Open-File Report 2007–1390
U.S. GEOLOGICAL SURVEY
Open-File Report 2007–1390
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ADEC, ENRI, and USGS personnel collected (standard dip-sampling) and processed stream-water quality samples according to established USGS protocols (U.S. Geological Survey, 1997–99) for the USGS samples. Most of the USGS samples were analyzed for dissolved organic carbon and dissolved trace elements because there will be implications for the carbon-cycle trace-element mobility if permafrost continues to thaw in the Tanana River Basin. Additional water samples, in-situ measurements (pH, dissolved oxygen, specific conductance, and flow), stream macroinvertebrates and periphyton, and physical habitat data were collected at the wadeable stream sites following USEPA EMAP wadeable stream protocols.
The USGS NRP Laboratories in Boulder, Colorado, analyzed all samples for dissolved and whole-water constituents using documented USGS methods and quality-assurance practices (table 3). Data collected during 2004 included laboratory measurements of pH, specific conductance, alkalinity, chloride, nitrate, sulfate, and dissolved organic carbon (DOC) (table 4). In 2005, Specific Ultraviolet-visible Light (UV) Absorbance (SUVA) was added to the list of parameters (table 5). During 2006, the program was expanded to include field measurements of specific conductance and alkalinity and laboratory analysis of water samples for stable isotopes of deuterium and oxygen-18, Ultraviolet-Visible Light Absorption Analyses (UV-Vis), sodium, ammonium, potassium, magnesium, and calcium. The average ionic balance of the 27 samples collected in 2006 varied by less than 2 percent providing a high level of confidence in the accuracy of the data.
DOC, UV-Vis, and SUVA analyses were filtered in the Fairbanks or Anchorage field office using a 60-mL Becton Dickinson™ plastic syringe with Luer-lok™ fitting and a 25-mm Gelman Acrodisk™ filter with 0.45-µm SUPOR™ membrane into 40-mL baked, brown glass vials with Teflon®‑lined caps. These samples were immediately refrigerated and shipped on ice overnight to the USGS NRP laboratories. Samples were refrigerated at the laboratory and analyzed within 2 weeks of arrival. The analytical methods used to determine DOC, UV-Vis, and SUVA are listed in table 3 (at back of report). Results are shown in tables 4, 5, and 6 (at back of report).
DOC Concentrations.—DOC was measured using the platinum catalysed persulfate wet oxidation method on an O.I. Analytical Model 700 TOC Analyzer™ (Aiken, 1992). The instrument was warmed up for 24 hours before analyzing samples. Samples and standards were loaded onto an autosampler for analysis and introduced into the reaction vessel by means of a fixed-volume sample loop. The volume of the sample loop was kept small, usually 1 mL, to maintain linear instrument response (0–50 µg of carbon). The standard, automated analytical conditions called for 0.5 mL of 5 percent by volume phosphoric acid to be added to the sample. The sample was then purged for 2.0 minutes with nitrogen to remove inorganic carbon, after which 0.5 mL of 0.42 M sodium persulfate solution was added. The standard reaction time of 5 minutes was used for the persulfate oxidation step. The instrument was calibrated with solutions of reagent-grade potassium hydrogen phthalate in distilled water. The standard curve, consisting of a minimum of five standards over the range of interest, was repeated for every eight water samples analyzed in duplicate. Reported values are the averages of duplicate analyses. Standard deviation for the DOC measurement was determined to be ±0.2 mg carbon/L.
Specific UV Absorbance (SUVA).—SUVA, defined as the UV absorbance of a sample measured at a given wavelength (λ) divided by the DOC concentration, is an average molar absorptivity for all molecules that comprise the DOC in a water sample. SUVA, therefore, is a parameter that indicates the nature or quality of DOC in a given sample and has been used as a surrogate measurement of DOC aromaticity (Chin and others, 1994). SUVA values at 254 nanometer (nm) (SUVA254) are used in this report because (1) natural organic matter absorbs strongly at this wavelength giving increased sensitivity, and (2) strongly correlates with aromatic-carbon content of organic matter. SUVA values are reported as L/(mg carbon * m) and have a standard deviation of ±0.1.
Ultraviolet-Visible Light Absorption Analyses (UV-Vis).—UV-Vis measurements were made on a Hewlett-Packard Model 8453™ photo-diode array spectrophotometer between λ=200 and λ=800 nm with distilled water as the blank utilizing a 1-cm path-length quartz cell. Results are reported for the λ=254 nm in dimensionless absorbance units. The wavelength of λ=254 nm was chosen because it is the wavelength commonly associated with the aromatic moieties in a sample (Chin and others, 1994). Samples filtered at room temperature were analyzed using a quartz cell in the manual mode. The cell was rinsed with a small volume of sample before adding sample for analysis. The cell was then rinsed with distilled water before analyzing the next sample. Standard deviation for a UV measurement at 254 nm is ±0.002 angstrom.
Samples for major ion analyses were filtered in the Fairbanks or Anchorage field office using 60 mL Becton DickinsonTM plastic syringes with Luer-lokTM fittings and a 25-mm Gelman Acrodisk filter with 0.45-µm SUPORTM membrane (Babiarz and others, 2000) into clean 125 mL high density polyethylene bottles. The samples were shipped chilled to the USGS NRP labs in Boulder, CO. Concentrations of major ions were determined by ion chromatography using a Dionex DX120 ion chromatographTM (Fishman and Freidman, 1989; Fishman, 1993).
Samples for oxygen-deuterium isotopes were processed at the Fairbanks or Anchorage field office by filling 40-mL baked, clear glass bottles with Poly-Seal™ caps with sample water leaving no air space. Samples were sent to USGS Isotope laboratory in Reston, VA. Hydrogen-isotope-ratio analyses were performed using a hydrogen equilibration technique (Coplen and others, 1991; Kinga Revesz and Tyler Coplen, U.S. Geological Survey, written commun., 2003). Water samples are measured for δO18 using the CO2 equilibration technique of Epstein and Mayeda (1953), which has been automated according to Kinga Revesz and Tyler Coplen (U.S. Geological Survey, written commun., 2003). Therefore, both oxygen and hydrogen isotopic ratio measurements are reported as activities.
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