15 Freshwater Resources: Natural Systems, Human Impact, and Conservation Part D PowerPoint® Slides prepared by Jay Withgott and Kristy Manning Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings

Groundwater pollution Worse than surface water pollution, because it is longer lasting (e.g., persistent toxicants get washed out of rivers, but remain in groundwater until they break down.)

Groundwater pollution Sources are both natural and anthropogenic. NATURAL SOURCES: Arsenic Aluminum Fluoride Nitrates Sulfates HUMAN SOURCES: Leaky underground storage tanks (oil, gas, industrial chemicals, septic waste) Nitrates from fertilizers Pesticides Pathogens from wells and feedlots Contamination from underground hazardous waste disposal Industrial chemical waste Compounds from military sites

Groundwater pollution Thousands of wells dug by international aid workers for the benefit of Bangladesh’s citizens turned out to be poisoned with natural sources of arsenic. Mapped arsenic concentrations; red is highest

Success stories Many water pollution problems have decreased since the 1960s and 1970s, due to legislation: Clean Water Act of 1977 in the U.S. Similar acts in other nations The Great Lakes: Canadian and U.S. governments decreased PCBs, DDE, fertilizers, etc., by 70–90%. Fish and bird populations are now recovering.

Pollution prevention Drinking water is treated before it reaches your tap. But it is easier and more cost effective to prevent pollution than to mitigate it once it occurs.

Wastewater and its treatment Wastewater = water that has been used by people in some way Septic systems = most popular method of wastewater disposal. Wastewater treatment involves: Primary treatment: physical removal of contaminants in settling tanks Secondary treatment: water is aerated by being stirred up; aerobic bacteria degrades organic pollutants.

Wastewater and its treatment The wastewater treatment process

Natural treatment Artificial wetlands can aid treatment.

Conclusion Ensuring adequate freshwater involves citizen action, legislation and regulation, new technologies, economic incentives, and public education. The world is approaching widespread water scarcity. Water depletion and pollution are affecting developing countries and arid areas of the developed world. But potential solutions are numerous.

QUESTION: Review Which of the following is NOT true about aquifers? a. They hold surface water. b. They can be “confined” or “unconfined.” c. They can become polluted by numerous toxic substances. d. They generally are very slow to recharge. Answer: A

QUESTION: Review Which water body would contain many nutrients and low oxygen levels? a. An oligotrophic lake b. A eutrophic lake c. A pristine fast-flowing mountain stream d. The deep ocean e. All of the above Answer: B

QUESTION: Review Which of the following is NOT true about dams and their associated reservoirs? a. They alter riparian habitat. b. They can capture sediment. c. They can provide irrigation, hydropower, flood control, and drinking water. d. They can never be removed once built. e. They promote some types of recreation and inhibit others. Answer: D

QUESTION: Review Which is a possible effect of groundwater depletion? a. Subsidence and sinkholes b. Sediment capture c. Saltwater intrusion into aquifers d. Both (a) and (b) e. Both (a) and (c) Answer: E

QUESTION: Weighing the Issues As cities of the arid U.S. southwest grow and water becomes scarce, what should these metropolises do? a. Pull as much water as they can from the Colorado River b. Build desalination plants c. Regulate industry and agriculture more heavily to restrict water waste d. Promote conservation measures through education and market incentives Answer: ANY

QUESTION: Interpreting Graphs and Data What proportion of ALL water on Earth do lakes contain? a. 52% c. 0.013% b. 1% d. It cannot be calculated from the information given. Answer: D

QUESTION: Interpreting Graphs and Data For each of its citizens, North America has…? a. Less water than Asia c. Less water than Australia b. Less water than Europe d. 47,000 km3/yr Answer: C

QUESTION: Viewpoints Should we remove dams? a. Yes; they have more costs than benefits. b. Sometimes; we should judge them on a case-by-case basis. c. No; they have more benefits than costs. d. No; money and resources are best spent on other things. Answer: ANY