Geochemical Controls on Carbonate Equilibria and Mass Transport in Glaciated Mid-Continent Watersheds

冰川期中大陆流域碳酸盐平衡和质量传输的地球化学控制

• 批准号: 0208182
• 负责人: Lynn Walter
• 金额: $ 19.89万
• 依托单位: Regents of the University of Michigan - Ann Arbor
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-08-01 至 2005-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0208182&HistoricalAwards=false
• 关键词: Geochemical; Controls; Carbonate; Equilibria; Mass

The continuing emission of CO2 from fossil-fuel burning in the 21st century is, volumetrically, earth's most significant environmental pollutant. The dissolution of calcite and dolomite is very rapid and solubility is strongly CO2-dependent, which forges a close linkage between carbonate weathering and organic carbon respiration rates. This will be especially important in near surface groundwaters and streams, because these systems will be the first to respond to climatic and atmospheric changes due to the short residence time of water in these reservoirs. Thus, factors limiting dissolved inorganic carbon fluxes from watersheds will be very important in predicting the response of earth's surface reservoirs to anticipated changes in biomass and carbon budgets in the next few centuries, the timescale of most pressing human and environmental concern.For North America, nearly 90% of the HCO3- flux is derived from the mid-continent region, which has a high proportion of sedimentary bedrock mantled by carbonate-bearing glacial drift. Importantly, the low temperature of these temperate weathering environments maximizes carbonate mineral solubility. Indeed, Michigan watersheds have some of the highest area-normalized carbon fluxes in the world. This region thus provides an ideal field laboratory in which to assess controls on the HCO3- content of streams and the shallow groundwaters interacting with them on human timescales. Our proposed research program involves field study of the hydrogeochemistry of 6 endmember watersheds in the Great Lakes region, spanning the upper and lower peninsulas of Michigan. The specific field sites were selected on the basis of water chemistry, bedrock lithology, drainage basin type, land use and ecosystem type, mean annual temperature, and availability of real-time USGS gauging stations. Our goal is to produce a high quality analytic and theoretical characterization of the dissolved inorganic and organic carbon systematics of surface waters and groundwaters in the glaciated mid-continent region. Our initial studies demonstrate that surface and groundwater Mg concentrations are excellent conservative tracers of carbonate dissolution. As such, the Mg/HCO3 ratio provides a sensitive indicator of mass balances of carbonate dissolution versus precipitation in the streams, wetlands and lakes present within the watershed boundaries. The new data set we produce will integrate physical factors (type of river basin drainage, discharge, annual cycles) and with measured inorganic and organic carbon fluxes. Identifying equilibrium versus kinetic controls on carbonate mass transfer will permit more accurate predictions to be made of how earth's landscapes and surface hydrogeochemical systems will respond to increasing rates of carbon metabolism and fluxes in an elevated CO2 world.

从体积上讲，21世纪世纪化石燃料燃烧产生的CO2持续排放是地球上最重要的环境污染物。方解石和白云石的溶解是非常迅速的，溶解度是强烈的CO2依赖性，这锻造碳酸盐风化和有机碳呼吸速率之间的密切联系。这对近地表地下水和溪流尤其重要，因为这些系统将首先对气候和大气变化作出反应，因为水在这些水库中的停留时间很短。因此，限制流域溶解无机碳通量的因素对于预测未来几个世纪地球表面水库对生物量和碳收支的预期变化的响应将非常重要，这是最紧迫的人类和环境问题的时间尺度。对于北美，近90%的HCO 3-通量来自大陆中部地区，它有一个高比例的沉积基岩覆盖碳酸盐冰川漂移。重要的是，这些温和风化环境的低温使碳酸盐矿物溶解度最大化。事实上，密歇根流域的面积归一化碳通量是世界上最高的。因此，该地区提供了一个理想的现场实验室，可以评估人类时间尺度上对溪流和与之相互作用的浅层地下水中HCO 3含量的控制。我们提出的研究计划包括在五大湖地区的6个端元流域的水文地球化学的实地研究，横跨密歇根州的上半岛和下半岛。根据水化学、基岩岩性、流域类型、土地利用和生态系统类型、年平均温度和美国地质勘探局实时测量站的可用性，选择了具体的实地地点。我们的目标是产生一个高质量的分析和理论表征的溶解无机和有机碳系统的表面沃茨和地下沃茨在冰川中部大陆地区。 我们的初步研究表明，地表和地下水镁浓度是碳酸盐溶解的良好的保守示踪剂。因此，Mg/HCO 3比提供了一个敏感的指标，碳酸盐溶解的质量平衡与降水的溪流，湿地和湖泊内的分水岭边界。我们产生的新数据集将整合物理因素（流域排水类型，流量，年周期），并与测量的无机和有机碳通量。 确定平衡与动力学控制碳酸盐物质转移将允许更准确的预测地球的景观和地表水文地球化学系统将如何应对碳代谢和通量在一个升高的CO2世界的增长率。