Collaborative Research: Are Carbon Fluxes from Marine Sediments Enhanced by Submarine Ground Water Discharge?

海洋沉积物中碳的通量可能会受到海底地下水排放(SGD)的影响，这可能会增强埋藏的碳的再矿化并将其输送到水柱中。以往的研究表明，SGD既包括来自大陆含水层的大气降水，也包括通过波浪和潮汐抽水、密度驱动流和生物灌溉等过程混合到浅层沉积物中的地表水。地表水被氧气饱和，因此应该重新矿化原本会被隔离在沉积物中的有机碳。将在印第安河泻湖系统(佛罗里达州东部)研究混合和强化再矿化的过程，此前曾在该系统中使用过水柱盐度和孔隙水的变化，并将在本研究中用于追踪含氧地表水向沉积物中的泵入。这项研究将使用时间序列测量和对保守示踪剂(电导率、氯离子浓度、222Rn活度和温度)的监测，以确定混合的时间和空间尺度，以及区域含水层排放的时间和空间变化。将氯离子和电导率结合起来，可以比单独使用其中任何一种方法获得更高的时间和空间分辨率。同时测量氯离子浓度、电导率和222Rn活度提供了独特的信息，因为它们在终端成员的水源中具有不同的组成。水文研究将与沉积物中C的再矿化研究相结合，使用C浓度和13C和14C作为C来源的示踪剂。混合区的碳将在14C中枯竭，因为碎屑有机碳将根据埋藏深度而达到几千年的历史。大气水中的碳将在14C中消耗得更多，这取决于流动的路径和速度。D13C值将由碳酸盐或有机质中的碳源控制，并为14C测量提供强大的补充。研究结果应提供关于碳转化效率的信息、对沿海沉积物中这些转化和通量的水文控制的空间和时间变化的信息，以及关于来自水文过程的海洋沉积物中碳循环的信息，这是对全球碳循环来源进行定量估计的重要的第一步。这项研究还将开发新的同位素示踪技术来研究这些过程。这项研究对当地的研究地点具有重要的管理意义，该地点在国家河口计划中，是美国生物多样性最丰富的河口之一，是21个濒危或受威胁物种的家园。该项目通过高中到研究生的参与，影响了佛罗里达大学(一个研究I机构)、佛罗里达农工大学(历史上一直是黑人和少数民族服务的学院/大学)和路易斯安那州立大学(位于EPSCoR州)的教育使命，既通过将链接到佛罗里达州海洋科学教育卓越中心(FCOSEE)门户网站的课程作业，也通过直接参与该项目，提供了广泛的学习机会(水文学和生物地球化学)。

0403842CherrierThe flux of C from coastal marine sediments is likely to be influenced by submarine ground water discharge (SGD), which may enhance remineralization of buried C and transport it to the water column. Previous studies reveal that SGD includes both meteoric water from continental aquifers and surface water mixed into shallow sediment through processes such as wave and tidal pumping, density driven flow, and bioirrigation. Surface water is saturated with oxygen, and thus should remineralize organic carbon that otherwise would be sequestered in the sediments. The process of mixing and enhanced remineralization will be studied in the Indian River Lagoon System (eastern Florida), where changes in water column salinity and pore waters have been used previously, and will be used in this study, to trace pumping of oxygenated surface water into the sediments. The study will use time-series measurements and monitoring of conservative tracers (conductivity, Cl- concentration, 222Rn activity, and temperature) to determine the temporal and spatial scales of mixing, as well as variations through time and space of discharge from the regional aquifers. Combining Cl- and conductivity allows greater temporal and spatial resolution than either one alone. Simultaneous measurements of Cl- concentration, conductivity, and 222Rn activity provide unique information because of their distinct compositions in end-member water sources. The hydrologic studies will be coupled with studies of remineralization of C in the sediments using C concentrations and 13C and 14C as tracers of the sources of C. Carbon in the mixed zone will be depleted in 14C because detrital organic carbon will be up to several thousand years old depending on depth of burial. Carbon in the meteoric water will be even more depleted in 14C depending on the flow paths and rates. The d13C values will be controlled by the source of C from carbonate or organic matter and provides a powerful complement to the 14C measurements. Results of the study should provide information on the efficiencies of C transformation, spatial and temporal variations of hydrologic controls on those transformations and fluxes in coastal sediments, and information on C cycling in marine sediments from hydrologic processes, an important first step toward quantitative estimates of sources to the global C cycle. The study will also develop new isotopic tracing techniques to study these processes. The study has important management implications for the local study site, which is in the National Estuaries Program, is one of the most biologically diverse estuaries in the nation, and home to 21 endangered or threatened species. The project impacts the educational missions of the University of Florida (a Research I institution), Florida A&M University (a Historically Black and Minority Serving College/University), and Louisiana State University (located in an EPSCoR state) through involvement of high school to graduate students, both through course work that will be linked to the Florida Center for Ocean Science Education Excellence (FCOSEE) web portal, and directly in the project, which offers a broad range of learning opportunities (hydrology and biogeochemistry).