Earth's Resources : Hydrosphere

Earth's Resources : Hydrosphere - Key SQA Definitions

• Evaporation  - The process of turning from liquid into vapour or gas

• Condensation - The process of a vapour or gas turning into a liquid

• Precipitation - Moisture that falls from the air to the ground (rain, snow, sleet, hail, drizzle, fog, mist)

• Transpiration - The evaporation of water from plants’ leaves, stems or flowers

• Run-off - The precipitation that flows across the surface of the ground

• Infiltration - The physical movement of water through soil (relative to the soil’s porosity and permeability)

• Percolation - The movement of water through soil by gravity and capillary forces

• Throughflow - The horizontal flow of water within soil

• Groundwater - Water that occupies pore spaces in soil and bedrock

• Groundwater flow - The movement of groundwater horizontally

The Hydrosphere

The hydrosphere consists of all of the water on, in or around the Earth. This includes water in the three states of matter; Solid (snow, ice, hail etc.), Liquid (rivers, lakes, oceans etc.) and Gas (water vapour in the atmosphere). 

There are several processes that form part of the hydrosphere, with the processes collectively making up the 'Water Cycle'.  

Water is the exception to the rule of all of Earth's resources being present since the formation of the Earth. Some water has indeed been present since the Earth's formation, having been bound up in the forming earth with the dust and gas. However, a large part of the water present on Earth is thought to have come from water-rich asteroids and comets colliding with the Earth early in its history (during the Hadean Aeon) . 

The Water Cycle

The 'Water Cycle' describes how water changes state and moves through the environment, water is not static but changes over time through a variety of processes. 

The diagram below shows an overview of the processes that make up the Water Cycle:- 

A description of any cycle can start at any point, but in this case the starting point will be taken as the water present in an ocean. Sunlight falling on the ocean provides enough energy for some of the water to evaporate (to change state from a liquid to a gas). This  invisible 'water vapour' will cool as it gets higher, condensing to form small droplets of liquid water suspended in the air, forming clouds. The water within the clouds can then travel huge distances before falling as 'precipitation' (rain, hail, snow etc.) 

This precipitation can then move through the environment in a range of ways. Some will be stored for long periods of  geological time as snow or ice on mountains, within glaciers or within the polar ice caps. Other water will fall onto porous rock and move downwards into the ground (this is known as percolation), forming groundwater. Alternatively, some water will fall on non-porous rock and flow along the surface (known as surface run off). When this surface runoff collects together whilst moving it forms streams and rivers, or if it becomes stationary it forms lakes. 

The water then can follow two paths; the surface runoff and groundwater can pass through rivers and lakes (or directly through the ground in a process known as 'throughflow') back to the ocean to begin the cycle again, or the water can be absorbed by vegetation (plants and trees). The water that is absorbed by vegetation then escapes from the leaves and stems of the plan (in a process known as 'transpiration'), again entering the air as water vapour.

In the water cycle, there are many examples of water being stored for long periods of time. The diagram below shows how the Earth's water is distributed between the various 'water stores':-

As can be seen from this diagram, less than 1% of the water on Earth is easily accessible to living organisms, including Humans and, as such, liquid freshwater is a resource that must be managed very carefully and sustainably (for further information, see - Sustainability : Water). 

Industrial Water Use

Manufacturing and other industries use water during the production process for either creating their products or cooling equipment used in creating their products. 

Industrial water is also used for fabricating, processing, washing, diluting, cooling, or transporting a product.

Water is also used by smelting facilities, petroleum refineries, and industries producing chemical products, food, and paper products. Large amounts of water are used mostly to produce food, paper, and chemicals. 

Effluents, i.e. liquid waste and domestic waste, are sometimes released into water systems. These substances can be hazardous to the environment, killing off aquatic organisms. 

The video below shows an example use of water in Industry:-

Note - This video was produced by the company Chevron, a major Oil and natural Gas producer. Do we feel that the video represents an unbiased view?  For more information on identifying reliable, unbiased sources, please see - Research Skills 

Industrial Water Use Case Study : Torness Nuclear Plant

As a coolant, cold water is piped around the machinery to cool it down and released back into the river or sea, raising the water temperature where it is released. 

This can allow species to invade Scottish waters from warmer countries whilst at the same time, killing off native species that need colder water to survive (such as the cold water corals on the west coast of Scotland).

At the Torness Nuclear Plant in East Lothian in 2011, both reactors had to undergo an emergency shut down after the coolant intakes (which draw water from the sea) became blocked by Jellyfish. This meant that the reactors could not be cooled properly and had to be shut down for safety until the Jellyfish could be cleared. 

Agricultural Water Use

To ensure that food crops have a good water supply, the fields are irrigated. This is when water is artificially applied to the crops or soil. 

This water is taken from rivers or from underground via boreholes or wells, which lowers the water levels present in the rivers and in underground supplies. 

This loss of river water can result in the death of organisms that need lots of water to survive, and in poorer, warmer countries could mean that the people no longer have a water supply.  

The video below shows an example use of water in Agriculture:-

Agricultural Water Use Case Study : The Aral Sea (Kazachstan & Uzbekistan) 

Aral Sea was once the fourth-largest freshwater lake in the world. But the Soviet Union’s agricultural policies in the 1950s led to water from two rivers – the Amu Darya and the Syr Darya – being diverted away from the sea to irrigate Central Asia’s desert steppes to boost cotton production.  

This led to a catastrophic loss of water feeding the sea, causing it to lose ~90% of its area : 

Domestic Water Use

In houses, water is used for washing, cooking, heating and sanitation. In warmer climates or in times of drought, governments may apply water use restrictions and limit the volume of water piped to houses. This can have serious impacts, including:-

• Public health – Lack of clean drinking water and sanitation can result in disease.

• Contamination of water supplies – When water levels are low, water pumps can cause saltwater to migrate inland contaminating freshwater supplies. If the water source is a freshwater lake or loch, then silt for the bottom can also contaminate the supply.

• Conservation – Dried up waterways and lack of water resources can kill organisms and reduce biodiversity.

• Damage to the tourist industry - Countries or organisations may be unable to offer water sports or sailing activities, and drought can put many tourists off a region due to lack of facilities to access clean drinking water. Water scarcity also can lower the appeal of natural beauty in certain areas, for example low water levels in Waterfalls, or reduced autumn colouring in trees. 

The video below shows an example use of water in Domestic settings:-

Agricultural & Domestic Water Use Case Study : Water Scarcity in Scotland (Summer 2022)

In 2022, the east of Scotland experienced its driest January since 1940. This was followed by lower-than-average spring and summer rainfall. This meant that by August, Water availability in the East of Scotland dropped to very low levels. 

The Scottish Environment Protection Agency (SEPA) classes parts of Fife as having reached the highest level for water scarcity. Other parts of the country over that summer experienced similar conditions. These included the Tweed area, the Ythan, Dee and Don areas, and the Firth of Forth, Firth of Tay and the Almond and Tyne being graded at moderate scarcity.

The video below shows a news report from August 2022:-

By mid-August the water levels in the river Eden in Fife dropped so low that SEPA suspended the right to river water abstraction (removing water from rivers to water crops) in the affected area. This risked the loss of crops in the area that required this water to survive, as well as triggering the possibility of water restrictions to homes:-

Agricultural & Domestic Water Use Case Study : Flooding in Scotland

Flooding occurs when water overflows from its usual location (river, lake, ocean etc.) onto land that is normally dry. Flooding occurs for a range of reasons:-

• During heavy or persistent rain

• Ocean waves coming onshore during a storm

• Rapid snow melt

• Dams or levees breaking

Due to their destructive nature, flooding is very damaging to ecosystems and human developments, so flooding is classed as a 'Natural Disaster'.

Flooding is also made worse by human activities such as:- 

• Deforestation - The removal of trees and other vegetation reduces the interception of water, which increases surface runoff. The lack of vegetation to bind the soil together can also increase the risk of landslips.

• Urbanisation -  Increased unbanisation causes increased surface runoff by reducing infiltration (water passing down into the ground) due to the use of impermeable ground coverings such as concrete or tarmac. 

• Climate Change - Human-accelerated climate change increases the risk of flooding due to increased or more intense rainfall. This is because warmer air can hold more moisture (for every 1℃ of warming, the atmosphere can hold 7% more moisture). 

In Scotland, flood risk management and flood response is managed by SEPA (The Scottish Environment Protection Agency). It is SEPA's role to assess and manage the risk of flooding across Scotland by creating models of flood risk, which are used by the Scottish Government and the general public to plan for future flooding.

Using the SEPA Flood Map website, it is possible to generate layered maps showing the flood risk for any location in Scotland. 

For example, the river Forth passes through Stirling before becoming the wider Firth of Forth. The city of Stirling areas of Raploch, Cornton and Causewayhead, along with the town of Bridge of Allan are built along both sides of the river, as shown in the map below:-

If a layer (light blue area)  is added to the map to show the current medium level (0.5% chance of flooding per year) risk of river flooding due to the river Forth, the following map is generated:-

As can be seen by comparing the two maps, relatively few homes are currently within the medium risk flood areas, however, large areas of farmland are currently at risk of flooding, which is something that the land owners must take into account. 

As part of their work, SEPA have also modelled the future flood risk across Scotland based on current climate prediction models. If a layer is added to the map to show the future (2080s) medium level (0.5% chance of flooding per year) risk of river flooding due to the river Forth, then the additional areas in dark blue will also be at risk of flooding:-

As can be now seen, the community of Cornton is predicted to be entirely at risk of flooding, as well as the southern half of Bridge of Allan. The Scottish Government, working with SEPA, will then use data such as this when planning for future flood defenses and other methods of reducing this risk in order to protect communities from damage. 

Energy from Water : Hydro-Electric

Hydroelectric power uses the Energy of water flowing rapidly downhill to generate Electricity. The diagram below shows a simplified cross-section of a Hydroelectric Power Station:-

As the water is at a high point above the dam, the water contains Gravitational Potential Energy.  As the water flows down the penstock (tunnel through the dam), the Gravitational Potential Energy is converted to Kinetic Energy. This Kinetic Energy is used to turn a turbine and drive a generator, which generates Electricity. 

The energy changes in a Hydroelectric Power Station are:-

1. Stored in Loch behind Dam - Gravitational Potential Energy.

2. Water flowing downhill - Gravitational Potential Energy converted to Kinetic Energy.

3. Turbine and Generator - Kinetic Energy converted to Electrical Energy.

Hydroelectric power generation can only occur in areas which match the following requirements:-

• A location with a steep gradient to allow the water to flow quickly downwards through the system. 

• High rainfall to allow a continuous supply of water to the system. 

• A narrow, deep valley to allow efficient construction of a dam across it.

• Impermeable rock to prevent water infiltration.

• Access to populated areas with connection to the National Grid. 

• Water/Land use by other stakeholders can accommodate the Hydroelectric power generator.

Energy from Water : Tidal

A Tidal Turbine uses the Energy of water flowing in tides to generate Electricity. The diagram below shows a simplified diagram of a tidal turbine:-

The Tidal Turbine works in a very similar way to a wind turbine, with the motion of the water causing the blades of the wind turbine to rotate. These rotating blades are attached to a shaft which drives a generator, generating Electricity. 

The energy changes in a tidal turbine are:-

1. Moving water (tides)  - Kinetic Energy.

2. Turbine and Generator - Kinetic Energy converted to Electrical Energy.

Tidal power generation can only occur in areas which match the following requirements:-

• A narrow channel to provide a fast tidal current.

• A large tidal flow to provide a large amount of water to the tidal generator.

• Access to populated areas with connection to the National Grid. 

• Water use by other stakeholders can accommodate the tidal power generator.

Energy from Water : Wave

A Wave power generator uses the motion of waves to generate Electricity. This motion is used to drive a hydraulic generator, which generates Electricity. The diagram below shows a simplified diagram of a prototype wave power generator:-

In the above system, the yellow section of the device float on the water's surface. As the waves pass, the device opens and closes, forcing sea water into the flow line. This drives either a hydraulic pump or a Hydroelectric system on the land, which generates Electricity. 

The energy changes in a Wave Power Generator are:-

1. Waves- Kinetic Energy.

2. Hydroelectric Generator - Kinetic Energy converted to Electrical Energy.

Wave power generation can only occur in areas which match the following requirements:-

• A location with the correct range of water depth. 

• A location with consistently high wave height. 

• Access to populated areas with connection to the National Grid. 

• Water use by other stakeholders can accommodate the Wave power generator.