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1. Describe the path a molecule of water might follow through the hydrologic cycle from the ocean to land and back again.
Water evaporates from the surface of the oceans to become vapor in the air. This vapor is pushed higher into the atmosphere by rising air currents, which turns the vapor into clouds because of cooler temperatures. The water then falls over land as rain, and rejoins the ocean as part of a stream or groundwater runoff.
Good
2. About what percent of the world's water is liquid, fresh, surface water that supports most terrestrial life (see fig. 10.3)?
Only .02% of the world's water is accessible to terrestrial life.
3. What is an aquifer? How does water get into an aquifer? Explain the idea of an artesian well and a cone of depression.
Aquifers are geologic layers that contain water. Water seeps in horizontally through the porous layers of rocks to fill up aquifers over thousands of years. An artesian well, or a spring, is where water flows freely up to the surface because of pressure in an underlying aquifer. A cone of depression happens when water is pumped out of an aquifer, leaving a void of water that is filled up by sand and rocks from above sinking down.
Good, recall how large they can be...
Like the Ogallala Aquifer, which is 174,000 mi² in area.
4. What is the difference between water withdrawal and consumption? Which sector of water use (see fig. 10.8) consumes most globally? Overall, has water use increased in the past century? Has efficiency increased or decreased in the three main use sectors?
Water withdrawal is the amount of water taken from a water body; this water is can be replenished and cycled back into the system. Water consumption is the loss of water caused by evaporation, absorption, or contamination. Most water is used for agriculture. Overall, water use has been going up, but water use efficiency has increased (not significant enough to compensate however).
What about trends in contamination?
Contamination happens similar to the cycle of water withdrawal; pollutants in the water generally leach down into the soil as part of water runoff and especially if the residence time is high, it will likely remain in the water for thousands of years (in the case of groundwater).
5. Describe at least one example of the environmental costs of water diversion from rivers to farms or cities.
Rivers are often diverted through the construction of dams and reservoirs. This impedes the natural flow of the water and the river ecosystem, preventing fish and other marine life from traversing freely up and downstream. Reservoirs behind the dam will also cause flooding of the area around it, destroying whatever land-based ecosystem that was there before. Similarly, the river will dry up in front of the dam.
Also heavy metal leaching into the cooler waters
6. Explain the difference between point and nonpoint pollution. Which is harder to control? Why?
Point pollution are sources of pollution that can be traced to a specific location, such as a sewage pipe or a factory. On the other hand, nonpoint pollution don't have particular sources that can be identified. Nonpoint pollution is harder to control because they include runoff from farms, golf courses, construction sites, roads... where the single origin of the pollution is harder to trace.
Good
7. Why are nutrients considered pollution? Explain the ideas of eutrophication and an oxygen sag (see fig. 10.15).
Nutrients can cause "blooms" of algae on the surface of the water, choking out competition and making the lake toxic for other lifeforms. Eutrophication is an increase in nutrient levels and biological productivity, and can cause these algae blooms. An oxygen sag is a decline in oxygen downstream from the pollution source, due to decomposers metabolizing the waste material.
Make sure you are clear on the eutrophication process...it's the decay of the algae once dead that alters the O2 content
8. Describe primary, secondary, and tertiary water treatment.
Primary water treatment separates solid waste from sewage using settling tanks.
And screens
It's a purely physical process
Secondary treatment removes pathogens and organic matter from the water using aerobic bacteria, chlorine, and ultraviolet light.
A purely biological process
Tertiary water treatment removes any remaining dissolved metals or nutrients.
A purely chemical process...look up chelation, and it's root in Greek
9. What are some sources of groundwater contamination? Why is groundwater pollution such a difficult problem?
Groundwater contamination can happen because of septic systems, landfills, and industrial activity that leaches pollutants into the aquifer recharge zone. Deep wells provide a direct method for pollution to enter groundwater. Groundwater pollution is hard to deal with because the residence time for water in aquifers is so long; it may be possible to pump the water out, clean it, and then pump it back in, but this method of clean up is not financially viable.
How does fracking bear on this?
Fracking is the extraction of substances from rock using high-pressure water to crack a rock layer. Because deep veins are being opened into the rock, it provides another channel for pollutants to seep deep inside the ground, especially where groundwater is. Proppants, or the substance used to prop the rock layer apart after injection, is a common pollutant.
10. Why are nutrients important factors in water pollution and eutrophication? What two elements are the most important nutrients in water pollution?
Nutrients cause the growth of photosynthetic algae that pollute the water and is one of the cause for eutrophication. The two most important elements in water pollution are phosphorus and nitrogen.
Remember that the algae also block sunlight from reaching other plants below, once the algae peaks, the lower plants are dead, unable to produce O2
hoang phong
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