关键词:
DEEP-WATER RENEWAL
AUTOTROPHIC PICOPLANKTON
PHOTOSYNTHETIC PIGMENTS
AULACOSEIRA-BAICALENSIS
MICROCYSTIS-AERUGINOSA
ELEMENTAL COMPOSITION
SPRING PHYTOPLANKTON
CHLOROPHYLL MAXIMA
CLIMATE-CHANGE
ALPINE LAKES
摘要:
Recent research has highlighted how Lake Baikal, Siberia, has responded to the direct and indirect effects of climate change (e.g., ice-cover duration), nutrient loading, and pollution, manifesting as changes in phytoplankton/zooplankton populations, community structure, and seasonal succession. Here, we combine and compare analyses of chlorophyll a (an estimate of total algal biomass), carotenoid pigments (biomarkers of algal groups), and lake water silicon isotope geochemistry (delta Si-30(DSi)) to differentiate spatial patterns in dissolved silicon (DSi) uptake at Lake Baikal. A total of 15 sites across the three basins (south, central, and north) of Lake Baikal were sampled in August 2013 along a depth gradient of 0-180 m. Strong, significant correlations were found between vertical profiles of photic zone DSi concentrations and delta Si-30(DSi) compositions (r = -0.81, p < 0.001), although these are strongest in the central basin aphotic zone (r = -0.98, p < 0.001). Data refute the hypothesis of DSi uptake by picocyanobacteria. Algal biomass profiles and high surface delta Si-30(DSi) compositions suggest greater productivity in the south basin and more oligotrophic conditions in the north basin. delta Si-30(DSi) signatures are highest at depth (20 m) in central basin sites, indicating greater (10-40%) DSi utilization at deep chlorophyll maxima. DSi limitation occurs in the pelagic central basin, probably reflecting a high diatom biomass bloom event (Aulacoseira baicalensis). Meanwhile in the more hydrologically restricted, shallow Maloe More region (central basin), both high delta Si-30(DSi) compositions and picocyanobacteria (zeaxanthin) concentrations, respectively point to the legacy of an "Aulacoseira bloom year" and continuous nutrient supply in summer months (e.g., localized eutrophication).