on the ecological alterations associated with the construction and opera- 

 tion of a new central treatment complex in unmodified marsh. 



Attribute alterations are similiar in scope but smaller in scale than for 

 wellsite preparation. Site preparation for the treatment complex removes 

 all biotic components within the construction boundaries through dredging, 

 spoiling, digging, filling, and pile-driving activities. A direct loss 

 of approximately 0.4 ha (1 acre) of sustaining habitat results for primary 

 and secondary consumers. 



Food and cover losses are particularly significant for small mammals, 

 local insect populations, and some aquatic invertebrates as propor- 

 tionally larger portions of their resource base are removed or altered. 

 The carrying capacity of the marsh for supporting secondary consumers 

 such as the predatory mammals and birds, waterfowl, wading and shore- 

 birds, alligator, and aquatic vertebrates is certainly reduced by such 

 habitat alterations. The significance of such an incremental loss at the 

 ecosystem level of consideration is unknown, however. Evaluation must be 

 made in context with other surrounding or associated alterations. 



Reworking the marsh substrate to build ring levees and spoil pads, as 

 well as for placing pilings and other support structures, causes 

 increased levels of suspended sediments, dissolved nutrients, water 

 turbidity, and biological oxygen demand at the construction site. 

 Subsequent weathering and erosion of barren spoil deposits and routine 

 maintenance traffic through the access canals sustain these alterations 

 for longer periods, but at reduced levels. Construction-associated 

 increases are typically short term and are usually confined to the site 

 area, especially if the surrounding marsh is densely vegetated and has 

 few or no open-water bodies. Open-water bodies or channels may permit 

 extension of these effects over wider marsh areas, depending on local 

 currents and flow velocities, but the affected areas remain relatively 

 small . 



Although care is exercised at the production complex to avoid release of 

 toxic substances into the marsh, small-scale discharges of oil, gas, 

 gasoline, assorted treatment chemicals, and brine inevitably occur in 

 spite of the preventive and maintenance procedures instituted. Ecolog- 

 ical alterations associated with large spills, discharges, and associated 

 cleanup procedures are treated as a separate section. Toxicity of 

 petrochemical hydrocarbons is a function of the quantity released, distil- 

 late fraction(s) discharged, and susceptibility of the biota to those 

 fractions. The constant low-level release of toxic petrochemicals over 

 long periods and their subsequent effects upon fresh marsh dynamics are 

 not well understood and have not been satisfactorily evaluated. Effects 

 of occasional low-level discharges are rarely felt beyond the immediate 

 site, as certain microbial elements of the marsh muds can readily absorb 

 and decompose small quantities. 



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