| Cybernetic | (Environmental Engineering) Systems which change in response to feedback. |
| Epilimnion | (Environmental Engineering) The top layer of a lake. |
| Eucaryotic organisms | (Environmental Engineering) Organisms which possess a nuclear membrane. This includes all known organisms except viruses and bacteria. |
| Greenhouse gases | (Environmental Engineering) Gases which trap solar radiation. Of the solar energy entering the earth's atmosphere a portion is reflected back and a portion penetrates onto the earth's surface. The portion reflected back from the earth's surface is at a different wavelength that when it entered. Carbon dioxide and other gases, which pass solar radiation, absorb this reflected radiation, increasing the earth's temperature. This is much like a greenhouse, hence the name. |
| Hypolimnion | (Environmental Engineering) The lower layer of a lake. |
| Influent | (Environmental Engineering) The fluid entering a system, process, tank, etc. An effluent from one process can be an influent to another process. See effluent. |
| Ion exchange | (Environmental Engineering) An adsorption process in which one ion is exchanged for another ion of like charge. There is an equivalence of exchanged charge. |
| Kerogen | (Environmental Engineering) A fossilized organic material present in oil shale and some other sedimentary rocks. |
| Ketones | (Environmental Engineering) Organic compounds with two hydrocarbon groups bonded to a carbonyl group. |
| Metalimnion | (Environmental Engineering) The middle layer of a lake. |