Land and Water Use

How this unit is tested

What you have to know

14 practice questions

1. A mountain pasture is open for any local herder to graze livestock at no cost, with no limit on herd size. Over time the pasture becomes barren and can no longer support grazing. This scenario best illustrates which concept?
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   Answer. Tragedy of the commons

   Because the pasture is an unregulated, shared (open-access) resource, each herder benefits fully from adding more animals while the cost of overgrazing is spread across everyone, so no individual has an incentive to limit their own use. This leads to collective overuse and degradation.
2. Which change to an irrigated field's water delivery system would most directly reduce the risk of salinization?
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   Answer. Switching from flood irrigation to drip irrigation

   Flood irrigation applies large volumes of water that evaporate and leave salts behind in the topsoil. Drip irrigation delivers small, targeted amounts of water directly to plant roots, reducing standing water and evaporation, which slows salt accumulation.
3. Explain why heavy, repeated use of a single broad-spectrum pesticide often leads to a larger pest outbreak within a few growing seasons.
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   Answer. Natural selection favors resistant pests that survive and reproduce, while the pesticide also kills the natural predators/parasites that had been keeping the pest (and other secondary pests) in check.

   Repeated exposure selects for resistant individuals in the pest population, so resistance spreads. At the same time, broad-spectrum pesticides are non-selective and kill beneficial predator and parasitoid species, removing natural biological control and allowing both the resistant target pest and previously minor secondary pests to increase.
4. A country has an ecological footprint of 6.0 global hectares (gha) per person and a biocapacity of 2.5 gha per person. Calculate the ecological deficit per person and state what it means.
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   Answer. 3.5 gha per person deficit; the country's population is consuming resources and generating waste faster than its own land and water can supply or absorb, so it must import resources or draw down natural capital.

   Ecological deficit is found by subtracting biocapacity from footprint: $6.0 - 2.5 = 3.5$ gha per person. A positive deficit means the population is in overshoot relative to its own territory's biological capacity.
5. In the IPAT equation, which factor is most directly reduced when a country adopts more energy-efficient manufacturing technology, holding population and per-capita consumption constant?
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   Answer. Technology (T)

   IPAT states $Impact = Population \times Affluence \times Technology$, where Technology represents the environmental damage caused per unit of goods consumed. More efficient technology lowers this per-unit impact factor without requiring changes in population size or consumption levels.
6. Compare the environmental trade-offs of raising cattle in a CAFO versus on open, free-range pasture.
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   Answer. CAFOs concentrate waste in a small area, raising the risk of water pollution and disease, but use less land per animal produced; free-range grazing spreads waste over a larger area but requires much more land and risks overgrazing and desertification if stocking rates are too high.

   The key trade-off is land use versus waste concentration: CAFOs are land-efficient but create point-source pollution risks (manure lagoons, runoff), while free-range systems are more land-intensive and can degrade grassland ecosystems through overgrazing if not carefully managed.
7. Why does farming a carnivorous fish species such as salmon typically have a lower net environmental benefit than farming an herbivorous species such as tilapia?
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   Answer. Carnivorous farmed fish require fishmeal and fish oil made from wild-caught fish, so producing one kilogram of farmed salmon consumes more kilograms of wild fish than it replaces (a high fish-in:fish-out ratio), which can worsen depletion of wild fish stocks.

   Because of energy loss between trophic levels, feeding a carnivore requires far more input biomass than feeding an herbivore. Tilapia and other herbivorous or omnivorous farmed species can be fed plant-based feed, reducing pressure on wild fisheries, while carnivorous aquaculture often still depends heavily on wild-caught feed fish.
8. A commercial shrimp trawler's net also catches sea turtles and juvenile fish that are not sold and are discarded, often dead. What is this unintended catch called?
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   Answer. Bycatch

   Bycatch refers to non-target organisms unintentionally captured during fishing operations. It reduces populations of species beyond the one being targeted and is a major driver of biodiversity loss in commercial fisheries, distinct from the general depletion of the target species caused by overfishing.
9. Which best describes a key environmental impact caused specifically by mountaintop removal mining, beyond that of typical subsurface mining?
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   Answer. Large-scale removal of forest and topsoil and burial of streams with waste rock (valley fill), causing extensive surface habitat destruction

   Mountaintop removal strips away vegetation, soil, and rock layers over wide areas and dumps the waste into adjacent valleys, burying streams and destroying surface ecosystems, whereas subsurface mining disturbs a much smaller surface footprint (though it has its own risks like subsidence and mine drainage).
10. Explain the chemical process that produces acid mine drainage and why it harms aquatic ecosystems.
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    Answer. Sulfide minerals exposed by mining react with water and atmospheric oxygen to form sulfuric acid; this acidic runoff lowers the pH of streams and also leaches toxic heavy metals from surrounding rock, together killing fish and other aquatic organisms.

    Mining exposes previously buried sulfide-rich rock to air and water for the first time, triggering an oxidation reaction that generates sulfuric acid. The low pH directly stresses aquatic organisms, and the acidic conditions also dissolve heavy metals (like iron, copper, and aluminum) out of the rock, adding toxicity.
11. A logging company wants to harvest timber while minimizing soil erosion, habitat disruption, and loss of biodiversity in a mixed-age forest. Which harvesting method best meets these goals?
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    Answer. Selective cutting

    Selective cutting removes only certain mature or targeted trees while leaving most of the canopy and understory intact, which maintains soil-holding root structure, preserves wildlife habitat, and allows continued forest regeneration, unlike clear-cutting, which removes the whole stand at once.
12. Define urban sprawl and give one major environmental consequence of it.
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    Answer. Urban sprawl is the outward, low-density expansion of a city into surrounding undeveloped land; one major consequence is increased impervious surface area, which increases stormwater runoff and reduces groundwater infiltration.

    Because sprawl spreads development thinly over a large area rather than concentrating it, it paves over more land per resident, fragments wildlife habitat, and increases dependence on automobiles, all of which are tied to the loss of natural, permeable land surface.
13. A city government proposes rezoning to allow mixed residential and commercial buildings within walking distance of public transit stops, rather than separated single-use zones reachable only by car. What planning approach is this, and what is its main environmental benefit?
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    Answer. Smart growth; it reduces automobile dependence and associated fossil fuel use, air pollution, and habitat loss from new road and parking construction by concentrating development and enabling walking and transit use.

    Smart growth strategies aim to increase density and mix land uses near existing infrastructure and transit, which shortens trip distances and reduces the need for car travel, in contrast with sprawl, which spreads low-density, single-use development that requires driving between destinations.
14. A forest's timber regenerates at a sustainable yield of 500,000 board feet per year, but a logging company harvests 700,000 board feet per year for several consecutive years. Is this practice sustainable, and what is the long-term consequence?
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    Answer. No; the company is harvesting 200,000 board feet per year more than the forest can regenerate, so the timber stock will progressively shrink, leading eventually to reduced future harvests, soil erosion, and habitat loss as the forest fails to recover between cuts.

    Sustainable yield sets the ceiling for harvest that allows the resource to fully regenerate. Harvesting above that ceiling draws down the standing stock each year, which is unsustainable and will eventually force a reduction in harvest or collapse of the resource if not corrected.

What people get wrong

1. Treating 'ecological footprint' as if it only measures carbon emissions. Instead, remember it also includes cropland, grazing land, forest land, fishing grounds, and built-up land — it is a total land-use measure, not just a carbon metric.
2. Assuming tragedy of the commons requires greed or bad intent. Instead, recognize it arises from rational self-interest acting on an unregulated shared resource; the fix is regulation, quotas, or property rights, not appeals to individual morality.
3. Assuming all aquaculture reduces pressure on wild fish stocks. Instead, check the trophic level of the farmed species — carnivorous fish like salmon require large amounts of wild-caught fishmeal (a fish-in:fish-out ratio greater than 1), which can worsen wild stock depletion, while herbivorous species like tilapia are far more efficient.
4. Confusing salinization with eutrophication because both involve water and nutrients/chemicals. Instead, keep the mechanisms separate: salinization is salt buildup in soil from evaporating irrigation water, degrading soil fertility; eutrophication is nutrient (nitrogen/phosphorus) enrichment of water bodies causing algal blooms and oxygen depletion.
5. Applying the IPAT equation as if reducing population is the only lever for lowering impact. Instead, remember Affluence and Technology multiply population just as strongly, so improving efficiency or reducing per-capita consumption can lower total impact just as effectively as reducing population.