Collaborative Research: RUI: Human Alterations of Sediment Delivery to the Coast- Legacies of Land Use, Costal Wetland Accretion, and Future Vulnerability to Sea Level

潮汐沼泽是富有成效的生态系统，为社会提供关键服务，如风暴潮缓冲和水质缓解。海岸带湿地的长期稳定性可以用海平面、植物生长、泥沙供应和湿地增积的相互作用来解释，但海岸带湿地的稳定性受到环境条件变化的威胁。泥沙供应已被认为是许多潮汐湿地潜在垂直增加率的最终控制因素，因此也影响了它们与海平面同步的能力。人类在流域的活动极大地改变了从流域到海岸的沉积物输送，确实有证据表明，过去潮汐湿地的扩张是对沉积物供应增加的反应。然而，最近的土地利用变化、重新造林和大坝建设减少了许多流域向海岸的沉积物输送。该项目的目标是了解过去和现在流入美国东海岸的流域的土地利用如何改变河流中的沉积物浓度，确定沉积物供应的变化如何影响沿海湿地的沉积物积累速率，并在海平面上升和沉积物供应的各种情况下预测未来东海岸湿地的脆弱性。这些信息是迫切需要的，并且将对研究人员、管理人员和利益相关者有用。这个合作项目包括将研究和本科教育结合起来，增加科学多样性的坚定承诺。该项目的牵头机构主要为本科生服务，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。该项目采用了一种新颖的方法，记录了过去一个世纪中时间变化的湿地增加率，以评估美国东海岸9个河口流域泥沙供应的变化。将对这些流域同一时期的土地利用变化进行研究，以确定泥沙供应变化的主要驱动因素。研究者将测试以下假设：H1。近几十年来，由于人口密度增加、农业用地转移和流域大坝建设，许多（但不是全部）汇入东海岸的河流中悬浮沉积物浓度（ssc）有所下降。最近河流SSC的下降反映在许多沿海河口湿地的湿地矿物增加率降低。最近沉积物增加率的地理格局反映了沉积物减少的区域格局，其中大西洋中部湿地减少最多，H3。在SSC有效度较高和植物捕获SSC的样地，泥沙淤积和沼泽增积更大。此外，由于沼泽高程、沉积物沉积和植物生产之间复杂的生态地貌反馈，植物生产力将响应SSC有效性和H4。沿海湿地对当前海平面上升的脆弱性遵循一个区域模式，该模式既反映了相对海平面上升的速度（大西洋中部最高），也反映了南纬温度（东北部和东南部最低）。然而，变化的南中国海和矿物增加率（大西洋中部下降幅度最大）将改变未来易受海平面上升影响的区域模式。研究人员将使用创新的实验来控制几年来在一个缺乏沉积物的沼泽系统中淹没的水中的悬浮沉积物浓度，以直接评估沉积物沉积速率、植物生长和沼泽海拔，为沉积物可用性在沼泽生态地貌反馈过程中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（Marsh均衡模型）。然后，该模型将用于预测沼泽的增积率，并在沉积物可用性和相对海平面上升率的各种未来情景下预测沼泽的稳定性。土地利用变化和河流沉积物供应分析将与沼泽增积率的临时变化测量和建模相结合，以提供对河口湿地对海平面上升的脆弱性的全面检查。这项研究将提供河口沼泽对海平面上升和沉积物可用性的综合评估。

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.