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

从体积上看，21世纪燃烧化石燃料持续排放的二氧化碳是地球上最严重的环境污染物。方解石和白云石的溶蚀非常迅速，溶解度强烈依赖于co2，这使得碳酸盐风化作用与有机碳呼吸速率密切相关。这在近地表地下水和溪流中尤其重要，因为这些系统将首先对气候和大气变化作出反应，这是由于水在这些水库中停留时间短。因此，限制来自流域的溶解无机碳通量的因素对于预测地球表面水库对未来几个世纪生物量和碳收支预期变化的反应将是非常重要的，这是人类和环境最紧迫关注的时间尺度。对于北美，近90%的HCO3-通量来自大陆中部地区，该地区有高比例的沉积基岩被含碳酸盐的冰川漂移覆盖。重要的是，这些温带风化环境的低温使碳酸盐矿物的溶解度最大化。事实上，密歇根流域拥有世界上最高的区域标准化碳通量。因此，该地区提供了一个理想的实地实验室，可以在人类时间尺度上评估对溪流和浅层地下水中HCO3含量的控制。我们提出的研究计划包括对横跨密歇根上下半岛的五大湖地区6个末端流域的水文地球化学进行实地研究。具体场址是根据水化学、基岩岩性、流域类型、土地利用和生态系统类型、年平均温度以及USGS实时测量站的可用性来选择的。我们的目标是对冰川覆盖的中大陆地区地表水和地下水的溶解无机碳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Mg浓度是碳酸盐溶解的优良保守示踪剂。因此，Mg/HCO3比值提供了流域边界内溪流、湿地和湖泊中碳酸盐溶解与降水质量平衡的敏感指标。我们制作的新数据集将整合物理因素（流域排水类型、排放量、年循环）以及测量的无机和有机碳通量。确定碳酸盐质传递的平衡控制与动力学控制，将使我们能够更准确地预测地球景观和地表水文地球化学系统将如何对二氧化碳浓度升高的世界中碳代谢和通量的增加率作出反应。

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.