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Table 1 Definition of “present” and “past” sediment parameters

From: Shifts among Eukaryota, Bacteria, and Archaea define the vertical organization of a lake sediment

We define present parameters as the principal components of all context
data derived from (a) pore water analysis, which indicates that chemical
gradients are caused by the consumption and production of ongoing
biological processes (e.g., sulfate and methane), and from (b) directly
measured parameters of microbial activities (e.g., bacterial protein
production). The present parameters are therefore an expression of
recent microbial processes.
Past parameters are the principal components of conservative
parameters, which once introduced into the sediments will not change
significantly and are therefore an expression of the lake’s history (e.g.,
heavy metals). Here, we also categorize the total amount of elemental
carbon, nitrogen, hydrogen, and sulfur as mainly conservative parameters.
The past parameters are therefore an expression of historical changes.