The Heterotrophic, Nitrate‐Reducing Bacterial Flora of Grasmere, English Lake District

Abstract

During 1976 the temperature, dissolved oxygen and nitrate content of Grasmere water at 6 m and 20 m depth were determined on a seasonal basis and the isolated heterotrophic, nitrate‐reducing bacterial flora analysed both quantitatively and qualitatively under aerobic and anaerobic conditions. Throughout the year 8 population cycles of nitrate‐reducing heterotrophs were observed to occur simultaneously at both horizons which related to changes in the nitrate and dissolved oxygen content of the water. Nitrite producers were most numerous during the isothermal and early thermally stratified periods of the lake water, particularly when the nitrate content was rising. The qualitative analyses indicated seasonal variation in the bacterial populations isolated on the culture media and the dominant taxonomic groups could be related to the nitrate and dissolved oxygen content of the lake water. Pseudomonas. Moraxella/Acinetobacter, Flavobacterium/Cytophaga, Aeromonas and Enterobacteriaceae were the principal taxonomic groups in the Grasmere heterotrophic, nitrate‐reducing flora. Aeromonas with, possibly, Pseudomonas and Enterobacteriaceae are implicated in lowering the nitrate content of Grasmere water at 20 m depth when it becomes anoxic.