Collaborative Resarch: A Comparative Study of Carbonate Weathering Mechanisms and Fluxes in Carbonate-Rich, Mid-Latitude Watersheds Across Landscape and Landuse Types

在全球变暖、大气二氧化碳增加、土地利用变化和酸化的影响下，矿物风化速率在未来可能会增加。由于碳酸盐矿物的溶解依赖于二氧化碳，反应速度快，陆地碳酸盐溶解通量会发生变化，并可能反馈到气候系统，并影响地表水的地球化学。我们以前对中西部北部和斯洛文尼亚富含碳酸盐的流域的水文地球化学研究表明，土壤带二氧化碳与浅层地下水二氧化碳有着密切的联系。这两个地区都是世界上归一化溶解无机碳通量最大的地区之一。如果碳酸盐的风化加速，溶解无机碳的河流出口可能会增加，也可能受到农业石灰的影响，这是中西部和世界其他潮湿农业区的常见做法。密西西比河已经显示出无机碳出口增加的证据。石灰对大气二氧化碳的净影响是不确定的，因为表层土壤中石灰矿物的溶解可能会根据pH值的不同而隔离或产生二氧化碳。碳酸盐矿物的溶解也影响硅酸盐矿物的风化，特别是通过控制土壤pH值，从而进一步影响对大气二氧化碳的风化反馈。事实上，在含硅酸盐和碳酸盐的集水区土壤中，斜长石风化的钠通量似乎比温暖环境下花岗岩流域的钠通量要高得多。智力上的优点：本提案是一项新的跨学科合作，将首席研究员和斯洛文尼亚合作者聚集在一起，致力于碳酸盐地球化学几个不同但高度相关的研究领域。以协同方式共同努力，将扩大和统一对碳酸盐矿物在景观规模溶质通量和土壤-大气二氧化碳交换中的作用的理解。沃尔特在水文地球化学方面有着丰富的工作经验，在不同的景观中进行矿物风化。拟议研究的一部分是以前资助下启动的项目的延伸，包括将密歇根冰川流域的溪流和地下水的碳酸盐地球化学与斯洛文尼亚高山和喀斯特地区的碳酸盐地球化学进行比较。汉密尔顿最近开始研究与石灰有关的碳酸盐通量，这与LTER关于农业行作物生态系统的项目有关。通过与密歇根州立大学凯洛格生物站的斯蒂芬·汉密尔顿进行新的合作，沃尔特将把她的工作扩展到密歇根州的农业土壤，将地球化学专业知识应用于农业对本地矿物风化的影响以及添加到土壤中的石灰的影响和命运等问题上。办法将包括研究森林和施石灰和不施石灰的行作物下土壤剖面中的碳酸盐和硅酸盐地球化学，检查化学风化产品在河流中的出口，以及在配备土壤整体的种植系统中试验性添加石灰，以便对不同深度的土壤溶液和气体进行采样。特别注意不同土地利用类型的近地表土壤和空间离散集水区，这些地区的反应速度很快，人为活动影响最大。广泛影响：教育影响包括培训几名研究生以及与斯洛文尼亚进行科学交流。与LTER网站的联系带来了外展和K12教育机会。社会影响包括了解全球变化对风化速率的影响以及潜在的重大反馈。研究石灰对大气二氧化碳的净影响对于综合评估农业对温室气体通量的贡献至关重要，并可能揭示减少行作物系统全球净变暖潜力的机会。

EAR-0518965WALTERMineral weathering rates are likely to increase in the future under the influence of global warming, increasing atmospheric CO2, changing land use, and acidification. Because carbonate mineral solubility is CO2-dependent and reaction rates are rapid, terrestrial carbonate dissolution fluxes will change and may feed back to the climate system as well as influence the geochemistry of surface waters. Our previous work on the hydrogeochemistry of carbonate-rich watersheds in the Upper Midwest and in Slovenia shows that there is close linkage between soil zone PCO2 and that of shallow groundwaters. Both of these regions have among the largest area normalized dissolved inorganic carbon fluxes in the world. Riverine export of dissolved inorganic carbon could increase if weathering of carbonates accelerates, and may also be influenced by agricultural liming, a common practice in the Midwest and other humid agricultural regions of the world. The Mississippi River already shows evidence of increasing inorganic carbon export. The net effect of liming on atmospheric CO2 is uncertain because the dissolution of lime minerals in surface soils may sequester or generate CO2 depending on pH. Carbonate mineral dissolution also impacts weathering of silicate minerals, especially by controlling soil pH, which further influences weathering feedbacks to atmospheric CO2. In fact, the Na fluxes from plagioclase feldspar weathering appear to be significantly higher in catchment soils with both silicates and carbonates than in granitic watersheds in warmer settings.Intellectual Merit: The present proposal is a new cross-disciplinary collaboration that brings together a Principal Investigator and a Slovenian collaborator to pursue several distinct, but highly interrelated, lines of research on carbonate geochemistry. Combining efforts in a synergistic way will broaden and integrate the understanding of the roles of carbonate minerals in landscape-scale solute fluxes and soil-atmospheric CO2 exchanges. Walter has extensive experience working on the hydrogeochemical aspects mineral weathering in diverse landscapes. Part of the proposed research is an extension of projects initiated under previous funding, including comparisons of carbonate geochemistry of streams and groundwaters in glaciated Michigan watersheds with those in alpine and karst regions of Slovenia. Hamilton has recently begun to investigate carbonate fluxes associated with liming in connection with an LTER project on agricultural row-crop ecosystems. Through a new collaboration with Stephen Hamilton at the Kellog Biological Station at Michigan of Michigan State University, Walter will extend her work to Michigan agricultural soils, bringing geochemical expertise to bear on the questions of how intensive agriculture affects the weathering of native minerals as well as the effects and fate of lime added to soils. Approaches will include the study of carbonate and silicate geochemistry in soil profiles beneath forests and limed and unlimed row crops, examination of riverine export of chemical weathering products, and experimental lime additions to cropping systems equipped with soil monoliths that permit sampling of soil solutions and gases at various depths. Particular attention is devoted to the near-surface soils and spatially discrete catchments of different land use types where reaction rates are intense and anthropogenic activities exert the most influence.Broader Impacts: Educational impacts include training of several graduate students as well as scientific exchanges with Slovenia. The association with an LTER site brings outreach and K12 educational opportunities. Societal impacts involve understanding global change effects on weathering rates and potentially significant feedbacks. Investigation of net effect of liming on atmospheric CO2 is critical to the integrated assessment of the contribution of agriculture to greenhouse gas fluxes and may reveal opportunities to reduce the net global warming potential of row crop systems.