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Lecture

BIOA02H3 Lecture Notes - Biogeochemical Cycle, Smog, Convection Zone


Department
Biological Sciences
Course Code
BIOA02H3
Professor
Mary Olaveson

Page:
of 5
Chapter 56 Ecosystem & Global Economy
Unlike energy, which is lost as it travels up the trophic levels; chemical compounds remain unchanged
and can be reused, in processes which are often cyclic
The movement of energy and materials on Earth is between 4 compartments: Oceans, Fresh Waters,
Atmosphere, and Land
Oceans
At one point or another, most materials that cycle through the four compartments end up in oceans
Despite their massive size, oceans only exchange materials with the atmosphere on the surface
therefore they respond very slowly from input of other departments
In most of the oceans, there is very slow mixture. Most material sink to the bottom and stay there for
millions of years, however sometimes the material is brought back up to surface water, causing
upwelling zones which support high rates of photosynthesis
Freshwater
Freshwater consists of rivers, lakes, and groundwater. Water travels very fast through them
In lakes, minerals and nutrients are taken up by organisms which they incorporate into their cells. Once
these organisms die, they take with them the nutrients and minerals. Often, deteritivores consume the
oxygen by eating their tissues
Therefore the surface waters of lakes quickly become depleted of nutrients while deeper waters
become depleted of oxygen
This is often resolved by a process known as turnover, which brings nutrients to the surface of lakes and
oxygen to the bottom of the lakes
Turnovers in shallow lakes are driven by winds whereas in deep lakes, it is driven by temperature
In the case of deep lakes, turnovers occur because water is at its densest at 4®, anything above or below
that causes it to expand. Therefore in the winter, the coldest waters float to the surface and are usually
covered by ice and the waters below remains at 4®. When spring comes and ice melts, the surface also
becomes 4®. At this point all the water is uniform and the wind can mix the water, allowing nutrients to
float to the top and oxygen to reach the bottom
SEE FIG. 56.3
Atmosphere
The atmosphere is a thin layer of gas surrounding Earth that contains the highest levels of nitrogen
(78.08%) and oxygen (20.95%) of anywhere on Earth
Troposphere: the lowest layer of the atmosphere. Contains 80% of the atmospheric mass.
Also, most global air circulation is found in this level as well as virtually all the
water vapour 10-17km from Earth’s surface
Stratosphere: Extends from the top of the troposphere to 50 km above Earth’s surface
Material enters the stratosphere through the troposphere in the inter-tropical convection zone, where
hot air raises to high altitudes
A layer of ozone in the stratosphere absorbs most of the biologically damaging short wavelength UV
radiation entering the atmosphere
Also, it has an important role in temperature regulation because it is transparent to light however it
traps heat and doesn’t allow it to leave
Greenhouse Gases: Chemical gases which are especially good at trapping heat. I.e. carbon dioxide
Land
Covers about 25% of earth’s surface
The terrestrial compartment is connected to the atmosphere by organisms that take chemical elements
from, and release them back into the atmosphere
It is connected to oceans by the soils which are carried into the ground water and eventually into the
oceans
Although land covers a small amount of Earth’s surface, much of life depends on the soil’s fertility and
the productivity of terrestrial ecosystems
Solar Energy
All energy utilized by organisms has come from the sun (with the exception of few ecosystems like
caves, deep sea hydrothermal vents, etc)
Solar energy enters ecosystems by way of plants and other photosythesizer organisms. Despite that,
only 5% of all the solar energy that hits Earth is captured by photosynthesis. The rest is reradiated back
into the atmosphere or taken up by chemical compounds
Gross Primary Productivity (GPP): The rate at which energy is incorporated into the bodies of
photosynthetic organisms (primary producers)
Gross Primary Production: the accumulated energy of GPP
GPP is the rate; gross primary production is the product
Net Primary Production (NPP): The amount of energy available to a primary consumer. It is the gross
primary production minus the amount of energy expanded on its own
metabolism
Only the NPP is available to organisms consuming it
The geographic distribution of the energy assimilated by primary producers depends on the distribution
of land mass, temperature, moisture etc.
Those areas with adequate factors such as the tropics thrive in ecosystem productivity while other areas
that do not possess these factors do not thrive (i.e. desserts, poles)
Human advances change the way GPP and NPP is used by other organisms and its distribution in both
good ways (increased agriculture) and bad ways (cutting down forest for urbanization)
Biogeochemical Cycle: The cycle in which chemicals that organisms need in abundance
(oxygen, carbon dioxide, nitrogen etc) cycle through organisms bodies,
into the atmosphere, and back again
Each element has its own biogeochemical cycle, depending on its properties and all chemical cycles are
very short because no organisms live long in geographical terms
2 very important factors in the biogeochemical cycle are water and fire. Water transfers many chemical
elements between the atmosphere, land, fresh water and oceans. Fire is a powerful agent that speeds
up the process of the cycle
Hydrological Cycle: the cycling of water through oceans, atmosphere, fresh water and land
The hydrological cycle is possible because more water evaporates than is returned to Earth in form of
precipitation, therefore water evaporates, is moved by winds, and precipitates in different areas
Water stays in rivers/lakes much shorter (average residence of 4.3 years) than in oceans (average
residence of 2640 years), and even shorter in humans (5.6 days)
Humans have manipulated the spatial and temporal locations of water by building dams, canals and
reservoirs which caused more water to evaporate from land
Aquifers: Amounts of groundwater present in underground pools
Fire