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Oil in the Sea III: Inputs, Fates, and Effects
but probably not complete. The population of fiddler crabs in the Wild Harbor marsh was reduced relative to that in Sippewissett marsh for at least seven years (Krebs and Burns, 1977). Behavioral effects, abnormal burrow shapes, and reduced female-to-male ratios were seen in Wild Harbor. Crab density was negatively correlated with aromatic hydrocarbon concentrations within the marsh, as was the density of newly settled juveniles.
Other sources of oils that may directly affect salt marshes or mangroves are produced water discharges. Results from Louisiana estuaries indicate that discharges of produced waters directly onto salt marshes will kill the vegetation, but discharges into receiving waters do not affect the peripheral marsh vegetation (Boesch and Rabalais, 1989a). Within the Nueces Bay estuary of Texas, however, Caudle (1995) identified extensive marsh areas in the bay that were denuded of vegetation due to long-term exposure to produced water.
Documented recovery times (return to some precursor percent cover of vegetation, diversity, or height and biomass of plants) for oiled marshes range from a few weeks to decades (reviewed by Hoff, 1996). There are several well-studied marsh sites where recovery times ranged from five years to greater than 20 years, including two sites in Buzzard’s Bay. Massachusetts, the Miguasha spill in Quebec, the Metula spill in Chile, and the Amoco Cadiz in France (Table 5-4). The reasons for longer recovery times were related to the following characteristics: (1) northern, temperate, cold environments, (2) the high organic content of the peaty soils, (3) sheltered location, (4) heavy oiling, (5) spills of fuel oils (bunker C or No. 2 fuel), and (6) physical disturbance during response activities, particularly for the Amoco Cadiz.
In contrast, recovery times of three years or less have been documented for sites at several locations in the Gulf of Mexico: Neches River, Texas (Esso Bayway), Harbor Island, Texas pipeline, and a pipeline rupture in southeastern Louisiana (Table 5-5). These marshes exhibiting quicker recovery share the following characteristics: (1) warm climate, (2) more mineral-rich soils, (3) light to moderate oiling, (4) spills of light to medium crude oil, and (5) variety of cleanup methods that were less intrusive. In many instances, cleanup techniques delayed recovery time, from physical disruption of roots, flushing of soils, thus lowering the soil surface below levels where vegetation could re-establish, and activities that mix oil deeper into the marsh soils.
There are numerous documentations of the death, defoliation, genetic, and other damage to mangroves and their associated communities after exposure to oil (e.g., Proffitt et al., 1995). Damage to mangrove forests varies with the amount and toxicity of the spilled oil product(s) with or with
TABLE 5-4 Examples of Oil-impacted Marshes with Recovery Times of Five Years or More, Documented by Follow-up Studies (from Hoff et al., 1996).