Human activities and the Ecosystem
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Human activities and the Ecosystem
Effects of Human Exploitation of Natural Resources on the Modification of the Environment（人類
開發天然資源如何改變環境）
Man’s influence ranges from very little (e.g. natural grassland for grazing animals) to drastic (green
houses which forms a complete artificial environment).
Pre-industrial humans on the environment
(a)
Human as a hunter（獵人）:
Early humans hunted, fished and removed trees to make fires and shelters, but as the population size is small and
they did not remain in one place for long, there is no significant impact on the environment. As they moved on,
the natural environment rapidly recovered. Though they might use
fire and might accidentally burnt down a
large part of the forest, on the whole, their total impact was small.
(b)
Human as shepherds（放牧）:
Human domesticated animals such as sheep, cattle, goats etc. To extend the grasslands for grazing, humans
deliberately burnt large areas of trees causing deforestation.
Increase the size of the herds will subsequent
result in over-grazing with resultant loss of soil fertility leading to erosion, with the possibility of turning forests
to deserts.
©Humans as farmers:
Farming will keep humans to stay in a place for long time. This marked the most significant event on the
environment. They formed permanent settlement by building shelters for them and the animals, and for storing
their crops. More wood was chopped down for timber. Humans cleared much forest (Deforestation 濫伐林木) to
provide a greater area and used as farmland. With no knowledge of minerals, they continued to grow the same
crop on the same piece of land for many years, thus depleting it of essential nutrients. This easily turned the
forests into deserts.
Post-industrial humans on the environment
- Industrialization (工業化)
With the industrial revolution,
-- machines were invented to carry out lots of work including ploughing, sowing, harvesting, etc.
-- more fuels would be used to drive these machines. Fossil fuels like coal, and more recently, oil,
were used as the energy sources. [ depletion of fossil fuels]
-- in addition, the use of fertilizers (肥料), pesticides (殺蟲劑)
These helped in an increase in crop yield supporting an exponential growth in human population. This
further increases the need for more exploitation of natural resources.
- urbanization 都市化 and modern civilization:
-- economic growth and living standard improved
 more resources consumed for convenience, recreation, desire…etc
-
In order to support the growing population, to improve living standard, for recreation…etc. Human
explore more and more natural resources ( such as crystals, minerals, metals, land for farming,
residential and urban infrastructure development) by various ways. As the size of human population
increases, the effect of human activities on the environment is proportionally increased that human
exploitation of natural resources has modified the environment.
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B. Over-exploitation of Natural Resources（天然資源的過度開發）
Resources for man
= include everything man needed from the environment to keep a good quality of life
over-exploitation of natural resources, particularly the non-renewable ones, will quicker the exhaustion of
these resources. This is due to 2 factors:
1. Rapid growth of human population uses the available resources at a faster rate.
2. The increase in living standard and economic growth, due to industrialization（工業化）and modern
civilization（現代文明）, people of the developed countries（發展國家） consume much more
resources than that should be used.
- Two kinds of natural resources
i. Renewable resources （可再生資源）(= they are things which grow)
-- they are living (biotic) resources which have the reproductive property so that they can
compensate for loss and increase in amount.
e.g. foods and raw materials such as timber, cotton, leather, fish…etc. All the plants, animals
and things derived from plants and animals.
-- they are not, however, produced in limitless quantities (i.e. they have a sustainable yield)
Maximum Sustainable Yield (MSY 最高可持續產量) of a population
= the largest number of individuals that can be removed from the population without causing
long-term changes to the population, or
= the highest rate at which a potentially renewable resource can be used without reducing its
available supply throughout the world or in a particular area.
-- if the removal rate exceeds the production rate, their supply is ultimately exhausted. (e.g. over
fishing, the rate of deforestation > the rate of afforestation) So the amount removed should be
equal, or less than, the amount of production (yield)
-- if their harvests is well controlled within the compensatory power of their nature cycle of
renewal, there will be a continuous yield of these resources
(i.e. a sustainable yield can be taken indefinitely)
Over-exploitation leads to a rapid decline in number of plant and / or animal species, probably
resulting in the extinction（絕種）of these organisms and a reduction in species diversity（減低
物種多樣性）.
Examples:
1. Modern fishing always lead to over-fishing（過量捕魚）because sustainable yields have been
exceeded and stocks（儲備）depleted. Such stocks need many years to recover.
2. Over-exploitation of timber（木材的過度開發）would also destroy the natural forests causing
soil erosion resulting in some places turning arid but other places frequently flooded. Many
forest animals lose their natural habitats and a lot of natural ancient trees being chopped down.
A lot of precious plant and animal species become endangered（瀕危） and perhaps extinct
（絕種）. No plants to return O2 back to the atmosphere. The CO2 concentration in the
atmosphere cannot be lowered and this may cause green house effect（溫室效應）resulting in
global warming（全球暖化）.
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ii. Non-renewable resources （不可再生資源）
-- these are resources which are not replaced or regenerated as they are used
-- they are non-living (abiotic) materials
e.g. --- minerals: iron, copper, aluminium
Mineral and metal can recycle（再循環）theoretically, however, in practice（實行）it is difficult
because:
i.
oxidized metal is not suitable for recycling;
ii.
quantities of metal in a product is so small that not worth for recycling;
iii.
most metal is combined with other substances, which are hard to separate them
--- fossils fuels（化石燃料）: petroleum, coal, natural gas

Oil and natural gas supplies can last no more than 50 years because they are being
extracted at a much faster rate than they were formed.

Burning of fossil fuels will produce lots of pollutants（污染物）. Thus humans should try
to use other alternative energy sources.
--- Land
-- there is a fixed quantity of these resources on the planet and has the potential for renewal
only by geological, physical, and chemical processes taking place over hundreds of
millions to billions of years. Sooner or later they will run out.
-- If such a resource is used faster than it is replenished, it can be depleted.
(* Fossil fuels are continually being formed, but the process is so slow compared to their rate
of consumption that for all practical purposes they may be considered as a non-renewable
resource)
1. Over-exploitation of Land
a.
Destruction of ecosystems and extinction of species
-- natural balance of ecosystems are disturbed
 cycling of chemicals is disrupted
e.g. - reduction of organic litter in forest
- removal of carbon dioxide from air decreased as plants ( hence the
photosynthetic rate) reduced
-- natural habitats are destroyed
 extinction of species
e.g. in China, the giant panda is threatened with extinction because deforestation has
destroyed its natural habitat
destroyed by :
i. mining,
ii. deforestation (land clearance),
Deforestation
As a means to clear land for agriculture(農業是林地減少的原因) and ranching
 In order to clear land for agriculture and animal grazing, tree copy（樹冠）and even other plant cover
（植被） are totally removed from the ground exposing the top-soil（表層泥土） which is no longer
protected by the leafy canopy of the forest. This thin layer of top-soil is easily washed away by heavy
rains or blown away by strong wind. This is particularly serious if this happens in steep slope （斜坡）.
 Removal of trees or plants reduces biodiversity（生物多樣性） and habitats.
constructionwithout
and reclamation
Trees always act iii.
as wind-break,
them, soil[AL99-IIC-8]
erosion（土壤侵蝕） by wind also easily occurs.
iv. …etc.
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b. Over-grazing
-deforestation
 - extend grassland
--
growing points of grasses may be destroyed due to over-grazing by herbivores, without plant
cover the land, the soil is exposed to factors (winds, rain…) that cause erosion:
- the sun dries the soil;
- light, sandy soils with limited humus content get blown away by wind, washed away by
rain or runoff
--
trampling of a large population of animals on soil rapidly compact it into a hard layer that can
hardly absorb any rain.
 - eventually the soil becomes dry and is easily blown away or
- soil is therefore washed away to leave bare rocks
c. Agriculture
Agricultural ecosystem is designed to suit man’s own purposes. Therefore it is an Artificial
Ecosystem（人工生態系）.
To meet the demand of the ever-growing human population, intensive farming（密集式耕作）is
taken in many countries.
-- habitat is made very uniform and artificial, natural communities are destroyed, the total number
of species in the habitat is very restricted
 - varieties of species decreased and the environment become unstable and unbalanced
Inappropriate agricultural practices 某些農耕方法對生態系的不良影響
i.
Ploughing（翻土） loosens the soil which can then easily break down into pieces.
ii.
After harvesting several crops without adding humus will greatly reduce the retentivity 儲
水能力 (water-holding ability) of soil so that the soil will dry up quickly and will be blown
away easily.
 once, it is abandoned it will be subjected to erosion and may gradually lose the productive
top soil or even change into a desert
iii. Drastic changes in microclimates of the habitat due to harvesting of crops
iv. overcropping (over-harvesting) and continue to grow the same crop on the same piece of land for
many years thus depleting it of essential nutrients and become infertile; or
v.
artificial treatment of farm land (e.g. change of pH value) changed natural texture of soil and
cause death of beneficial microorganisms inside soil reduce recycle of minerals; or
All the above cases would finally lead to soil erosion（土壤侵蝕）.
Problems resulting from soil erosion:
i.
there is a loss of valuable agricultural land (see the
relationship between soil properties and crop growth) or even
with desertification occurs
ii. the soil washed down to rivers may lead to flooding
iii. loss of valuable native species of plants (or extinction of
endangered species)
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iv. affect local climate indirectly due to the change of local
hydrologic condition
vi. Monoculture（單種栽培 ）
= the practice of planting a single species of crop on a large area of land
 easy management and harvest
chemical control of weeds and pests (化學控制害蟲及雜草)
-- weed (includes plants other than the actual crops) compete with crops for light, water and
nutrients
herbicides (chemical weedkillers 化學除草劑),
e.g. the carcinogenic 2, 4 – D
 control broad-leaved weeds 闊葉雜草(dicot.) in cereals 穀物 (monocot.) by affecting
metabolism and cause death of dicot. But the monocotyledonous plants (crop) remain
unaffected.
-- spread of pests（害虫） that feed on crops
-- After several years of growing a single crop i.e. monoculture on the same piece of land, the
soil will be exhausted of certain essential mineral salts and become infertile. Monoculture
thus need extensive use of fertilizers,
--- once its use exceeds the economical point, the land will be abandoned and will be
subjected to erosion and may gradually change into a desert. The loss of this natural
resource, soil, is very serious.
v. Pests and weeds control
Pests refer to any animals or plants which we find annoying or which damages
or destroys our interest in some way.
They are mostly insects. They are annoying because:
(1) they compete with us for crops
e.g. aphids（蚜虫）, caterpillars（毛虫）, beetles（甲虫）, locusts
（蝗虫）cause enormous damage to crops of all kinds.
(2) they are associated with spread of diseases
e.g.
mosquitoes - malaria（瘧疾）, yellow fever（黃熱病）,
fleas（蝨、蚤）- plague（鼠疫）
Difficulty in control of pests
1.
They have rapid reproductive rate.
2.
They have great mobility（移動能力高）: They are able to move
long distance in search of new food sources
3.
They are often accidentally transported by human from one place to
another..
e.g. in cargoes（貨物）of food and timber
‘ foreign’ pests are most dangerous because of absence of natural
enemies and reach enormous number.
Pests are usually killed by chemical means ( chemical control ) or find other organisms to act
as predators (biological control 生物控制方法) . It depends on the interactions of predators
and preys. Recently more research has been done on the use of steriled males in biological
Human activities and the Ecosystem
control.
P. 6 / 33 16/03/09 04:50 AM
control of pests with pesticides [include herbicides]
Advantages:
1. They are easily transported .
2. They are cheap because they are produced in large quantities.
3. They are easy to apply（容易應用）.
4. They have immediate effect（立即見效）and achieve the maximum possible percentage
kill（可以殺滅最多）among pests.
Disadvantages:
< harmful side-effect > 有害的副作用
1. If pesticides are not specific enough, they may cause death to human, domestic animals
家畜 and pets due to accidental misuse.應用不當
e.g. 150 human deaths per year in USA from insecticides
2. they may cause disruption to ecological systems.破壞生態系
- disturb the food chains as the preys (pests) are removed may cause the lost of
ecological balance
- beneficial soil organisms may be killed due to the wide spectrum of effect of the
pesticides, this may even affect the soil structure and texture adversely.
3. they cause pollution and biological magnification
e.g. Resides 殘餘物質 of some persistent toxic pesticides are quite long-lasting 長久
殘存 in soil or fresh water (e.g. insecticide: dichlorodiphenyl trichloroethane/
DDT 二氯二苯三氯乙烷 / 滌滴涕; herbicide: picloram, the commercial
name, 毒莠定). If they enter the food chains, they may pass from one trophic
level to anther and accumulation and concentration of pesticides along food
chains. They may be stored in concentrated amount especially in fat deposits 脂
肪儲存物 (e.g. over the last 40 years, insecticides have entered food chains in
all parts of the world, terrestrial and freshwater, marine etc. habitats)
4. pest resurgence（害虫再現）
If pesticides are not specific enough, they may kill pests as well as their
predators .There will be a possibility of increasing number of pests once the
effect of pesticides has worn off but the number of predators not yet recovered.
5. Risk of outbreak（爆發）of new pest species after treatment against a familiar one（熟
識品種） because insecticides are more deadly to some species than others.
Predator A
Predator B
Before treatment
Herbivore A
(Pest)
Herbivore B
Plant
Predator A
Predator B
After treatment
Herbivore A
(Pest)
Herbivore B
Plant
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(therefore there is an increase in number and B becomes pest)
6. pest resistance 抗虫
Extensive use of pesticides will lead to evolution（演化）of resistant strain（有抵抗
力的品系）of insect and need to acquire more powerful and toxic pesticides. It is
because the members of a pest species are not equally vulnerable 受到相同的傷害 to
a particular pesticide. They are genetically different 有基因差異 and under the pressure
of natural selection 自然選擇 / 天擇. Besides, genetic mutation 基因突變 provides
extra 額外的 resistance 抵抗力. They develop resistance to the insecticides. Thus it is
necessary to develop new insecticides to kill the new strains 品系 of the pests.
e.g. 1950: < 20 pest spp. were pesticide-resistant 有抗（殺虫）藥性
1975 : < 250 pest spp. were pesticide-resistant
including some populations of malarial mosquito（瘧蚊）,
rats : many food-destroying spp.
vi. Excessive Use of Chemical (Inorganic / artificial) Fertilizers （過度使用化學肥料）
Chemical (Inorganic / artificial) Fertilizers （化學肥料）
 They are mainly in the form of nitrogenous and phosphorus compounds (e.g. ammonium nitrate,
ammonium phosphate, ammonium carbonate, etc.)
Advantages 優點
1. They are concentrated, of known mineral content (constituents 成分, amount, proportions 比例 easily
controlled).
2. They increase the mineral contents of the soil.
3. They act quickly so they must be added immediately before the crop is grown.
4. easy to handle and transported.
5. cheap
Disadvantages 缺點
1. Their production required considerable industrial treatment, hence waste a lot of power.
2. If they are used over a long period of time, the soil will become acidic.
3. They tend to degrade 降低質素 soil structure and, at least, give no improvement to the soil texture 質地.
4. They are not available in a lot of countries and have to be imported 入口 and hence expensive.
5. They contain no humus so that they do not improve the texture (physical properties) of soil.
6. Excessive use of fertilizers will lead to leaching, and causing water pollution and eutrophication of nearby
water sources .
Exercise: [AL98-IIC-7]
1. To increase production in agriculture, man has used various methods based on biological principles. Describe these
methods and the principles behind them. Discuss their benefits and drawbacks.
(20 marks)
(人類依據生物學的原理，用不同的方法來增加農業生產。描述這些增產方法及其所依據的原理，並討論其利與弊。)
-- solutions:
- crop rotation prevent spread of pests (reduce the use of pesticides) and depletion of essential
nutrients on the land
- planting of species with higher resistance to pests
- organic fertilizer provide humus (the slow breakdown of humus releases valuable minerals  better than
easily leaching of fast dissolved inorganic artificial fertilizer) and minerals, assist growth of beneficial
microorganisms and also improve soil texture (humus acts rater like sponge in retaining water and
in this way improves the structure of sandy soils. It equally beneficial to a clay soil where it helps to
lighten the soil by breaking up the clods and thereby improving aeration and drainage.)
Human activities and the Ecosystem
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- set up of windbreak (e.g. trees) surrounding the farmland to reduce soil erosion by wind
d.
The Effects of Urbanisation and Industrialisation（都市化和工業化的影響）
闢地及填海 (住宅及基建) :影響, 本地個案, 利弊, 生態影響
Land clearance and reclamation（闢地及填海）
The increasing population and continuous economic expansion cause large areas of
agricultural land changed to residential, commercial and industrial uses. Examples are found
in the development of the new towns in Sha Tin and Tuen Mun. Land is also reclaimed from
the sea in these two places to acquire more spaces to meet the needs.
Exercise:
1.
Land reclamation in Hong Kong is associated with intensive dredging activities
carried out in the waters of Hong Kong and around Hong Kong. These dredging
activities involve the digging up of the sea floor for sand to reclaim land. Discuss the
impact of these activities on marine organisms and on the marine ecosystems of the
dredged and reclaimed areas.
(20 marks)
香港的填海工程，涉及在本港和鄰近海域進行龐大的挖泥作業，從海底挖沙造陸。這些
工程對海洋生物在挖泥區、填海區的海洋生態系統有何影響？試加以討論。(20 分)
[AL99-IIC-8]
2.
Debate on the pros and cons of the development of a local infrastructure.
辨論本地大型基建發展的利與弊。
3.
Analyse the pros and cons of urban and industrial developments on the ecosystem.
分析市區和工業發展對生態系的利與弊。
Besides the effects listed above, urbanization and industrialization will also cause air and water
pollution.
Human activities and the Ecosystem
8.
8.
P. 9 / 33 16/03/09 04:50 AM
[HKALE 99 IIC]
Land reclamation in Hong Kong is associated with intensive dredging activities carried out
in the waters of Hong Kong and around Hong Kong. These dredging activities involve the
digging up of the sea floor for sand to reclaim land. Discuss the impact of these activities
on marine organisms and on the marine ecosystems of the dredged and reclaimed areas.
香港的填海工程，涉及在本港和鄰近海域進行龐大的挖泥作業，從海底挖沙造陸。這些工
程對海洋生物在挖泥區、填海區的海洋生態系統有何影響？試加以討論。(20 marks)
[Bonus mark should be given to examples of specific sites, organisms or specific
infrastructural development in Hong Kong (e.g. airport project)]
(a) Destroy the habitats of marine organisms
 loss of marine habitats along the original shore line due to reclamation
 loss of breeding ground or feeding ground of many species such as horseshoe-crab
 loss of shore animals
 loss of specific environment such as protected or semi-protected bays
 destroy the unique habitat of endangered species
(b) Directly kill marine organisms by
 burying the animals as a result of dumping of soil at the reclaimed sites
 mechanical damage due to dredging activity
 remove the organisms from the sea bottom during dredging and then disposing them
with the soil at the reclaimed areas
(c) Discharge a lot of suspended solids in the water column
 reduce light penetration in the water column
 affect photosynthetic activity of phytoplankton due to low lighting conditions
 affect zooplankton conununity that graze on phytoplankton
 further affect predator community such as fish and the entire food web
 directly clog fish gills
 affect feeding of benthic suspension / filter feeders
 smothers corals
 high turbidity affects visibility of animals, thus affects their feeding
(d) Release nutrients / chemicals into the sea
 nutrients in the sediment is released into the water column, causes eutrophication,
increase phytoplankton productivity
 release heavy metals into the water column
 release organic pollutants into the water column
 affect microbial loops recycling
(e) Affect the life of marine animals and their behaviors due to underwater dredging
activity
 noise pollution in the ocean - affect sonic communication of organisms e.g. dolphin
 changes. in benthic community, affect migration of many organisms
(f) Reclaimed land creates new habitats for new colonizers



max.5
max.3
max.6
max.4
max.2
max.3
newly-claimed shore line provides new habitats for new colonizers
new habitats allow the establishment of new ecosystems - new community
structures
new interactions among species, new food web
max.2
(g) Changes in shore line affects flow pattern and flow rate of water
 increased wave action in harbour (Victoria Harbour) due to excessive reclamation
 change food web and marine ecosystem
content:max.15
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2. Over-exploitation of Water resources
- water resources can be divided into rainfall, ground water, and surface water resources.
- Improper management of water resources may lead to
-- water pollution,
-- reduction of area of lakes,
-- reduction of water table of aquifer, or
-- even drying up of water sources.
- shortage of potable water supply,
- reduction in yield of fish stock
- replacement of valuable native species by pollution adapted species
( diversity reduced)
- solution:
-- conserve the environment around the water sources and water channels
-- prevent water loss for sources
-- reservoir for water from rainfall
-- proper management and sharing of potable water (water for washing, drinking, waste disposal
and as industrial water.
--reuse waste water after proper sewage treatment processes
3. Deflected succession 偏途演替
-
4.
normal succession has been artificially changed
the resultant plagioclimax is not true climax but sub-climax ones resulting from human activites
e.g. around 4000 years ago much of lowland Britain was a climax community of oak woodland, but most of this
forest was cleared to allow grazing and cultivation. The many heaths and grasslands which we now refer to as
‘ natural ‘ are the result of this clearance and subsequent grazing by animals but not true climax communities.
Exotic species carried by human
TV : evolution IV
外來生物入侵——生態系統的癌變
(http://202.130.245.40/chinese/2001/Dec/86463.htm)
5. Pollution
- Definition should take account of:
-- addition of a substance to the environment at a rate faster than the environment can
accommodate it
-- substance (may in forms of chemicals or energy like heat, sound, α-particles, β-particles,
and X-rays) with natural level exceed certain critical values can be considered pollutants
which are potentially harmful to life
 So,
Pollution
= any undesirable change in the physical, chemical and biological characteristics of our
environment as a result of man’s activity
Pollutants（污染物）
= are particular chemical or form of energy that can adversely affect（不良影響） the
health, survival, or activities of humans or other living organisms e.g. SO2,
particulates（微粒）.
* While exploitation of various resources causing adverse effect to the environment, actually
human activity always increases the disposal of the above undesirable substances to a level
that cannot be absorbed by the nature
Human activities and the Ecosystem
- Types of pollution (mainly have 4 kinds)
i. Air pollution
ii. Water pollution
iii. Land pollution
iv. Noise pollution
P. 11 / 33 16/03/09 04:50 AM
Identify the most air-polluted area in Hong Kong based on the available information from the
Environment Protection Department.
i. Air Pollution 解決及個人角色; API (見中五列表筆記)
- existed since human first used fire but it is only since the industrial revolution in 19th century that
its effect have become significant
- Air pollutants are mainly emitted from the combustion of fossil fuels in industrial plants, power
station, incineration（焚化爐）, oil refineries（煉油廠）and internal combustion engine of motor cars.
(Fig 9) Harmful Effects of Air Pollutants on Trees
Human activities and the Ecosystem
a.
P. 12 / 33 16/03/09 04:50 AM
- Types of air pollutants and their effects
Particulate air pollutants（空氣污染微粒）
- has multiple components: sulfate salts, sulfuric acid droplet, salt of metals, dust from finely
divided particles of carbon or silica …etc.
- decrease photosynthetic rate of plants since:
-- reduce light intensity at ground level and, thus,
-- deposits of particles may coat plant leaves, especially plants with rough and hairy leaves
can easily trap smoke or dust particles that will weaken their survival value
 - blocking stomata and decrease gaseous exchange rate
- preventing light penetrating into mesophyll
-- deposited on clothes, cars and buildings
- although rain generally tends to clean particulate matter out of the air, it is not very effective
in removing pieces smaller than 2um in diameter
- once a particle gets inside the lungs (<10um, greatest efficiency 2-4um) its effect depends on
its chemical nature.
- Incomplete combustion may produce carbon particles and tarry（含焦油的）hydrocarbons.
These visible particulate substances constitute smoke
1) Smoke
= tiny carbon particles of soot and ash suspended in the air produced by incomplete
combustion
 - blacken alveoli causing damage to their delicate epithelial linings,
also aggravates respiratory ailments, e.g. bronchitis
-- Smog (smoke + fog) （煙）
formed when smoke together with exhaust fumes are trapped in a fog during temperature
inversion
e.g. 1952 The great London smog:
- visibility was reduced to one meter, also reduce light intensity that in turn will
decrease the rate of photosynthesis.
- killed 4,000 people in one week’s time, mainly elderly, new-born, and patients
suffered from respiratory diseases, particularly bronchitis
中: 生物學探究 P. 468 大氣污染的控制
2) Dust（塵）
-- consists of particles larger than that in smoke
-- thus it easily settles out from air
 - act as lung irritants causing respiratory diseases
- e.g. asbestos（石棉） dusts are carcinogenic that may lead to lung cancer
- Dust will block the stomata of leaves and thus reduce photosynthesis.
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Thermal inversions:
i. radiation thermal inversion (ground inversion)
- ground is cooled at night by thermal radiation
- these are normal nighttime phenomena and are usually destroyed by the
morning sun which peeks over the horizon. However the inversion may
hangs on if the ground air is cooled too much or because of clouds.
ii. subsidence inversion
- upper air masses compress ( in high- pressure areas) lower air masses
upper portion of lower air mass is compressed more and thus heated more
-
may last several days or longer
 pollutants produced from ground rise with warm ground air up to the inversion
layer then stops rising due to the warmer air in the inversion layer above or
around it
convection halted and pollutants trapped
(Fig 2) Normal Air Condition
(Fig 3) Thermal Inversion Occurs
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b. Gaseous air pollutants
1) Sulphur dioxide
-- about 70% of sulphur dioxide in atmosphere comes from the decomposition of vegetation,
while the rest comes from man’s activity
-- acidic gas
 - causes respiratory disease by irritation of respiratory system and damage to the
epithelial lining of alveoli
- also irritate the conjunctiva of the eye
- more harmful to plants than animals:
-- it diffuses through stomata and dissolves on the moist mesophyll cells to from
sulphurous acid which disrupts photosynthesis
( reduce growth of many plant and thus decrease the crop yield)
- plants have different degree of tolerance to sulphur dioxide
e.g. Lichen distribution:
- very sensitive to polluted air because it may be killed in a small trace of
sulphur dioxide in air
- the tolerance of lichen and moss species to sulphur dioxide is very variable
 act as an indicator organism for measuring sulphur dioxide pollution
- about 1/3 dissolves in rain water to form sulphurous and sulphuric acids. ( sulphur
dioxide can also react with ozone, hydrogen peroxide, water vapour and other
substances in atmosphere to form sulfuric acid) The rain therefore has a low pH and is
known as acid rain
 - corrode metals, marbles, paper and textiles
- increase acidity of soil
- decrease soil fertility because
-reduce bacterial activities
-leaching of minerals
( water pollution, e.g. accumulation of Al in lakes affect the gills
and osmoregulatory mechanism, and hence, kill many species)
 plants produce smaller leaves and crop yield decrease
- plants may even cannot grow in acidic soil
- can reduce sulphur dioxide emissions through:
- *‘cleaner’ fuels, e.g. natural gas; or
- fitting desulphurization units
 remove sulphur dioxide from the flue gases at power stations
* Fuels vary greatly in their sulfur content:

high sulfur coal from certain areas might have as much as 5% sulfur
low-sulfur fuels are those with less than 1% sulfur content
natural gas contains only trace amounts of sulfur
control on sulfur dioxide emissions from plants, factories, power generating station … is necessary.
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Acid Rain





Natural precipitation is slightly acidic with a pH of 5.0-5.6. However, most rainfall in
United States is now with a pH of 4.3, which is 100 times more acidic than normal rain.
Acid rain is formed by reaction of nitrogen dioxide and sulphur dioxide with water, forming
nitric acid and sulphuric acid.
Acid rain reacts with the soil and leaching out large quantities of the calcium and
magnesium salts.
Acids also dissolve out and mobilize some toxic elements such as aluminium and
contaminate both the soil surface and the groundwater.
Acid rain increases the acidity of soil. The acidic soil will reduce the bacterial activities and
this reduce the soil fertility. As a result plants produce smaller leaves and crop yield is
reduced. The soil around some industrial areas may become so acidic that plants cannot
grow.
(Fig 8) Formation of Acid Deposition and Its Effects

Most freshwater lakes, ponds, and streams have a natural pH in the range of 6 to 8,
acidification of this freshwater bodies leading the aquatic lives inside become severely
stressed, and many die.

Acid rain will corrode（腐蝕）metals, marbles（大理石）, paper and textiles. It also
deteriorated artifacts（人工製品）. Limestone（石灰岩） and marble are favored materials
for the outlining of buildings and for monuments（紀念碑 / 紀念物）. The reaction
between acid rain and limestone causing these structures to erode at a accelerated pace.
The acid gases such as oxides of sulphur and nitrogen also cause respiratory diseases of
man.

Human activities and the Ecosystem
2) Carbon dioxide
-- formed during
P. 16 / 33 16/03/09 04:50 AM
- respiration of organisms
(usually not accumulate because of photosynthesis)
- burning of fossil fuels and other carbon-containing materials
-- no direct health effect but
The natural removal of carbon dioxide cannot keep pace with the production rate of carbon
dioxide by human activities. The excess carbon dioxide is suspected to be the main
contributor to green house effect.

increase atmospheric carbon dioxide concentration and prevent more of the sun’s heat
(infrared radiation) escaping from earth, much in the way the glass in a greenhouse does
resulting in increase of air temperature (i.e. Greenhouse Effect)
gradual melting of polar ice caps
consequent rise in sea level
expansion of oceans and flooding of low-lying land
* other greenhouse gases: e.g. water vapour, methane and nitrogen oxides
but carbon dioxide contribute most to global warming and remains in air much longer than these gases
(carbon dioxide about 100 years; methane about 10 years; carbon monoxide about few months)
- it is estimated that the present concentration of carbon dioxide of 0.033% will be increased
up to 0.045% in the year 2050 and average global temperature is increased by about 3oC to
4 oC
 individual plant and animal species would be much affected,
- particularly in their areas of distribution
- others e.g. -- extra generation of insects in longer summer;
-- more male lizards and more female turtles
(because sex ratio in these organisms is determined by nest temp)
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Effects on weather, climate and atmospheric processes
Global warming (Warming of the Earth) 全球暖化
Global warming is an increase in the average temperature of the Earth's atmosphere and oceans.
The term is also used for the scientific theory of anthropogenic global warming, which attributes much of the
recently observed and projected global warming to a human-induced intensification of the greenhouse effect.
Greenhouse effect（溫室效應） and global warming（全球暖化）

Greenhouse effect is a natural effect that traps heat（infra red 紅內線）in the atmosphere near
the earth’s surface. Some of the heat flowing back toward space from the earth’s surface is
absorbed by water vapor, carbon dioxide, ozone, and several other gases in the lower
atmosphere and then radiated back toward the earth’s surface resulting in the increase of
atmospheric temperature (Global Warming).

Greenhouse gases are gases in the earth’s lower atmosphere that cause the greenhouse effect.
These include carbon dioxide, chlorofluorocarbons (CFCs), ozone, methane, water vapor,
and nitrous oxide.

Main source of greenhouse gases come from combustion of fossil fuels, burning and
removal of tropical rainforest.
(Fig 7) Greenhouse Effect and Global Warming


Since 1860, the average global temperature has risen 0.4 - 0.7oC.
It is estimated that the present carbon dioxide concentration of 0.033% will be increased up
to 0.045% in the year 2050 due to industrial activities and the average global temperature is
increased by 3oC to 4oC.
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Effects of global warming: Increase in average global temperature will lead to changes in
climate.
(1) causes the melting of ice in the polar regions and hence the rising of the sea level resulting in
the loss of land and terrestrial habitats for many terrestrial organisms living in the lower areas
or by the sea shore. This would lead to the rising of sea levels and flooding, and loss of
biodiversity.
(2) Increases the instability of the global weather pattern. Eventually, these changes will cause
droughts, increased rainfall and storms in certain areas,
(3) Has severe adverse effects on organisms living in the higher altitude and attitude. This in turn
will seriously threaten the global food production.

The following methods can help to slow down the global warming progress:
a. Reduce the use of fossil fuel (especially coal);
b. Improve energy efficiency;
c. Shift to renewable energy resources;
d. Reduce deforestation;
e. Use sustainable agriculture;
f. Slow population growth.
Human activities and the Ecosystem
3) Carbon monoxide
P. 19 / 33 16/03/09 04:50 AM
Although human beings contribute only about 10% of CO load dumped into atmosphere (naturally produced
from decaying material, forest and grass fire, and volcanoes), it is a problem because most of what we generate is
dumped into the areas in which we also live and breath.
-- mainly occurs in exhaust emissions from cars and other vehicles
-- due to incomplete combustion of fuels
-- poisonous due to higher affinity for haemoglobin (250 times greater) than that of oxygen
irreversibly form a stable compound carboxyhaemoglobin（碳氧血紅蛋白）, prevent
oxygen combining with haemoglobin, leaving non to transport oxygen and reducing the
oxygen carrying capacity （氧容納量）of blood making the body unable to get sufficient
oxygen
- carbon monoxide concentration in air up to 0.5% causing dizziness and headache, or
even fatal when in continued inhalation of up to 1% in air
-- can be break down by certain bacteria and algae
--solution:
adjustments in combustion processes to allow more complete combustion of fuels
eg. Increase the air-to-fuel ratio in the internal combustion engine.
4) Nitrogen oxides
-- produced by the burning of fuel in car engines and emitted as exhaust and
wherever temperature are high enough to cause atmospheric nitrogen and oxygen to
combine
Oxides of N :
 Nitric oxide and nitrogen dioxide are the major nitrogen air pollutants.
 Nitric oxide has a similar effect to carbon monoxide in that it decreases the blood’s ability to hold oxygen.
 Nitrogen dioxide will form nitric acid with water, which is one of the components of acid rain.
 Nitrogen dioxide irritates the eyes, nose and lungs and high concentrations can prove fatal.
 Nitrogen dioxide trigger the reaction which produces photochemical smog.
-- acidic gases, e.g. nitrogen dioxide
 contribute to acid rain and causing respiratory diseases in man
-
nitric oxide (NO) is not very harmful and does not do much damage because it cannot readily dissolve in
water or in tissue. However through action of sunlight, it with react with oxygen to form nitrogen dioxide
-- contribute to the formation of photochemical smog
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Photochemical smog 光化毒霧
 A temperature inversion（ 逆溫現象）traps pollutants at high concentration near the surface.
Photochemical smog is formed when these air pollutants, such as smoke and exhaust fumes,
react with hydrocarbons and nitrogen oxides under the influence of sunlight (UV) to produce
a complex toxic mixture including ozone, peroxyacyl nitrates (PANs)
/ 硝
, ozone and various aldehydes（醛）. All these harmful and dangerous
substances are trapped in a fog and it can be fatal.
 Photochemical smog will cause severe eye-irritation, damage mucous membranes（黏膜）and
kill plants. The great London smog killed 4,000 people in 1952 within one week’s time.
(Fig 1) Formation of Photochemical Smog
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5) Photochemical oxidants
Ozone
is an indicator of the presence of the family of photochemical oxidants that make up
photochemical ‘smog’ (as ozone account for as much as 90% of oxidant chemicals in
smog)
- pollutants are trapped at high concentration near the surface by a temperature inversion
- under intense sunlight, the UV light causes pollutants, particularly nitrogen oxides and
hydrocarbons to under go photochemical reactions to form Peroxacyl nitrates (PAN)
and ozone (O3) (there are other products as well)
UV ray
nitrogen oxides + hydrocarbons ------------------- > PAN + O3
( motor car exhausts)
- first reported in Los Angeles in 1946
- PAN and ozone will cause -- severe eye-irritation,
-- damage mucous membranes, and
-- kill plants
-
in nature: oxygen molecules absorb ultra-violet radiation to oxygen atoms that eventually go to form
ozone
but this occurs to a significant extent only high in the atmosphere and does not reach the earth’s
surface
NO2 (a efficient uv absorber) absorbs UV and photolysed
If no other factors involves, O3 break down as quickly as it is formed
NO2 + O2  NO +O3 (reversible)
6) Lead
-- most lead in the air is emitted from car exhausts since tetraethyl lead (TEL) is added to
petrol as an anti-knock agent to promote the efficiency of the motor cars
-- It is accumulated along food chains and can reach toxic levels for human and other
organisms.
-- small amount can be eliminated in urine and faeces, however, any excessive intake will be
accumulated in the bones
-- adverse effects:
- digestive problems e.g. intestinal colic
- impairing the functioning of the kidney
- nervous problems, including convulsions
- brain damage and mental retardation in children
* ‘unleaded fuel’ with anti-knock agent without lead may contain higher level of benzene that
is carcinogenic and more harmful than lead
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7) Chlorofluorocarbons (CFCs)
-- a family of chemicals containing chlorine, fluorine and carbon
-- the best known chemical of that depleting the ozone layer:
- chlorine break down ozone
- each spring a hole the size of the USA appears in the ozone layer over Antarctica in
1989
- depleted ozone layer causes increase in the incidence of skin cancer caused by
Ultra-violet radiation
(since ozone layer between 15 and 40 km above the earth act as a shield, protecting the
earth from the potentially harmful ultra-violet radiation from the sun.)
* C.f.: ozone, generated by car exhaust system, close to the earth’s surface causing
damage to plant tissues in crops and trees
-- CFCs are used in
- in refrigerator coolant,
- as propellants in aerosol sprays,
- make up the bubbles in many plastic foams,
e.g. expanded polystyrene
- deodorants, and
- fly killer
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Ozone depletion（臭氧層損耗）

Stratospheric（平流層的 / 同溫層的）ozone layer lies 25-30 km above sea level in the
atmosphere. It acts as an ozone shield（阻隔層）, as it absorbs over 99% of UVB (which is
more energetic and therefore more dangerous) radiation from the sun.

However, there is serious concern because this shield seems to be breaking down. In 1985,
some British atmospheric scientists reported a gaping ‘hole’ (actually thinning)in the
stratospheric ozone shield over the South Pole. A hole the size of the USA appears in the
ozone layer over Antarctica（南極圈）in 1989. A similar hole was found to have appeared
over the Arctic（北極圈）.

If UV penetrates the atmosphere and being absorbed by biological tissues, UV radiation
damages protein and DNA molecules at the surfaces of all living things.

UV also responsible for all the sunburns and more than 700,000 cases of skin cancer and
precancerous ailments per year in North America, as well as inhibiting the growth of plant
crops.

The damage is believed to be caused by humans releasing into the atmosphere a family of
chemicals containing chlorine, which are known as chlorofluorocarbons (CFCs)（氯氟化
碳）.
Because of the low boiling points of cfc’s, and because they are non-reactive, nontoxic, non-caustic,
non-corrosive and non-flammable, they are in many ways, ideal for use as aerosol can propellants, as
solvents (cleaning agents)…etc.
However the non-reactivity allows them eventually reach the stratosphere where they interact with
UV to release Cl atom which then react with and continuous converse ozone into oxygen.
One chlorine atom has potential to eliminate tens of thousands of ozone molecules.
Chlorine atom persist until it drifts low enough with Cl-reservoir molecules to be washed out in rain.
Even if CFC production stopped today (1987) , the removal of ozone would continue for ‘at least
another century’.

CFCs would be break apart under the intense UV radiation and releasing free chlorine
radicals. The free chlorine radicals then break the ozone layer.
CFCl3 + UV —————>
Cl
+ O3
ClO + ClO

Cl
+ CFCl2
—————>
ClO + O2
—————>
2Cl
+ O2
Every chlorine atom in the stratosphere has the potential to cause the breakdown of 100,000
molecules of ozone.
Following a world conference in 1989, it was decided to ban all use of CFCs by A.D. 2000.
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8) Fluorine
-- released during the industrial production of phosphate fertilizers, steel, aluminum and brick
-- is a persistent pollutant that can undergo biological concentration of up to 2,000 ppm in
grasses
 when highly contaminated grasses are eaten by grazing animals, the animals will have
swollen joints, softened bones and eventually die
(because excessive fluorine inhibits enzyme activities)
Fluorine is a very reactive oxidant that is capable of reacting with and impairing
enzymes and other chemicals.
A little fluoride helps strengthen teeth (hence fluoride toothpaste and fluoridated
water), but too much can cause disruption of phosphocalcium crystal formation and
produce mottled teeth.
In excess, fluoride actually decalcifies bones and teeth, making them brittle.
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ii. Water Pollution
= the addition of undesirable matter into water that contaminates and deteriorates the quality of water
due to human’s activities and makes it unsuitable for man’s uses in respect to drinking, washing, irrigation（灌溉）,
industry and recreation（文娛）or to support aquatic life.
- Causes of water pollution
usually water gets polluted because it can wash away wastes, including heat, and the sewage is
discharged into rivers and sea before adequately treated:
a. Domestic wastes
human sewage, refuse and detergents
b. Agricultural wastes
manure of poultry and pigs, pesticides and excessive fertilizers
c. Industrial wastes
organic matter, detergents, poisonous chemicals, hot water, oil and suspended particles
d. excessive slit from erosion of watersheds that discharged into water sources
caused by improper control of soil during agriculture practice, overgrazing, mining and
timbering
[淡水溪流或海邊污染物類別, 來源及影響]
- Important types of water pollutants
a. biological agents
b. chemicals that enrich and overenrich water ( both organic and inorganic chemicals)
c. chemical toxins
d. heat
e. suspended solids and liquids
f. suspended or sedimentary solids
g. radioactive substances
* Some pollutants are actually beneficial to water quality and aquatic ecosystem in small amount.
Other types of pollutants are harmful at almost any level
(energy or ‘nutrients’ Vs toxic substances)
a. Biological Agents
-- in any case, the problem of waterborne disease can be simply and somewhat grossly stated as the
contamination of human’s drinking water with human’s disease organisms-bearing waste
-- example of these biological agents:
- vibrio cholerae,
- salmonellas,
- E. coli of pathogenic types,
- Hepatitis virus A
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b. Chemicals that Enrich
1) Energy-rich organic chemicals
-- in itself, the organic chemical is harmless, but it acts as a food source for many saprobiontic
organisms (decomposers), especially bacteria
-- aerobic saprobionts decompose the organic material into simple inorganic compounds (e.g.
CO2, H2O, No3-, SO32-, Po43- …etc.) and in so doing use up oxygen in water
(i.e. Self-purification of water 水的自我淨化)
If the amount of organic pollutants is small and the water is well aerated, they are rapidly decomposed by aerobic
bacteria and fungi into simple inorganic compounds which are beneficial to aquatic plants.
-- Biochemical oxygen demand / biological oxygen demand (BOD)
= a quantitative expression of the oxygen-depleting impact (via the action of decomposers) of
a given amount of organic matter
(i.e. how much oxygen is needed (in mg per litre) for microbes to oxidize that organic
matter present in a sample of water kept at 20 oC for 5 days)
- The higher the BOD (i.e. higher oxygen demand) the higher is the degree of organic
pollution. [比較淨水及污水的含氧量 (數據收集儀)]
- the inorganic nutrients are beneficial to aquatic plant and the consumed oxygen can be
replenished by oxygen dissolved from air and these released by aquatic green plants
- the degree to which pollution by organic material will remove oxygen from water depends
on a number of factors:
-- the amount of oxygen in water (inversely proportional to water temperature)
-- the amount of water (greatest in ocean) receiving the waste discharge
-- current or flowing rate of water
-- temperature of water (affecting activities of decomposer and hence the rate of oxygen
removal for decomposition)
-- the amount of sewage being discharged in a given time
--
Anaerobic decomposition（缺氧分解）of organic matter
- if the BOD is great enough to remove entirely the dissolved oxygen (near-absolute
depletion of oxygen), aerobic species including aerobic bacteria（需氧細菌）, fish and
zooplankon die due to suffocation（窒息） and the presence of poisonous gases.
- dead bodies decomposed makes the conditions worse and leaving only anaerobic ones.
- anaerobic bacteria becomes active and they will undergo incomplete decomposition （不完
全分解）of the organic matter in the absence of oxygen
 - as a result, some poisonous gases such as methane, ammonia and hydrogen sulphide
will be produced to give a very unpleasant smell
- it also help in the spreading of pathogenic （致病）organisms
e.g. cholera and typhoid
- the population levels of animal species vary according to their level of oxygen in the water.
These organisms act as indicator species (or index species) for polluted water
 - to indicate the relative degree of pollution
- water polluted with organic matter has lower oxygen content so that the more
sensitive organisms disappear, whereas the detritus feeders, particularly if they can
tolerate the low oxygen level, grow prosperously
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(Fig 10) BOD, indicator species found and pollution
E. coli ------- Indicator Organisms（指示生物）found in Aquatic Pollution（水污染）
Escherichia coli (E. coli)（大腸桿菌）is an indicator organism for aquatic organism for aquatic
pollution It is an non-pathogenic organism which lives in the intestine and being discharged with
faeces. Thus the coliform（大腸桿菌的）count can be used to measure the faecal pollution, and the
relative amount of pathogenic organisms.
What is the biological principles behind which some organisms can be used as pollution
indicators? 一些生物可作為污染指標的生物學原理？
Criteria for selecting organisms to act as a pollution indicator:
1. The indicator organisms should be very commonly found in the polluted or unpolluted
environment.
2. The polluted chemicals / substances being tested must not be toxic to the indicator organisms
so as to kill all the indicator organisms once when the substance is present.
3. The indicator organisms must be very sensitive to the polluted substances to give a very quick
response.
4. The population size of these indicator organisms should be directly or inversely proportional
to the concentration of the pollutants being tested.
In addition to the above requirements,
E. coli is chosen as the pollution indicator as it is found inside the human colon and, together with
the faeces, pass out of the body. Hence, the concentration of E. coli in a certain volume can
indicate the extent that the water body is polluted with organic wastes, faeces in this case.
* 香港環保署的泳灘水質等級 污染溪流的指示生物為污染指標的生物學原理, 數據分析
Human activities and the Ecosystem
see Sewage Treatment plant (P.472 生物學探究)
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8. Waste treatment and proper disposing
 remove the pollutants by treatments, or reduce the adverse effects caused by pollutants in wastes
onto the environment
- Sewage Treatment Plant
sewage is treated to different stages and by different processes
a.
Primary Treatment
during this treatment the solid matter and suspended particles are removed away (by physical
method)
i. Screening
sewage passes through a sieve (grid) which screens out bulky solid matter such as bottles,
paper, sticks and stones
ii. Sedimentation (settling)
the suspension flows into the sedimentation tank where the large particles of organic matter
settle down at the bottom as primary sludge within 10 hours. Some fats and wood will float
on the surface. These scums are skimmed off
b.
Secondary Treatment
during this treatment the organic matter in effluent is oxidized to harmless forms (involve
biological system)
i. Activated sludge method
- the effluent introduced into the aeration tank is aerated by either violent mechanical
stirring or by the bubbling of compressed air through the fluid. This encourages the
growth of bacteria and protozoa to consume much of the organic matter of the sewage
- the sewage is passed into a settlement tank where micro-organisms and large particles
settle down as sludge. The effluent is chlorinated and discharged into river
ii. Sludge digestion chamber (fermentation tank)
- the sludge in this chamber undergoes anaerobic decomposition to produce carbon dioxide
and methane. Methane can be used as fuel for power generation of for heat
- the remains of sludge can be dried and used as fertilizer
c.
Advanced Treatment
during this treatment the fertilization elements, mainly inorganic phosphate and nitrates are
removed to reduce the danger of eutrophication (chemical precipitation  filtration)
*Like most sewage treatment works, treatment process at Shatin treatment plant involves primary and
secondary treatment only.
[* 不適當污水處理引起的問題 - 水質變壞, 水資源受微生物威脅]
Human activities and the Ecosystem
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2)
Inorganic chemicals that enrich
- e.g. phosphates and nitrates added to aquatic ecosystems directly or, indirectly in the form of
phosphorus- and nitrogen- containing organic pollutants
- Detergent
-- old types of detergents (soapless) are non-biodegradable as they contain branch-chained
molecules
-- they cause foaming in rivers and lakes
 - this floating mass (‘swans’) decrease penetration of light to submerged plants
- impedes the movement of the surface dewellers
- put sewage treatment plant out of action
(soapy only foaming in fresh water)
-- many detergents today contain phosphates as builders to reduce hardness of water and hence
increase the efficiency of foaming of the soapy detergent
 cause eutrophication in rivers, lakes and streams
-- even detergent as low as 0.1 ppm (parts per million), reduces the rater of oxygen dissolving in
water by 50%
- Excess Artificial fertilizers
-- nitrates and phosphate in fertilizers pollute water and contribute to eutrophication and plant
growth
-- increase nitrate content of water in reservoirs, in the order of 8 or 9 ppm can cause a human
disease methaemoglobin anaemia in babies
(because oxyhaemoglobin is modified  reduce oxygen carrying capacity of blood)
c. Chemical toxins
- pesticides (agricultural) [e.g. DDT --- see Understanding Biology: P.376-378; 生物學探究:
P.476] and heavy metals (e.g. mercury, industrial)
-- from argicultural and industrial discharge respectively
-- may accumulate along food chain and poison man or other non-target organisms
生物學探究: P.474
(Fig 11) Biomagification from chemical pollution
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-- Eutrophication (overfeeding of aquatic ecosystem)
= a natural process during which the concentration of nutrients (salts) builds up in bodies of
water
生物學探究: P.474
It occurs largely in lakes and the lower reaches of rivers. The salt accumulate until an
equilibrium is reached where they are exactly counterbalanced by the rate at which they are
removed.
Oligotrophic
= water with low (nutrients) salt concentration
 limiting plant growth
Eutrophic = water with high (nutrients) salt concentration
 much less limitation on growth
- eutrophication cause plant growth or even abnormal algal bloom occur where the waters
become densely populated with species of algae and blue-green bacteria (Cyanobacteria) in
particular
 - density of these blooms increases to a point where light is unable to penetrate to any
depth.
algae in deeper regions of lake are unable to photosynthesis and die
decomposition of dead algae by aerobes creates a considerable BOD resulting in
deoxygenation of all but the very upper layers of the water
aerobic life in the lower regions die
(* ironically, plant increase oxygenation due to photosynthesis; plant respiration and
decomposition of dead plant material consume oxygen)
- green algae growth limited by nutrients content in water, but blue-green bacteria can
fix atmospheric nitrogen and cause more serious effect
Effects of Eutrophication:
encourages the growth of floating plants forming a thick mat (氈) which
i/ will reduce the penetration of light to the submerged plants.
ii/ on a cloudy day or at night will compete with fish for dissolved
oxygen. The depletion of the oxygen content may kill the fish as well
as the submerged plants. The decomposition of the dead bodies
further deplete the oxygen content of water down to zero.
iii/ may interfere both navigation（航道）and irrigation（灌溉）.
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- Red tide
= a population explosion, or bloom, of dinoflagellates
(http://www.info.gov.hk/epd/tc_chi/laws_regulations/envir_legislation/laws_overvi
ew.html
- it is not known what environmental conditions initiate blooms, but they are more
common in the warm waters of late summer
- dinoflagellates:
-- one of the most important groups of producers in aquatic ecosystems
-- belongs to the protoctista
-- most species are marine
-- a few of the dinoflagellates are known to have occasional population explosions
or blooms
-- these bloom frequently colour the water orange, red, or brown and are known as
red tides
-- some of the species that form red tides produce a toxin that affects the nervous
system of fish, leading to massive fish kills
-- some other species that produce a toxin are eaten by mollusks, which apparently
are not harmed, however, the toxin accumulates within their tissue making them
poisonous to humans.
It is not known what environmental conditions initiate blooms, but they are more
common in warm waters of the late summer. It is thought that the concentrations of
nutrients released from sewage may become so high that they cause eutrophication
which may promote red tide.
-
The salts necessary for eutrophication of lakes and rivers are largely nitrates and phosphates from 3
sources: (Understanding Biology. P.375; 生物學探究 P.475)
1. leaching from surrounding land
2. Sewage
- soluble phosphate from detergent and sewage discharge after secondary (or tertiary)
treatment
- solutions: reduce phosphate content in detergents and remove phosphate by
advance sewage treatment.
3. Fertilizers - major constituent of inorganic fertilizer is nitrate which is highly soluble and
readily be leached
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d. Floating Solids and Liquids
- reduce light penetration
- retard the diffusion of gases such as oxygen
- contribute to BOD
- may concentration toxin in water and deliver these to filter-feeding organisms
(e.g. oil droplets can accumulate fat-soluble toxins such as DDT)
- e.g. Oil
- either due to illegal washing at sea of storage tanks of oil tankers or accidental
spillage
-- coats and prevent photosynthesis and kills seaweeds
-- covering the seashores kills seaweeds, molluscs and crustaceans.
-- covers the gills and interfering with feeding and respiration of shellfish
-- kills sea birds due to
--- feathers soaked with oil making them cannot fly
--- ingest poisonous level during cleaning feathers
--- interferes insulation function of feather of die of cold or pneumonia
(hypothermia)
-- contaminate beaches and spoils valuable recreational resource
- effect are localized, temporary and shores commonly recover within two years,
however, increase ecological damage when cleaning by:
-- spraying detergent  toxic
-- sawdust or chalk used  creating new disposal problem: sunken oil may smother
（窒息）the bottom dwelling organisms
- some of the latest methods include the use of microorganisms that can degrade oil
e.

Suspended or sedimentary solids
From naturally runoff, contributed by agriculture and industries like the china (clay) industry,
construction and reclamation
-
silt and other types of insoluble materials clog waterways
fill up dams
make water cloudy or muddy
cause physical problems for gill breathers (e.g. fish) and filter feeders (e.g. clams)
by adsorption and in other physical and chemical ways, suspended organic and mineral solids can
also concentrate metals and other toxins and then deliver them to various organisms in the food
chain. (e.g. pesticides can be concentrated in and on suspended
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f. Heat / Thermal Pollution（熱能污染）
- from cooling system of power stations or industry
- high temperature reduce oxygen dissolve in water but may compensate by spraying of water
in cooling towers
- increase solublity of certain chemicals
- determine distribution or even disappear of life forms with different temperature tolerance,
hence the species composition of an aquatic habitat
( because high specific heat of water buffers the temperature changes, aquatic organisms are
less tolerant of temperature fluctuations generally)

main effect is to alter balance of river by favouring warm-water species at the expense of
cold-water ones
e.g. Coarse fish such as roach and perch may, for example, replace salmon and trout
- solids)
g.
Radioactive substances
- mainly from: -- the processing of uranium ore
-- nuclear power plant, nuclear weapon testing
-- wastes form research laboratories
-- wastes from hospitals using isotopes in diagnostic and therapeutic
procedures