Sustainability of coastal marshes under accelerated relative sea-level rise

就商品和服务而言，沿海沼泽是世界上最有价值的生态系统之一；它们的命运将对沿海渔业、养分循环、风暴潮防护和相关过程产生重大影响。由于海平面加速上升和其他人为造成的压力，沿海沼泽也在迅速退化。路易斯安那州是世界上沿海湿地流失速度最快的地区之一，是美国其他沿海地区的风向标。目前正在这一领域启动数十亿美元的海岸恢复项目，这些投资必须以现有的最佳科学信息为指导。在确定沿海环境在海平面相对上升时的恢复能力方面已经付出了相当大的努力，但这些研究在很大程度上仅限于短期（年至十年）时间尺度上的观测。该项目将通过对过去几千年密西西比三角洲沉积沉积物的分析来填补这一重要空白。该项目涉及与路易斯安那州海岸保护和恢复机构在总体规划范围内的密切互动，该总体规划很可能只能部分维持。此外，该项目还将用于改善新奥尔良一所少数族裔学生就读的科学和数学高中的课程。以下两个假设将得到验证：(1)密西西比三角洲的沿海沼泽能够跟上相对海平面上升的速度，上升速度约为10毫米/年；(2)密西西比三角洲沿海沼泽通过有机质的积累在很大程度上跟上了相对海平面的上升。这些方法将包括根据前几年收集的数百个钻孔的数据重建三角洲的沉积环境。古沼泽对当代海平面相对上升速率~0.5至10毫米/年（即，从工业化前时期到21世纪末预测的海平面上升速率的整个范围）的响应将通过沉积模式与海平面上升速率的直接比较来确定。为了将地层学分析应用于今天的沼泽动态，将对路易斯安那州沿海100多个地点的现代沼泽表面高程变化和土壤特性进行测量汇编。总的来说，这将使在广泛的时间尺度上对沼泽的可持续性进行严格的比较。

Coastal marshes rank as some of the world's most valuable ecosystems in terms of goods and services; their fate will have major consequences for coastal fisheries, nutrient cycling, storm-surge protection, and related processes. Coastal marshes are also rapidly degrading due to accelerated sea-level rise and other human-induced stresses. Louisiana experiences some of the world's most rapid rates of coastal wetland loss, constituting a bellwether for other coastal regions around the nation. Multi-billion dollar coastal restoration projects are currently being initiated in this area, and it is paramount that these investments be guided by the best available scientific information. Considerable effort has been expended to determine the resiliency of coastal environments in the face of relative sea-level rise, but these studies have largely been limited to observations over short (annual to decadal) timescales. This project will fill this important gap through an analysis of the sedimentary deposits of the Mississippi Delta over the past few thousand years.The project involves close interaction with the Louisiana Coastal Protection and Restoration Agency within the context of the Master Plan for a coast that in all likelihood can only be partially sustained. Furthermore, the project will be used to enhance the curriculum at a minority-serving New Orleans science and math high school.The following two hypotheses will be tested: (1) coastal marshes in the Mississippi Delta can keep pace with rates of relative sea-level rise up to about 10 mm/yr; and (2) coastal marshes in the Mississippi Delta keep up with relative sea-level rise to a significant extent by means of the accumulation of organic matter. The methods will involve a reconstruction of sedimentary environments in the Delta based upon data from hundreds of boreholes that have been collected in previous years. The response of ancient marshes to contemporary rates of relative sea-level rise of ~0.5 to 10 mm/yr (i.e., the full range from the pre-industrial period to rates predicted for the end of the 21st century) will be determined from a direct comparison of the sedimentary patterns with the rates. In order to apply the stratigraphic analysis to present-day marsh dynamics, a compilation of measurements of modern marsh surface-elevation changes and soil properties from over100 sites in coastal Louisiana will be carried out. Collectively, this will enable a rigorous comparison of marsh sustainability over a wide range of time scales.