phytoplankton Communities of Lakes Experimentally Acidified with Sulfuric and Nitric Acids

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Abstract
Additions of sulfuric acid to the South Basin and nitric acid to the North Basin of Lake 302 caused major changes in the phytoplankton communities. The basins were separated by a nylon-reinforced vinyl sea curtain. In the South Basin, below pH 5.6, species composition shifted from chrysophycean dominance to one of Dinophyceae. Diatoms and cyanophytes were eliminated below pH 5.3. Phytoplankton species diversity decreased as pH decreased. Total epilimnetic biomass was unchanged, except in late fall, when entrainment of dense layers of hypolimnetic species caused increases. The assemblage in the North Basin changed immediately upon additions of HNO3 to resemble systems experimentally fertilized with nitrogen. Chrysophycean dominance gave way to chlorophytes and dinoflagellates. Once pH decreased below 6.0, diatoms and cyanophytes were eliminated from the assemblage, as in the South Basin. Phytoplankton species diversity decreased, but total epilimnetic biomass remained unaffected.