Comparison of methods for the characterization and quantification of carbon forms in estuarine and marine sediments from coal mining regions

Organic matter (OM) in sediments plays a vital role in the global carbon cycle, yet its quantification remains a major analytical challenge. The applicability of various techniques for characterizing the OM in six estuarine sediment samples from the coal-mining region of Northumbria and Tyne and Wear (UK) and three marine sediment samples from the lignite mining region of Aliveri (Greece) was tested. The techniques included wet chemical oxidation according to Walkley-Black and thermal oxidation (16 h, 375 °C), automatic carbon analysis after thermal (24 h, 500 °C) and acid treatment, organic petrography, Rock-Eval pyrolysis and thermogravimetric analysis combined with data from X-ray diffraction. The total organic carbon (TOC) content determined after HCl or thermal treatment correlated well but HCl treatment tended to record lower TOC content. Known additions showed that coal OM is partially resistant to wet chemical oxidation and does not contribute to the thermally resistant OC fraction.