AP Environmental Science Land and Water Use Guide
Return to the AP Environmental Science exam guide.
Land and Water Use in the AP Environmental Science blueprint
College Board assigns Unit 5, Land and Water Use, 10–15% of AP Environmental Science multiple-choice questions. This range describes the multiple-choice section, not a percentage of the total exam score.
Land and Water Use
- May 2027
- Bluebook
- Clean-room teaching
- Read the evidence surface.
- Trace the environmental mechanism.
- Check units, scale, and claim scope.
What Land and Water Use covers
Within Land and Water Use, use these routes to connect official topics to evidence, calculations, and environmental decisions.
Unit 5: Land and Water Use
5.1 The Tragedy of the Commons
When studying Land and Water Use, a tragedy of the commons can occur when individuals gain from using an open-access resource while depletion costs are shared.
5.2 Clearcutting
5.3 The Green Revolution
5.4 Impacts of Agricultural Practices
5.5 Irrigation Methods
5.6 Pest Control Methods
5.7 Meat Production Methods
5.8 Impacts of Overfishing
5.9 Impacts of Mining
5.10 Impacts of Urbanization
5.11 Ecological Footprints
5.12 Introduction to Sustainability
5.13 Methods to Reduce Urban Runoff
Green roofs, rain gardens, vegetated swales, retention basins, and permeable pavement slow or infiltrate urban runoff.
5.14 Integrated Pest Management
Integrated pest management combines monitoring, thresholds, biological and cultural controls, and limited targeted pesticide use.
5.15 Sustainable Agriculture
Sustainable agriculture protects soil and water through practices such as crop rotation, cover crops, reduced tillage, and precise inputs.
5.16 Aquaculture
Aquaculture raises aquatic organisms in controlled systems but can concentrate waste, spread disease, enable escapes, and depend on feed inputs.
5.17 Sustainable Forestry
Sustainable forestry uses harvest limits, longer rotations, selective cutting, habitat buffers, and regeneration to maintain ecosystem function.
Vocabulary anchors
The Tragedy of the Commons; Clearcutting; The Green Revolution; Impacts of Agricultural Practices; Irrigation Methods; Pest Control Methods; Meat Production Methods; Impacts of Overfishing; Impacts of Mining; Impacts of Urbanization; Ecological Footprints; Introduction to Sustainability are the official topic anchors used throughout this unit.
Evidence lab: Forest blocks under three harvest plans
Forest blocks under three harvest plans Measurements are taken ten years after harvest in comparable blocks. Plan | Trees removed (%) | Stream summer temperature (°C) | Soil loss (t/ha/yr) | Nesting pairs clearcut | 95 | 22.8 | 8.4 | 3 selective | 35 | 18.6 | 2.1 | 11 no harvest | 0 | 16.9 | 0.7 | 14
Which plan has the largest measured watershed impact?
Clearcut — It has the highest stream temperature and soil loss.
Both impact measures are intermediate. It has the lowest measured impacts. The table shows large differences.
Two-variable comparison in one table.
Why can clearcutting warm a stream?
Removing riparian canopy increases direct solar heating. — Shade loss raises incident radiation on the water.
It increases rather than stops exposure. Erosion does not cause freezing. The primary mechanism is radiation.
Connects land cover to stream energy balance.
By what percent is soil loss lower under selective harvest than clearcutting?
75% — (8.4-2.1)/8.4 ×100=75%.
That is the remaining fraction. The denominator is reversed. The mass difference is mislabeled as a percent.
Percent reduction with units and denominator choice.
What prevents concluding that tree removal alone caused every nesting difference?
Other habitat features and preharvest nest abundance were not reported. — The blocks are described as comparable but baseline and habitat covariates remain unmeasured.
Pairs are a valid breeding metric. A decade can be ecologically informative. That unit is appropriate.
Identifies baseline and covariate limits.
Which policy best addresses timber yield, erosion, and bird habitat?
Set retention and riparian-buffer rules, monitor all three outcomes, and reduce harvest if thresholds are exceeded. — The policy links practices to measurable ecological limits.
That ignores measured impacts. Without monitoring, thresholds cannot guide management. That omits erosion and habitat objectives.
Integrates multiple objectives and adaptive thresholds.
Evidence lab: Irrigation trial in an arid valley
Irrigation trial in an arid valley Equal crop areas receive the same seasonal water allocation. Method | Water reaching roots (%) | Drainage salinity (g/L) | Yield (t/ha) flood | 48 | 6.2 | 4.1 sprinkler | 69 | 4.4 | 5.0 drip | 88 | 2.5 | 5.6
Which method delivers water most efficiently to roots?
Drip — Eighty-eight percent reaches roots, the largest share.
It has the smallest delivery share. Its value is intermediate. The percentages differ.
Direct efficiency comparison.
Why can flood irrigation increase soil salinity?
Evaporation leaves dissolved salts behind as water is repeatedly added. — Water is removed to the atmosphere while salts accumulate in soil or drainage.
Most dissolved salts do not evaporate with water. Shallow water tables can enhance it. The salts are dissolved ions, not fixed atmospheric nitrogen.
Explains a water-salt mass balance.
How many percentage points more water reaches roots under drip than flood irrigation?
40 percentage points — 88-48=40 percentage points.
That is a relative increase, not the requested percentage-point difference. The values were added. The ratio was mislabeled as a difference.
Distinguishes percentage points from relative percent.
What additional variable is needed before selecting drip solely from this trial?
Installation and maintenance cost over the system life — Efficiency and yield benefits must be compared with the resource cost of adoption.
That does not alter system performance. Longitude alone does not supply cost or feasibility. That is not a decision variable.
Adds economic feasibility to environmental performance.
If drip adoption reduces drainage volume but raises salt concentration, what should managers compare?
Total salt load, calculated as concentration times drainage volume, rather than concentration alone. — A smaller volume can carry a lower or higher mass depending on both factors.
Color is not salt load. That omits off-site impact. The premise says drainage volume changes.
Requires converting concentration and flow to load before judging a tradeoff.
Evidence lab: Tomato greenhouse pest trial
Tomato greenhouse pest trial Treatments were randomly assigned to twelve equal greenhouse bays. Treatment | Pests per leaf | Beneficial insects per bay | Marketable yield (kg/bay) broad pesticide | 1.2 | 3 | 920 predatory insects | 2.1 | 48 | 955 monitoring threshold + spot spray | 1.7 | 31 | 970 untreated | 8.9 | 44 | 710
Continue in the A+ teaching layer for the remaining evidence labs, figure, and final audit.
How the AP Environmental Science assesses Land and Water Use
| Item | Weight / count | What it means |
|---|---|---|
| Official topic denominator | 17 | |
| Multiple choice | 80 questions in 90 minutes | |
| Free response | 3 questions in 70 minutes | |
| Calculation credit | ||
| Administration | May 2027 |
Irrigation efficiency
Read each question as it appears on the exam paper, choose your answer, then tap it to see the feedback.
Practice 1: Calculate irrigation efficiency
A farm withdraws 9,600 m³ of water, and 6,720 m³ reaches crop roots.
What is the combined conveyance and application efficiency?
Select the best answer.
A. (9,600 − 6,720) ÷ 9,600 × 100 = 30%
❌ Not quite 😭 This calculates the fraction lost before reaching roots. Loss fraction is not the requested delivery efficiency.
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B. 6,720 ÷ 9,600 × 100 = 70%
✅ Correct! 😊 Useful delivery is correctly divided by total withdrawal. The ratio directly measures the requested efficiency.
C. 9,600 ÷ 6,720 × 100 ≈ 143%
❌ Not quite 😭 This reverses the ratio and produces an impossible efficiency above 100% for a system with water losses.
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D. 9,600 − 6,720 = 2,880%
❌ Not quite 😭 The subtraction gives 2,880 m³ of water lost, not a percentage. A denominator and conversion to percent are missing.
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Full explanation
- Step 1Identify 6,720 m³ as useful water delivered and 9,600 m³ as total input.
- Step 2Calculate efficiency = useful delivery ÷ withdrawal × 100.
- Step 36,720 ÷ 9,600 × 100 = 70%.
Practice 2: Analyze irrigation tradeoffs
Equal crop areas receive the same seasonal allocation. Flood irrigation delivers 48% of water to roots with drainage salinity of 6.2 g/L; sprinkler delivers 69% with 4.4 g/L; drip delivers 88% with 2.5 g/L.
Identify the most efficient method, calculate its percentage-point advantage over flood irrigation, explain how flood irrigation can increase soil salinity, and identify additional evidence needed before recommending a method.
Show your work.
A. Choose drip because 88 − 48 = 40 percentage points, then also evaluate cost and total salt load in drainage.
✅ Correct! 😊 This correctly reports an absolute percentage-point difference and adds feasibility and off-site salt mass to the decision.
B. Call the difference 40% and assume the lowest salinity concentration always means the lowest salt load.
❌ Not quite 😭 The displayed efficiencies differ by 40 percentage points, not 40%. Salt load also depends on drainage volume as well as concentration.
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C. Choose flood irrigation because evaporated water carries dissolved salts into the atmosphere.
❌ Not quite 😭 Most dissolved salts remain when water evaporates, which can concentrate salts in soil or drainage. The mechanism is reversed.
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D. Add efficiency and salinity values into one score and choose the largest total.
❌ Not quite 😭 Percent and g/L are unlike quantities and cannot be added meaningfully. The tradeoff requires separate measures or a justified common basis.
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Full explanation
- Step 1Drip delivers the largest share to roots: 88%.
- Step 2Its advantage over flood irrigation is 88 − 48 = 40 percentage points.
- Step 3Flood irrigation can leave dissolved salts behind as applied water evaporates or plants transpire it.
- Step 4Compare installation and maintenance cost and calculate salt load as concentration × drainage volume before deciding.
Key terms for Land and Water Use
- The Tragedy of the Commons
- Clearcutting
- The Green Revolution
- Impacts of Agricultural Practices
- Irrigation Methods
- Pest Control Methods
- Meat Production Methods
- Impacts of Overfishing
- Impacts of Mining
- Impacts of Urbanization
- Ecological Footprints
- Introduction to Sustainability
Land and Water Use FAQ
What makes a resource problem a tragedy of the commons?
Individuals receive much of the benefit from additional use while depletion costs are shared, encouraging overuse of an open-access resource. Ownership, rules, monitoring, and enforcement can change that incentive.
How should clearcutting tradeoffs be evaluated?
Compare timber yield and operational efficiency with erosion, stream temperature, carbon storage, habitat structure, and recovery time. The relevant conclusion depends on scale, rotation, safeguards, and the stated objective.
Why can irrigation create salinization?
Irrigation water contains dissolved salts. When water evaporates or plants transpire it, salts remain; inadequate drainage and repeated application can concentrate them in the root zone.
What separates integrated pest management from routine pesticide use?
Integrated pest management monitors pest abundance, uses action thresholds, combines biological, cultural, mechanical, and targeted chemical controls, and evaluates outcomes instead of spraying on a fixed calendar.
How is maximum sustainable yield used cautiously?
The model estimates a harvest compatible with population replacement, often near intermediate abundance. Uncertain stock size, age structure, environmental variability, bycatch, and illegal harvest justify conservative limits.
Continue through the APES system
How to study Land and Water Use
Organize land and water use by pathway: resource extraction, altered cover, soil or nutrient movement, ecological response, and human outcome. A proposed practice earns value only if it interrupts a named pathway at the correct farm, forest, fishery, or city scale.
Build comparison tables for irrigation, tillage, forestry, mining, pest control, and aquaculture. Include yield, water, energy, erosion, pollution, habitat, resistance, labor, and verification so a single advertised benefit does not dominate the decision.
For commons problems, identify who receives the marginal benefit and who bears depletion costs. Then test quotas, property rights, community governance, fees, monitoring, and enforcement against uncertainty and incentives rather than treating regulation as a magic word.
