Hydrological Controls on the Seasonal Variability of Dissolved and Particulate Black Carbon in the Altamaha River, GA

Plain Language Summary Rivers play an important role in the transport of organic carbon from terrestrial to marine environments. A significant portion of this material is black carbon (BC), a residue of incomplete biomass and fossil fuel combustion. BC is mobilized in fluvial systems as both particulate BC (PBC) and dissolved BC (DBC), and the export of BC to coastal environments may have significant implications for carbon cycling in marine environments. However, while little is known regarding the potential connectivity between riverine export of PBC and DBC or the potential importance of such a relationship in constraining future BC budgets, current knowledge suggests that fluvial export of PBC and DBC are decoupled in small fire-impacted watersheds. This study aims to further address this subject on a larger watershed scale. For this study, 13 monthly samples were collected (September 2015 to September 2016) near the mouth of the Altamaha River, Georgia. PBC and DBC were characterized using the benzenze polycarboxylic acid method. Seasonal hydrology and regional shifts in storm events play an important role for both PBC and DBC export during high flow months. The DBC concentrations were comparable among wet and dry seasons, whereas evidence of seasonal salt water intrusions suggests an additional estuarine contribution of PBC at the sampling location. The DBC and PBC fluxes were generally coupled, although this pattern was disrupted during initial storm pulses. While this is the first report of potential coupling between DBC and PBC export, environmental drivers controlling this behavior between DBC and PBC remain to be constrained. Rivers play a critical role in the annual transport of organic material from terrestrial to marine environments. A significant portion of this material is a residue formed from incomplete combustion of plants and fossil fuels. Such pyrogenic materials can be mobilized from soils to rivers and transported in both particulate and dissolved forms. Their export to coastal environments may have significant implications for carbon cycling in marine environments. Here we study a subtropical watershed covering most of the U.S. state of Georgia, to investigate the effect of climateparticularly precipitationon the export and linkages between particulate and dissolved combustion products.