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Lake Michigan Mass Balance
What is a "Mass Balance" Study?
Mass balance is based on the principle of 'conservation of mass':
the amount of a pollutant entering a system should equal the amount
of that pollutant leaving, trapped in, or chemically changed in the system.
Determining the amount of pollutants entering a lake via air and rivers,
and understanding how they move through the lake and its foodweb is
like piecing together a complex puzzle. The solution to this puzzle
is arrived at through collecting environmental samples and then using
mathematical models to develop the links between samples. Mass balance
is a valuable tool enabling resource managers to design cost-effective
strategies for reducing toxic loads and minimizing human and ecosystem
health risks.
The Lake Michigan Mass Balance (LMMB) began in 1994 and will be concluded in
2000. Four major chemicals are being studied including polychlorinated biphenyls
(PCBs), atrazine (an agricultural herbicide), trans-nonachlor (a pesticide),
and mercury. The Lake Michigan Mass Balance is helping us understand where these
chemicals are entering the Lake and what happens to them as they move through the
ecosystem. This study will identify relative pollutant loads from rivers, air
deposition, and sediment resuspension, and will allow us to predict the benefits
associated with reducing loads. Within these pages you will learn about the fate
of toxic chemicals in Lake Michigan, you will gain insight on the cutting-edge
science used in doing a mass balance, and you will begin to understand the complexities
of managing one aspect of a large-scale ecosystem.
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