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I , " 002:i Manganese was always well below the max- imum recommended limit of 1.0 mg/L (Davies and Goettl, 1976 1341) except at AR-3 im- mediately downstream of California Gulch. The highest concentrations at this station were de- tected during the low-flow period of late winter. Manganese concentrations were usually lower below the Lake Fork inflow, indicating a freshen- ing inflow. These concentrations were far below toxic levels and. according to Blabaum and Nichols (1956) 1111. may be antagonistic to the toxic effects of other heavy metals which were at high levels. The principal reason for limiting the concentration of manganese is to reduce esthetic and economic problems. Iron concentrations in the upper Arkansas River were highly dependent on flow. On the average, the concentrations of iron downstream from AR-3 were more than three times greater during the peak of spring runoff than during the low- flow periods. During the low-flow periods. iron concentrations were usually lower below the Lake Fork inflow, indicating an addition of better quality water. It appeared that during the winter. due to the constant influx of mine drainage, sediment iron concentrations in the upper portion of the study area continued to increase. High spring flows then resulted in increased iron levels in the river, particularly below the inflow of Iowa Gulch. Ap- parently Iowa Gulch, Empire Gulch. Big Union Gulch, Box Creek, and various other sources are also carrying high iron loads during the runoff period. Decker and Menendez (1974) 1361 showed that 1.75 mg/L of iron was toxic to brook trout. Ionic iron concentrations were prob- ably lower than this in the river as much of the iron was in a particulate form. It is unlikely that macroinvertebrates were adversely affected by iron toxicity durin9 high flows because they are usually more resistant to it than are fish. Copper is extremely toxic to aquatic organisms. Even though the USPHS (U.S. Public Health Service) Drinking Water Standards for 1962 rec- ommend that copper concentrations not exceed 1.0 mg/L, acute toxicity has been shown in trout at much lower levels. Copper levels in the study area were, in general. above the limits of 0.01 mg/L recommended by Davies and Goettl ('9761 1341. Sylva (1976) 11451 has deter- mined that aquatic systems are capable of de- creasing ionic copper levels to very low values even in the presence of high copper levels. Ephemere//a, a taxon known to be highly sen- sitive to copper (Warnick and Bell. 1969 [1591 l. was most abundant in the upper sec- tions of the river, particularly at EF.l and AR-2. This may indicate that copper pollution was more severe in other areas of the river. Since copper is highly retained in liver tissue. concentrations in brown trout livers tend to be higher downstream of the Leadville Drain and California Gulch. However, low correlations found for copper concentrations between the discharges and the river indicate that the Lead- ville Drainage Tunnel and California Gulch may not be the only contributors of copper. At all sta- tions sampled. copper levels were far in excess of what is considered a normal or baseline con- centration for fish tissue. Zinc severely affects aquatic communities. Ex- cept at the uppermost station EF.l, zinc was always present in high concentrations in the up- per Arkansas River, making it a severe form of heavy metals pollution. Occasionally. higher concentrations of zinc below AR-5 indicated that it was entering the river from other sources besides the Leadville Drainage Tunnel and California Gulch. At stations EF-' and AR-2, zinc was present in the livers of brown trout in con~ cent rations similar to background levels found in fish from pristine waters. Stations EF.2 and AR- 7 contained fish that had mean liver concen- trations of zinc that were considerably higher. Macroirwertebrates in general are more resistant to zinc pollution than are fish and is a probable reason for why they were found below the California Gulch inflow where no fish were col- lected. Lead concentrations below AR-4, downstream of the Lake Fork inflow, were highly dependent on flow, with concentrations increasing during the spring runoff......5ediments carrying lead are suspended during high. flows and carried down the river. Lead levels above the Lake Fork inflow are inversely correlated with flow and are de- pendent upon concentrations in the Leadville Drainage Tunnel and California Gulch. Enk and Mathis (1977) 14BI have shown that detritus feeders and grazers contain lead in concentra- tions higher than that of the sediments. This may be the situation for the macroinvertebrates in the upper Arkansas River. Davies et al. (19761 37