Link to USGS home page.
Publications—Scientific Investigations Report

Prepared in cooperation with the Metropolitan District Commission

Surface-Water Quality and Nutrient Loads in the Nepaug Reservoir Watershed, Northwestern Connecticut, 1999–2001

By Jonathan Morrison and Michael J. Colombo

 

U.S. Geological Survey Scientific Investigations Report 2006-5272

 

The body of the report is available in PDF Format (1,158 KB)

Abstract

Water quality was characterized at three tributary watersheds to the Nepaug Reservoir—Nepaug River, Phelps Brook, and Clear Brook—from October 1998 through September 2001 to document existing water-quality conditions and evaluate potential future effects of the removal of sand and gravel from areas of the watershed. Some removal operations may include removal of vegetation and top soil and steepening of slopes. Routine water samples collected monthly in all three watersheds were analyzed for nutrients, organic carbon, major ions, and fecal indicator bacteria. Results of the analyses indicate that, in general, the water quality in all three tributary watersheds is good and meets standards established for drinking-water supplies for nitrate, but does not always meet contact-recreation standards for bacteria. Median concentrations of total nitrogen, total phosphorus, and total organic carbon were highest in the routine monthly samples from Phelps Brook and lowest from Clear Brook. Samples also were collected during selected storms to examine changes in concentrations of nutrients during periods of high streamflow. The maximum values measured for total nitrogen, total phosphorus, and total organic carbon were in storm samples from Clear Brook.

The Nepaug River watershed delivered the largest loads of total nitrogen, total phosphorus, and total organic carbon to the reservoir. Yields of nutrients and organic carbon differed significantly from year to year and among the three watersheds. Yields of total nitrogen and total organic carbon were largest from Phelps Brook and smallest from Clear Brook. The yields of total phosphorus were largest from Nepaug River and smallest from Phelps Brook. In comparison to other watersheds in Connecticut, annual loads and yields from the three streams were lower than those of developed urban areas and comparable to those of other rural and forested basins. Delivery of nutrients and organic carbon to the reservoir took place mostly during the spring with the exception of those constituents delivered during Tropical Storm Floyd, a large fall storm.

TABLE OF CONTENTS

Abstract

Introduction

Purpose and Scope

Previous Studies

Description of the Study Area

Methods of Data Collection and Analysis

Precipitation Measurements

Streamflow Measurements

Water-Quality Sampling

Water-Quality Data Analysis

Load Estimation

Precipitation, Streamflow, and Runoff in the Nepaug Reservoir Watershed

Surface-Water Quality in the Nepaug Reservoir Watershed

Physical and Chemically Related Properties

Major Inorganic Constituents

Nitrogen, Phosphorus, and Organic Carbon

Fecal Indicator Bacteria

Surface-Water Quality During Storms in the Nepaug Reservoir Watershed

Storm Samples Collected by Automated and Manual Methods

Physical and Chemically Related Properties

Phosphorus, Nitrogen, and Organic Carbon

Storm Samples Collected by Automated Composite Methods

Data from Continuous Monitors

Nutrient Loads and Yields to the Nepaug Reservoir

Nitrogen Loads and Yields

Phosphorus Loads and Yields

Organic Carbon Loads and Yields

Limitations of the Nutrient Load Models

Comparison of Yields in the Nepaug Reservoir Watershed to Other Watersheds in Connecticut

Summary and Conclusions

Acknowledgments

References Cited

Figures

  1. Map showing location of the Nepaug Reservoir watershed and the North and South Areas, northwestern Connecticut

2–12. Graphs showing:

2. Precipitation at Burlington, Connecticut, water years 1999-2001
3. Streamflow at three U.S. Geological Survey stations indicating dates and flow conditions when water samples were collected, water years 1999-2001: A, station 01187800 Nepaug River near Nepaug, Connecticut; B, station 01187830 Phelps Brook near Collinsville, Connecticut; and C, station 01187850 Clear Brook near Collinsville, Connecticut
4. Streamflow in A, Nepaug River and Clear Brook; and B, Phelps Brook and Clear Brook, adjusted by size of drainage basin, for water years 1999-2001
5. Flow-duration curves showing streamflow normalized by drainage area at three U.S. Geological Survey stations during the study period and the long-term period of record: A, station 01187800 Nepaug River near Nepaug, Connecticut; B, station 01187830 Phelps Brook near Collinsville, Connecticut; and C, station 01187850 Clear Brook near Collinsville, Connecticut
6. The distribution of the concentrations of A, fecal coliform bacteria; and B, enterococci bacteria, Nepaug Reservoir watershed, Connecticut
7. The distribution of the concentrations of fecal coliform bacteria by season at three U.S. Geological Survey stations, 1999-2001: A, station 01187800 Nepaug River near Nepaug, Connecticut; B, station 01187830 Phelps Brook near Collinsville, Connecticut; and C, station 01187850 Clear Brook near Collinsville, Connecticut
8. The distribution of the concentrations of enterococci bacteria by season at three U.S. Geological Survey stations, 1999-2001: A, station 01187800 Nepaug River near Nepaug, Connecticut; B, station 01187830 Phelps Brook near Collinsville, Connecticut; and C, station 01187850 Clear Brook near Collinsville, Connecticut
9. Continuous water-quality-monitoring data and concentration of total phosphorus at two U.S. Geological Survey stations: A, station 01187800 Nepaug River near Nepaug, Connecticut; and B, station 01187830 Phelps Brook near Collinsville, Connecticut, March 10-14, 2000
10. Continuous water-quality-monitoring data and concentration of total phosphorus at A, station 01187850 Clear Brook near Collinsville, Connecticut; and B, station 01187800 Nepaug River near Nepaug, Connecticut, May 19-21, 1999
11. Relation of total phosphorus to turbidity at three U.S. Geological Survey stations: A, station 01187800 Nepaug River near Nepaug, Connecticut; B, station 01187830 Phelps Brook near Collinsville, Connecticut; and C, station 01187850 Clear Brook near Collinsville, Connecticut
12. Continuous water-quality-monitoring data, U.S. Geological Survey station 01187850 Clear Brook near Collinsville, Connecticut, September 14-21, 1999

Tables

  1. U.S. Geological Survey stations in the Nepaug Reservoir watershed used for this study
  2. Precipitation data used for this study
  3. Statistical summary of surface-water data for U.S. Geological Survey stations in the Nepaug Reservoir watershed, water years 1999–2001
  4. Statistical summary of monthly water-quality data for U.S. Geological Survey stations in the Nepaug Reservoir watershed, water years 1999–2001
  5. Statistical summary of fecal coliform and enterococci bacteria data for U.S. Geological Survey stations in the Nepaug Reservoir watershed, water years 1999–2001
  6. Sampled storms in the Nepaug Reservoir watershed during the study period
  7. Statistical summary of water-quality data for selected storms during the study period for U.S. Geological Survey stations in the Nepaug Reservoir watershed
  8. Explanatory variable terms, term coefficients, and coefficients of determination used in nutrient load estimates for tributaries to the Nepaug Reservoir
  9. Annual loads and yields of nutrients and total organic carbon for U.S. Geological Survey stations in the Nepaug Reservoir watershed
  10. Example of a storm-load calculation of total phosphorus and total nitrogen by LOADEST and mass-integration methods for U.S. Geological Survey stations in the Nepaug Reservoir watershed, May 1999

If you have Adobe® Acrobat® or Adobe® Acrobat® Reader® installed on your computer, you may view and print the PDF version of this report. Acrobat Reader, is a free download from Adobe Systems, Inc. Users with disabilities can view information concerning accessibility at access.Adobe.com .


For further information, contact:

Virginia deLima, Director
Connecticut Water Science Center
101 Pitkin St.
East Hartford, CT 06108
Phone: (860) 291-6741
Email: dc_ct@usgs.gov

Web site: http://ct.water.usgs.gov

U.S. Department of the Interior, U.S. Geological Survey
Persistent URL: http://pubs.water.usgs.gov/sir20065272
Page Contact Information: GS Pubs Web Contact
Last modified: Thursday, January 10 2013, 05:47:43 PM
FirstGov button  Take Pride in America button