Agroecosystems

• Ecosystem - The interaction between abiotic and biotic factors in the environment
• Agroecosystem - The interaction between abiotic and biotic in a farming environment

Features of a natural ecosystem	Features of an agricultural ecosystem	Reason	Environmental effect
Climax Community forms	A plagioclimax is maintained = deflected succession	Need to grow crops not a woodland	Reduced habitat diversity, reduced niches
Many plant species	One species – a monoculture	Easier to manage one crop – 2 crops in one field would make planting, weeding and harvesting harder	Removes natural predators of pests and makes crop susceptible to a pest epidemic so pesticides are essential. Pesticides may contaminate food, leach into water supplies or move up food chains, harming useful organisms – pollinating insects or pest-eating birds for example. May lead to nutrient deficiency as all individuals need same nutrients. Thus, artificial fertilisers are needed
Genetic diversity within crop species	Reduced genetic diversity within crop	Crop likely to be genetically engineered for a small number of desirable characteristics	Loss of genetic diversity that may be needed if environmental conditions change or if a new disease/pest emerges
Soil always covered by some plant species	Soil often left bare after harvesting	Not economic to plant second crop in same year/growing season may make it impossible	Soil erosion
Nutrient cycling occurs via death and decomposition of plants and animals	Harvesting removes plants. Animals are killed by pesticides or kept out by enclosures. So nutrient recycling is impossible. Nutrient additions must be made in the form of fertilisers	The crop is needed for sale. Fertilisers must be used to return the nutrients lost when the crop was removed	Nitrates high soluble so may leach. Phosphates erode. Entry of nitrates and phosphates into water course leads to eutrophication. Loss of fertilisers means more must be applied therefore more must be made which increases the use of fossil fuels
Relatively low productivity	High productivity	Crop receives huge energy input in the form of artificial fertilisers/pesticides etc	Energy is from fossil fuels, the extraction and burning of which leads to global warming. Fossil fuels are finite so system may be unsustainable and unethical – future generations will have no choice but to find alternatives or change their agriculture systems

 

Oil and Gas

• Non-renewable resources - rate of formation < rate of consumption

• Formed from dead tropical marine plankton
• Formed over millions of years in anaerobic conditions with heat and pressure
• Moves from kerogen to oil shales to tars to heavy oils then light oils then diesel and petrol and eventually natural gas
• Young oil is more viscous - doesn't run - hard to extract
• Stored in porous reservoir rocks eg. Sandstone
• Cap rock needed above to contain the deposits - impermeable rock
• California - Lake View Gusher, Micricopa
• Primary recovery whereby the oil and gas comes to the surface under its own pressure(a gusher)
• Pressure is created by water below or gas above, or both
• Secondary recovery - pumping down water or gas to increase the pressure
• Tertiary recovery - attempts to increase the mobility of the oil making it less viscous
• Involves injecting stream or detergents in to the reservoir rock to make the oil flow more readily


Problems of oil recovery:
• Young oils too viscous to flow
• Oil deep below surface (5km) difficult to reach as friction increases and pumping fluids in to carry out rock fragments becomes harder
• Oil beneath deep water (2km) hard to exploit as anchoring floating rig is hard
• Oil that is very viscous or in impermeable rock will not flow to the extraction well
• Many oil fields are too small to be exploited profitably

Uses:
• Range of different uses - very versatile
• Main uses
 - building and process heating
 - vehicle fuels
 - electricity generation and petrochemicals

Environmental Impacts:
• Exploration
 - seismic surveys - affects whales
 - explosions to test for oil - habitat disturbance
 - benthic species - sea bed species
• Extraction
 - leaks eg. BP oil spill
 - anchoring rigs - destroys sea bed - benthic species
• Transport
 - pipelines - habitat destruction
 - fuel for transport
• Process
 - air pollution - fractional distillation
 - energy intensive
• Use
 - fuels - petrol/diesel - nitrous oxide = acid rain
 - habitat destruction - building petrol stations
• Waste
 - air pollutants
 - plastics - don't biodegrade

Future:
• As oil and gas become exhausted we are needing to use technology to find and extract oil and gas in new ways
• Oil sands and shales eg. Alberta, Canada
• Drilling in deep water eg. Gulf of Mexico - deep water horizon
• Drilling in difficult environments eg. the North Sea
• Drilling in harsh climates eg. the Artic
• Fraking eg. in USA

• These less conventional methods of extracting oil are likely to have greater environmental impacts and as they are more expensive ways of extracting the resources global prices are likely to increase