Organic geochemical investigations of urban sediments by pyrolysis-gas chromatography / mass spectroscopy.

摘要

An urban sediment is not simply defined by proximity to a city. Because cities have anthropogenic contamination, one important urban sediment characteristic is ongoing recontamination. Another is legacy contamination from industrial activity and a third is the alteration of natural bio-geochemical systems.;Two case studies are presented. The surface sediments of the Gateway National Recreation Area were sampled during the summer of 2007. The ratio of two pyrolysis products, Vinylguiacol, from terrestrial plant lignins, and Indole, from proteins, (VGI Index) is moderately well correlated with the sediment C/N ratios. A low VGII (0.33) suggests that the primary input of organic matter along the shores of the National Park's Jamaica Bay is terrestrial while the inputs are primarily marine in areas where there has been a dramatic loss of salt marshes. In contrast, healthy marshes on the park's nearby Sandy Hook unit had a VGII of 0.82. The VGII could also be correlated with the Carbon Preference Index (CPI) (r = 0.54) and the Syringol / Vanillyl (S/V) ratio (r = 0.87). Increased values of the CPI often indicate an organic input from terrestrial plants while increasing S/V values are often associated with grasses. A Principle Component Analysis (PCA) grouped the sample points associated with either water pollution control plants or combined sewer overflows into one component. This serves to reinforce the observation that most of the current freshwater inputs to Jamaica Bay have been from sewer discharges.;The suitability of Py-GC/MS to study conditions in a sediment core is the focus of the second case study. A 2-meter sediment core was obtained from the Passaic River's Dundee Lake. The core was taken from a highly disturbed part of the river and clear temporal trends were not discernible. Compounds of the same chemical class showed clear patterns of co-occurrence and correlations were frequently 0.9 or higher among petrogenic compounds. These results suggest related co-deposited compounds tend to remain together even in disturbed areas.;Because the majority of human populations now live near the coastlines a more sustainable sediment management policy needs to replace the current system of "dredge and dump." One challenge in the future will be to have an adequate supply of sediment to protect the coasts against rising sea levels. Characterizing the organic matter in those sediments is another potentially useful application of py-GC/MS.