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https://nap.nationalacademies.org/catalog/27432/critical-issues-in-transportation-for-2024-and-beyond

SAV Mitigation Strategies for Shallow, Turbid, Oligohaline Waters of the NC Coast

North Carolina Department of Transportation (NCDOT) has recently applied wave attenuation in polyhaline (i.e., salinity of 18-30ppt) patchy submerged aquatic vegetation (SAV) habitats as a mitigation strategy to facilitate coalescence of patches by colonization within gaps, producing new and permanent seagrass acreage. While it is expected that oligohaline SAV communities may respond similarly (i.e., increased cover with decreased wave energy) , little has been done to document the fidelity of the SAV response to waves in oligohaline waters, nor has it been applied to mitigation needs. The project team proposes to examine SAV patch coalescence response to wave reduction in oligohaline waters and how the life history strategy of key oligohaline species influences that response. The team will examine biological and physical parameters influencing the presence and abundance of SAV in Currituck Sound to develop mitigation approaches for impacts to submerged aquatic vegetation (SAV) associated with coastal bridge projects. This project has two primary objectives relevant to SAV mitigation: (1) SAV life history strategies and response to physical processes (e.g., waves, salinity, etc.) and (2) SAV response to wave attenuation in the wind-driven Currituck Sound. Capitalizing on the project team's strong partnerships with the U.S. Army Corps of Engineers-Engineer Research & Development Center's (USACE-ERDC’s) Field Research Facility (FRF) and Queens University, the project team will use data from the recently installed observing platforms in Currituck Sound to develop a wind driven circulation/wave model that will provide critical information on variability of physical drivers in the system and predict changes to these parameters associated with the new bridge and wave attenuation strategies. Understanding the variability of the physical setting is important for evaluating life history strategies by which native and dominant SAV maintain their populations in the sound. Linking these data will allow NCDOT to utilize mitigation practices that are consistent with the species’ ecology and the environmental setting. Further, the suite of highly localized environmental data being collected provides the project team's proposed work with an unusual opportunity to understand the relationship of SAV abundance and distribution at relevant spatial and temporal scales. The manipulation of wave energy, coupled with an understanding of the fine-scale SAV spatial dynamics and life history strategies will provide NCDOT with a mitigation methodology for oligohaline SAV species that will be supported by scientifically defensible (and published) data. This tightly integrated, applied science package will provide the NCDOT with a low-risk, strategic position by which to quickly resolve habitat impacts.