III. Estuaries

Estuaries are extremely productive and valuable ecosystems. They are often subjected to the intense pressure of multiple uses by man—expected to assimilate domestic and industrial wastes and accommodate marine transportation, yet continue to remain productive in fishes and shellfishes. Because of the increasing trend toward tanker-transported crude and refined oils and the proximity of estuaries to population centers, estuaries are convenient sites for oil receiving ports and refineries. Many estuaries must cope with increasing levels of petroleum pollution from accidental spills, ships, and industrial and domestic effluents. Thus, certain estuarine environments may be subjected to frequent small spills, often of more toxic refined products, or continuous low-level additions from refineries, petrochemical plants, oil field wastes, and even domestic sewage and urban runoff.

Probably because the oil spills that have taken place in estuaries have generally been small, their biological effects have generally not been well studied. A few broad observations may nonetheless be made based on what we know about the behavior of oil in the environment and the characteristics of estuaries. Several characteristics of estuaries suggest that oil pollution may have serious effects there. Because estuaries are generally confined and relatively shallow bodies of water, oil spills may not spread over a large area of the water's surface and have little chance to be swept to sea. Instead, there is a high likelihood that the oil will reach shore or the bottom. Estuaries are typically turbid, and therefore floating oil may tend to absorb onto fine sediment particles and sink to the bottom, where it may kill or contaminate bottom-dwelling organisms, including shellfish and bottom-feeding fishes. Indeed, this process seemed to be the principal cause of the widespread contamination following the West Falmouth oil spill (). The oleophilic nature of detritus, which is typically abundant in estuaries, increases the probability of ingestion of oil by estuarine detritivores. If oil is deposited in sediments, it may persist for long periods under the anaerobic conditions typical of subsurface estuarine sediments. Also, long-term and rather high-level contamination of sediments may result from continuous low-level inputs (industrial and domestic sources). The serious biological effects of sediment contamination in Los Angeles-Long Beach Harbor have been described by Reish ().

On the other hand, we know that the microbial biota of estuaries is abundant, thus indicating that at least aerobic degradation is rapid. Also, assuming that the pollution is strictly acute (that is, no persistent contamination results), recovery of damaged communities should be rapid because of the great