After Hurricanes Irma and Matthew: Living Shorelines Stabilize Sediments

Abstract

Constructed intertidal oyster reefs, an example of a “living shoreline”, can protect against erosion and loss of habitat, but can they prevent erosion during high-energy storm events such as hurricanes? Oyster reefs were constructed in 2012 within the Guana Tolomato Matanzas National Estuarine Research Reserve in Northeast Florida to stabilize the shoreline sediment and prevent erosion of an archeological site. Sediment cores were collected behind constructed oyster reefs before and after hurricanes Matthew (2016) and Irma (2017) to study changes in sediment particle size due to these high-energy storms. Pre-hurricane data were collected in 2016 from three different constructed reefs, as well as three control sites where no reef was present. Pre-hurricane sediment profiles behind the constructed reefs consisted of finer sediments, ~36% silt and clay, in the surface ~10-12 cm, with decreasing silt and clay and increasing sand content as depth increased. This was different than the sediment from the control sites with ~4% silt and clay in all depths sampled. Like the sediment profiles before the high energy storms, the post-hurricane sediment data showed a clear layer of finer sediment ~10-12 cm over coarser sediment. Although they were high-energy storms, the storms did not appear to significantly affect the sediment behind the constructed oyster reefs. Sediment profiles remained consistent after these storms but may not remain undisturbed during the next storm without some intervention because the oyster reefs have been degrading. KEYWORDS: Oyster Restoration; Living Shorelines; Hurricanes; Coastal Erosion; Sedimentation; Salt Marsh

Controls on Surface and Downcore Sedimentary Organic Matter in a Constructed Oyster Reef

“…The December 2017 cores exhibit substantial variability within the top 10 cm that could be related to erosion and/or deposition during these hurricanes. However, a previous study at this site did not find significant changes in particle size associated with Matthew and Irma [44]. Overall, the storms do not appear to fully explain the OM decrease, as it continued to decline after December 2017.…”

“…The proportion of each size fraction is calculated as a percent of the total OM-free dry sediment mass. We only report silt + clay content here in order to highlight changes in the fine particle fraction; a more comprehensive analysis of all particle sizes in 2016 and 2017 cores appears in a separate article [44]. The standard deviation of sample splits averaged 2%.…”