abiotic A nonliving factor or element (e.g., light, water, heat, rock, energy, mineral).

acid deposition Precipitation with pH less than 5.6 that forms in the atmosphere when certain pollutants mix with water vapor.

benthic A bottom dwelling species.

biological diversity The variety and complexity of species present and interacting in an ecosystem and the relative abundance of each.

biotic An environmental factor related to or produced by a living organism.

camouflage A disguise or false appearance that is used to hide something by making it look like its surroundings.

combined sewer Sewer carrying a combination of sanitary sewage and storm runoff. Combined sewers are typical in most older cities.

combined sewer overflow (CSO) Overflow of combined sewer into a stream as a result of excess stormwater entering during wet weather from roof leaders, cracked and disjointed pipes, et cetera.

compost A mixture of decaying leaves, manure, and other nutritive matter, for improving and fertilizing soil.

concentric An expanding set of circles sharing the same center. Concentric circles form as a raindrop falls into a puddle.

condensation When water changes from vapor to a liquid. Clouds, fog, and dew are examples of naturally condensed water.

contour The outline or shape of something.

culvert A pipe designed to bury a stream and carry stormwater to a downstream location. In old urban watersheds, such as Nine Mile Run, culverts may be contaminated by CSOs and SSOs during wet weather.

divide A ridge of land so situated that the streams on one side flow in the opposite direction to the streams on the other side; edge between two regions drained by different river systems; watershed. A ridge of land that separates two areas that are drained by different rivers.

downstream With the current of a stream; down a stream.

ecosystem A community of living organisms and their interrelated physical and chemical environment.

environment 1. All of the surrounding things, conditions and influences affecting the growth or development of living things. 2. The condition of the air, water, soil, plants, and animals; natural surroundings.

equilibrium The ability of an ecosystem to maintain stability among its biological resources (e.g., forest, fisheries, crops) so that there is a steady optimum yield.

erosion The act or process of gradual eating into or wearing away by glaciers, temperature changes, running water, waves, ice. or wind.

evaporation When water is placed in a shallow pan it disappears, changing from a liquid to vapor. Higher temperatures cause water to evaporate more quickly.

flow Movement of water in a stream; any continuous rate of flowing, the volume of fluid that flows through a passage or point at any given amount of time.

gradation Shading with a pencil or changes in paint-pigment intensity (light-dark) which can simulate in painting and drawing the effect of light and shadow on a three-dimensional form.

groundwater Water below the surface of the earth, the source of spring and well water. Groundwater flows as surface water does; only more slowly since it has to move through small openings between the soil particles.

groundwater contaminant Any chemical compound harmful to human health and the environment that reaches groundwater and moves in it. Improper home waste disposal, (cleaning chemicals, paint thinner, oil, gasoline etc.) undetected chemical leaks in industrial plants and accidental chemical spills typically result in groundwater contamination.

homeostasis The tendency for a system by resisting change to remain in a state of equilibrium.

human impact An ecological (or environmental) effect created by human activities.

impervious surface Roofs, roads, sidewalks, parking lots etc. where rain water flows as runoff over the surface and does not soak in.

incinerating Burning to ashes; reducing to ashes.

integrated pest management A variety of pest control methods that include repairs, traps, baits, poison, etc. to stimulate pests.

lentic Relating to, or living in still water.

lotic Relating to, or living in actively moving water.

mitigation The policy of constructing or creating man-made habitats, such as wetlands, to replace those lost to construction and development.

mouth of river A part of a river or the like where its waters are emptied into the sea, another river, or some other body of water.

niche (ecological) The role played by an organism in an ecosystem; its food preferences, requirements for shelter, special behaviors and the timing of its activities (e.g., nocturnal or diurnal), interaction with other organisms and its habit.

non-point source pollution Contamination that originates from many locations that all discharge into a location (e.g., a lake, stream, land area). Example: In a city pollution can emanate from a roadway (salts and oils) from yards (pesticides and fertilizers) and from construction sites (mud and silt).

non-renewable resources Substances (e.g., oil, gas, coal, copper, gold) that, once used, cannot be replaced in this geological age.

organisms A living body having organs that work together to carry on the processes of life; individual animal or plant.

permeable Permeable surfaces allow water to soak through them (soil, grass, etc). Impermeable surfaces like roads, sidewalks and roofs cause water to either pool or flow across there surfaces.

point source pollution Pollutants discharged from a single identifiable location (e.g., pipes, ditches channels, sewers, tunnels and containers of various types).

pest A name applied to an organism when it is in competition with humans for some resources.

permeable A material's ability to allow water to penetrate. Refers to water's ability to move down into soil layers.

precipitation Condensed water that falls through the atmosphere to the surface of the earth in the form of rain or snow.

primary colors A color in a group of colors which, when mixed together, will produce all other colors.

primary colors of light Red, green, and blue.

primary colors in pigment Magenta (dark pink), yellow and Cyan (turquoise blue) are the primary colors in pigments.

recycling Collecting and reprocessing a resource, product or waste-product to make into new products.

renewable A naturally occurring raw material or form of energy that will be replenished through natural ecological cycles or sound management practices (e.g., the sun, wind, water, trees).

riffle A rapid and shallow part of a stream.

risk management A strategy developed to reduce or control the chance of harm or loss to one's health or life.

runoff Rain water that flows across the surface of the land, especially across impervious surfaces.

sanitary sewer Sewer carrying sanitary (household) sewage. May carry roof leader runoff by design or from illegal connections. Often accompanied by a separate storm sewers for street runoff.

sanitary sewer overflow (SSO) Overflow of sanitary sewer into a stream as a result of excess storm water entering during wet weather from roof leaders, cracked and disjointed pipes, etc.

stream order Energy and nutrient flow that increases as water moves toward the oceans (e.g., primary the smallest spring, meets with other springs at secondary order, which then meet with other secondary to create a creek which is tertiary order. This "ordering" continues until the rivers flow into oceans).

surface water Precipitation water pooling or flowing on grass, soil or paved land towards storm water pipes and rivers. Part of this water evaporates; another part infiltrates into the soil, another part is discharged into storm water systems.

sustainability The ability to keep in existence or maintain; a sustainable ecosystem (e.g., herbivore, carnivore, decomposer).

topography The shapes and forms of the land in a particular region; valleys, plains, lakes, rivers.

transpiration When we breathe, some of the water within us rejoins the atmosphere through exhaled vapor. This is a form of evaporation called transpiration. Plants also transpire by excreting water vapor through stomata --small holes or pores -- on the underside of leaves. Because plants consume carbon dioxide and release oxygen, their transpiration is especially important to the quality of the earth's atmosphere.

tributary A river or stream that flows into a large river.

upstream Against the current of a stream; up a stream.

waste stream The flow of (waste) materials from generations, collection and separation to disposal.

watershed The land area from which surface runoff drains into a stream, channel, lake, reservoir or other body of water; also called a drainage basin.

wetland Lands where water saturation is the dominant factor determining the nature of the soil development and the plant and animals communities; sloughs, estuaries and marshes.