Characterization of the lignin signature in Lake Mead, NV, sediment: comparison of on-line flash chemopyrolysis (600 degrees C) and off-line chemolysis (250 degrees C).

The distribution of lignin in sediment is a useful tool for tracing the transport of land-derived organic matter in an aquatic environment. Tetramethylammonium hydroxide (TMAH) flash chemopyrolysis, or chemolysis followed by GC-MS analysis can be used for evaluating the origin of organic carbon in sediments. TMAH chemopyrolysis or chemolysis of organic matter produces a myriad of semi-volatile products. Among these products are methylated phenols which are an indirect measure of lignin in sediment. In this study, total organic carbon, elemental carbon, and lignin were measured in Lake Mead sediments. This study indicates that terrestrial runoff makes a contribution to Lake Mead sediments, and that this contribution is most apparent in sediment that is close to the Las Vegas Wash. Two chemolysis methods (on-line and off-line) were examined and compared for detection of lignin phenols. The results from these sediment cores indicate that comparable results can be obtained from the two approaches, although detection levels are significantly lower for the off-line approach.