Prepared in cooperation with the Connecticut Department of Energy and Environmental Protection and New England Interstate Water Pollution Control Commission Use of Dissolved Oxygen Monitoring to Evaluate Phosphorus Loading in Connecticut Streams, 2015–18 Scientific Investigations Report 2021–5024 U.S. Department of the Interior U.S. Geological Survey Cover. Photograph showing continuous water-quality monitor taken at Salmon River near East Hampton, Connecticut, on August 3, 2017, by Brittney Izbicki, U.S. Geological Survey. Use of Dissolved Oxygen Monitoring to Evaluate Phosphorus Loading in Connecticut Streams, 2015–18 By Brittney Izbicki and Jonathan Morrison Prepared in cooperation with the Connecticut Department of Energy and Environmental Protection and New England Interstate Water Pollution Control Commission Scientific Investigations Report 2021–5024 U.S. Department of the Interior U.S. Geological Survey U.S. Geological Survey, Reston, Virginia: 2021 For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment—visit https://www.usgs.gov or call 1–888–ASK–USGS. For an overview of USGS information products, including maps, imagery, and publications, visit https://store.usgs.gov/. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner. Suggested citation: Izbicki, B., and Morrison, J., 2021, Use of dissolved oxygen monitoring to evaluate phosphorus loading in Connecticut streams, 2015–18: U.S. Geological Survey Scientific Investigations Report 2021–5024, 25 p., https://doi.org/ 10.3133/ sir20215024. Associated data for this publication: Izbicki, B.J., and Morrison, J., 2021, Stream metabolism estimated from dissolved oxygen data in Connecticut streams, 2015–18: U.S. Geological Survey data release, https://doi.org/10.5066/P9HW6IP1. U.S. Geological Survey, 2020, USGS water data for the Nation: U.S. Geological Survey National Water Information System database, https://doi.org/10.5066/F7P55KJN. ISSN 2328-0328 (online) iii Acknowledgments The authors would like the thank the Connecticut Department of Energy and Environmental Protection and New England Interstate Water Pollution Control Commission. We also would like to thank the following dedicated U.S. Geological Survey employees: Guy Holzer, Michael Colombo, Joseph Martin, Colin Sweeney, Kaitlin Laabs, and Theresa Armijo for data collection, analysis, and approval; John Mullaney for assistance with data processing in streamMetabolizer; and Caroline Mazo for geographic information system mapping. v Contents Acknowledgments ........................................................................................................................................iii Abstract ...........................................................................................................................................................1 Introduction.....................................................................................................................................................1 Purpose and Scope ..............................................................................................................................3 Description of Study Area and Data-Collection Sites ....................................................................3 Methods...........................................................................................................................................................3 Characterization of Study Sites ..........................................................................................................3 Continuous Monitoring Data Collection and Analysis ....................................................................3 Discrete Sampling Data Collection and Analysis ............................................................................7 Stream Metabolism Computations ....................................................................................................7 Model Input Variables .................................................................................................................7 Model Outputs ..............................................................................................................................8 Model Validation ..........................................................................................................................8 Analysis of Dissolved Oxygen Concentrations .........................................................................................8 Analysis of Stream Metabolism Outputs .................................................................................................16 Discussion .....................................................................................................................................................22 References Cited..........................................................................................................................................23 Figures 1. Map showing monitoring stations for the study, major streams, and drainage basins in Connecticut ...................................................................................................................4 2. Box plots showing daily ranges in study sites in Connecticut across the 4 years ..........12 3. Graph showing daily fluctuations of dissolved oxygen and pH in response to stream metabolism for North Branch Park River at Hartford, Connecticut ......................13 4. Box plot showing total phosphorus concentrations at selected sites in Connecticut with discrete sampling during the study for June–September ....................14 5. Scatter plots showing total phosphorus concentrations (in milligrams per liter) against discharge (in cubic feet per second) for selected sites in Connecticut .............14 6. Graph showing average annual summertime maximum daily dissolved oxygen range and average annual summertime total phosphorus concentrations for study sites in Connecticut for June–September ...................................................................15 7. Scatter plots showing daily estimates of gross primary productivity and ecosystem respiration for each study site in Connecticut and year it was active ..........17 8. Scatter plot showing average annual summertime gross primary productivity estimates and average annual summertime total phosphorus concentrations for study sites in Connecticut for June–September .............................................................20 9. Scatter plot showing average annual summertime gross primary productivity estimates (in grams of oxygen per meter squared per day) and average annual summertime maximum daily dissolved oxygen ranges (in milligrams per liter) for study sites in Connecticut for June–September .............................................................21 vi Tables 1. Summary of continuous monitoring, discrete phosphorus sampling, and streamMetabolizer modeling for study sites in Connecticut �������������������������������������������������5 2. Site characterization including the physical and environmental characteristics of study sites in Connecticut .......................................................................................................6 3. StreamMetabolizer outputs and model diagnostics for study sites in Connecticut .........9 4. Summary of daily dissolved oxygen minimum value, dissolved oxygen maximum value, and maximum daily dissolved oxygen range for every Connecticut site each year it was active ..............................................................................................................11 Conversion Factors U.S. customary units to International System of Units Multiply By To obtain Length foot (ft) 0.3048 meter (m) Area square mile (mi2) 259.0 hectare (ha) square mile (mi2) 2.590 square kilometer (km2) International System of Units to U.S. customary units Multiply By To obtain Mass gram (g) 0.03527 ounce, avoirdupois (oz) Transmissivity meter squared per day (m2/d) 10.76 foot squared per day (ft2/d) Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows: °F = (1.8 ×°C) + 32. Datum Vertical coordinate information is referenced to the North American Vertical Datum of 1988 (NAVD 88). Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83). Altitude, as used in this report, refers to distance above the vertical datum. vii Supplemental Information Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius (µS/cm at 25 °C). Concentrations of chemical constituents in water are given in either milligrams per liter (mg/L) or micrograms per liter (µg/L). A water year is the period from October 1 to September 30 and is designated by the year in which it ends; for example, water year 2016 was from October 1, 2015, to September 30, 2016. Abbreviations CT DEEP Connecticut Department of Energy and Environmental Protection CV coefficient of variation DO dissolved oxygen EPA U.S. Environmental Protection Agency ER ecosystem respiration GPP gross primary productivity K600 gas exchange rate MLE maximum likelihood estimation NPDES National Pollutant Discharge Elimination System