Massachusetts Estuaries Project Linked Watershed-Embayment Model to Determine Critical Nitrogen Loading Threshold for the Menemsha-Squibnocket Pond Embayment System, Wampanoag Tribe, the Towns of Chilmark & Aquinnah, MA University of Massachusetts Dartmouth Massachusetts Department of School of Marine Science and Technology Environmental Protection DRAFT REPORT – JUNE 2017 Massachusetts Estuaries Project Linked Watershed-Embayment Model to Determine Critical Nitrogen Loading Threshold for the Menemsha-Squibnocket Pond Embayment System, Wampanoag Tribe, the Towns of Chilmark & Aquinnah, MA DRAFT REPORT – JUNE 2017 Brian Howes Roland Samimy David Schlezinger Ed Eichner Trey Ruthven John Ramsey Contributors: US Geological Survey Don Walters and John Masterson Applied Coastal Research and Engineering, Inc. Elizabeth Hunt and Sean Kelley Massachusetts Department of Environmental Protection Charles Costello and Brian Dudley (DEP project manager) SMAST Coastal Systems Program Jennifer Benson, Michael Bartlett, and Sara Sampieri Martha's Vineyard Commission Chris Seidel and Sheri Caseau ACKNOWLEDGMENTS The Massachusetts Estuaries Project Technical Team would like to acknowledge the contributions of the many individuals who have worked tirelessly for the restoration and protection of the critical coastal resources of the Menemsha-Squibnocket Pond Embayment and supported the application of the Linked Watershed-Embayment Model to Determine the Critical Nitrogen Loading Threshold for this estuarine system. Without these stewards and their efforts, this project would not have been possible. First and foremost we would like to recognize and applaud the significant time and effort in data collection and discussion spent by members of the Martha's Vineyard Commission. These individuals gave of their time to develop a consistent and sound baseline of nutrient related water quality for this system, without which the present analysis would not have been possible. Also, we would like to thank the long standing efforts of the Wampanoag Tribe of Aquinnah (specifically Bret Stearns) who have been steadfast champions for monitoring the state of the pond, educating the public, supporting the MEP field teams logistically during data gathering phases of the MEP analysis and driving the need to complete the MEP analysis for the Menemsha-Squibnocket Pond system. The MEP team is also grateful to both Tim Carroll (Executive Secretary to the Chilmark Board of Selectmen) and Adam Wilson (Town Administrator, Aquinnah) for their commitment to the process and their endless well of patience. The MEP Technical Team would also like to thank Senior Chief Robert Riemer from the United States Coast Guard for facilitating the deployment of instrumentation at the USCG boathouse dock thus enabling the collection of up to date water levels in the estuary that where critical to being able to develop the hydrodynamic model of the system. Staff from the Martha's Vineyard Commission have provided essential insights toward completion of this long running effort. Of particular note has been the efforts of Bill Wilcox (former MVC Water Resources Planner), who prior to his retirement spent countless hours reviewing data and information with MEP Technical Team members in support of the MEP analysis of Menemsha and Squibnocket Ponds. In addition, Sheri Caseau (current MVC Water Resources Planner) has provided local insights, critical field support and worked to formulate refinements to databases as necessary. Chris Seidel, GIS Specialist from the MVC, provided significant support for the MEP land-use analysis, particularly analysis of parcel information and site-specific loading information (e.g. related to wastewater disposal) without which the MEP analysis could not be completed. In addition to local contributions, technical, policy and regulatory support has been freely and graciously provided by our MassDEP colleagues: Rick Dunn and Dave DeLorenzo prior to their retirement. We are also thankful for the long hours in the field and laboratory spent by the technical staff, interns and students within the Coastal Systems Program at SMAST-UMD. Support for this project was provided by the Wampanoag Tribe of Aquinnah, the Town of Chilmark and the Town of Aquinnah, all supporting a collaborative effort aimed at achieving protection and restoration of the Menemsha-Squibnocket Pond embayment system for the benefit of present and future generations. PROPER CITATION Howes B.L., E.M. Eichner, R.I. Samimy, H.E. Ruthven, D.R. Schlezinger, J. S. Ramsey, (2017). Linked Watershed-Embayment Model to Determine the Critical Nitrogen Loading Threshold for the Menemsha-Squibnocket Pond Embayment System, Chilmark/Aquinnah, Massachusetts. SMAST/DEP Massachusetts Estuaries Project, Massachusetts Department of Environmental Protection. Boston, MA. © [2017] University of Massachusetts & Massachusetts Department of Environmental Protection All Rights Reserved No permission required for non-commercial use MASSACHUSETTS ESTUARIES PROJECT TABLE OF CONTENTS I. INTRODUCTION ................................................................................................................... 1 I.1 THE MASSACHUSETTS ESTUARIES PROJECT APPROACH ...................................... 8 I.2 NUTRIENT LOADING .................................................................................................... 11 I.3 WATER QUALITY MODELING ...................................................................................... 13 I.4 REPORT DESCRIPTION ............................................................................................... 14 II. PREVIOUS STUDIES RELATED TO NITROGEN MANAGEMENT ....................................15 III. DELINEATION OF WATERSHEDS ....................................................................................31 III.1 BACKGROUND ............................................................................................................ 31 III.2 MENEMSHA POND - SQUIBNOCKET POND CONTRIBUTORY AREAS ................... 31 IV. WATERSHED NITROGEN LOADING TO EMBAYMENT: LAND USE, STREAM INPUTS, AND SEDIMENT NITROGEN RECYCLING ...................................................36 IV.1 WATERSHED LAND USE BASED NITROGEN LOADING ANALYSIS ........................ 36 IV.1.1 Land Use and Water Use Database Preparation ................................................ 37 IV.1.2 Nitrogen Loading Input Factors .......................................................................... 39 IV.1.3 Calculating Nitrogen Loads ................................................................................ 47 IV.2 ATTENUATION OF NITROGEN IN SURFACE WATER TRANSPORT ....................... 52 IV.2.1 Background and Purpose ................................................................................... 52 IV.2.2 Surface water Discharge and Attenuation of Watershed Nitrogen: Black Brook Discharge to Squibnocket Pond ............................................................... 57 IV.2.3 Surface water Discharge and Attenuation of Watershed Nitrogen: Pease Point Creek discharge to Menemsha Pond ........................................................ 62 IV.2.4 Surface water Discharge and Attenuation of Watershed Nitrogen: Un-named Creek to Inner Turning Basin of Menemsha Pond (Lower Creek) ...................... 64 IV.2.5 Surface water Exchange Between Squibnocket Pond and Menemsha Pond - Herring Creek Tidal Flux Results ..................................................................... 67 IV.3 BENTHIC REGENERATION OF NITROGEN IN BOTTOM SEDIMENTS .................... 71 IV.3.1 Sediment-Watercolumn Exchange of Nitrogen ................................................... 72 IV.3.2 Method for determining sediment-watercolumn nitrogen exchange .................... 73 IV.3.3 Rates of Summer Nitrogen Regeneration from Sediments ................................. 76 V. HYDRODYNAMIC MODELING ...........................................................................................81 V.1 INTRODUCTION ........................................................................................................... 81 V.2 DATA COLLECTION AND ANALYSIS .......................................................................... 83 V.2.1 Bathymetry Data ................................................................................................. 83 V.2.2 Tide Data Collection and Analysis ....................................................................... 83 V.2.2.a Tide Datums ................................................................................................. 86 V.2.2.b Tide Flood and Ebb Dominance .................................................................... 92 V.3 HYDRODYNAMIC MODELING ..................................................................................... 93 V.3.1 Model Theory ...................................................................................................... 93 V.3.2 Model Setup ........................................................................................................ 94 V.3.2.1 Grid generation ............................................................................................ 94 V.3.2.2 Boundary condition specification .................................................................. 96 V.3.2.3 Calibration ................................................................................................... 96 V.3.4 Model Circulation Characteristics ...................................................................... 102 i MASSACHUSETTS