Freshwater Systems and Resources

Lecture Objectives

• 15.1 Describe the distribution of fresh water on Earth and the major types of freshwater systems.

• 15.2 Discuss how we use water and alter freshwater systems.

• 15.3 Assess problems of water supply and propose solutions to address depletion of fresh water.

• 15.4 Describe the major classes of water pollution and propose solutions to address water pollution.

• 15.5 Explain how we treat drinking water and wastewater.

Freshwater Distribution

• 97.5% of Earth's water is saltwater; only 2.5% is fresh water.

• Freshwater is relatively pure and not salty.

• Water cycles through precipitation, surface runoff, aquifers, rivers, and wetlands.

Groundwater Role in the Hydrologic Cycle

• Surface water includes rivers and lakes, while groundwater resides in soil and rock.

• Groundwater can remain underground for thousands of years.

• Aquifers: Porous rock formations that store groundwater, separated by the water table.

• Recharge zones allow water to infiltrate and reach aquifers.

• Confined vs. Unconfined Aquifers: Confined aquifers are trapped between impermeable layers, while unconfined are not.

River and Stream Ecosystems

• Runoff forms streams which merge into rivers, eventually flowing into lakes or oceans.

• Watershed: Land area drained by a river system and its tributaries.

• Braided rivers have many interconnecting channels; meandering rivers form larger bends.

Lakes and Ponds

• Littoral Zone: Shallow areas with aquatic plants.

• Limnetic Zone: Sunlit upper layer for photosynthesis.

• Benthic Zone: Bottom layer, habitat for decomposers.

• Oligotrophic lakes (low nutrient, high oxygen) can transition to eutrophic lakes (high nutrient, low oxygen).

Freshwater Wetlands

• Types include marshes, swamps, and bogs.

• Wetlands provide ecosystem services: flood control, aquifer recharge, and pollutant filtration.

• They are threatened by human activities like draining and construction.

Human Impact on Waterways

• Water demand: Majority (70%) for agriculture, 20% industry, and 10% residential.

• Water mining occurs when water is withdrawn faster than replenished.

• Dams and aqueducts alter natural waterways, impacting ecosystems.

Water Pollution

• Sources: Point sources (discrete locations), Non-point sources (larger areas).

• Types of pollutants include pesticides, heavy metals, thermal pollution, and disease-causing organisms.

• Eutrophication caused by nutrient pollution leads to dead zones (e.g., in the Gulf of Mexico).

Groundwater Pollution

• Groundwater can retain pollutants for long periods due to slow breakdown.

• Pollution sources include agricultural runoff, industrial leaks, and fracking.

Water Treatment

• Drinking water undergoes chemical treatment, filtration, disinfection, and testing.

• Wastewater Treatment: Uses physical and biological processes to remove contaminants.

• Constructed wetlands can be used as a natural method for treating wastewater.

Solutions to Depletion of Fresh Water

• Options to increase supply include desalination, which is expensive and energy-intensive.

• Demand reduction strategies include efficient irrigation practices, low-flow household fixtures, and xeriscaping.

• Market-based approaches and local control strategies may help manage water more sustainably.

International Cooperation on Water Issues

• Shared river systems can lead to disputes, but many nations cooperate to manage water resources.

• Examples include agreements between India and neighboring countries.

Conclusion

• Managing freshwater systems presents both challenges and opportunities for improving ecological health and human welfare.

• Continued education and proactive solutions are vital for sustainable water use.