Acadia National Park - FLOW: Overview

Water moves through the water cycle in three ways: as an airborne gas, as moisture in the soil, and as a liquid.

As a gas, water exists as a colorless vapor in the air until it condenses in liquid form on the surfaces of airborne particles which, when heavy enough, fall to earth as precipitation (rain, snow, sleet, dew, etc.).

As soil moisture, water flows largely unseen through particles of mineral and organic matter in the warmer months, or if the temperature falls below freezing, is locked in place as ice. If absorbed by root hairs, water enters plants from the soil, rises through stems and branches into leaves, where it supports food production and reenters the atmosphere through the process of evapotranspiration. Alternatively, utilizing cracks in bedrock or spaces between soil particles, water enters the watertable to temporarily become stored as groundwater.

As a flowing or standing liquid, water runs off or seeps from the land to collect in streams, ponds, wetlands and, ultimately, oceans, from whose surfaces it eventually evaporates, returning to the atmosphere as vapor, completing the cycle.

Only about 3% of earth"s water is fresh, and most of that is locked in ice caps and glaciers. Of the small remainder, at any given time, there is about twice as much water in the soil as in the atmosphere, while streams and rivers contain less than one-tenth of that in the atmosphere.

Watersheds, as naturally-bounded geographical areas, are vital to the maintenance of almost every familiar form of life. They are land basins that receive precipitation, store it, and control its flow downward toward the ocean. Watersheds are one of the primary ways the natural world organizes itself. All life on earth depends on water, and watersheds are systems for distributing water across time and space, making it available on a reliable enough basis for individual plants--and life dependent on those plants--to survive. Watersheds take water from large areas of higher ground on their peripheries and distribute it to ever smaller, concentric areas lower down, conveying a flow of water, soil particles, and nutrients downward toward a central focus. Almost everything we take for granted on earth stems from the cyclical movement of water.

FLOW provides background on the nature, function, and importance of watersheds in general, and on those on Mount Desert Island, Maine, in particular. For water cycle visuals plus other water science information for schools from the U.S. Geological Survey, go to http://wwwga.usgs.gov/edu/