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Water mining occurs when water is withdrawn faster than replenished.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