The physiological ecology of a Scenedesmus population in the hypolimnion of a hypertrophic pond. I. Photoautotrophy

Abstract

Dense populations of Scenedesmus quadricauda (Turp.) Bréb. (up to 1118 μg chlorophyll per 1) were recorded in the hypolimnion of a hypertrophic pond (Priest Pot, English Lake District) throughout the summer of 1978. Cell concentrations increased exponentially with depth to a maximum at the sediment surface. Although the Scenedesmus cells maintained an operational photosynthetic apparatus, they occurred below the 1% light level in anoxic water. Samples from the hypolimnion could not fix carbon by cyclic photophosphorylation and their capacity for non-cyclic photophosphorylation was extremely low by comparison with surface populations. Thus the biomass accumulation in the hypolimnion could not be explained by photosynthetic production there.