Two weeks ago, while delivering an invited talk about our Baikal project at Michigan Technological University located on the south shore of L. Superior, I was struck by the many similarities and important differences between Lakes Superior and Baikal . While at Michigan Tech, I toured the university’s impressive new Great Lakes Research Center and I met with multiple scientists – remote sensing experts, stream ecologists, limnologists, fishery biologists, and algal biochemists – who are probing fascinating processes within L. Superior or its watershed. Also, during my visit, I toured the local area with my hosts, Dr. Charlie Kerfoot and Lucille Zelazny, and through them I learned about the rich history of the local area.
Both lakes are amazingly similar physically, chemically and biologically. For example, both are cold, oligotrophic (low in nutrients) and share similar water transparency and photic zone depths (Table 1). Furthermore, both lakes are responding to contemporary climate change with their surface temperatures warming and duration of winter ice cover shortening significantly. Although both L. Superior and L. Baikal are claimed as the largest in the world, the former is largest in surface area while the latter is largest by volume. Chemically, both lakes exhibit low calcium concentrations with this feature protecting L. Superior from the establishment of the invasive dreissenid mussels, while in L. Baikal low calcium purportedly explains the thin shells of the lake’s small snails. Biologically, the top pelagic fish predators of both of these cold lakes include coregonids (whitefish) while the summer phytoplankton communities are both dominated by autotrophic picoplankters. Finally, much of the watershed of both lakes is surprisingly undeveloped; however, mining is an anthropogenic activity common to both lakes’ watersheds. For example, mining for molybdenum, gold, and other metals is occurring presently in the Selenga River portion of Baikal’s watershed, whereas copper mining occurred throughout much of the 20th century on the south shore of L. Superior, leaving a legacy in the sediments of the littoral zone.
Table 1. Comparison of limnological variables describing Lake Baikal and Lake Superior. Secchi depth and photic zone depths in addition to rates of annual primary production (PPR) and annual surface water temperatures are similar between the two lakes. However, nutrients limiting primary production and the percent of the lakes’ surface area covered in ice each winter differ.
|Attributes||L. Baikal||L. Superior|
|Secchi depth (m)||6-30||15-20|
|Photic zone depth (m)||60-70||46-60|
|Annual primary production (mg C m-2 d-1)||235-390||200-350|
|Limiting nutrients||N, P||P, Fe|
|Avg. annual H2O Temp (C)||5||7|
|Avg. % ice cover in winter||100||12-24|
Differences between these two lakes include the nutrients that limit primary production, the extent of winter ice cover (Table 1), and the degree of contemporary geological activity. Phosphorus and possibly iron limit primary production in L. Superior while nitrogen and phosphorus appear to limit phytoplankton growth in L. Baikal. Interestingly, nitrate-nitrogen in offshore waters of L. Superior has increased inexplicably over the last 70 years. Unfortunately, long-term measurements of nutrient concentrations in Baikal’s offshore waters prevent a comparison. On a different note, we do know that all of L. Baikal is covered in ice for 5-6 months each year, and the lake’s top predator – the seal – and its dominant primary producers – the diatoms – depend upon ice for reproduction and recruitment. In contrast, only 12-24 % of L. Superior is ice-covered in recent winters with no known species requiring ice to complete their life cycle. Finally, L. Baikal, unlike Superior, is very active geologically with frequent earthquakes and methane emissions on the lake floor that support hydrothermal vent communities.
The greatest biological difference between Baikal and Superior, however, is arguably their species richness. L. Baikal contains many more species than any other lake in the world; however, 82% of Baikal’s species diversity occurs on the substrate of the lake’s littoral zone. Furthermore, there is a species diversity paradox in Baikal. Its pelagic community is remarkably species poor, containing many fewer species than most other lakes in the world including that of L. Superior. Only 1-2 species dominate the biomass at each pelagic trophic level in Baikal. For example, Epischura baikalensis comprises 90% of the crustacean zooplankton biomass in this lake and the oilfish (Comephorus spp. or golomyanka) constitutes 95% of the offshore pelagic fish biomass. Furthermore, all these dominant pelagic species in Baikal are endemic, cold-water stenotherms. To adapt and persist to climate change, these endemics must have adequate genetic and functional diversity. This is what our team is determining. Comparing the genetic and functional diversity of Baikal’s few dominant pelagic species to that of the more numerous pelagic species in the cold waters of L. Superior would be interesting!