Lacustrine organic geochemistry—an overview of indicators of organic matter sources and diagenesis in lake sediments

Abstract

The factors affecting the amounts and types of organic matter in lacustrine sediments are summarized in this review, and synthesis, of published studies. Biota hving in the lake and in its watershed are the sources of the organic compounds initially contributed to the lake system. Microbial reworking of these materials during sinking and early sedimentation markedly diminishes the total amount of organic matter while replacing many of the primary compounds with secondary ones. Much of the organic matter content of sediments is the product of this microbial reprocessing. Various organic matter components of lake sediments nonetheless retain source information and thereby contribute to the paleohmnological record. Carbon/nitrogen ratios of total organic matter reflect original proportions of algal and landderived material. Carbon isotopic compositions indicate the history of lake productivity and carbon recycling. Biomarker compounds provide important information about contributions from different biota. Sterol compositions and chainlength distributions of n-alkanes, n-alkanoic acids, and n-alkanols help distinguish different algal and watershed sources and also record diagenetic alterations. Stabilization of functional-group-containing biomarkers by conversion into saturated or aromatic hydrocarbons or by incorporation into bound forms improves their preservation and hence record of source information. Lignin components provide important evidence of watershed plant cover, and pigments reflect algal assemblages. The interplay of the factors influencing the organic matter content of lake sediments is illustrated by overviews of sedimentary records of four lake systems-Lake Biwa (Japan), Lake Greifen (Switzerland), Lake Washington (Pacific Northwest), and the Great Lakes (American Midwest).

Characterization of phosphorus forms in lake macrophytes and algae by solution 31P nuclear magnetic resonance spectroscopy

“…When 92 kinds of marine plants from different habitats were studied, the C/N ratio was approximately 18.3, while C/P was approximately 550, and N/P was approximately 30 (Atkinson and Smith 1983). The C/N ratios for terrestrial plants were generally greater than 20 (Meyers and Ishiwatari 1993). In this study, C/N and C/P of aquatic macrophytes from Tai Lake were between those of singlecelled algae and those of marine benthonic plants.…”

Sources and preservation of sedimentary organic matter in the Southern Bohai Sea and the Yellow Sea: Evidence from lipid biomarkers

“…n-Alkanes are commonly used to obtain a broad and directly overview of hydrocarbon sources ranging from terrestrial vascular plant material to marine-derived phytoplankton or algae. Generally, the short-chain n-alkanes (nC15-nC20, SCalks) (the nC17 homologue is dominant) are presumed to originate from phytoplankton or algae (Meyers and Ishiwatari, 1993;Meyers, 2003), while the long-chain n-alkanes (nC26-nC31, LCalks) such as the nC27, nC29 and nC31 compounds are mainly produced by terrestrial plants (Logan and Eglinton, 1994). A correlation analysis was performed to reveal internal relationship of these n-alkanes.…”

Assessment of historical fecal contamination in Curitiba, Brazil, in the last 400 years using fecal sterols

“…Nevertheless, the sterol profiles of herbivores such as sheep or cows are dominated by specific sterols, including sitosterol, stigmasterol, and campesterol, but contain very little coprostanol, while the sterol profiles of humans and pigs are dominated by coprostanol (Leeming et al, 1996). According to Meyers and Ishiwatari (1993), sterols can be used to examine (a) historical contributions by sewage to a water body and (b) the distribution and transportation of sewage into the environment and the age of the effluent.…”