Roberts SL, Swann GEA, McGowan S, Panizzo VN, Vologina EG, Sturm M, et al. (2018) Diatom evidence of 20th century ecosystem change in Lake Baikal, Siberia. PLoS ONE 13(12): e0208765. https://doi.org/10.1371/journal.pone.0208765
Located in Siberia, Russia, Lake Baikal is the deepest lake in the world (Figure 1). Similar to other waterbodies around the world, both big and small, Lake Baikal is exhibiting changes in the community composition of its primary producers that make up its base of its food web in response to climate change induced changes in surface temperatures and nutrient inputs. In this study, scientists examine community composition shifts in a group of primary producers known as diatoms and examine the influence of climate change on this shift.
Figure 1. Lake Baikal in Siberia, Russia. Image credit: Wikimedia Commons
Southern Siberia, the region where Lake Baikal is located, is experiencing regional warming on a scale that has not been observed for 1000 years. This regional warming translates to warmer surface water temperatures and a shorter duration of ice cover. Both conditions are favorable for summer algal blooms, which have been observed more frequently in the southern basin over the last 60 years. Given the community composition shifts observed in other major global waterbodies, Sarah Roberts from the Canada Centre for Inland Waters and colleagues examined shifts in diatom community composition in response to warming temperatures. Diatoms are single-celled algae that are easy to identify because they have shapes and silica shells (known as frustules) that are unique to each species (Figure 2). Even though they are single-celled, they can often be found in colonies, as well as chain and thread-like filamentous formations.
The researchers were particularly interested in whether endemic species (species that are unique to a particular geographic location) were being replaced by more generalist species that were better equipped to deal with changing environmental conditions. Additionally, the research team was keen to identify any evidence of the impacts of shoreline development on near-shore lake habitat. As changes in diatom community composition may indicate the presence of multiple stressors (climate change + land use change/development), which can significantly impact the ability of the lake to maintain its ecosystem function in its current state.
Figure 2. Example of diatoms. Image credit: Wikimedia Commons.
To study these multiple angles of interest, the authors collected sediment cores (Figure 3) from the lake bottom from both the southern and northern basins of Lake Baikal and multiple sites between the basins, for comparison. They then used the sediment cores to reconstruct diatom community composition over the past 30 years. If you would like to know more about sediment cores and the role they play in understanding changes in environmental conditions, check out these Envirobites articles related to the topic.
Figure 3. Example of a sediment core. Image credit: Wikimedia Commons
What they found:
Roberts and colleagues found that the results confirmed their hypothesis. Endemic diatom species in Baikal evolved to thrive in cooler water temperatures, but they are now being out-competed by generalist species able to thrive in warming waters. While endemic species are still common in the north basin where silica is abundant and temperatures are cooler, in the south basin, heavily silica-dependent diatoms are being replaced by species not dependent on large quantities of silica. While endemic species have evolved a few strategies for dealing with increasing temperatures, e.g., producing resting stages that are able to survive high temperatures, the authors found that when the endemic diatoms come out of the resting stages during favorable temperatures, the generalist species have already taken up a large portion of the nutrients in the water column. Because generalists are able to survive in increased temperatures and capitalize on the nutrient inputs coming into the lake while endemic species are still in their resting stages. It is worth noting that due to increased precipitation in recent decades, and associated increases in river discharge, the generalist diatoms have access to a larger nutrient pool.
Importantly, the research team found evidence of localized impacts from poorly treated/untreated discharge from sewage treatment facilities that have resulted in poor water quality in the study area. Therefore, the authors suggest immediate improvements to sewage treatment facilities to ensure these localized impacts do not spread throughout the lake. Over the past few decades, the surface water temperature of Baikal has increased by 2ºC and will continue to warm as climate change continues. This change has resulted in a shorter duration of ice cover, decreased mixing in the water column, and algal blooms near surface waters in the summer.
Why use diatoms?
You may wonder why it is important to identify such community composition shifts of diatoms. In many ways diatoms act as the ‘canary in the coal-mine’ for lake ecosystems, and are one of the earliest, clearest lines of evidence for impacts of climate change.