Origins and diagenesis of organic compounds in freshwater and marine sediments.

Abstract

Perylene, a naturally occurring five-ring polycyclic aromatic hydrocarbon (PAH), is ubiquitous in freshwater and marine sediments. Most previous studies have attempted to identify specific natural precursors of perylene, although a few of them have linked perylene to anthropogenic sources. Initial results of this project helped formulate the hypothesis that perylene formation is primarily governed by diagenetic processes rather than by the availability of some precursor compound. Various source and process parameters were measured from different depositional settings (i.e. Lake Ontario, Green Bay, and Saanich Inlet). The measurement of organic geochemical and sedimentary parameters enabled the depositional environments of each setting to be characterized. No relations were found between perylene and anthropogenic contributions of organic matter. However, proxies for neither aquatic nor terrigenous sources of organic matter correlate significantly with sedimentary perylene. The results suggest that perylene formation is controlled by diagenesis rather than sources of organic matter. Furthermore, differences in the amount of organic matter and microbial activity between the depositional settings suggest that perylene formation may be microbially mediated. Stable carbon isotopic signatures of perylene in Saanich Inlet sediments imply that perylene originates from both aquatic and terrigenous sources of organic matter. These values vary between $-$27 and $-$22%, whereas bulk organic carbon $\delta\sp{13}$C values are heavier and range only between $-$22 and $-$21%.