Utilisation of different carbon sources in a shallow estuary identified through stable isotope techniques
Zetsche, E.; Thornton, B.; Midwood, A.J.; Witte, U. (2011). Utilisation of different carbon sources in a shallow estuary identified through stable isotope techniques. Cont. Shelf Res. 31(7-8): 832-840. dx.doi.org/10.1016/j.csr.2011.02.006
In: Continental Shelf Research. Pergamon Press: Oxford; New York. ISSN 0278-4343; e-ISSN 1873-6955, more
Organic carbon in estuarine sediments can have many different sources. Terrestrial, riverine, estuarine and marine C pools may all contribute to and influence the organic C (Corg) inventory of the estuarine sediments and the differing stable isotope signatures of the sources are reflected in the sediment's overall 13C content. Ecological interpretations of sedimentary isotope data may, however, be limited by the fact the total Corg inventory of a sediment may not be an accurate representation of the fraction that is labile and being actively turned over by the sedimentary community. To gain a better understanding of sedimentary Corg dynamics in estuaries and the relationship between the sedimentary C pool and the Corg undergoing mineralisation, we studied three components of an estuarine system: (1) the sedimentary Corg inventory on a transect from the mouth to the upper end of the estuary, (2) temporal changes of sedimentary Corg at one station throughout a year, and (3) the d13C of respired CO2 compared to the d13C of available source material and sedimentary Corg in a novel application of methods developed for soil science. Our experiments demonstrated that material of marine origin dominated the studied estuary. At the time-series station, material of marine origin dominated the sedimentary Corg throughout the 1-yr study period. d13C values of CO2 released from the sediment differed significantly from the sedimentary Corg inventory at all study sites, but also clearly reflected differences between the main sections of the estuary. These results suggest that d13C measurements of respired CO2 are promising as a tool to advance our understanding of C cycling in estuaries, and highlight that the sedimentary Corg pool alone may not be a satisfactory indicator of OM utilisation in estuarine sediments.
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