Urbanization and agriculture are two key factors that place demands on water resources and serve as sources of anthropogenic pollution into inland waterways. The San Antonio River, which is sourced from a karst aquifer, plays an important recreational and scenic role, yet effective management is often hampered by the lack of understanding of the chemical characterization of the water system. The karst-dominated Edwards Aquifer watershed in south-central Texas is an ideal watershed to understand water–rock interaction (carbonate dissolution) and anthropogenic impact on our water resources. In order to understand groundwater–surface water interactions, we made chemical and isotopic measurements over a 17-km stretch of the San Antonio River beginning at the headwater sanctuary and moving downstream. The chemistry of the headwaters and at along the longitudinal profile of the river showed that the Edwards Aquifer is dominated by Ca²⁺, Mg²⁺ and HCO₃⁻ ions resulting from carbonate dissolution. The carbon isotopic signature of dissolved inorganic carbon (δ¹³C_DIC) showed that the Edwards Aquifer is in chemical and isotopic equilibrium with soil CO_2(g). The relationships between δ¹³C_DIC and solutes (Cl⁻, Na⁺, F⁻, NO₃⁻) showed that anthropogenic sources of these solutes are associated with low δ¹³C_DIC values, indicating that carbon isotopic composition of dissolved inorganic carbon can be a useful tracer for contaminants in the environment. The anthropogenic inputs into the San Antonio River were sourced mainly from effluents of the San Antonio Zoo, waste discharge from the River Walk in downtown San Antonio and from fertilizers and animal waste in the less urbanized section of the sampled area (Mission Concepcion to Mission Espada). To protect and sustain the water quality of urban waterways and karst aquifers, urban sewage and effluents must be treated and controlled.

城市化和农业是对水资源提出需求并成为内陆水道人为污染源的两个关键因素。源自喀斯特含水层的圣安东尼奥河发挥着重要的娱乐和景观作用，但由于对水系统的化学特征缺乏了解，有效的管理常常受到阻碍。位于德克萨斯州中南部的以岩溶为主的 Edwards Aquifer 流域是了解水岩相互作用（碳酸盐溶解）和人为对水资源的影响的理想流域。为了了解地下水-地表水的相互作用，我们在圣安东尼奥河 17 公里的河段上进行了化学和同位素测量，该河段从源头保护区开始向下游移动。²⁺、Mg ²⁺和HCO ₃ ^-离子由碳酸盐溶解产生。溶解无机碳 (δ ¹³ C _DIC ) 的碳同位素特征表明 Edwards 含水层与土壤 CO _2(g)处于化学和同位素平衡。δ ¹³ C _DIC与溶质（Cl ^-、Na ⁺、F ^-、NO ₃ ^-）之间的关系表明，这些溶质的人为来源与低 δ ¹³ C _DIC相关。值，表明溶解的无机碳的碳同位素组成可以作为环境中污染物的有用示踪剂。进入圣安东尼奥河的人为输入主要来自圣安东尼奥动物园的污水、圣安东尼奥市中心河滨步道的废物排放以及抽样区域中城市化程度较低部分的肥料和动物废物（康塞普西翁使命到埃斯帕达使命）。为了保护和维持城市水道和岩溶含水层的水质，必须对城市污水和流出物进行处理和控制。