Chapter 4 Flashcards
Water budget
A quantitative estimate of the amounts of water in storages and flows of the water cycle
What drives the water cycle
Energy from solar radiation and the force of gravity
Water: renewable and non-renewable
Depending on where it is stored, can easily slide from being renewable to non-renewable if poorly managed
Renewable: atmospheres, rivers
Middle ground: groundwater aquifers
Non-renewable: oceans and icecaps
Aquifer
A layer of porous rock, sand or gravel underground that holds water. In aquifers, it takes longer than a human lifetime to replenish the water extracted
Water cycle - transfers
Stays in the same state: advection (wind-blown movement), flooding, surface run-off, infiltration and percolation (when water runs into and through soil or rocks), stream flow and current
Water cycle - transformations
Evapotranspiration (liquid to water vapour), condensation (water vapour to liquid), freezing (into solid snow and ice)
Water cycle - storages
Oceans, soil, groundwater (aquifers), lakes, rivers and streams, atmosphere, glaciers and ice caps
Human impact on water cycle
Withdrawals (domestic use, irrigation in agriculture/industry)
Discharges (adding pollutants to water, chemicals, fertilisers, sewage)
Changing speed at which water can flow/where it flows (building roads, channelling rivers, canalizing, dams, barrages and dykes, reservoirs)
Diverting rivers or sections of rivers (to avoid flood damage, to improve storage)
Canalizing
Straightening large sections of rivers in concrete channels to facilitate more rapid flow through sensitive areas
Flash floods
Occur when rainfall or snowmelt cannot infiltrate the soil and runs off on the surface
Due to land being hard-baked in hot, dry areas, but due to the CITY-based surface (urbanization!!!)
Ocean currents
Movements of water both vertically and horizontally. They move in specific directions and are found on the surface and in deep water
Ocean currents importance
Global distribution of energy
Without them, we could not understand the global atmospheric energy changes
Surface currents
Upper 400m of ocean, are moved by the wind
Earth’s rotation deflects them and increases their circular movement
Deep water currents (thermohaline currents)
Make up 90% of ocean currents and cause the oceanic conveyor belt
Deep water currents key ideas
Due to differences in water density caused by salt and temperature
Warm water can hold less salt than cold water so is less dense and rises - cold water holds more, sinks
Upwellings
When warm water rises, cold has to come up from depth to replace it
Downdwellings
When cold water rises, it has to be replaced by warm water
Cold ocean currents
Runs from the poles to the equator (e.g. Humboldt Current and Benguela Current)
Warm ocean currents
Flow from the equator to the poles (e.g. Gulf Stream and Angola Current)
Water and its effect on temperature
Water has a higher specific heat capacity than land
Water masses heat up and cool down more slowly than landmasses
Land CLOSE to seas and oceans has a mild climate with moderate winters and cool summers
How ocean currents affect local climate
Gulf Stream moderates the climate of Northwestern Europe, which otherwise would have a sub-arctic climate
(Cold) Benguela Current moderates the climate of the Namibian desert
Humboldt Current impacts the climate in Peru
El Niño Southern Oscillation (ENSO)
A phenomenon in the Pacific Ocean - pressure differences across the ocean is reversed (called the Southern Oscillation)
These pressure differences alter both the directions of the wind and the warm surface current
El Niño Southern Oscillation (ENSO) effects
Local effects - collapse of anchovy fish stocks, massive death of sea birds and storms and flooding in the coastal plain of Peru
Humans use fresh water for…
Domestic purposes (drinking, washing, cleaning), agriculture (irrigation, for animals to drink), industry (manufacturing, mining), hydroelectric power generation, transportation (ships), marking the boundaries between nation states (rivers and lakes)
Water scarcity
A measure of how much water there is and how we use it
Major rivers
Danube River - runs through 19 countries and is shared by 81 million people
Who owns the water? another Tragedy of the Commons -> many disputes over who owns it, especially since it becomes increasingly needed and scarce
Sources of freshwater
Surface freshwater (rivers, streams, reservoirs and lakes) and underground aquifers
Aquifer
A layer of porous rock (holds water) sandwiched between two layers of impermeable rock (does not let water through)
Aquifers key ideas
water flow in aquifers is extremely slow -> aquifers often used unsustainably
many are also ‘fossil aquifers’, meaning that the recharge source is no longer exposed at the surface and they are never refilled -> these can NEVER be used sustainably
Problems related to freshwater use
Climate change disrupts rainfall patterns, causing further inequality of supplies
Low water levels in rivers and streams (e.g. Colorado River, now is a tiny stream)
Slow water flow in the lower courses of rivers results in sedimentation, which makes the already shallow river even shallower
Underground aquifers are being exhausted, aquifer cannot be used anymore -> strongly affects agriculture
Problems related to freshwater use (part 2)
Pumping rates from aquifers are too fast -> causes exhaustion making the well unusable
Freshwater becomes contaminated and unusable
Fertilisers and pesticides used in agriculture often pollute water streams and rivers
Industries release pollutants into surface water bodies
Industries and electricity plants release warm water into rivers
Irrigation
Often results in soil degradation, especially in dry areas
Salinisation
Water used in irrigation evaporates before it is absorbed by the crops. Dissolved minerals remain in the top layer of soil, making it too saline (salty) for further agriculture
Effects of warm water in rivers
Holds less dissolved oxygen than cold water, so aquatic organisms that take oxygen from water (fish) are negatively affected
Changes the species composition in the water
Solutions to problems related to freshwater use
increase freshwater supplies by reservoirs, redistribution, desalinisation plants, rainwater harvesting systems (large and small scale), artificially recharging aquifers
Reduce domestic use of freshwater by using more water-efficient showers, dishwashers, and toilets
Wash cars in car washes with a closed water system
Grey-water recycling - water from showers, baths etc that can be reused for garden irrigation, flushing, etc
Selecting drought resistant crops can reduce the need for irrigation
Solutions to problems related to freshwater use (part 2)
Reduce the amount of pesticide and fertiliser used, prevent over-spray directly into a stream
Replace chemical fertilisers with organic ones (release of nutrients is slower and more likely to be absorbed)
Use highly selective pesticides instead of generic pesticide
Industries can remove pollutants from their wastewater with water treatment plants
Regulate maximum temperatures of released cooling water (don’t release warm water)
Grey water
Very lightly used water that can be reused (to irrigate gardens, clean cars, flush WCs, etc)
case study: Israel’s water shortage
greatest water drought in the past decade, caused by population growth and an improvement in quality of life (greater desire to water lawns and gardens)
will launch a conservation campaign, targeting mostly household use - has already reduced by more than 50% the drinking water supplied to farmers, increasing their need for recycled water
has two desalinisation plants that supply about 1.3 of water needed
case study: China’s Three Gorges dam
this hydroelectric dam on the Yangtze river was one of the largest engineering projects in the world (estimated cost US$30 billion)
provides 9% of all China’s output, savings in CO2 emissions are huge, also stops river from flooding
criticisms: environmental degradation, refugees, destroy archaeological sites, threaten wild species, silt up, pollution from building the dam
risk of energy security - if it is destroyed, all of this power generation is lost ( too dependant?)
Marine ecosystems
Oceans, mangroves, estuaries, lagoons, coral reefs, deep ocean floor - are usually very biodiverse and so have high stability and resilience
Continental shelf
The extension of continents under the seas and oceans
Importance of continental shelf
Has 50% of oceanic productivity but 15% of its area
Upwellings bring nutrient-rich water up to the continental shelf
Light reaches the shallow seas (producers can photosynthesise)
Countries can claim it as theirs to harvest and exploit
UN Convention on the Laws of the Sea (UNCLOS)
1982 - designated continental shelves as belonging to the country from which they extend
Phytoplankton
Single-celled organisms that can photosynthesise and are the most important producer in the oceans, producing 99% of primary productivity
Zooplankton
Single-celled animals that eat phytoplankton and their waste
Marine organisms can be classified as…
Benthic - living on or in the sea bed
Pelagic - living surrounded by water from above the sea bed to the surface
Fishery
When fish are harvested in some way. It includes capture of wild fish (also called capture fishing) and aquaculture or fish farming
Aquaculture
The farming of aquatic organisms in both coastal and inland areas involving interventions in the rearing process to enhance production
Why is fish farming increasing?
Diets changing - more fish instead of meat with saturated fat
Ways in which fish farming is sustainable
Fishmeal uses more trimmings and scraps which would have been wasted in the past
Livestock and poultry processing wasted is also substituted for fishmeal
US Department of Agriculture has proven that 8 species of carnivorous fish can get enough nutrients from alternative sources without eating other fish
Fish farms impacts
Loss of habitats
Pollution (with feed, antifouling agents, antibiotics and other medicines added to the fish pens)
Spread of diseases
Escaped species including genetically modified organisms which may survive to interbreed with wild fish
Escaped species may also outcompete native species and cause the population to crash
Fish stocks are shrinking because
Industrialised nations subsidise their modern fleets by an estimates US$50 billion a year
Demand outstrips supply
Sustainable yield (SY)
The increase in natural capital (e.g. natural income that can be exploited each year without depleting the original stock or its potential for replenishment)
Sustainable yield of an aquifer
The amount that can be taken each year without permanently decreasing the amount of water stored
Maximum sustainable yield
Highest amount that can be taken without permanently depleting the stock
Carrying capacity for each species depends on
Its reproductive strategy, its longevity, the indigenous resources of the habitat/ecosystem
Sustainable yield formula
(Total biomass at time t + 1 / energy) - (total biomass at time t / energy)
or
Annual growth and recruitment - annual death and emigration
Why harvesting the MSY leads to population decline and loss of resource base
Population dynamics of the target species are normally predicted (modelled) rather than the species numbers being measured (counted)
Often impossible to be precise about the size of a population
Estimates are made on previous experience
Model does not allow for monitoring of the dynamic nature of the harvest in terms of age and sex ratio
Disease may strike the population
If you extract/harvest at the MSY, you will…
Deplete a population in poor recruitment years
Optimal sustainable yield (OSY)
Requires less effort than MSY and maximises the difference between total revenue and total cost
Has a much greater safety margin than MSY, still may have an impact on population size if there are other environmental pressures within a system
