basically modified upland systems, remain relatively undisturbed by 

 primary, secondary, or tertiary alterations. 



Within the easement, however, system alterations may be severe. If the 

 flotation method is utilized without backfilling so an open channel is 

 produced, then that particular site is completely altered, but the 

 functional integrity of the ecosystem remains essentially unchanged. The 

 importance of this alteration depends essentially upon what proportion of 

 the entire ecosystem the altered site represents. In most cases this 

 percentage will be very small. In those instances where the ditch is 

 backfilled and the levee segment rebuilt following line installation, the 

 effects are essentially temporary. If the site is reshaped to approximate 

 the original conditions and quickly stabilized and revegetated, then plant 

 recovery can be accomplished within two growing seasons. 



The following changes nevertheless occur within the easement corridor. 

 Excavation means complete plant removal, usually of Spartina patens , 

 Baccharis spp. , Iva spp. , and various herbaceous forbs. Consumers of 

 limited mobility may die if they remain within the construction corridor. 

 These would primarily be small mammals, a few insects, and perhaps a few 

 semiaquatic vertebrates. Food and cover aspects are altered for all 

 consumer groups utilizing the levee system. Subsequent effects on local 

 consumer populations, however, are probably not noticeable due to the 

 relatively small quantitative decrease. 



Removal of plant cover and reworking of the levee substrates exposes bare 

 sediments and alters soil structure. The erosive action of surface water 

 transports sediments and nutrients into adjacent aquatic or marsh systems, 

 increasing local water turbidity and sedimentation rates. Within the 

 working easement, changes in soil structure occur as installation equip- 

 ment variously compacts or loosens the soil. Compaction results from 

 vehicular traffic of all types. Soil loosening occurs by digging, piling, 

 and refilling activities. Decreased soil structure reduces water infil- 

 tration rates, locally increasing surface-water runoff also. If the 

 disturbed area is flat and relatively small in areal coverage, this runoff 

 is then moderated by surrounding vegetative cover. Otherwise, excess sur- 

 face water can accumulate. Soil structure regulates not only the soil 

 moisture regime but soil air, another important plant regulator, as well. 

 These changes are probably of greater significance to well developed, 

 mature plant communities. Plant recovery on a mature chenier would pro- 

 bably be quite different from the initial floristic composition due to 

 changes in soil structure and the resultant soil-water/air-micropore 

 equilibrium. On relatively recent spoil levees and banks where the sub- 

 strate is essentially without structure, soil disturbances would have 

 little subsequent influence on plant composition. Hardy pioneering 

 species would reinvade the abandoned site, where essentially little sub- 

 strate changes had occurred as a result of construction. 



Even though conditions may be significantly altered within the easement 

 zone, very little ecosystem alteration is effected. The primary signifi- 



306 



