ENVIRONMENTAL IMPACTS OF

PORTS ON FLORIDA EAST COAST

INDIAN RIVER LAGOON, FLORIDA

AN EXECUTIVE SUMMARY

 

Author: Hugo Thouverez

Advisor:  Dr. John G. Windsor Jr.

 

 

Sponsored by: The Saint Lucie Waterfront Council and

Marine Resources Council of East Florida

 

April 2000

 

 

 

INTRODUCTION

           

           

            This report, is a scientific literature survey of more than 200 studies that have considered the impacts of shipping and port activities on the environment worldwide.  The results of these studies show that port activities, port development and shipping activities impact coastal environments in both a positive and negative fashion.  In this report, special attention is focused on the Indian River Lagoon, the Port of Fort Pierce, and Port Canaveral.

  A major goal of this report is to determine what are the major impacts from shipping and ports activities on the Indian River Lagoon. Major impacts of concern include the introduction of exotic species and the production of turbidity. It is well known that environmental impacts can have profound long-term economic effects, although analysis and quantification of such effects is beyond the scope of this study which focuses on the analysis of environmental events.  It is sufficient to note that policy decisions concerning predictably destructive development should be based on a measured understanding of what economic interests are being preferred over others and at what cost.

 

 

1. FROM DREDGING 

                                   

Impacts of dredging are very broad and occur not only on the dredged site but also on the adjacent site. 

·       Dredging can destroy the benthic ecosystem (Al Hashmi et al, 1997) if the bottom is colonized by organisms.  Usually a benthic ecosystem has limited diversity because such places have been dredged before and are deep (waterways, entrance channels, turning basins): sufficient amount of light cannot reach the submerged aquatic vegetation (SAV).

·       Dredging generates suspended sediments that increase turbidity.  As a result, light penetration on-site and off-site would be reduced producing stress for the SAV.  The magnitude of the impacts on SAV depends on the duration and intensity of the dredging and on the SAV itself.  Seagrasses require more light than macroalgaes and some seagrasses require more light than others (Gilmore and Hanisak, 1991).      

·       Suspended sediments harm benthic organisms by settling onto them (Newcombe and MacDonald, 1991).  If the right dredging technique is not used, blanketing of organisms occur causing various effects: choking of filtering organisms, smothering of aquatic vegetation, and smothering of coral reefs.

           

Dredged material can be disposed of at sea on regulated sites as long it does not pose a threat of mortality to organisms.  Discharge can occur at regulated sites (Offshore Dredged Material Disposal Sites).   However, it has been documented that re-suspended spoil in the form of fine clay particles can be transported large distances if currents in the area are strong enough  (Vann, 1995).  At Port Canaveral, the mud from the dredge spoil dump site has spread over an area of 360 square miles (Vann, 1995). 

If 6 to 10% of the dredged material, (as found by Vann, 1995) spread outside the disposal site, it could represent a significant area of coverage.  If this 6 to 10% of the dredged material formed a layer of similar thickness as to that formed in Port Canaveral (0.65 millimeter thick) between 41.6 Km² (16 mi²) and 69.4 Km² (26.8 mi²) of reef area could have been covered in the Fort Pierce area.

Dredged material experiences in Port Canaveral and in Fort Pierce suggest that dispersion of dredged material occurs when strong currents transport the fine particles away from the regulated disposal site (EPA, 1997).  Sediment dispersal not only occurs during the actual discharge of material, but also sediment is transported by water when the pile of dredged sediments is exposed to bottom currents.  Indeed, newly deposited sediments are much more easily resuspendable than native bottom sediments (Schoellamer, 1996; Onuf, 1994).

 

 

 

 

 

2.   FROM THE PROPELLER ACTION

 

            A major concern associated with ship traffic is the flow induced by the propeller of the ship (McMahon, 1989; Osborne and Boak, 1999; Sawicki et al, 1998; Schoellhamer, 1996; Ebbesmeyer et al 1995).  The rotation of the propeller will pulse water at a higher speed than surrounding waters resulting in the formation of turbulence in the water column (Figure 2.4).  Such turbulence is able to resuspend bottom sediment in the water column (EPA 1974; Paulson and Da Costa, 1991). 

According to Ebbesmeyer et al (1995) maneuvering vessels may be a significant factor in sediment resuspension and transport in ports.  Ebbesmeyer et al (1995) measured currents generated by the propellers of various vessels along the Seattle waterfront (Table 2.5).  The magnitude of this flow is proportional with the diameter of the propeller and its speed.  Some propeller-induced flows can reach a speed of 136 cm/s (3 mph) and have a mixing action up to 153 meters (502 feet) behind the propeller of a cruise vessel. The values of the currents generated by these vessels are much higher than tidal current values.  In the Seattle area threshold velocities for silt resuspension by tidal currents is 25 cm/sec (0.56 mph) and tidal currents on the Seattle waterfront do not exceed 5-10 cm/sec (0.11-0.22 mph) (Ebbesmeyer et al, 1995).  Such values demonstrate that maneuvering vessels are a significant factor in sediment resuspension and transport.

Figure 2.4.  Conceptual model of flow induced by a propeller.  Aft of a propeller having diameter D_p, the flow develops in three stages: 1) within a distance equaling approximately 0.5 D_p, velocity vectors are uniform over the propeller’s depth range; 2) between distances of 0.5 to 2.7 D_p, the uniform velocity zone entrains surrounding fluid by turbulence represented by circular velocity vectors; and 3) established flow in which the velocity profile with depth is a gaussian distribution (Ebbesmeyer et al, 1995).

 

A study conducted by the U.S. Geological Survey (1995) measured the total suspended solids generated by propellers of a cruise ship entering and exiting the Port of St. Petersburg, Florida.  The draft of the ship was 5.1 meters (17 feet) and the average depth of the port was 6.7 meters (22 feet). 

            The study revealed that more particles were resuspended during the ship’s arrival than during its departure.  During the departure, two tugboats were used to swing the bow into position for the cruise ship to leave the port.  The USGS (1995) noted: “normally, the tugboats are not used, but at that time, the side thrusters of the cruise ship were not operating.”

            Resuspension of sediments was observed, caused by the propeller wash during both arrival and departure (Figure 3.2).  During departure, maximum resuspended solid concentrations were observed 20 minutes after the beginning of the movement and was about 130 mg/liter at a depth of 3 meters (10 feet) (background level was 21 mg/liter).  Measurements were done on the path of the ship.  During arrival, maximum turbidity was 250 mg/liter at a depth of 3 meters (10 feet), on the path of the ship.  The cruise ship resuspended more sediments during its arrival because the vessel reversed its propellers to slow down, turn around, and dock at the terminal.  For arrival and departure, the time to return to background levels was two hours.

This study shows that large vessels resuspend sediments when entering and exiting ports.  The lack of strong tidal currents and the lack of large waves in the study area caused rapid settling of resuspended sediments (less than 2 hours).  Other studies clearly show that vessels are responsible for sediment resuspension through the jet produced by their propellers (Michelsen et al., 1998; Verhey, 1987; Fuehrer et al, 1987).

Such experimental study results are verified by personal experiences of people related to the Lagoon by their profession.  Divers, fishermen, tropical fish collectors experiences in and nearby Key West Harbor have been reported in the Miami Herald Tribune (April 1999).

 

 Figure 3.2.  Total Suspended Solids generated by the propeller wash of a vessel (draft of 17 feet) in the Port of St. Petersburg, Florida, during departure and arrival (US Geological Survey, 1993).

 

 

3. FROM THE GENERATED WAVE

 

Sediments resuspended by VGW, and newly deposited, are more susceptible to be resuspended by tidal currents than undisturbed bottom sediments (Schoellhamer, 1996).  The same author has calculated that for VGW, assuming 0.7 waves per day that increase suspended solids concentration 50 mg.l^-1 in one-quarter of Hillsborough Bay (Tampa Bay), the annual mass of resuspended sediments is 1*10⁹ kg.  Also, Schoellhamer has noticed: “when relatively large (9-14 cm.s^-1) tidal currents were present, resuspended sediments remained in suspension for about 2 hours.” Therefore, considering the potential amount of sediments to be suspended by VGW and their capability to remain 2 hours in suspension (caused by tidal currents), SAVs could be impacted by turbidity.

            By using Schoellamer’s formula and assumptions, we can find a relationship between ship traffic and total mass of sediment resuspended in a bay or estuary during a period of time.  We can not predict the exact amount of suspended sediments a single ship will generate but we can assume the annual mass of resuspended sediments in shallow waters by knowing: (1) the number of waves per day that resuspend sediments; frequency of traffic and vessels that generate waves that resuspend sediments (beam, draft, speed of the ship, depth of the channel, width of the channel); (2)  the volume of the Bay or estuary; (3) the proportion of the bay or estuary where long waves that resuspend sediments are generated and, (4) by assuming that suspended solids will increase by 50 mg.l^-1.  Table 3.5 summarizes the amount of turbidity generated by dredging, dredged material disposal, propeller wash, and vessel-generated waves.

 

Table 3.5 Anthropogenic activities related to shipping that produce turbidity, the amount of turbidity generated and time to return to background levels after perturbation.

Anthropogenic activity	Percentage of the volume dredged (1) or disposed of (2)	Generated suspended solids concentration (mg/l)	Time to return to background level
Dredging	4%1; 5%2 (1)	0 to 5301	1.5 hour1
Dredged material disposal	6%3; 10%3 (2)
Propeller wash		1304 (departure of ship) 2504 (arrival of ship)	Less than 2 hours4
Vessel-generated wave		505 (by one generated wave)	2 hours5

¹ Pennekamp et al, 1996.

² Priestley, 1994.

³ Vann, 1995.

⁴ US. Geological Survey, 1995.  Measures are for depths of 10 feet.  Background TSS levels were 20 mg/l.

⁵ Schoellhamer, 1996.

 

 

 

 

 

 

 

 

 

           

            Maturo and Caldwell (1981) compared the effects of meteorological events and man-induced turbidity on seagrass beds net productivity (Table 3.6).  Severe early in the day thunderstorms were shown to cause the greatest reduction in net productivity (44.7% reduction of the daily total production) whereas dredging without a curtain and dredging with a curtain respectively, were reducing the net productivity by 11.2% and 8.4%.  This study showed that dredging impacted seagrass productivity less than early thunderstorms. 

The same study reveals that impact of dredging on seagrasses is maximum if conducted during the time of the day when photosynthetic rates are the highest due to the maximum light incidence on  seagrasses.

            Turbidity generated by dredging activities (dredging, dredged material disposal), and shipping (vessel-generated waves and propeller wash) can be considered to have short impacts (less than 2 hours to return to background levels. However, fine material like muck, once in the water column can remained resuspended up to weeks due to wind-generated turbulence). These impacts are also local in nature provided there is no strong current when the turbidity is generated (Onuf, 1994).  The same author noted: “seagrasses must tolerate periods of at least several days of reduced light, because periods of naturally occurring low light during storms and dense cloud cover are that long.” In other words, if anthropogenic ‘turbidity production’ match natural occurring events, damage occurring to seagrasses would be minimized.

 

Table 3.6.  Effect of different shading effects on the primary productivity of seagrass beds (Thalassia testudinum as the dominant species, and patches of Halodule wrightii and Syringodium filiformis) (Maturo and Caldwell, 1981).

Event	Reduction in net primary productivity (%)
Thunderstorm, severe early in the day	74.6
Dredge without curtain	46.4
Thunderstorm, severe late in the day	40.1
Rain	33.8
Normal thunderstorm	29.9
Tug plume	27.7
Dredging with curtain	27.6
Scattered clouds	27.6
Short thunderstorm	17.6
Distant thunderstorm	12.1

 

            In the same report, Onuf (1994) linked the turbidity generated by the dredging of the Laguna Madre, Texas, to the loss of over 150 Km² (58 square miles) of seagrasses of laguna bottom.  The initial dredging was shown to have short term effects (Table 3.5), but materials that were dredged and redeposited were easier to resuspend than surface materials of the native bottom (Schoellamer, 1996) (Onuf, 1994).  Thus a critical turbidity problem associated with dredging is the disposal of the dredged material nearby sensitive ecosystems (seagrasses, coral reefs): the newly deposited material will act as a source of turbidity as soon as it is acted upon by waves or currents (during storms, hurricanes, tidal currents, or wind generated waves).  Seagrasses will then be exposed to turbidity as long as the pile of dredged material is not fully eroded or stabilized.  Turbidity generated by propeller’s shear and the generated waves of just one vessel has a short life span (Table 3.5) and will not impact seagrasses.  In contrast, if vessel traffic is constant, seagrasses will be impacted if the turbidity reaches the seagrass beds.

              Goldsborough and Kemp (1988) reported: “such plants (seagrasses) subjected to decreased light penetration will grow higher into the water column, resulting in a structurally weaker plant which is more susceptible to breakage).  Reproduction has also been shown to be inhibited in SAV exposed to low light conditions.  Goldsborough and Kemp (1988) also noted: “propagule abundance (tubers) was directly proportional to light intensity and that under low light conditions (11% ambient) there was a significant reduction in abundance.” Experiences realized by Tomasko (1992) on the seagrasses Posidonia spp showed that a reduction of 50% of available light to the plant had reduced the productivity of the seagrass beds by about 80% in nine months.  He then noted : “during the first three months, no decrease in the standing crop has been observed showing that seagrasses were adapted to light reduction.”

            Seagrasses are naturally able to withstand periods of shading (cloud cover, natural events-generated turbidity).  The question is ‘are they more able to withstand  100% reduction of available light for a short period of time or a 10% light reduction for a longer period of time’.  According to Ruffin (1998), it is the duration of light inhibition that will determine whether longer-term SAV growth is affected because estuarine plants and animals are adapted to intermittent events of high turbidity/low light.  Therefore, a total suppression of light for a short period will impact seagrasses less than a slight light reduction for a longer period of time.

            Regarding the specific case of the IRL, impacts from shipping will be restricted to ports.  Port Canaveral being a closed basin (connected to the IRL by only one lock), there is no risk of impacts on the IRL seagrasses.  However, the port of Fort Pierce is in the IRL and is located next to an extensive seagrass bed (Jim Island seagrass beds) that could be jeopardized if ship traffic were to increase.

 

 

 

To maintain their trim, big vessels use containers that can be filled with water or oil.  Intake of water and release of ‘foreign waters’ generally take place in the seaport itself, even if such practice is prohibited in the port by international regulations.  These operations are responsible for the introduction of exotic species (The Chesapeake Bay Commission and Ballast Water, 1995) and viruses from other ports throughout the world (McCarthy and Khambaty, 1994).  Table 2.11 shows examples of introduction of exotic species to an area from other parts of the world.

            The IRL may already have received exotic species from ballast water.  One species which may have originated from ballast water discharge into the IRL is the dinoflagellate Gymnodinium pulchellum.  Steidinger et al (1998) noted: “fish and invertebrate kills were reported from September to October 1996 in the IRL, coincident with blooms of the dinoflagellate Gymnodinium pulchellum).” Fish and invertebrate species affected included: common snook (Centropomus undecimalis), striped mullet (Mugil cephalus), hardhead catfish (Arius felis), red drum (Sciaenops ocellatus), sheeps head (Arcosargus probatocephalus), black drum (Pogonias cromis), blue crab (Callinectes sapidus), and shrimp (Penaeus spp).  Fish kills caused by Gymnodinium pulchellum have also occurred in Japan and Australia.

            In Tampa Bay, a new species the Asian Green Mussel, has been observed (Pittman, 1999).  Native to the Indian and Pacific oceans, the mussel is thought to have traveled to Florida in the ballast water of a bulk cargo ship.  A 1995 study in Chesapeake Bay showed that the two ports of Norfolk and Baltimore received 9,325,000 and 2,834,000 metric tons of foreign ballast water per year, respectively (The Chesapeake Bay Commission and Ballast Water, 1995).  Another study for the same commission has revealed that more than 90% of the 70 vessels arriving in Chesapeake Bay ports each year carry live organisms in the ballast water, including barnacles, clams, mussels, copepods, diatoms, and juvenile fish.

The Chesapeake Bay Commission (1995) reported: “the U.S. Fish and Wildlife Service (1993) determined that non-indigenous species significantly contributed to the listing of 160 native species as endangered or threatened under the Endangered Species Act.” Exotic species can compete and displace indigenous species.  In the Great Lakes and San Francisco Bay, non-indigenous bivalve species (the zebra mussel and an Asian clam) are replacing other benthic organisms and eliminating plankton communities that provide food and larvae for local aquatic populations from overlaying waters (The Chesapeake Bay Commission, 1995). The overall result is an elimination of the basis of food chain and a threat to the ecosystem.

In addition to ecological effects, non-indigenous species invasion can have adverse economic and social impacts.  The Commission (1995) reported: “for the zebra mussel alone, the U.S. Congress estimated that nationwide, costs will exceed $3 billion over the next decade to prevent clogging of municipal and industrial water supply systems.”

So far the IRL has had limited exposure to foreign ballast water discharge because Port Canaveral is almost isolated from the IRL (connected only by a lock) and the Port of Fort Pierce has a very low vessel traffic.  However, if the expansion of the Port of Fort Pierce were to occur, more vessels would enter the Lagoon.  Unlike Port Canaveral the Port of Fort Pierce is completely within the Lagoon with no locks or structures to isolate it from the rest of the Lagoon.  Therefore, the amount of discharged ballast water would increase as well as the risk of exotic species invasion. Theoretically, the amount of exotic organisms in ballast water could be reduced by a set of operations such as microfiltration during ballasting, selectivity in location of ballasting, reballasting at sea, sterilization in transit (chemicals, biocides, ozone, oxygen deprivation, filtration, UV, heat) (Hayes, 1998).  Such practices however do not occur because of the lack of regulations and the difficulties of enforcement.