Sustainability Practices

Why This Matters

Sustainability isn't just a buzzword—it's the framework connecting nearly every major topic in AP Environmental Science. When you study sustainability practices, you're really exploring how humans can meet current needs without compromising the ability of future generations to meet theirs. This concept threads through land use decisions, water management, pollution control, energy systems, and ecosystem services. The exam will test whether you understand how these practices address specific environmental problems like eutrophication, air pollution, habitat loss, and resource depletion.

You're being tested on your ability to connect solutions to problems. Don't just memorize that "drip irrigation saves water"—know that it reduces agricultural runoff, which prevents nutrient loading that causes eutrophication and dead zones. Each sustainability practice exists because it interrupts a specific environmental harm. Master the mechanism, and you'll crush both multiple choice and FRQs.

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Pollution Prevention and Treatment

These practices target pollutants before they enter ecosystems or remove them after release. The key principle is intervention at different points in the pollution pathway—source reduction, treatment, and remediation.

Sewage Treatment Systems

• Primary, secondary, and tertiary treatment remove progressively more contaminants—primary uses physical settling, secondary uses aerobic bacteria to reduce BOD, tertiary removes nitrogen and phosphorus
• Activated sludge process—the heart of secondary treatment where microorganisms break down organic matter in aeration basins before clarification
• Tertiary treatment prevents eutrophication by using chemical precipitation or constructed wetlands to strip nutrients that would otherwise fuel algal blooms

Air Pollution Control Technologies

• Catalytic converters transform $CO$, $NO_x$, and hydrocarbons into less harmful $CO_2$, $N_2$, and $H_2O$ through chemical reactions
• Wet scrubbers (FGD) remove sulfur dioxide from coal plant emissions using limestone, preventing acid deposition—this technology enabled compliance with Clean Air Act standards
• Electrostatic precipitators and baghouse filters capture particulate matter using electrical charge or fabric filtration, reducing respiratory health impacts

Nutrient Management Practices

• Riparian buffers—vegetated strips along waterways that intercept agricultural runoff before nitrogen and phosphorus reach streams
• Best management practices (BMPs) include cover crops, contour plowing, and controlled fertilizer application to minimize nonpoint-source pollution
• Constructed wetlands provide natural filtration through plant uptake and microbial denitrification, converting nitrates to harmless nitrogen gas

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Sustainable Food Production

These practices address the environmental costs of feeding 8 billion people. Industrial agriculture degrades soil, pollutes water, and reduces biodiversity—sustainable alternatives maintain productivity while minimizing ecosystem damage.

Sustainable Agriculture Techniques

• Crop rotation and cover cropping restore soil nitrogen naturally, reducing synthetic fertilizer needs and subsequent nitrate leaching into groundwater
• Integrated pest management (IPM) minimizes pesticide use through biological controls, reducing bioaccumulation in food webs and protecting pollinator populations
• Organic farming eliminates synthetic inputs, though yields may be lower—the tradeoff is reduced chemical runoff and improved soil biodiversity

Sustainable Aquaculture

• Recirculating aquaculture systems (RAS) filter and reuse water in closed loops, dramatically reducing nutrient effluent compared to open-net pens
• Integrated multi-trophic aquaculture (IMTA) combines species at different trophic levels—shellfish and seaweed absorb waste nutrients from fish, mimicking natural nutrient cycling
• Feed conversion ratio (FCR) measures efficiency; lower ratios mean less fishmeal needed, reducing pressure on wild fish stocks used for feed

Sustainable Fisheries Management

• Catch quotas and seasonal closures allow fish populations to recover, maintaining stocks above minimum viable population thresholds
• Marine protected areas (MPAs) serve as refugia where fish can reproduce undisturbed, with spillover benefits to adjacent fishing grounds
• Bycatch reduction devices prevent unintended capture of non-target species, protecting biodiversity and ecosystem food web structure

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Energy and Emissions Reduction

These practices tackle the root cause of climate change by reducing fossil fuel combustion. The principle is simple: replace carbon-intensive energy sources and improve efficiency to reduce greenhouse gas emissions per unit of economic activity.

Renewable Energy Systems

• Solar and wind power produce electricity with zero direct emissions during operation, though manufacturing has embedded carbon costs (life cycle assessment matters)
• Hydroelectric power provides reliable baseload energy but disrupts river ecosystems, alters sediment transport, and can displace communities
• Energy independence results from diversified renewable portfolios, reducing vulnerability to fossil fuel price volatility and supply disruptions

Transportation Alternatives

• Electric vehicles (EVs) eliminate tailpipe emissions of $CO$, $NO_x$, and particulates, though total emissions depend on electricity grid composition
• Public transit and active transportation reduce per-capita emissions by moving more people with less fuel—urban design determines feasibility
• Ultra-low sulfur diesel (ULSD) and biofuels like E10/E85 reduce emissions from existing internal combustion fleets during the transition period

Energy Efficiency Measures

• Building insulation and LED lighting reduce energy demand at the consumption end, often the most cost-effective emissions reduction strategy
• Energy audits identify inefficiencies in heating, cooling, and electrical systems—behavioral changes can yield 10-30% savings without capital investment
• Industrial process improvements capture waste heat and optimize operations, reducing energy intensity per unit of production

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Ecosystem Conservation and Restoration

These practices protect and rebuild the natural systems that provide ecosystem services. Healthy ecosystems regulate climate, filter water, cycle nutrients, and support biodiversity—degradation of these functions has cascading environmental and economic consequences.

Forest Conservation

• Carbon sequestration—mature forests store massive amounts of carbon in biomass and soil; deforestation releases this stored carbon as $CO_2$
• Watershed protection results from intact forest cover, which reduces erosion, filters runoff, and maintains stream flow during dry periods
• Sustainable forest management balances timber harvest with regeneration, maintaining forest structure and biodiversity over time

Biodiversity Preservation

• Protected areas and wildlife corridors maintain habitat connectivity, allowing species to migrate in response to climate change and maintain genetic diversity
• Endangered species programs target species at risk of extinction, often focusing on keystone species whose loss would trigger ecosystem collapse
• Invasive species management protects native biodiversity from competitors and predators that lack natural population controls

Ecosystem Restoration

• Wetland restoration recovers lost ecosystem services including flood control, water filtration, and habitat for migratory species
• Coral reef rehabilitation addresses damage from ocean warming, sedimentation, and destructive fishing through coral gardening and stress reduction
• Degraded land reclamation converts abandoned mines, landfills, and industrial sites back to functional ecosystems through soil remediation and revegetation

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Resource Efficiency and Waste Reduction

These practices address the material throughput of human economies. Linear "take-make-dispose" systems deplete resources and generate pollution; circular approaches keep materials in productive use longer.

Circular Economy Principles

• Design for durability and repair extends product lifespans, reducing raw material extraction and manufacturing emissions
• Material recovery and recycling captures value from waste streams, though recycling rates vary dramatically by material type and local infrastructure
• Industrial symbiosis connects businesses so one company's waste becomes another's input—mimicking nutrient cycling in natural ecosystems

Water Conservation

• Drip irrigation delivers water directly to plant roots, reducing evaporative losses and agricultural runoff compared to flood or spray irrigation
• Rainwater harvesting and greywater recycling reduce demand on freshwater supplies, particularly important in water-stressed regions
• Drought-resistant crop varieties maintain yields with less irrigation, an adaptation strategy for climate change impacts on agriculture

Waste Management Hierarchy

• Source reduction prevents waste generation entirely—the most effective strategy but requires changing consumption patterns
• Composting organic waste diverts material from landfills where it would generate methane (a potent greenhouse gas) under anaerobic conditions
• Landfill gas capture collects methane from existing waste for energy generation, converting a climate liability into a resource

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Quick Reference Table

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Self-Check Questions

1. Which two practices both reduce eutrophication but target different pollution source types? Explain how their mechanisms differ.

2. Compare open-net pen aquaculture with recirculating aquaculture systems (RAS). What environmental problems does RAS solve, and what tradeoffs does it introduce?

3. An FRQ asks you to recommend strategies for reducing nitrogen pollution in a watershed with both a sewage treatment plant and surrounding farmland. Which practices would you propose for each source, and why?

4. How do catalytic converters and wet scrubbers differ in the pollutants they target and the pollution sources they address? Which Clean Air Act pollutants does each technology reduce?

5. A city wants to reduce its carbon footprint. Rank these three approaches by typical cost-effectiveness: installing solar panels, improving building insulation, or purchasing carbon offsets. Justify your ranking using environmental science principles.