Figure 20.10 Adding phosphorus to half of a lake. (a) Researchers split a Canadian lake in half and then added carbon and nitrogen to one side and carbon, nitrogen, and phosphorus to the other side. (b) Compared to a reference lake that received no nutrient additions, the side that received additions of carbon and nitrogen from 1973 to 1980 experienced a modest increase in NPP, as measured by the biomass of phytoplankton in the epilimnion. The side of the lake that received additions of carbon, nitrogen, and phosphorus experienced a large increase in NPP. When the addition of phosphorus stopped in 1980, NPP in the fertilized side of the lake declined to levels that were similar to the control.

Data from D. L. Findlay and S. E. M. Kasian, Phytoplankton community responses to nutrient addition in Lake 226, Experimental Lakes Area, Northwestern Ontario, Canadian Journal of Fisheries and Aquatic Sciences 44 (Suppl. 1) (1987): 35–46. Photo courtesy of David W. Schindler, from Science, 184: 897–899 [1974].