Photoautotrophic community changes in Lagunillo del Tejo (Spain) in response to lake level fluctuation: Two centuries of sedimentary pigment records

Lagunillo del Tejo is a small doline lake in a karstic region of the Iberian Ranges (central-eastern Spain) that undergoes significant lake level fluctuation in response to changing aquifer influxes. In order to assess changes in the primary producer community in the lake over the last two centuries and to elucidate whether these were conditioned by climatic variability, photosynthetic pigments and their derivatives were extracted from the sediments and the data analysed using multivariate statistical techniques. Quantitative variations in total pigment concentrations through the sedimentary sequence are considered a result of changes in sedimentation rate, largely due to lake level fluctuation. Rapid lowering of the level results in an increase in detritic mineral matter eroded from the sides of the lake, which accumulates in the sediment and dilutes the organic matter content in the corresponding sediment layers. On the other hand, shifts in the relative abundances of the different pigments suggest the development of two different primary producer communities: (i) planktonic, comprising cyanobacteria, chlorophytes, cryptophytes and purple sulfur bacteria and (ii) primary producers related to the littoral environment, mostly submerged macrophytes. These two communities showed alternating relative importance over the last two centuries, as a biotic response to lake level fluctuation during wet and dry periods, respectively.