ABSTRACT
There have been many efforts to plant salt-marsh grass to trap suspended sediments and reduce coastal erosion� These are generally successful where plants can be protected against erosion from storm waves before they are fully established, but fail in many places where storms erode them before they are deeply rooted� Methods that accelerate their growth rates, densities, root growth, overwinter survival, and ability to grow deeper in the intertidal, seaward of the normal lower limit,
CONTENTS
Introduction ������������������������������������������������������������������������������������������������������������������������������������ 169 Site History ������������������������������������������������������������������������������������������������������������������������������������ 170 Spartina Ecology and Physiology �������������������������������������������������������������������������������������������������� 170 Pollution Effects ����������������������������������������������������������������������������������������������������������������������������� 171 Methods ����������������������������������������������������������������������������������������������������������������������������������������� 173 Results �������������������������������������������������������������������������������������������������������������������������������������������� 175 Extreme Stress Site ������������������������������������������������������������������������������������������������������������������������ 176 Discussion �������������������������������������������������������������������������������������������������������������������������������������� 177 Conclusions ������������������������������������������������������������������������������������������������������������������������������������ 177 References �������������������������������������������������������������������������������������������������������������������������������������� 178
would greatly aid those efforts� Here, we demonstrate for the first time a new method that enhances growth rates and survivorship�
SITE HISTORY
College Point is located in Queens, New York, on Long Island Sound next to Flushing Bay, near where the East River connects to New York Harbor� The bay was an important source of food for the Matinecock and Lenape Native Americans and early European settlers, providing abundant fish, shellfish, and waterfowl until the early nineteenth century (Waldman 1999; Kurlansky 2006)� Spartina salt marshes provide food and shelter for many species, including oysters, mussels, crabs, fish, and birds, maintaining biodiversity� Spartina spp� inhabit the same ecosystem as economically valued mussels (Mytilus edulis) and American oyster, Crassostrea virginica�
After the civil war, the area surrounding the bay became a waterfront resort for the wealthy and then for industrial development, including shipyards� By 1900, it had become a degraded and polluted ecosystem with few living organisms in the coastal zones� In the early 1950s and 1960s, it was a dumping ground for incoming ships to dispose of wastes as they entered New York Harbor� Pollution caused major die-off of marine plants and shellfish along most New York coastlines� S. alterniflora is native to New York City; however, it has become rare except in Jamaica Bay� With water quality restoration efforts, in particular the construction of a sewage treatment plant in Flushing in 1977, Spartina are now starting to recover in College Point and Flushing Bay (https:// www�dec�ny�gov/lands/5489�html)�
The New York State Department of Environmental Conservation Tidal Wetlands Program was established to protect wetlands under the Tidal Wetlands Act (Article 25 of the Environmental Conservation Law)� Marine intertidal wetlands trend analyses have been conducted by the New York State Department of Environmental Conservation for the past 20 years, with an emphasis toward mitigation and restoration of intertidal coasts in New York City� We chose this intertidal wetland location for its variety of pollutant runoff� One end of the intertidal zone is a NYC Park (Herman McNeill Park), and the other was an illegal landfill that has recently been converted into a residential development� This development is itself adjacent to a State Superfund site that has yet to be remediated� It was declared a Superfund site by the Department of Environmental Conservation after pollutants were found (https://www�nytimes�com/2011/10/23/realestate/college-point-queensliving-in-attention-shore-lovers�html?pagewanted = all)�
McNeill Park remains in good environmental condition, but the landfill under the new residential development has been shown to leach dangerous HAZMAT chemicals like polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), hydrocarbons, and solid waste trace metals such as mercury, cadmium, and lead� While Spartina has begun to regenerate in front of McNeill Park, there has been no natural recovery in front of the former dump site�
Although preliminary (builder and state) cleanup was somewhat successful, our research group conducted chemical tests in soil samples along the coast of the development that still show “fingerprint” signatures of high concentrations of hazardous materials� No Spartina grows naturally along the severely contaminated shoreline of the development� The Resource Conservation and Recovery Act (RCRA), enacted in 1976, is the principal federal law in the United States that governs the disposal of solid wastes and hazardous wastes�
SPARTINA ECOLOGY AND PHYSIOLOGY
Spartina and other intertidal marine plants are photosynthetic autotrophs that convert carbon dioxide into organic compounds, most notably sugars, using adenosine triphosphate energy made from sunlight� S. alterniflora is a perennial grass commonly found in intertidal wetlands and salt
marshes: it dominates coastal salt marshes along low-wave-energy coasts in mid and high latitudes� Its distribution is affected by inundation periods, controlled by elevation in the intertidal zone, that affect the salt, temperature, and nutrient balance (Brown et al� 2006; Kamel et al� 2009), and by wave energy�
Intertidal marine plants benefit the ecosystem because of their ecological interactions with many marine organisms such as mussels, oysters, fish, crabs, and shore birds (Chung et al� 2004)� Mussels help hold Spartina plants in place during tidal surges and intense wave energy� Marine plants also play a significant role in the coastal carbon and nitrogen cycles� Reintroducing mussels and oysters simultaneously prevents oxygen deficiency in the rooting zone, which occurs in polluted degraded intertidal sites that are not restored (Drew 1997)� Loss of shellfish leads to poor sediment retention after rain or tidal fluctuations, causing depressed growth and yield�
We have tested whether low-voltage direct current electrical stimulus can protect and help accelerate restoration of Spartina in severely stressed urban intertidal zones�
POLLUTION EFFECTS
This wetland restoration experimental site is next to a former landfill and US Navy shipyard (Figures 15�1 and 15�2) and has experienced high amounts of pollution from PCBs, PAHs, hydrocarbons, and other RCRA hazardous metals from previous industrial use and illegal dumping (https:// www�queenstribune�com/deadline/TideTurnsToxicOnCollegePoi�html; https://www�queenstribune �com/feature/WhatLiesBeneathScientistsa�html)�
Sediments at the site where our experimental Spartina plots were planted at College Point have been polluted by heavy metals such as copper, zinc, mercury, and lead from the seeps draining the former dump (Figure 15�3)� S. alterniflora has a low tolerance for highly concentrated toxins in the sediment, such as sulfur, PCBs, and copper (Burke et al� 2000; Mateos-Naranjo et al� 2008)�
Due to past losses of salt marsh, it is important to increase Spartina biomass to restore biodiversity and improve water quality through the filtering action of salt marsh plants and shellfish� Increasing Spartina biomass will increase mussels and other shellfish, which will increase fish and birds, helping restore a healthy marine ecosystem� The roots of Spartina are also deep enough to
maintain costal shorelines by preventing sediment erosion in the winter� Marine plants, specifically Spartina, are also linked to controlling low levels of metal pollution�
Mateos-Naranjo et al� (2008) designed an experiment to test the effect that copper has on photosynthesis and growth of Spartina densiflora. Spartina resisted high concentrations because its roots acted as a “barrier” to copper uptake� The leaf concentration hardly increased when the external concentration exceeded 9 mM of copper during these experiments, but copper and other metals were found to be highly toxic to plants in amounts exceeding 9 mM� Copper reduces plant growth by reducing photosynthetic and respiratory activities of most plants� Exposure of high and lethal concentrations
of copper and other metals to plants may lead to chlorosis� Fortunately, Spartina has high tolerance to heavy metals due to its ability to control excessive ion transport into leaves and sequester them in tissues or cellular compartments; therefore, the species has not completely died off, even in severely contaminated areas� Additionally, there was a rise in nitrogen concentration at the highest copper concentration tested, 9 mM� Copper levels over 9 mM can inhibit the uptake efficiency of water, calcium, magnesium, and phosphorus needed for photosynthesis and growth, due to chloroplast membrane damage, leading to a decline in Spartina growth� Our planting efforts were in the areas near the dump where there has been no natural regeneration, although there has been farther away�
We hypothesized that Spartina under electrical stimulus has higher growth rate and ability to function under stressful conditions, based on previous experiments with corals and oysters� If so, implementation of this technology in severely distressed urban environments may promote restoration of marine vegetation, higher biodiversity, reintroduction of shellfish, help improve coastal water quality, and enhance protection against shoreline erosion while buffering runoff damage to coastal zones�
METHODS
This experiment was conducted on the southern shore of the Western end of Long Island Sound in College Point, New York, near 5th Avenue and 119th Street� The Spartina reestablishment is a 7�62 × 7�62 m2 quadrat with 15 cm spacing between each plant� Each quadrat contained approximately 30 plants� Three different S. alterniflora quadrats were grown (Figures 15�4, 15�5, and 15�6)�
Young Spartina plants averaging 20�3 cm tall from Pinelands Nursery were planted at a density of approximately 12-15 plants/m2� Quadrats 2 and 3 were much closer to the polluted landfill adjacent to the bay than the control sites, and so would have been expected to show slower growth�
For planting, a shovel was inserted into the sediment to the full depth of the blade to create a V-shaped opening� With the shovel still in place, an ounce of slow-release Miracle Gro® fertilizer was added� Marsh grass requires a small amount of fertilizer at the time of planting to provide nutrients throughout the first growing season� The young plant was inserted into the hole and the sediment around it was compacted by hand and foot�
Quadrat 1 is S. alterniflora that had naturally regenerated since the 1970s and served as the control� Quadrat 2, with low electrical current, is S. alterniflora planted in June 2010� The S. alterniflora in Quadrat 3, planted in June 2010, was grown under higher electrical current� The current was supplied from photovoltaic modules, which supplied electricity to metal grids at ground level with Spartina growing in 6 inch (15 cm) square spaces�
The heights of 20 random S. alterniflora plants from each quadrat were measured by tape measure every week at low tide in July 2010 to September 2010, and then again from May 2011 to September 2011� To measure the height, the plants were delicately stretched, to make the leaves stand straight and vertically, and measured from the top of the highest leaf to the sediment surface�
Helical steel loops were attached to each quad to monitor carbonate deposition� If calcium carbonate coated the loop, this indicated that carbonate was being deposited from seawater� For all quadrants, the plants’ mean height and standard deviation were calculated and plotted using Excel�
A best fit line was calculated� Growth rates were calculated using G H
T =
∆ ∆
where G = growth rate, ∆H = change in mean height, and ∆T = time change�
We used common concrete reinforcement metal mesh of 1/8″ steel wire welded together to form a 6-inch-square grid pattern� Three 1 m2 metal wire grids were secured to the sediment surface� The higher-current mesh grid was connected directly to a solar panel, and the second grid received a much lower current via an indirect connection via the first grid, while the third was left without electrical stimulus, as a control�
Another set of charged and control sites, called the extreme stress site, was planted below the extreme lower limit of Spartina growth and in an area affected by drainage from a groundwater spring draining the former waste dump (Figures 15�7 and 15�8)� These plots were followed for three years�
RESULTS
Height averages for each quadrat were calculated in mid-September 2011� The higher-current electrically stimulated Spartina had the fastest growth rate (11 cm per week) and the tallest plants� The low current group had the second-highest growth rate (9 cm per week), and the control group had the lowest growth rate (5 cm per week)� Figure 15�9 shows the average heights for each of the three quadrats for the first 11 weeks of the experiment�
EXTREME STRESS SITE
Three grids were set up in front of the metal-rich seep shown in Figure 15�3 to specifically investigate the role of electrical stimulus closest to the landfill in an area where no natural Spartina regeneration had taken place� This site is severely stressed for two reasons� First, it is right next to the edge of the landfill, located in a groundwater seep that drains the landfill� Second, this site is lower in the intertidal than the normal lower tolerance limit of Spartina� Three plots were established: two controls and one electrified plot�
For three growing seasons, we saw positive growth and regrowth following the winter season in only the electrified plot, with very high overwinter survival� In contrast, the control plots grew much more slowly than the electrified plot and suffered 100% mortality every winter (Figure 15�10)� New plants were planted every spring, and they did poorly and died the following winter�
DISCUSSION
Mateos-Naranjo et al� (2008) suggest that metal contaminants in sediment may slow Spartina growth rate� The rapid plant growth seen in severely metal-polluted electrified site suggests that electrical stimulus improves Spartina growth despite what should be a toxic habitat�
Since Spartina has many positive ecological relationships with other species, the use of electrical stimuli to increase Spartina growth, biomass, and survival could help restore an important ecosystem whose growth has suffered badly from pollution� Salt marsh ecosystems in Louisiana, Mississippi, Alabama, and Florida damaged by the Gulf oil spill in 2010 could benefit greatly from the results of this experiment� The BP oil spill resulted in damage to many ecosystems, including coastal salt marshes (Lin and Mendelssohn 2012)� The positive effect of electrical stimuli on S. alterniflora in severely stressed environments may provide a valuable restoration tool for ecosystems impaired by the oil spill�
The procedure used to measure Spartina growth could be improved by calculating leaf surface area, leaf and shoot numbers, and the date on which the plant begins to flower, in addition to measuring height� In future experiments, we hope to calculate the leaf surface area, photosynthetic capacity, the number of leaves, the number of stems per clump, and root and rhizome biomass, in addition to height when analyzing the effect of electrical stimulus on Spartina growth� It will also be important to see what the effects are on root growth (Valiela et al� 1976), sediment trapping (Mudd et al� 2010), and carbon storage� The faster and denser the plants grow, the better they trap sediment and cause vertical growth of the marsh surface (Mudd et al� 2010) and the better their chance of keeping up with sea level rise�
Coastal wetlands are significant carbon sinks, and it will be important to see how this process affects carbon accumulation underground as roots, rhizomes, and organic carbon (Rabenhorst 1995; Chmura et al� 2003)� It will also be important to assess how the number and biological activity of mussels and other animals are affected, because they play key roles in stabilizing the roots against wave erosion, filtering water, trapping sediment, and oxygenating sediments, which benefits root growth (Drew 1997)�
CONCLUSIONS
The Spartina that received electrical stimulus had faster growth and greater height than the control Spartina, the leaves appeared distinctly darker green, and the roots appeared darker and thicker at the holdfast� Electrically charged Spartina had high survival under conditions of high metal pollution and deeper in the intertidal than the species could otherwise survive, under which the controls all died� This implies greatly improved root and rhizome growth� Near the end of the experiment, a hard layer of calcium carbonate had formed over the grid� This could promote growth of mussel and oyster shells, increasing biodiversity� Calcium carbonate acts as a buffer to increase the pH of the seawater to ensure survival of more marine organisms in areas of high-impact CO2 acidification�
Our work shows that salt marsh can be restored using electrical currents even in severely stressed sites where normal growth is impossible� Because Spartina can now be grown seaward of its normal lower limit, salt marshes can be extended seaward, reversing the coastal erosion caused by the rising sea level� The techniques developed here could be applied to Jamaica Bay, the largest salt marsh in New York City, which has lost a significant amount of Zostra (eel grass) and high marsh marsh area and is steadily retreating as a result of global sea-level rise (Hartig et al� 2002)� Many coastal wetlands around the world are threatened by sea-level rise, and these methods could assist in maintaining marshes by making them grow faster, a critical parameter in adaptation to sea-level rise� In particular, this could also be done on a large scale in places like Louisiana, where coastal salt marshes are vanishing from sea-level rise and oil pollution (Lin and Mendelssohn 2012) at rates of up to hundreds of meters a year�
REFERENCES
