Environmental systems: biodiversity, soils, water and energy resources
This domain applies system thinking to resources: biodiversity, soils, water and energy. The PAU asks you to describe a resource, quantify its use and evaluate sustainability, often with a Castilla-La Mancha case such as the Alto Guadiana aquifer or the Tablas de Daimiel.
Biodiversity
Levels are genetic, species and ecosystem. Diversity is measured by richness and evenness (Shannon index). Mediterranean Iberia is a hotspot of endemism with distinctive steppe birds; the Natura 2000 network protects habitats. Main threats are habitat fragmentation, invasive species, fires and climate change.
Soils
A profile runs O, A, B, C, R. Formation depends on climate, organisms, relief, parent material and time. Texture (sand, silt, clay) controls drainage and fertility; pH, organic matter and cation exchange capacity are the key chemical variables. Water erosion is estimated with the Universal Soil Loss Equation (R × K × LS × C × P); salinisation follows irrigation with poor drainage, as in parts of the Ebro and La Mancha depressions.
Water
Renewable resources depend on recharge; aquifers are free (unconfined) or confined, and fossil water is non-renewable. Overexploitation lowers the water table, dries springs such as those feeding Daimiel, causes subsidence and allows saline intrusion. Pollution is dominated by agricultural nitrates and diffuse pesticides, and demand is dominated by irrigation.
Energy
Non-renewable sources (coal, oil, gas, nuclear) versus renewable (wind, solar, hydro, biomass, geothermal). Spain's wind and photovoltaic capacity is large, but intermittency requires storage and grid management. Energy return on investment and life-cycle emissions are better criteria than a simple "clean" label.
Worked example
An aquifer receives 45 mm/yr of recharge over 500 km². Reasoning: 45 mm = 0.045 m, so recharge = 0.045 × 5 × 10⁸ m² = 2.25 × 10⁷ m³/yr, that is 22.5 hm³/yr. If abstraction is 40 hm³/yr, the aquifer is overexploited by 17.5 hm³/yr and the water table must fall.
Traps that cost marks
- Confusing recharge with total precipitation.
- Claiming all aquifers are renewable.
- Confusing biodiversity with abundance of individuals rather than species richness.
- Describing soil as inert dirt and omitting organic matter and soil biota.