Warming of Lake Baikal
An important paper soon to be published synthesizes a suite of datasets collected by three generations of biologists working on Lake Baikal (Hampton et al. 2008). In this study, time-series of lake-water temperature, zooplankton and phytoplankton were taken off-shore from Bol’shie Koty at better-than-monthly resolution since 1945. A shorter record for chlorophyll a (as a proxy for phytoplankton biomass) has been obtained since 1979. Time-series analyses were used to determine trends in biological data over the monitoring period. Multiple regression techniques were then employed to determine potential factors which have influenced variation in the plankton of Lake Baikal, including month of year, regional snow depth, the Arctic Oscillation and the El Niño oscillation.
Since the start of the record, Hampton et al. (2008) demonstrate significant increases in water temperature: for example, surface waters during the summer had increased by 0.38 °C / decade, while even waters 25 m depth warmed by 0.22 °C / decade during summer months. Such increases in temperature are likely to have important consequences for limnological processes such as ice-cover, water column turnover and summer stratification, which in themselves will impact on the foodweb structure of Lake Baikal (Mackay et al. 2006).
Of great interest are shifts in zooplankton communities that have occurred since 1945. One of the dominant zooplankton species is the endemic copepod Epischura baicalensis, which shows a weak decline (Fig 1).
Fig 1: Average quarterly zooplankton abundance (grey lines) and Discrete Short-Time Fourier Transform de-seasoned, log-transformed zooplankton abundance (ln(individuals L-1+1)), with abundance segregated by quarter in the right column. Winter (December previous year, January, February) and Spring (March, April, May) were typically ice-covered. Summer (June, July, August) and Fall (September, October, November) have had incomplete or no ice cover over this time period. Linear regression was used to detect long-term trends, after tests for autocorrelation within de-seasoned and de-trended residuals.
Rotifers on the other hand show a strong decline. Most notable however, was the marked, significant increase in planktonic cladocera by over 335 %, especially during summer and autumn months. This dramatic increase showed the strongest correlation with the concomitant increase in higher water temperatures. Why is this important? Cladocerans can fundamentally change the foodweb structure of a lake, with respect to e.g. grazing intensity, but also to the recycling of nutrients in the water column, important for algal growth and primary productivity. As Lake Baikal continues to warm into the future, our understanding of how its ecology and ecosystem structure and function are likely to adapt are almost completely unknown.
Hampton, S.E., Izmest’eva, L.R., Moore, M.V., Katz, S.L. Dennis, B. & Silow, E.A. in press. Sixty years of environmental change in the world’s largest freshwater lake–lake Baikal, Siberia. Global Change Biology doi: 10.1111/j.1365-2486.2008.01616.x
Mackay, A.W., Ryves, D.B.. Morley, D.W., Jewson, D.J. & Rioual, P. 2006. Assessing the vulnerability of endemic diatom species in Lake Baikal to predicted future climate change: a multivariate approach. Global Change Biology, 12, 2297–2315. doi: 10.1111/j.1365-2486.2006.01270.x