Human Impact on Earth’s Resources: Water and Soil Limits
Earth’s Carrying Capacity and Resource Consumption
Carrying Capacity: This refers to the maximum number of individuals (population) that the planet can sustainably support.
Population and Resources
The concept of carrying capacity limits human population, estimated to be around billions of inhabitants, potentially coinciding with projections for the 21st century. We are approaching the limit the planet can sustain. The planet’s carrying capacity is affected by resource consumption, which is increasing faster than population growth. Consequently, the actual carrying capacity might be lower than anticipated. Developed countries contribute significantly more to this consumption (approximately a 10 to 1 ratio compared to developing countries).
Changes generated by consumption impact the biosphere, leading to:
- Climate change
- Extinction of species
- Increased resource demand: more cultivated land, more livestock, more pastures, hunting, fishing, dam construction for water, etc.
Water Resources and Consumption
Food and Water per Person
During the 20th century, water consumption per person rose from 350 to 900 m3.
Causes:
- Changes towards diets with more meat: Meat production requires more water than a vegetarian diet for the same caloric intake.
- Development of infrastructures.
- Migration of the population to urban areas, where water consumption doubles.
Water: A Vital Resource
Most large cities have grown on the banks of rivers. Water is the most abundant element on the planet, covering 2/3 of its surface. Small changes in water availability can produce significant changes for living beings. Water circulates on the Earth’s surface between oceans, the atmosphere, and continents in a continuous process of change (the hydrological cycle).
Processes that regulate the hydrological cycle include:
- Precipitation
- Evaporation
- Evapotranspiration (from plants)
- Recharge and discharge of aquifers
- Water runoff over the surface
- Respiration or transpiration from animals.
Drinking Water
Only 3% of the Earth’s water is freshwater. Of this, only 1% is easily accessible; the rest is frozen or too deep underground. Current freshwater use is allocated as follows:
- 70% to agriculture (of which 60% is lost/wasted)
- 22% to industry
- 8% for domestic use and services.
In the last 70 years, total water consumption has increased 6 times, while the population has tripled, meaning per capita water consumption has doubled. Currently, 54% of total accessible freshwater is being used. Over 1 billion people lack access to safe drinking water, and half the world’s population lacks basic sanitation infrastructure. More humans are alive today than ever before.
Soil Resources and Transformation
Transformation of the Ground
Soil is an essential, non-renewable resource. Its main threats are:
- Erosion
- Loss of organic matter
- Contamination
- Loss of biodiversity
- Landslides
- Salinization
- Flooding
These changes may be irreversible or persist for generations.
Land Use and Consequences
Uses: Agriculture, livestock grazing (grasslands), expanding urban areas.
Consequences: Diminution, fragmentation, and reduction of habitat space, decreasing the number of species. Destruction often accompanies the economic growth of territories. The surface area of artificial soil has increased by 30%. Land allocation includes: agricultural areas (50%), forest areas, and water bodies.
Specific Cases: Water and Soil
Water in Spain
From a biological-physical perspective, Spain exhibits climatic and geological diversity, leading to varied river regimes, animal life, vegetation, soils, and landscapes.
Water distribution: This environmental diversity results in highly disparate hydrological areas. Areas with abundant rainfall correspond to the northern third of the country. The rest of Spain is dry, especially the southern third. Water demand has been growing in recent decades due to factors like tourism and sports habits. There are discrepancies regarding water distribution, particularly in the most disadvantaged areas.
The Soil
Soil is a layer of variable thickness located on the surface of the Earth’s crust. It forms from bedrock through the action of living organisms and climate.
Composition: Soil is composed of mineral particles from rock decomposition, organic matter, water, air, and living organisms.
Formation:
- Colonization of bare rock by organisms with low nutritional needs (e.g., lichens).
- The remains of these organisms mix with eroded rock particles.
- Decomposers transform these remains, removing toxicity and creating nutrients.
- This initial layer allows plants to establish, which further breaks down rock with acids and contributes more organic matter.
- Progressively, a thicker, mature soil layer forms.