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2. Freshwater systems and resources
AP Environmental Science Review #13

3. What percentage of all water on Earth is freshwater?
About 2.5%, most of which is found in glaciers, ice caps, and aquifers

4. Why is freshwater usually considered a renewable resource?
Water is naturally recycled by the water cycle

5. Why might freshwater sometimes be considered a nonrenewable resource?
If it is being used faster than it can be recycled; if it becomes polluted and unusable

6. Name the term
Water located atop Earth’s crust (rivers, lakes, ponds etc.)
Surface water
Water located beneath the surface held within pores of soil or rock
Groundwater (or ground water)

7. What are areas beneath the ground that stores water called?
Aquifers (porous formations of rock, sand or gravel that hold water)

8. Draw a cross-section of an aquifer, and label the water table, zone of saturation, and zone of aeration.
Zone of aeration should be rocks on top, water table should be in the middle, and zone of saturation should be saturated rocks at the bottom

9. Contrast artesian aquifers with unconfined aquifers.
In an artesian aquifer, water is under great pressure because it is trapped between two layers of less impermeable substance (like clay). Water is under less pressure in an unconfined aquifer, because it has no impermeable upper layer. These aquifers recharge faster than artesian aquifers.

10. What is runoff, and how does it relate to pollution?
Runoff is water from precipitation or springs that flows across the land. Runoff can pick up pollutants, such as nutrients and chemicals from artificial fertilizers or pesticides, and transport these into waterways.

11. Name the Term The area of land drained by a river system
Drainage basin (or watershed)
Areas nearest to a river’s course that are periodically flooded
Floodplains

12. Name the freshwater ecosystem zone
The area ringing the edge of a body of water
Littoral zone
The bottom of a lake or pond
Benthic zone

13. Name the freshwater ecosystem zone
Shallow waters away from the shore than receive light
Limnetic zone
Deeper water that sunlight does not reach
Profundal zone

14. Describe the process of eutrophication.
Runoff carrying nutrients enters a lake or pond. These nutrients allow algal blooms to form, which blocks light from aquatic life. Over time the algae decays, which requires oxygen. This creates a hypoxic (oxygen-poor) environment which most organisms cannot survive in.

15. What is a wetland? How are humans negatively impacting these ecosystems?
Ecosystems where the soil is saturated with shallow water and vegetation (sometimes seasonal)
Humans have drained them for agriculture and development and they are also impacted by water pollution.

16. True/False
Freshwater and humans are unevenly distributed across our planet.
True
70% of America’s annual freshwater use is for industry.
False; 70% is for agriculture, 20% for industry, and 10% for municipal use

17. Contrast consumptive and nonconsumptive freshwater use.
Consumptive use involves taking water out of an aquifer and not returning it (Ex uses include for industry, irrigation, household use)
Nonconsumptive use involves only temporarily removing water, or not removing water at all (Example use includes water recreation)

18. True/false
Excessive aquifer withdrawals can drain them, and the rivers and lakes they are connected to.
True
Surface water is more easily depleted than groundwater.
False; surface water recharges faster

19. Provide two other consequences of over extraction from aquifers other than a depleted water supply.
In coastal regions, over extraction from aquifers can cause ocean water to enter aquifers, making the water undrinkable
Over extraction can lead to sinkholes (areas where ground gives way and that can cause homes and businesses to sink)

20. Explain why single use plastic water bottles negatively impact the environment.
It is heavily packaged, made of plastic (which requires oil), transported long distances (which requires fossil fuels), most of these bottles are not recycled, once in a landfill they can add toxins to leachate

21. What is a dam? Provide pros and cons of these structures.
A dam is an obstruction placed in a stream or river to block its flow
Pros: can create reservoirs for recreation, can be used to generate hydroelectric power, provide artificial lakes for irrigation
Cons: can disrupt aquatic migration routes, disrupt riparian habitats, fossil fuels required for construction

22. Provide examples of ecosystems services which wetlands provide.
Filtration of pollutants, storm surge barriers for coastal areas, provide habitat for unique wildlife, maintain drinking supplies, plants store carbon

23. Name the term Removing the salt from seawater
Desalinization (desalination)

24. Describe two methods of desalinization.
Distillation-using heat to evaporate seawater and condensing the water vapor
Reverse osmosis-forcing seawater at high pressure through membranes to filter out the salts

25. Provide some pros and cons related to desalinization.
Pros: provides freshwater for irrigation and drinking, reduces extraction from aquifers and allows them time to recharge
Cons: expensive, requires fossil fuel inputs, kills aquatic life at water intake sites, generates salty waste

26. provide examples of how agricultural freshwater demand could be decreased.
Line irrigation canals to prevent leaks, level fields to minimize runoff, use drip- irrigation, plant crops that match the climate, plant drought-resistant GMOs

27. Contrast point-source and non-point sources of water pollution.
Point source pollution is originating at one specific site, such as a sewage pipe. Non-point source pollution arises from multiple inputs, such as large residential neighborhoods or several farms.

28. Provide some examples of surface water pollution.
Oil spills, toxic chemicals, nutrient pollution from artificial fertilizers, pathogens, sediment, thermal pollution from factories, biodegradable wastes

29. Provide examples of groundwater pollution.
Heavy metals, wastes from agriculture, chemicals from herbicides, oil from tanker leaks, pathogens from livestock

30. What are some sources of wastewater?
Showers, sinks, dishwashers, toilets, storm runoff drains, manufacturing or industrial cleaning processes requiring water

31. Where are septic systems most commonly used?
In rural areas

32. Describe how septic systems work.
Wastewater runs from the house or business to an underground septic tank which separates the contents of the water by density. Solids accumulate at the bottom, and water is on top. The water then moves downhill to perforated pipes in gravel-filled trenches for further filtration.

33. Primary or secondary water treatment?
Settling tanks remove about 60% of dissolved solids
Primary treatment
Water is stirred and aerobic bacteria are added to degrade solids
Secondary treatment
Chlorine and ultraviolet light is added