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

Abstract

Lake Baikal has been experiencing limnological changes from recent atmospheric warming since the 1950s, with rising lake water temperatures, reduced ice cover duration and reduced lake water mixing due to stronger thermal stratification. This study uses lake sediment cores to reconstruct recent changes (c. past 20 years) in Lake Baikal’s pelagic diatom communities relative to previous 20th century diatom assemblage records collected in 1993 and 1994 at the same locations in the lake. Recent changes documented within the core-top diatom records are in agreement with predictions by Mackay et al (2006) and Moore et al (2009) of diatom responses to warming at Lake Baikal. Sediments in the south basin of the lake exhibit clear temporal changes, with the most rapid occurring in the 1990’s with shifts towards higher abundances of the cosmopolitan Synedra acus and a decline in endemic species, mainly Cyclotella minuta and Stephanodiscus meyerii and to a lesser extent Aulacoseira baicalensis and Aulacoseira skvortzowii. The north basin, in contrast, shows no evidence of recent diatom response to lake warming despite marked declines in north basin ice cover in recent decades. This study also shows no diatom-inferred evidence of eutrophication from deep water sediments. However, due to the localised impacts seen in areas of Lake Baikal’s shoreline from nutrient pollution derived from out-dated sewage treatment plants, urgent action is vital to prevent anthropogenic pollution extending into the open waters.

Changing nutrient cycling in Lake Baikal, the world’s oldest lake

“…4). Community changes in Lake Baikal in the second half of the 20th century and the expansion and displacement of endemic taxa have previously been attributed to increased SWT and summer thermal stratification (14,16) (Fig. 4).…”

“…While it remains unclear to what extent these changes can also be directly attributed to the concordant increase in photic zone nutrient supply, redundancy analysis suggests that nutrient supply may account for almost one-quarter of diatom community variation exhibited. Furthermore, changes in community turnover are strongly associated with relative abundance increases in the endemic Aulacoseira skvortzowii (r = −0.68, P < 0.005) and cosmopolitan Ulnaria acus (r = −0.83; P < 0.005), trends that are mirrored elsewhere across the lake (14,16,22,44) (Fig. 4).…”

“…Concerns exist over the future health of this unique ecosystem, amid evidence of extensive shoreline eutrophication (11,12) and climate-induced shifts in primary productivity (13,14). Together, these changes have impacted organisms ranging from sponges and gastropods to ciliates, flagellates, and algal communities (15).…”

Human impact and ecosystemic health at Lake Baikal

“…As has now been shown by long-term studies, in the overwhelming majority of cases, Spirogyra blooms profusely only opposite coastal settlements, and only in autumn, when the massive influx of tourists to Lake Baikal ends (Timoshkin, 2019). However, as waters continue to warmparticularly in the south basin-and the tourist economy continues to grow without robust regulation and treatment of discharged wastewater, the threat of further degradation in water quality will increase (Roberts et al, 2018). Solving these problems would require addressing the lack of waste infrastructure, regulating the phosphate content of detergents, and controlling the trajectory of continued coastal development.…”

“…The dominant diatom algae, such as Aulacoseira baicalensis , A. islandica and Stephanodiscus meyerii and dinoflagellates such as Gymnodinium baicalense , develop in mass under ice, providing food for other organisms—predominantly zooplankton, mostly represented by the microscopic crustacean Epischurella baikalensis . Monitoring data demonstrate a significant warming‐related shift in species composition both in phyto‐ and zooplankton: the number of cold‐loving and ice‐related endemic species is declining, while warm‐loving cosmopolite species are becoming more dominant (Bondarenko, Vorobyova, Zhuchenko, & Golobokova, 2020; Izmest'eva, Silow, & Litchman, 2011; Roberts et al, 2018; Rusanovskaya et al, 2020). Additionally, the depth distribution of many plankton groups has changed due to increased stratification and reduced mixing (Hampton et al, 2014).…”