Collaborative Research: RUI: Human Alteration of Sediment of Delivery to the Coast - Legacies of Land use, Coastal Wetland Accretion, and Future Vulnerability to Sea Level Rise.

潮汐沼泽是多产的生态系统，为社会提供关键服务，如风暴潮缓冲和水质缓解。滨海湿地的长期稳定性可以用海平面、植物生长、泥沙供应和湿地堆积之间的相互作用来解释，但滨海湿地的稳定性受到环境条件变化的威胁。泥沙供应被认为是对许多潮汐湿地潜在垂直淤积速率的最终控制，因此，它们与海平面保持同步的能力。流域中的人类活动显著改变了从流域到海岸的泥沙输送，确实有证据表明，过去由于泥沙供应增加而扩大了潮汐湿地。然而，最近的土地利用变化、植树造林和大坝建设减少了从许多流域到海岸的泥沙输送。该项目的目标是了解排入美国东海岸的流域过去和现在的土地利用如何改变河流中的泥沙浓度，确定泥沙供应的变化如何影响沿海湿地的泥沙堆积速率，并预测在海平面上升和泥沙供应的各种情况下，东海岸未来湿地的脆弱性。这些信息是非常需要的，并将对研究人员、管理人员和利益相关者有用。这一合作项目包括将研究与本科教育相结合并增加科学多样性的坚定承诺。该项目的牵头机构主要服务于本科生，本科生暑期实习生和学年论文研究学生将参与该项目的各个方面。该项目采用了记录过去一个世纪湿地吸积率随时间变化的新方法，以评估美国东海岸九个河口分水岭衍生的沉积物供应的变化。这些集水区将研究同一时期内土地用途的变化，以确定泥沙供应变化的主要驱动因素。调查人员将检验以下假设：H1。近几十年来，由于人口密度的增加，农业用地的转移，以及流域的大坝建设，许多(但不是所有)流入东海岸的河流的悬浮泥沙浓度(SSC)都有所下降。最近河流相SSC的下降反映在许多沿海河口湿地较低的湿地矿物吸积率上。近期沉积速率的地理模式反映了沉积物减少的区域模式，其中大西洋中部湿地H3的减少幅度最大。泥沙淤积和沼泽淤积将在具有较高SSC有效性和植物诱捕SSCs的地块中较大。此外，由于沼泽海拔、沉积物沉积和植物生产之间复杂的生态地貌反馈，植物生产力将对SSC可用性和H4做出反应。沿海湿地对当前海平面上升的脆弱性遵循既反映相对海平面上升速度(大西洋中部最高)和SSC(东北部和东南部最低)的区域模式。然而，改变SSC和矿物吸积率(在大西洋中部下降最大)将改变未来易受海平面上升影响的区域模式。研究人员将利用创新的实验，在缺乏泥沙的沼泽系统中，操纵几年来水淹沼泽中的悬浮泥沙浓度，以直接评估泥沙沉积、植物生长和沼泽海拔的速率，为泥沙有效性对沼泽生态地貌反馈过程的作用提供经验证据。这些数据将用于验证、参数化和扩展现有模型(达什均衡模型)。然后，该模型将被用来预测沼泽淤积率，并在各种未来泥沙可获得性和相对海平面上升速度的情况下预测沼泽稳定性。土地利用变化和河流沉积物供应分析将与随时间变化的沼泽淤积率的测量和建模相结合，以全面检查河口湿地对海平面上升的脆弱性。这项研究将提供河口沼泽对海平面上升和沉积物有效性的响应的综合评估。

Tidal marshes are productive ecosystems that provide key services to society such as storm surge buffering, and water-quality mitigation. The long-term stability of coastal wetlands is explained by interactions between sea level, plant growth, sediment supply, and wetland accretion, but coastal wetland stability is threatened by changes in environmental conditions. Sediment supply has been implicated as the ultimate control on potential vertical accretion rates in many tidal wetlands and, hence, their ability to keep pace with sea level. Human activities in watersheds have significantly altered the delivery of sediment from watersheds to the coast, and indeed there is evidence of past expansion of tidal wetlands in response to increased sediment supply. However, more recent land use change, reforestation, and dam construction have reduced sediment delivery from many watersheds to the coast. The goal of this project is to understand how past and current land use in watersheds that drain to the East Coast of the United States has altered sediment concentrations in rivers, to determine how changes in sediment supply influences sediment accumulation rates in coastal wetlands, and to project future wetland vulnerability along the East Coast under various scenarios of sea level rise and sediment supply. This information is critically needed, and will be of use to researchers, managers, and stakeholders. This collaborative project includes a strong commitment to integrate research and undergraduate education and increase diversity in the sciences. The lead institution on this project serves primarily undergraduate students, and undergraduate student summer interns and academic year thesis research students will be involved in all aspects of the project. This project takes the novel approach of documenting temporally-variable wetland accretion rates over the past century to evaluate changing watershed-derived sediment supply in nine estuaries along the East Coast of the United States. Land use change over the same time period will be examined in these watersheds to determine the major drivers of changing sediment supply. The investigators will test the following hypotheses: H1. Suspended sediment concentrations (SSCs) have decreased in many (but not all) rivers draining to the East Coast in recent decades due to increased population densities, shifts away from agricultural land-use, and dam construction in watersheds, H2. Recent declines in fluvial SSC are reflected in lower wetland mineral accretion rates in many coastal estuarine wetlands. Geographic patterns of recent accretion rates reflect regional patterns of sediment decline, with the greatest reductions in mid-Atlantic wetlands, H3. Sediment deposition and marsh accretion will be greater in the plots with higher SSC availability and with plant trapping of SSCs. Further, due to complex ecogeomorphic feedbacks between marsh elevation, sediment deposition, and plant production, plant productivity will respond to SSC availability, and H4. Coastal wetland vulnerability to current sea level rise follows a regional pattern that reflects both the rate of relative sea level rise (highest in mid-Atlantic) and SSC (lowest in Northeast and Southeast). However, changing SSC and mineral accretion rates (greatest declines in mid-Atlantic) will alter future regional patterns of vulnerability to sea level rise. The researchers will use innovative experiments to manipulate suspended sediment concentrations in water flooding a marsh over several years in a sediment-poor marsh system to directly evaluate rates of sediment deposition, plant growth, and marsh elevation, yielding empirical evidence for the role of sediment availability on ecogeomorphic feedback processes in marshes. These data will be used to validate, parameterize, and expand an existing model (the Marsh Equilibrium Model). The model will then be used to hindcast marsh accretion rates and to forecast marsh stability under various future scenarios of sediment availability and rates of relative sea level rise. The land use change and fluvial sediment supply analyses will be coupled with measurements of temporally-variable marsh accretion rates and modeling to provide a comprehensive examination of estuarine wetland vulnerability to sea level rise. This research will provide integrated assessment of estuarine marsh response to both sea level rise and sediment availability.