Concepts of Environmental Science
Environmental Systems: Biogeochemical cycles
Biogeochemical cycles involve biological, geologic, and chemical interactions that represent the
cyclic movement of matter from one part of an ecosystem to another. They are significant part of
the environment as nutrient transfer and recycling supports the maintenance of life on earth.
However, anthropological activities have affected the natural flow of biogeochemical cycles. The
biogeochemical cycles to be discussed include the hydrologic cycle, carbon cycle, nitrogen
cycle, phosphorus cycle, and sulfur cycle.
Hydrologic cycle or Water cycle
Perhaps, the water cycle is the most familiar of all biogeochemical cycles. Water is responsible
for metabolic processes in cells, flow of key nutrients, and distribution of heat and energy. Water
is needed for life to exist.
Water from the oceans and open fresh water systems evaporate to the atmosphere.
Transpiration or the evaporation of water through the leaves of plants would also contribute to
the available water vapor in the atmosphere. The concentration of water vapor in the atmosphere
would form clouds which may be moved to other places through air currents. Eventually,
condensation and precipitation (rain) would occur. Some of the rain would reach the rivers and
streams, eventually, excess water would runoff to the seas and oceans as these bodies of water
are connected. Some rainfall would penetrate the soil through percolation, and eventually reach
the depths belowground, replenishing the ground water resource. The ground water may be
released slowly through seepage to the bodies of water.
Human activities have affected the water cycle. Groundwater resource has been depleted because
of overuse of wells and pumps. Leaching of toxins to the groundwater resource also pose threat
to environmental health. Waste, excess nutrients and toxic chemicals have spread to the
environment through runoffs. Eventually, these pollutants would be carried by the movement of
water and may be difficult to retract.
Carbon cycle
Carbon is a structural component of organic molecules. Chemical bonds in carbon compounds
provide metabolic energy. The carbon cycle involves carbon fixation through photosynthesis.
, Through respiration, carbon dioxide is released to the atmosphere. When living organisms die,
the organic carbon in their bodies would be also be released as carbon dioxide to the atmosphere
through decomposition. Sometimes the organic carbon in dead organisms would be stored
underground, and over time, would form coal and fossil fuels. The coal and fossil fuels would
serve as carbon sinks to limit the release of carbon dioxide to the atmosphere.
Human activities led to greater concentration of carbon dioxide in the atmosphere. Coals and
fossil fuels are mined and burned to supply industrial activities. Upon burning, carbon dioxide
and other greenhouse gases are released to the atmosphere. Human practices also include slash
and burn (kaingin) which also release carbon dioxide to the atmosphere. The destruction of
carbon sinks (natural carbon storage systems) because of human activities altered the amounts
of carbon present in the atmosphere and in the biomass.
Nitrogen cycle
Nitrogen is an extremely important nutrient for living organisms as it is a component of proteins
and nucleic acids. Nitrogen is also a major component of fertilizers. Around 78% of the
atmosphere is made up of nitrogen gas but this cannot be readily used by plants. How is nitrogen
fixed and incorporated in the nitrogen cycle?
Atmospheric nitrogen is biologically converted to ammonium and ammonia by nitrogen-fixing
bacteria in soil. This process is called ammonification. Ammonium may be converted by other
bacteria into nitrates through nitrification. Plants, through assimilation, can use ammonia,
ammonium, and nitrates to form organic nitrogen compounds. Animals can get nitrogen by
consuming plants. When plants and animals die and decompose, the organic nitrogen compounds
return to ammonia, ammonium, and nitrates in the soil. Denitrifying bacteria can convert nitrates
to atmospheric nitrogen through denitrification, completing the nitrogen cycle. Lightning may
also convert atmospheric nitrogen to introduce inorganic nitrogen compounds to the soil.
Human activities altered the availability of nitrogen in the environment. Commercial and
agricultural nitrogen fixation trapped the nitrogen from the atmosphere into synthetic fertilizers.
These fertilizers are used to grow crops to meet the demand for food. When fertilizers are
introduced, there is excess nitrogen in the environment. With the excess nitrogen, harmful algal
blooms can emerge and cause death of organisms when oxygen is depleted. Excess nitrogen also
Environmental Systems: Biogeochemical cycles
Biogeochemical cycles involve biological, geologic, and chemical interactions that represent the
cyclic movement of matter from one part of an ecosystem to another. They are significant part of
the environment as nutrient transfer and recycling supports the maintenance of life on earth.
However, anthropological activities have affected the natural flow of biogeochemical cycles. The
biogeochemical cycles to be discussed include the hydrologic cycle, carbon cycle, nitrogen
cycle, phosphorus cycle, and sulfur cycle.
Hydrologic cycle or Water cycle
Perhaps, the water cycle is the most familiar of all biogeochemical cycles. Water is responsible
for metabolic processes in cells, flow of key nutrients, and distribution of heat and energy. Water
is needed for life to exist.
Water from the oceans and open fresh water systems evaporate to the atmosphere.
Transpiration or the evaporation of water through the leaves of plants would also contribute to
the available water vapor in the atmosphere. The concentration of water vapor in the atmosphere
would form clouds which may be moved to other places through air currents. Eventually,
condensation and precipitation (rain) would occur. Some of the rain would reach the rivers and
streams, eventually, excess water would runoff to the seas and oceans as these bodies of water
are connected. Some rainfall would penetrate the soil through percolation, and eventually reach
the depths belowground, replenishing the ground water resource. The ground water may be
released slowly through seepage to the bodies of water.
Human activities have affected the water cycle. Groundwater resource has been depleted because
of overuse of wells and pumps. Leaching of toxins to the groundwater resource also pose threat
to environmental health. Waste, excess nutrients and toxic chemicals have spread to the
environment through runoffs. Eventually, these pollutants would be carried by the movement of
water and may be difficult to retract.
Carbon cycle
Carbon is a structural component of organic molecules. Chemical bonds in carbon compounds
provide metabolic energy. The carbon cycle involves carbon fixation through photosynthesis.
, Through respiration, carbon dioxide is released to the atmosphere. When living organisms die,
the organic carbon in their bodies would be also be released as carbon dioxide to the atmosphere
through decomposition. Sometimes the organic carbon in dead organisms would be stored
underground, and over time, would form coal and fossil fuels. The coal and fossil fuels would
serve as carbon sinks to limit the release of carbon dioxide to the atmosphere.
Human activities led to greater concentration of carbon dioxide in the atmosphere. Coals and
fossil fuels are mined and burned to supply industrial activities. Upon burning, carbon dioxide
and other greenhouse gases are released to the atmosphere. Human practices also include slash
and burn (kaingin) which also release carbon dioxide to the atmosphere. The destruction of
carbon sinks (natural carbon storage systems) because of human activities altered the amounts
of carbon present in the atmosphere and in the biomass.
Nitrogen cycle
Nitrogen is an extremely important nutrient for living organisms as it is a component of proteins
and nucleic acids. Nitrogen is also a major component of fertilizers. Around 78% of the
atmosphere is made up of nitrogen gas but this cannot be readily used by plants. How is nitrogen
fixed and incorporated in the nitrogen cycle?
Atmospheric nitrogen is biologically converted to ammonium and ammonia by nitrogen-fixing
bacteria in soil. This process is called ammonification. Ammonium may be converted by other
bacteria into nitrates through nitrification. Plants, through assimilation, can use ammonia,
ammonium, and nitrates to form organic nitrogen compounds. Animals can get nitrogen by
consuming plants. When plants and animals die and decompose, the organic nitrogen compounds
return to ammonia, ammonium, and nitrates in the soil. Denitrifying bacteria can convert nitrates
to atmospheric nitrogen through denitrification, completing the nitrogen cycle. Lightning may
also convert atmospheric nitrogen to introduce inorganic nitrogen compounds to the soil.
Human activities altered the availability of nitrogen in the environment. Commercial and
agricultural nitrogen fixation trapped the nitrogen from the atmosphere into synthetic fertilizers.
These fertilizers are used to grow crops to meet the demand for food. When fertilizers are
introduced, there is excess nitrogen in the environment. With the excess nitrogen, harmful algal
blooms can emerge and cause death of organisms when oxygen is depleted. Excess nitrogen also
