EVANS and RICE: EFFECTS OF OIL ON ECOSYSTEMS 



these factors; and because they are interdepen- 

 dent, the reliabihty of our predictions concerning 

 the impact of a spill is limited by our knowledge of 

 the least understood variable. 



Straughan (1972) noted our general inability to 

 predict the environmental impact of a spill be- 

 cause of the complexity of the matter, and 

 identified several factors that govern biological 

 damage caused by a spill: 1) type of oil spilled, 2) 

 dose of oil, 3) physiography of the area of the spill, 

 4) weather conditions at the time of the spill, 5) 

 biota of the area, 6) season of the spill, 7) previous 

 exposure of the area to oil, 8) exposure to other 

 pollutants, and 9) treatment of the spill. Several of 

 these factors are touched upon below. 



Natural Physical Processes 

 Affecting Oil in the Water Column 



Once oil is spilled, it is dissipated by evapora- 

 tion, dissolution, and mixing or dilution in the 

 water column. The natural processes are speeded 

 by wind action and by waves and currents that 

 increase spreading and vertical mixing. Various 

 fractions respond differently to these processes, 

 and the weathered residue behaves differently 

 than the material originally spilled. A contami- 

 nated bay may be flushed by freshets, tidal action, 

 or longshore currents. Some oil sinks directly to 

 the bottom, especially in fresh water, where some 

 oil fractions have densities approaching that of 

 fresh water, and in water with high sediment 

 loads. Certain fractions may undergo autoxida- 

 tion. 



Conover (1971) reported that sedimentation of 

 fecal-bound oil that had been ingested by zoo- 

 plankton may have accounted for up to 20% of the 

 spilled oil entering the water column at 

 Chedabucto Bay, Nova Scotia. Oil can also be re- 

 moved from the water column by absorption 

 within organisms and accumulation within the 

 food chain. Suspended sediments carried by runoff 

 from a major flood entered the Santa Barbara 

 Channel area immediately before and after the 

 well blowout (Kolpack, 1971). Kolpack noted that 

 adsorption of oil on the flocculated suspended par- 

 ticles followed by decomposition was a major fac- 

 tor in carrying much of the oil to the sea floor. 

 Kinney et al. (1970) reported, however, that in 

 Cook Inlet, Alaska, glacial silt from the inlet had 

 no apparent effect on the emulsion properties or 



the sinking of the type of crude oil found in that 

 area. 



Forrester (1971) noted the extensive distribu- 

 tion of oil particles stirred into the water by wave 

 action after a bunker C oil spill in Chedabucto 

 Bay. Oil particles were found to a depth of 80 m 

 inside the bay and to depths of 45 m at a distance of 

 65 km outside the bay. Near-surface distribution 

 of particles extended 250 km southwest along 

 Nova Scotia in a band extending up to 25 km 

 offshore. Berridge, Thew, and Loriston-Clark 

 (1969) indicated that the stabilization of emul- 

 sions like those observed at Chedabucto Bay and 

 elsewhere was caused by complex chemical com- 

 ponents in the nonvolatile residues and not by 

 bacterial activity, marine organisms, or sus- 

 pended solid matter. 



Environmental Differences 



The fate and effects of oil spilled in the marine 

 environment are difficult to generalize because 

 several types of environments may be involved. 

 Some extreme comparisons are tropics versus arc- 

 tic, open ocean versus estuaries, and the differ- 

 ences between the intertidal and subtidal zones. 



Within these environments are several diverse 

 physical conditions such as temperature, salinity, 

 oxygen, and nutrient concentrations, as well as 

 biological differences such as species composition, 

 diversity and density, and community metabolic 

 rate. The prediction or assessment of pollution 

 effects on the basis of observations extrapolated 

 from one environment to another is seldom sup- 

 ported by adequate data. Unfortunately, however, 

 few data on pollution effects exist for most areas 

 and species, which has led to the use of informa- 

 tion from areas that may be dissimilar in critical 

 respects. 



There are arguments as to which environment 

 is the most stable and capable of withstanding 

 attacks by additional pollution stresses. Copeland 

 (1970), discussing the response of ecological sys- 

 tems to stress, suggested the principle that 

 ". . .those systems already subjected to energy- 

 requiring stresses are more likely to resist the 

 changes than those (such as tropical systems) 

 adapted to relatively constant environments." He 

 concluded that estuarine ecosystems composed of 

 organisms capable of wide adaptations and 

 generalizations, such as north temperate systems, 

 would be relatively unaffected by the same mag- 

 nitude of disturbance that would drastically alter 



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