Hi Laura,

I think, in this case it is a question of the amount of phytoplankton in water and the deposition of it to the bottom of lake during the sedimentation. They form colloids with clay mineral, and when deposited on the bottom sediments, they protect underlying sediments from the erosion during changes in the lake bottom (caused by, for example, climatic changes or changes in water streaming within the lake body). If organic production is low or missing, mineral sediments are bare at the bottom and easily eroded during the changes in water body.

Are those organic compounds any more 'active', when deposited or buried into the bottom sediments, I don't know. Maybe it is more or less died material in that phase.

Of the mineral material, 'optically active' are quartz and felspar.

I hope, that was an answer to your question.

Regards,

Pertti

Hi Pertti and thanks for your answer.

In this case would you say so: longer ice covering > lower amount of optically active substances (or the other way around??) > less protection and more erosion in sediments?

If as above (any of the two), would you include among the substances that may/may not be protected in the sediments even extracellular DNA (normally found as bounded to inorganic material)? 

So in few words: do you think DNA in sediments is more protected when we have ice covering or not?