USGS Open-File Report 2008-1268

Prepared in cooperation with the Spartanburg Water System

Limnological Conditions in Lake William C. Bowen and Municipal Reservoir #1, Spartanburg County, South Carolina, August to September 2005, May 2006, and October 2006

By Celeste A. Journey and Thomas A. Abrahamsen

U.S. Geological Survey Open-File Report 2008-1268, 96 pages (Published online, September 2008)

This report is available online in PDF format: OFR 2008-1268 (Opens the PDF file in a new window. ) (4.5 MB)

Cover thumbnailThe U.S. Geological Survey, in cooperation with the Spartanburg Water System, conducted three spatial surveys of the limnological conditions in Lake William C. Bowen (Lake Bowen) and Municipal Reservoir #1 (Reservoir #1), Spartanburg County, South Carolina, during August to September 2005, May 2006, and October 2006. The surveys were conducted to identify spatial distribution and concentrations of geosmin and 2-methylisoborneol, common trophic state indicators (nutrients, transparency, and chlorophyll a), algal community structure, and stratification of the water column at the time of sampling. Screening tools such as the Carlson trophic state index, total nitrogen to total phosphorus ratios, and relative thermal resistance to mixing were used to help compare data among sites and among seasons. Water-column samples were collected at two depths at each selected site: a near-surface sample collected above a 1-meter depth and a lake-bottom sample collected at a depth of 2.5 to 7 meters, depending on the depth at the site.

The degree of stratification of the water column was demonstrated by temperature-depth profiles and computed relative thermal resistance to mixing. Seasonal occurrence of thermal stratification (August to September 2005; May 2006) and de-stratification (October 2006) was evident in the depth profiles of water temperature in Lake Bowen. The most stable water-column (highest relative thermal resistance to mixing) conditions occurred in Lake Bowen during the August to September 2005 survey. The least stable water-column (destratified) conditions occurred in Lake Bowen during the October 2006 survey and Reservoir #1 during all three surveys. Changes with depth in dissolved oxygen (decreased with depth to near anoxic conditions in the hypolimnion), pH (decreased with depth), and specific conductance (increased with depth) along with thermal stratification indicated Lake Bowen was exhibiting characteristics common to both mesotrophic and eutrophic conditions.

Nutrient dynamics were different in Lake Bowen during the May 2006 survey from those during the August to September 2005 and October 2006 surveys. Total organic nitrogen concentrations (total Kjeldahl nitrogen minus ammonia) remained relatively constant within the surveys and ranged from 0.15 to 0.36 milligram per liter during the period of study. Nitrate was the dominant inorganic species of nitrogen during May 2006. Ammonia was the dominant species during the August to September 2005 and October 2006 surveys. During the August and September 2005 survey, ammonia was detected only in bottom samples collected in the near anoxic hypolimnion, but during the October 2006 survey, ammonia was detected under destratified conditions in surface and bottom samples. In Lake Bowen, total phosphorus concentrations in bottom samples did not exhibit the dramatic, high values during the May 2006 and October 2006 surveys (0.009 to 0.014 milligram per liter) that were identified for the August to September 2005 survey (0.022 to 0.034 milligram per liter). Chlorophyll a concentrations appeared to vary with the species of inorganic nitrogen. Greater chlorophyll a concentrations were identified in samples from the May 2006 survey (6.8 to 15 micrograms per liter) than in the August to September 2005 (1.2 to 6.4 micrograms per liter) and October surveys (5.6 to 8.2 micrograms per liter) at all sites in Lake Bowen and Reservoir #1. For the three limnological surveys, surface concentrations of chlorophyll a and total phosphorus were well below established numerical criteria for South Carolina.

In general, the computed trophic state indices indicated that mesotrophic conditions were present in Lake Bowen and Reservoir #1. The total nitrogen to total phosphorus ratios in Lake Bowen and Reservoir #1 were below 22:1 for the August to September 2005 survey, indicating a high probability of dominance by nitrogen-fixing cyanobacteria. Ratios during the May and October 2006 surveys at some sites in Lake Bowen were above 22:1, indicating a lower probability of cyanobacterial dominance. Total nitrogen to total phosphorus ratios were consistently below 22:1 for a site in Reservoir #1 (MR1-14).

For all three surveys, 2-methylisoborneol concentrations were below the laboratory reporting limit of 0.005 microgram per liter. Of the three surveys, the highest concentrations of geosmin were measured during the August to September 2005 survey in samples collected near the bottom of Lake Bowen when stratified conditions existed. Elevated geosmin concentrations ranged from 0.016 to 0.039 microgram per liter at sites and depths that had elevated ammonia and total phosphorus concentrations in Lake Bowen. Geosmin levels were lower in samples from sites in Reservoir #1 than those from Lake Bowen. The lowest geosmin concentrations for Lake Bowen were measured during the October 2006 survey (less than 0.005 to 0.007 microgram per liter) when destratified conditions existed.

Members of the division Cyanophyta (also known as cyanobacteria or blue-green algae) were present in the greatest abundance of all the phytoplankton divisions in Lake Bowen and Reservoir #1 at every site and sampling depth during all three surveys. For the three surveys, phytoplankton cells in the division Cyanophyta composed 91 to 99 percent of the total phytoplankton community among all sites and depths. During the August to September 2005 survey, several potentially geosmin-producing genera were identified in Lake Bowen and Reservoir #1 samples. The most abundant genera were Lyngbya and Synechococcus. During the May and October 2006 surveys, fewer potentially geosmin-producing genera were identified in Lake Bowen and Reservoir #1 samples; the most abundant genera were Synechococcus. Overall, the cyanobacterial communities in these samples were dominated by the picoplankton, Synechococcus sp.1, and other unidentified members of Chroococaceae, Cyanogranis ferruginea, and periodically, Lyngbya limnetica. No pattern between the algal cell density of the potentially geosmin-producing genera of cyanobacteria and geosmin occurrence was identified during the three surveys.

CONTENTS

Abstract

Introduction

Purpose and Scope

Description of Study Area

Previous Investigations

Approach and Methods

Data Collection

Data Analysis

Quality Assurance

Limnological Conditions

Stratification

Nutrient and Chlorophyll a Levels

Trophic Status

Wastewater Indicator Compound Occurrence

Geosmin and MIB Occurrence

Phytoplankton Community Structure

Summary

Acknowledgments

References

Appendix A. National Land Cover Database (NLCD) Land Cover Classification System Key and Definitions

Appendix B. Laboratory Reporting Levels and Method Descriptions for Selected Analytes in Water Samples Collected from Lake William C. Bowen and Municipal Reservoir #1, Spartanburg County, South Carolina

Appendix C. Phytoplankton Taxonomy at selected sites in Lake William C. Bowen and Municipal Reservoir #1, Spartanburg County, South Carolina, August 2005 to October 2006

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Suggested citation: Journey, C.A., and Abrahamsen, T.A., 2008, Limnological conditions in Lake William C. Bowen and Municipal Reservoir #1, Spartanburg County, South Carolina, August to September 2005, May 2006, and October 2006: U.S. Geological Survey Open-File Report 20081268, 96 p.

For more information, please contact Celeste A. Journey.

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