ess: chapter 4 - water, food production systems and society

water budget

water budget

quantitative estimate of amounts of water in storages and flows of water cycle

eg flows in water cycle

• transfers (same state): flooding, infiltration, current

• transformations (changes state): evapotranspiration, condensation

eg storages in water cycle

ocean, soil, atmosphere, lakes

turnover time

time for water molecule to enter and leave part of the system

freshwater

2.6% (69% of which = frozen)

hydrological cycle

driven by solar radiation and gravity

human impact on the water cycle

1. withdrawals: domestic use, irrigation for agriculture and industry

2. discharges: adding pollutants

3. changing speed and locations: roads, channels, canals, dams

4. diverting rivers/sections: away to avoid floods, towards dams

flash floods

urbanisation thus land cannot absorb precipitation

ocean currents

important in global distribution of energy

• surface currents (400m) are moved by wind and earth’s rotation

• deepwater currents/thermohaline circulation makes up the oceanic conveyor belt:

  • due to difference in density because of salt and temperature

  • cold at poles travels to the equator

  • Gulf Stream

  • climate

    • water cools and heats slower than land

    • Gulf stream heats Europe, ENSO impacts Peru

grey water

very lightly used water

salinisation

dissolved minerals not evaporated after irrigation

aquifer

layer of porous rock and water sandwiched between layers of impermeable rock, filled continuously by infiltration of precipitation in limited areas

desalination plans

• expensive, require fossil fuels, harms ocean-bottom ecosystems when salt is released

• solution to freshwater scarcity

water scarcity

not only when lacking, but also with unjust division in an area

tragedy of the commons

who is responsible for the water? tension between common good and needs of individual (advantage for individual > individual cost) → short term worth exploiting, otherwise someone else will

sustainable water use

when there is full natural replacement and recovery of the ecosystem

freshwater use issues

• climate change disrupts rainfall

• low water levels in rivers

• sedimentation due to slow water flow → shallower river and sea

• aquifers become exhausted → soil shrinks, agriculture difficult

• freshwater contaminated

• irrigation → salinisation

• fertilisers and pesticides → pollute

• industries and electricity plants → warm water, thus less oxygen → fish affected

freshwater use solutions

• increased freshwater supply (reservoirs, redistribution, desalination, rain when harvest, artificial recharge of aquifers)

• reduce domestic use (water efficient showers, toilets)

• grey water recycling

• more efficient irrigation

• optimize area use

• reduce pesticides, use organic fertilisers

• water treatment plants in industries

water wars

dispute over unequal distribution of water (eg. Israel/Palestine, Chinese Three Gorges dam)

fishery

wild fish capture and aquaculture

aquaculture

farming of fish with interventions to enhance production

maximum sustainable yield (MSY)

highest amount that can be taken without depleting stock permanently

optimal sustainable yield (OSY)

safer version of MSY

continental shelf

extension of continent under sea

phytoplankton

single celled organisms, photosynthesise, 99% of (global? marine?) primary productivity

marine ecosystems

biodiverse thus stable and resilient, over half are above continental shelf (where upwellings bring nutrient rich water, light reaches, but countries can claim)

UNCLOS (laws of sea)

(part of it:) continental shelf belongs to country it extends from

benthic

marine organism on/in sea bed

pelagic

marine organism surrounded by water

pros and cons aquaculture

pros:

• becoming more sustainable (their food more efficient)

• most is in rice paddies in China (mutual benefit system)

cons

• loss of habitat

• pollution (feed, antibiotics)

• spread of diseases

• escaped GMO fish interbreed with wild

• escaped outcompete native

unsustainability of wild fish industry

• technology too advanced

• too small fish caught

• fleets have factory ships

• trawlers clearcut seabeds

• dead by-catch thrown back

biochemical oxygen demand (BOD)

amount of dissolved oxygen required to break down organic material by aerobic biological activity by microorganisms in given volume of water

indicator species

show something about environment through presence/absence and abundance/scarcity, chosen because sensitive to change

biotic index

indirectly measures pollution, assaying impact on species according to tolerance, diversity and relative abundance

eutrophication

when water receives input of nutrients → excess growth of plants and phytoplankton

dead zones

caused by eutrophication; when not enough oxygen

water pollutants

1. anthropogenic or natural

2. point source or non-point source

3. organic or inorganic

4. direct or indirect

organic:

• sewage, animal waste, washing powder → eutrophication

• pesticides → loss of biodiversity

• invasive species → decimates indigenous

inorganic:

• nitrates and phosphates → eutrophication, changes biodiversity

• hot water → kills fish, changes biodiversity

• oil → contaminates birds, reduces oxygen

• noise → disrupts turtles, upsets bird cycles

BOD vs indicators

BOD: current measure, indicator: summary of recent history

eutrophication impacts

• anaerobic water

• loss of biodiversity

• death of plants and aerobic organisms

• increased turbidity

red tides

eutrophication with dinoflagellate; red and harmful to humans

management strategies

• alter human production of pollution

• regulate pollutant where emitted

• clean up and restore