GEOCHEMICAL STUDY OF SMALL STREAMS IN THE BALTIMORE AREA SUGGESTS ENHANCED CARBON EXPORT FROM URBAN SETTINGS

The transport of carbon in streams is an important component of the carbon cycle, indirectly connecting the atmosphere and the oceans and thus having the potential to regulate climate change and to buffer the oceans. Studies have suggested that urbanization could enhance the export of carbon from continents, but the confounding effects of bedrock composition and climate have masked the results of these studies. To evaluate the effect of urbanization on carbon export, we studied four small streams within the Baltimore metropolitan area, Maryland, and one stream with a watershed of secondary forests. The watersheds of the studied streams are all located in the Piedmont physiographic province, which has a bedrock consisting primarily of schist, gneiss, gabbro, quartzite, and marble. Our approach relied on a synoptic study of baseflow geochemistry conducted weekly over a period of rainfall minima. Results revealed elevated concentrations of dissolved inorganic carbon, pH values ranging from 7.5 to 8.2, and oversaturated levels of dissolved carbon dioxide in all studied streams. Preliminary evidence suggests that the weathering of carbonate minerals is responsible for the obtained data. However, the urban streams exported about four times more dissolved inorganic carbon relative to their forested counterpart. These preliminary results point to the role of land-use change in urban/suburban areas on enhancing the export of carbon from continents to both the atmosphere and the oceans.