| 英文摘要: | 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. |