DAVIS, Calif. -- Weighing in on the ecological debate about how best to control human-induced algae growth in naturally clear lakes, University of California, Davis, researchers have made a bottom-line discovery.

Tinkering with food webs may not help restore most lakes to their previous clarity. This is because in most cases the upper levels of a lake's food web cannot exert enough influence to control the algae feeding on polluting nutrients coming into the lake.

Instead, limiting the supply of nutrients in a lake appears to be a stronger mechanism for controlling algae blooms, according to a meta-analysis of eight lake studies involving 11 experiments in Canada, Czechslovakia, Norway and the United States, said Michael Brett, a staff research associate in the UC Davis environmental studies division.

Brett and UC Davis professor Charles Goldman, director of the UC Davis Castle Lake and Lake Tahoe research groups, published the results of the analysis in the Jan. 17 issue of the weekly journal Science.

The analysis also casts doubt on a popular model of how energy moves through food webs in general and of how many plants and animals can be found at each level of the web. The way energy moves through food webs plays a key role in determining fisheries production in lakes and oceans.

In most lakes around the world, the most common pollutants causing murky water are actually nutrients that fuel the growth and number of tiny plants at the bottom of the food chain. Limnologists have long recognized that nitrogen (typically from sewage and fertilizer) and phosphorus (from nearby construction or logging) feed the tiny marine plants known more commonly as algae.

Algae thrive on these pollutants. The quantity of algae directly determines water clarity. In a process called eutrophication, algae can deplete oxygen, killing fish, and severe algae blooms can water to sm
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Contact: Carol Morton
ccmorton@ucdavis.edu
916-752-7704
University of California - Davis
17-Jan-1997