Densities of Benthic Protozoa and Nematodes in a Piedmont Stream

Abstract

Densities of protozoa in sediments and leaf accumulations in a first-order spring seep, and in sediments and on stones in a third-order stream reach were determined over a 17-mo period. Higher densities were obtained from microscopic counts than from determinations of most probable number (a statistical estimate of number derived from growth responses when serial dilutions of sample are inoculated into replicate cultures of bacterized Cerophyl). Protozoa densities were higher per unit area of sediment than per unit area of leaves or rock surfaces. Microflagellate densities in sediments ranged from 9.00 .times. 105 to 2.29 .times. 107/cm2 (.hivin.x .+-. 1 SD = 5.32 .+-. 7.36 .times. 106, n = 15) in the seep and from 6.00 .times. 105 to 1.04 .times. 107/cm2 (2.06 .+-. 2.32 .times. 106, n = 18) in the stream. Ciliate densities ranged from 5.00 .times. 103 to 3.32 .times. 104/cm2 (1.54 .+-. 1.09 .times. 104, n = 5) in the seep and from 5.00 .times. 103 to 3.65 .times. 104/cm2 (1.09 .+-. 0.88 .times. 104, n = 12) in the stream. Nematodes were separated from sediments by a combination of sieving, flotation in sucrose, and centrifugation, and were counted microscopically. Nematode densities in sediments in the stream ranged from 0.90 to 8.85/cm2 in fine sediments (.hivin.x .+-. 1 SD = 4.2 .+-. 1.9, n = 15) and from 0.20 to 1.80/cm2 (1.1 .+-. 0.2, n = 7) in coarse sediments.