at least possible that both hypersensitivity and acquired resistance occur. Neither is 

 well documented at the system level. However, the section to follow may have some 

 bearing on the sensitivity question. 



DIFFERENTIAL ECOSYSTEM SENSITIVITY 



There is some preliminary evidence that communities in the active colonization 

 process may be more sensitive to toxicants than mature communities. ^'t If this is 

 generally true, communities recovering from one perturbation may be more vulner- 

 able to a second shock than they would otherwise be. The regulatory implication of 

 this is that recovering ecosystems need even more protection than healthy ones if 

 they are to recover as rapidly as possible. 



DOES IMPROVED WASTE TREATMENT RESULT IN ECOSYS- 

 TEM RECOVERY 



The important question "Will improved waste treatment produce significant 

 biological improvements in damaged ecosystems?" has not inspired many studies in 

 which evidence on direct correlation between the two events has been obtained. 

 However, such evidence is not difficult to obtain. Two examples follow. 



Shenandoah River 



Beginning in 1972, 10 surveys of benthic invertebrates and 9 static fish bioassays 

 have been carried out to assess the impact of AVTEX Fibers. Inc. effluent on the 

 lower South Fork of the Shenandoah River.''' AVTEX (previously FMC Corpora- 

 tion) produces rayon and polyester fibers in Front Royal, Virginia. Benthic inverte- 

 brates were collected at four stations, one above and three below plant discharges 

 (Figure 5). River surveys in 1972 and 1973 indicated a severe impact on the benthic 







2 



_i Miles 







Kilometers 



N F. 

 Shenandoah 



Front Royal 

 AVTEX 



S F 

 Shenandoah 



Figure 5. Location of the sampling stations on the South Forkand the main stem of the 

 Shenandoah River, Warren County, Virginia. 



230 



