On the contribution of phytoplankton and benthic biofilms to the sediment record of marker pigments in high mountain lakes

Abstract

This study compares the marker pigment composition in three different lake compartments: the water column; the surface sediment biofilm (0–0.5 cm), where production and main degradation processes take place; and the deep sediment (15–17 cm), where the signal is finally stored and marker pigments are used as a proxy in paleolimnological studies. The aim was to evaluate which marker pigments better record in the sediment the relative contributions of planktonic and benthic production in high mountain lakes, taking into account the differential preservation existing among pigments. A survey of 82 high mountain lakes distributed along the major environmental gradients was carried out in the Pyrenees. Comparison of pigments between the three compartments revealed that both water column and sediment biofilm signals could be distinguished in old sediment layers, despite the observation that some of the most characteristic carotenoids that appeared frequently and in high concentrations in the water column were already less common or even absent from the sediment biofilm. In the shallowest lakes, pigment composition in the sediment biofilm was typical of photosynthetically active communities and their deep sediment samples were characterised by a substitution of fucoxanthin by diatoxanthin as the dominant diatom marker pigment. However, in the deepest lakes the pigment composition of the sediment biofilm and deep sediment was similar, characterised by marker pigments of mainly planktonic algal groups and pheophytins, which are typical pigments of decaying communities. Results are discussed in terms of how pigment source (planktonic or benthic) and pigment type (lability of molecule) interact to shape pigment composition in the sediment record of high mountain lakes.