Distribution of phototrophic microorganisms in the anaerobic and microaerophilic strata of Lake Vechten (The Netherlands). Pigment analysis and role in primary production

Dense populations of photoautotrophic bacteria (total chlorophyll concentrations up to 200 mg·m−3) were found sequentially layered in meta‐ and upper hypolimnion during summer stratification of Lake Vechten (Netherlands). Pigment analysis by chromatographic and spectrophotometric techniques and phase microscopy were used to reveal the structure and relative seasonal abundance of the populations. The predominant bacteria were identified as members of the genera Synechococcus, Chloronema, Chromatium, and Thiopedia. Unidentified brown Chlorobiaceae also were present. Maximal development of the populations was found in late August and September. The primary production, distribution of sulfide, oxygen, chlorophyllous pigments and ATP, and temperature profiles were determined through the summer. Oxygenic (algal) and anoxygenic (bacterial) photosynthesis were distinguished by using the inhibitor DCMU. The phototrophic sulfur bacteria accounted for 3.9–17.5% of the total daily primary production. The contribution of bacterial photosynthesis to the total pelagic annual primary production of the lake was 3.6%. The main factors determining the growth of photosynthetic sulfur bacteria in Lake Vechten are light and sulfide concentration.