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Germán Mora,Lenna Blaser 한국지질과학협의회 2020 Geosciences Journal Vol.24 No.1
Urbanization has the potential to affect riverine carbon exports, but relatively few studies have evaluated the potential effect of lithology on carbon fluxes in urban settings. To address this gap, four first-order streams in the Baltimore metropolitan area exhibiting different levels of impervious surfaces and catchment lithologies were examined for a span of ten weeks during a period of rainfall minima with the purpose of identifying sources and magnitudes of inorganic carbon transported by these streams during base flow conditions. Discharge, alkalinity, pH, temperature, and dissolved oxygen were measured in situ, whereas the carbon isotopic composition of dissolved inorganic carbon (DIC) was determined in the laboratory. Abundances of DIC and pCO2 were estimated from the collected data, revealing that the stream with an increased forest coverage and a calcareous catchment consistently had the highest values for DIC, pCO2, alkalinity, and stable isotope ratios. DIC yields for the four studied streams were relatively low, ranging from 2.6 to 21.8 mmol C/m2-yr, and calculated pCO2 evasion rates were some of the lowest recorded values in temperate and boreal regions, ranging from 184 to 6451 g C/day. These low values possibly resulted from the low rainfall amount that prevailed during the sampling period, which limited both the transfer of soil-derived DIC to the studied streams and the subsequent emission of CO2 to the atmosphere. Stable isotope data linearly correlated with DIC, and this relation could reflect the lithological control of inorganic carbon in the studied streams, with a 13C-enriched source of DIC probably representing the dissolution of calcareous metamorphic rocks and some contribution of soil-respired CO2 and with a 13C-depleted source interpreted to result from a predominant contribution of soil-respired CO2. Thus, our results point to the dominant effect of catchment lithology in regulating stream DIC budgets in the studied suburban streams during low discharge conditions.