Chemical Analysis of Ken Lake, Olympia, WA
Alan Arvidson, Jon Clemens, Jeff Taisch
March 1, 2003
Materials and Methods
Ken Lake is located at the foot of the black hills near the intersection of U.S.
Highway 101 and Black Lake Boulevard, on the border of quadrangles 20 and 21
(T18N/R2W) about 3 miles west of Olympia, Washington (figure 1). It covers a total area
of approximately 111,000 m2, and has a perimeter of about 1800 m (calculated using GIS
ArcView v3.3). The lake is about 3 m at its deepest point. The most frequented sampling
site was at the coordinates 47 1’ 59.1” N latitude, 122 57’ 4.6” W longitude.
Samples were collected from the lake on 10/25/02, 11/08/02, 12/18/02, and
2/08/03. The samples were taken in duplicate from depths of 0.5, 1.5, and 2-3 m with the
Van Dorn sampling equipment. They were contained in one-liter, Nalgene bottles and
Whirl-Pak plastic sampling bags for transport and storage. All samples, except those used
for the total phosphorus analysis were vacuum filtered using 0.45 μm membrane filter.
Alkalinity measurements were made the same day using Environmental Protection
Agency method 310.1 approved for National Pollutant Discharge Elimination System.
Secchi disk readings were taken at each location (Figure 1). The pH determinations were
made on site using Oakton 35613 pH meter. A Yellow Springs Instruments meter was
used for the measurements of temperature, salinity, dissolved oxygen, and specific
conductance at one-meter intervals.
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For preparation of cation analysis, about 250 mL of the filtered samples were
placed into HNO3 acid-washed 500 mL Nalgene bottles and treated with enough HNO3 to
lower the pH of the water to < 2.00. An additional 125 mL was put into clean Nalgene
bottles for ion chromatograph analysis. Samples were refrigerated until analyzed. The
unfiltered samples were frozen until analyzed for total phosphorus.
For anion analysis, samples were filtered through a 0.2 μm filter and run
undiluted through the Dionex 2020I Ion Chromatograph. The data was logged and
integrated for anion concentrations using Vernier Logger Pro software and the linear
regression analysis was carried out with Microsoft Excel. The Perkin-Elmer Model 305A
atomic absorption instrument was used for cation analysis; all samples were run
undiluted. Ten mL of 10,000 ppm CsCl solution was added to samples and standards for
Na and K analysis, and 5 mL of 40,000 ppm La solution was added to samples and
standards for the Ca and Mg analysis. Regression analysis and calibration curve
calculations were carried out with Microsoft Excel.
Results
The pH of Ken Lake is neutral to slightly acidic, with a mean pH of 6.70
(standard deviation 0.50 pH). Mean specific conductance was 34.1 μS (standard
deviation 0.3 μS). Secchi disk readings showed visibility to the lake floor on all sampling
dates. Dissolved oxygen varied according to sampling date with a mean of 7.70 mg/L.
Average alkalinity was about 9 mg/L CaCO3, but this varied by date and is summarized
in Table 1. Ion concentrations are organized by sampling date and summarized in Table
1. The total phosphorus for samples taken on 2/08/03 had a mean concentration of 21
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μg/L (standard deviation 8 μg/L). The mean ion balance for samples having a complete
analysis was 43%. Ion balances for all samples are summarized in Table 2.
The Carlson Trophic Status Index (Phosphorous) (TSI(P)) was calculated for both
December and February samples. The TSI (P) value for the samples taken on December
18th was 36.6 and the TSI (P) for samples taken on Feburary 8th was 48.3.
Notes
A depth profile of Ken Lake would be relatively useless, since the lake showed no
change in chemical composition by depth. Samples taken on 10/25/02 and 11/08/02 were
not analyzed for calcium or magnesium. Some data was omitted using the q test for bad
data (90% confidence). Ion balances for samples containing bad data were not calculated.
In all samples, there was a positive ion balance result, which seems to suggest that there
are anions in Ken Lake that this study did not consider.