Sample Collection and Analysis

Synoptic water samples were collected on August 30, 2000, at 49 mainstem and inflow sites along Miller Creek and on August 31, 2000, at 7 sites in the East Fork Miller Creek watershed (fig. 2). One site (3,205) at the mouth of East Fork Miller Creek was sampled twice--once during the mainstem synoptic and once during the East Fork sampling. The samples were analyzed for pH, selected major ions, and dissolved and total-recoverable metals (table 2). Owing to the shallow depths, samples during this study were collected using grab methods. Six sites (5,790; 9,735; 10,280; 14,160; E550; and E700) were very shallow and impossible to sample without introducing some streambed sediment into the sample. This additional sediment would have likely erroneously elevated the total-recoverable metal concentrations. Therefore, samples from these six sites were not analyzed for total-recoverable metal concentrations.

Table 2. Water-quality data for surface-water samples collected in the Miller Creek watershed, Montana, August 30-31, 2000 (click here for pdf file) (click here for xls file)

Samples were collected in acid-washed 4-L polyethylene bottles at each site. Water-quality samples were transported to a central processing location near the middle of each study reach as soon after collection as possible. Values of pH were determined on an unfiltered aliquot of each sample. A second unfiltered aliquot was drawn for analysis of total-recoverable metals. A third aliquot was filtered through a 0.45-µm capsule filter for the analysis of dissolved major cations and metals. The latter two aliquots were acidified with ultra-pure nitric acid to a pH of less than 2. A fourth filtered aliquot was drawn for the analysis of anions. Sample processing, filtration, and preservation were performed according to procedures described by Ward and Harr (1990), and Horowitz and others (1994).

The USGS National Water Quality Laboratory in Denver, Colo., analyzed water samples collected during this study. All concentrations of dissolved and total-recoverable metals, except for iron, were analyzed using inductively coupled plasma-mass spectrometry. Iron concentration was determined by inductively coupled plasma. Dissolved calcium and sodium concentrations were determined by inductively coupled plasma-atomic absorption spectrometry. Dissolved chloride and sulfate concentrations were determined by ion chromatography. The analytical methods used are described by Fishman and Friedman (1989), Fishman (1993), Garbarino and Taylor (1996), and Garbarino and Struzeski (1998).

Streambed-sediment samples were collected at 16 sites throughout the watershed (fig. 2). The streambed-sediment samples were analyzed for leachable metals (table 3). A composite sample was collected at each of the 16 sites by scooping sediment deposited in pools and in low-velocity areas. Using streamwater, the samples were wet-sieved onsite through a 10-mesh (2-mm) stainless-steel screen and collected into a plastic pan. After a sufficient amount of sediment was collected at each site (about 3 kg), samples were sealed in acid-washed plastic containers.

Table 3. Sediment-quality data for streambed-sediment samples collected in the Miller Creek watershed, Montana, August 2000 (click here for pdf file) (click here for xls file)

The USGS laboratory of the Geologic Discipline in Denver, Colo., analyzed streambed-sediment samples collected during this study. In the laboratory, streambed-sediment samples were dried in ovens at about 50°C and sieved to 100-mesh (<150 mm). Samples were partially digested using warm (50°C) 2 molar hydrochloric acid-1 percent hydrogen peroxide solution for 3 hours with continuous agitation. Partial digestion releases the leachable fraction of trace elements associated with hydrous amorphous iron- and manganese-oxide mineral coatings and colloidal particles on the surface of the sediment sample. The leachate from the digestion was analyzed for 35 elements using inductively coupled plasma-atomic emission spectrometry as described by Church and others (1997).

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