«Presented by the Carolina Environmental Program Morehead City Field Site Students: Joseph Hester, Alison Kitto, Elizabeth Newland, Erika Poarch, ...»
Armoring the Coast: The Effects of Bulkheads on Salt Marsh Habitats
Presented by the Carolina Environmental Program Morehead City Field Site Students:
Joseph Hester, Alison Kitto, Elizabeth Newland, Erika Poarch,
Ashley Smyth and Zachary Williams
Under the direction of Institute of Marine Sciences faculty members:
Rachel T. Noble
Michael F. Piehler
Charles “Pete” Peterson
Carolina Environmental Program, Morehead City Field Site University of North Carolina at Chapel Hill Fall 2006 Acknowledgements This project was successful due to the combined efforts of many people. We would like to thank Rachel Noble for her words of wisdom and encouragement through the tough spots.
Without Mike Piehler, this project would not have been successful. Mike was always available to answer questions and provide guidance. We thank Charles “Pete” Peterson, for just being Pete.
Thanks to Reagan Converse for help in organizing this project and sorting through aerial photographs. Denene Blackwood is deserving of an extra special recognition. Her help in the field, on the boat, in the lab, and with questions was the reason this project was successful.
Thanks to Suzanne Thompson for help with laboratory analysis. We would also like to thank everyone at UNC-IMS for their support and help throughout the semester.
ii Abstract Shoreline hardening structures, such as bulkheads, are becoming an increasingly popular method of mitigating shoreline erosion. However, few studies have examined the ecological impacts of such structures. Salt marshes are highly productive ecosystems that act as a medium of exchange between marine and terrestrial environments. Bulkheads are thought to disrupt the natural processes associated with salt marshes. Our project was a two-pronged effort 1) we synthesized currently available literature and information regarding the presence and roles of shoreline hardening structures found in estuarine and sound-side locations of eastern NC, and 2) we conducted a field study that examined differences between bulkheaded and natural marshes at four sites located along Bogue Sound, North Carolina. An observational survey quantified the presence or absence of marsh in front of bulkheads. Greater than half of the bulkheads surveyed had marsh; indicating that marshes can coexist with properly cited bulkheads along Bogue Sound. Relative marsh health was experimentally determined by the presence and quantity of Spartina spp., chlorophyll a concentration, and sediment organic matter. Results indicate that bulkheads had no immediately apparent deleterious influence on salt marsh health. However, we also noted extremely high variability among sites for all metrics that we examined, thereby reducing our ability to note significant impacts from bulkheads. Furthermore, when results were broken down by site, we had small sample sizes also limiting our power to assess differences between bulkheaded and natural marsh areas. Even though our results imply that bulkheads may not have dramatic deleterious effects on natural marsh systems, it is clear that further research is needed to confirm our findings.
iiiTable of Contents
Chapter I: Understanding Shoreline Hardening Structures………………………………………....1 Figure 1: Various Shoreline Stabilization Methods
Figure 2: Linear miles of authorized bulkheading, NC
Figure 3: A series of breakwaters
Figure 4: Stone revetment on the Potomac River, VA
Figure 5: Structural types of a groin
Figure 6: Shoreline along the Rappahannock River, Virginia as a result of groin construction.......6 Figure 7: A stone sill found along St. Mary's River, MD.
Figure 8: Wooden Bulkhead as used in NC Sounds
Figure 9: Depiction of how bulkheads affect the intertidal zone (NRC 2006)
Figure 10:The flow of water at the sides of the bulkhead can lead to erosion behind the bulkhead as well as scouring at the sides.
Chapter II: The Effects of Bulkheads on Salt Marsh Habitats………………………………….....18 Figure 1: The Southeast Region of the US showing Bogue Sound, NC (NOAA)
Figure 2: Location of our four study sites (MV, PKS, MC, and AB) (Google Earth)
Figure 3: Diagram of sample site
Figure 4: Diagram showing sample transects
Figure 5: Numbers of bulkheads on Bogue Sound with and without marsh
Figure 6: Average percent organic matter for the landward side
Figure 7: Average percent organic matter for the seaward side
Figure 8: Average chlorophyll-a concentration (mg/m2).
Figure 9: Average Stem Height (cm) for Spartina.
Figure 10: Average live and dead stem counts per 0.25m2
References………………………………………………………………………………………………………....29 Appendix 1: Research Needs…………………………………………………………………………………37
Eastern North Carolina is a gently sloping coastal plain drainage basin containing many brackish lagoons, sounds, and salt marshes. These coastal estuaries are a natural by-product of flooded river valleys and coastal plains due to rising sea level. North Carolina has 2.2 million acres of estuarine waters and hosts the second largest estuary in the country, the AlbemarlePamlico Estuarine System. These shorelines provide valuable natural aesthetic value to coastal communities, and they can be used for many recreation activities. As well, estuarine waters can act as a nursery habitat for marine organisms. Shoreline marshes help to improve water quality by acting as a buffer for stormwater runoff that can rapidly introduce sediments, pollutants, and pathogens into the estuary (Mallin 2000).
Biologically productive coastal watersheds are home to over 70% of the world’s population, with population growth expected to continue in the foreseeable future (Vitousek 1997). North Carolina’s eight coastal counties experienced a 32% increase in population from 1977 to 1997 (Mallin 2000). Population and development pressures bring with them environmental degradation in the form of increased fertilizer, pesticide, and sediment introduction into estuarine waters. These changes have led to an excess of nutrient inputs in the estuarine systems leading to a decrease in water quality and frequent algal blooms (Paerl et al.
1998). In addition to local problems, global climate changes, such as rising water temperatures and sea level rise, have altered estuarine environments. Food web disruption, coupled with the effects of shoreline erosion on sedimentation and nutrient flux in the estuaries, could lead to serious water quality problems not only for coastal residents, but also for estuarine organisms.
Such changes have made coastal ecosystems more vulnerable to habitat loss and degradation.
In periods of sea level rise, landward migration of the shoreline occurs. Erosion and inundation of coastal property are inevitable in this landward migration. In North Carolina, the statewide average of relative sea level rise is 2.88 mm/yr and is likely to increase due to the effects of global warming (Zervas 2004). Faced with the potential to lose their valuable coastal property, significant shoreline alterations are being undertaken by property owners.
Tourism in North Carolina is based largely on the availability of coastal vacation spots, but not simply for the ocean and the beautiful view. The commercial and recreational fisheries along the Carolina coast are a significant revenue source for local economies. The decline of the North Carolina oyster industry is a prime example of how vulnerable estuarine fauna can be to ecological disruption. If development continues along North Carolina’s estuarine shorelines, the coastal ecosystem will look vastly different 100 years from now. Not only does sea level rise have an immediate negative impact on coastal property values due to the risk associated with building so close to rising waters, shoreline hardening could potentially alter the coastline so as to make waterfront properties much less attractive to buyers. Unproductive fisheries, eroding shorelines, rising waters, and disappearing marshes could all serve to severely inhibit coastal real estate, thereby eliminating millions of revenue dollars from the coastal North Carolina economy every year.
Shoreline stabilization is the modification of natural shoreline in order to reduce erosion of land and protect the owner’s property. Marsh rehabilitation, oyster reef restoration, biologs, and beach fill are considered to be “soft” stabilization methods, whereas sills, groins, breakwaters, revetments, riprap, seawalls, and bulkheads are forms of “hard” shoreline stabilization (Figure I-1). These forms differ in their cost, effectiveness, and environmental impact, and it is likely that they will be utilized more frequently as people continue to move to the coast.
Soft shoreline stabilization methods, termed “living shorelines,” are recommended as more environmentally friendly than hardening structures. Biologs are coils of biodegradable fibrous material. Marsh rehabilitation and oyster reef restoration involve the planting or replanting of marsh grass and establishment of oyster reefs along shorelines, respectively. These methods act as a buffer to dissipate wave energy and prevent erosion. Beach fill, the adding of sand to an eroded beach, is another soft stabilization technique, and it can be maintained indefinitely by adding amounts of sediment equal to the amount lost by erosion. While the reduced cost, habitat value, and lack of required permits make “living shorelines” a favorable alternative to hardened shorelines, private property owners have not yet embraced these techniques on a wide scale (Berman et al. 2005; NCDCM 2006).
Hard shoreline stabilization techniques, termed shoreline hardening structures (SHS), are an increasingly popular erosion prevention method among landowners. Breakwaters and sills are submerged structures that parallel the shoreline. Groins are barriers that project into the water, perpendicular to the shoreline. Revetments are stone or concrete blocks installed on existing shoreline to absorb wave energy. Bulkheads and seawalls are vertical walls that protect the shoreline (NCDCM 2006; Dean and Dalrymple 2004).
The shoreline, defined as the mean high tide watermark, is the legal boundary between private and public lands. However, temporal variations of both the beach profile and the sea level blur the line between public intertidal lands and private coastland. Consequently, SHS are often installed in areas where no significant erosion is taking place, but rather are being used as a means of delineation or even extension of individuals’ private property. Lax permitting regulations and enforcement have allowed some individuals to claim public land as their own by building bulkheads that extend out from the shoreline into public trust waters.
Increases in bulkhead permits seem to correlate with times of economic prosperity and periods after large storm events. North Carolina’s Department of Coastal Management issued permits to install bulkheads on 11.7% of the state’s estimated 3,900 miles of estuarine shoreline between 1984 and 2000 (Figure I-2). Permitted bulkheads are not necessarily built, and until 2001 permits were not required to build a bulkhead less than 500 ft. long. Therefore, the actual amount of bulkheaded shoreline could be more or less than estimated (Street et al. 2005).
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