Benthic Diatom Distribution in the Cedar River Basin, Iowa

Counting approximately 500 diatoms from each of 16 benthic diatom samples collected 11 October 1975 from the Cedar River and its tributaries, the Shell Rock and Little Cedar Rivers, in NE Iowa has yielded 118 taxa. These waters were alkaline (160-210 ppm HCO3; pH 8.4-9.5); turbidity was negligible in the Little Cedar and rose to 40 FTU in the Cedar. The 5 most abundant taxa and their distributions were: Stephanodiscus subtilis (Van Goor) A. Cleve, more than 40% of the 2 Shell Rock samples and rare in the 4 Little Cedar samples; Cyclotella meneghiniana Kutz., found in all samples (3%-26%) but most abundant in Cedar River samples; Diatoma vulgare Bory, associated mostly with epiphytic samples; Skeletonema potamos (Weber) Hasle , most abundant in Cedar River samples; and Nitzschia acicularis (Kutz.). W. Sm., present in all samples and over 50% of one sediment sample from the Little Cedar. The widespread occurrence of Cyclotella meneghiniana and the scattered appearance of samples dominated by one taxon is suggestive of the presence of organic or other pollutants. Seasonal sampling of this diatom flora at these stations and others is continuing