The cycles of C and N in the St. Lawrence Estuary: a molecular and isotopic approach

人类活动以深刻影响全球碳循环，特别是大气二氧化碳收支的方式影响着全球环境。虽然工业化是人为二氧化碳排放的主要部分，但森林砍伐和农业也导致陆地和大气碳库之间的二氧化碳通量发生重大变化，并极大地改变了陆地有机物（TOM）向水生生态系统的通量。TOM是河口和三角洲还原性碳的巨大来源，在那里，它被沉积和矿化广泛地带走，以至于在海洋的溶解有机碳（DOC）池或海洋沉积物中几乎找不到它的踪迹。像下圣劳伦斯河口（lslle）这样的环境是去除TOM的首选地点，在那里，盐度的快速增加导致小颗粒和胶体颗粒的凝固和沉积。由于森林砍伐和农业活动极大地增加了流入河流的有机质通量和河流内有机质的代谢，它们对水生系统的地球化学影响是巨大的。TOM在排放到河口后如此迅速地被氧化或被清除的详细机制在很大程度上仍是未知的。因此，目前不可能(i)破解河流/河口与大气之间二氧化碳通量的精细（分子）控制，（ii）全面评估直接（污染、养分施肥、土地利用变化）和间接（气候强迫）人为干扰对河口生物地球化学环境的影响（包括最近发展的低氧水柱，如lle）。（三）有效地连接全球碳和氮循环的陆地和海洋领域。为了填补这些知识空白，我们将使用新的采样技术，结合最先进的体同位素和分子同位素方法（包括化合物特异性同位素分析），研究碳和氮的生物地球化学循环，并破译lslle中TOM的命运。

Human activities have affected the global environment in ways that have profoundly impacted the global carbon cycle and, in particular, the atmospheric CO2 budget.  While industrialization is responsible for the major fraction of anthropogenic CO2 emissions, deforestation and agriculture also lead to significant changes in CO2 fluxes between the terrestrial and atmospheric carbon pools and dramatically modify terrestrial organic matter (TOM) fluxes to aquatic ecosystems.  TOM represents a huge source of reduced carbon to estuaries and deltas where it is so extensively removed by sedimentation and mineralization that very little trace of it can be found either in the dissolved organic carbon (DOC) pool of the ocean or in marine sediments.  Environments such as the Lower St. Lawrence Estuary (LSLE) constitute the preferred sites of removal for TOM, where the rapid increase in salinity results in the coagulation and sedimentation of small and colloidal particles.  As deforestation and agriculture dramatically increase TOM fluxes to and TOM metabolism within rivers, their impact on the geochemistry of aquatic systems is substantial.  The detailed mechanisms by which TOM is so rapidly oxidized or removed following its discharge to estuaries are still largely unknown.  Consequently, it is currently impossible (i) to decipher the fine (molecular) controls on CO2 fluxes between rivers/estuaries and the atmosphere, (ii) to comprehensively assess the impact of direct (pollution, nutrient fertilization, land use change) and indirect (climate forcing) anthropogenic disturbances on the biogeochemical environment of estuaries (including the recent development of hypoxic water columns as in the LSLE), and (iii) to efficiently link the terrestrial and marine domains of the global carbon and nitrogen cycles.  To fill these gaps in our knowledge, we will use novel sampling techniques, coupled to state-of-the-art bulk and molecular isotopic methods (including compound-specific isotope analysis), to study the biogeochemical cycles of carbon and nitrogen, and decipher fate of TOM in the LSLE.