Sedimentary pigments in 308 alpine lakes and their relation to environmental gradients

We undertook a comprehensive comparison between the pigment composition of surface sediment samples and contemporary catchment and limnological data deriving from 308 mountain lakes in I I mountain regions (Lake Districts) covering a wide latitudinal and longitudinal gradient across Europe. This paper examines whether photosynthetic algal and bacterial pigments stored in the lake sediment can be used to identify different lake typologies and population dynamics of primary producers. We focus on a multivariate numerical analysis relating the relative abundance of marker pigments of algae, cyanobacteria and phototrophic sulphur bacteria to a set of physical and chemical factors (both natural and anthropogenic) determining the environmental conditions in mountain lakes. Redundancy Analysis (RDA), including partial RDA, of carotenoid assemblages constrained by environmental variables suggests that the main differences between lake districts are caused by geographic position (e.g. longitude), catchment characteristics (e.g. % carbonate rocks) and chemical variables (e.g. Mg, NO(3)). Other variables such as temperature and phosphorus play a minor role, probably because of the short length of the gradient covered by these cold and mostly oligotrophic lakes. Pigment composition varies primarily in response to catchment geology and pollution (i.e. acidification from long range transport) gradients. Purple sulphur photosynthetic bacteria (okenone) and cyanobacteria (echinenone, canthaxanthin, scytonemin) are replaced by siliceous algae (fucoxanthin and diatoxanthin), cryptophytes (alloxanthin) and dinoflagellates (diadinoxanthin). With respect to site classification, the pigment ordination shows a clear distinction between the more pristine lakes (in the Pyrenees) and the more polluted sites (in the Tatra Mountains and Central Southern Alps) or those with water higher in solute content (the Julian Alps and Greenland).