BIO 317
Conservation of Wildlife Resources
Lecture Notes 5


Where is Earth's water?

Water Source
% of total water

Icecaps, glaciers
Ground water
Fresh-water lakes
Inland seas
Soil moisture


The Water Cycle:


Water Use - Worldwide:

Since 1940, the amount of fresh water used has roughly quadrupled as world population has doubled. Some water
experts estimate the practical upper limit of usable renewable fresh water lies between 9,000 and 14,000 cubic kilometers
yearly. That suggests a second quadrupling of world water use is unlikely.

The planet’s renewable fresh water is finite—10,000 cubic miles’ worth is available each year on average—and constraints on its availability and use are increasingly evident. The growth of the human population inevitably limits the average availability fresh water per person, and the growing human thirst for fresh water comes at the expense of natural ecosystems and threatens the survival of animal and plant species.

In the past, water scarcity was at most a local or temporary problem, but it is now becoming pervasive and persistent in some regions of the world.

In 1995, about 386 million people in 31 countries lived in conditions of water stress or water scarcity, based on hydrological benchmarks of the minimum annual per capita availability of renewable fresh water needed for economic development. By 2020 the number of people living in such conditions could be as high as 2.9 billion or as low as 1.2 billion, depending on the rate of population growth over the next 24 years. By one recent estimate, more than half of all the world’s accessible renewable fresh water is already being used, indicating the problems the world may face if population doubles.

Lack of water is already a problem in densely populated urban environments such as Mexico City and Beijing. This is not just a developing world problem. Rapidly growing cities in Texas, California, Florida, Arizona and Nevada are finding that the availability of renewable fresh water is constraining their prospects for continued growth.

Fresh water is essential for farming, for industry, for human health and life itself. Every living being on land and in lakes and rivers requires it, and the more water humans use the less remains for these nonhuman species, many of them already threatened by habitat loss.

Water Use in the United States:


The bars that stand out most are the blue ones -- water for electricity production. Electricity water use increased almost
   500% from 1950 to 1990. Irrigation water use increases by about 50% -- it takes more water to grow
   food for our increasing population.

Water pollution

Used with permission of Gilbert N. Hanson

Mountaintop mining

Water pollutants vary in degree to which they're degradable by natural processes:

Sources of water pollution:

Waste-water treatment:

1. Screening. Wastewater entering the treatment plant includes items like wood, rocks, and even dead animals. Unless they are removed, they could cause problems later in the treatment process. Most of these materials are sent to a landfill.

2. Pumping. The wastewater system relies on the force of gravity to move sewage from your home to the treatment plant. So wastewater-treatment plants are located on low ground, often near a river into which treated water can be released. If the plant is built above the ground level, the wastewater has to be pumped up to the aeration tanks (item 3). From here on, gravity takes over to move the wastewater through the treatment process.

3. Aerating. One of the first steps that a water treatment facility can do is to just shake up the sewage and expose it to air. This causes some of the dissolved gases (such as hydrogen sulfide, which smells like rotten eggs) that taste and smell bad to be released from the water. Wastewater enters a series of long, parallel concrete tanks. Each tank is divided into two sections. In the first section, air is pumped through the water. As organic matter decays, it uses up oxygen. Aeration replenishes the oxygen. Bubbling oxygen through the water also keeps the organic material suspended while it forces 'grit' (coffeegrounds, sand and other small, dense particles) to settle out. Grit is pumped out of the tanks and taken to landfills.

4. Removing sludge. Wastewater then enters the second section or sedimentation tanks. Here, the sludge (the organic portion of the sewage) settles out of the wastewater and is pumped out of the tanks. Some of the water is removed in a step called thickening and then the sludge is processed in large tanks called digesters.

5. Removing scum. As sludge is settling to the bottom of the sedimentation tanks, lighter materials are floating to the surface. This 'scum' includes grease, oils, plastics, and soap. Slow-moving rakes skim the scum off the surface of the wastewater. Scum is thickened and pumped to the digesters along with the sludge. Many cities also use filtration in sewage treatment. After the solids are removed, the liquid sewage is filtered through a substance, usually sand, by the action of gravity. This method gets rid of almost all bacteria, reduces turbidity and color,  removes odors, reduces the amount of iron, and removes most other solid particles that remained in the water. Water is sometimes filtered through carbon particles, which removes organic particles. This method is used in some homes, too.

6. Killing bacteria. Finally, the wastewater flows into a 'chlorine contact' tank, where the chemical chlorine is added to kill bacteria, which could pose a health risk, just as is done in swimming pools. The chlorine is mostly eliminated as the bacteria are destroyed, but sometimes it must be neutralized by adding other chemicals. This protects fish and other marine organisms, which can be harmed by the smallest amounts of chlorine. The treated water (called effluent) is then discharged to a local river or the ocean.

R. Wastewater Residuals. Aother part of treating wastewater is dealing with the solid-waste material. These solids are kept for 20 to 30 days in large, heated and enclosed tanks called 'digesters.' Here, bacteria break down (digest) the material, reducing its volume, odors, and getting rid of organisms that can cause disease. The finished product is mainly sent to landfills, but sometimes can be used as fertilizer.

Freshwater Ecosystems


SOURCE: EPA -Wetland Functions and Values


Used with permission - Source =
Littoral zone - light penetrates to the bottom, allowing aquatic plants to grow

Limnetic zone - the open water area where light does not generally penetrate all the way to the bottom

Euphotic zone - the layer from the surface down to the depth where light levels become too low for photosynthesis

Benthic zone - the bottom sediment


The ocean bottom is the benthic zone and the water itself (or the water column) is the pelagic zone. The neritic zone is that part of the pelagic zone that extends from the high tide line to an ocean bottom less than 600 feet deep. Water deeper than 600 feet is called the oceanic zone, which itself is divided on the basis of water depth into the epipelagic, mesopelagic, and bathypelagic zones. These zones roughly correspond to the three other zones divided on the basis of the amount of sunlight they receive. In the sunlit zone, enough light penetrates to support photosynthesis. Below that lies the twilight zone, where very small amounts of light penetrate. Ninety percent of the space in the ocean lies in the midnight zone, which is entirely devoid of light.

Two important communities found in the neritic province are:

Environmental problems facing our oceans:

Useful links:

Introduction to Watershed Ecology

Water pollution and society

Water use in the United States

Water use in the World: present situation/future needs

Wetland Functions and Values

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