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0023 DISCUSSION The primary objectives of the study were to identify the types and abundance of aquatic macrofauna in the upper Arkansas River and to determine the effects of heavy metals pollution on macrofauna distribution. Physical parameters of the river water that were considered included temperature, current, substrate, conductivity, and oxidation-reduction potential. Chemical parameters included pH. dissolved oxygen. ma- jor anion and cation content, nitrogen and phos- phorus compounds, and the selected heavy metals manganese. iron, copper. zinc, lead, molybdenum, and cadmium. The macrofauna represented were considered with respect to their physical and chemical tolerances. Temperature Water temperature generally increased down- stream from stations EF-l to AR-9. Also, at any given station temperature increased throughout the year until late summer. Low, shallow flows. warm tributaries, and the relative absence of shade would account for higher temperatures reached during the late summer. An increase in temperature is usually correlated with an in- crease in numbers and diversity of aquatic in- vertebrates (Armitage, 1958 [4J l. The results of this study did not totally support these find- ings due to the variations in water quality. Tem- peratures found were acceptable for the survival of brown, brook, and rainbow trout, as well as longnose and white suckers (Scott and Crossman. 1973 [136]. ). Dissolved Oxygen (D.O.) Dissolved oxygen concentrations at all stations in the upper Arkansas River were greater than 90-percent saturation and on occasion slightly exceeded 100 percent. These levels of dissolv- ed oxygen would provide suitable conditions for aquatic macro invertebrates and fish. Therefore. oxygen was not a limiting factor. pH The pH in the river throughout the study indi- cated the water was slightly alkaline. and was generally higher during the late summer and fall when primary production was greatest. ThiS higher pH was also reflected in a higher total dissolved solid (TDSI concentration. The pH was nearly always within a range considered op- timum for fish production and for the survival of most aquatic macroinvertebrates. McKee and Wolf (19631 [1 05J cited data that indicate that the upper pH limit for trout is 9.2. This level was reached on one occasion at AR-3 due to the in- fluence of California Gulch, and may be a reason why no fish were collected at this station. However. this high reading may have been In error due to interference by overhead power lines which may have affected the electronics in the meter. The pH values generally found in the river throughout the study indicated that most of the heavy metals would likely not be in a highly toxic ionic form. Conductivity The conductivity of the river water was always at a level conducive to supporting fish and aquatic macroinvertebrates. The Leadville Drain and California Gulch had conductivity values considerably higher than the river, but levels lower than those that would likely cause an osmotic imbalance in aquatic organisms (McKee and Wolf, 1963 [1051). Conductivity was generally highest during the low flows of late fall and winter due to high concentrations of dissolved solids, and lower during the high flows of spring and summer because of the dilution ef- fect of snowmelt. Oxidation-Reduction Potential (Ehl A moderately low pH and a reducing environ- ment generally favor the bioavailable soluble and exchangeable chemical forms of metals, while soluble metal oxides and hydroxides predom- inate at higher pH and oxidation levels (Gambrell et aI., 1976 [60J I. All Eh values measured dur- ing the study would indicate that the river was in an oxidized state except during periods of late winter. Eh corrected to E, measurements show that. on occasion. reducing conditions existed in California Gulch, which resulted in lower Eh values at AR-3. 33