Early diagenesis in Canadian Shield lakes

Abstract

The biologically catalyzed degradation of organic matter is the driving process leading to chemical change in surficial sediments. The consequences of these oxidation and fermentation transformations are the released, in the interstitial waters, of metabolite compounds such as SCOz, CH4, N O j, ~-'NH3, and ~PO4, and the mobilization of reduced species, e.g., Mn 2÷, Fe 2÷ (Berner, 1980). One way to estimate the extent of organic matter decomposition in sediments is to look at the depth distribution of the by-products of organic matter diagenesis. But, in order to quantify these transformations one needs to derive stoichiometric mass balances which assess the entire suite of reactions that affect the chemical species of interest. Because sediments are open systems and the site of numerous secondary reactions, it is not always straightforward to determine the stoichiometry of the geochemical reactions. The purpose of this paper is to demonstrate that in selected environments, simple stoichiometric relationships can be utilized to depict and quantify early diagenetic processes. In Canadian Shield lakes, because the numbers of secondary reactions are limited, one can construct simple sets of stoichiometric relations that lead to valuable information on the relative importance of the different processes responsible for organic matter decomposition. 2. Environmental setting and analytical methods