This Study Involved the Sampling and Profiling of Three Eastern Washington Lakes: Soap

Abstract

This study involved the sampling and profiling of three Eastern Washington lakes: Soap Lake, Blue Lake and Deep Lake. Physical data was collected at one-meter intervals. Water samples were analyzed for pH, alkalinity and ion concentrations. Baseline measurements of physical and chemical data were established for Blue Lake and Deep Lake. The data collected for Soap Lake was compared to previously available data. It was found that Soap Lake had the highest sulfate and chloride concentrations for the three lakes. These were considerably higher than the sulfate and chloride concentrations found in samples from Deep Lake and the mixolimnion of Blue Lake. Samples of Deep Lake had detectable levels of nitrite, nitrate, sulfate, phosphate and chloride.. It was established from physical and chemical data that Blue Lake is meromictic. Data from Soap Lake and Deep Lake indicated a non-meromictic status.

Introduction

Water quality analysis was performed on several Eastern Washington Lakes near the Sun Lakes State Park by six teams of Environmental Analysis students. This study concerned Soap Lake, Deep Lake, and Blue Lake. The physical and chemical compositions of the lakes were measured. The chemical analysis consisted of quantitative anion and cation measurements as well as alkalinity and pH determinations. The United States Department of the Interior geological survey from 1988 and table 8-1 from the book Lakes (Lerman et al. 1978) were used as a basis of temporal comparison for our chemical analysis of Soap Lake. The physical analysis consisted of measurements of dissolved oxygen, specific conductance, salinity and temperature.

The term meromictic refers to a type of lake that has a monolimnion, or a lower layer that does not mix with the rest of the lake during seasonal turnover. This leads to different chemistry and physical characteristics in the lower lake water. Water samples and physical data can show evidence of a lake’s mictic status. The purpose of this study is to establish the mictic status of these lakes.

Materials/Methods

Soap Lake is in Grant County WA, northeast of Ephrata by Highway 28 (Figure 2). The surrounding area of the lake and its vegetation was consistent with the high desert climate of Eastern Washington. The lake has a white ring from deposits, believed to be calcite, gypsum, and halite and the lake is blue-green in color (Stroh, personal communication). At its deepest point the lake is approximately 30 meters.

Deep Lake is south of the Sun Lakes State Park and campground, also in Grant County (Figure 3). It lies about 25 kilometers north of Soap Lake. The water is clear dark blue and the greatest depth measured via depth finder was at 34m.

Blue Lake is in Okanogan County, WA near the Canadian border, about 170 kilometers north of Soap Lake (Figure 4). Measurements taken showed it to be at lest 30 meters deep in places.

The samples were taken over three days from 15-17 October, 2002. Secchi disk readings were taken at each location (Figures 2-4). Water samples were collected using Van Dorm sampling equipment and Nalgene bottles for transport and storage. The pH determinations were made on site using Oakton 35613 pH meter. A YSI meter was used for the measurements of temperature, salinity, dissolved oxygen, and specific conductance at one-meter intervals. Samples were vacuum filtered with a 0.45 micron filter and alkalinity measurements were made that day using NPDES approved method 310.1.

Soap Lake was sampled at UTM coordinates 311,145 E and 5,254,354 N. Physical data was acquired to depth of 18 meters, but following an interruption, water samples from below the chemocline could not be gathered after the boat drifted.

The Blue Lake samples and measurements were taken at UTM coordinates 317,229 E and 5,419,989 N. Pink, sulfate enriched water was collected at 20-meters depth and yellow sulfate enriched water at 28-meters. Physical data was acquired to a depth of 30 meters.

Deep Lake was sampled at UTM coordinates 325,013 E and 5,273,246 N.

The maximum depth that could be reached with the equipment was 30 meters.

For anion analysis, samples were filtered through a 0.2 micron filter and run through a Dionex 2020I Ion Chromatograph. The Perkin-Elmer Model 305A was used for cation analysis.

Results

The results can be divided into chemical and physical data. The physical data is best represented in separate depth profiles for each lake. Deep Lake and Blue Lake showed a sudden drop in temperature at the thermocline, at depths of 14 m and 13 m, respectively (Figure 5). Additionally, each lake showed a drop in dissolved oxygen in the depth range of 13-14 m, although the decline in Deep Lake was more gradual (Figure 6). The Secchi disk visibility for the lakes were as follows: 6 m for Blue Lake, 7.3 m for Deep Lake, and 9 m for Soap Lake. Salinity data for each lake remained fairly constant. Soap Lake showed salinity values from 12.3 ppt, lowering slightly to 11.9 ppt at the deepest data point. In Deep Lake, salinity values varied only from 0.1 to 0.2 ppt throughout. Blue Lake showed a slow increasing trend of salinity with depth, from 2.3 to 4.1 ppt. The chemical data including alkalinity, pH, and ion concentrations are displayed according to depth in Table 1.

Discussion

The data collected in this study helps to elucidate the mictic status of the Eastern Washington Lakes. The sample site in Soap Lake had a depth of only 18 m, compared to the lake’s deepest point of 30 m. As a result, neither a thermocline nor a chemocline was observed at this site. With respect to temperature, Soap Lake showed no stratification. Additionally, no evidence for a chemical stratification of Soap Lake was gathered, since the deepest sample from Soap Lake was 10 m. However, it was confirmed in a previous study that Soap Lake is indeed meromictic (Walker, 1973). The study presented here did not show such evidence.

The alkalinity for Soap Lake is relatively high, with an average of 6253 mg/L CaCO3 (Table 1). These high values were expected upon seeing the white crystalline precipitation along the shoreline. Soap Lake sulfate concentrations were within one standard deviation of the values from both the Department of the Interior and the Lerman, et al study. The chloride levels were similar to the Lerman value of about 5000 mg/L (Table 1). The D.O.I. report lists a mean sulfate concentration for the corresponding depth range we studied as 2950ppm. Table 8-1 from Lakes (Lerman et al. 1978) listed the mean concentrations as 6020ppm sulfate and 4680ppm chloride however it is unclear which depth ranges were sampled to produce these values.

Blue Lake showed a very defined thermocline (Figure 4). Additionally, a sample taken from 28 m depth showed much higher ion concentrations than the samples taken from 20 m and above. This is evidence for chemical stratification and meromictic status for Blue Lake. The dissolved oxygen profiles further clarify the mictic status. Blue Lake showed relatively constant dissolved oxygen values for the epilimnion with a sharp drop at 13 m depth, coinciding with the thermocline. The alkalinity values for the sample taken at 28 m were more than double the concentrations for all samples above that depth. This evidence supports the hypothesis that Blue Lake is indeed meromictic.

Sampling of Deep Lake, like Soap Lake, provided inconclusive evidence to determine whether the lake is meromictic. Deep lake had the lowest alkalinity and salinity of the three lakes. A thermocline was observed at 14m but there was no evidence of a chemocline to a depth of 30m. Due to equipment limitations complete physical profiles and sampling was unattainable. For these reasons, the mictic status of Deep Lake is inconclusive.

The anion analysis performed concurs with hypotheses about the mictic status of the lakes studied. Deep Lake showed the lowest values for anion concentrations. It is interesting to note that Deep Lake was the only lake in the study that had measurable concentrations of NO2, NO3 and PO4.

Of the lakes studied, only Blue Lake offered conclusive evidence it is meromictic. The evidence gathered from Soap Lake and Deep Lake is inconclusive in the determination of mictic status. Further analysis must be done to conclude the missing data from table one.

References

Pielou, E. C., Freshwater. University of Chicago Press. Chicago, Il. c1998. pg.149-183.

This text was used for general material on lakes: chemistry and characteristics in this report.

K. F. Walker, The stability of meromictic lakes in central Washington. University of Washington, Seattle 98195. c1973.

This text provided information on meromictic lakes and comparitive analysis for the lakes.

John D. Hem, Study and Interpretation of the Chemical Characteristics of natural Water.

U. S. Geological Survey, U. S. Government Printing Office. c1985.

This text provided information that contributes to our quanitative and qualitative analysis of the species found at these project sites.

Lakes, chemistry, geology, physics, edited by Abraham Lerman; with contributions by P. Baccini…[et al.], Pub info New York: Springer-Verlag, c1978.

This text provided information that gives table background comparison of Soap Lake.

this text provided location information for site description.