Department of Plant and Soil Sciences, University of Delaware , Newark, Delaware 19716, United States.
Environ Sci Technol. 2015 Jan 6;49(1):203-11. doi: 10.1021/es504648d. Epub 2014 Dec 17.
Nutrient contamination has been one of the lingering issues in the Chesapeake Bay because the bay restoration is complicated by temporally and seasonally variable nutrient sources and complex interaction between imported and regenerated nutrients. Differential reactivity of sedimentary phosphorus (P) pools in response to imposed biogeochemical conditions can record past sediment history and therefore a detailed sediment P speciation may provide information on P cycling particularly the stability of a P pool and the formation of one pool at the expense of another. This study examined sediment P speciation from three sites in the Chesapeake Bay: (i) a North site in the upstream bay, (ii) a middle site in the central bay dominated by seasonally hypoxic bottom water, and (iii) a South site at the bay-ocean boundary using a combination of sequential P extraction (SEDEX) and spectroscopic techniques, including (31)P NMR, P X-ray absorption near edge structure spectroscopy (XANES), and Fe extended X-ray absorption fine structure (EXAFS). Results from sequential P extraction reveal that sediment P is composed predominantly of ferric Fe-bound P and authigenic P, which was further confirmed by solid-state (31)P NMR, XANES, and EXAFS analyses. Additionally, solution (31)P NMR results show that the sediments from the middle site contain high amounts of organic P such as monoesters and diesters, compared to the other two sites, but that these compounds rapidly decrease with sediment depth indicating remineralized P could have precipitated as authigenic P. Fe EXAFS enabled to identify the changes in Fe mineral composition and P sinks in response to imposed redox condition in the middle site sediments. The presence of lepidocrocite, vermiculite, and Fe smectite in the middle site sediments indicates that some ferric Fe minerals can still be present along with pyrite and vivianite, and that ferric Fe-bound P pool can be a major P sink in anoxic sediments. These results provide improved insights into sediment P dynamics, particularly the rapid remineralization of organic P and the stability of Fe minerals and the ferric Fe-bound P pool in anoxic sediments in the Chesapeake Bay.
营养物污染一直是切萨皮克湾的一个长期存在的问题，因为湾的恢复受到 temporally 和季节性变化的营养源以及输入和再生营养物之间复杂相互作用的影响。沉积物磷（P）库对施加的生物地球化学条件的不同反应能力可以记录过去的沉积历史，因此详细的沉积物 P 形态分析可能提供有关 P 循环的信息，特别是 P 库的稳定性和一个 P 库的形成以牺牲另一个 P 库为代价。本研究使用连续磷提取（SEDEX）和光谱技术（包括（31）P NMR、P X 射线吸收近边结构光谱（XANES）和 Fe 扩展 X 射线吸收精细结构（EXAFS）），从切萨皮克湾的三个地点（i）上游湾的北地点、（ii）以季节性缺氧底层水为主的湾中部地点和（iii）湾-海洋边界的南地点检查了沉积物 P 的形态。连续磷提取的结果表明，沉积物 P 主要由铁结合的 P 和自生的 P 组成，这进一步通过固态（31）P NMR、XANES 和 EXAFS 分析得到证实。此外，溶液（31）P NMR 结果表明，与其他两个地点相比，中间地点的沉积物含有大量有机 P，如单酯和二酯，但这些化合物随着沉积物深度的增加而迅速减少，表明再矿化的 P 可能已沉淀为自生的 P。Fe EXAFS 能够识别中间地点沉积物中响应施加的氧化还原条件的 Fe 矿物组成和 P 汇的变化。中间地点沉积物中存在纤铁矿、蛭石和 Fe 蒙脱石表明，一些铁矿物仍然存在，同时还有黄铁矿和蓝铁矿，并且铁结合的 P 库可以成为缺氧沉积物中 P 的主要汇。这些结果提供了对沉积物 P 动态的深入了解，特别是有机 P 的快速再矿化以及缺氧沉积物中 Fe 矿物和铁结合的 P 库的稳定性。
