BIOTIC INTEGRITY OF STREAMS IN THE SAVANNAH RIVER SITE INTEGRATOR OPERABLE UNITS, 1996 TO 2003
IBI, HDMI, and MHSP scores) and minimal levels of pathology among individual fish (e.g., presence of tumors or extreme thinness), indicating that contaminant levels were generally insufficient to cause significant ecological degradation. A few areas did exhibit ecological degradation, as indicated by low IBI, HDMI, or MHSP scores. Most were small tributaries or the smaller upper reaches of larger streams. These areas included Tims Branch, Crouch Branch, McQueen Branch, and the upper portions of
... Fourmile Branch, Steel Creek, and Meyers Branch. Degradation in upper Steel Creek was probably at least partly the result of habitat (isolation of this portion of the stream by L Lake plus erosion and siltation), and degradation in the upper portion of Tims Branch was probably at least partly related to naturally occurring low oxygen levels and high iron levels. Degradation in Crouch Branch, a small tributary of Upper Three Runs, may have been partly habitat related but was also related to the discharge of an NPDES effluent with elevated copper levels. Conditions in this stream have improved with improvements in effluent quality. Degradation in the upper portion of McQueen Branch appears to be habitat related, but the possible influence of NPDES discharges cannot be excluded. The cause of degradation in Fourmile Branch near Road 4 is uncertain but may be related to elevated metal concentrations as a result of past industrial operations. The upper portion of Meyers Branch was upstream from all waste sites and industrial areas, and low biotic integrity in this area was habitat related. Repeated sampling of fish and macroinvertebrate assemblages at a number of sites during 1996 to 2003 suggested that no streams declined in ecological health over time and that several (i.e., Fourmile Branch and Crouch Branch) improved . Similarly, there was no evidence that fish tissue contaminants increased over time in any stream, and tritium levels decreased in Fourmile Branch fish.