unit 4

Question 1

water on earth

Answer 1

Fresh water only makes up a small fraction (approximately 2.5% by volume) of the Earth’s water storages
Of this fresh water, approximately 68.7% is stored in glaciers and ice sheets and 30% is stored as groundwater
The remaining 1.3% of freshwater is in rivers, lakes and the atmosphere
All water is part of the hydrological cycle

Question 2

the hydrological cycle

Answer 2

The hydrological cycle is a closed system
Within the hydrological cycle, there are stores and transfers (flows)
The hydrological cycle is a series of processes in which water is constantly recycled through the system
The cycle also shapes landscapes, transports minerals and is essential to life on Earth

Question 3

the main processes that occur within the hydrological cycle

Answer 3

Evaporation - the sun evaporates surface water into vapour
Condensation - water vapour condenses and precipitates
Flows - water runs off the surface into streams and reservoirs or beneath the surface as ground flow

These processes transfer the water on Earth from one store to another (river to ocean or ocean to atmosphere)

Question 4

The hydrological cycle involves energy exchange, leading to local temperature fluctuations

Answer 4

As water evaporates, it absorbs energy from its surroundings
This effectively cools the environment
The reverse happens when water condenses (heat is released)
This heat exchange influences the local climate

Question 5

storages in the hydrological cycle include

Answer 5

Rivers, lakes and oceans
Groundwater (aquifers)
Soils
The atmosphere
Glaciers and ice caps
Organisms (e.g. trees)

Question 6

flows in the hydrological cycle include

Answer 6

Evapotranspiration
Sublimation
Evaporation
Condensation
Advection
Precipitation
Melting
Freezing
Flooding
Surface run-off
Infiltration
Percolation
Stream-flow or currents

Question 7

evaporation

Answer 7

The process by which liquid water changes into a gaseous state (water vapour) and enters the atmosphere from water bodies such as oceans, lakes, and rivers

Question 8

transpiration

Answer 8

The process by which plants absorb water from the soil through their roots and release it as water vapour through tiny openings called stomata in their leaves

Question 9

evapotranspiration

Answer 9

The combined process of water vaporisation from the Earth’s surface (evaporation) and the release of water vapour by plants through transpiration

Question 10

sublimation

Answer 10

The direct transition of water from a solid (ice or snow) to a vapour state without melting first

Question 11

condensation

Answer 11

The process in which water vapour in the atmosphere transforms into liquid water, forming clouds or dew, as a result of cooling

Question 12

advection

Answer 12

The horizontal movement of water vapour, clouds, or precipitation caused by the prevailing wind patterns

Question 13

precipitation

Answer 13

The process of water falling from the atmosphere to the Earth’s surface in the form of rain, snow, sleet, or hail

Question 14

melting

Answer 14

The process by which solid ice or snow changes into liquid water due to an increase in temperature

Question 15

freezing

Answer 15

The process by which liquid water changes into a solid state (ice or snow) due to a decrease in temperature

Question 16

flooding

Answer 16

The overflow of water onto normally dry land, often caused by heavy rainfall, melting snow, or dam failure

Question 17

surface run-off

Answer 17

The movement of water over the Earth’s surface, typically occurring when the ground is saturated or impermeable, leading to excess water

Question 18

infiltration

Answer 18

The process of water seeping into the soil from the surface, entering the soil layers and becoming groundwater

Question 19

percolation

Answer 19

The downward movement of water through the soil and underlying rock layers, eventually reaches aquifers or groundwater reservoirs

Question 20

stream-flow or currents

Answer 20

The movement of water in streams, rivers, or other water bodies, driven by gravity and the slope of the land, ultimately leads to oceans or lakes

Question 21

human impact on the hydrological cycle

Answer 21

Human activities, such as agriculture (specifically irrigation), deforestation, and urbanisation, have significant impacts on the hydrological cycle, altering the natural processes of surface run-off and infiltration

Question 22

The impact of agriculture and irrigation on the hydrological cycle

Answer 22

Irrigation is the process of artificially supplying water to agricultural crops
It has a direct impact on the hydrological cycle by modifying the water distribution and availability in a region
Increased irrigation leads to artificially high evapotranspiration rates as more water is supplied to plants than would occur naturally, resulting in increased atmospheric moisture levels
This can lead to localised increases in precipitation downwind of irrigated areas, altering rainfall patterns in the region
Additionally, excessive irrigation can result in increased surface run-off
When water is applied faster than the soil can absorb it, it flows over the surface, carrying sediments, fertilisers, and pesticides, leading to water pollution and nutrient imbalances

Question 23

the impact of deforestation on the hydrological cycle

Answer 23

Deforestation refers to the clearing or removal of forests, primarily for agriculture, logging, or urban development purposes
Forests play a crucial role in the hydrological cycle
They act like natural sponges, absorbing rainfall and facilitating infiltration, which helps recharge groundwater and maintain stream flows
When forests are cleared, surface runoff increases significantly
Without the tree canopy and vegetation to intercept and slow down rainfall, more water reaches the ground surface, leading to higher surface runoff rates
Deforestation also reduces evapotranspiration rates
As trees are removed, there is less transpiration and evaporation occurring, resulting in reduced moisture release into the atmosphere
Overall, deforestation disrupts the balance between surface run-off and infiltration, leading to increased erosion, reduced groundwater recharge, and altered stream flow patterns

Question 24

the impact of urbanisation on the hydrological cycle

Answer 24

Urbanisation involves the transformation of natural landscapes into urban areas with buildings, roads, and infrastructure
Urban development dramatically alters the hydrological cycle by replacing permeable surfaces (such as soil and vegetation) with impermeable surfaces (concrete, asphalt)
Impermeable surfaces prevent infiltration, leading to reduced groundwater recharge
Instead of infiltrating into the soil, rainfall quickly becomes surface runoff, resulting in increased flooding and diminished water availability during dry periods
Urban areas typically have efficient drainage systems designed to remove the excess water quickly
This further accelerates surface runoff, which can overload natural water bodies and cause downstream flooding
Urban areas often experience higher temperatures due to the urban heat island effect
This effect, caused by the concentration of buildings and paved surfaces, increases evaporation rates, altering local precipitation patterns

Question 25

what causes ocean circulation

Answer 25

Ocean circulation systems are driven by differences in temperature and salinity
The resulting difference in water density drives the ocean conveyor belt, which distributes heat around the world and thus affects climate

Question 26

ocean conveyor belt

Answer 26

Ocean currents redistribute heat energy around the globe
The currents (warm or cold) act a bit like ‘rivers’ of water in the sea
Cold currents move towards the equator and warm currents towards the poles
Each ocean has its own pattern of currents
E.g. the warm Atlantic Ocean waters of the low latitudes are moved to high latitudes via the North Atlantic Drift

Question 27

how are ocean currents triggered

Answer 27

by the prevailing surface winds created by global atmospheric circulation

Question 28

how is ocean circulation maintained

Answer 28

hrough convection currents driven by cold water freezing into ice at the poles
The polar cold waters contain denser, saltier sea water, which sinks to the ocean floor
Water then flows in above it at the surface, which forms a current
The deep ocean currents then flow towards Antarctica along the western Atlantic basin, before splitting off into the Indian and Pacific Oceans where the water begins to warm up
The warming makes the water less dense so it loops back up to the ocean surface in the South and North Atlantic Ocean
The warmed surface waters continue to flow around the globe and eventually return to the North Atlantic, where the cycle begins again
This movement of water is known as the thermohaline circulation and drives the ocean conveyor belt

Question 29

Access to an adequate supply of freshwater varies widely across the globe due to a number of factors:

Answer 29

1. Geographic location
2. Climate
3. Topography
4. Population density
5. Water management and infrastructure
6. Economic development
7. Political stability and governance

Question 30

the key problems facing freshwater access include:

Answer 30

• the impacts of climate change
• increasing population, irrigation and industrialisation
• contamination
• unsustainable abstraction

Question 31

the impact of climate change on freshwater access

Answer 31

Climate change can disrupt rainfall patterns, leading to increased variability and unpredictability in precipitation
This can result in more frequent and severe droughts and floods, impacting the availability of freshwater resources
Rising temperatures can accelerate evaporation rates, further reducing water availability in already water-stressed regions
Melting glaciers and reduced snowpack in mountainous areas can affect the timing and magnitude of water flow in rivers, potentially leading to water scarcity during dry seasons
Sea-level rise can lead to saltwater intrusion in coastal areas, contaminating freshwater sources and making them unsuitable for human consumption and agriculture

Question 32

access to fresh water in developing countries

Answer 32

The increasing global population, along with expanding agricultural practices and industrial activities, puts significant pressure on freshwater resources
As the population grows, so does the demand for food production, which often requires extensive irrigation
This further strains water supplies as large amounts of water are diverted for agricultural purposes
Industrialisation demands substantial water resources for manufacturing processes, energy production, and cooling purposes
The growth of industrial sectors intensifies competition for freshwater, particularly in water-stressed regions

Question 33

contamination regarding access to freshwater

Answer 33

Freshwater supplies can become contaminated due to various human activities, including industrial discharges, agricultural runoff containing fertilisers and pesticides, and improper waste disposal
Pollution from industrial chemicals, heavy metals, and sewage can render water sources unsafe for consumption and harm ecosystems
Contamination of freshwater bodies, such as lakes and rivers, can make water treatment more challenging and costly, reducing the availability of clean and safe drinking water

Question 34

unsustainable attraction regarding access to freshwater

Answer 34

Unsustainable abstraction refers to the excessive withdrawal of water from freshwater sources without allowing sufficient time for replenishment
Over-extraction of groundwater through wells and boreholes can lead to declining water tables, depletion of aquifers, and land subsidence
In some regions, surface water bodies, such as rivers and lakes, are over-allocated for abstraction, leading to reduced flows and ecological degradation
Lack of proper regulation and monitoring of water abstraction practices can exacerbate water scarcity issues, particularly in areas with high water demand

Question 35

freshwater conflicts occur over a variety of reasons

Answer 35

1. Competition over lined resources
2. Transboundary water disputes
3. Environmental degradation
4. Climate change and drought

Question 36

strategies used to enhance fresh water supplies

Answer 36

• reservoirs
• redistribution
• desalination
• artificial recharge of aquifers
• rainwater harvesting

Question 37

other key consideration for fresh water management

Answer 37

1. Conservation and efficient waste use
2. Water recycling and re-use
3. Sustainable agricultural practices
4. Protecting ecosystems and natural water resources

Question 38

why is the demand for aquatic food resources experiencing a significant increase

Answer 38

due to the combined effects of a growing human population and dietary changes
As populations expand and economies develop, there is a higher demand for seafood products to meet nutritional needs and culinary preferences

Question 39

The main factors behind the increase in demand for aquatic food resources are as follows:

Answer 39

1. Growing human population
2. Changing dietary patterns
3. Nutritional benefits of sea food
4. Urbanisation and the rising middle class
5. Global trade and supply changes
6. Aquaculture and production

Question 40

what does photosynthesis by phytoplankton form

Answer 40

the foundation of marine food webs, supporting a highly diverse range of organisms within marine ecosystems
Phytoplankton utilise sunlight, carbon dioxide and nutrients to produce organic matter through photosynthesis
The organic matter produced by phytoplankton serves as a vital food source for various marine organisms, including zooplankton, invertebrates and small fish
The energy derived from phytoplankton is then transferred up the food chain, sustaining larger predators such as marine mammals, birds, and humans

Question 41

Phytoplankton productivity is highest near the coast or in shallow seas due to specific environmental factors:

Answer 41

Upwellings occur when wind-driven movements bring cold, nutrient-rich water from the deeper ocean layers to the surface
Upwelling zones promote phytoplankton growth by providing an abundance of nutrients like nitrogen, phosphorus, and iron that are essential for their photosynthetic activity
Nutrient enrichment of surface waters in these regions stimulates the growth of phytoplankton, leading to increased productivity and biomass
The high productivity near the coast and in shallow seas create ideal conditions for the development of diverse food webs
In addition to upwellings, other factors such as coastal runoff and mixing of nutrient-rich freshwater also contribute to the enrichment of surface waters, supporting phytoplankton growth and food web complexity
These regions serve as crucial hotspots for marine biodiversity and play a significant role in the overall health and functioning of marine ecosystems

Question 42

finfish and shellfish

Answer 42

finfish such as salmon, tilapia, and catfish are commonly harvested through aquaculture
They are reared in ponds, cages, or tanks and fed a controlled diet until they reach market size
Shellfish, including oysters, mussels, and clams, are cultivated in coastal areas or specialised farms
They are grown on submerged structures or suspended ropes, allowing them to filter feed and grow

Question 43

shrimp and prawns

Answer 43

Shrimp and prawn farming is prevalent in both freshwater and marine environments
Ponds or enclosed systems are used to cultivate these crustaceans
They are fed a formulated diet and managed until they reach harvestable size

Question 44

seaweed and algae

Answer 44

Ropes, nets, or floating structures are used to grow these aquatic plants in coastal or oceanic waters
Harvesting involves manually cutting or collecting mature seaweed or algae biomass from the cultivation structures

Question 45

molluscs and bivalves

Answer 45

Molluscs such as scallops, abalone, and snails, as well as bivalves like mussels and clams, are often harvested from natural or artificial beds in both freshwater and marine environments
They are often collected using handpicking, rakes, or dredges, depending on the species and harvesting location

Question 46

aquaculture

Answer 46

plays a crucial role in meeting the growing demand for seafood while reducing pressure on wild fish populations
Aquaculture has experienced significant growth to meet the increasing global demand for seafood, which is driven by population growth, changing dietary preferences, and rising incomes
By cultivating fish, shellfish, and other aquatic organisms through aquaculture, the pressure on wild fish populations can be reduced, allowing them to recover and the ecological balance of these marine ecosystems to be restored
Aquaculture has the potential to provide a reliable and sustainable source of seafood, helping to meet the protein needs of a growing population, whilst also minimising the impact on wild fish stocks

Question 47

in what ways is aquaculture beneficial

Answer 47

1. Providing additional food resources
2. Supporting economic development

Question 48

The growth of aquaculture is expected to continue in the coming years due to several factors:

Answer 48

Rising global demand for seafood
Technological advancements
Environmental considerations
Innovation and diversification
Policy support

Question 49

issues around aquaculture include

Answer 49

Habitat loss
Pollution (with feed, antifouling agents, antibiotics and other medicines added to fish pens)
Spread of diseases
Escaped species (sometimes involving genetically modified organisms)
Ethical Issues and biorights
Rights of indigenous cultures

Question 50

In addition, issues in aquaculture can often arise regarding international conservation legislation

Answer 50

Aquaculture must comply with international conservation legislation and regulations to ensure the sustainable use of resources and to protect biodiversity
International frameworks such as the Convention on International Trade in Endangered Species (CITES) and the Convention on Biological Diversity (CBD) have implications for aquaculture operations involving endangered or protected species
Compliance with these regulations helps prevent the exploitation of threatened species, maintain ecological balance, and ensure the long-term viability of aquaculture practices

Question 51

why are fish stocks in the ocean declining

Answer 51

overfishing

Question 52

overfishing may result in

Answer 52

Some species of fish completely disappearing in certain areas or even going extinct (e.g. we are at risk of losing cod completely in the north-west Atlantic)
Ocean food chains being disrupted, affecting many other aquatic species
Fewer fish for human consumption – this would be especially problematic for populations that rely on fish as a main source of food

Question 53

sustainable fishing means

Answer 53

Leaving enough fish in the ocean
Protecting habitats and marine food webs that fish rely on
Human communities that catch and process fish can maintain their livelihoods

Question 54

Increasing the size of gaps in fishing nets can help in two main ways:

Answer 54

Fewer unwanted species (that are often simply discarded) will be caught and killed, as they can escape through larger net gaps (as long as they are smaller than the species being caught – the accidental capture and killing of larger species is still a problem that is reducing the populations of these species)
Juvenile fish of the fish species being caught can escape through larger net gaps, meaning they can reach breeding age and have offspring before they are caught and killed. This ensures the population of the fish species being caught can be replenished

Question 55

government regulation can be enforced by

Answer 55

Establishing fishing quotas
Agreeing areas of the ocean where fishing is banned (e.g. spawning grounds) and permitted (e.g. within a country’s territorial waters)
Regulating mesh size of nets (to allow undersized/juvenile fish to escape)
Limiting the size of the fishing fleet by issuing licenses
Inspecting the catch as a fishing boat returns to port
Banning certain practices e.g. gillnets (static nets that catch anything that swims by, and the fish struggle and die in distress)
Promoting sustainable practices such as trolling (different to trawling) that reduces bycatch

Question 56

types of aquatic pollutants

Answer 56

Organic material
Inorganic nutrients (nitrates and phosphates)
Toxic metals
Synthetic compounds
Suspended solids
Hot water
Oil
Radioactive pollution
Pathogens
Light
Noise
Invasive species

Question 57

different water quality parameters

Answer 57

1. pH
2. temperature
3. Dissolved oxygen
4. suspended soils (turbidity)
5. Metals
6. Nitrates and Phosphates

Question 58

biodegradation of organic material

Answer 58

refers to the natural process where microorganisms break down organic substances into simpler compounds
During biodegradation, microorganisms utilise oxygen for the breakdown of organic matter
High levels of organic material can lead to increased microbial activity and oxygen consumption in water bodies

Question 59

what doe excessive biodegradation or organic materials do

Answer 59

deplete dissolved oxygen levels, leading to anoxic conditions (low oxygen) in the water
In anoxic conditions, anaerobic decomposition occurs, carried out by bacteria that do not require oxygen

Question 60

biochemical oxygen demand (BOD)

Answer 60

is a measure of the amount of dissolved oxygen required to break down the organic material in a given volume of water through aerobic biological activity
Aerobic organisms rely on oxygen for respiration
When there is a higher abundance of organisms or an increased rate of respiration, more oxygen is consumed
This means that the biochemical oxygen demand (BOD) is influenced by:
The quantity of aerobic organisms present in the water
The rate at which these organisms respire

Question 61

BOD can be used as an indirect measure to evaluate pollution levels in water

Answer 61

The introduction of organic pollutants, such as sewage, leads to an increase in the population of organisms that feed on and break down the pollutants
This, in turn, results in elevated BOD values
Certain species, such as bloodworms and Tubifex worms, show tolerance to organic pollution and the associated low oxygen levels
On the other hand, mayfly nymphs and stonefly larvae are typically only found in clean-water environments

Question 62

example of how BOD is used to indirectly measure the amount of organic matter within a sample

Answer 62

High BOD values indicate a larger amount of organic matter present in the water sample, as more oxygen is needed for its decomposition
By measuring the decrease in dissolved oxygen levels over a specific incubation period, BOD provides an estimate of the organic load or pollution level in the water
BOD values are typically expressed in milligrams of oxygen per litre of water (mg/L) or as a percentage of the initial dissolved oxygen level
The BOD test involves collecting a water sample in a closed container and measuring the dissolved oxygen concentration initially and after a specific incubation period (often 5 days) at a constant temperature

Question 63

indicator species

Answer 63

are organisms that are used to assess the quality of an environment or indicate the presence of specific environmental conditions, including pollution
Different groups of organisms, including invertebrates, plants, and algae, can serve as indicator species in polluted waters

Question 64

limitations of using indicator species

Answer 64

Although using indicator species is a fairly simple and cost-effective method of determining whether a habitat is polluted or not, it has some drawbacks
For example, it can’t give accurate numerical (quantitative) figures for exactly how much pollution is present
In addition, the presence or absence of indicator species can also be affected by factors other than pollution (e.g. the presence of predators or disease)
If more detailed information on pollution levels is required, non-living indicators can be used instead

Question 65

biotic index

Answer 65

is a tool used to assess the overall health and pollution levels of an ecosystem based on the presence, abundance, and diversity of indicator species within a community
It provides an indirect measure of pollution by evaluating the impact on different species according to their tolerance, diversity, and relative abundance

Question 66

different steps of a biotic index

Answer 66

step 1 - selection of indicator species
step 2 - sampling and data collection
step 3 - calculation of biotic index
step 4 - interpretation of biotic index

Question 67

algal bloom

Answer 67

When lakes, rivers, estuaries and coastal waters receive artificially large inputs of nutrients (such as nitrates and phosphates), this results in excess growth of plants and phytoplankton
For example, when the mineral ions from excess fertilisers leach from farmland into waterways, they cause rapid growth of algae at the surface of the water

Question 68

the effect of algal bloom

Answer 68

can completely block out sunlight and stop it from penetrating below the water surface, so aquatic plants below the surface of the water start to die as they can no longer photosynthesise
The algae also start to die when competition for nutrients becomes too intense
As aquatic plants and algae die in increasing numbers, decomposing bacteria feed on the dead organic matter and also increase in number
As they respire aerobically, these bacteria use up the dissolved oxygen in the water
As a result, the amount of dissolved oxygen in the water rapidly decreases, so aquatic organisms such as fish and insects may be unable to survive
Dead zones in both oceans and freshwater can occur when there is not enough oxygen to support aquatic life

Question 69

three levels of pollution management

Answer 69

Changing human activity
Regulating and reducing quantities of pollutants released at the point of emission
Cleaning up the pollutant and restoring the ecosystem after pollution has occurred