for oil and gas activities. If the area were not intensively used 

 or were left abandoned, some consumer populations might develop from 

 the few hearty species that remained. There would be limited oppor- 

 tunity for movement into the impounded area by aquatic species, 

 though high waters from storms and transport via birds could allow 

 population establishment. Consumer groups likely to develop include 

 meiofauna, zooplankton and small crustaceans especially adapted for 

 feeding on phytoplankton, and small fishes such as cyprinodonts. In 

 some instances the wind protection afforded by the levee banks would 

 allow the water to be clear and productive. In this instance the 

 impounded area could be very attractive to waterfowl, raccoons, and 

 wading shorebirds. In other cases, however, especially where the 

 area is intensively used, the impounded wellsite might offer little 

 attractive habitat. 



In all cases it is likely that the ecosystem created is less produc- 

 tive than the original marsh it replaced. 



During this phase of operations (one to three months), the water and 

 soil systems are exposed to a wide variety of pollutants from drill- 

 ing mud, sump discharge, and vehicle and equipment waste (exhausts, 

 oil, grease, gasoline). The kinds and amounts of these materials, 

 and hence their effects, are site specific. Consequences are diffi- 

 cult to predict due to the large number of site specific variables 

 involved. Spills and cleanup operations are treated in a later 

 section of this report. 



Displacement due to activity and noise during construction is short 

 term since the operation takes only 10 to 14 days. However, subse- 

 quent activities, drilling and production, may continue for months 

 and years, and the area affected extends considerably beyond the 

 leveed site and borrow pits. 



4. Key attribute alterations 



The key attribute alterations include direct removal of vegetation 

 and consumers, localized changes in land elevation, and introduction 

 of pollutants. Since the area affected by excavation is small 

 (relative to the pristine marsh), the loss of food and cover for 

 supported consumers is insignificant. The changes in land eleva- 

 tions can influence waterflow regimes, but the total area affected 

 is usually minor in comparison to the undisturbed marsh. The extent 

 of impacts from pollutants is not predictable. Chronic effects of 

 persistent toxins are more important than the acute effects, which 

 are confined to a much smaller area. 



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