Spatial differences in dissolved silicon utilization in Lake Baikal, Siberia: Examining the impact of high diatom biomass events and eutrophication

Abstract

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 (δ30SiDSi) 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 δ30SiDSi 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 δ30SiDSi compositions suggest greater productivity in the south basin and more oligotrophic conditions in the north basin. δ30SiDSi 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 δ30SiDSi 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).

The stable isotope composition of organic and inorganic fossils in lake sediment records: Current understanding, challenges, and future directions

“…Compared to d 18 O diatom studies, the application of d 30 Si diatom , d 13 C diatom and d 15 N diatom techniques are in their relative infancy, with only a few studies being applied in lacustrine systems (Alleman et al 2005;Street-Perrott et al 2008;Swann et al 2010;Hurrell et al 2011;Hernández et al 2011Hernández et al , 2013Opfergelt et al 2011;Chen et al 2012;Barker et al 2013;Cockerton et al 2015;Webb et al 2016;Panizzo et al 2016Panizzo et al , 2018a. There are several reviews of the use of isotopes in biogenic (including diatom) silica (including Leng and Barker 2006;Swann and Leng 2009;Leng et al 2009;Leng and Henderson 2013;Sutton et al 2018), which highlight, in detail, the many issues associated with such analyses.…”

“…climate and riverine source water changes) ( Fig. 2; Alleman et al 2005;Street-Perrott et al 2008;Opfergelt et al 2011;Panizzo et al 2016Panizzo et al , 2017Panizzo et al , 2018a.…”

Diatom evidence of 20th Century ecosystem change in Lake Baikal, Siberia

“…In the north basin of Lake Baikal however, lower Spring primary production (e.g. [24,57]) means that phosphate concentrations rarely fall below the threshold level of 15-23 μg/L needed to induce A. skvortzowii spore formation [53]. Moreover, when phosphate concentrations do decline below the threshold level, it is often after isothermal mixing, meaning that growth of A. skvortzowii in the north basin is poor [53].…”

“…It is also able to grow through the summer months (e.g. [41,57]) due to its low biovolume and higher surface-volume ratio, enabling it to stay in the photic zone longer than heavily silicified endemic species. So as heavily silicified, endemic diatom species find growth in increasingly warmer [9].…”

Eutrophication disrupts summer trophic links in an estuarine microbial food web

“…Moreover, nutrient loading is often linked with the limitation of diatom growth due to silicate deficiency and the proliferation of non-siliceous, unpalatable algae (Officer and Ryther 1980, Breton et al 2006, Panizzo et al 2018. Alternatively, primary producers and heterotrophic bacteria may utilize inorganic nutrients outside the Redfield ratio thus altering their intracellular C:N:P ratio (Mills and Arrigo 2010, Meunier et al 2014, Trautwein et al 2017).…”