What does it tell us?

Lake color can tell us about the influence that soils and geology, plants and trees, and land use activities in the watershed have on a lake. Color is measured by comparing a sample of the lake water to Standard Platinum Units (SPU). Lakes that are considered colored (>25 SPU) can have reduced transparency. This does not mean the lakes are more productive, the color simply interferes with transparency test. Color in Maine lakes varies from 0 to 250, with the average being 28 SPU.

Dissolved Organic Carbon
Scientists test for dissolved organic carbon (DOC) to gain clues about the health and function of the ecosystem. Like any other long term study, by collecting data over time, we can tell if conditions are staying the same, or if they are changing for some reason. DOC is a part of both the chemical and biological systems in a lake, and changes in DOC may affect both of these systems.

DOC influences the chemical system in a lake because different levels of DOC can influence the acid-base relationship in a lake, which in turn may affect many other chemical relationships in the lake (see pH and Alkalinity pages for more info on acid base relationships in lakes). .

Dissolved organic matter is a food source for microorganisms in a lake, and DOC measurements give scientists an idea of how these organic materials are used in the lake system. Increases in DOC may indicate increases in biological activity in the land systems surrounding the lake system. In other words, increases in plant production in the watershed may lead to increases in the DOC imported into the lake. This import of material is greatly effected by rain and precipitation events which move the DOC into the lake.

In Maine DOC measurements are also conducted to trace toxic materials in the ecosystem. Many toxins in the environment such as Mercury bind to organic material, and may be traced with DOC measurements.

DOC is measured in parts per million, or ppm. Mean (or average) DOC levels in Maine is 5.7 ppm (parts per million) (from EPA Environmental Monitoring and Assessment Program)
 
Resources:

Bronmark, Christer and Lars-Anders Hansson. 1998. The Biology of Lakes and Ponds. New York. Oxford University Press.

Kalff, Jacob. 2002. Limnology. Upper Saddle River, N.J. Prentice Hall.

Wetzel, Robert G. 2001. Limnology, Lake and River Ecosystems. New York. Academic Press.

Water on the Web www.waterontheweb.org