Sedimentary photosynthetic pigments as indicators of climate and watershed perturbations in an alpine lake in southern Spain

Abstract

Sedimentary photosynthetic pigments as indicators of climate and watershed perturbations in an alpine lake in southern Spain A short core was collected in Rio Seco Lake, an alpine and oligotrophic lake located in the Sierra Nevada Mountains (in the southeast region of Spain) to determine the algal group changes over the past 200 years. In particular, it was analysed for fossil pigments and their derivatives and the geochemical (C/N ratio, grain-size analyses and isotopic dating) and climatic (temperature and rainfall values obtained from a long instrumental series) variables. The main pigments were carotenoids that indicate cyanobacteria (zeaxanthin, echinenone and myxoxanthophyll), diatoms and chrysophytes (fucoxanthin and diadinoxanthin) and green algae (lutein). The changes in pigment abundance over time were mainly explained by the temperature. Zeaxanthin showed a marked decrease from the 19 th century to the present and is attributed to picoplanktonic cyanobacteria in Rio Seco Lake. This decrease may result from climate-driven factors affecting herbivorous grazing pressure and water residence time. The increasing human activity around the lake likely generated a high input of carotenoid-poor pigmented organic matter and led to the dilution of chlorophylls and labile carotenoids observed over recent decades.