In the Upper Uncompahgre River Watershed, many of the metals harmful to aquatic life are brought into the river by natural erosion and acidic water drainage from mines and other exposed rock. Most of this metal-contaminated water drains first into Red Mountain Creek and Sneffels Creek, and then into the Uncompahgre River.
These graphs show how the concentrations of dissolved zinc (top graph) and total iron (bottom graph) in the Uncompahgre change as the river descends, and streamflow increases, to Ridgway Reservoir. The concentration of dissolved zinc starts out very high, and well above the aquatic life standard, in Red Mountain Creek. Then as streamflow increases the zinc concentration decreases steadily to a minimum below Ridgway Reservoir. This pattern suggests Red Mountain Creek is the source of zinc, and its concentration is diluted by water entering the river below the creek.
Total iron also shows very high concentrations in Red Mountain Creek, which causes a large increase in iron concentration in the Uncompahgre from above (1st site on the graph) to below the creek (4th site on the graph). However, unlike zinc, iron concentrations below the creek remain relatively constant or increase slightly as streamflow increases down to the site just above Ridgway Reservoir (7th site on the graph). For the iron concentration to remain relatively constant, the mass of iron entering the river had to increase as streamflow increased.
