†Department of Plant and Soil Sciences, University of Delaware, Newark, Delaware 19716, United States.
‡Environmental Molecular Science Laboratory, Pacific Northwest National Laboratory, Richland, Washington 99354, United States.
Environ Sci Technol. 2015 May 19;49(10):5887-96. doi: 10.1021/es5059617. Epub 2015 Feb 17.
Chesapeake Bay, the largest and most productive estuary in the U.S., suffers from varying degrees of water quality issues fueled by both point and nonpoint nutrient sources. Restoration of the Bay is complicated by the multitude of nutrient sources, their variable inputs, and complex interaction between imported and regenerated nutrients. These complexities not only restrict formulation of effective restoration plans but also open up debates on accountability issues with nutrient loading. A detailed understanding of sediment phosphorus (P) dynamics provides information useful in identifying the exchange of dissolved constituents across the sediment-water interface as well as helps to better constrain the mechanisms and processes controlling the coupling between sediments and the overlying waters. Here we used phosphate oxygen isotope ratios (δ(18)O(P)) in concert with sediment chemistry, X-ray diffraction, and Mössbauer spectroscopy on sediments retrieved from an organic rich, sulfidic site in the mesohaline portion of the mid-Bay to identify sources and pathway of sedimentary P cycling and to infer potential feedbacks on bottom water hypoxia and surface water eutrophication. Authigenic phosphate isotope data suggest that the regeneration of inorganic P from organic matter degradation (remineralization) is the predominant, if not sole, pathway for authigenic P precipitation in the mid-Bay sediments. This indicates that the excess inorganic P generated by remineralization should have overwhelmed any pore water and/or bottom water because only a fraction of this precipitates as authigenic P. This is the first research that identifies the predominance of remineralization pathway and recycling of P within the Chesapeake Bay. Therefore, these results have significant implications on the current understanding of sediment P cycling and P exchange across the sediment-water interface in the Bay, particularly in terms of the sources and pathways of P that sustain hypoxia and may potentially support phytoplankton growth in the surface water.
切萨皮克湾是美国最大、生产力最高的河口，受到来自点源和非点源营养物的不同程度的水质问题的影响。湾的恢复受到多种营养物来源、它们的可变输入以及输入和再生营养物之间复杂相互作用的限制。这些复杂性不仅限制了有效恢复计划的制定，而且还引发了关于营养负荷责任问题的争论。对沉积物磷（P）动态的详细了解提供了有关溶解成分在沉积物-水界面交换的信息，还有助于更好地约束控制沉积物和上覆水之间耦合的机制和过程。在这里，我们使用磷酸盐氧同位素比值（δ¹⁸OP）与沉积物化学、X 射线衍射和中湾中低盐度部分富含有机物和硫化物的沉积物上的穆斯堡尔光谱相结合，以确定沉积物磷循环的来源和途径，并推断对底层水缺氧和地表水富营养化的潜在反馈。自生磷酸盐同位素数据表明，从有机物降解（再矿化）中再生无机 P 是中湾沉积物中自生 P 沉淀的主要（如果不是唯一）途径。这表明，再矿化产生的多余无机 P 应该已经超过了任何孔隙水和/或底层水，因为只有一部分作为自生 P 沉淀。这是第一项确定切萨皮克湾中再矿化途径和 P 内循环优势的研究。因此，这些结果对当前对湾内沉积物 P 循环和 P 在沉积物-水界面交换的理解具有重要意义，特别是在维持缺氧和可能支持地表水浮游植物生长的 P 来源和途径方面。
