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），这影响了美国大部分地区的饮用水供应。DIC向地表水的运输增加使饮用水处理复杂化，促进藻类生长，增加水的硬度，并腐蚀水基础设施，如水管和管道。DIC还在河流和沿海海洋中提供缓冲能力（它可以作为“抗酸剂”）。由于农业石灰化、混凝土结构破坏和污水泄漏，农业和城市地区有可能增加DIC的来源和运输。然而，以前的研究并没有集中在城市地区。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，以及来源如何随风暴和不同土地利用而变化。它将比较在森林参考条件下向溪流输送的DIC的数量和来源。该研究将首先使用最先进的地球化学示踪剂“指纹”DIC源（混凝土，土壤，废水，岩石等）。然后，它将估计城市溪流在将DIC输送到敏感的接收水域（如切萨皮克湾）之前保留DIC的能力。该项目将是第一个同时提供DIC来源和运输信息的项目之一，这些信息有助于美国河流碱化程度的增加。研究结果将对预测土地开发对饮用水质量的影响、估计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河流具有重要意义。溶解无机碳（DIC）的浓度在美国东部的溪流和河流中增加。DIC从流域到溪流的运输有助于河流碱化，从而影响饮用水硬度，改变沿海碳循环，并增加初级生产的碳酸氢盐可用性。一些研究表明，在城市化流域的溪流和河流中，DIC和碳酸盐碱度的输运显著增加。大多数关于DIC命运和运输的工作集中在森林和农业流域；因此，我们对城市化流域DIC的来源和运输变化知之甚少。本研究探讨了三个问题：1)土地利用如何影响DIC出口量和水文时间；2) DIC的来源如何随城市化的增加和整个风暴过程而变化；3)城市化如何改变流域DIC出口的流内命运和运输？该研究将：a)在巴尔的摩长期生态研究（LTER）站点每周分析森林、农业、郊区和城市流域DIC和其他风化产物的浓度和通量；b)估算不同土地利用梯度的累积DIC分布曲线和DIC输出时间的变化。在此基础上，利用DIC δ 13C、主元素地球化学特征和DIC形态特征，对具有相似岩性的流域（2个森林流域和2个郊区流域）的潜在DIC源端组分进行地球化学识别；b)评估这些流域在风暴演变过程中DIC浓度和潜在来源的变化；c)通过在选定的河流中注入13c标记的NaHCO3来测量DIC吸收率和瞬时储存。预期的结果将把流域城市化与DIC动态变化联系起来，作为土地利用、河流流量和渠化的函数，并将阐明河流碱化增加的机制。这将是第一个利用综合水文学和地球化学方法同时产生关于城市河流中DIC的来源、运输和命运的信息的项目之一。

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.