Lakes are in a continuous state of change. Some changes occur over very short periods of time on the order of hours and minutes. Other changes mark long-term trends in the biological and physical condition of a lake. Among the long-term trends in many lakes are a decrease in depth
and an increasing productivity in a process called eutrophication. Typically, eutrophication occurs over a time scale of centuries. However, man-made changes to the watershed of a lake may result in a rapid acceleration of eutrophication such that significant changes in the water quality
of the lake are noticed in a time span of a few years. Anthropogenic acceleration of eutrophication, known as cultural eutrophication, is due to agricultural, urban, and recreational development in the watershed of a lake which causes an increase in the nutrient loading to a lake.
In response to the concern for the water quality of an eutrophic lake, many lake treatment practices have been developed. Treatment processes can be divided into watershed practice methods, inflow-outflow methods, and intake treatment methods. A partial list of these practices is provided in
Table I. In some instances, treatment methods have been implemented without significantly improving the quality of a lake. The failure of a treatment method is often a result of a poor understanding of the short term dynamics of a lake which affect the rate and extent of cycling of
nutrients within the water column, sediment, and biological components of a lake. To evaluate the effectiveness of lake treatment methods on Minnesota lakes, the Minnesota Lake Model (MINLAKE) has been proposed to model the principal dynamic relationships in a lake on a daily time scale. Treatment methods can then be modeled by modifying those components of the model which will be directly affected by the treatment process. The model can then predict the indirect and direct effects over a period of several months.