Potomac Basin Large River Environmental Flow Needs
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Potomac Basin Large River Environmental Flow Needs PREPARED BY James Cummins, Claire Buchanan, Carlton Haywood, Heidi Moltz, Adam Griggs The Interstate Commission on the Potomac River Basin 51 Monroe Street Suite PE-08 Rockville, Maryland 20850 R. Christian Jones, Richard Kraus Potomac Environmental Research and Education Center George Mason University 4400 University Drive, MS 5F2 Fairfax, VA 22030-4444 Nathaniel Hitt, Rita Villella Bumgardner U.S. Geological Survey Leetown Science Center Aquatic Ecology Branch 11649 Leetown Road, Kearneysville, WV 25430 PREPARED FOR The Nature Conservancy of Maryland and the District of Columbia 5410 Grosvenor Lane, Ste. 100 Bethesda, MD 20814 WITH FUNDING PROVIDED BY The National Park Service Final Report May 12, 2011 ICPRB Report 10-3 To receive additional copies of this report, please write Interstate Commission on the Potomac River Basin 51 Monroe St., PE-08 Rockville, MD 20852 or call 301-984-1908 Disclaimer This project was made possible through support provided by the National Park Service and The Nature Conservancy, under the terms of their Cooperative Agreement H3392060004, Task Agreement J3992074001, Modifications 002 and 003. The content and opinions expressed herein are those of the authors and do not necessarily reflect the position of the policy of the National Park Service or The Nature Conservancy and no official endorsement should be inferred. The opinions expressed in this report are those of the authors and should not be construed as representing the opinions or policies of the U. S. Government, or the signatories or Commissioners to the Interstate Commission on the Potomac River Basin. Acknowledgments This project was supported by a National Park Service subaward provided by The Nature Conservancy Maryland/DC Office and by the Interstate Commission on the Potomac River Basin, an interstate compact river basin commission of the United States Government and the compact's signatories: Maryland, Virginia, Pennsylvania, West Virginia and the District of Columbia. We wish to recognize and thank the following individuals for their assistance in preparing materials for this document, contributing text, and/or their helpful reviews of various drafts: Colin Apse, Mark Bryer, Judy Dunscomb, Stephanie Flack, Eloise Kendy, Christian Marks, Tara Moberg, Michele DePhilip, Mark P. Smith, and Julie Zimmerman (The Nature Conservancy) Mary Freeman, Bruce Taggart (USGS) Steve Schreiner (Versar, Inc.) Claire O’Neill, Andrew Roach (U.S Army Corps of Engineers, Baltimore District) Doug Curtis, Chris Lea, and Marian Norris (U.S. National Park Service) Alex Graziano (George Mason University) Joe Flotemersch (U.S. EPA) Jan Ducnuigeen, Sarah Ahmed, and Jim Palmer (ICPRB) Front cover: the Potomac River from South Mountain, downstream of Harpers Ferry. Photo by Jim Palmer, ICPRB. ii Potomac Basin Large River Environmental Flow Needs Table of Contents List of Tables ................................................................................................................................................................iv List of Figures ............................................................................................................................................................ v EXECUTIVE SUMMARY ........................................................................................................................................ vii CHAPTER 1: INTRODUCTION ................................................................................................................................. 1 Summary .................................................................................................................................................................... 1 Background ................................................................................................................................................................ 2 Methodology .............................................................................................................................................................. 3 Hydrologic Indicators ................................................................................................................................................ 4 Factors Influencing Potomac River Hydrology ......................................................................................................... 5 Topography and Geology ...................................................................................................................................... 7 Climate and Vegetation ......................................................................................................................................... 8 Water Uses ............................................................................................................................................................. 9 Land Uses ............................................................................................................................................................ 11 CBP Watershed Model Results ............................................................................................................................ 13 Assessing Risk of Hydrologic Alteration ................................................................................................................ 13 Hydrologic Alteration Cumulative Risk Index ..................................................................................................... 13 Regions of Special Interest Due to Risk of Hydrologic Alteration ....................................................................... 14 The Potomac River Gorge and Flow-By Requirement at Little Falls .................................................................. 16 Wastewater and Pollutant Removal ..................................................................................................................... 18 Introduced Species ............................................................................................................................................... 19 CHAPTER 2: RIVERINE ECOLOGICAL INDICATORS ....................................................................................... 20 Summary .................................................................................................................................................................. 20 The Riverine Habitat and Biological Communities ................................................................................................. 20 Water Quality and Drought in the Potomac River Mainstem .............................................................................. 22 Riparian Plant Communities ............................................................................................................................... 23 Fishes ................................................................................................................................................................... 27 Mussels ................................................................................................................................................................ 46 Flow-Ecology Hypotheses for Potomac Nontidal River Communities ................................................................... 50 CHAPTER 3: TIDAL FRESHWATER ECOLOGICAL INDICATORS ................................................................... 52 Summary .................................................................................................................................................................. 52 The Tidal Freshwater Habitat and Biological Communities.................................................................................... 52 Anthropogenic Impacts on Freshwater Flow to the Estuary ............................................................................... 54 Phytoplankton ...................................................................................................................................................... 57 Submerged Aquatic Vegetation (SAV) ................................................................................................................. 60 Zooplankton ......................................................................................................................................................... 62 Benthic Macroinvertebrates ................................................................................................................................ 63 Fishes ................................................................................................................................................................... 65 Flow-Ecology Hypotheses for Biological Communities in the Tidal Freshwater Potomac Estuary ....................... 70 CHAPTER 4: FLOW NEEDS SYNTHESIS AND STUDY CONCLUSIONS ......................................................... 72 Summary .................................................................................................................................................................. 72 Key Considerations that Shaped the Study Team's Conclusions and Recommendations ........................................ 75 Potomac Large River Flow Needs Assessment Conclusions ................................................................................... 76 Workshop Review of Flow Component Needs ......................................................................................................