ENVIRONMENTAL SCIENCE

(PE014IU)

LECTURE 2
ECOSYSTEM

MAppSc. Dao Bui

 Outlines

1. Ecological concepts

2. Energy flow

3. Biogeochemical cycles
 Ecological concepts
❖ What is ecology?
 Ecological concepts
❖ What is ecology?
– Krebs (1985) “the scientific study of the interactions
that determine the distribution and abundance of
organisms”
– Chapman & Reiss (1992) “study of organisms in
relation to the surroundings in which they live”
– The branch of biology that deals with the relations of
organism to one another and to their physical
surroundings. (Oxford Dictionary)
➢ Key point:
– ………………………………………………………
………………………………………………………
 Ecological concepts
❖ What is ecology?
– Krebs (1985) “the scientific study of the interactions
that determine the distribution and abundance of
organisms”
– Chapman & Reiss (1992) “study of organisms in
relation to the surroundings in which they live”
– The branch of biology that deals with the relations of
organism to one another and to their physical
surroundings. (Oxford Dictionary)
➢ Key point:
– Interactions between organisms and their
environment…………………………..………………
Chapman & Reiss liken ecology to “an enormous
jigsaw puzzle”

For simplicity, this figure

is 2 dimensional, but the
ecological interactions of
Organisms and their
environment are
really multi-dimensional.
Multi-dimensional puzzle

By remove 1 piece, all

pieces will be separated
• Concept of ecology “Earth as a system”
• A living, working and dynamic system.

→ It is important to understand patterns and

processes to fixing and minimizing the effects of
human activities.

• If we want to make predictions about what will

happen to an ecosystem, or if we wish to restore an
ecosystem, we need to apply knowledge gained
from answering these 2 main questions:
1. Why are there so many different species?
2. How have they come to live together?
❖ Ecosystem:

System involving the interactions between a

community of living organism in a particular area
and its nonliving environment.

• Ecosystems are dynamic: composed of biotic and abiotic

components that interact with earth other.

• An ecosystem can be small, such as the area under a pine

tree or a single pool at rocky shore, or it can be large, such
as the Rocky Mountains, the rainforest or the Antarctic
Ocean.

• Life exists on land system are called biomes and under

water are called aquatic life zones.
❖ Biome:
A complex biotic community characterized by
distinctive plant and animal species and
maintained under the climatic conditions of the
region.

• Tropical rainforest
• Savanna
• Desert
• Tundra
• Wetland
❖ The biosphere share common characteristics, however
each ecosystem is unique in its own way

❖ Understanding of ecosystems and its interaction help to

see how they affect or be affected by human activities
and how to make them sustainable is vital for survival of
human.

❖ Multitudes of tiny microbes such as bacteria, protozoa,

fungi and yeast help keep us alive
Living (biotic)
and non-living
(abiotic)
components
of an
ecosystem
 Environmental Unity
❖ Concept that everything in the environment is
connected, directly or indirectly to everything else

❖ Any change in system is likely to produce secondary

and tertiary effect with in system and connected systems
 Common limiting factors
• In terrestrial ecosystems : Precipitation, temperature,
nutrients

• In aquatic ecosystems: temperature, sunlight, nutrients,

dissolve oxygen and salinity

Law of tolerance
• The existence, abundance and distribution of a species is
determined by levels of one or more physical and
chemical factors.
❖ Tolerance limits: minimum and maximum levels beyond
which a particular species cannot survive or reproduce

❖ Limiting factors determines distribution

How Do Ecosystems Benefit Human Wellbeing?
 Discussion

What are the most basic important components

of ecosystem?

Remind: Ecosystem is system involving the interactions

between a community of living organism in a particular
area and its nonliving environment.
❖ The important components of ecosystem include soil, water,
atmosphere, solar radiation and living organism

• Soil provides nutrient, water, a home and a structure

medium for the roots of plants

• Sun provides energy in form of radiation which is used

to generate heat and power photosynthesis.

• Water is incorporated into bodies of organism, is

medium for nutrient exchange between soil and life and
is used in photosynthesis, respiration, evapo-transpiration
and precipitation

• Atmosphere is an sink for oxygen, CO2 and water

 Earth’s systems
Four major systems

➢ Lithosphere: Earth’s
crust that include
rocks and soil

➢ Hydrosphere: Liquid
water on surface
and underground,
ice (cryosphere) and
water vapor

➢ Biosphere: Living
and dead organisms
 Earth’s systems
➢ Atmosphere: Thin
membrane of air
• Troposphere
• Stratosphere
• Mesosphere
• Ionosphere
 Three factors sustain the
Earth’s life?
• Energy
• Nutrient
• Gravity
The Natural of Ecology
❖ Level of study in ecology:
• Biosphere – all ecosystems in the
entire Earth.
• Ecosystem – a community +
physical environment
• Community – population living together
in a particular place & their interactions
• Population – a group of the same
species
• Species – a group of organisms able to
breed and fertile offspring.
• Organism – an individual living thing
❖ Dynamics of an ecosystem involve 2 main processes:
✓ energy flow
✓ chemical cycling

Question:

▪ What is energy?

▪ Where is energy of the earth come from?

 Energy flow
❖ Energy changes are governed by 2 scientific laws

• The first law of thermodynamics: Whenever energy is

converted from one form to another in a physical or
chemical change, no energy is created or destroyed

• The second law of thermodynamics: we always end up

with a lower quality or less “usable” energy

❖ Energy efficiency is measure of how much useful work is

accomplished by a particular input of energy into a system
Function of sunlight energy
 Cycling of Nutrients
❖ The cycling of nutrients through parts of the biosphere.
❖ The earth is closed to
significant inputs of matter
from space, its essentially
fixed supply of nutrients must
be continually recycled to
support life.
❖ Nutrient movements in
ecosystems and in the
biosphere are round trips
take from seconds to
centuries to complete. (The
law of conservation of matter)
Biological components of ecosystem
❖ Some organisms in ecosystems product food while
others consume food

❖ Producer (Autotroph – self feeder) : Organisms use

solar energy (green plants, algae and cyanobacteria) or
chemical energy (some bacteria) to manufacture their
nutrient as organic compounds. Photosynthesis /
chemosynthesis process involve

Light
Carbon dioxide + Water Glucose + Oxygen
Bacteria
Biological components of ecosystem
❖ Consumer (Heterotroph – other feeder): Organisms that
can not synthesize organic nutrient by themselves , they
have to get it by feeding on tissues of producer or of
other consumers.

❖ Decomposer (bacteria / fungi): recycle organic matter by

break down dead organic material or detritus into
single inorganic compounds, recycle nutrients in
ecosystems.

❖ Detritivores: (waste eaters and degrader): feed on

detritus (dead organic materials); can transform a fallen
tree trunk into simple inorganic molecules
 Aerobic and Anaerobic Respiration: Getting
Energy for Survival
❖ Aerobic respiration
❑ Organisms break down carbohydrates and other
organic compounds in their cells to obtain the energy
they need.
❑ This is usually done through aerobic respiration.
❑ The opposite of photosynthesis
 Aerobic and Anaerobic Respiration: Getting
Energy for Survival
❖ Anaerobic respiration or fermentation:

❑ Some decomposers get energy by breaking down glucose

(or other organic compounds) in the absence of oxygen.

❑ The end products vary based on the chemical reaction:

• Methane gas
• Ethyl alcohol
• Acetic acid
• Hydrogen sulfide
❖ Food chains: sequence of organisms which is a source of food
for the next level, each of which serves as a source of nutrients
and energy for the next organisms / A linear series of feeding
relationships in an ecosystem
• Energy and nutrient are passed from organism to organism
through the food chain .
❖ Food webs: In natural, most consumers feed on more
than 1 type of organism. Organism in ecosystems form a
complex network of interconnected food chains.
❖ Food web:
• A more complex than
a linear food chain
https://www.youtube.com/watch?v=LVJ5BKcAhAg
❖ Trophic levels: Each step in the flow of energy through
an ecosystem / the organism position in the food chain
❖ Trophic levels: Each step in the flow of energy through
an ecosystem / the organism position in the food chain
• Autotroph are at the base
• Herbivores / primary consumers eat autotrophs (feed
on plants)
• Carnivore / secondary consumer eats herbivores
(feed on animals)
• Carnivore / Tertiary consumer can eat other
secondary consumer
• Omnivores do not specialize in diets. (Feed on both
plants and animals)
• Some other species do not limit their diet to
organism of only 1 trophic level
 Autotrophs Heterotrophs

Producers Consumers Detritus feeders Decomposer

Primary consumers/
Photosynthesis Primary detritus Fungi and bacteria
carnivores (feed on
green plants feeders that cause rotting
plants)

Photosynthesis Omnivores (feed on Secondary detritus

bacteria plants/animal) feeder

Secondary
Chemosynthesis
consumers/
bacteria
carnivores
Higher orders of
consumers/
carnivores
Parasites
❖ Usable energy decreases with each link in a food chain or
web
• There is less high-quality energy available to organisms
at each succeeding feeding level because when chemical
energy is transferred from one trophic level to the next,
about 90% the energy is lost as heat
• Food chains and webs rarely have more than four or five
trophic levels. WHY?
• There are far fewer tigers (top predator) in the world
than there are insects (primary/ secondary consumer).
WHY?
Pyramid of Energy flow showing the decrease in usable
chemical energy available at each trophic level
• Solar energy enters ecosystems by plant through
photosynthesis that use CO2 , water and sunlight to
convert into glucose and oxygen. Glucose can be
altered; through the addition of other chemicals, into
pigments, lipids, sugar, protein and nucleic acids; and
passed on to other organisms through consumption and
assimilation.
• Decomposers remove the last energy from the remains
of organism. Inorganic nutrients are cycled, energy is
not
• One of major properties of an ecosystem is its
productivity, the amount of biomass (biological
material) produced in a given area during a given period
of time.
 • The intensity of light varies over space and time.
Photosynthesis rate increase down to certain depth and
then decrease beyond that.

• Exposure to high intensity of light inhibit photosynthesis

(ultraviolet radiation destruct photo-oxidation reaction)

• Rate of supplied nutrient may determine rate of primary

production. It is often man-originated enrichments that
change the nature of aquatic ecosystem.

❖ Eutrophication is the ecosystem response to the addition of

artificial or natural substance (such as Nitrogen and
Phosphorus) to aquatic system. Example: Algae bloom, red
tide.
Algae bloom in China

Red tide at New Zealand

https://www.youtube.com/watch?v=6LAT1gLMPu4
 Primary production
❖ Is the production of organic compounds by living
organism / process where plants absorb solar energy and
fix carbon in form of sugars.

• It can be expressed in terms of energy per unit area per

unit time, or as biomass of vegetation added to the
ecosystem per unit area per unit time.

• Organic matters support biological activities in water

column and mainly synthesized by photosynthesis or
chemosynthesis mechanism.
➢ How organic matter is produced in aquatic system?
➢ How the rate of production are controlled?
 ❖ Rate of primary production vary greatly in different area and at
different times.

• Gross primary production is total amount of photosynthesis

achieved by plant and algae during a certain time. Measured in
terns of energy production per unit area over a give length of time
(kcal/m2/year)

• During time, organism is carrying respiration, some of biomass

must be used for the producer’s own respiration. Net primary
production is the organic material that stored after photosynthetic
or available to other consumers in an ecosystem

Net primary production = Gross primary production – Total respiration

❖ Some ecosystems produce plant matter faster than others do

NPP in major life zones and ecosystems
NPP in major life zones and ecosystems
❖ An important lesson from nature

• Only the biomass represented by NPP is available as

nutrients for consumers. Thus, the planet’s NPP
ultimately limits the number of consumers (including
humans) that can survive on the earth.

• Some ecologists estimate that humans now use, waste, or

destroy 10–55% of the earth’s total potential NPP.
While the human population makes up less than 1% of
the total biomass of all of the earth’s consumers that
depend on producers for their nutrients.
 Primary production
❖ 2 principal primary production control mechanisms are
bottom - up and top - down. The evidence are light and
nutrients.

• Bottom-up control: nutrient supply, productivity

and primary producer control ecosystem structure.
Primarily nutrient and light influence net primary
production in water column and hence on rest of
food web.

Nutrient limitation: after nutrition are added, net

primary production increase. The changes of species
composition often result from the enrichment
• Top-down control: top predator control the structure
or population dynamic of an ecosystem. Example:
sea otters eat urchins, which eat kelp. If otter are
removed, urchin populations grow and reduce the
kelp forest. This mechanism is more important in
fresh water ecology

→ →
 Matters vs Energy
Matter Energy
• Has mass • Has no mass
• Affected by gravity • Has the ability to perform work
• Can be recycled • Flows through the ecosystem in
one direction
 Outlines

1. Ecological concepts

2. Energy flow

3. Biogeochemical cycles/ Nutrient cycles

 Biogeochemical/ nutrient cycles
❖ Global cycle of nutrients through the air, soil, rock,
water and living organisms. These cycles are driven
directly or indirectly by solar energy and gravity.

❖ Important cycles include:

• Hydrologic cycle (H2O)
• Carbon cycle
• Nitrogen cycle
• Phosphorus cycle
Water cycle
❖ Water play an important role in functioning of an ecosystem.
Water corporate into bodies of organism, medium for nutrient
exchange between soil and life and use in photosynthesis,
respiration, evapo-transpiration and precipitation
❖ Water is filtered and partly purified as it moves through the
hydrological cycle of can be stored as ice in glaciers or in
underground aquifers.
❖ Human influence of water cycle include
• Withdraw water from inland watershed for development
purpose (underground, lake, stream….)
• Constructing surface (roads, building…)
• Destructing vegetation (forest)
• Modifying nutrient and chemical (to watershed,
underground water)
Rural area Urban area
 Carbon cycle
❖ Carbon is the basic building block of the carbohydrates,
fats, protein, DNA and other organic compound and the
energy holding chemical bonds.

❖ Carbon circulates through the biosphere, hydrosphere,

and atmosphere.

❖ Producers, consumers and decomposers circulate carbon

in the biosphere.

❖ Fossil fuels contain carbon.

Carbon cycle
 Carbon cycle
❖ Humans are altering
atmospheric carbon
dioxide mostly by our use
of fossil fuels and our
destruction of the carbon-
absorbing vegetation.
❖ Human influence of
carbon cycle include
• Burning fossil fuels
and wood
• Cleaning vegetation
faster than it is
replaced
 Nitrogen cycle
❖ Main reservoir for nitrogen is the atmosphere. Nitrogen gas
makes up 78% of volume of the atmosphere.
❖ Nitrogen is a crucial component of protein, many vitamins
and nucleic acids (DNA). Nitrogen gas can not be absorbed
and used directly as a nutrient by multi-cellular plants or
animals.
 Nitrogen cycle

N2 → NH3 → NH4 + → NO3- → NH3 / NH4 + → N2

The nitrogen cycle includes the following steps:
❖ Atmospheric electrical discharges can convert N2 → NH3
❖ Specialized bacteria convert gaseous nitrogen to ammonia
in nitrogen fixation. (N2 → NH3)
❖ Specialized bacteria convert ammonia in the soil to nitrite
ions and nitrate ions; the latter is used by plants as a
nutrient. This process is nitrification.(NH3 → NO2-/ NO3- )
❖ Decomposer bacteria convert detritus into ammonia and
water-soluble salts in ammonification.
❖ In denitrification, anaerobic bacteria in soil and bottom
sediments of water areas convert nitrite and nitrate back into
NH3 and NH4+ , or into nitrogen gas and nitrous oxide gas,
which are released into the atmosphere. (→ N2 )
Effect of human activities on Nitrogen cycle
❖ Human activities have more than doubled the annual release of
nitrogen from the land into the rest of the environment, mostly
from the greatly increased use of inorganic fertilizers to grow
crops. This excessive input of nitrogen into the air and water
contributes to pollution and other problems
❖ We alter the nitrogen cycle by:
• Adding gases that contribute to acid rain.
• Adding nitrous oxide to the atmosphere through farming
practices which can warm the atmosphere and deplete ozone.
• Contaminating ground water from nitrate ions in inorganic
fertilizers.
• Releasing nitrogen into the troposphere through deforestation.
Phosphorus cycle
❖ Phosphorus cycle does not include the atmosphere. The
major reservoir for phosphorus is phosphate salt in
terrestrial rock and ocean bottoms sediments.

❖ This is a slow cycle.

❖ Phosphorus is a components of biologically molecules

(nucleic acids), energy transfer molecules (ADP and ATP)
and components of vertebrate bones and teeth.

❖ Human influence of phosphorus cycle include

• Removing large amount of phosphate to make fertilizer
• Cleaning forest → reducing phosphorus in tropical soils
• Introduce phosphorus to soil as fertilizer
Sulfur cycle
❖ Sulfur is stored underground in rocks and minerals and deep under
ocean sediments. The rate of this cycle are extremely variable as
result of variable rate of decomposition. Decomposition can take up
to 50 years in tundra while the tropical forest can occur much faster
❖ Sulfur is an essential components of proteins. Hydrogen sulfide (H2S)
is released from volcanoes and anaerobic decomposition of organic
matter in bogs and swamps.
❖ Human influence of sulfur cycle include
• Releasing large amounts of sulfur dioxide into atmosphere by
burning sulfur containing coal and oil to produce electric power
• Refine sulfur containing petroleum to make gasoline, heating oil
and other products.
• Convert sulfur containing metallic ores into 3 metals such as
copper, lead and zinc
 Summary
• Section 3-1: What Keeps Us and Other Organisms Alive?

• Section 3-2: What Are the Major Components of an Ecosystem?

• Section 3-3: What Happens to Energy in an Ecosystem?

• Section 3-4: What Happens to Matter in an Ecosystem?

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