ANCIENT SEDIMENTARY ORGANIC MATTER IN A MODERN RIVER CARBON CYCLE: THE HUDSON-MOHAWK RIVER SYSTEM, NEW YORK, USA

The connection between erosion of rocks on the continents and deposition of marine sediments is riverine transport. Current understanding of the geochemical carbon cycle holds that rivers carry relatively modern dissolved and particulate organic matter derived from autochthonous sources, watershed vegetation and soils, and that OM from shale-rich lithologies exposed in the watershed is fully oxidized upon soil formation. In some systems, this is not the case. Ancient rock-derived organic matter may play an important role in the modern carbon cycle through erosion, delivery, utilization and transformations between particulate and dissolved carbon pools. Our work seeks to quantify ancient OM contributions to the Hudson-Mohawk watershed of upstate New York, USA. Large portions of this watershed are underlain by organic matter-rich Paleozoic sedimentary rocks. This river system provides an ideal natural laboratory for distinguishing rock, soil, terrestrial vegetation and authochthonous sources of dissolved and particulate organic matter to natural waters.

Prior research has indicated a significant flux of radiocarbon-depleted organic matter to the Lower Hudson River (Raymond and Bauer, 2001). Our preliminary results suggest substantial fluxes of organic carbon out of small catchments draining lithologies rich in organic carbon. These fluxes may also relate to land-use patterns (forested, pasture, tilled agricultural and urbanized). Through a combination of elemental analysis, stable carbon and nitrogen isotopic analysis, pyrolysis-gas chromatography, and radiocarbon analysis, we are examining dissolved and particulate river organic matter, soils and sediments to trace the delivery of ancient organic matter from weathered sedimentary rocks to modern river systems.

Weathering of ancient, organic matter-rich sedimentary rocks may prove to be an important source of organic matter to some river systems. As such, these systems would represent “short-circuits” in the geochemical carbon cycle and may impact the composition and apparent age of coastal waters and sediments.