Theme: Our Water Environment
Topic 1. Importance of Water
A.
Planet of Water

Earth - a planet of water. Water covers about 70% of the earth’s surface. All organisms
on earth are made up mostly of water, e.g.

—
A tree contains about 60% water by weight;
—
Mushrooms contain about 80 – 90% water,
—
And most animals contain about 50 – 65% water.
Without water, no life could exist.
1.
Properties of Water in Relation to its Uses
Chemical Properties

A universal solvent that can carry water-soluble nutrients to and transport wastes from
cells and tissues of living organisms to environment.

Facilitates dispersal of nutrients and water-soluble wastes in the ecosystem.

A common reactant in many chemical reactions that include hydrolysis, oxidation and
reduction. It plays an important role in biochemical reactions and industrial processes.
Physical properties

Water changes temperature slowly as it stores a huge amount of heat for raising one
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degree of temperature.
— This high specific heat capacity moderates the earth’s climate.
— Allows living organisms especially the warm – blooded animals to withstand
temperature fluctuations.
— Makes it an excellent coolant for heat – producing industrial processes such as
generating electricity in power plant.

Strong attractive forces formed by hydrogen bonds between water molecules are
responsible for the cohesion and adhesion which are employed in fluid transfer in
organisms, such as fluid transfer up the plants.

Liquid water has a higher density than solid ice. Ice floats on water in open oceans and
lakes, so aquatic lives still survive in the aquatic liquid body in cold climates.
2.

Plants
Importance of Water to Human
absorb
solar energy and
synthesize
carbohydrates
(sugars)
through
photosynthesis.
— This provides basic food source for organisms which could not convert atmospheric
carbon dioxide into sugars by themselves.
6H2O + 6CO2
C6H12O6 + 6O2
Raw materials: water in plant cells, carbon dioxide from the atmosphere. Photosynthesis is the
fixation of atmospheric carbon dioxide into glucose in a plant cell with the release of
oxygen.

Human needs to drink 8 cups of water daily (2L) to maintain the water balance in the
body.

Water has multiple uses in our daily lives, such as washing, cleaning, cooking and
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recreational uses (e.g. water sports).

Since the beginning of human civilization,
— A population explosion reaching a current size of 6.2 billion.
— With it, people spend abundant water in irrigation in agriculture and manufacturing
processes in industry. Irrigation accounting for 70% of water use grows 40% of the
world’s food to feed the people (Montaigne, 2002).
— In 1995, Philippines used 88% of freshwater withdrawal in agriculture. In contrast
USA, a developed country, utilized 42% in agriculture (Table 1).
Table 1. Agriculture consumes a lot of freshwater (modified from Gleick, 2002).
Country
Philippines
Australia
USA
1995 Freshwater withdrawal (km3/yr)
55.42
17.80
469.00
Agriculture use (%)
88
75
42
3. Seawater and freshwater

Seawater contains about 3.5% salt (e.g. sodium chloride) in concentration.

Freshwater: the natural occurring water (e.g. lake and river) having low concentrations
of salts, suitable for abstraction and treatment to produce drinking water.

Limited Freshwater resource
- Limited freshwater resources in the world (Table 2).

About 97% of water found in oceans are too salty for drinking and irrigation.

Remaining 3% is freshwater but most of it is unavailable as icecaps and glaciers or
brackish ground water.

Less than 1% of earth’s water is available for our uses.
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Table 2. Distribution of water on earth (modified from Gleick, 2002).
Oceans
Saline/Brackish groundwater
Glaciers, permanent snowcover
Fresh groundwater
Freshwater lakes
Soil moisture
Atmospheric water vapour
Rivers
Incorporated in biota

Volume (1000km3)
1,338,000
12,870
24,064
10,530
91
16.5
12.9
2.12
1.12
% of Total Water
96.54
0.93
1.74
0.76
0.007
0.001
0.001
0.0002
0.0001
"Pilot Analysis of Global Ecosystems (PAGE): Freshwater Systems" released by the World
Resources Institute on Oct 25, 2000 reports degradation of our freshwater systems.
— PAGE says that four out of every 10 people currently living in river basins are
experiencing water scarcity.
— Dams, diversions or canals fragment 60% of the world's largest 227 rivers leading to
freshwater degradation.
— Although dam construction helps to provide drinking water, increase agricultural yield by
irrigation and provide flood control and most importantly hydropower for economic
development, we have withdrawn about half of the readily available water in rivers.
— Building dams decrease water supply to the lower regions and affect the
biodiversity there. River modification has affected the natural flow of rivers to a
point where many no longer reach the ocean during the dry season, e.g. Huang-He.
4. Uneven Distribution of water resource

Distribution of water resources in the world is not even.
— E.g. countries in tropical area have more rainfall than those in the subtropical area.
— 21% of the world’s population lives in China but only 7% of world’s freshwater supply.
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— In contrast, Canada only has 0.5% of world’s population with 20% of world’s
freshwater supply.

The uneven distribution of water may even trigger the battle for freshwater supply
especially in drought seasons.

Uneven distribution of water not only occurs geographically but also seasonally.
— In spring and summer, flooding strikes countries destructive to both life and
economy. E.g. in Hong Kong, the prices for vegetables rise after a flooding event.

Figure 6 shows the unit cost of various freshwater resources. Importing of Dongjiang
water is not the only choice to ensure the supply of clean water but simply as the
cheapest means. However with advancement in science and technology, recycling
effluent is expected to catch up.
Figure 6. Unit cost of various freshwater resources (Data source: Advisory committee on the
Quality of Water Supplies, HKSAR.http://www.info.gov.hk/wsd/acqws/eng/home.htm)
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i.
Local Water Treatment Works

The freshwater from Dongjiang and collected by reservoirs requires further purification
to meet safety requirements for drinking water.

Shatin Water Treatment Works is one of the treatment facilities built to provide an
adequate supply of treated freshwater to new towns.

In the treatment works, alumina sulphate is added to coagulate suspended solids into
large particles which can later be separated from the treated water by sedimentation.
— The water then passes through a filtration plant to filter out the fine particles.
— The water is dosed with chlorine for disinfection, and a fluoride compound is added
for dental protection.
— After these processes and monitoring, the purified water meeting the required
standard and is ready for distribution to the consumers.
i. Ensure Safe Freshwater Supply

Since China opened its economy in the 1980s, many Hong Kong companies have moved
their manufacturing plants to the Dongjiang basin.
— The increase in social and economic activities causes deterioration of Dongjiang
water quality.
— To ensure the supply of clean water, the intake of Dongjiang water has been moved
upstream and a closed aqueduct is being built.
— A biological nitrification plant has also been added to provide a steady and quality
freshwater supply.
Suggested Student Activity：
Visit Water Treatment Plant.
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B.
Importance of Water for Life on Earth

Life contains water as its major component.

Water cycle replenishes and purifies freshwater supply.

Many factors affect water cycle and water quality, e.g. climate, geography.

Life adapts to the water availability by synchronizing the growth and reproduction
cycle, e.g. lichens in tundra. Herbivores migrate to find water and food sources.
 Water dilutes pollutants to reduce pollution problem.
1. Introduction to aquatic habitats and their roles
a. Freshwater habitats
e.g. Streams, rivers, lakes

Many animals gather around the aquatic body for water (e.g. horses) but not residents
(e.g. fishes, submerged and floating plants).

High biodiversity around these freshwater habitats. Thus aquatic bodies are included in
terrestrial protected areas.

Biodiversity in rivers are affected by:
- Water collection (extraction) to reservoirs, pollution, limited water supply, significant
seasonal changes, and other physical factors including:

- Current flow, substratum characteristics (muddy, sandy or rocky), temperature, and
dissolved oxygen, etc.
Biodiversity and water flow are dynamic in rivers.
Examples: Lam Tsuen River runs from Tai Mo Shan to Tai Po and Pui O Stream in Lantau
Island
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
Insects are commonly found in local streams.
They include:
— Water skaters, larvae of beetles, dragonflies, etc.

Water fleas and shrimps (e.g. freshwater shrimp) are also common.

Guppy, tilapia and eel are commonly found in local streams.

Local inland waters have many precious fish species and invertebrates, e.g. tree frog.
Native tree frog (AFCD, http://www.afcd.gov.hk/conservation/conf.htm).
b. Ocean: marine habitats

Oceans provide the nutritious proteins to many people.

Fish catch is still the major supply for global fish harvest. Overfishing, however,
drives many whales into extinction.

Among ecosystems, oceans are the most productive in conversion of solar energy
into plant biomass. Further, whale watch as a type of ecotourism provides a major
income to countries, e.g. Canada and Australia.

On earth aquatic transport is the major route for bulky cargoes.

Waste disposal in many cases ends in oceans.

Oceans are open and huge system. It is the location where dilution and natural
degradation of pollutants take place to fit into various nutrient cycles.

When pollution takes place in aquatic systems, the marine lives are harmed. Red tide
is in many cases caused by human pollution.
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
Tidal flushes are unique to oceans. Waves are driven by wind. Otherwise, oceans are
more or less steady.

Stratification is obvious. It is divided by water depth, water pressure, light
penetration and dissolved oxygen, etc. However, our knowledge with oceans is still
scarce.

Among the marine habitats, coral communities show the highest biodiversity,
comparable to tropical rain forests in terrestrial habitats.

Coral reefs only exist in coastal regions and are characteristic of tropical and
subtropical regions.

Animals associated with corals include: Coral fishes such as butterfish, and
Invertebrates, e.g. shrimps, starfish, crabs, etc.

Significance of coral communities:
o Important spawning grounds and nursery grounds for many commercially
significant fishery resources, such as fish and shrimps.
o Protect the coastline and stabilize the substrata from wave action and storms.
They are extremely important to water and soil protection of the coast.
o Corals and many coral-associated organisms contain natural products that are
important pharmaceutical resources, etc.
o Important for ecotourism.
o Examples in Hong Kong:
o Coral communities in local waters: mostly located in the eastern part of Hong
Kong in exposed or sheltered rocky shores under oceanic influence.
o There are reef building corals with symbiotic zooxanthella and non – reef
building corals.
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c. Coastal habitats
Include:
— Estuarines, seashores, bays, wetland, mangrove, etc.
— Seashores: rocky, muddy, sandy, etc. All affected by tides, river flows and
weathering.

Rocky shores that are habitats of: sea anemone, barnacles, mussels, hermit
crabs, sea cucumber, starfish, seaweeds, oysters, etc.

Muddy and sandy shores: king crab (horseshoe crab), oysters, mantis shrimp
could be found.
Wetlands

Definition: They are places where land meets water, supporting specially adapted plants
and animals. They are not deeper than 6 m at low tide.


Wetlands
-
may be natural, e.g. lakes, rivers, mudflats, mangrove, and
-
reedbeds or man-made, e.g. reservoirs, fishponds and rice fields.
Open system usually reserves significant amounts of nutrients to feed and sustains the
flora and fauna. Usually have high productivities in terms of the yield and diversity of
species found in a unit area.

Marshes with mangrove plants and reed support bird communities for building nests and
provide seeds and fruits for feeding of juveniles and adults.

Inter-tidal marine organisms or fauna living in swallow waters are valuable foods for
birds and their juveniles.
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-
Mangroves:
— Unique coastal habitats that cover about 75% of the shore areas in tropical and
subtropical regions throughout the world.
— Mangrove ecosystems are highly productive. Support a wide diversity of
organisms and provide food for people by means of fishery and aquaculture.
— Provide important foraging and resting grounds for birds, fishes and numerous
other organisms, e.g. crabs, barnacles, shrimps, mudskipper.
— Protect the shoreline from erosion by strong winds and tidal actions
— Many of the mangrove ecosystems throughout the world are being overexploited.
They are being chopped down for firewood, turned into aquaculture ponds or area
for urban developments.
— Act as the natural water purification system

Example: Mangroves are widely distributed from Deep Bay to Mirs Bay, Sai Kung,
Lantau Island, Tai Tam in Hong Kong.
A mangrove adapts to survive in a wetland.
Suggested Student Activity：
Fieldtrip / virtual fieldtrip, e.g. wetland, country park, marine park.
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References:
1.
Gleick, P. H. (2000) The World's Water: the Biennial Report on Freshwater Resources,
1998 – 1999. Washington, D.C.: Island Press.
2.
Gleick, P. H. (2002) The World's Water: the Biennial Report on Freshwater Resources,
2000 – 2001. Washington, D.C.: Island Press.
3.
Miller, G. T. (2002) Environmental Science: Working With the Earth. Belmont,
California: Wadsworth Pub.
4.
Montaigne, F. (2002) Water pressure. National Geographic 202, 22-33.
5.
Nature
publishing
group.
Nature
science
update
web
site.
Web
address:
http://www.nature.com/nsu/index.html
6.
The Green LaneTM Environmental Canada. Freshwater website. Web address:
http://www.ec.gc.ca/water/e_main.html
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