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.

中文翻译：

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降雨最小期间，流域岩性对马里兰州巴尔的摩市郊流中溶解性无机碳收支的影响

城市化有可能影响河流的碳出口，但很少有研究评估岩性对城市环境中碳通量的潜在影响。为了解决这一差距，在降雨量最小的时期内，对巴尔的摩大都会地区表现出不同水平的不透水表面和集水岩性的四个一级流进行了为期十周的检查，目的是确定所运输的无机碳的来源和数量这些水在基本流动条件下被这些流。在原位测量放电，碱度，pH，温度和溶解氧，而在实验室中确定溶解无机碳（DIC）的碳同位素组成。DIC和pCO _2的丰度根据收集的数据进行估算，结果表明，森林覆盖率增加和钙质集水区的水流始终具有最高的DIC，pCO ₂，碱度和稳定的同位素比值。四个研究流的DIC产量相对较低，范围从2.6至21.8 mmol C / m ² -yr，计算出的pCO ₂逃逸率是温带和北方地区最低的记录值，范围从184至6451 g C /天。这些较低的值可能是由于采样期间普遍存在的低降雨造成的，这既限制了土壤衍生的DIC向研究河流的转移，也限制了随后的CO ₂排放。大气。稳定的同位素数据与DIC线性相关，这种关系可以反映所研究流中无机碳的岩性控制，其中富含¹³ C的DIC来源可能代表了钙质变质岩的溶解和土壤呼吸的CO _2的贡献。并具有¹³ C贫化源，其解释为是土壤呼吸的CO ₂的主要贡献。因此，我们的研究结果表明，在低流量条件下，流域岩性在调节所研究的郊区河流的河流DIC预算方面起着主导作用。