Optimization of salt marsh management at the Moosehorn National Wildlife Refuge, Maine, through use of structured decision making

Prime Hook National Wildlife Refuge and its adjacent water bodies are important natural features along western Delaware Bay, USA. Historically salt and brackish marsh habitats, portions of the Refuge were diked and managed as freshwater impoundments starting in the early 1980s. Over the past decade, some of these impoundments have reverted to saline conditions, largely due to several storm events (including Hurricane Sandy in 2012) that have caused flooding, erosion, and opened several breaches between the Refuge and Delaware Bay. Because of these significant morphologic changes, the United States Fish and Wildlife Service (USFWS) completed a series of surveys, numerical modeling using Delft3D and coastal engineering analyses to aid in developing restoration alternatives for managing the Refuge and its marshlands. This work will review the results of the strategic planning used to recommend a preferred restoration alternative for managing the Refuge under the new environmental regime aimed at resilience. As a result of this effort, a project for restoring and managing the Refuge was recommended and constructed in 2018. Total cost of the project was $40 million US and was the largest restoration/recovery project authorized to address the impacts of Hurricane Sandy.The project included two major components: 1) shoreline reconstruction and 2) marsh restoration. &#160;The shoreline reconstruction portion of the project included placing approximately 1.2 million cubic meters of sand from an offshore borrow area along the shoreline to reconstruction a 12 m wide dune, 45 m beach berm and 30 m back-bay marsh platform (essentially rebuilding the entire barrier island). In addition, the project included a major marsh restoration effort including dredging 48 km of conveyance channels and &#8220;thin layer&#8221; disposal of 460,000 cubic meters of sediment to create 2,000 hectares of salt marsh.Herein will present findings from an analysis using monitoring data and observations to evaluate converting freshwater wetlands to saltwater marshes and the resulting increase in carbon sequestration. As tidal marshes are restored, harmful emissions decline as the project site transforms from a freshwater to a saltwater environment. Therefore, carbon is stored in the soils more readily under tidal marsh conditions. The findings will show the increase in carbon sequestration as a result of the vegetation community response and discuss future projections.&#160; Methodologies used for identifying vegetation community response included:<ul><li>Salt Marsh Integrity (SMI) and Saltmarsh Habitat & Avian Research Program (SHARP)</li> <li>Mid-Atlantic Tidal Rapid Assessment Method (MidTRAM)</li> <li>Normalized Difference Vegetation Index (NDVI)</li> </ul>This work will show the importance of incorporating coastal restoration projects and carbon sequestration into policies and management in the coastal zone.

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High Times and Dry Times In a Salt Marsh: Budgeting For Supplemental Freshwater Needs at the Big Boggy National Wildlife Refuge, USA

10.21203/rs.3.rs-1178631/v1 ◽

2022 ◽

Author(s):

Matthew Madewell ◽

Rusty Feagin ◽

Thomas Huff ◽

Bill Balboa

Keyword(s):

Salt Marsh ◽

Salt Marshes ◽

Freshwater Input ◽

National Wildlife Refuge ◽

Management Options ◽

Wildlife Refuge ◽

Management Actions ◽

Seasonal Droughts ◽

Freshwater Inflows ◽

Vegetation Loss

Abstract Salt marshes can be vulnerable to reduced freshwater input. Reduced freshwater inflows, particularly during a hot or dry summer season, can be catastrophic for vegetation productivity, organic accretion and inorganic sedimentation, and the ability of a marsh to maintain a sustainable elevation facing relative sea level rise (RSLR). Unfortunately, it is challenging for scientists to obtain inflow records for ungauged watersheds and link them with historical trends of salt marsh loss. We sought to address this challenge in Big Boggy National Wildlife Refuge (NWR), a small watershed in East Matagorda Bay, Texas. Our objective was to link the quantity of freshwater inflow with salt marsh sustainability and recommend management actions for the NWR. We first explored land cover trends and found that this watershed lost more than one-third of its low marsh since 1953. We then measured the streamflow into and out of the watershed, created a water budget, and modeled historical and future inflows from 1953 to 2100. Freshwater inflows have been increasing on average since 1953, but a combination of RSLR, sediment starvation, and punctuated seasonal droughts are likely responsible for the loss of salt marsh. We also estimated supplemental water needs during potential droughts out to 2100. We conclude that managers cannot fundamentally alter the accretion versus RSLR balance in this basin except by modifying freshwater input. Thus, during droughts, they should focus on providing these inputs and avoiding vegetation loss. Our work points to both water purchases and land management options that can achieve this goal.

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