TRANSPORT AND TRANSFER OF CARBON TO THE ATMOSPHERE BY SMALL STREAMS EXHIBITING DIFFERENT LEVELS OF URBANIZATION IN SUBURBAN BALTIMORE, MARYLAND

Streams and rivers are important components of the global carbon cycle. Not only do they transport between 0.8 and 1.6 Pg C/yr to oceans, with as much as half corresponding to dissolved forms of carbon, but they also transfer significant amounts of carbon dioxide to the atmosphere via degassing. Urbanization has the potential to alter these fluxes primarily through land-use changes and the addition of calcareous materials to watersheds, among other processes. To explore the effect of urbanization on the transport and transfer of carbon to the atmosphere, four first-order streams in suburban Baltimore, Maryland were examined. These streams exhibit different levels of urbanization as reflected by the percentage of impervious surfaces present in their watersheds. Results show that both DIC and DOC (dissolved inorganic and organic carbon), as well as particulate organic carbon positively correlate with discharge, which in turn is dependent on precipitation. The stream with the least amount of impervious surfaces, however, consistently showed elevated DIC concentrations, with values as high as 2.95 mM. This stream also had the highest amount of carbon dioxide evasion and the least negative stable isotope composition of DIC, with an average value of -10.78 per mil. These results suggest the influence of a more calcareous-rich source of DIC for this stream, likely corresponding to metamorphic rocks containing marble. In contrast, the other three studied streams exhibit lower DIC concentrations and isotope values, indicative of a more significant influence of soil-derived DIC. The variability observed in the data for these streams could result from changes in lithology, as well as anthropogenic effects that have altered the hydrology of the studied streams.