The later but better-known "before-and-after" experimental liming of Cather Lake in 1950 (Hasler, 1964) and "paired manipulation" of Lakes Peter and Paul by University of Wisconsin limnologist Arthur Hasler (Johnson and Hasler, 1954; Stross and Hasler, 1960) are sometimes cited as the first ventures in whole-lake experimentation. In the latter case, a small, colored, two-basin lake was separated into two lakes by an earthen dike. One basin was treated with lime in an effort to improve water clarity and increase primary production; the other basin was retained as a control. Hasler's group was involved in several other whole-lake manipulations during the 1950s and 1960s. Examples include the first whole-lake experimental acidification, which involved a small bog lake (Zicker, 1955); aeration-induced destratification experiments on several eutrophic lakes (Schmitz and Hasler, 1958); and the addition of short-lived radioisotopes to the water of stratified lakes to measure rates of water movement (e.g., Likens and Hasler, 1960). Hasler's group also pioneered the use of small artificial ponds (wading pool size) treated in various ways to simulate lakes.
An earlier whole-lake radiotracer experiment by G. Evelyn Hutchinson at Yale University actually predates all of the lake manipulation experiments of Hasler's group in Wisconsin. In June 1946, he added approximately 10 millicuries of 32P-phosphate to Linsley Pond, a small lake in Connecticut. The distribution of radiophosphorus was determined in several strata of the water column and in littoral macrophytes on two dates over the following month (Hutchinson and Bowen, 1947).5 Compared with the sophistication and complexity of limnological papers published today, the 32P tracer experiment on Linsley Pond was extremely simple. It involved only a few crude measurements and only the simplest mathematical analysis of the data. Techniques available to measure the radiotracer in lake samples were very crude (a simple Geiger counter) compared with the sophisticated and highly sensitive tools available today. Also, the regulatory climate for use of radioisotopes in the ambient environment was much more relaxed in the 1940s than it is today.
Today, experimental limnologists conduct at least three types of whole-lake manipulations:
stress-response experiments, in which a whole lake (or one basin of a multibasin lake) is treated with some chemical stressor, such as excess nutrients or acid, and the responses of the lake system are studied;
remediation and rehabilitation manipulations, involving hydrologic manipulations such as water level fluctuations to improve littoral (near-Shore)