Effects of Urbanization on Sources and Transport of Dissolved Inorganic Carbon in Watersheds

人类活动增加了溪流和河流中的溶解无机碳(DIC)，从而影响了美国大片地区的饮用水供应。向地表水输送DIC的增加使饮用水处理复杂化，鼓励藻类生长，增加水的硬度，并腐蚀供水基础设施，如自来水总管和管道。DIC还在河流和沿海海洋中提供缓冲能力(它可以起到“抗酸剂”的作用)。由于农业石灰、混凝土结构损坏和污水泄漏，农业和城市地区有可能增加DIC来源和运输。然而，以往的研究并没有把重点放在城市地区。该项目将调查农业和城市土地利用如何影响河流中DIC的来源、数量和运输，以及来源如何随着风暴和不同土地用途的变化而变化。它将把向河流输送的DIC的数量和来源与森林参考条件进行比较。这项研究将首先对DIC来源(混凝土、土壤、废水、岩石等)进行“指纹”识别。使用最先进的地化示踪剂。然后，它将评估城市河流在将DIC输送到切萨皮克湾等敏感接收水域之前保留DIC的能力。该项目将是第一个提供有关导致美国河流碱化加剧的DIC来源和运输的同步信息之一。结果和结果将对预测土地开发增加对饮用水质量的影响、估计对沿海海洋酸化的影响、为城市流域管理提供信息以及恢复城市溪流具有重要意义。溶解无机碳(DIC)在美国东部的溪流和河流中的浓度增加。DIC从分水岭到溪流的运输导致河流碱化，从而影响饮用水的硬度，改变沿海碳循环，并增加初级生产所需的碳酸氢盐的可用性。一些研究表明，排出城市化集水区的溪流和河流中的DIC和碳酸盐碱度的运移显著增加。关于DIC的去向和运输的大部分工作都集中在森林和农业流域；因此，我们对城市化流域DIC的来源和运输的变化知之甚少。本研究探讨了3个问题：1)土地利用如何影响DIC出口的数量和水文时间；2)DIC的来源如何随着城市化和整个暴雨的增加而变化；以及3)城市化如何改变流域DIC出口的河流命运和运输？这项研究将：a)每周分析DIC和其他风化产物在巴尔的摩长期生态研究(LTER)站点的森林、农业、郊区和城市流域的浓度和通量；以及b)估计DIC的累积分布曲线和土地利用梯度上DIC出口时间的变化。然后，研究将：a)利用DIC三角洲13C、主要元素地球化学和DIC形态形成，在相似岩性的流域(两个森林覆盖和两个郊区)以地球化学方法确定DIC源的潜在终端成员；b)评估这些流域风暴演变期间DIC浓度和潜在来源的变化；以及c)在选定的溪流河段中使用13C标记的NaHCO3溪流注入测量DIC吸收速率和瞬时储存。预期成果将把流域城市化与DIC动态变化联系起来，作为土地利用、径流和河道化的函数，并将阐明河流碱化加剧的机制。这将是首批利用综合水文学和地球化学方法同时提供城市河流中DIC的来源、运输和去向的信息的项目之一。

Human activities have increased dissolved inorganic carbon (DIC) in streams and rivers, which impacts drinking water supplies across large regions of the U.S. Increased transport of DIC to surface waters complicates drinking water treatment, encourages algal growth, increases water hardness, and corrodes of water infrastructure, such as water mains and pipes. DIC also provides buffering capacity (it can act as an "antacid") in rivers and the coastal ocean. Agricultural and urban areas have the potential to increase DIC sources and transport because of agricultural liming, breakdown of concrete structures, and sewage leaks. However, previous research has not focused on urban areas. This project will investigate how agricultural and urban land uses impact sources, amounts, and transport of DIC in streams and how the sources change with storms and different land uses. It will compare the amount and sources of DIC transported to streams with forest reference conditions. The research will first "fingerprint" DIC sources (concrete, soils, wastewater, rocks, etc.) using state-of-the-art geochemical tracers. Then, it will estimate the ability of urban streams to retain DIC before it is transported to sensitive receiving waters, like Chesapeake Bay. This project will be one of the first to provide simultaneous information on sources and transport of DIC contributing to increased river alkalinization in the U.S. Results and outcomes will be important for predicting impacts of increasing land development on drinking water quality, estimating the effects on acidification of coastal oceans, informing urban watershed management, and restoring urban streams. Concentrations of dissolved inorganic carbon (DIC) have increased in streams and rivers in the eastern U.S. The transport of DIC from watersheds to streams contributes to river alkalinization, which impacts on drinking water hardness, shifts the coastal carbon cycle, and increases bicarbonate availability for primary production. Some studies suggest that transport of DIC and carbonate alkalinity are significantly elevated in streams and rivers draining urbanized watersheds. Most work on DIC fate and transport has focused on forest and agricultural watersheds; so we know little about changes in sources and transport of DIC in urbanized watersheds. This research investigates 3 questions: 1) How does land use influence the amounts and hydrologic timing of DIC exports; 2) How do sources of DIC change with increasing urbanization and throughout storms; and 3) How does urbanization alter in-stream fate and transport of watershed DIC export? The research will: a) analyze concentrations and fluxes of DIC and other weathering products weekly in forest, agricultural, suburban, and urban watersheds at the Baltimore Long-Term Ecological Research (LTER) site; and b) estimate cumulative DIC distribution curves and changes in DIC export timings across the land-use gradient. Then, the research will: a) geochemically identify potential end members of stream DIC sources in watersheds of similar lithology (two forested and two suburban) using DIC delta 13C, major element geochemistry, and DIC speciation; b) evaluate shifts in DIC concentrations and potential sources during the evolution of storms in these same watersheds; and c) measure DIC uptake rates and transient storage using stream injections of 13C-labelled NaHCO3 in selected stream reaches. Expected outcomes will link watershed urbanization to changes in DIC dynamics as a function of land use, streamflow, and channelization and will elucidate mechanisms for increased river alkalinization. This will be one of the first projects to produce simultaneous information on the sources, transport, and fate of DIC in urban streams using integrated hydrologic and geochemical approaches.