Integrated foundations: DSST Environmental Science
Environmental systems, measurement and management decisions
Environmental science connects biological, chemical, physical and social processes. Define a system boundary and a time period before calculating a budget. Water entering a catchment, energy reaching an ecosystem and emissions from an activity are different quantities with different units. A change in storage equals inflows minus outflows for the defined account. A useful model states its assumptions rather than presenting one local result as a universal constant.
Ecosystems and populations
Producers use light energy or, in some systems, chemical energy to build organic matter. Consumers and decomposers participate in transfers and nutrient cycling. Net primary production is gross primary production minus the producers' respiration under the relevant definition. Transfer efficiency between trophic levels varies; a supplied ten-percent assumption can support a classroom calculation but is not a law applying identically to every ecosystem. Population growth depends on resources, interactions and environmental conditions. Exponential and logistic models describe selected behavior rather than guaranteeing a permanent growth rate or carrying capacity.
Pollution and exposure
Identify a pollutant, its source, the pathway by which it moves and the organisms exposed. A concentration is not the same as a total emitted mass. Effects can depend on dose, duration, chemical form and vulnerability. Nutrient enrichment can stimulate production and later oxygen consumption as organic matter decomposes; this differs from saying nutrients directly remove every oxygen molecule. Warm water can hold less dissolved oxygen than cooler water under otherwise comparable conditions, while organisms' demands may also change. One measurement cannot establish every cause of a fish decline.
Evaluate management alternatives
Prevention, reuse, treatment and restoration address different stages of an environmental problem. Compare alternatives using an explicit outcome, relevant side effects and an appropriate life-cycle boundary. Moving a waste stream elsewhere does not automatically eliminate its impacts. A protected area or an efficient device can help with a defined objective, but effectiveness depends on implementation, use and ecological context. Hazardous-waste tracking is a management concept; exact legal classifications and current handling duties require the applicable rules rather than an invented universal procedure.
Make the evidence usable
Use appropriate sampling, transparent units and uncertainty statements. A before-and-after comparison can reveal change while remaining vulnerable to other changing conditions. Combine monitoring with a defensible decision rule and review whether the intended result occurred. Distinguish an empirical prediction from a judgment about acceptable tradeoffs. Shared questions from environmental-science courses support these foundations without establishing official DSST coverage, current local regulation or a guaranteed examination result.
The Living World: Ecosystems
What you must know
An ecosystem is the community of organisms plus the abiotic environment they exchange matter and energy with. Be able to trace energy flow (sunlight → producers → consumers → decomposers) and matter cycling (carbon, nitrogen, phosphorus, water). Energy is unidirectional and lost as heat at each trophic level; matter is recycled. Know the 10% rule: roughly 10% of energy transfers between trophic levels, so food chains rarely exceed four or five links and top predators are few. Understand primary productivity (GPP vs. NPP = GPP minus respiration), net primary productivity patterns (highest in tropical rainforests, estuaries, and wetlands; low in deserts and open ocean per unit area), and biogeochemical cycles including the roles of nitrogen fixation, nitrification, denitrification, and the phosphorus cycle's lack of an atmospheric phase.
Traps
- Confusing energy (flows, lost as heat) with matter (cycles).
- Assuming removing a top predator only affects its prey - expect trophic cascades.
- Mixing up GPP (total fixed) with NPP (net stored).
- Forgetting phosphorus has no gaseous reservoir, so it limits productivity in many freshwater systems.
Worked example / rule of thumb
If producers fix 20,000 kcal, herbivores assimilate about 2,000 kcal, and secondary consumers about 200 kcal. Rule: multiply by 0.10 per level up; divide when working downward.
The Living World: Biodiversity
What you must know
Biodiversity has three levels: genetic, species, and ecosystem/habitat diversity. Understand species richness (count) versus species evenness (relative abundance) and how both shape diversity indices. Learn the types of speciation (allopatric via geographic isolation, sympatric without it) and extinction (background vs. mass). Know ecosystem services - provisioning, regulating, supporting, cultural - and the difference between generalist and specialist species. Island biogeography predicts richness from island size and distance to mainland. Ecological tolerance and range of tolerance explain why species distribution is limited by abiotic factors; indicator species signal environmental quality.
Traps
- Equating high richness with high diversity - evenness matters; a community dominated by one species can be less diverse despite many species.
- Confusing habitat diversity with species diversity.
- Misreading island biogeography: larger and closer = more species.
- Assuming specialists adapt better; generalists tolerate disturbance but specialists are more extinction-prone.
Worked example / rule of thumb
Two plots each have 5 species. Plot A: 90% one species, 2% each of four others. Plot B: 20% each of five species. Both richness = 5, but Plot B has higher evenness and therefore higher diversity. Rule: richness counts names; evenness weighs balance.
Populations
What you must know
Track population size, density, dispersion, age structure, and sex ratio. Distinguish exponential (J-shaped) growth, which occurs with unlimited resources, from logistic (S-shaped) growth, which levels at carrying capacity (K). Know biotic potential, environmental resistance, and density-dependent (disease, competition, predation) versus density-independent (fire, drought, storms) factors. Interpret survivorship curves (Type I late loss, Type II constant, Type III early loss). Use the rule of 70 (doubling time ≈ 70 / growth rate %). Understand demographic transition stages and how age-structure diagrams (pyramids vs. columns) predict future growth. Know r- vs. K-selected strategies.
Traps
- Calling a population "growing exponentially" when it is logistic and slowing near K.
- Mixing density-dependent with density-independent factors.
- Forgetting a broad-based age pyramid means high future growth (population momentum).
- Miscalculating growth rate: it is (births − deaths + immigration − emigration) per capita, often expressed as a percent.
Worked example / rule of thumb
A population grows 2% per year. Doubling time ≈ 70 / 2 = 35 years. Rule: 70 divided by percent growth rate gives doubling time; higher r means faster doubling.
Earth Systems and Resources
What you must know
Understand Earth's spheres (lithosphere, atmosphere, hydrosphere, biosphere) and their interactions. Know plate tectonics: divergent, convergent, and transform boundaries and the hazards/landforms each produces (volcanoes, earthquakes, ridges, trenches). Identify rock types (igneous, sedimentary, metamorphic) and the rock cycle. Master soil - horizons (O, A, E, B, C, R), texture (sand, silt, clay), porosity vs. permeability, and how soil forms. Know atmosphere layers (troposphere, stratosphere with ozone, mesosphere, thermosphere) and global wind and ocean circulation driven by unequal heating, the Coriolis effect, and convection. Understand El Niño/La Niña and upwelling. Know mineral resources and the difference between reserves and resources.
Traps
- Confusing porosity (space for water) with permeability (ability to transmit water); clay is porous but low-permeability.
- Placing the ozone layer in the troposphere - it is in the stratosphere.
- Mixing convergent (destructive) with divergent (constructive) boundaries.
- Forgetting the Coriolis effect deflects winds, not the underlying pressure gradient.
Worked example / rule of thumb
A soil that is 40% sand, 40% silt, 20% clay is a loam - good for agriculture because it balances drainage and water retention. Rule: sandy soils drain fast and hold few nutrients; clay soils hold water and nutrients but drain poorly.
Land and Water Use
What you must know
Examine agriculture: subsistence vs. commercial, slash-and-burn, monocropping, CAFOs, and integrated pest management. Know irrigation types (drip, flood, furrow, center-pivot) and their water-use efficiency and salinization risks. Understand forestry (clear-cutting vs. selective logging, sustainable yield), rangeland management and overgrazing/desertification, and urban land use (urban sprawl, smart growth, zoning). Study fisheries and the tragedy of the commons. Distinguish renewable from nonrenewable land/water resources and the concept of maximum sustainable yield. Know mining impacts (surface vs. subsurface, acid mine drainage) and water use in agriculture, industry, and homes.
Traps
- Assuming all irrigation is equally efficient - drip is most efficient; flood is least.
- Confusing sustainable yield (harvest at regeneration rate) with maximum exploitation.
- Overlooking salinization and waterlogging from over-irrigation.
- Treating the tragedy of the commons as inevitable - it is a governance failure, not a resource property.
Worked example / rule of thumb
A fishery with a sustainable yield of 100 tons/year should be harvested at ≤100 tons. Rule: harvest at or below the regeneration rate; exceeding it depletes the stock.
Energy Resources and Consumption
What you must know
Classify energy sources as renewable (solar, wind, hydro, geothermal, biomass) and nonrenewable (coal, oil, natural gas, nuclear). Know energy quality, EROI (energy returned on energy invested), and the electricity generation sequence: source → turbine → generator. Understand fossil fuel formation, combustion products (CO₂, SO₂, NOx, particulates, mercury), and nuclear fission, fuel cycle, and waste issues. Study renewable technologies: photovoltaic cells, wind turbines (intermittency), hydropower (dams and habitat disruption), geothermal, and biomass (carbon neutrality caveats). Know energy conservation vs. efficiency and cogeneration. Understand energy use patterns by sector and the role of fossil fuel subsidies.
Traps
- Calling nuclear "renewable" - it is nonrenewable (finite uranium) though low-carbon.
- Assuming biomass is always carbon-neutral; it depends on regrowth and transport.
- Confusing conservation (using less) with efficiency (using less for the same output).
- Forgetting wind and solar are intermittent, requiring storage or backup.
Worked example / rule of thumb
If a power plant burns fuel with 30% efficiency and produces 300 MWh of electricity, it consumed about 1,000 MWh of fuel energy (300 / 0.30). Rule: efficiency = useful output / total input.
Atmospheric Pollution
What you must know
Learn the six criteria pollutants (CO, lead, NO₂, ozone, particulates, SO₂), their sources and health effects. Distinguish primary from secondary pollutants (ozone and PAN are secondary). Understand photochemical smog (NOx + VOCs + sunlight) and industrial smog (SO₂ + particulates). Know acid deposition (SO₂ and NOx → sulfuric and nitric acid) and its effects on soils, lakes, and structures. Study stratospheric ozone depletion by CFCs and the Montreal Protocol, and do not confuse it with tropospheric ozone as a pollutant. Understand indoor air pollution (radon, CO, VOCs, asbestos, mold) and thermal inversions that trap pollution.
Traps
- Confusing ozone depletion (stratosphere) with smog (troposphere) - opposite problems.
- Calling ozone a primary pollutant; ground-level ozone is secondary.
- Mixing acid deposition chemistry: it is sulfur and nitrogen oxides, not CO₂.
- Forgetting indoor air can be more polluted than outdoor air.
Worked example / rule of thumb
On a sunny, windless day with heavy traffic, expect high photochemical smog: NOx and VOCs react in sunlight to form ozone. Rule: sunlight + NOx + VOCs + still air = smog.
Aquatic and Terrestrial Pollution
What you must know
Identify point-source vs. nonpoint-source pollution. Know major water pollutants: sediment, nutrients (nitrogen and phosphorus causing eutrophication and dead zones), pathogens, heavy metals, PCBs, oil, and thermal pollution. Understand wastewater treatment (primary, secondary, tertiary) and septic systems. Study solid and hazardous waste - landfills, leachate, incineration, brownfields, and the waste hierarchy (reduce, reuse, recycle). Know bioremediation and phytoremediation. Understand pesticide persistence and bioaccumulation/biomagnification up food chains. Know noise and light pollution and brownfield redevelopment.
Traps
- Reversing bioaccumulation (organism takes up) and biomagnification (concentration rises up the chain).
- Calling agriculture nonpoint - it usually is, unlike a factory pipe.
- Forgetting sediment is a major water pollutant by volume.
- Assuming recycling is the top of the hierarchy - reduction and reuse come first.
Worked example / rule of thumb
A lake receiving fertilizer runoff from many farms is nonpoint-source nutrient pollution → algal bloom → oxygen depletion → dead zone. Rule: nutrients in, algae up, oxygen down.
Global Change
What you must know
Understand the greenhouse effect and the enhanced greenhouse effect from CO₂, CH₄, N₂O, and CFCs, including relative global warming potential. Know evidence for climate change (ice cores, sea-level rise, temperature records, phenology shifts) and feedbacks (positive: permafrost methane release, ice-albedo; negative: increased plant growth). Study consequences: sea-level rise, ocean acidification (CO₂ + water → carbonic acid), coral bleaching, shifts in species ranges, and extreme weather. Learn mitigation (renewables, efficiency, carbon capture, sequestration) vs. adaptation (sea walls, drought-resistant crops). Know ozone depletion as a separate global change and the success of the Montreal Protocol. Understand invasive species and habitat fragmentation as global-change drivers.
Traps
- Confusing the greenhouse effect (natural, necessary) with the enhanced greenhouse effect (human-driven).
- Mixing mitigation (reduce cause) with adaptation (cope with effect).
- Treating ocean acidification as the same as warming - it is a chemical change from dissolved CO₂.
- Forgetting positive feedbacks amplify change while negative feedbacks dampen it.
Worked example / rule of thumb
Burning fossil fuels adds CO₂ → more heat trapped → warming → ice melt → lower albedo → more warming. Rule: identify whether a feedback amplifies (positive) or dampens (negative) the initial change.