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

潮汐沼泽是生产性生态系统，为社会提供关键服务，如风暴潮缓冲和水质缓解。沿海湿地的长期稳定性是由海平面、植物生长、沉积物供应和湿地生长之间的相互作用来解释的，但沿海湿地的稳定性受到环境条件变化的威胁。沉积物的供应已被认为是许多潮汐湿地潜在的垂直增长率的最终控制因素，因此，它们能够跟上海平面的步伐。流域内的人类活动已显著改变了流域向海岸的沉积物输送，事实上，有证据表明，过去潮汐湿地因沉积物供应增加而扩大。然而，最近的土地利用变化，重新造林，水坝建设减少了沉积物从许多流域输送到海岸。该项目的目标是了解过去和现在的土地利用在流域，排水到美国东海岸已经改变了河流中的泥沙浓度，以确定如何在沉积物供应的变化影响沉积物积累率在沿海湿地，并预测未来湿地的脆弱性沿着东海岸海平面上升和沉积物供应的各种情况下。这些信息是迫切需要的，并将对研究人员，管理人员和利益相关者有用。这个合作项目包括一个强有力的承诺，整合研究和本科教育，增加科学的多样性。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生将参与项目的各个方面。该项目采用记录过去世纪随时间变化的湿地增长率的新方法，以评估美国东海岸沿着9个河口流域沉积物供应的变化。将在这些流域检查同一时期的土地利用变化，以确定改变沉积物供应的主要驱动因素。研究人员将测试以下假设：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（但不是所有）流向东海岸的河流的悬浮泥沙浓度（SSC）有所下降。最近河流SSC下降反映在许多沿海河口湿地的湿地矿物吸积率较低。最近的加积率的地理模式反映了沉积物下降的区域模式，在大西洋中部湿地，H3的减少最大。在具有较高SSC可用性和植物捕获SSC的地块中，沉积物沉积和沼泽增生将更大。此外，由于沼泽海拔，沉积物沉积和植物生产之间的复杂的生态地貌反馈，植物生产力将响应SSC的可用性，和H4。沿海湿地对当前海平面上升的脆弱性遵循一种区域模式，反映了相对海平面上升的速度（大西洋中部最高）和SSC（东北部和东南部最低）。然而，不断变化的SSC和矿物积累率（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。 研究人员将使用创新的实验来操纵悬浮泥沙浓度的水淹没沼泽在一个沉积物贫乏的沼泽系统，直接评估沉积物沉积，植物生长和沼泽海拔的速度，产生经验证据的作用沉积物的可用性生态地貌反馈过程中的沼泽。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，该模型将被用来后报沼泽的增长速度，并预测沼泽的稳定性，在各种未来的情况下，沉积物的可用性和相对海平面上升的速度。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增生率的测量和建模相结合，以提供一个河口湿地对海平面上升的脆弱性的全面检查。这项研究将提供综合评估河口沼泽响应海平面上升和沉积物的可用性。

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.