Water quality of a mountain watershed in Colorado

February 1967.Includes bibliographical references (pages 98-103).Covers not scanned.Print version deaccessioned 2021.Water quality was investigated from April, 1964 to September, 1965 on a mountain watershed in the Colorado Front Range. The primary objectives of the study were: 1. To assess water quality characteristics v/within the catchment at varying natural flow regimes under conditions of limited to no land use; 2. To measure the impact of land use on water quality. Ten stations, ranging in elevation from 7,600 to 9,790 feet, were sampled during the two runoff years. Samples were collected on a weekly to ten-day basis from May to September, and several times during the rest of the year. A total of 604 samples were taken. The parameters measured were: flow; water temperature; pH; turbidity; suspended sediment; dissolved solids; and total, coliform, fecal streptococcus (FS), and fecal coliform (FC) bacteria. Statistical and graphical analyses indicated that the bacteria groups were closely related to the physical parameters of the stream and were especially dependent on the “flushing effect" of runoff from snowmelt and rain, summer storms, or irrigation. The seasonal trend for the coliform, FC, and FS bacteria groups was similar: (1) low counts prevailed while the water was 0°C, although bacteria from all groups were isolated during winter; (2) high counts appeared during the rising and peak flows caused by June snowmelt and rain; (3) a short "post flush" lull in counts took place as runoff receded in early July; (4) high counts were found again in the July-August period of warmer temperatures and low’ flow’s; and (5) counts declined in September. Coliforms fluctuated from 0 to about 300 colonies/100 ml depending on the site and season. The FG and FS ranged from 0 to about 75 colonies/100 ml. A few counts following summer storms and during extreme spring flooding rose to several thousand coliform colonies/100 ml and several hundred FC and FG. The FC, FS, and coliforms all clearly defined grazing-irrigation impact; the FG showed the "highest sensitivity" to such pollution. The coliforms rated slightly less, while the FS were the least sensitive. Samples from above and below two campgrounds along streams did not indicate human contamination nor physical pollution. A greater number of correlations were found among the physical factors during the high flow period of May-June in both years. Minimum pH values occurred near the peak flow with a total range of from 6.3 to 8.7 pH units observed. There v:as a 0.1 to 0.2 pH unit decrease per 1000 feet of elevation. Turbidity and suspended sediment were positively related to flow and to each other. An approximate 5:1 sediment-turbidity ratio was found. Maximum storm readings were 724 mg/I for sediment and 475 Hellige units (ppm Si02) for turbidity. Most of the sediment appeared to be from roads; the periodic, sediment readings did not reflect a grazing-irrigation impact. Water temperatures ranged from 0 to 24°C. Dissolved solids ranged between 0 to 205 mg/1; no relations between dissolved solids and other physical or bacterial parameters were found