Contemporary limnological and sedimentary analyses to investigate anthropogenic changes in nutrient fluxes at Lake Baikal, Siberia

Large tectonic freshwater lakes face serious threats to their water quality, biological diversity and endemism through pollution and global warming. Lake Baikal is an important example as anthropogenic stressors (industrial pollution and cultural eutrophication) along with climate change could greatly affect the lake's unique ecosystem and pristine water conditions. Phosphorus, nitrogen and silica are thought to control phytoplankton development, however recent changes in nutrient impacts on Lake Baikal's phytoplankton remains unproven. This research aims to investigate the effect of anthropogenic and environmentally-driven changes on this large and biodiverse lake through seasonal sampling of the phytoplankton community (determined by chlorophyll and carotenoid pigments), chemical parameters (total phosphorus, dissolved organic carbon, silicate, nitrate and other major ions) and vertical profiles of pH, temperature and photosynethetically active radiation. Results show seasonal, vertical and spatial variability in the lake's phytoplankton biomass and composition with higher summer mixed-layer pigment concentrations in the south basin resulting in higher light attenuation coefficients and lower photic zone depths (R2=0.86, p < 0.05). Redundancy analysis shows that this distribution is primarily influenced by average dissolved organic carbon concentrations within the mixing layer, with the strongest negative correlation between picoplankton biomarkers and dissolved organic carbon concentrations (R2=-0.60, p < 0.05). Geochemical biomarkers (pigments and organic carbon [δ13Corganic]) from several sediment cores place these modern day observations within an historical context and allow the impact of past environmental changes on Lake Baikal's primary productivity over the last 60 years and natural climate-driven trends in past centuries to be assessed. These results show clear spatial and temporal changes between sites over this interval with greater increases in chlorophylls and their transformation products, along with biomarkers for diatoms, cryptophytes, green algae and cyanobacteria within the south and central basin.