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MEPS prepress abstract   -  DOI: https://doi.org/10.3354/meps13728

Utilizing airborne LiDAR data to quantify marsh edge morphology and the role of oyster sreefs in mitigating marsh erosion

Sara Hogan*, Patricia Wiberg, Matthew Reidenbach

*Corresponding author:

ABSTRACT: We develop methods to quantify marsh edge morphology using airborne LiDAR data and validate these methods with in-situ observations. We then apply these methods within the context of oyster reef restoration within the shallow coastal bays of Virginia, USA by comparing retreat and morphology quantified at paired reef-lined and control marsh edges at ten different marsh sites. Retreat metrics were analyzed between 2002 and 2015, utilizing a LiDAR derived edge for the year 2015 from points of maximum slope and aerial imagery pre-2015. Retreat was also compared before and after oyster reef restoration to determine if reefs slow erosion. We found that slope statistics from airborne LiDAR elevation data can accurately capture marsh edge morphology. Retreat rate, measured at edges typically found near the vegetation line, was not significantly different between reef-lined and control marshes and ranged from 0.14 to 0.79 m yr-1. Both retreat rate (ρ = -0.90) and net movement (ρ = -0.88) were strongly correlated to marsh edge elevation. Exposed control marshes had significantly greater mean and maximum slope values compared to reef-lined marshes. The mean edge slope for exposed marshes was 11.40 and for reef-lined marshes was 6.00. We hypothesize that oyster reefs are causing an elongation of the marsh edge by reducing retreat at lower elevations of the marsh edge. Therefore, changes in marsh edge morphology may be a precursor to changes in marsh retreat rates over longer timescales and emphasizes the need for repeated LiDAR measurements to capture processes driving marsh edge dynamics.