ess unit 4 - water systems

the Earth’s water budget

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

70% of the earth’s surface is covered by water

• 97% is ocean salt water

• 3% is fresh water

• 0.3% is in lakes and rivers

7 sources of fresh water (in order of volume contained)

1. ice caps and glaciers

2. groundwater

3. lakes

4. soil water

5. atmospheric water vapour

6. rivers

7. biota (water in living things)

stages of the water (hydrological) cycle

• stage 1: evaporation

• stage 2: condensation

• stage 3: precipitation

• stage 4: infiltration and percolation

• stage 5: groundwater flow

or

• stage 4: surface flow/run off

• stage 5: evapotranspiration

solar radiation drives the water cycle

flow/ processes in the hydrological (water) cycle

• evaporation

• precipitation

• infiltration

• percolation

• evapotranspiration

• surface run off

• groundwater flow

• ice melt

precipitation

the fall of liquid or solid water from the atmosphere to the ground or surface water

evaporation

the change of water from a liquid to a gas upon warming

condensation

the change of a gas to a liquid (water) upon cooling

evapotranspiration

the process by which water is transferred from the land to the atmosphere, by water leaving the soil (evaporation) and water lost through plant leaves and stems (transpiration)

→ liquid to water vapour

water → soil → plants → leaf surface → evaporation happens

percolation

the soaking of water down through layers of soil/rock

infiltration

physical process of water soaking into soil

transfers (stays in same state) in the water cycle

• advection (wind blown movement)

• flooding

• surface run off

• infiltration or percolation

• stream flow and current

transformations (changes state) in the water cycle

• evapotranspiration

• condensation

• freezing

• evaporation

• precipitation

• ice melt

storages in the water cycle

• oceans

• soil

• lakes and rivers

• groundwater

• atmosphere (water vapour, rain)

• snow and ice

human impacts on the water cycle

1. withdrawals → domestic use, irrigation in agriculture and industry

2. discharges → adding pollutants to water e.g. fertilisers, sewage

3. changing speed of water flow and where e.g. urbanisation, dams, reservoirs, canals

4. diverting rivers

ocean currents definition

movements of water both vertically and horizontally, they have an important role in the global distribution of energy

surface currents

the upper 400 m of ocean which are moved by the wind, the earth’s rotation deflects them and increases their circular movement

deep water (thermohaline) currents

make up 90% of ocean currents and cause the oceanic conveyor belt

process of ocean water circulation

• warm water can hold less salt than cold water so it is less dense and rises

• cold water holds more salt and is denser so it sinks

• when warm water rises cold water has to come up from depth to replace it (upwellings)

• when cold water rises, it also has to be replaced by warm water (downwellings)

• this makes water circulate

cold ocean currents direction and examples

run from the poles to the equator e.g. the Humboldt current (coast of Peru), the Benguela current (coast of Namibia)

warm ocean currents

run from the equator to the poles e.g. the Gulf stream (in North Atlantic ocean), the Angola current (coast of Angola)

how ocean currents affect local climate with examples

water has a higher heat capacity than land causing water to heat up and cool down slower than land, meaning that land close to oceans has a milder climate with moderate winters and cool summers

e.g. the North Atlantic Drift moderates the climate of Northwestern Europe which would otherwise have a sub-artic climate

drinking water definition

water used for any domestic purposes including drinking, cooking and personal hygiene

when is water deemed as accessible (water security)

when the source of water is less than 1 km away and it is possible to obtain at least 20 litres per member of household per day on a reliable basis

safe drinking water

water with bacterial (no pathogens), chemical (salt, led, nitrates, mercury) and physical characteristics that meet WHO guidelines or national standards for drinking water quality

• 20% of the world’s population lacks access to safe drinking water

physical water scarcity

when the demand for water exceeds the supply

• common in arid and semi-arid areas where rainfall is low

economic water scarcity

occurs when water is available but some people cannot afford to obtain it for reasons of poverty

reasons for decrease in water security (countries)

• political instability

• economic instability

• conflict

• disaster

• poverty

• lack of infrastructure

• weak accountability and monitoring

e.g. Papua New Guinea, impacts of colonisation

reasons for increase in water security

• international co-operation and aid

• economic development

• better policy making and government monitoring

e.g. in Botswana from 1970 to 2008, diamond mining and increased prioritisation from government

factors that affect future water use

• growing populations (urbanisation, population density)

• economic development (industrialisation, agriculture)

• climate change (change in rainfall patterns, low water levels in rivers)

• public attitudes towards water

environmental problems related to water usage

• depletion of surface and groundwater

• land and ecosystem degradation (irrigation)

• floods

• drought

• fertilisers polluting rivers

human problems related to water usage

• thirst

• hunger

• conflicts over water

• increasing distances to water resources

• slowed economic growth

management strategies to reduce water scarcity

• quotas (limits on usage)

• government legislation

• rainwater harvesting

• smart water application technology (SWAT e.g. irrigation, water purification and distribution systems)

• nature inspired water usage e.g. use less, polluting less

• higher prices for water

reasons countries are seeing more stress on their water supplies

• population growth

• increased demand for water in industrial and agricultural sector

• uneven distribution of water within/among countries

• depletion and shrinking of underground reserves

issues changing access to freshwater

• climate change is changing rainfall patterns

• low water levels in rivers and streams

• exhausted underground aquifers which cannot be used anymore

• fertilisers and pesticides used in agriculture pollute streams and rivers

• pollutants from industries into water bodies

solutions to improve freshwater supply

• reservoirs

• desalination plants

• rainwater harvesting

• artificially recharging aquifers

• reduce domestic use of freshwater e.g. showers

• recycling grey water (excess water from domestic uses)

• more effective irrigation and selecting drought resistant crops

• reduce the amount of pesticides and fertiliser used

• industries can remove pollutants from their wastewater with water treatment plants

continental shelf and its significance

the extension of continents under the seas and oceans

• it has 50% of oceanic productivity but 15% of its area

  → light reaches the shallow seas so producers can photosynthesise

• upwellings bring nutrient-rich water up to the continental shelf

• countries can claim it as theirs to exploit and harvest

• average 80km shelf width

two classifications of marine organisms

benthic → living on or in the sea bed

pelagic → living surrounded by water from above the sea bed to the surface

phytoplankton

single-celled organisms that can photosynthesise

• the most important producer in the oceans

• they produce 99% of primary productivity

• zooplankton eat the phytoplankton and their dead organic matter

  → these organisms support the complex food webs of the oceans

estuaries and their significance

section of a river which meets the sea

significance:

• contain high levels of biodiversity as there are so many zones per abiotic factor so many species find their own niche

• areas around estuaries (swamps and marshes) have high biodiversity and net primary productivity

• reduction of river flow reduces estuaries and biodiversity

• provide breeding grounds

importance of tidal zones near the coast and shallow seas

• highest levels of productivity

• high nutrient richness (upwelling of nutrients from deeper sea from death and decomposition)

• high oxygen content

• slower current

• warmer water

• many zones for each measured abiotic component

• high light availability

• shallow

abiotic factors that change as the river runs into the sea

• salinity (low to high)

• temperature

• currents (high to low)

• water clarity

• pollutant concentrations e.g. nitrates from Colorado river into Gulf of Mexico

• depth

challenges with fish farming today

• wild caught fish has reached its limit as we have overexploited them

• farmed fishing is unsustainable

• human diets are changing and people are consuming more fish due to health concerns

reasons for increase in fish production/farming and consumption

• reduction in costs

• growth of the middle class

• perceived sustainability of fish

• perceived health benefits

• improvement in global trade e.g. cold chain transport

negative impacts of fish farms

• loss of habitats

• pollution (feed, antibiotics and other medicines)

• spread of diseases

• escaped genetically modified organisms interbreed with wild fish

• escaped species may outcompete native species and cause population to crash

issues with wild fish capture techniques

• fish populations can deplete very quickly

• pollution from supply and factory ships

• indiscriminate fishing gear takes all organisms in an area not just targeted fish

• huge nets are dragged over seabeds destroying them

• refrigeration means they can stay at sea for weeks leading to larger fishing fleets

• commercial fishing has high level satellite technology, GPS navigation to find fish too easily

ways to make fish farming more sustainable

• using more scraps in fishmeal which would have been wasted

• substituting livestock and poultry processing waste for fishmeal

  → some carnivorous fish (trout, salmon) can get enough nutrients from alternative sources without eating other fish

examples of international crises about fishing rights

1970s: Iceland banned all foreign vessels from fishing in Icelandic waters, this led to three 'Cod Wars' between Britain and Iceland.

1994: British and French fishermen competed with Spanish fishermen for tuna in the Bay of Biscay

tragedy of the commons

where individuals exploit shared resources for personal gain, leading to overuse and depletion because advantages to individuals outweigh the shared disadvantages for the population

e.g. overfishing, traffic congestions, fast fashion, groundwater use

maximum sustainable yield

the increase in natural capital income that can be exploited each year without depleting the original stock or its potential for replenishment

→ it is important for commercial ventures

→ this is a crucial amount in fisheries showing how many fish and of what size can be taken in any year so that the harvest is not hurt in following years

SY = annual growth - annual decline

→ if the difference in population from initial size to new population size after the population grows is harvested the population will remain the same

→ in practice MSY lead to population decline

types of water pollutions

• anthropogenic (created by human activities)

• natural e.g. volcanic eruptions, algal blooms

• point source e.g. sewage pipe

• non-point source e.g. fertilisers from agriculture

• organic e.g. animal waste

• inorganic e.g. nitrates from fertilisers

• direct

• indirect

sources of freshwater pollution

and sources of marine pollution

freshwater pollution:

• agricultural run-off

• sewage

• industrial discharge

• solid domestic waste

marine pollution:

• rivers

• pipelines

• the atmosphere

• human activities at sea

• operational and accidental discharges

3 ways to measure water pollution

1. biochemical oxygen demand (BOD) → 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

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

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

eutrophication

occurs when water bodies receive inputs of nutrients (nitrates and phosphates) which result in excess growth of plants and phytoplankton

(can be a natural process but anthropogenic eutrophication is more common)

→ when it is severe it results in dead zones where there is not enough oxygen to support life

→ when it is less severe biodegradation of organic material can lead to low oxygen levels which releases toxic gases such as methane, hydrogen sulphide and ammonia

the process of eutrophication

1. fertilisers wash into water body

2. high levels of phosphate allow algae to grow faster

3. algal blooms form that block out light to plants beneath them and they die

4. more algae means more food for the zooplankton and the small animals that feed on, leading to less zooplankton

5. algae die and are decomposed by bacteria

6. however there is not enough oxygen in the water, the food chain collapses and everything dies

7. oxygen levels fall lower, dead organic material forms sediments on bed and turbidity (cloudiness of water) increases

8. eventually all life is gone and the sediment settles to leave a clear blue lake

impacts of eutrophication

• oxygen deficient (anaerobic) water

• loss of biodiversity and shortened food chains

• death of higher plants (flowering plants, reeds, etc.)

• death of aerobic organisms (invertebrates, fish and amphibians)

• increased turbidity (cloudiness) of water

• bad smells from gases like hydrogen sulphide

red tides

algal blooms (large numbers of phytoplankton) are sometimes caused by excess nutrients, creating a red bloom (if the phytoplankton are a species of dinoflagellate)

which can be dangerous as the algae produce toxins which kill fish and accumulate in shellfish making humans who eat it seriously ill

eutrophication management strategies

• ban or limit detergents with phosphates

• plant buffer zones between the fields and water bodies to absorb the excess nutrients

• stop leeching of slurry and sewage

• minimise fertiliser usage on agricultural lands

• remove excess weeds from water

• restock water bodies with appropriate organisms

salmon farm inputs and outputs

inputs:

• labour

• young salmon

• lice treatments

• genetically modified dish

• fish food

• automated feeding mechanisms

outputs:

• high and dependable salmon yield

• uniform fish

• no influence by weather/climate

• excess antibiotics

• salmon biomass

• dead salmon

salmon farm compared to commercial fishing system characteristics

salmon farm characteristics:

• high yield

• intensive farming

• high startup costs

• fast growth of fish biomass

• high resilience

• data led process

• very profitable

commercial (wild) fishing characteristics:

• small yield

• high value

• low cost

• simple technology

• time consuming

• labour intensive

• season and nature dependent

• higher socio-cultural significance

environmental impacts of salmon farms

• can set surrounding loch ecosystem out of balance

• left over food accumulates causing eutrophication

• high concentration of fish causing parasite accumulation

• chemicals used to kill parasites can kill other small organisms