Department of Chemistry, Louisiana State University, Baton Rouge, LA 70803, USA.
Department of Oceanography and Coastal Sciences, Louisiana State University, Baton Rouge, LA 70803, USA.
Sci Total Environ. 2014 Jul 1;485-486:518-527. doi: 10.1016/j.scitotenv.2014.03.121. Epub 2014 Apr 16.
The Mississippi River Flood of 2011 prompted the opening of the Bonnet Carré Spillway (BCS) in southeastern Louisiana to protect the City of New Orleans. The BCS diverted approximately 21.9 km(3) of river water into the oligohaline Lake Pontchartrain Estuary over the course of 43 days. We characterized estuarine dissolved organic matter (DOM) dynamics before, during, and after the diversion in order to better understand the biogeochemical dynamics associated with these immense freshwater inflows. Dissolved organic carbon (DOC) exhibited a large degree of variability during and after the period of elevated primary productivity that occurred following the diversion. Furthermore, DOC analysis provides limited insight into carbon cycling during these dynamic periods. In order to overcome the limitations of DOC, spectroscopic methods were used to gain insights into chemical composition dynamics. Both ultraviolet visible (A254, A350, SUVA254, spectral slope, and normalized UV/Vis) and fluorescence spectroscopy (excitation emission matrices and fluorescence and biological indices) were used to study the compositional changes of DOM over time. Collectively, our results document a perturbation in DOM chemistry in Lake Pontchartrain due to the diversion and a subsequent return toward pre-diversion conditions. Immediate increases in A350 indicate that BCS freshwater contained elevated concentrations of lignin of terrestrial origin. Ensuing declines in A350, along with changes in the fluorescence and biological indices, indicate that DOM rapidly became more microbial in composition. Our results provide insights into estuarine DOM dynamics relevant to systems receiving flood pulses of freshwater due to either hydrologic manipulation or precipitation events.
2011 年密西西比河洪水促使路易斯安那州东南部的 Bonnet Carré 溢洪道（BCS）开启，以保护新奥尔良市。BCS 在 43 天的时间内将大约 21.9 公里的河水引流入寡营养盐水体庞恰特雷恩湖。我们描述了分流前后的河口溶解有机物质（DOM）动态，以便更好地了解与这些巨大淡水流入相关的生物地球化学动态。在分流后发生的初级生产力升高期间和之后，溶解有机碳（DOC）表现出很大的可变性。此外，DOC 分析在这些动态时期的碳循环中提供的见解有限。为了克服 DOC 的局限性，使用光谱方法来深入了解化学组成动态。使用紫外线可见（A254、A350、SUVA254、光谱斜率和归一化 UV/Vis）和荧光光谱（激发发射矩阵以及荧光和生物指数）来研究 DOM 随时间的组成变化。总的来说，我们的结果记录了由于分流而导致庞恰特雷恩湖 DOM 化学的扰动，以及随后向分流前条件的回归。A350 的立即增加表明 BCS 淡水含有较高浓度的来自陆地的木质素。随后 A350 的下降以及荧光和生物指数的变化表明，DOM 迅速变得更具微生物组成。我们的结果为由于水文操纵或降水事件而接收淡水洪水脉冲的河口 DOM 动态提供了深入的了解。
