Our research aims to investigate the impact of both anthropogenic activity and natural climate variability on Lake Baikal’s ecosystem. Over the past 60 years, industrialisation and land-use development, as well as global warming have lead to increased nutrient loading into the lake. This nutrient loading impacts Lake Baikal’s algal communities, which are the building blocks of the ecosystem. At present the full impact of these changes remains largely unknown.
To investigate these human and climate-driven pressures we will be using silicon isotopes, as a proxy of nutrient utilisation, and sedimentary algal pigments, as a proxy of primary production. These techniques will be applied to sediment cores to reconstruct changes over time. Firstly, we aim to reconstruct the natural baseline of nutrient utilisation and algal communities, by reconstructing changes over the last 100 years. Secondly, assess the impact of recent changes on the ecosystem, and thirdly, examine the impact of natural climate driven variability on rates of nutrient utilisation and algal community composition.This is by reconstructing over the last 1000 years.
Our main research objectives are:
(1) To use the δ30Si signal in diatoms (siliceous microscopic algae) to investigate historical changes in nutrient utilisation, and to assess the impact of environmental variables in the lake on the δ30Si signal. To investigate this, seasonal samples will be taken through the water column, at fluvial inflow and outflow sites, from both winter ice and snow, and from rock and soil samples in the catchment. These will help us understand the natural inputs of δ30Si into Lake Baikal.
(2) To explore the impact of human-driven changes on the ecosystem, by collecting sediment cores from the north and south basin of Lake Baikal. Sedimentary algal pigments and diatom δ30Si will then be investigated to reconstruct changes in algal communities and silicic acid utilisation over the last 100 years.
(3) To understand the impact of natural variability, sedimentary algal pigments and diatom δ3 Si measurements on the sediment cores will be extended to the last 1000 years. This time period is important to investigate, as two major climate events took place. These are the Little Ice Age and the Medieval Warm Period, which are likely to have impacted the ecosystem, through changes in ice cover and lake water mixing.
Algal biomarkers and diatom silicon isotopes…
Tiny plants (known as algae) form the foundations of Lake Baikal’s ecosystem and consist of many different types of algae (such as diatoms which are algae encased in a silicon skeleton, and many other soft bodied non-siliceous algal groups). Algae are very sensitive to changes in light intensity and nutrient availability. Any significant changes in their community composition will naturally impact the lake’s food web and entire ecosystem. This research is focussing on the use of silicon isotopes in diatom frustules (skeleton) and algal biomarkers to produce independent primary productivity records in Lake Baikal.
Pigments (chlorophylls and carotenoids) are produced by all photosynthetic organisms, and can be used as biomarkers to identify specific algal groups. As the majority of algal groups are soft bodied (unlike diatoms), pigments are the only detectable remains which can be analysed to determine species composition. Therefore pigments provide an extremely useful tool for reconstructing algal communities and primary productivity.
Diatoms take up silicon from freshwater to form their silicon frustules. Therefore, investigating silicon stable isotopes provides excellent insight into the diatom community productivity. Diatoms preferentially take up lighter silicon isotopes (28Si) leaving the lake water more enriched in the heavier silicon isotope (30Si). This fractionation is important and measuring the isotopic composition of silicon within diatoms provides an indicator of their nutrient utilisation, and overall primary productivity.