sediment introduction may cause significant system changes. Treat- 

 ment of impacts in adjacent systems, therefore, requires analysis of 

 appropriate aquatic ecosystems with altered inputs of sediment and 

 nutrients. Other aspects of soil structure include: soil moisture 

 and soil aeration linkages to the flora; groundwater recharge, 

 percolation, infiltration, and water-holding capacity linkages to 

 the hydrosphere; and evaporation pathways to the atmosphere. Even 

 though these aspects are seriously altered on the site (usually 

 reduced), they are not considered for further analysis because 

 either (1) biotic implications are not relevant since plant and 

 animal recovery is precluded by drilling activities, or (2) the com- 

 parative effects from a single small site on the ecosystem's hydro- 

 logic or atmospheric regimes are considered to be very minor. 



Pad construction may disrupt existing surface hydrology by obstruc- 

 tion or filling of intermittent drainages and shallow depressions. 

 Site placement in marshes or small ponds is treated in the discus- 

 sions of the marsh ecosystems. Drainage blockage may result in 

 temporary ponding of the upper drainage and an increase in the 

 macropore water storage. Site buildup in moist upland areas in- 

 creases the zone of aeration in the soil. Either alteration may 

 cause a local change in the existing soil air-moisture regime such 

 that the existing floristic assemblages are replaced by species 

 favored by the new equilibrium conditions. Dependent consumer 

 groups may change accordingly, depending upon the areal extent of 

 the alteration. Typically, the effects will be localized and result 

 in no fundamental ecosystem changes unless numerous alterations are 

 concentrated in a restricted area (as in the development of an 

 extensive oil field). 



Large and indiscriminate releases of toxic or noxious substances 

 into the environment are regulated by numerous restrictions, regula- 

 tions, and guidelines. Small-scale releases to the site, either 

 accidental or intentional, occur regardless of the regulatory stat- 

 utes. Ecological alterations associated with spills and cleanup are 

 treated as a separate section of this discussion. Specific data 

 documenting the ecological effects of toxic chemical discharge into 

 upland communities have not been readily attainable in the scien- 

 tific literature. However, soil salinity, which inhibits or pre- 

 vents vegetative growth, is increased by seepage of oil field brine. 

 It is reasoned that attribute alterations are very restricted in 

 areal extent due to the low-volume discharge and limited lateral 

 mobility of substances through soil strata. Local biotic effects 

 are a function of the substance's toxicity, quantity released, 

 ability to move through the food chain, persistence, and presence of 

 sensitive biota; well drilling precludes the presence of plants and 

 animals on the site. The effects of chemical residuals on site 

 restoration are treated in a separate section of this discussion. 

 The recuperative abilities of the soil's micro- and macrobiota and 

 of more complex flora, from petrochemical discharges are not well 

 understood. 



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