EFFECTS OF NITRATE AND PHOSPHATE CONCENTRATION ON NATURAL AQUATIC BACTERIAL POPULATIONS1

Abstract

ABSTRACT: Natural aquatic bacterial populations in three streams located at the Savannah River Project, Aiken, S.C. have been studied in relation to the effects of ambient temperatures, dissolved River Project, Aiken, oxygen (DO), nitrate and phosphate concentrations.3 Samples collected at monthly intervals for a period of one year from each system, were plated in duplicate at each of two dilutions on 1/4 strength Standard Plate Count Agar (Difco). After incubation at 25±1 °C for four days, total colony forming units, percent chromagens, and number of colony types (diversity) were determined and colonies were picked for identification.Temperatures were generally equal in two of the streams throughout the year, being lowest in Upper Three Runs (U3R) and Tirns Branch (TB), and highest in the Ash Basin System (ABS). DO content did not vary appreciably between the streams. Nitrates and phosphates were lowest in U3R, next lowest in TB, higher in the last station in ABS, and highest in the ash basin per se. Total colony forming units were highest in the ash basin, whereas chromagen percentage and diversity were highest in the last station in ABS. Results of these studies indicate that high nitrates and phosphates, in the absence of high organic carbon concentrations, have little, if any detrimental effect on the stability of natural aquatic bacterial populations.