WHAT IS IT?

Chlorophyll is the green pigment that is found in all plants which allows them to photosynthesize. In photosynthesis, plants use the sun's energy to convert carbon dioxide and water into oxygen and cellular material.

Clumps of algae in water.
Photo courtesy of Senator George J. Mitchell Center

Lake scientists test lakes for chlorophyll to get an estimate of the amount of algae growing in a lake. Algae are plants (often microscopic) that float in water or are attached to rocks and soil. Algae and other plants are the base of the food chain in a lake (like plants are in the food webs of land animals), and produce much of the oxygen needed by organisms. Therefore, algae are very important to the lake ecosystem. 

If populations of algae grow too fast in relation to the rest of the system, though, they may create water quality problems in the lake ecosystem, such as algal blooms.

By comparing chlorophyll samples from different years and different seasons, scientists can judge if chemical and biological processes in and around the lake that cause algal growth are staying the same, or if they are changing for some reason.

Algae viewed under a microscope