U.S. Geological Survey
Water-Resources Investigations Report 02-4073

Prepared in cooperation with
CITY OF OLATHE, KANSAS, and the
KANSAS DEPARTMENT OF HEALTH AND ENVIRONMENT

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Sediment Deposition and Selected Water-Quality Characteristics in Cedar Lake and Lake Olathe, Northeast Kansas, 2000

By David P. Mau

Shoreline of Lake Olathe, northeast Kansas, October 2001.

CONTENTS

Abstract
Introduction

Previous Investigations
Description of Current Investigation
Purpose and Scope
Acknowledgments

Description of Lake Olathe Watershed
Methods

href Bathymetric Surveys
Estimation of Bottom-Sediment Depth and Volume
Reservoir Sediment-Core Collection, Processing, and Analysis
Analysis of Diatoms in Reservoir Sediment
Quality Control
Trend Analysis

Sediment Deposition in Cedar Lake and Lake Olathe

Calculated Bottom-Sediment Volume and Mass
Comparisons of Sediment Deposition Among Cedar Lake, Lake Olathe, and Hillsdale Lake

Water-Quality Characteristics

Phosphorus

Concentrations in Reservoir Bottom Sediment
Estimates of Phosphorus Loads and Yields in Lake Olathe Watershed

Nitrogen
Trace Elements
Selected Pesticides

Diatoms as Indicators of Lake Eutrophication
Summary and Conclusions
References
Supplemental Information

For additional information about the Lake Olathe Nutrient Study in Kansas, please visit:

FIGURES

Figure 1. Maps showing location of Lake Olathe watershed in northeast Kansas and bottom-sediment coring sites in Cedar Lake and Lake Olathe
Figure 2. Map showing land use in Lake Olathe watershed, 1993
Figure 3. Graphs showing number of acres harvested and livestock in Johnson County, Kansas, for selected years between 1960 and 1999
4-8. Maps showing:

Figure 4. Average length of bottom-sediment cores collected from coring sites in Cedar Lake and Lake Olathe, 2000
Figure 5. Bathymetric contours for Lake Olathe, 2000
Figure 6. Estimated thickness of sediment in Lake Olathe, 1956-2000
Figure 7. Mean concentrations of total phosphorus in bottom-sediment core samples collected from Cedar Lake and Lake Olathe, 2000
Figure 8. Mean particle-size composition of bottom-sediment cores collected from Cedar Lake and Lake Olathe, 2000

Figure 9. Graphs showing relation between concentrations of cesium-137 and depths of bottom-sediment samples from coring site 3 in Cedar Lake, 1938-2000, and coring site 5 in Lake Olathe, 1956-2000
Figure 10. Graph showing relation between total phosphorus concentrations in bottom-sediment samples and depths of samples from coring site 5 in Lake Olathe, 1956-2000
Figure 11. Map showing mean concentrations of total ammonia plus organic nitrogen as nitrogen in bottom-sediment samples from Cedar Lake and Lake Olathe, 2000
12-18. Graphs showing:

Figure 12. Relation between concentrations of total ammonia plus organic nitrogen as nitrogen in bottom-sediment samples and depths of samples from coring site 5 in Lake Olathe, 1956-2000
Figure 13. Relation between selected trace element concentrations in bottom-sediment samples and depths of samples from coring site 3 in Cedar Lake, 2000
Figure 14. Relation between selected trace element concentrations in bottom-sediment samples and depths of samples from coring site 5 in Olathe Lake, 2000
Figure 15. Relation between selected pesticide concentrations in bottom-sediment samples and depths of samples from coring site 3 in Cedar Lake, 2000
Figure 16. Relation between selected pesticide concentrations in bottom-sediment samples and depths of samples from coring site 5 in Lake Olathe, 2000
Figure 17. Relation between total number of identified diatom species in bottom-sediment samples and depths of samples from coring site 3 in Cedar Lake, 1938-2000, and coring site 5 in Lake Olathe, 1956-2000
Figure 18. Relation between total number of valves of identified diatom species per gram of material in bottom-sediment samples and depths of samples from coring site 3 in Cedar Lake, 1938-2000, and coring site 5 in Lake Olathe, 1956-2000

TABLE

Table 1. Location of bottom-sediment coring sites in Cedar Lake and Lake Olathe, northeast Kansas, 2000
Table 2. Analytical results and percentage differences for selected trace elements in split replicate samples of bottom sediment from coring site 5, Lake Olathe, northeast Kansas, 2000
Table 3. Sediment deposition, loads, and yields estimated for Cedar Lake, Lake Olathe, and Hillsdale Lake, northeast Kansas
Table 4. Estimated mean sediment bulk densities in both in-channel and out-of-channel bottom sediment, Cedar Lake and Lake Olathe, northeast Kansas, 2000
Table 5. Trend test analysis of concentrations of total phosphorus and total ammonia plus organic nitrogen (N) in bottom sediment from coring site 5 in Lake Olathe, northeast Kansas, 2000
Table 6. Total phosphorus sediment loads and yields estimated for Cedar Lake, Lake Olathe, and other selected reservoir watersheds in Kansas
Table 7. Mean concentrations and sediment-quality guidelines for selected trace elements in bottom-sediment samples from Cedar Lake and Lake Olathe, northeast Kansas, 2000
Table 8. Mean concentrations of selected pesticides in bottom-sediment samples from Cedar Lake and Lake Olathe, northeast Kansas, 2000
Table 9. Relative percentage abundance of six most-prevalent diatom species in bottom-sediment samples from Cedar Lake, 1938-2000, and Lake Olathe, 1956-2000, northeast Kansas
Table 10. Relation between relative abundance of selected species of diatoms and concentrations of total phosphorus, total ammonia plus organic nitrogen as nitrogen (N), and depths of samples from selected bottom-sediment cores from Cedar Lake and Lake Olathe, northeast Kansas, 2000
Table 11. Selected diatom species and their presence under various water-quality conditions
Table 12. Laboratory analysis methods for reservoir bottom-sediment constituents
Table 13. Nutrients analyzed in bottom sediment from Cedar Lake and Lake Olathe, northeast Kansas, 2000
Table 14. Selected metals and trace elements analyzed in bottom sediment from Cedar Lake and Lake Olathe, northeast Kansas, 2000
Table 15. Radiochemical analyzed for age dating bottom sediment from Cedar Lake and Lake Olathe, northeast Kansas, 2000
Table 16. Statistical summary of concentrations and comparison to sediment-quality guidelines for selected metals and trace elements in bottom-sediment sample from Cedar Lake coring site 3, northeast Kansas, 2000
Table 17. Statistical summary of concentrations and comparison to sediment-quality guidelines for selected metals and trace elements in bottom-sediment sample from Lake Olathe coring site 5, northeast Kansas, 2000
Table 18. Diatom taxa, relative percentage abundance, and total number of valves per gram of material in bottom-sediment sample from Cedar Lake coring site 3, northeast Kansas, 2000
Table 19. Diatom taxa, relative percentage abundance, and total number of valves per gram of material in bottom-sediment sample from Lake Olathe coring site 5, northeast Kansas, 2000

CONVERSION FACTORS, ABBREVIATIONS, AND VERTICAL DATUM

—Temperature in degrees Fahrenheit (÷F) can be converted to degrees Celsius (÷C) by the equation:

Sea level: In this report, "sea level" refers to the National Geodetic Vertical Datum of 1929-a geodetic datum derived from a general adjustment of the first-order level nets of the United States and Canada, formerly called Sea Level Datum of 1929.

Sediment Deposition and Selected Water-Quality Characteristics in Cedar Lake and Lake Olathe, Northeast Kansas, 2000

Abstract

INTRODUCTION

Many water-quality constituents adhere to sediment particles and are deposited in reservoirs, which act as sinks for these constituents. Large sediment concentrations frequently observed in Kansas reservoirs are responsible for turbidity levels that can reduce light penetration in the euphotic zone (that part of a water body in which there is sufficient light penetration to support photosynthesis). Large turbidity levels in combination with the presence of nutrients and pesticides may have detrimental effects on humans who use reservoirs as a drinking-water supply and on aquatic organisms, and can reduce the recreational value of the reservoir. Two reservoirs currently under investigation, Cedar Lake and Lake Olathe, are located in northeast Kansas (fig. 1). Lake Olathe serves as a supplemental drinking-water supply for approximately 90,000 residents in the city of Olathe and as a recreational resource for the community.

Cedar Lake was constructed by the city of Olathe in 1938 (Carly Adams, city of Olathe, written commun., 2001) and used as a supplemental water-supply source, but rapid sedimentation reduced the water-storage capacity of the lake. In response to the increasing water requirements of the city of Olathe, Lake Olathe was constructed in 1956 as a water-supply reservoir and to provide recreational use for boating, fishing, and swimming. As residential and commercial development increases in the Lake Olathe watershed, there is considerable interest in maintaining acceptable water quality in Lake Olathe for water supply and recreation.

Previous Investigations

The U.S. Geological Survey (USGS) has investigated reservoir sediment in Kirwin, Webster, and Cheney Reservoirs, and Waconda, Tuttle Creek, and Hillsdale Lakes (see fig. 1), index map) (Juracek, 1997; Christensen, 1999; Mau, 2001). These investigations included analysis of part or all of the following constituents: nutrients, selected trace elements, and pesticides. Sediment deposition varied considerably among the reservoirs investigated, increasing from west to east across the State along with increasing precipitation. Mean annual phosphorus yield showed similar increases from west to east with the lowest yield determined for Webster Reservoir, in the western part of Kansas, and the highest yield for Hillsdale Lake, located in the northeast part (Mau and Christensen, 2000).

Bathymetric surveys were done in 2000 for 23 small municipal lakes in Kansas, including Lake Olathe, by the U.S. Army Corps of Engineers, working for the Kansas Water Office. The total sediment deposition to Lake Olathe from 1956 to 2000, estimated on the basis of these surveys, was 30 acre-ft, or 0.67 acre-ft of sediment deposition per year (Kansas Water Office, 2001, p. 31).

Description of Current Investigation

Purpose and Scope

Acknowledgments

DESCRIPTION OF LAKE OLATHE WATERSHED

Cedar Lake has a surface area of about 54 acres and a current (2000) water-storage volume of 334 acre-ft at the dam crest elevation of 1,001.0 ft above sea level. Lake Olathe has a surface area of about 170 acres and a current storage volume of 3,102 acre-ft at the dam crest elevation of 937.5 ft above sea level. The watershed area of 16.9 miî (10,800 acres) encompasses both Cedar Lake and Lake Olathe as well as Cedar Creek, the main tributary joining the two lakes (fig. 1).

There are approximately 1,000 people in the watershed, most of whom live in single-family residences and farms in the area (Carly Adams, city of Olathe, written commun., 2001). Lake Olathe is located within the Olathe city limits, and there are no other towns in the watershed. A public, 18-hole golf course abuts Lake Olathe on the east.

The mean annual temperature in Olathe is about 55 ÷F, with a mean monthly range of 28 ÷F in January to 78 ÷F in July (National Oceanic and Atmospheric Administration, 1966-98). Mean annual precipitation (1961-90) is about 40 in., which occurs primarily during the growing season from April through September (National Oceanic and Atmospheric Administration, 1966-98).

The Lake Olathe watershed is underlain by sedimentary bedrock deposited during late Pennsylvanian time (about 285 to 300 million years ago) (Lee and Sears, 1985). The bedrock is mostly shale, with some prominent limestone layers and sandstone.

Pre-Illinoian glacial till and a thin lens of loess (windblown Pleistocene deposits) cover the bedrock. Soils in the watershed were formed from windblown loess, glacial outwash, and residuals derived from the weathering of shale and limestone bedrock (Lee and Sears, 1985).

Land use in the Lake Olathe watershed is primarily agricultural cropland and grassland, which represent 83 percent of the watershed (fig. 2) (Kansas Geological Survey, 1993). Crop-production statistics were not available for the Lake Olathe watershed; therefore, the following statistics were based on figures for Johnson County where the watershed is located (fig. 1, index map). Crop production in the county declined from 108,000 acres of harvested cropland in 1960 to 71,000 acres harvested cropland in 2000 (fig. 3A) (Kansas State Board of Agriculture and U.S. Department of Agriculture, 1960-95; Kansas Department of Agriculture and U.S. Department of Agriculture, 1996-2000). Production of wheat, rye, corn, oats, and sorghum declined between 1960 and 1999 (fig. 3A). However, soybean and all hay production increased during the same period. Residential and commercial land use in Johnson County increased during the 40-year period from 1960-99, and similar residential and commercial growth was evident in the Lake Olathe watershed, from 2.0 percent of the watershed in 1985 to 15 percent in 1999 (Lee and Sears, 1985; Kevin Dobbs, Kansas Biological Survey, written commun., 2001).

Livestock production in Johnson County has been relatively stable for cattle and calves, averaging about 25,600 head annually from 1960 to 1999. However, annual inventories of hogs, sheep and lambs, and chickens declined during the same period (fig. 3B) (Kansas State Board of Agriculture and U.S. Department of Agriculture, 1960-95; Kansas Department of Agriculture and U.S. Department of Agriculture, 1996-2000).

METHODS

Bathymetric Surveys

Estimation of Bottom-Sediment Depth and Volume

Reservoir Sediment-Core Collection, Processing, and Analysis

A gravity corer was used to collect bottom-sediment cores from Cedar Lake from one in-channel (historic stream channel prior to dam impoundment) coring site (Cedar Lake coring site 3) and two out-of-channel coring sites (Cedar Lake coring sites 1 and 2) (table 1, fig. 4). In-channel and out-of-channel sediment cores were collected to determine if there were any chemical or biological differences in sediment from the two topographical areas. Similarly, five sediment cores were collected from Lake Olathe from three in-channel coring sites (Lake Olathe coring sites 1, 2, and 5) and two out-of-channel coring sites (Lake Olathe coring sites 3 and 4) (table 1, fig. 4). The liner used in the gravity corer was transparent tubing made of cellulose acetate butyrate with a 2.88-in. outside diameter and a 2.63-in. inside diameter. Depending upon the required analyses, three to four sediment cores were collected at each coring site to provide sufficient material and briefly chilled prior to processing.

The sediment cores were processed at the USGS laboratory in Lawrence, Kansas. The plastic liners were cut longitudinally in two places and 180÷ apart. The cuts were partially completed using a rotary handsaw and finished with a retractable razor knife set at a depth to minimize penetration of the sediment core. The cores were split in half by pulling a tightly held nylon string through the length of the two cuts and allowing the halves to separate. Depending upon the type of analysis as well as available bottom material in each core, the cores then were subsectioned into equal length intervals, and sediment samples from each interval were removed for physical and chemical determinations (Cedar Lake coring site 3 and Lake Olathe coring site 5; fig. 1)

Analysis requirements from selected bottom-sediment sampling sites (Cedar Lake coring sites 1-2 and Lake Olathe coring sites 1-4; fig. 1) consisted of a mean chemical determination for the entire sediment core. In these instances, equal volumes of sediment from each interval were removed from the sediment core, placed in a mixing bowl, and mechanically homogenized. A sample of the homogenized mass then was sent to the USGS National Water-Quality Laboratory (NWQL) in Denver, Colorado, for chemical analysis.

Sediment mass (in pounds) is a product of sediment volume (cubic feet) and sediment bulk density (pounds per cubic foot). Sediment bulk densities were determined from selected sediment cores. These sediment cores were subsectioned, weighed, and oven dried to remove all moisture. The dried subsectioned cores were reweighed, and the weights divided by the subsection volume to determine bulk density. Mean bulk densities for the entire sediment core were determined from the subsectioned mean bulk densities. Sediment-core mean bulk densities were used to calculate average bulk density for each lake.

Subsections of selected cores were analyzed for bulk density at the USGS laboratory in Lawrence, Kansas, according to methods presented in Guy (1969). Subsections also were analyzed for percentage of sand and silt and (or) clay at the USGS sediment laboratory in Iowa City, Iowa, according to methods presented in Guy (1969). Core subsections from selected sites were analyzed at the NWQL in Denver, Colorado, for total phosphorus, total ammonia plus organic nitrogen as nitrogen, and selected trace elements according to procedures presented in Fishman (1993). Analytical methods and reporting limits are presented in tables 12-14 (in "Supplemental Information" section of this report). In addition, organochlorine insecticides, organophosphate insecticides, and acetanilide and triazine herbicides were analyzed for selected core subsections at the USGS Organic Geochemistry Research Laboratory in Lawrence, Kansas, on the basis of procedures given in Mills and Thurman (1992).

The use of a gravity corer, such as used during this investigation, may produce a "core-shortening" phenomenon (Blomqvist, 1985). Core shortening refers to the difference between the depth of sediment penetration by the sample tube and the length of the core inside the sample tube. This phenomenon has been documented at length and is described as being caused by friction of the sediment against the inner wall of the sample tube as the gravity corer penetrates the sediment (Emery and Hulseman, 1964; Blomqvist and Bostrom, 1987). The friction causes the core sample to underrepresent the entire thickness of the penetrated sediment bed, presumably through a thinning of individual sediment layers during the penetration process. Compression of the sediment and loss of water content have been suggested as mechanisms that would explain core shortening, especially in very soft muds (Hongve and Erlandsen, 1979). If compression of sediment is a dominant physical mechanism to explain the core-shortening phenomenon, then sediment densities and, ultimately, calculations of total mass presented in this report may be biased. However, for most sediment cores collected from Cedar Lake and Lake Olathe, very soft muds were evident only in the upper few inches of the cores. Although core shortening affects the length of the retrieved sediment core (fig. 4), the entire core sample represents a complete sediment profile and, thus, a potential record of historical trends in water-quality constituents.

Reservoir bottom sediment may undergo mixing during storms or periods of flooding. This mixing can create difficulties in the analysis of trends in water-quality constituents. To determine whether bottom sediment had been disturbed, sediment cores from both Cedar Lake (coring site 3) and Lake Olathe (coring site 5) (fig. 4) were analyzed for cesium-137 by the NWQL (table 15, in "Supplemental Information" section of this report). Cesium-137, a by-product of thermonuclear-weapons testing in the 1950s and early 1960s, was widely dispersed by atmospheric deposition and potentially sorbed to soil particles (primarily clay). Detectable cesium-137 concentrations in sediment began about 1952 and peaked in 1963-64, followed by a steady decline in concentrations. Identifiable spikes outside of the 1963-64 peak in cesium-137 concentrations in the bottom-sediment core profile may be indicative of turbulence and resuspension of sediment. Analysis of sediment for chemical trends would not be appropriate under these conditions.

Because of its wide dispersal, cesium-137 also can be used to date sediment layers (Holmes, 1998). The ability to date sediment layers is important in determining the effectiveness of BMPs in managing chemical inputs to reservoirs. For example, if particular pesticides are not permitted for use, identification of a nonpermitted pesticide near the water-sediment interface may suggest continued use of the pesticide in the watershed.

Physical markers (commercially available blue plastic tarps) were placed on top of the bottom sediment over a 30-by-30-ft area in both Cedar Lake and Lake Olathe. The intent was to place this minimal degradable material as a layer on top of the reservoir bottom sediment and return in several years to those locations and remove sediment cores. The tarps would be identified by distinct blue layers in the sediment cores, and any sediment above the markers attributed to sediment deposition since 2000. The locations of the tarps were marked using a handheld GPS.

Analysis of Diatoms in Reservoir Sediment

Quality Control

Analysis of split replicate samples from Lake Olathe coring site 5 showed little or no variability among the selected trace elements analyzed, with a median percentage difference of 1.71 percent (table 2). Percentage differences in holmium and silver were equal to or greater than 20 percent; however, the concentrations of these water-quality constituents were very low. The results generally indicate that laboratory precision and reproducibility differences were small (0 to 9.1 percent) and probably not a concern for this investigation.

Trend Analysis

SEDIMENT DEPOSITION IN CEDAR LAKE AND LAKE OLATHE

Calculated Bottom-Sediment Volume and Mass

Total sediment deposition in Lake Olathe was determined to be approximately 317 acre-ft. The sediment volume was calculated as the difference between the 1954 Lake Olathe design volume (3,419 acre-ft) determined from GIS coverage and the reservoir volume determined from the 2000 bathymetric survey at a water-surface elevation of 937.5 ft above sea level (3,102 acre-ft) (figs. 5-6). The mean annual sediment deposition rate for the period from 1956 through 2000 (45 years), calculated on the basis of 317 acre-ft, was 7.0 acre-ft/yr, or 0.42 (acre-ft/yr)/miî, when divided by the 16.6 miî (10,630 acres) of contributing-drainage area from the watershed to Lake Olathe. On the basis of the water-storage capacity design volume for Lake Olathe, the total sediment deposition in 45 years has reduced the water-storage capacity of Lake Olathe by approximately 10 percent. In contrast, approximately 2,100 acre-ft of total sediment deposition was estimated for Hillsdale Lake (approximately 15 mi south of Lake Olathe, fig. 1) for the period 1981-96, or 0.97 (acre-ft/yr)/miî, when divided by the 144 miî of contributing-drainage area from the watershed to the lake (Juracek, 1997).

Total sediment deposition was determined for Lake Olathe in two previous studies-the Kansas Clean Lakes Program (1982-83) (Lee and Sears, 1985) and the U.S. Army Corps of Engineers study done in 2000 for the Kansas Water Office (KWO) (Kansas Water Office, 2001). The Kansas Clean Lakes Program estimation of sediment deposition was based on a bathymetric survey done using a portable depth finder and stopwatch (Lee and Sears, 1985). The completed bathymetric map then was compared to the 1954 Lake Olathe topographic map to determine the sediment deposition during the intervening period. Total sediment deposition estimated from Lee and Sears (1985) was 16.3 acre-ft, substantially less than the 317 acre-ft determined during the 2000 investigation described in this report. Differences in deposition can be attributed in large part to technological advancements available in 2000 that were not available in 1982. Insufficient information describing the methods used to determine sediment deposition in 1982 preclude further comparison of the two methods.

The U.S. Army Corps of Engineers study for the Kansas Water Office was done in 2000 using a single-beam transducer and GPS system similar to the method used by the USGS, and total sediment deposition from this study was estimated to be 30 acre-ft (Kansas Water Office, 2001, p. 31), about 9 percent of the 317 acre-ft determined by the USGS. Data files from the U.S. Army Corps of Engineers study were made available to the USGS by KWO and indicated substantial differences in elevations used to define the reservoir bottom (E. Lewis, Kansas Water Office, oral commun., 2001). Elevation differences that were based on different reference datums may explain some, but not all, of the discrepancies between the USGS and U.S. Army Corps of Engineers studies. The USGS bathymetric study of Lake Olathe in 2000 used the 1935 reference datum (1,036.00 ft) and contour mapping to determine reservoir volume. The 1982-83 Kansas Clean Lakes Program used the same reference datum in their study. On the basis of the reservoir bottom elevations used by the U.S. Army Corps of Engineers, it is not clear how sediment deposition was calculated or whether historic design information from 1954 was used.

The total masses of bottom-sediment material in Cedar Lake and Lake Olathe were calculated by multiplying the bottom-sediment volume (total sediment deposition) from each lake by the mean sediment bulk densities (and appropriate conversion factor) as determined from the sediment cores from each lake (table 3). The mean bulk densities for each lake were calculated by averaging the mean bulk densities in the sediment cores from the in- and out-of-channel coring sites (table 4).

Comparisons of Sediment Deposition Among Cedar Lake, Lake Olathe, and Hillsdale Lake

The total sediment deposition at Hillsdale Lake was 2,100 acre-ft (from 1981-96), more than six times greater than either Cedar Lake or Lake Olathe (table 3; Juracek, 1997). When the comparison was made on the basis of mean annual sediment yield (mean annual sediment deposition divided by the contributing-drainage area), the Hillsdale Lake watershed was the largest contributor of sediment but not substantially greater than the mean annual sediment yield from the drainage area to Cedar Lake (table 3). If the drainage area to Cedar Lake was excluded from the Lake Olathe watershed, the mean annual sediment yield to Lake Olathe would increase from 0.76 to 1.2 million (lb/yr)/miî, which is a more comparable yield relative to those determined for the Cedar Lake watershed [1.56 million (lb/yr)/miî] and the nearby Hillsdale Lake watershed [1.84 million (lb/yr)/miî]. The implication of this calculation is that sediment deposition would be more substantial in Lake Olathe if Cedar Lake did not intercept much of the sediment yield from the watershed. Also, the contributing-drainage area to Cedar Lake represents only 37 percent of the watershed, and yet the mean annual sediment yield is almost twice that contributed to Lake Olathe (table 3).

WATER-QUALITY CHARACTERISTICS

Phosphorus

Concentrations in Reservoir Bottom Sediment

Mean concentrations of total phosphorus in the bottom-sediment cores from Cedar Lake ranged from 1,370 mg/kg at coring site 1, located upstream in the lake, to 1,810 mg/kg at coring site 3, located near the dam (fig. 7). The mean total phosphorus concentration in bottom-sediment samples from the three coring sites was 1,540 mg/kg. Although Cedar Lake is no longer used as a drinking-water supply, under anoxic conditions (low dissolved-oxygen concentrations) phosphorus released from the sediment to the water column could encourage algal blooms and lessen the suitability of water in the lake for aquatic habitat and recreation. Cedar Lake also discharges water to Lake Olathe through Cedar Creek when the water elevation of Cedar Lake exceeds the spillway elevation (1,001.0 ft above sea level); therefore, adverse water-quality conditions in Cedar Lake during such times could easily affect the water quality of the Lake Olathe drinking-water supply.

Mean concentrations of total phosphorus in the bottom-sediment cores from Lake Olathe ranged from 588 mg/kg at coring site 1, located the farthest upstream in the lake, to 1,030 mg/kg at coring site 5, located near the dam (fig. 7). The mean total phosphorus concentration in samples from the five coring sites was 774 mg/kg. It is possible that in-lake enrichment of phosphorus from phytoplankton growth and deposition as well as from lake hydraulics are contributing to the upstream-to-downstream increases in total phosphorus concentrations in Lake Olathe bottom sediment. External sources such as the public golf course and public latrines at the golf course and swimming beach also may contribute to the increased total phosphorus concentrations seen in the sediment cores near the dam (Carly Adams, city of Olathe, oral commun., 2001). There also may be some upstream-to-downstream transport of phosphorus through adsorption to silt and clay particles and the subsequent transport of these particles within the lake.

The difference in total phosphorus concentrations in bottom sediment between the two lakes may be related to historic agricultural and human-related practices. Fertilizer application to cropland as well as animal waste from livestock likely would include phosphorus compounds that could be transported to Cedar Lake, adsorbed to sediment, and deposited in the lake. It is also possible that septic systems from nearby farms and residences that existed or were developed in the 1930s, when Cedar Lake was created, may have leached phosphorus and other compounds into the lake. Cedar Lake also acts as a sediment trap for Lake Olathe, receiving sediment deposition that otherwise would be transported to Lake Olathe. Sediment transport of phosphorus and other hydrophobic compounds (compounds that adsorb to sediment) may be more prevalent in Cedar Lake than in Lake Olathe, where total sediment deposition is less.

Two previous reservoir-sediment studies of Cheney Reservoir in south-central Kansas (Pope, 1998; Mau, 2001) showed a strong linear relation between bottom-sediment particle size and total phosphorus concentration. The regression analysis by Pope (1998) was repeated in this investigation of Cedar Lake and Lake Olathe to determine whether a relation existed between the size of bottom-sediment particles and total phosphorus concentration.

Regression analysis is one method used to determine whether a relation exists between two variables. The correlation coefficient, r, is used as a measure of the strength of the relation and ranges from -1.0 to 1.0 depending on whether the relation is negative (indirect) or positive (direct). The closer the correlation coefficient is to -1.0 or 1.0, the stronger the relation between the two variables. The p-value (probability value) is used as a measure of the statistical significance of a relation. The statistical significance of a correlation increases as the p-value decreases. A 0.05 level of significance is used in this study to define statistically significant correlations.

Regression analysis to determine a relation between bottom-sediment particle size and total phosphorus concentration was inconclusive primarily because of a lack of variability in particle size; more than 97 percent of the sediment particle-size distribution in both lakes was represented by sediment particles less than 0.062 mm in diameter, the silt and clay fractions (fig. 8). The p-values for both lakes indicate that there is no statistical significance relating bottom-sediment particle size to total phosphorus concentrations.

The depositional trend of phosphorus in both Cedar Lake and Lake Olathe was compared to cesium-137 data. Cedar Lake was built in 1938; therefore, the cesium-137 profile of Cedar Lake was expected to be zero near the bottom of the core followed by increasing concentration until the 1963-64 nuclear test ban treaty, with a long period of declining concentrations to the present day at the top of the core. The actual cesium-137 profile peaked at the bottom of the core (oldest sediment) and steadily declined with a slight inflection near the middle of the core (fig. 9). Two possible explanations may account for the cesium-137 profile of Cedar Lake: (1) an incomplete bottom-sediment core was obtained, or (2) dredging activity occurred in Cedar Lake, and sediment containing older cesium-137 concentrations was removed. The sediment core obtained from Cedar Lake was nearly 5 ft long. The initial core analysis showed complete core-barrel penetration through the sediment into the original bottom material, indicating that a complete bottom-sediment core was obtained. Although there was no confirmation of dredging, repair work on the dam face occurred in 1995, following significant water-seepage loss through the earthen dam over a 24-hour period in 1994 (Carly Adams, city of Olathe, oral commun., 2001). Repair-work documents did not indicate the use of lake sediment to shore the dam face. However, because it is possible that sediment near the dam was disturbed either during the rapid loss of water from the lake or during repair work on the dam, comparison of constituent trends using analytical results from coring site 3, located closest to Cedar Lake Dam would be inconclusive.

The depositional trend of phosphorus at Lake Olathe was supported by the cesium-137 analysis (fig. 9). Cesium-137 data in bottom sediment showed a peak in cesium-137 concentrations near the bottom of the core followed by a gradual decrease to the more recent deposition. Dredging activity and removal of 3 acre-ft of bottom sediment that occurred in the upper end of Lake Olathe in 1980 (Lee and Sears, 1985) may have disturbed the sediment profile and accounted for slight variations in the cesium-137 profile near the top of the core. The cesium-137 data from the sediment core indicate that substantial disturbance of sediment layers has not occurred in Lake Olathe and, therefore, would not affect time-trend analysis.

Total phosphorus concentrations in a bottom-sediment core from Lake Olathe appeared to be increasing slightly from the older sediment to the newer sediment near the top of the core (fig. 10). However, the Kendall's tau trend test of the data set did not identify a trend (table 5). If there is a trend, the most likely source is leaking septic systems from residences located near Lake Olathe, which were identified in the 1982-83 Kansas Clean Lakes Program investigation of Lake Olathe (Lee and Sears, 1985). Additional sources of total phosphorus to Lake Olathe could include phosphorus adsorbed to suspended sediment particles transported from Cedar Lake via Cedar Creek, as well as fertilizer usage from either agricultural or urban sources. The extent of suspended sediment and nutrient transport from Cedar Lake to Lake Olathe via Cedar Creek is being investigated.

Estimates of Phosphorus Loads and Yields in Lake Olathe Watershed

Phosphorus loads and yields in the Lake Olathe watershed were calculated on the basis of total sediment deposition previously reported in table 4. The total sediment deposition then was multiplied by the mean total phosphorus concentration in bottom sediment from each lake and, using the appropriate conversion factors to convert from International System to inch-pound units of measurement, divided by the number of years of sediment deposition to determine the annual mean phosphorus load in pounds per year (table 6). The mean annual phosphorus yield was determined by dividing the mean annual phosphorus load by the drainage area to each lake. The results of the sediment-based phosphorus yields for the Cedar Lake and Lake Olathe watersheds were compared to yields determined for the Webster Reservoir, Cheney Reservoir, Tuttle Creek Lake, and Hillsdale Lake watersheds.

Results of the load and yield calculations for Cedar Lake and Lake Olathe indicated that mean annual phosphorus loads for Cedar Lake, 14,700 lb/yr, were more than 50 percent larger than for Lake Olathe, 9,720 lb/yr, and that mean annual phosphorus yields were about four times larger for Cedar Lake, 3.74 (lb/acre)/yr compared to 0.91 (lb/acre)/yr for Lake Olathe (table 6). The differences probably can be attributed to different agricultural and residential practices in the watershed as previously discussed in this report. The implication is that Cedar Lake acts as a water-quality buffer for Lake Olathe and that water quality in Lake Olathe would be changed substantially if Cedar Lake were removed and presumably would increase loads and yields to Lake Olathe.

Recent studies of phosphorus transported to Webster Reservoir (Mau and Christensen, 2000), Cheney Reservoir (Mau, 2001), Tuttle Creek Lake (Mau and Christensen, 2000), and Hillsdale Lake (Juracek, 1997) offer comparisons for the estimates of phosphorus transported into Cedar Lake and Lake Olathe. The mean annual phosphorus yield of the Cedar Lake subwatershed, 3.74 (lb/acre)/yr, was larger than the mean annual phosphorus yield from the other reservoir watersheds that were studied. The Lake Olathe watershed also transported more phosphorus annually per acre of drainage area, 0.91 (lb/acre)/yr, than the other reservoir watersheds studied by the USGS in Kansas, with the exception of Hillsdale Lake in northeast Kansas (Mau, 2001). However, if the Cedar Lake subwatershed was considered a noncontributing-drainage area to Lake Olathe, the mean annual phosphorus yield of the Lake Olathe watershed would be 1.41 (lb/acre)/yr, a difference of about 28 percent from the phosphorus yield estimated for Hillsdale Lake. On the basis of phosphorus deposited in reservoir bottom sediment, mean annual phosphorus yields were estimated to be 0.04 (lb/acre)/yr for the Webster Reservoir watershed (Mau and Christensen, 2000), 0.38 (lb/acre)/yr for the Cheney Reservoir watershed (Mau, 2001), 0.41 (lb/acre)/yr for the Tuttle Creek Lake watershed (Mau and Christensen, 2000), and 1.7 (lb/acre)/yr for the Hillsdale Lake watershed (Juracek, 1997).

Nitrogen

Mean concentrations of total ammonia plus organic nitrogen as nitrogen (N) ranged from 2,000 to 2,700 mg/kg in bottom-sediment samples from Cedar Lake and from 1,300 to 2,700 mg/kg in samples from Lake Olathe (fig. 11). The values are similar to concentrations of mean total ammonia plus organic nitrogen as nitrogen (N) analyzed in bottom-sediment cores collected in 1998 from Kirwin, Webster, and Cheney Reservoirs, and Waconda Lake (Christensen, 1999; Mau, 2001).

Total ammonia plus organic nitrogen as nitrogen (N) concentrations in bottom sediment were analyzed using the sediment profile at coring site 5 in Lake Olathe to determine whether trends existed from the older sediment deposited at the bottom of the core to the newer sediment at the top of the core. An evaluation of the correlation coefficient and p-value using a simple linear regression indicated that there was no statistical significance between total ammonia plus organic nitrogen as nitrogen (N) concentrations and depth (fig. 12). The application of Kendall's tau to the total ammonia plus organic nitrogen as nitrogen (N) data set for both lakes did not indicate trends in either lake (table 5).

Trace Elements

One bottom-sediment core from both Cedar Lake and Lake Olathe was analyzed for trace elements (table 7; tables 16-17, in "Supplemental Information" section of this report). Each core was divided into five equal subsections and analyzed for trace elements. The mean value of each trace element analyzed from the five subsections was used in the discussion that follows. The data from one core in each lake did not provide sufficient information to determine whether any upstream-to-downstream trends in trace element concentrations existed.

Mean concentrations of trace elements in bottom-sediment samples from Cedar Lake and Lake Olathe exceeded the USEPA TEL sediment-quality guidelines for six of the eight trace elements that had guidelines fig. 13-14, table 7). Mean concentrations of arsenic, chromium, copper, lead, nickel, and zinc exceeded the TELs in samples from Cedar Lake coring site 3 and from Lake Olathe coring site 5, placing them in the range where toxic effects occasionally occur. Cadmium and mercury concentrations in bottom-sediment samples from both lakes were less than the TEL sediment-quality guidelines. In addition, none of the PEL guidelines were exceeded in samples from either lake.

Mean concentrations of arsenic in bottom-sediment samples from both Cedar Lake and Lake Olathe were more than twice the TEL guideline for arsenic but much less than the PEL guideline (table 7). Arsenic has been used extensively as a pesticide, herbicide, and soil sterilant in agricultural soils in the United States, but it has only a moderate bioaccumulation effect because it is not very mobile (Pais and Jones, 1997, p. 86).

Mean chromium concentrations exceeded the TEL guideline by 79 percent in the bottom-sediment samples from Cedar Lake and by 73 percent in samples from Lake Olathe (table 7). Chromium is a toxic metal used in industry and is released in industrial wastewaters. The watershed does not support industrial activity; therefore, the source of chromium in the watershed is not well understood. However, chromium also is naturally present in the environment and may be a by-product of agricultural application of fertilizers. The content of chromium in most fertilizers ranges from 2 to 1,000 mg/g (Pais and Jones, 1997).

Mean copper concentrations in bottom sediment from both Cedar Lake and Lake Olathe exceeded the TEL guideline for copper (table 7). Copper is an essential micronutrient for plants and commonly is found in soil, and although the TEL concentration guidelines were exceeded by 84 percent in bottom-sediment samples from both Cedar Lake and Lake Olathe, the mean concentrations were substantially less than the PEL for copper (table 7).

Lead is a metal introduced primarily into the atmosphere through volatilization and combustion of leaded gasoline (Pais and Jones, 1997). Lead also can be introduced to the environment through agricultural fertilizer use; the lead content of fertilizers frequently ranges between 2 and 225 mg/g (Pais and Jones, 1997). Lead is not very mobile in soils or soluble in water. Mean lead concentrations exceeded the TEL guideline of 30 mg/g in bottom-sediment samples from both Cedar Lake and Lake Olathe by 10 and 13 percent, respectively, but were substantially less than the PEL guideline of 110 mg/g for lead (table 7).

Lead concentrations in bottom-sediment samples from Cedar Lake varied little with depth in the sediment profile (fig. 13), which may be related to the possible sediment disturbance from dam repair work in 1995. In contrast, the sediment profile from bottom sediment in Lake Olathe showed a slight decrease in lead concentrations from sediment in the bottom of the core to the water/sediment interface (fig. 14). The decrease in lead concentrations may be a result of the discontinued use of leaded gasoline in the early 1970s.

The typical total nickel content in uncontaminated soil is 25 mg/g, although concentrations in soil can range from 1 to 200 mg/g (Kabata-Pendias and Pendias, 1994; Pais and Jones, 1997, p. 124). Recent research suggests that nickel is an essential micronutrient for both plants and animals; however, in large concentrations it can be toxic (Pais and Jones, 1997, p. 125). Mean concentrations of nickel in bottom-sediment samples from both Cedar Lake and Lake Olathe were more than double the TEL guideline for nickel and slightly less than the PEL (table 7, figs. 13-14). With no apparent industrial source of nickel in the watershed, it may be that seepage from residential septic systems and surface runoff are contributing and concentrating nickel in the reservoir bottom sediment (Sedlack and others, 1997).

Zinc is an essential micronutrient for both plants and animals and is fairly uniformly distributed in soils (Pais and Jones, 1997, p. 147). Toxicity can occur from elevated zinc levels in industrial wastes or sewage sludge that can contain zinc at concentrations in excess of 1,700 mg/g (Pais and Jones, 1997, p. 148). Zinc also can be released to the atmosphere by electric-utility coal-burning operations as well as from the burning of industrial wastes (U.S. Public Health Service, 1994). The lack of industrial sources in the Lake Olathe watershed suggests that seepage from leaking septic systems may be a possible source of zinc in the reservoir bottom sediment. Concentrations of zinc in bottom-sediment samples from both Cedar Lake and Lake Olathe exceeded the TEL guideline for zinc by 30 percent and 18 percent, respectively, but were substantially less than the PEL guideline of 270 mg/g (table 7, figs. 13-14).

An examination of the subsectioned bottom-sediment cores from Lake Olathe for trends in five of the six selected trace elements was inconclusive (fig. 14). Arsenic, chromium, copper, nickel, and zinc fluctuated with depth with no apparent increasing or decreasing trend. The concentrations of these trace elements that exceed the TEL guidelines may be related more to natural conditions than to point or nonpoint sources. The Lake Olathe watershed does not have any large urban areas, an industrial base, or large population centers; therefore, any significant contributions from these sources would be limited.

Selected Pesticides

Bottom-sediment cores from both Cedar Lake and Lake Olathe were collected and analyzed for selected pesticides including organochlorine insecticides, organophosphate insecticides, acetanilide herbicides, and triazine herbicides (table 8). Organochlorine insecticides can be found in reservoir bottom sediment in watersheds where these compounds are used extensively to control insect damage to crops such as corn, wheat, and sorghum (Elder and Mattraw, 1984; Smith and others, 1987; Kalkhoff and Van Metre, 1997). These compounds also are used to control insects such as ants, termites, beetles, fleas, lice, mites, and mosquitos. The organophosphate insecticides have uses similar to organochlorine insecticides, may be used on human food crops such as fruits and vegetables, and are more water soluble and less persistent than organochlorine compounds (U.S. Environmental Protection Agency, 1989). The acetanilide and triazine herbicides are used for weed and grass control on crops such as corn, sorghum, and soybeans and along roadways and railroad rights-of-way (U.S. Environmental Protection Agency, 1989).

There were no detections of selected organochlorine or organo-phosphate insecticides in bottom-sediment samples from Cedar Lake or Lake Olathe (table 8). This is surprising because of their widespread use and prevalence in the environment. During the past 30 years, more than 400 scientific studies including five national programs have looked for pesticides in stream sediment or aquatic biota. Most of the compounds detected in these studies were organochlorine insecticides or their degradation products, which were detected in about 92 percent of the studies (Nowell and others, 1999). The results of these studies are a reflection of the hydrophobic nature and persistence of these compounds, and the fact that most of the monitoring programs analyzed for organochlorine compounds.

Some acetanilide and triazine herbicides were detected at low concentrations in bottom-sediment samples from Cedar Lake and Lake Olathe (table 8) (fig. 15-16). Trends in concentrations of pesticides in bottom sediment from Cedar Lake will not be compared to concentrations of pesticides in bottom sediment from Lake Olathe because of the uncertainty associated with the sediment data from Cedar Lake previously discussed.

Concentrations of alachlor in bottom sediment from Cedar Lake were higher in subsamples from the upper one-third of the sediment core (from 0.55 to 1.65 ft below the water/sediment interface) and, in bottom sediment from Lake Olathe, were higher in subsamples from the upper one-half of the sediment core (from 0.35 to 1.75 ft below the water/sediment interface). Concentrations of alachlor in Cedar Lake bottom sediment increased from less than 0.20 to 21 mg/kg as the water/sediment interface was approached (fig. 15). Similarly, concentrations of alachlor in Lake Olathe bottom sediment increased from 1.3 to 46 mg/kg as the water/sediment interface was approached (fig. 16). Alachlor was commercially introduced to the United States in 1969 for weed control (Ahrens, 1994).

Concentrations of metolachlor in bottom sediment from Cedar Lake were higher in subsamples from the upper one-third of the sediment core (from 0.55 to 1.65 ft below the water/sediment interface) and in Lake Olathe were higher in subsamples from the upper one-half of the sediment core (from 0.35 to 1.75 ft below the water/sediment interface). Concentrations of metolachlor in Cedar Lake sediment increased from less than 0.20 to 1.8 mg/kg as the water/sediment interface was approached (fig. 15). Concentrations of metolachlor in bottom sediment from Lake Olathe increased from less than 0.20 to 1.9 mg/kg in subsamples from the upper one-half of the sediment core as the water/sediment interface was approached (fig. 16). Metolachlor was commercially introduced to the United States in 1977 for weed control (Ahrens, 1994). The presence of metolachlor above detection levels in the bottom-sediment profile suggests that about one-half (2.75 ft) of the total sediment deposition to Lake Olathe has occurred sometime since the introduction of metolachlor in 1977.

Bottom-sediment samples from Cedar Lake and Lake Olathe also showed detections of the triazine herbicide atrazine. Concentrations of atrazine in Cedar Lake sediment ranged from 1.4 mg/kg, near the bottom of the sediment core farthest from the water/sediment interface, to 1.8 mg/kg, near the water/sediment interface (fig. 15). Concentrations of atrazine in Lake Olathe ranged from less than 0.20 mg/kg, near the bottom of the sediment core farthest from the water/sediment interface, to 2.4 mg/kg near the water/sediment interface (fig. 16). Atrazine became commercially available in the United States in 1958, 2 years after dam impoundment of Lake Olathe, and its continued and increased usage in the watershed is indicated in the bottom-sediment profile. However, the detection of atrazine in Cedar Lake at the bottom of the sediment core suggests that the sediment was disturbed because atrazine was not commercially available in 1938 when the dam was constructed.

Although the detected herbicides have large solubilities, they degrade rapidly (1 to 2 months), and probably have little long-term water-quality implications for aquatic organisms in either lake as a result of chemical storage in bottom sediment. However, there may be degradation compounds from the detected herbicides in the sediment that are toxic to aquatic organisms. Some, but not all, of the degradation compounds were analyzed. The USEPA has not proposed TEL or PEL guideline concentrations in bottom sediment for any of the organochlorine, organophosphate, acetanilide, or triazine pesticides.

Diatoms as Indicators of Lake Eutrophication

Diatom species were identified and counted in subsections of bottom-sediment cores from both Cedar Lake and Lake Olathe. The number of diatom species identified in the subsections ranged from 12 to 41 in the sediment core collected from Cedar Lake and from 27 to 50 in the sediment core collected from Lake Olathe (fig. 17) (tables 18-19 in "Supplemental Information" section of this report). However, the p-values were much greater than 0.05, suggesting no significance to the relation between depth and number of diatom species in the bottom sediment.

Estimates of the number of diatom valves per gram of sediment, a measurement of diatom density in sediment, ranged from 1.8 million to about 65 million valves per gram of material in bottom-sediment samples from Cedar Lake and from about 5.3 million to 26 million valves per gram of material in samples from Lake Olathe (fig. 18). Bottom-sediment samples from both lakes showed a general increase in diatom densities closer to the water/sediment interface compared to the bottom of the sediment core, especially at Lake Olathe, which had a correlation coefficient, r, of 0.72 and a p-value equal to 0.02. This trend may reflect an increase in the productivity of the diatom community over the time period represented by the sediment cores. However, some or all of the changes may be a result of other factors, such as variable sedimentation rates or preservation of the valves in the sediment (Pyle and others, 1998). At slower sedimentation rates, for example, there may be more valves per gram of material for the same rate of diatom productivity because there is less sediment to "dilute" the density of the valves.

Generally, in eutrophic water, the diatom community will be dominated by a few abundant species tolerant to nutrient and organic enrichment. In contrast, diatom communities in uncontaminated water (free of sewage or other organic enrichment due to waste discharge) consist of a greater number of more equally abundant species (U.S. Environmental Protection Agency, 1977). The abundance of diatom valves per gram of material, represented by the six most-prevalent diatom species from each lake, accounted for relative percentage abundances ranging from 37 to 89 percent (median; 74 percent) of the total diatoms in the bottom-sediment sample from Cedar Lake and from 51 to 87 percent (median; 77 percent) in the sample from Lake Olathe (tables 9, 10, and 11). These data indicate that, on the basis of a general definition of eutrophic water using diatom densities, both Cedar Lake and Lake Olathe probably have experienced eutrophic conditions throughout their history. However, diatom concentrations and the diversity of diatom species also can be affected by other factors such as turbidity, temperature, and solar intensity.

Selected diatom species in reservoir bottom sediment were compared to nutrient concentrations to determine whether a relation existed between the two variables. Six diatom species were selected that had the largest relative percentage abundance and that were found in most sediment-core subsections. Diatom abundances were compared to the total phosphorus concentrations, total ammonia plus organic nitrogen as nitrogen (N) concentrations, and sample depths from the sediment profile (table 10). Descriptions of each of the six diatom species and the environmental conditions that promote their growth are presented in (table 11).

An analysis for trends using Kendall's tau did not indicate any trend in bottom-sediment samples from Cedar Lake between total valves per gram of material for the six diatom species and concentrations of total phosphorus or total ammonia plus organic nitrogen as nitrogen (N) (table 10). The lack of any trend in samples from Cedar Lake may indicate that the diatom species are independent of nutrient concentrations or that the lake has historically been eutrophic. The dam repair work at Cedar Lake in 1995 also may have disturbed the deposition of bottom sediment and diatoms, and masked the occurrence of any possible trends. The presence of Cyclotella bodanica suggests water-quality conditions free of organic enrichment, whereas the presence of Aulacoseira cf alpigena and Cyclotella meneghiniana suggests just the opposite--a water body enriched with organic material. The apparent discrepancy may be related to seasonal water-quality variations in the lake. Water may be low in organic material part of the year, indicating perhaps less eutrophic conditions that encourage the growth of Cyclotella bodanica, and higher in organic material during other times of the year, encouraging the growth of Aulacoseira cf alpigena and Cyclotella meneghiniana. The genus Aulacoseira is a heavily silicified diatom that requires turbulence to maintain its presence in the water column. Increased turbulence along with increased nutrient concentrations during low lake stage can favor this genus over other planktonic species (Stoermer and Smol, 1999, p.188). Both Cyclotella bodanica and Cyclotella meneghiniana showed a negative correlation to total phosphorus concentration in Lake Olathe, indicating that the densities of both species decreased in the presence of total phosphorus concentrations (table 10). However, Cyclotella meneghiniana typically increases in the presence of phosphorus and organic-enriched material. This factor, in addition to the lack of a trend in total phosphorus concentration in the bottom-sediment profile, indicate that the Kendall's tau trend test may be inaccurate in this situation, possibly because of very little variability in abundance of Cyclotella meneghiniana in the bottom sediment of Lake Olathe.

An analysis of trends of the diatom species Stephanodiscus nigarae in bottom-sediment samples from Lake Olathe indicated a relation between total valves per gram of material of the species and total ammonia plus organic nitrogen as nitrogen (N) (table 10). Stephanodiscus nigarae is present in eutrophic water and is noted for imparting unacceptable taste to water (U.S. Environmental Protection Agency, 1977). Stephanodiscus nigarae was not present in each sediment-core subsection and had a low relative percentage abundance.

Diatom concentrations of Aulacoseira cf alpigena, Cyclotella meneghiniana, and Cyclotella striata correlated well with depths of sediment samples from Cedar Lake (table 10). Concentrations of Aulacoseira cf alpigena and Stephanodiscus nigarae in bottom-sediment samples from Lake Olathe similarly correlated well with depths of samples. Concentrations of these four diatoms were largest at the water/sediment interface (more recent deposition) and smallest at the bottom of the cores (older sediment). The presence of the diatom species Aulacoseira cf alpigena in bottom sediment from Cedar Lake suggests degrading water-quality conditions in the lake. However, because sediment in the lake may have been disturbed during dam repair work, trend analysis may be invalid for this lake, and water quality in Cedar Lake may or may not be degrading. The increased concentration of the eutrophic-indicator diatom species from the bottom of the cores to the water/sediment interface suggests that over time these lakes are eutrophic more often or eutrophic for longer periods.

SUMMARY AND CONCLUSIONS

REFERENCES

David Mau
U.S. Geological Survey
4821 Quail Crest Place
Lawrence, KS 66049-3839
Telephone: (785) 832-3517
Fax: (785) 832-3500
Email: dpmau@usgs.gov