Jump to main content.


Lake Michigan Mass Balance

Lake Michigan Mass Balance Study logo

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.

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 Study measured PCBs, mercury, trans-nonachlor, and atrazine in rivers, the atmosphere, sediments, lake water, and the food chain. A mathematical model will predict what effect reducing pollution will have on the lake, and its large fish (lake trout and coho salmon).  


Local Navigation


Jump to main content.