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

从体积上看，21世纪化石燃料燃烧持续排放的二氧化碳是地球上最重要的环境污染物。方解石和白云石的溶解速度非常快，溶解度强烈依赖于二氧化碳，这就形成了碳酸盐风化和有机碳呼吸速率之间的密切联系。这在近地表地下水和溪流中尤其重要，因为由于水在这些水库中的停留时间很短，这些系统将首先对气候和大气变化做出反应。因此，限制流域溶解无机碳通量的因素对于预测地球表层水库对未来几个世纪生物量和碳收支预期变化的响应将是非常重要的，这是最紧迫的人类和环境问题的时间尺度。对于北美来说，近90%的HCO3-通量来自中大陆地区，那里有很高比例的沉积基岩被含碳酸盐的冰川漂移所覆盖。重要的是，这些温带风化环境的低温最大限度地提高了碳酸盐矿物的溶解度。事实上，密歇根流域拥有世界上一些面积归一化的碳通量最高的地区。因此，这一区域提供了一个理想的实地实验室，用于评估对溪流和与其相互作用的浅层地下水中HCO3含量的控制情况。我们建议的研究计划包括对大湖区6个端元流域的水文地球化学进行实地研究，这些流域横跨密歇根州的上半部和下部半岛。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USGS实时测量站的可用性来选择特定的野外地点。我们的目标是对中大陆冰川地区地表水和地下水中溶解的无机和有机碳系统进行高质量的分析和理论表征。我们的初步研究表明，地表和地下水中的镁浓度是碳酸盐溶解的极好的保守示踪剂。因此，镁/HCO3比率提供了碳酸盐溶解与分水岭边界内河流、湿地和湖泊中的降水质量平衡的敏感指标。我们制作的新数据集将综合物理因素(流域排水类型、流量、年循环)以及测量的无机和有机碳通量。确定碳酸盐质量转移的平衡控制和动力学控制将使人们能够更准确地预测地球地貌和地表水文地球化学系统将如何应对二氧化碳升高世界中不断增加的碳代谢和通量。

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.