Chapter 4: Water, Food Production Systems, and Society

Question 1

4.1 Thermohaline circulation/ocean conveyor belt

Answer 1

Thermohaline circulation (THC) is a part of the large-scale ocean circulation that is driven by global density gradients created by surface heat and freshwater fluxes.[1][2] The adjective thermohaline derives from thermo- referring to temperature and -haline referring to salt content, factors which together determine the density of sea water. Wind-driven surface currents (such as the Gulf Stream) travel polewards from the equatorial Atlantic Ocean, cooling en route, and eventually sinking at high latitudes (forming North Atlantic Deep Water). This dense water then flows into the ocean basins. While the bulk of it upwells in the Southern Ocean, the oldest waters (with a transit time of around 1000 years)[3] upwell in the North Pacific.[4] Extensive mixing therefore takes place between the ocean basins, reducing differences between them and making the Earth’s oceans a global system. The water in these circuits transport both energy (in the form of heat) and mass (dissolved solids and gases) around the globe. As such, the state of the circulation has a large impact on the climate of the Earth.

Question 2

4.1 El Niño and La Niña

Answer 2

El Niño is the warm phase of the El Niño–Southern Oscillation (ENSO) and is associated with a band of warm ocean water that develops in the central and east-central equatorial Pacific (between approximately the International Date Line and 120°W), including the area off the Pacific coast of South America. The ENSO is the cycle of warm and cold sea surface temperature (SST) of the tropical central and eastern Pacific Ocean. El Niño is accompanied by high air pressure in the western Pacific and low air pressure in the eastern Pacific. El Niño phases are known to occur close to four years, however, records demonstrate that the cycles have lasted between two and seven years. During the development of El Niño, rainfall develops between September–November.[1] The cool phase of ENSO is La Niña, with SSTs in the eastern Pacific below average, and air pressure high in the eastern Pacific and low in the western Pacific. The ENSO cycle, including both El Niño and La Niña, causes global changes in temperature and rainfall.[2][3]

Question 3

4.1 The North Atlantic Oscillation (NAO)

Answer 3

The North Atlantic Oscillation (NAO) is a weather phenomenon in the North Atlantic Ocean of fluctuations in the difference of atmospheric pressure at sea level (SLP) between the Icelandic Low and the Azores High. Through fluctuations in the strength of the Icelandic low and the Azores high, it controls the strength and direction of westerly winds and location of storm tracks across the North Atlantic.[1] It is part of the Arctic oscillation, and varies over time with no particular periodicity.

Question 4

Floating debris (water pollution)

Answer 4

Floating debris mainly includes plastic but also lost or discarded fishing equipment.

Question 5

Organic pollution

Answer 5

Sewage or animal slurry.

Affects water quality with biological indicators correlating with distance from source.

Question 6

Inorganic Plant Nutrients

Answer 6

Soil erosion and land run-off results in high levels of nitrates and phosphates in the water.
This nutrient enrichment can lead to eutrophication with decreased oxygen levels.

Question 7

Hot water (energy pollutant)

Answer 7

Increasing temperature of water means less oxygen is able to dissolve in water.
Thermal power plants generate electricity using steam.
Although water is cooled before its release into the environment, it is still warmer and can affect the local ecosystem.

Question 8

Toxic metals

Answer 8

Mercury is an example.
It is common in seawater and comes from burning coal.
in the form of methylmercury, the metal can bioaccumulate and biomagnify.
This is one reason to reduce the consumption of top predators (as mercury has bioaccumulated in them).

Question 9

Synthetic compounds

Answer 9

Persistent Organic Pollutants (POPs) are an example of man-made (synthetic) compounds.
As they persist they can bioaccumulate and biomagnify.
Due to the Coriolis effect, these reach higher concentrations in polar regions.

Question 10

Suspended solids

Answer 10

Particles or sediment that float in water.
Reduce visibility - increases turbidity.
This reduces the productivity of producers as less light for photosynthesis.
Can be a non-point source from land run-off or point source from sewage pipe.

Question 11

Oil

Answer 11

Famous oil spills include Exon Valdez and Deepwater Horizon but oil has been spilled in large amounts during the Gulf Wars and West African oil fields.
Natural microbes occur that can metabolism oil but their work is made difficult by the chemical dispersants that are sprayed on oil spills.

Question 12

Radioactive pollution

Answer 12

Fukushima Daiichi nuclear power plant in Japan went into a meltdown following a tsunami in 2011.
Nuclear radiation entered the atmosphere and the Pacific Ocean.
The satellite images show how the radioactive pollution spread. The radioactive particles can bioaccumulate in organisms.
Also: Chernobyl.

Question 13

Pathogens

Answer 13

Pathogens are diseases causing organisms.
Fecal matter of an infected person reaching a water source contaminating the groundwater.
Diarrhea, vomiting, cholera, dysentery, typhoid, intestinal parasites, etc.
Strong socio-economic correlation with water-borne diseases and the percentage of access to sanitation and clean water.

Question 14

Light

Answer 14

Light pollution affects the behavior of organisms.
Causes circadian disruption (sleep patterns).
Disorientates migrating birds.
Prevents turtles from coming to nest on beaches or the hatchlings not be able to orient towards the sea.

Question 15

Noise

Answer 15

Affects marine organisms that navigate and communicate using sonar such as whales and dolphins.
Increasingly noisy oceans disorient these cetaceans and prevent their normal behavior.
Some forms of sonar may even cause hemorrhaging.

Question 16

Biological pollutants (invasive species)

Answer 16

These are zebra mussels, a serious invasive species in the US, especially in the Great Lakes.
Competition with native species can lead to extinction and have serious economic impacts.

Question 17

Types of water pollution

Answer 17

Pollutants can be:

• anthropogenic or natural
• point source or non-point source
• organic or inorganic
• direct or indirect

Question 18

Sources of freshwater pollution include:

Answer 18

-Agricultural run-off, sewage, industrial discharge and solid domestic waste.

Question 19

Source of marine pollution include:

Answer 19

-Rivers, pipelines, the atmosphere, and human activities at sea, both operational and accidental discharges.

Question 20

Biochemical oxygen demand (BOD)

Answer 20

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 by microorganisms.
It is a way of measuring water pollution.

Question 21

Biotic indices

Answer 21

A biotic index indirectly measures pollution by assaying the impact on species within the community according to their tolerance, diversity, and relative abundance.

Question 22

Indicator species

Answer 22

plants and animals that show something about the environment by their presence, absence, abundance, or scarcity.

Question 23

Eutrophication

Answer 23

Example of positive feedback (loop): when excess nutrients are added to an aquatic ecosystem. It can be a natural process but anthropogenic eutrophication is more common.

When it is severe, it leads to dead zones in oceans or freshwater where there is not enough oxygen to support life. In less severe cases, biodegradation of organic material uses up oxygen which can lead to anoxic (low oxygen) conditions and then anaerobic decomposition. This can release methane, hydrogen sulfide, and ammonia which are all toxic gases.

Leads to rivers ponds and lakes covered by green algal scum and duckweed with bad smell homie as well as the loss of biodiversity and shortened food chains.

The Gulf of Mexico has the largest dead zone in the USA (excess nutrients from the Mississippi River)

Question 24

Excess nutrients

Answer 24

nitrates and phosphates which come from:

detergents, fertilizers, drainage from livestock rearing units, sewage, and increased erosion of topsoil into the water.

Question 25

Process of eutrophication

Answer 25

1. Fertilizers wash into the river or lake.
2. High levels of phosphate in particular allow algae to grow faster (as phosphate is often limiting).
3. Algal blooms form (mats of algae) that block out light to plants beneath them, which die. No photosynthesis, and big fish can’t see and catch smaller fish.
4. More algae mean more food for the zooplankton and small animals that feed on them. They are food to fish which multiply as there is more food so there are then fewer zooplankton to eat the algae.
5. Algae die and are decomposed by aerobic bacteria. 6. But there is not enough oxygen in the water so, soon, everything dies as food chains collapse.
6. Oxygen levels fall lower. Dead organic material forms sediments on the lake or river bed and turbidity (unclearness/haziness of water) increases.
7. Eventually, all life is gone and the sediment settles to leave a clear blue lake.

Question 26

Direct measurements

Answer 26

Measuring turbidity (secchi disk): important to measure as amount of sediments and bacteria and other pathogen contents can block light to aquatic life.

Nitrate or phosphate content: nitrate and phosphate content cause algal blooming.

Question 27

Indirect measurements

Answer 27

BOD: measures among of dissolved oxygen required to break down the organic material – important as organic material can ruin aquatic life.

Biotic index: indirectly measures amount of a specific species in regard to its tolerance to pollution from which the pollution might be estimated.

Question 28

How to calculate biotix index

Answer 28

see biotic index.pdf (25 Jan)

e.g.:

Group 1: 0
Group 2: 24: 24*3= 72
Group 3: 41: 41*2= 82
Group 4: 33: 33*1= 33
Total number A=98
Total value B=187
Index= 1.908 (poor)

Question 29

Primary and secondary pollution

Answer 29

A primary pollutant is an air pollutant emitted directly from a source. A secondary pollutant is not directly emitted as such, but forms when other pollutants (primary pollutants) react in the atmosphere.

Primary pollutants include ammonia, sulfur dioxide, nitrogen dioxide and carbon monoxide. Secondary pollutants include ground-level ozone, acid rain and nutrient enrichment compounds

Question 30

Natural capital

Answer 30

natural assets in their role of providing natural resource inputs and environmental services for economic production. Natural capital includes land, minerals and fossil fuels, solar energy, water, living organisms, and the services provided by the interactions of all these elements in ecological systems.