The big picture: Introduction to water systems
Water is essential to all life. An insufficient supply of water can have a detrimental effect on ecological
systems and human societies.
We use the hydrological cycle to help us understand the movement of water around the planet. On a
global scale, the hydrological cycle is considered to be a closed system, with the amount of water
remaining fairly constant. However, components of the hydrological cycle are open systems. A lake is an
open system, it exchanges matter with the surrounding environment (e.g., input of surface run-off
containing nutrients) and energy (e.g., sunlight).
Human activity can alter the natural flow of water and have adverse effects on ecological systems. For
example:
Humans extract water from rivers and streams, which lowers the water level and reduces flow
rates. This then alters the environment for aquatic species.
Humans have drained some wetland areas to increase the amount of available agriculture land.
This loss of wetland habitats, and replacement with monoculture, has resulted in loss of overall
biodiversity.
We can also have a detrimental effect on the water quality. For example:
Humans discharge industrial waste containing toxic chemicals into rivers and oceans.
Deforestation can lead to soil erosion contributing to siltation of lakes and rivers.
Surface run-off can leach pesticides and fertilizers from farmland transferring them into nearby
watercourses.
By understanding our impacts on the hydrological cycle, we can learn to manage our environment in
more sustainable ways. We can adopt strategies that do not exhaust our water resources and are not
harmful to other species and habitats.
Most of the world’s water is found in the oceans. As ocean water circulates around the globe it
distributes heat which affects our climate. If this movement of ocean water stopped, it would have a
dramatic effect on the climate and therefore on habitats and species.
,The big picture: Access to fresh water
Rainfall is not equal across the world, which leads to an unequal supply of water. Many other factors
also affect access to an adequate and safe water supply, ranging from the cost of water to pollution of
supplies.
To be suitable for drinking, water needs to be safe and free of pathogens and contaminants. With
limited supplies, water shortages may occur. In rural areas people may need to walk further for supplies
and may only have access to contaminated waters.
Water related diseases are responsible for millions of deaths each year. Many water related diseases
like cholera infect the digestive system and cause diarrhoea that leads to dehydration and can result in
death. UNICEF estimates that diarrhoea leads to 1.8 million deaths each year of which 1.6 million are
children under the age of five years. This means on average 4,384 children die every day from diarrhoea.
Do your own calculations to work out how many that is per day or per minute.
Contamination of water with arsenic is a major problem is some countries. Arsenic occurs naturally in
the Earth’s crust, which leads to contamination of groundwater in some regions.
More people are affected in Bangladesh than any other country. Over 45 million people in Bangladesh
are exposed to Arsenic levels above the World Health Organization (WHO) guidelines of 10 µg/L.
, Use of groundwater contaminated with arsenic can lead to long term exposure. Effects include changes
to the pigmentation of the skin, development of skin lesions, and cancers of the skin, bladder, and lung.
Over abstraction can lead to depletion of water resources. With limited water supplies, the risk of
conflict over this resource increases. Disputes over ownership and water rights may occur between
individuals or groups within a country, or between countries where river systems are shared.
It is important to manage water supplies sustainably to ensure sufficient future supplies. Groundwater
and lakes need time to replenish. We need to control demand through water conservation strategies
and also increase supplies.
The big picture: Aquatic food production systems
Humans continue to explore how natural resources can meet the needs of a growing population.
Aquatic ecosystems provide us with a diverse range of potential resources.
Aquatic organisms at various different trophic levels have historically been exploited. Consumption of
primary produces such as seaweeds continues to be highly popular in many parts of the world.
Research is ongoing on how we could further harness phytoplankton, the microscopic primary
producers as:
A direct food resource, for instance the commercial production and use
of Chlorella and Spirulina species as protein and vitamin rich food.
A biofuel of the future
Phytoplankton and algae are also important in:
Supporting trophic levels within a food web including species harvested by humans.
Absorbing carbon dioxide and therefore playing a significant role in the regulation of our global
climate.
Producing oxygen through the process of photosynthesis.
The primary producers are eaten by the primary consumers that include zooplankton, microscopic
animals. They in turn are eaten by secondary consumers such as shellfish (e.g., mussels and clams) and
fish (e.g., herring and sardines). The next trophic level is the tertiary consumers such as predatory fish
(e.g., tuna), mammals (e.g., seals and dolphins) and seabirds followed potentially by quaternary
consumers such as larger fish (e.g., sharks) and mammals (e.g., polar bears).
Humans tend to harvest aquatic animals such as shellfish, fish and mammals from different trophic
levels. Some species are more intensively harvested than others and this can potentially have a knock-
on effect on other species within the ecosystem. For example, if a large numbers of secondary
consumers are removed, it may reduce food available for tertiary consumers, reducing the growth rate
and population number of these tertiary consumers. In addition, excessive removal of an aquatic species
can reduce the rate of population growth and replenishment. In extreme situations, harvesting of a
species could lead to its extinction.
Water is essential to all life. An insufficient supply of water can have a detrimental effect on ecological
systems and human societies.
We use the hydrological cycle to help us understand the movement of water around the planet. On a
global scale, the hydrological cycle is considered to be a closed system, with the amount of water
remaining fairly constant. However, components of the hydrological cycle are open systems. A lake is an
open system, it exchanges matter with the surrounding environment (e.g., input of surface run-off
containing nutrients) and energy (e.g., sunlight).
Human activity can alter the natural flow of water and have adverse effects on ecological systems. For
example:
Humans extract water from rivers and streams, which lowers the water level and reduces flow
rates. This then alters the environment for aquatic species.
Humans have drained some wetland areas to increase the amount of available agriculture land.
This loss of wetland habitats, and replacement with monoculture, has resulted in loss of overall
biodiversity.
We can also have a detrimental effect on the water quality. For example:
Humans discharge industrial waste containing toxic chemicals into rivers and oceans.
Deforestation can lead to soil erosion contributing to siltation of lakes and rivers.
Surface run-off can leach pesticides and fertilizers from farmland transferring them into nearby
watercourses.
By understanding our impacts on the hydrological cycle, we can learn to manage our environment in
more sustainable ways. We can adopt strategies that do not exhaust our water resources and are not
harmful to other species and habitats.
Most of the world’s water is found in the oceans. As ocean water circulates around the globe it
distributes heat which affects our climate. If this movement of ocean water stopped, it would have a
dramatic effect on the climate and therefore on habitats and species.
,The big picture: Access to fresh water
Rainfall is not equal across the world, which leads to an unequal supply of water. Many other factors
also affect access to an adequate and safe water supply, ranging from the cost of water to pollution of
supplies.
To be suitable for drinking, water needs to be safe and free of pathogens and contaminants. With
limited supplies, water shortages may occur. In rural areas people may need to walk further for supplies
and may only have access to contaminated waters.
Water related diseases are responsible for millions of deaths each year. Many water related diseases
like cholera infect the digestive system and cause diarrhoea that leads to dehydration and can result in
death. UNICEF estimates that diarrhoea leads to 1.8 million deaths each year of which 1.6 million are
children under the age of five years. This means on average 4,384 children die every day from diarrhoea.
Do your own calculations to work out how many that is per day or per minute.
Contamination of water with arsenic is a major problem is some countries. Arsenic occurs naturally in
the Earth’s crust, which leads to contamination of groundwater in some regions.
More people are affected in Bangladesh than any other country. Over 45 million people in Bangladesh
are exposed to Arsenic levels above the World Health Organization (WHO) guidelines of 10 µg/L.
, Use of groundwater contaminated with arsenic can lead to long term exposure. Effects include changes
to the pigmentation of the skin, development of skin lesions, and cancers of the skin, bladder, and lung.
Over abstraction can lead to depletion of water resources. With limited water supplies, the risk of
conflict over this resource increases. Disputes over ownership and water rights may occur between
individuals or groups within a country, or between countries where river systems are shared.
It is important to manage water supplies sustainably to ensure sufficient future supplies. Groundwater
and lakes need time to replenish. We need to control demand through water conservation strategies
and also increase supplies.
The big picture: Aquatic food production systems
Humans continue to explore how natural resources can meet the needs of a growing population.
Aquatic ecosystems provide us with a diverse range of potential resources.
Aquatic organisms at various different trophic levels have historically been exploited. Consumption of
primary produces such as seaweeds continues to be highly popular in many parts of the world.
Research is ongoing on how we could further harness phytoplankton, the microscopic primary
producers as:
A direct food resource, for instance the commercial production and use
of Chlorella and Spirulina species as protein and vitamin rich food.
A biofuel of the future
Phytoplankton and algae are also important in:
Supporting trophic levels within a food web including species harvested by humans.
Absorbing carbon dioxide and therefore playing a significant role in the regulation of our global
climate.
Producing oxygen through the process of photosynthesis.
The primary producers are eaten by the primary consumers that include zooplankton, microscopic
animals. They in turn are eaten by secondary consumers such as shellfish (e.g., mussels and clams) and
fish (e.g., herring and sardines). The next trophic level is the tertiary consumers such as predatory fish
(e.g., tuna), mammals (e.g., seals and dolphins) and seabirds followed potentially by quaternary
consumers such as larger fish (e.g., sharks) and mammals (e.g., polar bears).
Humans tend to harvest aquatic animals such as shellfish, fish and mammals from different trophic
levels. Some species are more intensively harvested than others and this can potentially have a knock-
on effect on other species within the ecosystem. For example, if a large numbers of secondary
consumers are removed, it may reduce food available for tertiary consumers, reducing the growth rate
and population number of these tertiary consumers. In addition, excessive removal of an aquatic species
can reduce the rate of population growth and replenishment. In extreme situations, harvesting of a
species could lead to its extinction.
