Editor's Note: This article is reprinted from The Delaware Estuary: Rediscovering a Forgotten Resource, which was published by the University of Delaware Sea Grant College Program in 1988. It was written by scientists Wendy Carey, Evelyn Maurmeyer, and Michael Gross.
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In September, 1985, the Panamanian tanker Grand Eagle ran aground on Marcus Hook Bar, near Claymont, Delaware, and began spilling oil into the Delaware Estuary. By the time the tanker was refloated with the assistance of tugs and reached the Sun Oil Refinery about a mile upstream, it had lost about 435,000 gallons of oil.
Although this oil spill was a major one by any standards, it could have been much worse. The Grand Eagle's ruptured Number 1 starboard tank's total capacity was 2.3 million gallons of oil.
Our dependence on oil, particularly imported oil, leads to greater potential contamination of the marine environment. In the past two decades, major accidents involving tanker groundings, collisions, and offshore oil-well blowouts have released over 200 million gallons of petroleum into the world's waterways. However, such catastrophic events actually represent only a small proportion of the oil reaching the marine environment. In 1975, the National Academy of Sciences estimated that 1.9 billion gallons of oil enter the world's oceans every year from the following sources: transportation activities (tankers, terminal operations, dry docking) --31.6%; tanker accidents --3.3%; coastal facilities (refineries, sewage plants, industrial wastes) --13.1%; offshore petroleum production --1.3%; river and urban runoff --31.3%; atmospheric fallout (smokestacks, tailpipes) --9.8%; and natural seepage --9.8%.
Major tanker transport routes, such as the Delaware Estuary, are especially vulnerable to potential oil spills. Every day, approximately 700,000 barrels (30 million gallons) of crude oil are transported by tanker through the estuary to refineries upstream. Much of the estuary fuel also is carried by barges and small coastal tankers to other cities along the Northeast Coast.
How Do Oil Spills Affect the Environment?
Oil spills can have numerous adverse effects on marine life in coastal environments where wetlands, bottom sediments, and recreational activities are concentrated. The severity of damage depends on the amount and type of oil spilled, season, wave and tidal conditions, and other environmental factors.
Oil's effect on fish, shellfish, crustaceans, and marine birds is toxic. When a blue crab, for example, becomes coated with oil, it asphyxiates. An oiled mallard may die a slower death. Its feathers can no longer produce their natural protective oil, providing buoyancy and warmth, so the animal cannot swim or forage for food. When the bird preens, it ingests oil, which may eventually destroy the stomach lining.
Oil can also destroy marine plankton and contaminate marshes and other highly productive estuarine areas. Thus, the effects may be manifested throughout the food web in a number of ways. Oil contains substances such as 3,4-benzopyrene, which have been proven to cause cancer. When on marine organism ingests these hydrocarbons, it may retain them and transfer them to its predators, which poses dangers to commercial fisheries and human consumers.
Yet the long-term effects of oil pollution on marine organisms are not yet fully understood. Chemoreception, the ability of marine organisms to detect chemical compounds (somewhat analogous to our sense of smell or taste), is important in selection of habitats, reproduction, and attraction of predators to prey. Oil can block receptors or mimic natural stimuli, resulting in false responses or no responses at all, which may affect a species' survival.
Oil accumulating on shore is not readily removed by natural wave and tidal forces. Low-energy environments (marshes, tidal flats) are most susceptible to long-term damage; wave-pounded rocky coasts are less vulnerable.
Although it is lighter than water, oil can eventually sink to the bottom via organism or mineral uptake. Clay minerals that absorb hydrocarbons retain oil and may be transported elsewhere by currents. Therefore, bottom pollution may exceed the area of the original spill. Furthermore, these oiled sediments survive for long periods of time because oil is extremely stable in this environment.
In addition to these effects, the visual pollution of an oiled beach diminishes recreational values in coastal communities, while industries such as fishing and shellfishing are destroyed.
The Spill's Impact on a Delaware Marsh
When the Grand Eagle ran aground in the Delaware Estuary in September 1985, it lost 10,000 barrels (435,000 gallons) of North Sea Oil ("Ninian"), a light crude oil containing wax, which contaminated the western shoreline of the estuary from Claymont to as far south as Deemer's Beach, near New Castle, Delaware. About 6,000 barrels (250,000 gallons) was recovered through skimmimg operations and related activities. The remaining 4,000 barrels (185,000 gallons) were presumably lost in evaporation, dissolution, incorporation into bottom sediments, microbial degradation, suspension formation, and adhesion to marsh vegetation.
Because tidal marshes are such an important part of the estuarine ecosystem, not only a habitat for finfish, shellfish, birds, and mammals, but for shoreline stabilization, a scientific research team began working to assess the impact of the Grand Eagle spill on a marsh near Battery Park at New Castle, Delaware.
The shoreline at Battery Park includes a sand-gravel beach and a narrow, broken band of marshes made up of five major types of vegetation: smooth cordgrass (Spartina alterniflora), common reed (Phragmites australis), common three-square (Scirpus spp.), and switch grass (Panicum virgatum) -- all perennials; and one annual, water hemp (Acnida cannabina). (In general, perennials will survive oil contamination better than annuals because new growth comes from large underground root systems even after the leaves and shoots have been destroyed.)
Smooth cordgrass is found at low elevations, between low and high tide. Three-square and water hemp are found at intermediate elevations (at or near high tide), and switch grass and common reed are found beyond. As is typical of this type of marsh, however, the zonation of the plants varies greatly.
Smooth cordgrass appeared to be most severely affected because oil-laden tidal waters could so easily wash over it. In much of the area, the entire plant was coated with oil. However, the oil only extended up a portion of the stems and stalks of taller plants like water hemp and common reed because of their height (some of the plants exceeded 7 feet). Oil was still present on these plants one month after the oil spill although the oiled unvegetated beach around Battery Park had been cleaned up by October/November.
Throughout the year after the spill, the research team noted no significant differences in populations of common three-square, switch grass, smooth cordgrass, or water hemp at Battery Park. But numbers of common reed declined significantly, and the average height of water hemp increased significantly. There is no way of knowing if these changes were a result of the oil, or simply a response to year-to-year variation in other factors such as precipitation and temperature.
Overall, from this preliminary assessment, it appears that the Grand Eagle spill had little impact on marsh vegetation at Battery Park. Local weather conditions, nature of the oil spilled (light crude is considered to be less toxic than refined oil), and the fact that the spill occurred as plants were entering their dormant stage probably contributed to the minimal impact that the oil had on the marsh.
Future oil spills, however, may have significantly greater effects on tidal marshes along the Delaware Estuary depending on time of year, weather conditions, and type and amount of oil spilled. A number of studies have shown that marsh plants can survive single events of light to moderate oiling. Heavy doses or multiple exposures to oil spills, however, can seriously damage marsh plants, and very heavy oiling can smother them because it prevents gas exchange between plant and atmosphere. Exposure to oil during the growing season can inhibit seed germination and damage newly formed seedlings. Oil may also adversely affect root development, and if plants are contaminated as flowering buds develop, it may reduce flowering, thereby diminishing seed production.
The Delaware Estuary was fortunate to survive the Grand Eagle oil spill without greater impact. However, our reliance on the estuary as a transportation corridor for oil creates the possibility of future oil spills. From this incident, we can see that whatever the degree of contamination by an oil spill on the Delaware Estuary, the effects of that oil spill on the environment are almost never positive. Although plants and animals may survive an oil spill, they may suffer the effects of that spill long after visual signs of it have disappeared.