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Guidance for Thin-Layer Sediment Placement As a Strategy to Enhance Tidal Marsh Resilience to Sea-Level Rise

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Guidance for Thin-Layer Sediment Placement As a Strategy to Enhance Tidal Marsh Resilience to Sea-Level Rise GUIDANCE FOR THIN-LAYER SEDIMENT PLACEMENT AS A STRATEGY TO ENHANCE TIDAL MARSH RESILIENCE TO SEA-LEVEL RISE RAPOSA, WASSON, NELSON, FOUNTAIN, WEST, ENDRIS, WOOLFOLK GUIDANCE FOR THIN-LAYER SEDIMENT PLACEMENT AS A STRATEGY Table of Contents TO ENHANCE TIDAL MARSH RESILIENCE TO SEA-LEVEL RISE Chapter 1: Consensus statement on thin-layer sediment placement in tidal January 2020 marsh ecosystems � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �1 Background � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �1 Prepared by: Appendix A � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 4 Researchers from eight National Estuarine Endnotes �� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 4 Research Reserves (NERRs) collaborated on a two-year NERRS Science Collaborative-funded field Appendix B � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 8 experiment investigating thin-layer placement of Glossary of terms� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 8 sediment in tidal marshes, beginning in Fall 2017. Literature cited in this Glossary �� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 8 An expert Advisory Committee for the two-year project was convened that helped prepare these Appendix C � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 9 guidance documents. Case studies �� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 9 For more information: Chapter 2: Thin-layer placement of sediment for tidal marsh resilience in the nerrssciencecollaborative.org/project/Raposa17 continental United States: a literature review �� � � � � � � � � � � � � � � � � � � � � � � � � � � � �13 Or: Introduction �� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �13 www.nerra.org/reserves/science-tools/tlp Projects sorted by location: clockwise around the U.S. by state, starting in the Or, contact Dr. Kenneth Raposa at kenneth.raposa@ Northeast �� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �14 dem.ri.gov or (401) 683-7849. Chapter 3: Guide to navigating the permitting process for thin-layer sediment placement projects in tidal marshes �� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 21 Suggested citation: Raposa, K., K. Wasson, J. Nelson, M. Fountain, J. West, C. Endris, and Step-by-step guide for permitting TLP projects �� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 21 A. Woolfolk. 2020. “Guidance for thin-layer sediment placement as a strategy to enhance tidal Chapter 4: Recommended monitoring for thin-layer sediment placement marsh resilience to sea-level rise.” Published in projects in tidal marshes �� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �25 collaboration with the National Estuarine Research Introduction �� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �25 Reserve System Science Collaborative. Temporal and spatial considerations for setting measurable objectives and monitoring �� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �26 Cover page photo credit: TLP objectives and monitoring �� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 30 The Little River, Wells NERR. Courtesy of the Elevation � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 30 Chesapeake Bay VA NERR. Resilience to sea-level rise (SLR) �� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �31 Vegetation �� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �31 Project Support: This work was sponsored by the National Estuarine Hydrology and inundation � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �32 Research Reserve System Science Collaborative, Ecological functions �� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 33 which supports collaborative research that Community engagement �� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 33 addresses coastal management problems important to the reserves. The Science Collaborative Compliance �� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 34 is funded by the National Oceanic and Atmospheric References �� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 34 Administration and managed by the University of Michigan Water Center (NAI4NOS4190145). Example monitoring plans from select TLP case studies �� � � � � � � � � � � � � � � � � � � � � 35 Guidance for thin-layer sediment placement as a strategy to enhance tidal marsh resilience to sea-level rise i CONSENSUS STATEMENT ON THIN-LAYER SEDIMENT PLACEMENT IN TIDAL MARSH ECOSYSTEMS NELSON, WASSON, FOUNTAIN, WEST CHAPTER 1: CONSENSUS STATEMENT ON THIN-LAYER SEDIMENT PLACEMENT IN TIDAL MARSH ECOSYSTEMS BACKGROUND The purpose of this consensus statement is to increase understanding of the potential benefits of, and tradeoffs involved in, thin-layer placement (TLP) of sediment as a tool to restore or enhance tidal marsh resilience in the face of sea-level rise (SLR). The intended audience is persons considering the use of TLP as a marsh restoration alternative, including landowners, coastal managers, NGO staff members, resource management agency personnel, and members of organizations that fund and permit such projects. This statement was created through a collaborative process with 25 coastal managers and scientists1. Notes are listed in Appendix A. A glossary of terms may be found in Appendix B. Case studies are in Appendix C. A literature review of published TLP studies is in Chapter 2. 1. Increasing tidal marsh resilience 2. One emerging climate adaptation 3. Thin-layer sediment placement in the face of sea-level rise strategy for tidal marshes is thin- emulates natural depositional will require implementation of layer sediment placement. processes in tidal marshes. climate adaptation strategies. Marsh sustainability and integrity are Modern tidal marsh ecosystems Many tidal marshes are threatened determined, in large part, by vertical evolved over thousands of years by multiple stressors, such as river elevation relative to sea-level, since to withstand the storm-driven diversion and loss of their historic the plants and animals that comprise deposition of large volumes of sediment supply, subsidence caused tidal marshes have tolerance limits sediment on the marsh plain6. by land use changes, ditching and to flooding frequency and duration. For example, many dominant draining for mosquito control or Sediment (or soils) may be added perennial wetland plant species are pasturelands, and adverse effects of to raise the elevation of the tidal rhizomatous, can withstand burial, invasive plant and animal species2. marsh platform to maintain the plant and can spread laterally and vertically Significant loss of tidal marsh has community relative to sea-level. through new sediment deposits. already occurred throughout the The term “thin-layer placement” Other wetland species, such as many coastal United States3. Added to (TLP) has been used to describe annuals, specialize in colonizing this is the emerging stressor of sediment additions (Figure 1) from bare deposits of fresh mud and accelerated sea-level rise (SLR)4. approximately 1 cm in depth to sand. Human development and the Without active management, such 50 cm or more5. Typical depths in construction of flood management as enhancing migration pathways or existing project-scale applications are infrastructure – such as levees, tide increasing sediment supply, many primarily in the 10-20 cm range. gates, breakwaters, and flood control tidal marshes are predicted to be channels – have in many locations lost in coming decades. Federal, altered the natural movement of state, and local agencies need a clear water and sediment from watersheds strategy and implementation plan for to tidal wetlands, and from high- conserving and restoring marshes energy shorelines to low-energy and their ecosystem functions. backbarrier embayments7. TLP has the potential to functionally re-create these natural episodic processes, thereby improving and maintaining topographic, substrate, and ecological diversity in tidal wetlands. Guidance for thin-layer sediment placement as a strategy to enhance tidal marsh resilience to sea-level rise 1 4. Uncontaminated dredged efforts should be implemented negative impacts, such as the sediments provide potential within an adaptive management burying of existing marsh vegetation, opportunities for sediment context to minimize potential harm
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