| NSF Org: |
EAR Division Of Earth Sciences |
| Recipient: |
|
| Initial Amendment Date: | November 30, 2018 |
| Latest Amendment Date: | November 30, 2018 |
| Award Number: | 1904496 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Justin Lawrence
jlawrenc@nsf.gov (703)292-2425 EAR Division Of Earth Sciences GEO Directorate for Geosciences |
| Start Date: | December 1, 2018 |
| End Date: | November 30, 2019 (Estimated) |
| Total Intended Award Amount: | $12,176.00 |
| Total Awarded Amount to Date: | $12,176.00 |
| Funds Obligated to Date: |
|
| History of Investigator: |
|
| Recipient Sponsored Research Office: |
1375 GREATE RD GLOUCESTER POINT VA US 23062-2026 (804)684-7000 |
| Sponsor Congressional District: |
|
| Primary Place of Performance: |
Post Office Box 1346, 1375 Great Gloucester Point VA US 23062-1346 |
| Primary Place of
Performance Congressional District: |
|
| Unique Entity Identifier (UEI): |
|
| Parent UEI: |
|
| NSF Program(s): |
XC-Crosscutting Activities Pro, Geomorphology & Land-use Dynam |
| Primary Program Source: |
|
| Program Reference Code(s): |
|
| Program Element Code(s): |
|
| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.050 |
ABSTRACT
Hurricanes are responsible for the destruction of sandy shorelines and devastation to coastal cities and residential communities. However, scientists have recently begun to recognize that they can have net positive influences on some coastal systems. In particular, although storm waves may cause surface excavation and erosion of the marsh edge in coastal wetlands, hurricanes may also cause net sedimentation during storm surge inundation: storm waves and currents stir sediment off the bottom in the nearshore and within bays and deposit this suspended sediment on marshes during the accompanying storm surge. Although this process is infrequent, a single hurricane can add more inorganic sediment to the marsh surface than is emplaced by daily processes acting over several decades. It has also been shown that marsh plant communities benefit from storm sedimentation due to the added nutrients derived from the new mud. Thus, hurricanes can significantly increase the resiliency of marshes and help their sustainability in a regime of accelerating sea-level rise. This past September, Hurricane Florence was predicted to be a category 4 hurricane and wreak havoc along the North Carolina coast. However, upper wind shear significantly reduced wind velocities, downgrading the storm to a category 1 hurricane by the time it made landfall. Still as the hurricane moved inland, precipitation associated with the storm deluged coastal regions of North and South Carolina with 6 to 20 inches of rain. This amount of rain over a three day period greatly increased the stage and discharge of local rivers, several of which empty directly into Winyah Bay in central South Carolina. These flood waters carried large plumes of suspended sediment to the coastal ocean and to the proximal marshes. We plan to measure this river-derived sediment in the Cape Romain region and compare this sedimentation event to storm-surge-derived deposits mapped in 2017 following Hurricane Irma.
The major goal of this study is to document the potential benefits of increased rates of inorganic sedimentation caused by Hurricanes Florence and Michael to the marsh system backing the Cape Romain cuspate foreland. Unlike Hurricane Irma in 2017, which generated high-energy waves, strong onshore winds, and a >1 m storm surge, and resulted in the deposition of a 1-2 cm thick mud layer, Hurricanes Florence and Michael had little direct impact on the marshes of central South Carolina due to their weaker winds and less impactful storm tracks. However, Florence, and to a much lesser extent Michael, produced intense precipitation, which vastly increased the stage and discharge of coastal rivers by an order of magnitude. Several of these rivers carried floodwaters and substantial quantities of suspended sediment directly into Winyah Bay and nearby marsh systems. Repeat coring of the Cape Romain marshes at locations previously sampled following Hurricane Irma would provide a rare opportunity to compare a high riverine sedimentation event to that produced by an energetic hurricane. We will revisit and resample our Cape Romain locations (10 stations along two transects), as well as measure our ten long-term SET sites near Muddy Bay (in Cape Romain). In addition, at least four other sites along the transects will be occupied to ensure broad spatial coverage of the hurricane-related deposit. Sediment cores, shallow surface sediment samples, and observations would be taken at each station to document new sedimentation, and determine if we can differentiate sediment delivered by each Hurricane Irma (wave- and storm-surge- induced from ambient sediment) and Hurricane Florence (introduction of new riverine sediment). The latter will be done via observations, sedimentological analyses (grain size, texture, physical structures, color) of short sediment cores and bulk geochemical analyses (TOC, TN, delta13CTOC, delta15NTN) of surface samples associated with each Hurricanes Irma and Hurricanes Florence/Michael. In addition, our existing SET records would be examined to determine if they capture past storm-associated spikes in sedimentation. Funds from NSF support field sampling and the lab processing and geochemical analyses of 20 surface sediment samples (10 each from Irma and Florence/Michael), and short-core analysis from our 10 cores to be collected at new sampling stations.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
In the Fall of 2018, following Hurricanes Florence and Michael, we were able to revisit saltmarsh sampling sites behind the Cape Romain (South Carolina) barrier islands. We first surveyed (collected samples, cores, and field mapping data) in December 2017, following Hurricane Irma. The goal of this work is to look for evidence of sediment deposits caused by the storm. The net impact of hurricanes on wetlands is still a topic of debate; they may be beneficial because of sediment deposition during storm surge inundation, or detrimental due to erosion of the marsh edge and surface excavation by storm waves. Rainfall associated with Hurricane Florence deluged coastal regions of North and South Carolina with 6 to 20 inches of water over a three-day period, thereby substantially increasing the water height and discharge of local rivers, several of which empty directly into Winyah Bay in central South Carolina. Given the high suspended sediment concentrations of coastal plain rivers, it is assumed that the coastal ocean Winyah Bay received a significant increase in suspended sediment load during the subsequent 6?8 weeks following Florence. Although some of this sediment is deposited within the proximal bay, much is conveyed directly to the coastal ocean, as evidenced by the large riverine sediment plumes discharging post Florence along the North Carolina coast. Some portion of this plume is expected to reach the Cape Romain marsh system via the Intracoastal Waterway and the coastal ocean during flooding tides.
We used our funding collect samples across the region impacted by this storm surge by revisiting our post-Irma backbarrier marshes at Cape Romain, SC. At each of our 10 Irma sampling stations we collected duplicate shore cores (each 50-cm long, 8 cm in diameter) to identify any surface storm deposit and compare it with underlying, non-storm sediments. We also collected surface samples of presumed Florence/Michael deposits for later inorganic sedimentologic and organic geochemical analyses. Finally, we collected a suite of samples representative of likely sediment sources: the nearshore the Pee Dee River, and the lagoons / tidal channels next to each of our marsh sampling stations. We made note of any new erosional features, wrack lines, and vegetation damage, related to hurricanes Florence/Michael at each site, although we found little evidence of erosional damage at any of our sampling stations. Presumed storm deposits were identified at all sampling locations.
We analyzed all of our samples collected from Cape Romain in 2017 and 2018 for grain size and bulk biogeochemical characteristics (total organic carbon, total nitrogen, and carbon and nitrogen isotopes). Preliminary results indicate that Irma and Florence/Michael sediment deposits are different (Figure 1): those from Florence/Michael look more like sediments in the local bays and channels, whereas those deposited during Irma appear to originate, at least in part, from local rivers. We also find trends across our marsh transects, in which samples collected closer to the barrier islands and tidal inlets appear to have greater influence of marine organic matter, whereas those collected from marshes closer to the mainland and Intercoastal Waterway appear to be more influenced by organic matter from land. In addition, we find differences between our two transects, in which samples from the northern transect, closer to the Pee Dee River, appear to have a greater land influences, where as those from the southern transect, further from the river, appear to be sourced more from the marine environment (Figure 2).
These results show that, not only are storms important in delivering sediment to the marsh surface, and therefore critical in helping these marshes keep pace with sea-level rise (a key finding of our post-Irma 2017 sampling campaign), but that the source of those sediments is highly dependent on where in the marsh you are located. This has important implications for the type and ?quality? of organic matter delivered to the marshes during storms, as well as the grain size and amount of sediment likely to be delivered. A general-interest scientific paper detailing these results is presently in preparation.
Last Modified: 03/02/2020
Modified by: Christopher J Hein
Please report errors in award information by writing to: awardsearch@nsf.gov.
