Environmental processes and pollution: air, water and soil
This domain tests pollutant sources, transport, transformation and effects in air, water and soil, using Andalusian cases such as the Guadiamar spill, Riotinto drainage, Almeria greenhouse agriculture and the Huelva industrial complex.
Air
- Primary pollutants are emitted directly (SO2, NOx, CO, particulate matter, volatile organic compounds); secondary pollutants form in the atmosphere (ozone, PAN, secondary aerosols).
- Photochemical smog requires sunlight, NOx and VOCs; acid deposition involves sulfuric and nitric acids.
- Temperature inversions trap pollution in valleys such as the Guadalquivir; greenhouse gases and air pollutants are overlapping but distinct categories.
Water
- Organic pollution is measured as BOD (biodegradable) and COD (chemical oxidation); eutrophication follows nitrogen and phosphorus enrichment.
- Heavy metals, nitrates, salinity and thermal pollution are key pressures; acid mine drainage lowers pH and mobilises metals.
- Mixing and dilution determine downstream concentrations; concentration is not the same as load.
Soil
- Contaminants include heavy metals, pesticides, hydrocarbons and excess salts; adsorption depends on clay, organic matter and pH.
- Erosion and salinisation are forms of degradation; bioaccumulation concentrates substances in organisms, biomagnification increases them along food chains.
Worked example
A river carries 2 m3/s at 5 mg/L BOD; a discharge adds 0.2 m3/s at 500 mg/L. Assuming conservative mixing, downstream concentration = (2 x 5 + 0.2 x 500)/(2 + 0.2) = 110/2.2 = 50 mg/L. The reasoning is a mass balance: flow times concentration, summed and divided by total flow.
Traps that cost marks
BOD and COD are treated as identical; concentration is confused with load; bioaccumulation is confused with biomagnification; persistence is confused with toxicity; greenhouse gases are confused with ozone-depleting substances.
Key points
- Primary versus secondary pollutants differ in origin.
- BOD measures biodegradable organic load; COD is broader.
- Eutrophication is nutrient-driven, especially by phosphorus and nitrogen.
- Acid mine drainage acidifies and mobilises metals.
- Mass balance solves mixing and dilution problems.
Environmental management, sustainability and natural risks
This domain tests management tools, sustainability principles and the treatment of natural risks. Questions often combine a definition with an applied Andalusian case, such as Donana, Sierra Nevada or coastal development.
Sustainability
- The Brundtland definition is development meeting present needs without compromising future generations; the Sustainable Development Goals operationalise it.
- Related concepts: carrying capacity, ecological footprint, circular economy and the waste hierarchy (prevent, reuse, recycle, recover, dispose).
- Principles include precaution, polluter pays and prevention at source.
Management tools
- Environmental impact assessment (EIA) is the process; the environmental impact statement (EIS) is the document. Steps: screening, scoping, baseline, alternatives, impact prediction, mitigation, monitoring.
- The mitigation hierarchy runs avoid, minimise, restore, offset, in that order.
- Protected areas include the RENPA network, Natura 2000 sites (SAC and SPA), Donana and Sierra Nevada; river basin management is organised through hydrographic confederations; integrated coastal zone management coordinates land and sea uses.
Natural risks
- Risk = hazard x exposure x vulnerability. Return period T is the average interval between exceedances; the probability of at least one event in n years is 1 - (1 - 1/T)^n.
- Structural measures (dams, defences) and non-structural measures (zoning, early warning, insurance, education) complement each other; land-use planning is often the most effective mitigation.
Worked example
A 100-year flood has T = 100. What is the probability of at least one such event in 30 years? Probability of no event in one year is 0.99; in 30 years, 0.99^30 = 0.740. So the probability of at least one event is 1 - 0.740 = 0.260, about 26%. Use the complement rule, not multiplication by 30.
Traps that cost marks
EIA and EIS are confused; the mitigation hierarchy order is reversed; sustainability is reduced to conservation; return period is misread as a fixed schedule; risk perception is treated as risk itself.
Key points
- EIA is the process; EIS is the resulting document.
- Mitigation hierarchy: avoid, minimise, restore, offset.
- Risk combines hazard, exposure and vulnerability.
- Probability of exceedance is 1 - (1 - 1/T)^n.
- Land-use planning is a core non-structural risk measure.