Transient Diagenesis in Organic Poor Sediments: Lake Superior

在这个项目中，明尼苏达大学德卢斯分校的研究人员将调查苏必利尔湖沉积物中有机碳、氮、磷和铁的地球化学特征，并量化它们的时空变化。目前苏必利尔湖氮磷地球化学收支不平衡，营养物浓度和初级生产力的主要变化趋势仍未解释。研究人员的初步数据表明，苏必利尔湖的沉积物在氧气渗透深度上经历了大规模的垂直迁移，类似于深海中缺乏有机物的沉积物。考虑到氧化还原条件对沉积物养分循环的重要性，他们希望阐明这些沉积物对水柱化学和生物生产力时间变化的季节性和多年代际响应。具体目标是：(1)研究苏必利尔湖沉积物中有机碳、氮、磷和铁的地球化学特征，并量化其时空变异特征；(2)模拟湖泊成岩生物地球化学循环，计算不同氧渗透点有机碳矿化途径的原位速率和沉积物-水养分通量；(3)阐明沉积物对有机碳沉降和底水氧、硝酸盐浓度变化的季节性和多年代际响应，量化沉积物对水柱氮、磷收支的贡献；(4)了解苏必利尔湖氮磷失衡加剧的原因、后果和动态。这些目标将通过直接测量湖泊和沉积物的地球化学参数来实现。结果将整合到泥沙反应输运模型和质量平衡水柱模型中，以检查原位过程速率，重建过去的动态和未来的预测。更广泛的影响：可以说，对苏必利尔湖这些现象的研究将促进对其他碳限制沉积物的地球化学动力学的理解。开发的沉积物化学模型将有助于苏必利尔湖正在进行的全系统建模工作，将服务于苏必利尔湖研究人员的大型社区，并将转移到其他环境。研究小组将包括研究生和本科生。

In this project, researchers at the University of Minnesota at Duluth will investigate the geochemistry of organic carbon, nitrogen, phosphorous, and iron in the sediments of Lake Superior and quantify their temporal and spatial variability. The geochemical budgets of nitrogen and phosphorus in Lake Superior are presently unbalanced, and major trends in nutrient concentrations and primary productivity remain unexplained. The researchers' preliminary data suggest that the sediments of Lake Superior have experienced large vertical migrations in the depth of oxygen penetration, analogous to those implicated in organic-poor sediments in the deep ocean. Given the importance of redox conditions for the sediment nutrient recycling, they hope to elucidate the seasonal and multi-decadal responses of these sediments to the temporal changes in water column chemistry and biological productivity. The specific objectives are: (1) to characterize the geochemistry of organic carbon, nitrogen, phosphorus, and iron in Lake Superior sediments and quantify their temporal and spatial variability; (2) to simulate the diagenetic biogeochemical cycling in the lake and calculate the in situ rates of the organic carbon mineralization pathways and sediment-water nutrient fluxes at sites with different oxygen penetrations; (3) to elucidate seasonal and multi-decadal sediment responses to variations in the organic carbon sedimentation and bottom water concentrations of oxygen and nitrate, and quantify sediment contributions to the water column N and P budgets; and (4) to gain insights into the causes, consequences, and the dynamics of the increasing N:P imbalance in Lake Superior. These objectives will be accomplished using direct measurements of geochemical parameters in the lake and sediment incubations. Results will be integrated into sediment reactive-transport models and mass-balance water column models for examination of in situ process rates, reconstructions of past dynamics, and future projections. Broader Impacts: Arguably, study of these phenomena in Lake Superior will advance understanding of geochemical dynamics in other carbon-limited sediments. The sediment chemistry models developed will contribute to the ongoing system-wide modeling efforts in Lake Superior, will serve the large community of Lake Superior researchers, and will be transferable to other environments. Graduate and undergraduate students will be included on the research team.