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

The use of natural 14C in aquatic and marine studies provides unique source, turnover and processing information with respect to local, regional and global carbon budgets. The number of 14C analyses in many aquatic ecosystems is small, however, thus limiting the full potential of 14C 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 Δ14C-DOC, and Δ14C-POC, Δ14C-DIC and their associated δ13C 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 modern post-bomb C to the coastal ocean. The large ranges in Δ14C 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 permit 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.