Sustainability of coastal marshes under accelerated relative sea-level rise

沿海沼泽地是世界上在货物和服务方面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、风暴潮保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压力，沿海沼泽地也在迅速退化。路易斯安那州经历了世界上一些最快的沿海湿地损失率，构成了全国其他沿海地区的领头羊。目前正在这一领域启动数十亿美元的沿海恢复项目，这些投资必须以现有的最佳科学信息为指导。在确定沿海环境面对相对海平面上升的复原力方面已经作出了相当大的努力，但这些研究主要限于短时间尺度（每年到十年）的观测。该项目将通过分析过去几千年来密西西比三角洲的沉积物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局在一个很可能只能部分维持的海岸的总体规划范围内密切互动。此外，该项目还将用于提高新奥尔良一所少数民族高中的科学和数学课程，并将检验以下两个假设：（1）密西西比三角洲的沿海沼泽地可以跟上相对海平面上升的速度，上升速度高达10毫米/年;（2）密西西比三角洲的沿海沼泽通过有机质的积累在很大程度上与相对海平面上升保持一致。这些方法将涉及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。古代沼泽对当代相对海平面上升率约为0.5至10毫米/年（即，从工业化前时期到预测的21世纪末的速率的整个范围）将通过直接比较沉积模式和速率来确定。为了将地层学分析应用于当今的沼泽动态，将对路易斯安那州沿海100多个地点的现代沼泽表面海拔变化和土壤性质的测量结果进行汇编。总的来说，这将使一个严格的比较沼泽的可持续性在广泛的时间尺度。

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.