Controls on the variability of organic matter and dissolved inorganic carbon ages in northeast US rivers

The use of natural C-14 in aquatic and marine studies provides unique source, turnover and processing information with respect to local, regional and global carbon budgets. The number of C-14 analyses in many aquatic ecosystems is small, however, thus limiting the full potential of C-14 as a tool in carbon studies in these systems. This is particularly true for rivers, which form key linkages between terrestrial and oceanic systems. As part of our on-going studies, radiocarbon-based measurements of dissolved and particulate organic carbon (DOC and POC, respectively), as well as dissolved inorganic carbon (DIC), are being conducted in a group of northeast US rivers. The values for bulk Delta(14)C-DOC, and Delta(14)C-POC, Delta(14)C-DIC and their associated delta(13)C ratios are reported for 64 measurements on seven different river systems. While the examined rivers occupy a relatively small geographic area, they individually export both ancient and fully modem post-bomb C to the coastal ocean. The large ranges in Delta(14)C for DOC, POC and DIC point to large spatial and temporal variability in the relative inputs of fossil vs. contemporary C, and the processing of each, in this geographically contiguous set of rivers. Although this represents a fairly well-studied group of rivers with respect to carbon ages, the sample number still precludes an in-depth understanding of specific sources of different aged components to these rivers, or to river systems in general. The collective data pen-nit some preliminary assessments concerning the relative importance of wetlands, ancient uplifted sedimentary marine OM, and within-system modification as important potential controls on riverine carbon ages. (C) 2004 Published by Elsevier B.V.