Improved understanding of Diatom stratigraphy in a varved sediment through a sediment trap, lake monitoring and a catchment study

Abstract:

Biological sediment remains reflect past lake surrounding conditions. Potential drivers of change in the biological sediment proxy can be environmental contributors like weather and temperature changes as well as man-made such as developments in agriculture and forestry. However we don’t know how these different factors contribute to the biological sediment signal. Here we are monitoring a boreal lake with a varved sediment to understand how the biological signal of diatom remains is formed in the annually layered sediment. We compare the diatom stratigraphy with a sequential sediment trap. For a deeper understanding of the underlying mechanisms we look at three full years of bi-weekly monitoring of physical, chemical and biological parameters and 15 years of water stratification data. We seek to link the monitored in-lake processes with the yearly environmental characteristics. The diatom sediment stratigraphy of the two most abundant species Asterionella formosa and Fragilaria delicatissima indicates three periods with a contrasting trend for both species from 1975 until 2014. In the first period Asterionella formosa is almost not abundant spanning one decade (1975-1985), reaching elevated abundance with a decreasing trend in period 2 over the following 17 years to be followed by a tripling of Asterionella fromosa remains in the sediment during the third period. The opposite trend is found for Fragilaria delicatissima. Linking the recorded data with the corresponding sediment stratigraphy allows us to distinguish between weather changes and catchment disturbances as potential drivers for changes in a sedimentary diatom signal.