The influence of depth and macrophyte habitat on paleoecological studies using chironomids: Enol Lake (Spain) as a case study

Paleolimnological studies often rely on a single sediment core for reconstructing past environmental changes of an entire lake system. This involves a number of assumptions about the correct representativeness of the living assemblage by the subfossil assemblage. This paper is aimed at understanding the main drivers affecting the dispersion and transportation of Chironomidae head capsules, which may affect the correct interpretation of downcore changes through overrepresentation or underrepresentation of certain taxa. We analyzed the chironomid living assemblage of Enol Lake (Picos de Europa National Park, Spain) and compared the subfossil assemblage at different depths. We found a highly homogeneous composition and density of recent subfossil assemblage along the depth transect (i.e. dominance of the Tanytarsini Paratanytarsus austriacus-type), which would indicate that a single core retrieved at any depth would be representative of the lake community. However, the composition of the benthic living assemblage changed significantly with depth, suggesting the existence of a driving force behind the dominance of P. austriacus-type in the subfossil assemblage. We argue that the dense mats of Characeae present in the sublittoral area (from 2 to 8 m) are most likely responsible for this homogenization, since this is the preferred habitat of Paratanytarsus, which was found at very high densities at this depth. Thus, we conclude that the interpretation of past changes in the lake conditions should be made with caution due to the overrepresentation of P. austriacus-type head capsules along the depth transect. Our findings show that it is important to explore the relationship between the living and the recent subfossil fauna of each lake in paleolimnological studies, since understanding deposition and transport patterns can help to avoid misinferring past environmental and limnological conditions.