced within the
atmosphere.
The four main processes that use atmospheric oxygen are:
Breathing – It is the physical process, through which all living organisms,
including plants, animals and humans inhale oxygen from the outside
environment into the cells of an organism and exhale carbon dioxide back into
the atmosphere.
Decomposition: It is one of the natural and most important processes in the
oxygen cycle and occurs when an organism dies. The dead animal or plants
decay into the ground, and the organic matter along with the carbon, oxygen,
water and other components are returned into the soil and air. This process is
carried out by the invertebrates, including fungi, bacteria and some insects which
are collectively called as the decomposers. The entire process requires oxygen
and releases carbon dioxide.
Read more: Decomposition
Combustion: It is also one of the most important processes which occur when
any of the organic materials, including fossil fuels, plastics and wood, are burned
in the presence of oxygen and releases carbon dioxide into the atmosphere.
Rusting: This process also requires oxygen. It is the formation of oxides which is
also called oxidation. In this process, metals like iron or alloy rust when they are
exposed to moisture and oxygen for an extended period of time and new
compounds of oxides are formed by the combination of oxygen with the metal.

Production of Oxygen
Plants: The leading creators of oxygen are plants by the process of photosynthesis.
Photosynthesis is a biological process by which all green plants synthesize their
food in the presence of sunlight. During photosynthesis, plants use sunlight, water,
carbon dioxide to create energy and oxygen gas is liberated as a by-product of
this process.
Sunlight: Sunlight also produces oxygen. Some oxygen gas is produced when the
sunlight reacts with water vapour in the atmosphere.
SOME INTERESTING FACTS ABOUT OXYGEN
•Phytoplankton is one of the most significant producers of oxygen, followed by
terrestrial plants and trees.
•Oxygen is also produced when the sunlight reacts with water vapour present in the
atmosphere.
•A large amount of oxygen is stored in the earth’s crust in the form of oxides, which
cannot be used for the respiration process as it is available in the combined state.
Importance of Oxygen Cycle
As we all know, oxygen is one of the most essential components of the earth’s
atmosphere. It is mainly required for:
•Breathing
•Combustion
•Supporting aquatic life
•Decomposition of organic waste.
Oxygen is an important element required for life, however, it can be toxic to some
anaerobic bacteria (especially obligate anaerobes).
The oxygen cycle is mainly involved in maintaining the level of oxygen in the
atmosphere. The entire cycle can be summarized as, the oxygen cycle begins with
the process of photosynthesis in the presence of sunlight, releases oxygen back into
the atmosphere, which humans and animals breathe in oxygen and breathe out
carbon dioxide, and again linking back to the plants. This also proves that both the
oxygen and carbon cycle occur independently and are interconnected to each
other.
 Phosphorus Cycle Definition
“Phosphorus cycle is a biogeochemical process
that involves the movement of phosphorus
through the lithosphere, hydrosphere and
biosphere.”
What is Phosphorus Cycle?
Phosphorus is an important element for all
living organisms. It forms a significant part of
the structural framework of DNA and RNA. They
are also an important component of ATP.
Humans contain 80% of phosphorus in teeth
and bones.
Phosphorus cycle is a very slow process.
Various weather processes help to wash the
phosphorus present in the rocks into the soil.
Phosphorus is absorbed by the organic matter
in the soil which is used for various biological
processes.
Since phosphorus and phosphorus-containing
compounds are present only on land,
atmosphere plays no significant role in the
phosphorus cycle.
Let us have a brief look at the phosphorus
cycle, its steps and the human impact on
Steps of Phosphorus Cycle phosphorus cycle.
Following are the important steps of phosphorus cycle:
1.Weathering
2.Absorption by Plants
3.Absorption by Animals
4.Return to the Environment through Decomposition
Weathering
Phosphorus is found in the rocks in abundance. That is why the phosphorus cycle
starts in the earth’s crust. The phosphate salts are broken down from the rocks.
These salts are washed away into the ground where they mix in the soil.
Absorption by Plants
The phosphate salts dissolved in water are absorbed by the plants. However, the
amount of phosphorus present in the soil is very less. That is why the farmers apply
phosphate fertilizers on agricultural land.
The aquatic plants absorb inorganic phosphorus from lower layers of water bodies.
Since phosphate salts do not dissolve in water properly, they affect plant growth
in aquatic ecosystems.

Absorption by Animals
The animals absorb phosphorus from the plants or by consuming plant-eating
animals. The rate of the phosphorus cycle is faster in plants and animals when
compared to rocks.
Return of Phosphorus Back to the Ecosystem
When the plants and animals die they are decomposed by microorganisms During this
process, the organic form of phosphorus is converted into the inorganic form, which is
recycled to soil and water.
Soil and water will end up in sediments and rocks, which will again release phosphorus
by weathering. Thus, the phosphorus cycle starts over.
Human Impact on Phosphorus Cycle
A number of human activities, use of fertilizers, artificial eutrophication, etc. has a great
impact on the phosphorus cycle.
The phosphorus fertilizers increase the level of phosphorus in the soil. Overuse of these
fertilizers reduces the fertility of the soil and is also harmful to the microorganisms
present in the soil. When these are washed away into the nearby water bodies, they are
hazardous to aquatic life.
During the shipping of food from farms to cities, the amount of phosphorus that is
washed away in water causes eutrophication. This leads to the growth of algae. These
form algal blooms or die, which is toxic to the aquatic ecosystem.
Sulphur is one of the most abundant elements on the earth. It is a yellow,
brittle, tasteless, odourless non-metal. Sulphur is present in all kinds of
proteins. Plants directly absorb sulphur-containing amino acids such as
methionine, cystine, and cysteine.
Sulphur is released into the atmosphere by the burning of fossil fuels, volcanic
activities, and decomposition of organic molecules.
On land, sulphur is stored in underground rocks and minerals. It is released by
precipitation, weathering of rocks and geothermal vents.

Sulphur Cycle
The process of sulphur cycle is explained below:
•The sulphur is released by the weathering of rocks.
•Sulphur comes in contact with air and is converted into sulphates.
•Sulphates are taken up by plants and microbes and are converted into
organic forms.
•The organic form of sulphur is then consumed by the animals through their
food and thus sulphur moves in the food chain.
•When the animals die, some of the sulphur is released by decomposition
while some enter the tissues of microbes.
•There are several natural sources such as volcanic eruptions, evaporation of
water, and breakdown of organic matter in swamps, that release sulphur
directly into the atmosphere. This sulphur falls on earth with rainfall.

Steps of Sulphur Cycle

Following are the important steps of the sulphur cycle:
Decomposition of Organic Compounds
Protein degradation releases amino acids that contain sulphur. Sulphates are
reduced to H2S by the action of Desulfotomaculum bacteria.
Oxidation of Hydrogen Sulphide to Elemental Sulphur
Hydrogen sulphide oxidises to produce elemental sulphur. Certain
photosynthetic bacteria from the families Chlorobiaceae and Chromatiaceae
initiate the oxidation process.
Oxidation of Elemental Sulphur
Elemental sulphur present in the soil cannot be utilized directly by the plants.
Therefore, it is converted into sulphates by chemolithotrophic bacteria.
Reduction of Sulphates
Sulphates are reduced to hydrogen sulphide by Desulfovibrio desulfuricans. This
occurs in two steps:
•Firstly, the sulphates are converted to sulphites utilizing ATP.
•Secondly, the reduction of sulphite to hydrogen sulphide.