Nutrient Loading and Algal Response in West Thompson Lake, Thompson, Connecticut, 2003–2005 By Jonathan Morrison and Michael J. Colombo Prepared in cooperation with the Connecticut Department of Environmental Protection Scientific Investigations Report 2008–5072 U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior DIRK KEMPTHORNE, Secretary U.S. Geological Survey Mark D. Myers, Director U.S. Geological Survey, Reston, Virginia: 2008 For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment: World Wide Web: http://www.usgs.gov Telephone: 1-888-ASK-USGS Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted materials contained within this report. Suggested citation: Morrison, Jonathan, and Colombo, M.J., 2008, Nutrient loading and algal response in West Thompson Lake, Thompson, Connecticut, 2003–2005: U.S. Geological Survey Scientific Investigations Report 2008–5072, 79 p., available only online at http://pubs.usgs.gov/sir/2008/5072. iii Contents Abstract ...........................................................................................................................................................1 Introduction.....................................................................................................................................................2 Purpose and Scope ..............................................................................................................................2 Description of the Study Area ............................................................................................................2 Previous Investigations........................................................................................................................4 Hydrologic Conditions During the Study Period ..............................................................................4 Precipitation During 2000–2005 .................................................................................................4 Streamflow ....................................................................................................................................6 Hydraulic Residence Time ..........................................................................................................6 Methods of Data Collection and Analysis .................................................................................................8 Stream Sampling ...................................................................................................................................8 Lake Sampling .......................................................................................................................................9 Lake-Bottom Sediment Sampling .....................................................................................................12 Nutrient Load Calculations ................................................................................................................12 Physical Properties and Concentrations of Nutrients and Chlorophyll-a in Water ..........................13 Quinebaug River ..................................................................................................................................13 West Thompson Lake .........................................................................................................................13 Stratification and Mixing in West Thompson Lake ................................................................................16 Algal Dynamics in West Thompson Lake .................................................................................................18 Chlorophyll-a and Algal Cell Density and Community Composition ...........................................18 Carlson Trophic-State Index .............................................................................................................22 Redfield Ratios.....................................................................................................................................24 Algal Growth Potential and Limiting Nutrient Analysis ................................................................24 Characteristics of Lake-Bottom Sediments ............................................................................................26 Sediment Thickness and Distribution ..............................................................................................26 Concentrations of Phosphorus in Lake-Bottom Sediments .........................................................26 Nutrient Loads and Yields in West Thompson Lake and Surrounding Watershed ...........................29 Annual Loads and Yields of Total Phosphorus ...............................................................................32 Annual Loads and Yields of Total Nitrogen .....................................................................................32 Seasonal Loads ...................................................................................................................................32 Water and Nutrient Budgets for West Thompson Lake ........................................................................35 Water Budget ......................................................................................................................................35 Nutrient Budgets .................................................................................................................................35 Summary and Conclusions .........................................................................................................................40 Acknowledgments .......................................................................................................................................41 References Cited..........................................................................................................................................41 Appendix 1. Daily Maximum, Minimum, and Mean Values of Water Temperature for USGS Station 01124149 at Top and Bottom Locations for Water Years 2003 and 2005 .......45 Appendix 2. Total Phosphorus and Nitrogen for the Quinebaug River Sites ..................................63 iv Figures 1. Map showing location of West Thompson Lake watershed in northeastern Connecticut and southern Massachusetts ..............................................................................3 2. Bathymetric map of West Thompson Lake, Connecticut, with sampling locations ..........5 3. Graphs showing streamflow at U.S. Geological Survey stations, indicating dates and flow conditions when water samples were collected, water years 2003–2005: (A) Quinebaug River at Quinebaug, Connecticut (USGS Site ID 01124000), and (B) Quinebaug River at West Thompson, Connecticut (USGS Site ID 01124151) ...............7 4. Boxplots showing distribution of concentrations of (A) total phosphorus, (B) total nitrogen, and (C) chlorophyll-a from Quinebaug River at Quinebaug, Connecticut (USGS Site ID 01124000), Quinebaug River at Red Bridge Road, Connecticut (USGS Site ID 01124120), and Quinebaug River at West Thompson, Connecticut (USGS Site ID 01124151) .........................................................................................................................14 5–10. Graphs showing— 5. Continuous water-quality-monitoring data for water temperature and dissolved oxygen at the near-surface and deep monitors, West Thompson Lake at Old West Thompson Road near West Thompson (USGS Site ID 01124149) during (A) water year 2003 and (B) water year 2005 ................................................................15 6. Profiles of water temperature data and concentrations of dissolved oxygen and total phosphorus from stations WT-1 and WT-3, West Thompson Lake, Connecticut, summer 2003 ...............................................................................................19 7. Profiles of water temperature data and concentrations of dissolved oxygen and total phosphorus from station WT-3, West Thompson Lake, Connecticut, summer 2004 .......................................................................................................................20 8. Profiles of water temperature data and concentrations of dissolved oxygen and total phosphorus from stations WT-1 and WT-3, West Thompson Lake, Connecticut, summer 2005 ...............................................................................................20 9. Concentrations of chlorophyll-a and algal cell counts in West Thompson Lake, June to September 2003 and 2005 ..................................................................................22 10. Continuous chlorophyll-a sensor data from West Thompson Lake at Old West Thompson Road near West Thompson, Connecticut (USGS Site ID 01124149), June 2005–September 2005 .............................................................................................23 11. Chart showing Carlson trophic state indexes for samples collected near the deep hole sampling station (WT-3) from West Thompson Lake, Connecticut, 1990 to 2005 ....24 12. Map showing sediment thicknesses and total phosphorus concentrations from upper 2 inches of sediment cores collected in West Thompson Lake, Connecticut,