Overfishing/ agricultural exploitation Flashcards
1
Q
What is agricultural exploitation?
A
The way agricultural land is used often conflicts with maintaining habitats and biodiversity. The efficiency and intensity of food production are continually increased to meet the demand for food
2
Q
Changes that contribute to agricultural exploitation:
A
- Removal of hedgerows to enable large machinery to prepare soil and harvest crops
- Monoculture which is when single crops e.g. wheat or barley are grown over a large area. Monoculture provides only one habitat and so it reduces species diversity
- Overgrazing by cattle cause grassland to become more unsustainable. Their hooves compact the soil, driving out the air and preventing water grazing through. Roots cannot penetrate the soil ad so grass for grazing cannot grow
3
Q
- If the same crop is grown on the same plot year after year, why does yield progressively decrease?
A
- The roots are always the same length so they extract the same minerals from the same minerals form the same depth of soil. Intensive farming has therefore hugely increased the use of inorganic fertilisers
- The same species is always susceptible to the same pests, which increases in number so more insecticides, herbicides and fungicides are used
4
Q
What can the EU and national schemes to encourage farmers to manage their farms for biodiversity
A
- Some land is given over to conservation and the farmers are given subsidies i.e. more money to compensate them for reduced income due to lowered crop production
5
Q
What are some reasons of deforestation?
A
- building materials
- fuel
- paper and packaging
- land cleared for farming
6
Q
What are consequences of deforestation?
soil erosion
A
- Soil erosion: tree roots bind soil together. Deforestation on the higher slopes of valleys allows heavy rain to sweep exposed topsoil down to the flood plains below. Topsoil is the fertile soil and what remains is not suitable for crop growth
7
Q
What are consequences of deforestation?
flooding
A
- Deforestation of uplands causes lowland flooding
8
Q
What are consequences of deforestation?
quality of soil
A
- Under normal conditions, on lower slopes plants, humus and leaf little act as a sponge, soaking up heavy rainfall, and water is only gradually released into the soil.
- Trees transpire and return water to the atmosphere. After deforestation, there are no plants and water evaporates from the soil.
- This diminishes the quality of the soil
9
Q
What are consequences of deforestation?
oxygen availability
A
- Evaporation returns water vapour to the atmosphere more slowly than transpiration, so soil on deforested land becomes wetter. Water fills the soils airspaces and so the oxygen available for roots decreases
10
Q
What are consequences of deforestation?
root activity
A
- It takes longer for a wet soil to warm up than a dry soil, so these soils are also cold. Germination and root activity are reduced
11
Q
What are consequences for deforestation?
fertility
A
- Cold, damp soil favours the growth of denitrifying bacteria, and so the soil loses its fertility
12
Q
What are consequences for deforestation?
desertification
A
- Less rainfall: water only returns to the atmosphere by evaporation from the soil, not by transpiration, and evaporation is slow. This accelerates desertification
13
Q
What are consequences for deforestation?
reduction in biodiversity
A
- Habitat loss and reduction in biodiversity. It is estimated that at least 50% of the earths species live in the tropical rain forest, which cover only about 10% of the earths land area.
- Destruction of such natural habitats may lead to the loss of some tropical species
- They may become extinct before their clinical properties have been investigated
14
Q
What are consequences for deforestation?
Effects on the atmosphere
A
- As photosynthesising trees are cut down, the removal of carbon dioxide from the atmosphere by photosynthesis is decreased. Cut trees may be burned or left to decay, releasing carbon dioxide in the atmosphere
15
Q
Forest management: slash and burn
A
- A small forest area is cut and burned. People grow crops on soil fertilised with ash from the burned trees
- When the soil is no longer fertile, people leave and the area regenerates
- This is sustainable on a small scale but not o the large scale it occurs in rain forests now
16
Q
Define managed forestry
A
- It involves sustainable replanting and regenerating
17
Q
Managed forestry: What is slash and burn
Is it sustainable on the large scale?
A
- A small forest area is cut and burned
- People grow crops on soil fertilised with ash from the burned trees
- When the soil is no longer fertile, people leave and the area regenerates
- This is sustainable on a small scale but not on the large scale it occurs in rain forests now
18
Q
Managed forestry: Coppicing
What is good about having a long rotation time?
A
- A tree trunk is cut, leaving a ‘stool’ a few centimetres high
- New shoots emerge from buds in the stool and grow into poles, which thicken over the years
- The poles can be cut on rotation to produce timber of different widths
- Coppiced plants can regenerate over long periods of time
- A long rotation time increases sustainability as many years are left between harvesting adjacent areas of forest and a variety of habitats develop, favouring diverse wildlife
19
Q
What is selective cutting and why is it advantageous?
A
- Instead of moving all the trees in an area at one time, selective cutting, can be used.
- This technique is vulnerable to erosion.
- Selective cutting also helps to maintain nutrients in the forest soil and minimises the amount of soil that is washed into nearby waterways
20
Q
Give an example of good forestry practice:
Where trees are planted
A
- Planting trees the optimum distance apart. If they are too close, intra-specific competition occurs and the trees grow tall and thin, producing poor quality timber
- Controlling pests and diseases so that trees grow well, producing high quality timber. Fewer trees need to be felled and best use is made of the land, reducing area required
21
Q
Give an example of good forestry practice:
Controlling pests and disease
A
- Controlling pests and diseases so that trees grow well, producing high quality timber
- Fewer trees need to be felled and best use is made of the land, reducing the total area required
22
Q
Give an example of good forestry practice:
When trees are planted
A
- Cutting a similar number of trees each year for long periods of time allows the forest ecosystem to be maintained
- Habitats are left intact and species are able to live in the forest even though timber is being extracted
23
Q
What is overfishing?
A
The dramatic increase in intensity and efficiency of commercial fishing has caused
24
Q
Causes of overfishing:
Nets with small nets
A
- Catch young fish before they have become sexually mature
- This means that as time goes by, there are fewer individuals left to reproduce and so the population size decreases
- It may be harder for remaining fish to find a mate and with a smaller number reproducing, the genetic diversity of the population decrease
25
Causes of overfishing:
| Drift netting
- Pelagic fish live in surface waters
- They swim into a net, suspended from floats, stretched between two boats
- But with thousands of miles of nets, non-target species e.g. dolphins and marine turtles are trapped
26
Causes of overfishing:
| Trawling
- Fish that live in deeper in water, the mid and bottom feeders are caught by a large net which is dragged through the water, catching whatever swims into it
- Equipment used in trawling has damaged the ocean bed, destroying the habitats of molluscs such as clams, and other organisms, putting populations at risk
27
What are some effects of overfishing on other wildlife
- When trawlers spread their nets, they catch a fish called capelin. These are not eaten by humans but they are not eaten by humans but they are not eaten by humans but they are an important prey species for cod, so removing them from the sea has contributed to the decline of cod stocks
- harvesting antartic krill, which are primary consumers that eat phytoplankton. They are the main food of whales, penguin squid and fish. Disturbs the ecological balance (badly effects the rest of their food web)
28
Methods to regulate and allow breeding stocks to recover
| (1) mesh size
- The mesh size of the nets must be large enough that young fish can swim through and survive. This is supported by legislation that prevents selling fish below a certain size
29
Methods to regulate and allow breeding stocks to recover
| (2) Quotas
-Quotas can be set so that only a certain mass of fish may be brought to land. It appears that however, that more fish are taken than allowed by the quotas and they are thrown dead into the sea
30
Methods to regulate and allow breeding stocks to recover
| (3) Exclusion zones
Exclusion zones prohibit fishing in defined areas at certain times of the year, allowing the fish to reproduce. The position of fishing trawlers can be monitored by satellite technology and fines imposed for non-compliance
31
Methods to regulate and allow breeding stocks to recover
| (4) consumer choice
- Consumers may choose to eat only those fish certified by the Marine Stewardship Council, which ensures fish are taken from sustainable sources
32
Methods to regulate and allow breeding stocks to recover
| (5) Legislation
Legislation controlling the size of fishing fleets
33
Methods to regulate and allow breeding stocks to recover
| (6) Fish farming
Fish farming reduce overfishing
34
What is fish farming?
- Fish can be bred and grown to maturity in ponds, lakes and enclosures in estuaries, where predation is reduced and food supplies are maintained
- For plankton feeders the growth of phytoplankton can be increased by the addition of artificial fertilisers to the water
- Fish grow rapidly when they are reared in the warm waters discharged from factories
- Fish are sometimes farmed in a pond, a large, steerable device, which can be moved, depending on prevailing ocean currents, on local water temperature and other abiotic factors
35
Advantages of fish farming
- Fish convert their food into protein more efficiently
- A greater proportion of fishes' bodies are edible
- Fish farming has a lower carbon footprint
36
Disadvantages of fish farming:
| Diseased fish
- Farmed salmon are often very densely stocked and so can easily transmit disease
- Huge doses of antibiotics are required to keep them moderately healthy
- The pesticides used to control fish parasites, such as sea lice, are known to harm marine invertebrates, especially molluscs
37
Disadvantages of fish farming:
| Pollution
- The ecological balance of waterways may be upset
- Eutrophication, for example can result when fish excreta, waste food and fertiliser are carried into the water around the rearing pens
38
Disadvantages of fish farming:
| Escaped fish
- Farmed fish have been selected for very rapid growth
- If they escape, they out-compete wild fish for food, habitat and mates
- They also transmit parasites and other infections
- Escaped farmed fish interbreed with wild fish and set up fast growing colonies which can push wild fish to extinction
39
Disadvantages of fish farming:
| Resource use
- Farmed salmon, which are carnivorous, eat three times their bodyweight in fish feed, which is made from other fish
- This is a poor use of resources from an environmental point of view
40
Disadvantages of fish farming:
| Environmental toxins
-e.g. methyl mercury, PCBs, dioxins and pesticides, are more concentrated in farmed than wild salmon, although their concentrations are so small that their effects do not outweigh the health benefits of eating fish
41
Disadvantages of fish farming:
| Environmental degradation
- The shrimp industry, in particular, has been blamed for the salinization of soil and groundwater and the destruction of the mangroves that normally protect coastal communities from tropical storms
