"Water moves." This is probably the simplest way to summarize the hydrologic cycle. A typical diagram of the hydrologic cycle (water cycle) can be seen here. It's a reasonable place to start our discussion of water quality, and allows us to consider terms that relate to the solid, liquid, and gas phases of water.
Gas phase:
1. evaporation = to change to a vapor state
The oceans lose about 3 feet / year through evaporation.
2. transpiration = to give off water vapor through animal or plant pores.
Water can enter the vapor state not only through physical evaporation, but plants and animals play a significant role in introducing water into the atmosphere.
3. evapotranspiration = the combined effect of evaporation and transpiration.
Quite often, the distinction between evaporation and transpiration may be blurred; therefore, we often combine the terms.
Liquid phase
4. precipitation = rain, hail, sleet, snow, dew.
Water that enters the gaseous state can, of course, be returned to its source by precipitation. About 2/3 of this rain returns to atmosphere. Of the remainder, roughly 1/3 finds its way to groundwater; and 2/3 to surface water (in the U.S.).
Solid phase
5. watershed runoff = water flowing across land to receiving water
After precipitation, water travels across land. We can refer to this as urban runoff or rural runoff, each with its own set of issues (pesticides, animal waste, cars, oil, etc.).
6. percolation = to filter through (removes solids)
As water infiltrates downward through soil and rock towards groundwater, the filtering effect of this media can contribute to the clarity of typical groundwater sources.
7. leaching = liquids that remove soluble solids.
Unfortunately, the flip side of percolation is leaching, whereby harmful agents may accumulate in water traveling towards the grounwater.
8. dissolving = to pass into solution
Some materials dissole more easily than others, but remember that water is practically an ideal solvent.
9. capillarity = surface attraction between liquid and solid
Capillarity can be seen in a glass of water, if you look closely at the sides of the glass. The water does not end at a perfect 90 degree angle at the sides of the glass, but instead curves ever-so-slightly towards the sides. This is capillarity, and without it, our soils would not be able to hold moisture for very long. Capillarity becomes important in examing water in soils and groundwater.
1. zone of aeration = vadose zone
This is the porous area between ground level and the beginning of a groundwater aquifer. This area is characterized by no free standing water (however, it does include capillary water).
2. zone of saturation: also called "aquifer" (latin for "water carrier")
This is a layer of underground sand, gravel, or porous rock that is saturated with water. It is the very source of groundwater.
3. confined aquifer = aquifers that are well below solid rock formations, and therefore more protected.
Sometimes referred to as "deep wells", confined aquifers can sometimes be some of the purest, highest quality of water available. Unfortunately, throughout the world, we are using up these aquifers.
4. porosity = the amount of water held by soil.
This amount is expressed as a % of the total volume. For example, if there are 100 cubic meters of an aquifer that has porosity of 50%, then we would have 50 cubic meters of water in this aquifer.
5. effective porosity = specific yield = % of total volume of water that drains freely from aquifer.
This term is quite different from porosity, because it is a fraction of the water. Continuing with our example with porosity, the 50 cubic meters of water may have an effective porosity of 60%, which means that 30 cubic meters (60% of 50 cubic meters) of water would drain freely from the aquifer. The significance of this measure is that it is not enough to know only the porosity -- we need to know how much of it we can actually access as a drinking source.
6. specific retention = % of total volume of water retained in aquifer
Specific retention is the complement to effective porosity -- in other words, the two values always add up to 100% (i.e., the water either drains freely or is retained). Continuing with our example, the specific retention would be 20 cubic meter of water (30 cubic meters that drains freely and 20 cubic meters that is retained is equal to 50 cubic meters of water),
7. water table = phreatic surface = the top of the zone of saturation.
As we use up our groundwater, the water table will be deeper belwo the ground. Phreatic surface is normally used in reference to the shape of the surface of the water table, often in reference to groundwater clean-up/
Limnology is the study of lakes. In this module, we have two major concerns with limnology. Our first concern is the process of eutrophication. Eutrophication refers to the aging of a lake. The literal definition is "new nourishment", which refers to nutrients being continually added to a lake throughout its lifetime (e.g., increased levels of nitrates, phosphates). Eutrophication is normally a natural process that normally occurs over geologic time. However, pollution from humans can dramatically speed up this process. As a result, we refer to at least three types of lakes within this process:
1. oligotrophic = a young lake (early in the eutrophication process).
2. mesotrophic = medium-aged lake
3. eutrophic = an older lake (high in nutrients).
Our second concern that relates to eutrophication is the development of layers within a river. We can find the most layers in the summertime within a deep lake, as shown in the accompanying diagram. To these three layers we add the thermocline, defined below. These layers will become critical in our upcoming discussion of seasonal effects on water quality.
4. epilimnion = top layer of a lake or reservoir
5. metalimnion = middle or transition layer of a lake or reservoir
6. thermocline = area of the metalimnion with the largest temperature change
7. hypolimnion = bottom zone of stagnation in a lake or reservoir.
Objective:
SOURCES :
The earth contains about 326,000,000 cubic miles of water. Most of it is in the oceans (about 97%). However, water goes through phase changes (solid, liquid, gas), and its movement is ultimately driven by the sun. For example, the oceans ultimately supply the following 3 sources:
USES :
The U.S. supplies billions of gallons/day in water, but most of it is lost to:
Average U.S. water use has been steadily increasing, although not all of it has been for drinking. Typical uses include:
Average home uses include:
Various fittings can save about 6-12 % in the average home (from toilets, showers, and laundry).
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