pollution-resistant lower order of fish, such as carp, replaces the original fish population. The amount of oxygen in a body of water is therefore one of the best measures of its ecological health.

If all the oxygen is used, an anaerobic (without air) decomposition process is set in motion with a different mixture of bacteria. Rather than releasing carbon dioxide in the decomposition process, anaerobic decomposition releases methane or hydrogen sulfide. In these highly polluted situations, the river turns dark and odors-like rotten eggs-penetrate the environment.

Heated water discharged into lakes and rivers often harms aquatic life. Heat accelerates biological and chemical processes that reduce the ability of a body of water to retain dissolved oxygen and other dissolved gases. Increases in temperature often disrupt the reproduction cycles of fish. By hastening biological processes, heat accelerates the growth of aquatic plants such as algae. Finally, the temperature level determines the types of fish and other aquatic life that can live in any particular body of water. The effects of excessive heat operate to change the ecology of an area-sometimes drastically, rapidly, and irreversibly.

One of the most serious water pollution problems is eutrophication - the "dying of lakes." All lakes go through a natural cycle of eutrophication, but this normally takes thousands of years. Lakes are deep and have little biological life. Lake Superior is a good example. Over a period of time, nutrients and sediments were added and the lake became more biologically productive and shallower. As nutrients continued to be added, large algae blooms grew, the fish populations changed, and the lake began to take on undesirable characteristics. After an extended time, a lake can become a swamp and finally a land area.

People greatly accelerate this process of eutrophication when they add nutrients to the water. Nutrients include detergents, waste food products, fertilizers, and human wastes. The actions of people can, in decades, cause changes that would take nature thousands of years.

Polluted waters harm human health as well as the natural environment. It is true that epidemics of typhoid, dysentery, and salmonellosis borne by polluted water are no longer serious public health threats in the United States. However, it is still vital that we maintain adequate protection of the public from these and other pollution dangers. Often water must be treated to very high levels before it is drinkable. Frequently, beaches must be closed and shellfish left unharvested. Inadequately disinfected municipal waste overflow from combined sewer systems and runoff from animal feedlots often create high bacteria densities in local water supplies. Ships that are anchored far upstream can contribute to a high bacteria count in a community's water supply. The Navy is exploring the use of many devices and schemes to lessen the effect of waste discharges in water.

Ground Pollution

Construction site work and repair and maintenance of facilities have the immediate potential for becoming polluting activities. Since the majority of construction efforts take place on land, project supervisors must identify potential pollution hazards and take steps to minimize the effects. Some of the most common pollution activities that affect the ground areas and water ecosystems are grubbing and equipment repair operations.

GRUBBING OPERATIONS. - Large-scale clearing and grubbing during the initial stages of a project often produce damaging environmental effects, such as increased soil erosion, reduction of atmospheric oxygen, and destruction of wildlife habitat. Another primary concern is the introduction of particulate matter into streams and riverbeds. Particulate matter released into waterways causes increased siltation and algae growth.

To prevent these damaging effects you should save as much vegetation as possible-trees, grass, and other plants-to hold the soil in place. Consider allowing tree rows to be left in place until the project is completed. Replant cleared areas. Construct a shallow trench around the perimeter of a project to help contain water runoff into streams and rivers and to prevent siltation. The decision to burn scrubs and stumps should be based on atmospheric conditions. Burn only when conditions are favorable and the material to be burned is totally dry.

A burn permit is required in all burning operations on NCF projects!

To prevent wild tires and production of smog, do NOT use petroleum-base fuels to start fires! Petroleum-base fuels do not burn completely, and the residue seeps into the underground water table.

EQUIPMENT REPAIR OPERATIONS. - Repair and maintenance of CESE whether in the shop or on the project site must always be under controlled and closely monitored conditions. Lubricating oil, fuel, hydraulic fluids, transmission fluids, and antifreeze contain extremely volatile chemical properties. When these petrochemicals are mixed with certain solvents or