δ13C Measurements as Indicators of Carbon Flow in Marine and Freshwater Ecosystems

Abstract

Stable carbon isotopic measurements provide useful information about wihich autoptrophs -plants and bacteria- are important sources of carbon in marine and freshwater sediments, POC, and food webs. Transect studies of sediments an POC (section 4) often show clear-cut patterns of isotopic change that can be directly related to the proximity of various carbon sources. This has led to use of simple mixing models (Fig. 1A) in which isotopic data indicate relative importances of plant carbon sources. However, isotopic interpretations of d13C data are not always easily made. For instance, while -2 o/oo isotopic values for POC in upper reaches of estuaries may indicate carbon from terrestrial C3, plants, phythoplankton in these locations may also have -27 o/oo values. (..)