Experimental Lakes Area: Whole-Lake Experiments in Eutrophication

The following whole-lake experiments are described:Lake 227, fertilized for 5 yr with phosphate and nitrate, has shown an enormous increase in phytoplankton, in spite of low carbon concentrations. The carbon necessary for production of algal blooms was found to invade from the atmosphere.Lake 304, eutrophied by fertilization with phosphorus, nitrogen, and carbon in 1971 and 1972, recovered rapidly when phosphorus fertilization was terminated.Lake 226 was split in half with a curtain. One half was fertilized with carbon and nitrogen and the other was fertilized with phosphorus, carbon, and nitrogen. The half of the lake receiving phosphorus developed an algal bloom and the other half did not.Lake 302, which had carbon, nitrogen, and phosphorus added to the hypolimnion, did not develop algal blooms in summer. Small phytoplankton blooms were found under ice in early December, but all nutrients were efficiently sedimented and unavailable the following year.The above studies illustrate clearly that phosphorus control is an efficient primary step in preventing or checking eutrophication problems.A review of other published and ongoing studies in the Experimental Lakes Area is given, illustrating the role which large-scale experiments can play in interpreting environmental problems.