HUMAN POPULATION, CARRYING CAPACITY, AND RESOURCE USE

3.6 Water Resources

Assessment Statements

3.6.1 Describe the Earth’s water budget. 3.6.2 Describe and evaluate the

sustainability of freshwater resource usage with reference to a case study.

3.6.1 Describe the Earth’s water budget.

70% of the Earth is covered in water. However, 97.5% is in salt water, leaving only 2.5% as fresh water.

Of this 2.5%, about 69% is in glaciers and ice caps, and 30% is ground water.

Our surface water (lakes and rivers) only make up about 0.3% which is the only renewable portion.

3.6.1 Describe the Earth’s water budget.

Turnover time – The time for a water molecule to enter and leave a part of the hydrological system. (the time taken for water to complete replace itself in part of the system) These times vary enormously.

River and soil moisture could be considered renewable resources as they recover fairly quickly. (1 year or less) However things like ground water aquifers should be considered non-renewable as they take much longer to recover. (300-1500 years)

3.6.2 Describe and evaluate the sustainability of freshwater resource usage with reference to a case study.

Human populations require water for home use, agriculture, industry, and hydroelectric power.

Water usage needs to be managed on a local level, with support from the government.

Water usage needs to be coordinated with natural processes to ensure that freshwater sources are not used at an unsustainable rate.

3.6.2 Describe and evaluate the sustainability of freshwater resource usage with reference to a case study.

Can be realized in cities by making new buildings water-efficient, fitting existing buildings with more water-efficient devices and appliances, expanding metering to encourage conservation

Can be realized in rural areas by selecting drought-resistant crop. Contamination of water supplies can be addressed by switching to organic fertilizers and biocontrol methods instead of pesticides

Industries can be forced to remove pollutants from their waste water through legislation.

3.6.2 Describe and evaluate the sustainability of freshwater resource usage with reference to a case study.

Many countries are currently drawing too much water from groundwater and degrading it with wastes faster than it can be replenished.

USA is one of the largest agricultural producers, but has been depleting groundwater sources for several years.

Fertilizer run-off has led to recordings of nitrates levels in groundwater exceeding the drinking water standards.

This is likely to deteriorate further as phosphates (also used in agriculture) can take many years to seep into groundwater from the soil.