Before you start, make sure you know: The hydrosphere (Secondary Year 2)
In the Gulf of California, shrimp and totoaba fishing has fed many families for generations, but it has also driven species like the vaquita porpoise to the brink of extinction. A living resource can produce year after year without running out, as long as we take no more than the population is able to replace. That idea is the foundation of sustainable management of any resource.
Renewable and nonrenewable resources
An oil well runs dry after a few decades of pumping, while a well-managed pine forest can supply timber for centuries. But if the whole forest is cut down in a few months, it will take centuries to recover, or it may never recover. What determines whether we can keep using a resource indefinitely?
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Distinguish between renewable and non-renewable resources by applying them to these three cases: a fishing ground, a riparian forest, and a coal deposit. Explain what…
Distinguish between renewable and non-renewable resources by applying them to these three cases: a fishing ground, a riparian forest, and a coal deposit. Explain what condition must be met for a living resource to continue behaving as renewable.
One Mexican example is the totoaba of the Gulf of California: excessive fishing (for its swim bladder) brought it close to extinction, and illegal nets also kill the vaquita porpoise. Another is overgrazing in the grasslands of northern Mexico, where livestock eat the grass faster than it regrows.
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Define overexploitation and give a real example of an overexploited living resource, explaining what signal indicates that exploitation exceeds the resource's capacity…
Define overexploitation and give a real example of an overexploited living resource, explaining what signal indicates that exploitation exceeds the resource's capacity for renewal.
The graph represents the natural renewal rate of a fishery according to its population size and the fleet's annual catch. a) Interpret why renewal is zero at both…
The graph represents the natural renewal rate of a fishery according to its population size and the fleet's annual catch. a) Interpret why renewal is zero at both extremes and maximum at intermediate sizes. b) Explain what point '?' represents and what will happen to the population if the catch remains higher than the renewal rate.
Explain what these three tools of sustainable fishing consist of — closed seasons, catch quotas, and minimum size limits — and what biological objective each pursues.
Explain what these three tools of sustainable fishing consist of — closed seasons, catch quotas, and minimum size limits — and what biological objective each pursues.
Aquaculture already provides nearly half of the fish consumed worldwide. Analyse two advantages and two environmental impacts of fish farms, and explain whether they can…
Aquaculture already provides nearly half of the fish consumed worldwide. Analyse two advantages and two environmental impacts of fish farms, and explain whether they can be considered the definitive solution to overfishing.
When a forest or jungle is cleared to open pastures or cropland, the climate, the soil, and biodiversity all change at once. It is a clear example of how overexploiting one resource throws an ecosystem out of balance.
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Deforestation of a forest triggers a chain of effects on climate, soil, and biodiversity. Explain this chain of effects and relate it to the increase in atmospheric…
Deforestation of a forest triggers a chain of effects on climate, soil, and biodiversity. Explain this chain of effects and relate it to the increase in atmospheric $\text{CO}_2$ and the loss of ecosystem services.
The ecological footprint for comparing production models
How do we compare two ways of producing corn if one uses more fuel, another more land, and another pollutes the water more? We need a common measure.
To compare models, we calculate the footprint per ton of product. All components are expressed in gha: the cropland area (converted with its equivalence factor, which here we assume equals 1 for simplicity) and the forest area that would be needed to absorb the CO₂ from fuel and fertilizers.
Cases for designing solutions
Hard cases call for combining everything above: the species' biology, data, enforcement, and social benefits.
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An anchovy fishery is depleted after decades of overfishing. Design a management plan to recover it: closed-season measures, scientific monitoring of stock, enforcement…
An anchovy fishery is depleted after decades of overfishing. Design a management plan to recover it: closed-season measures, scientific monitoring of stock, enforcement control, and a reopening schedule, justifying each decision using the species' biology.
Two adjacent 10 ha agricultural plots in the same region show the following annual balances: Plot A (intensive) produces 45 t/ha of citrus fruit, applies 200 kg N/ha in…
Two adjacent 10 ha agricultural plots in the same region show the following annual balances: Plot A (intensive) produces 45 t/ha of citrus fruit, applies 200 kg N/ha in synthetic inorganic fertilisers, uses flood irrigation, and consumes 14,000 kWh/year in machinery and pumping; Plot B (organic) produces 28 t/ha with cover crops, applies mature compost at a rate of 80 kg N/ha of organic nitrogen, uses drip irrigation, and consumes 6,500 kWh/year.
a) Predict and justify what quantitative and qualitative differences will be observed between both plots regarding nitrate leaching into groundwater, nitrous oxide (N₂O) emissions into the atmosphere, and the rate of soil carbon sequestration.
b) A technical report claims that "given that Plot B produces fewer kilograms per hectare, its ecological footprint per metric ton harvested is necessarily worse for the planet than that of Plot A". Refute this statement by analysing the fossil energy embedded in the synthesis of inorganic fertilisers (Haber-Bosch process) and the long-term degradation of natural capital.
c) Identify two negative environmental externalities of Plot A that are not reflected in the final market price of its citrus fruit, and propose a political or economic measure to internalise the real costs.
In an Extremaduran dehesa, livestock farming, hunting, and the conservation of threatened birds coexist. Outline the potential conflict between economics and…
In an Extremaduran dehesa, livestock farming, hunting, and the conservation of threatened birds coexist. Outline the potential conflict between economics and conservation and propose a management model that makes them compatible, explaining which ecosystem services the dehesa supports.