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THE IMPACT OF THE NEW COLLEGE OF FLORIDA SEAWALL PROJECT ON THE ADJACENT SEAGRASS BY CASSANDRA WOOD A Thesis Submitted to the Division of Natural Sciences New College of Florida in partial fulfillment of the requirements for the degree Bachelor of Arts Under the sponsorship of Dr. Sandra Gilchrist Sarasota, Florida February, 2013
ii Acknowledgements This project was funded in part by the Ne w College of Florida Council of Academic Affairs and the Pritzker Marine Biology Re search Center Laboratory Fee. I would like to thank my sponsor Dr. Sandra Gilc hrist and committee members Dr. Alfred Beulig and Dr. Steven Shipman, for their support and critique. I had a lot of additional help for this pr oject and I would like to thank everyone who gave it. NCF Architect Jack Whelan, who very generously gave me documents on the NCF seawall project and served as a li aison to the construc tion crew. Brad Petz and Mark Romance, Tandem Construction Pr oject Superintendents, for guiding me around the seawall project. Joel Beaver, Prit zker Laboratory Coordi nator, Id like to thank for help and guidance with field tool s. Id like to tha nk Dr. Duff Cooper for his invaluable statistics help. My field assistants Kirsten Wood, Kyra Murrell, Chelsea Hewitt, Elizabeth Brewer, and Al ex Wood, thank you for your patience and help. Finally, I would also like to thank my friends and family for their support and encouragement.
iii Table of Contents 1. Acknowledgements ... .ii 2. List of Figures ... .iv 3. List of Tables ... .vi 4. Abstract .. ...vii 5. Introduction ... .....1 6. Methods . ..24 a. Location .. .24 b. Data Collection .. ..25 c. Seagrass . ..26 d. Sediment .. 32 e. Abiotic Factors .. ...36 7. Results .. 40 a. Observations .40 b. Time Frame .. 55 c. Seagrass . ..55 d. Sediment .. 59 i. Sediment Trap (Large Grains) .. ...59 ii. Turbidity (Small Grains) .. 67 e. Abiotic Factors .. ...68 i. Nutrients . .68 ii. Water Temperature .. 68 iii. Water pH .. 69 iv. Salinity .. ...70 v. Precipitation . 71 f. Abiotic Factors Summary .. ...73 8. Discussion ... .76 a. Conclusion .. .84 9. References .. ..87
iv List of Figures Figure 1. Worldwide distri bution of seagrasses ..1 Figure 2. Map of Sarasota Bay ...7 Figure 3. Satellite image of Sara sota Bay with study area .7 Figure 4. Florida seag rass distribution 9 Figure 5. Major Hurricanes (Category 3-5) 2001-2010 ... .12 Figure 6. Hurricanes 2011 ... ..13 Figure 7. Hurricanes 2012 . 14 Figure 8 a-b. Seagrass Illustrations .. .15 Figure 9 a-b. Photos of seagrass samples .. ....16 Figure 10. Study area seagrass coverage .. ....16 Figure 11. New College of Florida Seawall .. ... 19 Figure 12. Ringling Museum shoreline in 1952 ... 20 Figure 13. Ringling Museum seawall ...20 Figure 14. Caples Seawall in 1992 ... 21 Figure 15. Caples shoreline ...21 Figure 16. Longshore current effect on a shoreline . .22 Figure 17. Sarasota Bay 24 Figure 18. Study area 25 Figure 19. NCF transects . .27 Figure 20. Ringling transects 27 Figure 21. Caples transects ...28 Figure 22. Tree landmark .. 28 Figure 23 a-b. Using the survey tape .. ..29 Figure 24. Diagram illustration geometry of Ringling seagrass data collection 30 Figure 25. Trapezoid area .31 Figure 26 a-b. Sediment traps .. ..32 Figure 27. NCF sediment trap locations .. ... ..33 Figure 28. Ringling sediment trap locations .34 Figure 29. Caples sediment trap locations 34 Figure 30. Ro-Tap and sieves ...35 Figure 31. Turbidity curtain aerial image ......37 Figure 32 a-b. Rain gauge .. 38 Figure 33. Turbidity curtain before placed in water ..40 Figure 34 a-b. Turbidity cu rtain at low tide .. 41 Figure 35 a-b. Loosening of the turbidity curtain .. ... .42 Figure 36 a-b. Disappearance of the turbidity curtain .. .43 Figure 37 a-b. Seawall debris removal south of dock . ... 44 Figure 38 a-b. Seawall debris removal north of dock ....45 Figure 39. Sea foam observed 46 Figure 40. Before construction NCF aerial ...47 Figure 41. Early during c onstruction NCF aerial ..47 Figure 42. Late during c onstruction NCF aerial ... 48 Figure 43. New stormwater drain exit ...49 Figure 44 a-b. Preand Po st-lagoon construction .. 50
v Figure 45. Sail Club at Caples ... 51 Figure 46. Boat trailer tracks .52 Figure 47. Location of the stormwater drai n between Caples and Ringling Museum ..53 Figure 48 a-b. Exposed sediment traps ..54 Figure 49. NCF seawall. 56 Figure 50. Change in seagrass distance from shoreline .56 Figure 51. Difference in seagrass di stance preand post-construction .57 Figure 52. Rate of sediment collection over time ... ..59 Figure 53 a-b. Rate of sediment colle ction over time in terms of phi . .61 Figure 54. Percentage of sediment t oo large for grain size analysis ..62 Figure 55. Turbidity relative to time and location 68 Figure 56. Water temperature over time 69 Figure 57. pH over time .70 Figure 58. Salinity over time .71 Figure 59. Rainfall over time .72 Figure 60. Location of rain gauge ..72 Figure 61. Dredging history of the Gulf In tracoastal Waterway in Sarasota Bay .78 Figure 62. Turbidity data ...81 Figure 63. Source of turbidity data 82 Figure 64. Wind data .82 Figure 65. Source of wind data ..83
vi List of Tables Table I. Examples of construction and its impact on seagrass 6 Table II a-b. Comparison of the characteristics of H. wrightii and S. filiforme 17-18 Table III a-b. Timing of data collection .................26 Table IV. Phi scale in comparison with grain size in micrometers ...35 Table V. Timeline of this study .55 Table VI. Seawall seagra ss distance statistics ...57 Table VII. NCF seawall restored vs. Ringling seagrass di stance statistics ...58 Table VIII. NCF seawall lagoon vs. Capl es seagrass distance statistics ...58 Table IX. Approximate amount of seagrass coverage change ...59 Table X. Sediment collec tion rate statistics ...60 Table XI. Sediment collection rate for larg e grains preand du ringconstruction ...63 Table XII. Sediment collection rate for large grains prea nd post-construction ...64 Table XIII. Sediment collecti on rate for large grains dur ingand post-construction 65 Table XIV. Sediment collecti on rate for small grains pr eand during-construction .66 Table XV. Sediment collection rate for sm all grains preand post-construction ..66 Table XVI. Sediment collecti on rate for small grains dur ingand post-construction ...67 Table XVII a-b. Summary of other ab iotic factors in Sarasota Bay.. ...73-75
vii THE IMPACT OF THE NEW COLLEGE OF FLORIDA SEAWALL PROJECT ON THE ADJACENT SEAGRASS Cassandra Wood New College of Florida 2013 ABSTRACT Seagrass is an important primary producer in marine ecosystems. It is under threat by many anthropogenic activities, pa rticularly the ones that re duce water clarity and uproot living seagrass. Coastal construction, such the New College of Florida (NCF) Seawall Project conducted spring 2012 by Tandem Cons truction, can disturb sediment and soil, causing it to cloud the water and cover the s eagrass, reducing seagrass coverage. To monitor the impact of the NC F seawall reconstruction on th e nearby seagrass cover, the changing distance of the seagrass Halodule wrightii from shoreline was determined and sediment and turbidity data were collecte d. The restoration construction did cause a recession in the seagrass, while the addition of a lagoon did not. However, the seagrass in the disturbed area did not recede past the loca tion of a turbidity curtain that was placed before construction was underway. This indicat es that the precautions for minimizing the effect of the construction project on the adjacent seagrass were effective in the short term. Dr. Sandra Gilchrist Division of Natural Sciences
1 Introduction Despite the valuable ecosystem services seagrass provides, on e-third of seagrass species are in decline globa lly (Short et al. 2011). Seagra ss occupies coastal waters (Figure 1) where it can be threat ened by anthropoge nic activities. Figure 1. Worldwide distribution of seagrasses (shown in red) ( http://www.flmnh.ufl.edu/.../Distribution.html ). In 2010, approximately 44% (3 billion) of the worlds population lived within 150 kilometers of the coast and with this distri bution comes environmental impacts in the area ( http://www.oceansatlas.org/... ). Coastal construction is a known cause of seagrass decline. The purpose of this project is to determine the impact of the spring 2012 New College of Florida (NCF) s eawall construction project on the nearby seagrass. Most of seagrass value lies in the fact that it is a primary producer (Zieman and Zieman 1985). Seagrass also shelters young aquatic animals, sh ielding them from predators. These two services are the main reasons that without seagrass, fisheries can suffer and the fishery-dependent economies ma y crash (Short et al 2011). In fact, in order to demonstrate the importance of seagra ss, several attempts have been made to
2 calculate the economic value of certain seagra ss services at select locations (Unsworth and Cullen-Unsworth 2010). However, there is currently no global calc ulation of the total economic value of seagrass. More recent calc ulations have been made for Australia and Florida. Australia has valued the fisheries pr oduction services of its gulf water seagrass to be $133 per hectare per year (McArthur a nd Boland 2006). In Florida, the cost of restoring the seagrass has been calculated to be $140,752 per hectare (Engeman et al. 2008). The benefits of seagrass presence exte nd downwards into the sediment. Seagrass roots stabilize sediment, preventing coastal erosion (Zieman and Zieman 1985). This is very important because of the value of th e coast (Phillips and Jones 2006). The shoots above the sediment slow water velocity so th at particles settle from the water column (van der Heide et al. 2011). In addition to stabilizing and in creasing the amount of substrate, when the seagrass dies, it adds nutrient value to the sediment (Zieman and Zieman 1985). There is a lot of this nutrient buildup from seagrass in part because seagrass grows so fast. However, despite the many services seagra ss provides, it is in decline throughout the world (Short et al. 2011). A review of 215 journal articles revealed that 110 km2 of seagrass disappeared globally per year between 1980 and 2006. In most cases, the seagrass decline is due to anthropogenic, not natural, events that reduce water clarity (Duarte et al. 2004). The most common of th ese are eutrophication and sediment loading (Burkholder et al., 2007; Dennison et al., 1993; de Boer 2007). The most widespread cause is eutrophication, which happens when waters are overloaded with nutrients, causing a phytoplankton bloom. The phytoplankton covers surfaces and clouds the water,
3 making it hard for seagrass to absorb much needed sunlight. Phytoplankton thrives in high-nutrient environments and seagrass has the competitive advantage in low-nutrient water, so elevated levels of nutrients cause a shift among prim ary producers (Hemminga and Duarte 2000; Hein et al. 1995; Duarte 1995). The other common method through which s eagrass decline occurs is sediment loading. This can be caused by coastal devel opment and can increase turbidity and cover the seagrass, making it difficu lt for light to get through (Erftemeijer and Lewis 2006). Fortunately, sediment settles soon after becomi ng disturbed, in part due to the ability of the seagrass to trap fine sediments. Most seagrass species can withstand a certain amount of burial, so sediment loading is not as bi g of a problem as eutr ophication (Cabaco et al. 2008; van Katwijk et al. 2010). Another cause of seagrass decline ma de relevant recently by the Deepwater Horizon oil spill of 2010 is hydrocarbon and dispersant exposure. Hydrocarbons can reduce seagrass tolerance to stre ss factors (Runcie et al. 2010). The degree to which this happens normally depends on the tide, because oil floats at the waters surface (Taylor and Rasheed 2011). However, in the Deepwa ter Horizon oil spill incident, two million gallons of dispersants were used, which cause d the oil to distribut e throughout the water column where the seagrass is (Schmidt 2010). Wh ile oil treated with dispersant tends to be less toxic to seagrass than oil alon e (Macinnis-Ng and Ralph 2003; Lewis and Devereux 2009; Baca and Getter 1984), disper sed oil can have a greater effect on seagrass growth than oil alone at high c oncentrations and during long treatment periods (Thorhaug et al. 1986). Also, care must be taken to ensure that an excess of dispersant is not used, because dispersant alone is toxic to seagrass (Scarle tt et al. 2004). It is possible
4 that the seagrass off the coast of the Gulf of Mexico was harmed because of this, but there is little research available to support that directly as of December 2012. However, there is direct evidence of o il spill impact. One study monitored the impact of the oil spill on fishes dependent on seagrass nursery habitat in the Gulf of Mexico and found that the fish were unexpectedly greater in number th an in previous years (Fodrie and Heck 2011). It is possible that this may be because predat ors were affected by the oil, but much more research must be performed in order to de termine the impacts of the Deepwater Horizon oil spill. Along with the indirect ways of harming seagrass, there are also direct methods. Two of them involve boats: propeller scar ring and anchor usage. In seagrass beds, propeller scars are areas in which the seagrass has been dislodged by the propeller of a boat (Zieman 1976; Sargent et al. 1995). Thes e scars can cause long-term damage to seagrass beds. For example, Thalassia testudinum re-growth over propeller scars in Tampa Bay, FL took an average of 3.5 to 4.1 years (Dawes et al. 1997). Anchor damage occurs when boats release anchors on top of seagrass beds, then take them up again (Francour et al. 1999). At Port -Cros National Park in the nor thwestern Mediterranean Sea, the release and retrieval of one anchor alone destroys an average of 34 Posidonia oceanica shoots. In Maho and Francis Bays, St. John, U.S. Virgin Islands, with traffic ranging from 15-50 boats per night, anchor scars caused a loss of up to 6.5 meters squared per day (Williams 1988). The seagrass t ook about 7 months to show visible regrowth over the scars. The gravity of the damage that boating can cause on seagrass can be expressed by how its impact can magnify seagrass damage by hurricanes. These tropical cyclones are
5 one of the few natural disturbances capabl e of significantly damaging a seagrass bed. However, they are more likely to do so if th e seagrass bed has already been damaged. For example, a seagrass bed that Category 5 Hurricane Katrina pa ssed over remained unharmed (Anton et al. 2009), while a seag rass bed that had already suffered boat damage was further damaged by a category 2 hurricane (Whitfield et al. 2002). Anthropogenic disturbance can not only cause a great amount of damage on seagrass, but it can also come in vary ing forms. Coastal construction is one anthropogenic activity that can cause seagrass decline through sediment loading. It can also create seagrass habitat, but this has been rare (Har rison 1987). Often dredging is involved, which not only directly damages s eagrass, but also causes sediment loading by removing and burying seagrass as well as in creasing turbidity (Erftemeijer and Lewis 2006). Not all species are aff ected equally, though. Large, slow-growing climax species, such as Thalassia testudinum of Sarasota Bay (Koch 1994), with energy reserves are more resilient towards dredging than smaller co lonizing species, but the colonizers return much faster after construction ends. There ar e numerous examples in which construction has threatened or otherwise modified seagrass populations (Table I).
6 Table I. Examples of Construction and its Impact on Seagrass Location Activity Effect Reference Tung Chung on Lantau Island, Hong Kong Dredging and reclamation activities Shrunk population of rare species Zostera nana to 15% of original coverage (Lee 1994) Southern Roberts Bank on the Pacific Coast of Canada Dredging and filling Decreased area cover of Zostera marina and Zostera japonica Created new habitat for Z. marina (Harrison 1987) Florida Keys Construction of a new pipeline Removal of Halodule wrightii and Thalassia testudinum (Thorhaug 1983) Sarasota Bay Dredging Intracoastal Waterway (ICW) Local seagrass decline (Davis and Zarillo 2003) (Estevez and Palmer 1990) Seawalls are one of the anthropogenic st ructures that fall completely in the category of coastal constructi on. Adding seawalls can alter se diment transport patterns by strengthening wave reflecti on (Duarte et al. 2004; Rakha and Kamphuis 1997). This can create a scenario where the s eawall causes erosion unless th ere is sediment supply nearby (Kraus 1988). However, creati ng holes in the seawall does ha ve the potential to dissipate waves (Zhu and Chwang 2001). Due to the nature of this study, it is important to note that it is likely that a restored seawall will ha ve the same effect as the original seawall on sediment transport patterns if it is placed in the same place. In the interest of increasi ng the amount of informati on available on the impact of seawall construction on seagrass and provide a service to local s concerned about seagrass, this project was conducted to monitor th e effects of the Spring 2012 NCF seawall construction on the nearby seagrass in Sarasota Bay, Florida, United St ates (Figure 2-3).
7 Figure 2. Map of Sarasota Bay (http:// www.sarasota.wateratlas.usf.edu/.../2011/) Figure 3. Satellite Image of Sarasota Bay w ith the study area indicated in red (Google Maps 2012).
8 Florida is home to about 10 species of seagra ss (Short et al. 2007). However, like in the rest of the world, the seagrass is experienci ng a great deal of anthropogenic influence due to the high numbers of people living on the Florida coast. From 1950 to 2000, the Florida population alone increased from 2.7 to 16 m illion (Tomasko et al. 2005). About 70% of those 16 million Floridians lived on the coast. Around the same time between the years of 1950 and 1990, the Floridian seagrass suffered a massive decline. In 1950 there were about five million acres that became two million by 1990 (Dawes et al. 2004). Fortunately, some progress has been made since in recovering some of the three million lost, but only by about 179 thousand acres (Yarbro and Carlson 2011). Furthermore, out of 30 estuarine coastal systems surveyed, ei ght had increasing seagrass and twelve had stable seagrass area by 2010 (Figure 4). Seve n out of 30 were experiencing seagrass area decline and three of the system statuses are unknown or require more information.
9 Figure 4. Florida seagrass dist ribution from Seagrass Integr ated Mapping and Monitoring program 2010 Annual Report (Debra Childs Woithe Inc. and PBS&J 2010) The reason why such little progress in in creasing the seagrass cover has occurred may lie in a conflict of interests in restor ing seagrass, since trade, tourism, and land development make greater contributions to th e economy than fishi ng with $149 billion in 2011 from trade ( http://www.eflorida.com/ ... ), $67 billion in 2011 from tourism ( http://www.stateofflorida.com/... ),$23 billion in 2012 from land development (Judy 2012)
10 versus $14 billion in 2010 from fishing (FFWCC 2010). Trade, tourism, and land development do not depend on seagrass nearly as much as the commercial and sport fishing industry does and they contribute towards seagrass declin e. However, it should be noted that some tourists may co me to Florida for the fishing. Fortunately for the seagrass there have been pushes in federal and state government to improve water conditions in coastal areas. Laws for increasing water quality, which reduces eutrophication, have been made for Florida since the early 1970s (Blake 1980). In 2012, this culminated in Environmental Protection Agency (EPA) implementing numeric nutrient criteria for Fl orida, restricting levels of anthropogenic nutrient use so that in no cas e shall nutrient concentrations of a body of water be altered so as to cause an imbalance in natural popul ation of aquatic flora or fauna (Sotsky and Karpatkin 2012). The EPA also implemente d a program entitled, Best Management Practices, that makes recommendations on methods to help reduce pollution of stormwater ( http://cfpub.epa.gov/.../menuofbmps/ ). Use of these methods is entirely voluntary. The Florida Department of Envir onmental Protection has also implemented a Best Management Practices program that gi ves suggestions for many different activities that require fertilizers; the mo st relevant to this study concer ns the use of fertilizer in urban and golf settings ( http://www.dep.state .fl.us/.../pubs.htm ). In addressing sediment loading, federal and state agencies have placed restrictions on construction, particularly dredging, by requiring many permits in Flor ida (PBS&J 2008). Florida government has created a Coastal Construc tion Control Line Program (Chapter 62B-33, Florida Administrative Code), whereby coastal constr uction is only allowed to occur if builders have satisfied special criteria that ensure that the new structure and its construction does
11 not destabilize or destroy the beach and dune system ( http://www.dep.state.f l.us/.../ccclprog.htm ). Sarasota Bay has increasing seagrass c overage likely due to improvement of water quality in the area. Between 1988 a nd 1996, anthropogenic nitrogen loads were decreased by 46% and seagrass coverage in creased in the bay (Tomasko et al. 2005). Later on in 2010, the seagrass coverage in Sara sota Bay continued to increase, exceeding the estimated 1950 coverage by 25%, gain ing 51 acres between 2008 and 2010 (Yarbro and Carlson 2011; Kane 2011). All of this occurre d in spite of a tremendous increase in anthropogenic pressure. Between 1980 and 2012, the number of people living in Sarasota County increased by 177,197 ( http://stateof thecoast.noaa.gov/.../welcome.html ). The more recent increase in seagrass may have been helped by not only federal and state government action, but also some by local laws. The aforementioned federal and state action in Florida concerning wa ter quality and eutro phication has caused chlorophyll a levels, an indicat or of phytoplankton presence, to decrease in the water (Tomasko et al. 2005). In 2011, chlorophyll a leve ls were consistently below the target level throughout most of the year ( http://www.sarasota.wateratlas.usf.edu/.../2011/ ). Sarasota County laws have followed suit with federal and state laws. In 2007, the county, inspired by algae blooms and red drift algae accumulation on beaches, passed the strictest fertilizer ordinance in the state at th e time (Whittle 2007). The ordinance forbids homeowners and business owners from using chemical fertilizers during the wet season from June through September and also limits the total amount of nitrogen and phosphorus that can be applied per year. Laws con cerning sediment loading have also been implemented. Sarasota County has imposed cons truction restrictions in conjunction with
12 those imposed by federal and state government s. Sarasota County has its own laws called the Gulf Beach Setback Line and the Barri er Island Pass Twenty-Year Hazard Line (Chapter 54, Article XXII of the Sarasota County Code) ( https://www.scgov.net/ ...). These laws place restrictions on construction in the area starting at a certain landward point all the way dow n to the shore. Other factors that might explain the increas e in seagrass coverage in Sarasota Bay include local efforts to mitigate damage caused by boats and the recent lack of major hurricanes in the area (Figure 5-7). Figure 5. Major Hurricanes (Category 3-5) 2001-2010 ( http://www.nhc.noaa.gov/ ...)
13 Figure 6. Hurricanes 2011. The magenta lines which designate category 3-5 hurricanes do not make landfall in Florida ( http://www.nhc.noaa.gov/... )
14 Figure 7. Huricanes 2012. The magenta lines which designate categ ory 3-5 hurricanes do not make landfall in Florida ( http://www.nhc.noaa.gov/... ) For instance, the Florida Fish and Wild life Commission, which is charged with protecting and managing numerous species in Florida, has made attempts at educating boaters about minimizing their impact on seag rass and has threatened a fine of up to $1,000 if seagrass is destroyed in Aqua tic Preserves (http://myfwc.com/about/; http://myfwc.com/.../protect/ ; FFWCC 2012). Also, all major hurricanes in the past eight years have made landfall away fr om Sarasota Bay (Figure 5-7) ( http://www.nhc.noaa.gov/ pastall.shtml#tcr ). The last major hurricane in the area was Category 4 Hurricane Charley in 2004.
15 There are two dominant species of seagrass: shoal grass ( Halodule wrightii ) (Figure 8a and 9a) and manatee grass ( Syringodium filiforme ) (Figure 8b and 9b) near the shoreline of at NCF and Ringling Museum (Figure 10). (a) (b) Figures 8 a-b. Illustrations of (a) Halodule wrightii (b) Syringodium filiforme ( http://ian.umces.edu/ ).
16 (a) (b) Figure 9 a-b. (a) Halodule wrightii and (b) Syringodium filiforme samples taken from Caples area. Photos taken 1/17/2013 Figure 10. Study area seagrass coverage outlined in a satellite image taken December 1, 2010. Red designates H. wrightii blue is for S. filiforme and white is unknown. The seaward areas adjacent to Ringling and Caples are the controls for this study. NCF stands for New College of Florida (Google Earth 2012)
17 The intertidal area of Sarasota Bay area direc tly to the west of the NCF campus where the seawall construction occurred in spring 2012 is covered with H. wrightii (Figure 10) This species is a primary successional specie s with high resource needs in comparison to species adapted to higher successional levels (Zieman and Zieman 1985; Fourqurean et al. 1995). Halodule wrightii is listed on the IUCN Red Li st as a non-threatened species ( http://www.iucnred list.org/.../173372/0 ). Syringodium filiforme can be found waterward of the control areas south of the main cam pus of NCF (Figure 10) It is similar to H. wrightii because it is also a colonizer species with high nutrient needs and has IUCN Red List non-threatened status (Short et al. 1993; Galle gos et al.1994; http://www.iucnredlist.org/.../173378/0). However, it is not as prolific and is only present in the tropical Atlantic and Mediterranean area with a st able population (Short et al. 2011). There are other points of comparison between the two species (Table II a-b). Table IIa. Comparison of the Characteristics of Halodule wrightii and Syringodium filiforme Halodule wrightii Syringodium filiforme Common References Generational Life Span (years) 3 3 (Short et al. 2011) Min. depth (meters) 0 0 (Short et al. 2011) Max. depth (meters) 18 20 (Short et al. 2011) Bioregion Temperate North Atlantic, Tropical Atlantic, Mediterranean, Temperate North Pacific, Tropical Indo-Pacific Tropical Atlantic, Mediterranean (Short et al. 2011) Population Trend Increasing Stable (Short et al. 2011) Minimum Light Requirements 5-30.5% SI 17.2-30.5% SI (Erftemeijer and Lewis 2006)
18 Table IIb. Successional Stage Colonizer Colonizer (Short et al. 1993) (Gallegos et al. 1994) (Fourqurean and Rutten 2004) Sediment Loading Sediment deposition (<1 to 50 cm) due to hurricane caused 11% loss of H. wrightii (Fourqurean and Rutten 2004) Sediment burial 50% mortality at 4.5 cm and 100% mortality at 10 cm after 60 days (Cabaco et al. 2008) Water Temperature Range (C) 12-30 9-32.3 (Lee et al. 2007) Optimal Temperature (C) 25-30 23-32 (Lee et al. 2007) Despite the fact that the species H. wrightii is not threatened, it still provides valuable ecosystem services and merited monitoring during the spring 2012 NCF seawall construction project. Any new negative impact will be important to note because the seagrass is doing so well in Sarasota Bay. My working hypothesis for this thesis was that the construction on the NCF s eawall would reduce the covera ge of the seagrass through sediment loading. This would be consistent with how coastal constr uction has influenced seagrass in the past. The goal of the seawall construction was to rest ore the southern half of the wall and to create a lagoon on the northern half (Figure 11).
19 Figure 11. New College of Florida seawall w ith white arrows showing the area where construction of a lagoon was planned and black arrows showing the area where seawall restoration occurred (Google Earth 2012) However, an extensive amount of thought concerning environmental impacts had to be done, especially before construction ev en started. An environmental assessment was undertaken of the construction area to check the seagrass an d the endangered species. It was concluded by a consultant to the constr uction company that the construction would have little impact on the seagrass and there were no endangered species present (PBS&J 2010). Permits were obtained before the cons truction process was st arted, so undesirable results could be avoided. For instance, the ne w dock was restricted by size so that it does not exceed the mean high water line, requiri ng additional permits. Stormwater was not allowed to be redirected through the lagoon due to the permits it would require as well as the diminishment of the lagoon as an educational area. There are two control areas in this thesis. They are the seagrass habitats south of the NCF seawall and adjacent to the Ring ling Museum and NCF Caples properties
20 (Figure 10). They were picked due to thei r similarities and differences to the NCF seawall area. They share similar environmenta l variables because of proximity and they all have or had a seawall at one time. Howeve r, the important difference lies in the fact that construction on the seawalls occurred at different times (Figures 12-15). Figure 12. Ringling Museum shoreline (white arrow) and future spot of the Ringling seawall in 1952. Photo taken from a spot s outh of the Ringling Museum dock (black arrow) (http://new s.google.com/...) Figure 13. Ringling Museum seawall (white arrow) and dock (bl ack arrow) as of September 8th, 2012 taken from an area south of the seawall facing northeast.
21 Figure 14. Caples Seawall (a rrow) in 1992 (NCF 1992) Figure 15. Photo of Caples shoreline as of January 19, 2012 that shows the change in the Caples shoreline after the seaw all was removed (Google Earth 2012) The construction project on the NCF seawall was during spring 2012 while records show that the last time restoration work was done on the Ringling Museum seawall was in
22 1952 ((http://news.google.com/...). Caples seaw all was removed in 1992, leaving plenty of time for the effects of the construction to fade (Morris 1990-1993). Due to these differences, the area around the Ringling Museum was an ideal control for the restoration section of the NCF seawall and the Caples area was a reasonable control for the NCF lagoon area. Other differences between the sites make it hard to test the null hypothesis, but they are symptomatic of performing work in the field instead of in a more controlled environment such as a laboratory. The cont rols are populated by a different seagrass species than the NCF area, S. filiforme The longshore current caused problems in maintaining similar conditions for all three areas during the study. The current reversed direction during construction, affecting the di rection of sediment loading in the area (Figure 16) ( http://www.crd.bc.ca/.../coastalsediment.htm ). Figure 16. Longshore current effect on a shoreline without a seawall ( http://www.crd.bc.ca/... /coastalsediment.htm ).
23 In addition, Caples is home to the NCF sail cl ub, near an extensive stormwater drain, and its seagrass are too far away from shoreline to compare sta tistically with the seagrass at the other two sites. Thus, the controls we re useful although they were not ideal.
24 Methods LOCATION From November 2011 to May 2012 and August 2012 to October 2012, data were collected on seagrass distribution and various factors that could influence seagrass health. Data were collected at three locations on the eastern coast of Sarasota Bay, Sarasota, FL (Figure 17): the main bayfront adjacent to New College of Floridas College Hall (27237 N 823355W), New College of Floridas Caples area (272248N 823352W), and Ringling Museum of Art (272256N 823353W) (Figure 18). Figure 17. Satellite Image of Sarasota Bay w ith the study area indicated in red (Google Maps 2012).
25 Figure 18. Satellite image of study area, incl uding New College of Florida, Ringling Museum of Art, and Caples bayfront (Google Earth 2012). The NCF bayfront represented the treated ar ea for this study and the Caples and Ringling bay fronts were the controls. Caples was th e control for seawall removal and Ringling was the control for seawall construction. DATA COLLECTION The immediate conditions were noted each time data were collected in the field: location, time, date, and approximate level of cloudiness, tide, windiness, and air temperature. Care was taken to make sure that certain environm ental conditions were similar between sampling days. Data were only taken when the tide was low, it was sunny with low to medium cloudiness, and wind was minimal. No data were taken during or around the time of more extreme meteorol ogical conditions, such as rain, lightning, and high wind. Over a time period of about a mo nth, attempts were made to collect each type of data needed at le ast once (Table III a-b).
26 Table IIIa. Timing of Data Collection. Each number repr esents the number of field samples during the month. All Seagrass Sediment Trap Turbidity Nitrate Phosphate Nov '11 3 1 Dec '11 3 3 3 3 Jan '12 3 3 7 7 7 Feb '12 1 3 4 3 4 Mar '12 3 Apri'12 2 3 May '12 3 3 3 Aug '12 3 2 2 Sep '12 3 3 1 1 Oct '12 3 Table IIIb. All Water Temperature pH Salinity Rainfall Longshore Nov '11 1 1 1 3 Dec '11 6 3 6 2 Jan '12 9 9 8 7 Feb '12 3 3 3 3 Mar '12 4 1 Apri'12 4 2 5 5 May '12 4 Aug '12 2 2 2 4 Sep '12 1 1 1 4 Oct '12 3 3 3 1 Nov 12 1 Data collected included minimum distance of the seagrass rhizomes from seawall, sediment mass and grain distribut ion of sediment collected in sediment traps, turbidity, longshore current, recent rainfall level, nitrate and phosphate c oncentrations in the water, water temperature, pH of water, and salinity. All data was put in bar graph form using the pre-, during-, and post-constr uction median data points. SEAGRASS Seagrass rhizome location was collected usi ng 50 meter survey tape. Initially, the seagrass was ground-proofed by comparing the s eagrass distribution out in the field with
27 seagrass images from Google Earth. For the NCF Bay Front, each transect point measured was selected in corresponden ce with a landmark (Figures 19-22). Figure 19. Satellite image with NCF bay front transect locations marked out (Google Earth 2012). Figure 20. Satellite image with Ringling Museum bay front transect locations marked out (Google Earth 2012).
28 Figure 21. Satellite image with Caples bay fr ont transect locations marked out (Google Earth 2012). Figure 22. Tree at point 15 used as a landmark. One end of the tape would begin at a poi nt along the seawall and the other end was placed in a line perpendicular to the seawa ll, ending where the seagrass was seen or felt to have minimal patchiness (Figures 23 a-b).
29 (a) (b) Figure 23 a-b. Using the survey tape. (a) The seag rass view of the tape and (b) is the land view of the tape. The seagrass was difficult to see in winter and early spring, because the seagrass leaves die back during these times. Instead of j udging seagrass location by sight, touch was used to determine where the rhizomes were under the sediment. The Ringling Museum shoreline was selected to be a control for the NCF seawall restoration construction and th e Caples shoreline was meant to be a control for the NCF lagoon construction. Transects were placed near major landmarks to keep track of them. Initially, the Ringling Museum seagrass was monitored with one person holding the survey tape from on top of the wall with another person in the water feeling for the S. filiforme seagrass in the deep water with their fe et. The last two rounds of measurements
30 were performed with both survey tape hol ders in the bay water. The Pythagorean Theorem was used to correct for this (Figure 24). Figure 24. Diagram illustrating the geometry of the Ringling seagrass data collection from a perspective perpendicula r to the seawall. Initial co llection method (1) and second collection method (2). The Pythagorean Theorem was used to estimate the distance (3) in order to figure out what the corresponding value of (2) for each value of (1) was. At Caples, measurements were performed c onsistently throughout the study period with one person holding each end of the survey tape and moving to figure out how many meters beyond 50 the S. filiforme seagrass occurred. A graph was made for each of the three locations comparing seagrass distances. To determine if the differences between seagrass measurements were significant, Wilcoxon signed-rank and Mann-Whitney tests were performed. The Wilcoxon was used
31 for matched data sets and the Mann-Whitney for independent data. For the independent data, post-construction data was subtracted by pre-construction data for each location separately before the statisti cal test was performed. This wa s done in order to correct for location differences. The alpha selected fo r determining significance was 0.05. I chose these nonparametric tests because I assumed th at the data were not normally distributed or large enough for parametr ic tests to be useful. To estimate the amount of seagrass lost n ear the NCF seawall, the equation for the area of a trapezoid was used (Figure 25). Figure 25. Birds-eye view example of how tr apezoid area (red) was calculated when estimating the seagrass area lost from satellite images. The height was determined by taking the di stance between transect points by using Google Earth satellite images and the ruler to ol. The two bases were the distances of the seagrass from the shore for the two transect s used. The trapezoid areas were then added
32 to get pre-construction and post-construction values. The post-construction value was subtracted by the pre-construction value to get estimated seagrass area lost. SEDIMENT Sediment mass and grain distribution was measured by first collecting sediment using traps (Figure 26 a-b). (a) (b) Figure 26 a-b. All six sediment traps used dur ing this study (a). Cutaway diagram of the inside of a sediment trap (b).
33 The traps were made by Joel Beaver, the NC F Pritzker Laboratory Coordinator, with 9 mm diameter holes in the lid. They were placed spike e nd in the sediment around the midpoint of the three locations approximately 17 meters fr om shore (Figure 27-29). The distance was chosen based on the location of the seagrass edge at the NCF seawall in November 2011. In the case of the NCF seawa ll site, this was seaw ard of the turbidity curtain. Figure 27. Sediment Trap locations (red dot) nearby NCF main campus seawall (a), (Google Maps 2012)
34 Figure 28. Sediment Trap locations (red dot) nearby Ringling s eawall (Google Maps 2012) Figure 29. Sediment Trap locations (red dot ) nearby Caples shorel ine (Google Maps 2012) Two were placed in each area, one that wa s emptied monthly before, during and after seawall construction and another emptied onc e in three months. There were no data collected June through July, but data were collected starting August 10, instead. Data for
35 March were also not collected because two sediment traps were knocked over then. After collection, the sediment was de-clumped, dried, weighed and shaken by a Ro-Tap through sieves placed larges t on top and smallest on bottom for one minute per sample (Figure 30). Figure 30. Ro-Tap and sieves. Sizes for these sieves included from larges t to smallest 1, 1.5, 2, 2.5, 3, 3.5, and 4 in the phi grain size scale (Table IV). Table IV. Phi Scale in Comparison with Grai n Size in Micrometers (Krumbein and Sloss 1963) Micrometers 500 350 250 177 125 88 62.5 Phi 1 1.5 2 2.5 3 3.5 4
36 Each part that was separated by the sieves wa s weighed to get separate and total weights. The sediment that did not get through the si eve with the largest holes was excluded from grain size calculations. This was because it consisted of clumps and other biological matter, not separated grains. The mass of th e separated samples was then divided by the mass of the whole sample in order to provide a percentage for grain size range. Grain size ranges were divided into two larger categories in order to make it easier to perform statistical tests on them: large (1-2 phi) a nd small (>3 phi). For demonstrative purposes, bar graphs were made of the total collect ed sediment, the phi percentages and the excluded sediment. To determine if there was a significant difference between two sediment factors (location and time) a Kruskal-Wallis twoway ANOVA was used. If a factor showed significant difference, a Kruskal-Wallis one-way ANOVA was performed on the groups if there were more than tw o. If there were two, a Mann-Wh itney test was performed. If the factor had more than two groups and wa s still significant, Ma nn-Whitney tests were performed between all possible pairs. The B onferroni Correction was used to determine the alpha for all pairwise comparisons. The starting alpha used was 0.05. I used these nonparametric statistics because the data were not normal or large enough for a parametric test to be effective. Turbidity was measured by gathering water samples from near the sediment traps at each site and placing them in a Hach Model 2100A Turbidimeter. A graph of the collected data was made. ABIOTIC FACTORS
37 All data except for the rainfall and l ongshore data were co llected outside the turbidity curtain (Figure 31) fo r NCF and near the sediment traps for all three locations. Figure 31. Aerial taken around March. The yello w line indicated by the arrows is the turbidity curtain (SC 2012). Nitrate and phosphate concentrations were measured using a Red Sea Fish Pharm saltwater nitrate mini lab testing kit (ARE20145) and a LaMotte individual phosphate testing kit (3114-01). Kits were not calibrate d with a standard. Samples were tested immediately to minimize biological conversion of the molecules. Water temperature was recorded using both an Extech Instruments Ex Stik II pH/Conductivity probe and an YSI
38 85 Oxygen Conductivity Salinity and Temperat ure probe. The pH of the water was measured using the Extech Instruments Ex Stik II pH/Conductivity probe. Salinity was taken using an YSI 85 Oxyge n Conductivity Salinity and Temperature probe. Rainfall was collected by monitoring a rain gauge (Fi gure 32 a-b) each time before entering the field. (a) (b) Figure 32 a-b. Rain gauge (a) and rain gauge location (b) on New College of Florida campus, Sarasota, FL (Google Maps 2012)
39 This gauge was located directly east of Pritzker Marine Scien ce Building, NCF, on the east stairway. Longshore current was estimated using observations of debris movement during the spring 2012. In fall 2012, the longshore current dir ection was estimated using a water-tight container filled about two-third with water releasing it to float about 20 meters away from the NCF Bay Front shorelin e. Statistical tests were not performed on abiotic data, but graphs were made. General observations were reco rded by taking photos.
40 Results OBSERVATIONS Some observations of note were made during the construction. They concern construction precautions, construction methods used near the restored area, longshore current directions, seagrass sp ecies distribution near NCF s eawall, sediment covering the seagrass near the restored area, stor mwater drain construction methods, lagoon construction methods, level of disturbance at Ringling and Caples, seagrass species distribution near Ringlin g and Caples, and sediment trap exposure. The contractor attempted to reduce the impact of th e construction on the local biota by putting up a turbidity curtain around 10-20 meters away from the seawall before construction started between January 12 and 14, 2012 (Figure 33-34 a-b). Figure 33. Turbidity curtain before it was pl aced in the water. Photo was taken January 12, 2012.
41 (a) (b) Figure 34 a-b. The turbidity curtain (arro ws) at low tide taken January 14, 2012. However, the turbidity curtain broke away sometime between March 7 and April 9, 2012 (Figure 35 a-b).
42 (a) (b) Figure 35 a-b. Aerials showing th e loosening of the turbidity curtain (arrows). (a) Secure turbidity curtain. Photo taken March 7, 2012. (b) Loose turbidity curtain. Photo taken April, 9, 2012 (Aeria l Innovations 2012) The curtain was removed sometime between May 9, 2012 and June 11, 2012 (Figure 36 a-b).
43 (a) (b) Figure 36 a-b. Disappearance of the turbidit y curtain (arrows) ad jacent to NCF main campus. (a) Last appearance of turbidity cu rtain. Photo taken May 9, 2012 (b) Absence of turbidity curtain. Photo taken J une 11, 2012 (Aerial Innovations 2012). In preparation for the modification of th e seawall, the construction company then dug up the area immediately seaward of the seawall. This was performed sometime between January 12th and 20th, 2012 (Figures 37 a-b and 38 a-b).
44 (a) (b) Figure 37 a-b. (a) The old NCF seawall to the so uth of the dock and the debris (arrow) on its seaward side. Photo was taken January 12, 2012 from on top of the old dock. (b) The restored seawall with an absence of debris (arrow) on the seaward side. Photo was taken January 6th, 2013 and taken from a similar angle to the previous photo.
45 (a) (b) Figure 38 a-b. (a) The debris (arrow) to the north of the dock conn ected to the old NCF seawall. This photo was taken January 12th, 2012. (b) Another photo taken from a similar angle to (a) eight da ys later on January 20th, 2012. The debris is no longer present (arrow). The longshore current of the area was extr apolated from the movement of floating debris (sea foam) during spring 2012 (3/12/ 2012) (Figure 39) and by observing a floating container in fall 2012 (11/19/12).
46 Figure 39. Sea foam (arrow) observed floating south to north at the NCF Bay Front on March 12, 2012. The longshore current was going S to N duri ng the spring during the first part of the study and was observed to be N to S during the following fall. The seawall restoration area was covered by transect points 11 through 18 and was mainly colonized by H. wrightii close to shore. Ar ound transects 14 through 18 (Figure 40-42), the process of removing the s eawall and replacing it from February to early May 2012 left behind a new layer of sand landward of the turbidity curtain.
47 Figure 40. Aerials of the NCF seawall restora tion. Before construction without sediment deposit (arrows). Photo taken 1/ 9/2012 (Aerial Innovations 2012). Figure 41. Aerials of the NCF seawall restora tion. Early during cons truction with turbid water (arrows) landward of the turbidity curtain. Photo ta ken February 13, 2012 (Aerial Innovations 2012).
48 Figure 42. Aerials of the NCF seawall restor ation. Late during c onstruction with new sediment deposit landward of the seawall (a rrows). Photo taken April 9, 2012 (Aerial Innovations 2012). The area was excavated on the landward side of the wall before the old wall was removed and the new wall placed. When the dock was removed around transects 14 and 15 in January 2012, the area was also made temporarily deeper. In the past, the area had been dredged to allow for boat traffic, creating a historic boat basin (2010 Preliminary Report). At 13, the construction of the new end to th e stormwater pipe (Figure 43) in May 2012 also created disturbance.
49 Figure 43. New stormwater drain exit (arro w) built May 2012. Photo taken January 6th, 2013. The seawall was completely removed from tr ansect 13 up to 11, wh ere boulders replaced the seawall. Whereas the restoration area of the New College of Florida Seawall had some noticeable disturbance, the lagoon ar ea (Figure 44 a-b) did not.
50 (a) (b) Figure 44 a-b. Preand postlagoon construc tion. (a) The old seawall (arrow). Photo taken January 20, 2012. (b) The old seawall af ter sections of th e length and the top portion were removed and capped. Photo taken January August 6th, 2013).
51 It was covered by transects 1 through 10 and was also mainly colonized by H. wrightii immediately seaward of the seawall. The construction in this area was minimal and primarily comprised of excavating the landwar d side of the seawall, removing the top portion of it and cu tting out portions. Adjacent to the Ringling Museum Seawa ll, there was little disturbance observed. Transects were labeled from 1 to 5 and the area adjacent to Ringling Museum was occupied by S. filiforme at the edge closes to the seawall. The seagrass adjacent to the Caples pr operty may have experienced disturbance. The NCF sail club occupies the south part of th e Caples property closest to the shoreline (Figures 45), so there is a lot of boat traffic in the area (Figure 46). Figure 45. Sail Club at the Caples property as in dicated by the red rectangle. Blue arrows indicate docked boats. Arrow labeled SWD designates the locati on of the exit of a stormwater drain. Satellite image was taken January 19, 2012 (Google Earth 2012)
52 Figure 46. Boat trailer tracks (a rrows) near the Caples shore line. Photo taken January 16, 2013. There is also a storm drain between the Ring ling Museum and Caples properties (Figure 45 and 47).
53 Figure 47. Location of the stormwater drain between the Caples and Ringling Museum property as seen from the Caples shoreline. Photo taken August 8th, 2012. There are some small patches of H. wrightii near the shore, but they are not very dense. The denser areas farther from shore were colonized mainly by S. filiforme Finally, it was observed that the NCF and Caples sediment traps were exposed often during the time of the study, particul arly during low tide (Figure 48 a-b).
54 (a) (b) Figure 48 a-b. Exposed sediment traps (arrows) at (a) NCF Bay Front and at (b) Caples. Photo taken October 16, 2012 and January 17, 2013, respectively.
55 TIME FRAME The main construction of the New College of Florida seawall occurred from mid January until late May, 2012. Data were taken from mid November to late May, and then from mid August to mid October, 2012 (Table V). Table V. Timeline of this study. Grey designates the timing of each activity. Timeline Nov '11 Dec '11 Jan '12 Feb '12 Mar '12 Apr '12 May '12 Jun '12 July '12 Aug '12 Sep '12 Oct '12 Construction Study Restoration Lagoon The construction started on the southern part of the seawall with the restoration and continued throughout the constr uction time period. The remova l of parts of the northern wall to finish the lagoon was star ted and completed in April 2012. SEAGRASS Halodule wrightii seagrass distances from shoreline showed a significant recession in the restored area when compared to the lagoon area (Figure 49-51) (Table VI).
56 Figure 49. NCF seawall in 2010; white arro ws are where the lagoon was created and black arrows show where the seaw all was restored (Google Earth 2012) Figure 50. Change in seagrass distance from shoreline. The red represents the preconstruction distance and the yellow repres ents the post-construction distance. The question marks represent lack of post data b ecause the seagrass coul d not be found within 30 meters of the shoreline. The area to the ri ght (south) in this aer ial shows the greatest difference in the seagrass distan ce post-construction (Google Earth 2012).
57 Median Seagrass Distance from Shoreline/Seawall Averages0 10 20 30 40 50 60 70 80 90 100 PrePost Time in Relation to Construction PeriodMedian Seagrass DIstance from Seawall/Shoreline + SE (m) NCF Restored NCF Lagoon Ringling Caples Figure 51. Difference in seagrass distance from coastline preand post-construction for all study locations. Table VI. NCF Seawall Seagrass Distance fr om Shoreline Statistics. Only Lagoon vs. Restored Seawall Data are Significant. Statistics Data Groups Test Results Prevs. Post-construction Wilc oxon signed-rank test S = 16.5, p = 0.4951 Lagoon vs. Restored Seawall Change Mann-Whitney test x2(1) = 4.9342, p = 0.0263 However, the post-construction seagrass m easurements along the entire NCF seawall were similar to the pre-construction ones. In comparison with the restoration c ontrol area (Ringling), the New College restored area showed a trend of recession after construction, but it was not significant (Table VII) (Fi gure 49-51).
58 Table VII. NCF Seawall Restored vs. Ri ngling (control) Seagrass Distance from Shoreline Statistics. No significance. Statistics Data Groups Test Result Prevs. Post-Construction NCF Restored Seawall Wilcoxon signed-rank test S = 12, p = 0.1094 Prevs. Post-Construction Ringling Seawall Wilcoxon signed-rank test S = 4.5, p = 0.3125 NCF Restored Seawall vs. Ringling Seawall Change Mann-Whitney test x2(1) = 3.0857, p = 0.0790 Preand post-construction data for the NCF re stored seawall were similar to each other. The Ringling data were also the same pre and post. The NCF restored seawall change was similar to that of Ringling da ta, but approached significance. The distances of the seagra ss in the NCF lagoon and Caples areas separately as well as between the two rema ined similar throughout the study period (Table VIII) (Figure 49-51). Table VIII. NCF Seawall Lagoon vs. Caples (c ontrol) Seagrass Distance from Shoreline Statistics. No significance. Statistics Data Groups Test Result Prevs. Post-Construction NCF Lagoon Seawall Wilcoxon signed-rank test S = 9.5, p = 0.3750 Prevs. Post-Construction Caples Seawall Wilcoxon signed-rank test S = 1, p = 0.75 NCF Lagoon Seawall vs. Caples Shoreline Change Mann-Whitney test x2(1) = 0.7143, p = 0.3980 Preand postconstruction NCF Bay Front lagoo n seagrass distances were similar. Preand postconstruction Caples seagrass dist ances were also similar. The lagoon and Caples distances were simila r preand post-construction. In terms of approximate area of seagrass lost, the seagrass near the restored section of the NCF seawall was damaged the most (Table IX).
59 Table IX. Approximate Amount of Seagrass Co verage Change between Preand PostConstruction (m2). Negative number indicates a decrease in coverage. Location NCF Seawall Total NCF Lagoon NCF Dock NCF Restored Seawall Ringling Caples (NCF) Seagrass Area Change (m2) -1,811.9 125 n/a -1,856 -43.2 110.8 The NCF lagoon, Ringling, and Caples seagrass changed only by small amounts, while the seagrass near the restor ed seawall lost over 1,000 m2. Not enough data were collected during the study to determine the amount of seagrass lost around the dock. SEDIMENT Sediment Trap (Large Grains: 1 to 4 phi) The rate of sediment collection for the NCF bay front rose slightly between the preand post-cons truction measuremen ts (Figure 52). Median Rate of Sediment Collection Over Time 0 2 4 6 8 10 12 Pre DuringPost Time in Relation to Construction PeriodMedian Rate of Sediment Collection + SE (g/day) NCF Bayfront Ringling Caples Figure 52. Rate of sediment collection over time in relation to the construction period and location. Standard error is shown.
60 The rate of sediment collection from th e controls followed a pattern of duringconstruction being the lowest, followed by pr e-construction and pos t-construction being the highest. The Caples data were always highest. Using Kruskal-Wallis ANOVA, the data showed that the sediment collection ra tes preand duringa nd post-construction at all three locations were similar (Table X). Table X. Sediment Collection Rates Statistics Statistics Data Factors Test Result Location (NCF Main Campus, Ringling, & Caples) vs. Time (Pre-, During-, and Post-Construction) Kruskal-Wallis ANOVA F(8,6) = 1.04, p = 0.4927 There were no interactions between lo cation and time using this analysis. No consistent rise in any grain size wa s seen in the NCF sediment in comparison to the control sediment (Figure 53 a-c).
61 (a) NCF Percentage Sediment Distribution by Phi Size 0.00% 5.00% 10.00% 15.00% 20.00% 25.00% 11.522.533.54 PhiPercentage Pre During Post (b) Ringling Percentage Sediment Distribution by Phi Size 0.00% 5.00% 10.00% 15.00% 20.00% 25.00% 30.00% 35.00% 40.00% 11.522.533.54 PhiPercentage Pre During Post (c) Caples Percentage Sediment Distribution by Phi Size 0.00% 10.00% 20.00% 30.00% 40.00% 50.00% 60.00% 11.522.533.54 PhiPercentage Pre During Post Figure 53 a-c. Rate of sediment collection ove r time for all three study locations in terms of phi. The distribution remains mostly constant over time for all locations.
62 The controls had larger proportions of sediment that were sized between 2.5 to 2 phi than the samples collection from the NCF seawall. All sediment larger than 1 phi was not included in the sediment grain size analysis. The percentage of sediment that was not included was unequally distributed th roughout the samples (Figure 54). Percentage of Sediment Larger Than 1 Phi0 10 20 30 40 50 60 70 80 90 100 PreDuringPost Time in Relation to Construction PeriodPercentage NCF Ringling Caples Figure 54. Percentage of sediment too large for grain size analysis. It was largest (70%) in the NCF during-construction data. When, considering the large grains (1 2 phi) for samples collected preand during-construction, only the sample collection rates from different locations and location vs. time were significantly different (Table XI).
63 Table XI. Sediment Collection Rate for Large Grains Preand Duri ng-Construction (1 2 phi). Location vs. Time, NCF Main Campus vs. Ringling, NCF Main Campus vs. Caples, and Ringling vs. Caples Data are Significant. Statistics Data Factors and Groups Test Result Location (NCF Main Campus, Ringling, & Caples) vs. Time (Pre& During-Construction) Kruskal-Wallis ANOVA F(5,12) = 16.56, p < .0001 Interaction Kruskal-Wallis ANOVA F(2,12) = 0.83, p = 0.4612 NCF Main Campus vs. Ringling Mann-Whitney test x2(1) = 6.5641, p = 0.0104 NCF Main Campus vs. Caples Mann-Whitney test x2(1) = 8.3077, p = 0.0039 Ringling vs. Caples Mann-Whitney test x2(1) = 6.5641, p = 0.0104 Prevs. DuringConstruction Mann-Whitney test x2(1) = 1.0312, p = 0.3099 Caples samples were much larger than the NCF samples with Ringling between the two. Preand during-construction sample rates were similar and there was no interaction overall between location and time. As with the preand duri ng-construction data, only lo cation was significant with the Caples and Ringling higher than NCF. Ringling and Caples rates were similar (Table XII).
64 Table XII. Sediment Collection Rate for Larg e Grains Preand Post-Construction (1 -2 Phi). NCF Main Campus vs. Ringling and NCF Main Campus vs. Caples Data are Significant Statistics Data Factors and Groups Test Result Location (NCF Main Campus, Ringling, & Caples) vs. Time (Pre& Post-Construction) Kruskal-Wallis ANOVA F(5,12) = 13.17, p = 0.0002 Interaction Kruskal-Wallis ANOVA F(2,12) = 1.94, p = 0.1866 NCF Main Campus vs. Ringling Mann-Whitney test x2(1) = 8.3077, p =0.0039 NCF Main Campus vs. Caples Mann-Whitney test x2(1) = 8.0377, p = 0.0039 Ringling vs. Caples Mann-Whitney test x2(1) = 2.0769, p = 0.1495 Prevs. Post-Construction Mann-Whitney test x2(1) = 1.2183, p = 0.2697 Preand post-construction sample rates were also similar and there was no interaction overall between location and time. Duringand post-construction, the sample collection rates we re significantly different between the NCF and Caples samples (Table XIII).
65 Table XIII. Sediment Collection Rate for La rge Grains Duringand Post-Construction (1 -2 phi). Location vs. Time, NCF Main Ca mpus vs. Caples, and Duringvs. PostConstruction Data are Significant Statistics Data Factors and Groups Test Result Location (NCF Main Campus, Ringling, & Caples) vs. Time (Duringvs. Post-Construction) Kruskal-Wallis ANOVA F(5,12) = 18.87, p < .0001 Interaction Kruskal-Wallis ANOVA F(2,12) = 2.30, p =0.1422 NCF Main Campus vs. Ringling Mann-Whitney test x2(1) = 4.3333, p = 0.0374 NCF Main Campus vs. Caples Mann-Whitney test x2(1) = 8.3077, p = 0.0039 Ringling vs. Caples Mann-Whitney test x2(1) = 0.9231, p = 0.3367 Duringvs. PostConstruction Mann-Whitney test x2(1) = 5.0702, p = 0.0243 Caples samples were higher than the NCF samples. The samples taken duringand postconstruction also showed signi ficant difference, with the pos t-construction samples being higher. There was no interaction overall, no significant difference between the sample rates of NCF vs. Ringling and Caples vs. Ringling, and no significant difference between the sample rates duringand post-construction. The small grain samples collection rates (> 3 phi) preand du ring-construction for all locations were similar (Table XIV).
66 Table XIV. Sediment Collection Rate for Sma ll Grains Preand During-Construction (>3 Phi). No significance. Statistics Data Factors and Groups Test Result Location (NCF Main Campus, Ringling, & Caples) vs. Time (Pre& During-Construction) Kruskal-Wallis ANOVA F(5,12) = 2.24, p = 0.1173 Interaction Kruskal-Wallis ANOVA F(2,12) = 0.10, p = 0.9023 Of the preand post-construction small grain samples, only the samples taken from NCF and Ringling were signi ficantly different (Table XV). Table XV. Sediment Collection Rate for Sma ll Grains Preand Post-Construction (>3 phi). Only NCF Main Campus vs. Ringling Data are Significant Statistics Data Factors and Groups Test Result Location (NCF Main Campus, Ringling, & Caples) vs. Time (Pre& Post-Construction) Kruskal-Wallis ANOVA F(5,12) = 4.41, p = 0.0164 Interaction Kruskal-Wallis ANOVA F(2,12) = 0.98, p = 0.4019 NCF Main Campus vs. Ringling Mann-Whitney test x2(1) = 6.5641, p = 0.0104 NCF Main Campus vs. Caples. Mann-Whitney test x2(1) = 5.0256, p = 0.0250 Ringling vs. Caples Mann-Whitney test x2(1) = 0.1026, p = 0.7488 Prevs. Post-Construction Mann-Whitney test x2(1) = 2.1228, p = 0.1451 Ringling was larger in rate than NCF. Ther e was no interaction, the sample rates of NCF vs. Caples and Ringling vs. Caples were sim ilar, and so were the rates preand postconstruction.
67 There was neither interaction nor pairwise significance between the sample rates of any of the three locations for the duringand post-construction small grains (Table XVI). Table XVI. Sediment Collection Rate for Sm all Grains Duringand Post-Construction (>3 phi). Duringvs. Post-Cons truction Data are Significant Statistics Data Factors and Groups Test Result Location (NCF Main Campus, Ringling, & Caples) vs. Time (Duringvs. PostConstruction) Kruskal-Wallis ANOVA F(5,12) = 7.29, p = 0.0024 Interaction Kruskal-Wallis ANOVA F(2,12) = 1.21, p = 0.3334 NCF Main Campus vs. Ringling Mann-Whitney test x2(1) = 3.1026, p = 0.0782 NCF Main Campus vs. Caples. Mann-Whitney test x2(1) = 4.3333, p = 0.0374 Ringling vs. Caples Mann-Whitney test x2(1) = 0.1026, p = 0.7488 Duringvs. PostConstruction Mann-Whitney test x2(1) = 6.7856, p = 0.0092 Duringand post-construction di d show significance in the pairwise comparisons, with post-construction being larger. Turbidity (Small Grains) The turbidity of all sites peaked in ear ly January and early September, 2012. Only the NCF area peaked around early-February, 2012 Only Caples peaked in late May, 2012. The lows for all sites were around mid-December, 2011, early January, and in midOctober, 2012. Only NCF was low late May, 2012. Both Caples and Ringling had a low in March, 2012. Turbidity was higher postthan pre-construction with the NCF Bayfront being the cloudiest, followed by Ring ling, then Caples (Figure 55).
68 Median Turbidity Over Time 0 2 4 6 8 10 12 PreDuringPost TimeMedian Turbidity + SE (NTU) NCF Bayfront Ringling Caples Figure 55. Turbidity relative to time and loca tion. There is a low for Ringling Museum and a high for Caples during-construction. NC F is similar to pre-construction value, although there was a large peak in turbidity during construction. Turbidity is overall higher after construction than before. ABIOTIC FACTORS Nutrients Phosphate and nitrate were below detect able levels throughou t the period of the study. The minimum detectable level for phos phate was 0.5 parts per million (ppm) and the minimum detectable level of nitrate was 2.5 ppm, respectively ( http://www.onlinepetdepot.com/... ; http://www.fieldandfacility.com/... ). Water Temperature Data collected on water temperature indica ted that there was a small peak towards the end of January, a larger one in Augus t and a low from November to January, excluding January 25 (Figure 56).
69 Median Water Temperature Over Time19 21 23 25 27 29 31 33 35 PreDuringPost Time in Relation to Construction PeriodMedian Water Temperature + SE (in degrees Celsius) NCF Bay Front Ringling Caples Figure 56. Water temperature over time. The te mperature is high af ter construction, but much lower the rest of the time. Data were always collected around low tide. Nine of the data points were taken 8-10 AM, 16 points were taken 10 AM-3 PM and three of the points were taken 5-6 PM. The average during the study was 23 degrees C. Water pH The pH of the water had highs in No vember and September (Figure 57).
70 Median pH Over Time6 6.5 7 7.5 8 8.5 9 9.5 PreDuringPostTime in Relation to Construction PeriodMedian pH + SE NCF Bay Front Ringling Caples Figure 57. pH over time for each location. There is a low during construction with a peak after construction for the NCF Bay Front. The Ringling and Caples data fit this pattern except that their low is in the pre-construc tion data. Data were always taken around low tide. Seven of the data points were taken around 8-10 AM, 13 of the points were collected 10 AM 3PM and, three points were taken 5-6 PM. The low was in December, but pH peaked in May. Ringling and Caples data were very close throughout the study. Aver age pH during the study was 7.64. Salinity Salinity shifted a great amount, with peaks in December, 2011 and May and October 2012 for Caples and Ringling (Figure 58).
71 Median Salinity Over Time28 30 32 34 36 38 40 PreDuringPost Time in Relation to Construction PeriodMedian Saliniy + SE (ppt) NCF Bay Front Ringling Caples Figure 58. Salinity over time for each location. There are multiple fluctuations. All data were taken around low tide. Eleven data poi nts were collected 8-10 AM, 13 points were collected 10AM-3PM, and three points were taken 5-6PM. The pattern at NCF was slightly different because it lacked a peak during May 2012. Lows occurred in early February and late A ugust. The average salinity for the duration of the study was 36 parts per thousand (ppt). Precipitation Rainfall had a peak in August with interm ittent periods of no to low rainfall the rest of the study period (Figure 59-60).
72 Median Rainfall Over Time0 2 4 6 8 10 12 14 PreDuringPostTime in Relation to Construction PeriodMedian Rainfall + SE (mm) Figure 59. Rainfall over time at Pritzker Labor atory. There is a spike in rainfall after construction with much lower rainfall the rest of the measured year. Figure 60. Location of rain gauge near Pritzker laboratory (arrow and circle) and east of the NCF seawall construc tion (Google Earth 2012).
73 ABIOTIC FACTORS SUMMARY Table XVIIa. Summary of Other Abiotic Factor s in Sarasota Bay dur ing the Study Period. Nitrate (g/l) Phosphate (g/l) Nitrogen (g/l) Phosphorus (g/l) Study Range Below detectable level 2,500 Below detectable level 500 Third-Party Range 26 10-30 250-550 50-225 Recommended Level Maximum 490 g/l Maximum 150 g/l Short Term Effect on Seagrass Fitness Fitness Fitness Fitness Time of High & Low (ThirdParty) High: April 12 & Aug 12 High: Jan 12 References ( http://www.onlin epetdepot.com/... ) ( http://www.saras ota.wateratlas.usf. edu/ /disclaimer.aspx ) ( http://www.field andfacility.com/... ) ( http://www.saras ota.wateratlas.usf. edu/ /disclaimer.aspx ) ( http://www .sarasota.wa teratlas.usf.e du/ /disclaimer. aspx ) ( http://www .sarasota.wa teratlas.usf.e du/ /disclaimer. aspx ) Possible Impact on seagrass? Unknown, but unlikely Unknown, but unlikely Unlikely Unlikely
74 Table XVIIb. Temperature (C) pH Salinity (ppt) Study Range 18.3-34 6.63-8.87 34.1-38.8 Third-Party Range 2-34 8.2-8.3 32.5-37 Good Level for H. wrightii 12-30 Best: 30 Resistant: 2-12 7.9-8.8 30-65 Short Term Effect on Seagrass Cover Fitness Fitness Time of High & Low (Study) High: Aug 12 Low: Dec 11 Feb 12 High: Sept-Oct 12; Low: Dec 11 High: April 12 Low: Sept 12 Time of High & Low (ThirdParty) High (Water): July-August 12 Low (Air): Dec 11 March 12 High: Nov 11 Jan 12 Low: May 12 July 12 High: Feb 12 Low: Nov 11 References (http://www.srh.noa a.gov/ )(Lee et al. 2007) (McMillan 1979) ( http://www.sarasota. wateratlas.usf.edu/ /disclaimer.aspx ) (Cho and May 2008) (Invers 1997) (Torquemada et al. 2005) ( http://www.sarasota.w ateratlas.usf.edu/ /disclaimer.aspx )(Mont ague and Ley 1993) (Koch et al. 2007) Possible Impact? Natural Seasonal Fluctuations Possibly Unlikely
75 Table XVIIc. Tide (ft) Precipitation (mm) Study Range 0-76 Third-Party Range -0.5 5 0-111.0 Good Level for H. wrightii 0-18 Short Term Effect on Seagrass Cover Fitness Time of High & Low (Study) High: Aug 12 Low: Nov 11 Time of High & Low (Third-Party) High: June Aug 12 Low: Jan Feb 12 High: Nov 11 Dec 11, Oct 12 Low: Jan 12 Feb 12) References ( http://www.sarasota.wate ratlas.usf.edu/ /disclaimer.aspx ) (Short et al. 2011) (Zieman and Zieman 1985) (http://www.srh.noaa.gov/ ) (Dillon and Chanton 2005) (Koch et al. 2007) Possible Impact? Natural Seasonal Fluctuation Natural Seasonal Fluctuations Table XVIId. Longshore Study May 12: South to North Nov 12: North to South Estimation Based on Third-Party Information Nov 11 Feb 12: South to North Feb12 Oct 12: North to South Best Direction for Minimizing Control Contamination South to North Short Term Effect on Seagrass Fitness References (Link 1996) ( http://www.cpc.ncep.noaa.gov/... ) (Climate Prediction Center/NCEP 2013) Possible Impact on Sediment Data? No
76 Discussion The working hypothesis of this study was th at construction of the New College of Florida seawall adjacent to the main campus would cover the seagrass with enough sediment to reduce coverage. As this is a pi lot study with an unre fined hypothesis, strong conclusions cannot be made. However, data i ndicate that the use of a turbidity curtain was a wise choice by the construction comp any. The hypothesis that the seagrass cover was reduced by the construction is not refute d by the data collected and estimations of changes in seagrass cover. Seagrass reced ed significantly, but only in the area most disturbed by construction and in comparison to the least disturbed construction area. It did not recede beyond the turbidity curtain. Ho wever, it is difficult to tell whether the turbidity and grain size data are influenced by construction sediment loading. In order to achieve a deeper understanding of the results, this discussion co mpares the results of this study with third-party information on dredgi ng, seagrass-sediment dynamics, local thirdparty turbidity data, and lo cal hurricane information. Research on dredging does not fail to refute the idea that the extensive construction disturbance that oc curred during this study affect ed seagrass cover. This is because the digging that occurred at the rest ored section of the NCF seawall was like dredging. In fact, seawall construction is known to impact water quality by altering sediment transport and suspending sediment and nutrients much like dredging (EPA 1999). Also like dredging, the digging that occurs during seawall construction is so damaging to seagrass that placement of turbidity curtain is recommended. Dredging, like the digging that occurred at the NCF seawall construction site, can destroy seagrass beds in more that one way. First, it directly damages the seagrass by
77 removing it and the sediment it is on fr om the seafloor and moving it elsewhere (Erftemeijer and Lewis 2006). Second, this rem oval disturbs the sediment nearby, which goes into suspension, reducing the amount of light that can get to the seagrass as well as burying the seagrass. Co lonizer species like H. wrightii the species whose coverage receded in this study, are not as resilient towa rds the effects of dredging as larger climax species (Short et al. 1993 ; Gallegos et al. 1994; Erftemeijer and Lewis 2006). The problem with dredging is so dire that it is now strongly recommended by the Florida Government that turbidity curtains be used every time dredging is performed in inland and protected waters (FFWCC 2003; PBS&J 2008). While seagrass beds were not dug up during this study, the H. wrightii near the construction site were exposed to disturbed sediment. There are numerous examples of dre dging in construction projects reducing seagrass cover. In Hong Kong, dredging a nd reclamation during airport construction threatened a population of Zostera nana shrinking it to 15% of its original size (Lee 1994). It is not known if a turbidity curtain was used in this example. Examples of seagrass damage from dredging are also found in Florida. In Biscayne Bay, FL, dredging a deep ship channel without a spoil curt ain was projected to destroy 5.4 acres of Thalassia testudinum 52.0 acres of Halodule wrightii and 24.1 acres of Halophila (Thorhaug 1987). The end result was so damagi ng to seagrass coverage that restoration was required by the Federal Government. In anot her project, dredging in order to place a pipeline through Lake Surprise in the Fl orida Keys destroyed approximately 20,000 m2 of seagrass beds (Derrenbacker and Lewis 1982) No turbidity curtain was used (Thorhaug 1983). In Sarasota Bay in particular, dredgi ng has also been known to cause seagrass
78 decline. Around the 1950s a nd 1960s, the Intracoastal Waterway (ICW) was dredged in the bay in order to maintain boat traffic in back-barrier waters (D avis and Zarillo 2003). Historically, maintenance dredging has occurr ed as needed since (Figure 61), but there has been debate as to whet her this should continue. Figure 61. Dredging history (red ) of the Gulf Intracoastal Waterway in Sarasota Bay and the bodies of water south of the bay (Antonini et al. 1999) Among other impacts to the ecosystem, mainte nance of the ICW has encouraged local seagrass decline (Estevez and Palmer 1990).
79 Thus, the idea that dredging and simila r construction activities cause seagrass cover to decrease due to sediment load ing and burial is already well-documented (Erftemeijer and Lewis 2006; EPA 1999). However, it is possible that there was an added interaction directly between the seagrass and settling sediment that caused seagrass loss in this study. Seagrass has two positive feedb acks in relation to sedi ment (de Boer 2007). This is because it has the ability to bring sediment out of suspension by slowing water currents. If there is a low amount of susp ended sediment, the seagrass can bring the sediment out of suspension with the benefit of increasing light availa bility. Conversely, if there is an elevated amount of suspended sedi ment, as in the case of this study landward of the turbidity curtain, the seag rass brings it out of suspension only to smother itself. It is possible that the seagrasses near the re stored NCF seawall smothered themselves, reducing the amount of sediment trave ling down the turbidity curtain to the comparatively unaffected lagoon area. These positive feedbacks are monitored in this study using two aspects of the sedimentation: the grain sizes of the settled sediment collected by the sediment traps (Youssef et al. 2008) and the turbidity level, which represents the sediment in suspension (de Boer 2007). Grain size analysis of settled sediment is relevant because when seagrass does encourage sediment to leave suspension, it a ffects small particles that would otherwise stay in suspension. Small sediment particles se ttle at slower current speeds than larger particles and seagrass slows the current enough to let the finer part icles settle (de Boer 2007). For example, in Queensland, Australia, finer sediment accumulated near Zostera capricorni in comparison with areas not dominated by this seagrass species (McKenzie 2007). Intertidal Zostera marina at the tidal flat Balgza nd in the western Wadden Sea
80 caused the silt fraction (<63 micr ometers) of the sediment nearby to increase while the sand fraction (63500 micrometers) decreased (Bos et al. 2007). Accumulation was high during the growing season and erosion occurred in winter. At 15 meter depth off Fenals Point near the northeast coast of Spain, Posidonia oceanica consistently took finer particles (<10 micrometers) out of suspension more than la rger particles in comparison with barren sand (Granata et al. 2001). This trend was tr ue for both low-energy and highenergy scenarios. However, th e seagrass monitored near th e construction in this study, Halodule wrightii is restricted in its growth because it grows in an intertidal area and is exposed to the air frequently during low tid e (Zieman and Zieman 1985). It is possible that because of its diminished leaf size, it is incapable of bringing small grains out of suspension like the other species. This may explain why there seems to be no relative increase in small grains during construction at the NCF site. Unlike with small grains, seagrass does not selectively bring large sediment grains out of suspension. Nonetheless, large grains can also play a part in causing seagrass recession. Large grains fall to the seabed more readily than smaller grains, because they do not need the water to be as slow (de Bo er 2007). The soil of Sarasota is extremely sandy and sand is the larger sediment type considered in this study (Wildermuth and Powell 1959). The fact that NCF land was briefly exposed to Sarasota Bay during construction means that some of the sand that is usually landward of the seawall may have gotten seaward of the seawall during c onstruction. However, the large grain data do not reflect this. As with the grain size data, data collec ted on turbidity in this study and from a local third-party source do not complete ly correspond with the hypothesis. While
81 turbidity was observed to have increased insi de the turbidity curtain during construction, measurements unexpectedly showed an increas e outside the curtain as well. The nutrient levels were low during the study ( http://www.sarasota.wateratlas.usf.edu/ /disclaimer.aspx ), so they are ruled out as a cause for eutrophication (Cloern 2001) and turbidity increase (Tomasko et al. 2005). This may mean that some sediment in the water column escaped the turbidity curtain. On the other hand, turbidity measurements from the side of Sarasota Bay (Figure 62) opposite the construction (Figur e 63) also show an increase in turbidity when the majority of construction occurred during February to May 2012. Figure 62. Turbidity data for the January 2011 to October 2012 ( http://www.sarasota.wateratlas.usf.edu/ /disclaimer.aspx )
82 Figure 63. Source of turbidity data, Station (7-1) ( http://www.sarasota.wateratlas.usf.edu/ /disclaimer.aspx ) As the prevailing wind in the area was eastward during the ti me of the study (Figures 6465), it is unlikely that turbidity from the NC F construction traversed to the western side of Sarasota Bay. Figure 64. Wind data near Station 7-1. Most of the wind is going in an eastern direction ( http://www.wunderground.com/... )
83 Figure 65. Source of wind data at Weather Station KillongB2 ( http://www.wunderground.com/... ) So it is possible that turbidity increased in the bay for some other reason such as the movement of the turbidity curt ain. Fortunately, if sediment did escape from the turbidity curtain, it probably did not have a large eff ect on the data in this study. The turbidity measurements taken during this study never exceeded 17 NTU and H. wrightii seagrass has been observed to be able to tolerate tu rbidity values fluctua ting between 0 and 30 NTU without a large loss in cover (Cho and May 2008). Finally, it is necessary to expound upon hu rricane activity around the time and place of this study because hurricanes can have a large effect on seagrass and sediment (Whitfield et al. 2002). It is not certain whether they influe nced this studys results, but two hurricanes were near Sarasota Bay around the time of the study. In June, 2012, the area was directly hit by Tropical Storm Debby ( http://www.nhc.noaa.gov/... ). This event did not seem to impact any of the seag rass significantly, as all the preand postconstruction seagrass locations were similar except in the case of the seagrass near the
84 restored section of the seawa ll. Hurricane Irene (Category 3) grazed the eastern side of the Florida coast in August, 2011. The data collected during this study do not indicate how much this hurricane influenced the seagrass in Sarasota Bay. CONCLUSION Thus, considering all the data and its relationship to othe r scientific literature, it looks like the sediment disturbed by the s eawall construction prim arily affected the seagrass adjacent to the most disturbed c onstruction area in a way similar to how dredging affects seagrass. The tu rbidity curtain that was placed at the edge of the seagrass before construction began appears to have been effective at mitigating constructionrelated sediment loading and its impact on seagrass coverage like it was designed to do. However, the uncertainty in the results shows that there is room for improvement in this studys methods. For example, the seagrass monitoring method was not very sensitive to fluctuations in the health of the seagrass, only to gross changes in distribution. Also, quantitative sediment-loading da ta were not taken landward of the turbidity curtain. As this is a pilot study and is in no way c onclusive, further research would need to be done in order to discern the impact of se diment disturbed by seawall construction on seagrass. The next step would be to conti nue to investigate th e effects of coastal construction on seagrass cover and sedime ntation while improving upon the weaknesses of this study. Some suggestions include usi ng satellite images, rea ssessing the sediment collected during this study, and studying how the new NCF seawall modifies sediment transport patterns. As direct study of the changes in seag rass cover preand du ring-construction is no longer possible, satellite images can be used instead to study the recovery of the NCF
85 main campus seagrass long term and over a great range of di stance. After all, H. wrightii has been documented to take three years to recover after dredging damage (Erftemeijer and Lewis 2006). However, the researcher must pay attention to details because there are many problems with using satellite images. Aeri als and satellite images that are available for free of Sarasota County are only provide d about once per year and it is difficult to determine exactly when they were taken (SC 2012; Google Earth 2012). Additional research on the construction sedimentation could be accomplished by conducting a fine grain analysis on the sediment that was co llected during the study. The sediment grain sizes that were assessed in this study were from 1 to 4 phi, so the finer sediments less than 4 phi were not measure d. Sediments smaller than 4 phi are in the range that tend to be selectiv ely brought out of suspension by seagrass (Bos et al. 2007; Granata et al. 2001). The sediment collected shou ld be reassessed to see if there was any significant difference in the fine sediment during-construction as opposed to any other time data were collected. The construction of the NCF lagoon also presents an interesting research opportunity. Seawalls are known to modify se diment transport patterns, causing erosion (Duarte et al. 2004). This has become such a problem in Sarasota County that legislators made it virtually impossible to build a ne w seawall in 2008 (Sword 2008). It may be advantageous to study this effect in the ne wly constructed disconti nuous seawall near the new NCF lagoon. It is in an interesting position where it is surrounded by natural shoreline to the north and s eawalls to the south. The lagoon area could be compared to areas that have non-continuous seawalls su rrounded by seawalls and other seawalls
86 surrounded by natural shoreline in order to figu re out if the status of the area surrounding the seawall in question has any impact on erosion.
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