ESS chap.4 Water, aquatic food production systems and societies

The hydrological cycle

movement of water between 3 storages (oceans, atmosphere, land) powered by the sun

• inputs : solar energy + precipitations

• outputs : evapotranspiration + runoff (ruissellement)

human impact : agriculture, deforestation, urbanisation → more runoff, less infiltration

Earth’s water budget

97% : salt water

3% : fresh water

• 70% ice caps and glacier

• 30% groundwater

• 2% others

Turnover

the time it takes for the water in a river, lake, or ocean (for instance) to regenerate

The human impact

Withdrawals : for domestic use + for irrigation

Discharges : pollution (chemicals from factories)

Change in the speed of water : hydraulic dams, mega pools

Diverting rivers : to avoid flood management and improve storage

Ocean conveyor belt

deep, large-scale circulation of the ocean’s waters that is largely responsible for the transfer of heat from the tropics to colder regions

Why is water a critical resource?

Unavoidable for

• domestic purposes

• agriculture

• industry

• hydroelectric power generation

• transportation

continental shelf

extension of continents under the sea

how many people are killed every day because of water pollution?

14 000

Types of water pollution

anthropogenic (by humans) or natural (volcanic eruption for ex)

point source or non-point source (easily and not easily identified source of polution)

organic (invasive species) or inorganic (inorganic plant nutrients)

direct or indirect

radioactive pollution

Measuring water pollution

using ph (simple and direct)

Biochemical oxygen demand (BOD): the measure of the amount of dissolved oxygen required to break down the organic material in a given volume of water through aerobic bioactivity

Biotic index: assess the impact on species (indirect)

• Trent biotic index: disappearance of indicator species as the level of pollution increases

indicator species: some species live in polluted environments only, some in non-polluted environments only (they indicate if the environment is polluted or not)

• salmon: only survive in a non-polluted environment

Common goods

global + individual needs

• exploration of the ocean

Max sustainable yield

max capital that can be exploited without deregulating the system

depends on the reproductive strategy, the longevity, the resource of the habitat

Water currents

Deep water currents (due to inferences in water density, change of salinity and temperature)

• cold currents : Humboldt (Peru) + Benguela (Namibia)

• hot currents : Gulf Stream (North Atlantic Ocean)

Water scarcity

a situation where there is not enough water to meet the needs of a region's population. It occurs when demand exceeds supply due to factors like climate change, pollution, and overuse of water resources.

Water conflicts

Egypt and Ethiopia over the Nil

Eutrophication

Natural or artificial enrichment of a body of water in nitrates or phosphates → lower oxygen levels + growth of algae

Causes :

• human activity (with detergents, fertilizers)

• decomposing biomass, runoff water

Impacts :

• + biomass of algae

• + death of plants so - biodiversity

• - oxygen levels so the death of organisms

• financial loss → treating nitrate-enriched water is expensive

• nitrate-enriched water - stomach cancer + blue baby syndrome (less oxygen in pregnant women’s blood)

Dead zones

spaces in oceans or freshwater where there is not enough oxygen to support marine life (can be a consequence of eutrophication)

Pollution management strategies

• Alter human activity

education for awareness

research to propose alternatives (avoid fertilizers in water as it is most likely to run off and pollute the water)

• Regulations and reduction to manage the release in the environment

• Clean up and remove the pollutant → stop or diminish long-term impacts

reintroduce plant and animal species

pump nutrient-rich sediment from eutrophic lakes

Terrestrial vs Aquatic Food Production Systems

Terrestrial :

• most food is harvested from low trophic levels (producers)

• less efficient energy conversions

• higher initial fixing of energy from the sun

Aquatic :

• most food is harvested from higher trophic levels

• more efficient energy conversions

• lower initial fixing of energy from the sun (because of reflection by the water)