WSP10284

• File Number: 8170
• Description: Arkansas Basin Water Quality Issues
• State: CO
• Basin: Arkansas
• Water Division: 2
• Date: 1/1/1998
• Author: USGS
• Title: Water-Quality Assessment of the Arkansas River Basin - Southeastern Colorado - 1990-93
• Water Supply Pro - Doc Type: Report/Study

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(May-June)

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EXPLANATION
POST-SNOWMELT RUNOFF -. - LOW FLOW
(July-September) (October,April)

Figure 20. Median total-recoverable lead concentrations by streamflow regime in the lower ArI<ansas River,
April 199O-March 1993.

could have been released from the bottom sediments
of John Martin Reservoir during anoxic reservoir
conditions. These results are similar to those described
for iron and seem to be limited to low-flow regimes.
Total-recoverable manganese concentrations generally
increased downstream from Pueblo Reservoir.
Concentrations increased about 150 to 300 percent
between Avondale and Catlin Dam during snowmelt
and post-snowmelt runoff regimes (fig. 21) probably
because of res us pension and tributary inflow. Two
stonn-runoff water samples collected from the
Apishapa River had total-recoverable manganese
concentrations of 5,800 Ilg/L and 6,400 Ilg/L (Dash
and Ortiz, 1996); these concentrations are about
two times higher than the highest instantaneous total-
recoverable manganese concentration measured at any
main-stem site in the lower basin. A sample collected
from the Purgatoire River during a stonn-runoff event
had a total-recoverable manganese concentration of
5,300 Ilg/L (Dash and Ortiz, 1996). About 99 percent
of the manganese was in the particulate phase. These
three stonn-runoff samples indicate that tributary
contributions of manganese to the lower Arkansas

River are substantial, especially during rainfall runoff.
The substantial increase in total-recoverable manga-
nese concentrations between Las Animas and Below
John Martin Reservoir during the low-flow regime,
could be caused by the release of dissolved manganese
from the reservoir's bottom sediments. There were no
exceeclances of the chronic stream-water-quality
standard for dissolved manganese at any site located
upstream from Las Animas (table 23). The chronic
stream-water-quality standard for dissolved manga-
nese was exceeded in about 21 percent and about
67 percent of the samples analyzed from the sites
Las Animas and Below John Martin Reservoir, respec-
tively (table 23). Sixty-two percent of these exceed-
ances occurred during the low-flow regime. Two
samples collected at Catlin Dam and six samples
collected at tbe Below John Martin Reservoir site
exceeded the chronic stream-water-quality standard
for total-recoverable manganese (table 23). The six
exceeclances from Below John Martin Reservoir
occurred during the low-flow regime and could be
attributable to the release of manganese from the
reservoir bottom sediments.

44 Water-Quality Assessment at the Arkansas River Basin, Southeastern Colorado, 199().-83