Massachusetts Estuaries Project Linked Watershed-Embayment Model to Determine Critical Nitrogen Loading Thresholds for the Slocum’s and Little River Estuaries, Dartmouth, MA University of Massachusetts Dartmouth Massachusetts Department of School of Marine Science and Technology Environmental Protection FINAL REPORT – December 2008 Massachusetts Estuaries Project Linked Watershed-Embayment Model to Determine Critical Nitrogen Loading Thresholds for the Slocum’s and Little River Estuaries, Dartmouth, MA FINAL REPORT – December 2008 Brian Howes Tony Millham Roland Samimy David Schlezinger John Ramsey Trey Ruthven Ed Eichner Contributors: US Geological Survey Don Walters and John Masterson Applied Coastal Research and Engineering, Inc. Elizabeth Hunt and Sean W. Kelley Massachusetts Department of Environmental Protection Charles Costello and Brian Dudley SMAST Coastal Systems Program Jennifer Benson, Michael Bartlett, Sara Sampieri, and Elizabeth White Lloyd Center for the Environment Mark Mello Cape Cod Commission Xiaotong Wu © [2007] University of Massachusetts All Rights Reserved 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 Slocum's and Little River Estuaries and supported the application of the Linked Watershed-Embayment Model to Determine Critical Nitrogen Loading Thresholds for these systems. 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 Coalition for Buzzards Bay's BayWatcher, Water Quality Monitoring Program. These individuals gave of their time to consistent and sound nutrient related water quality from this system for over a decade. These data were enhanced by short-term intensive water quality monitoring efforts by the Lloyd Center Staff and interns participating in the Turn the Tide Project. These multiple efforts have resulted in a solid water quality database for these estuaries, without which the present analysis would not have been possible. Of particular note has been the effort of the Coalition for Buzzards Bay's Monitoring Coordinator, Tony Williams, who has spent countless hours ensuring a scientifically defensible monitoring program and reviewing data and information with MEP Technical Team members. The present MEP Technical Report was developed as part of the on-going partnership project to restore the Town of Dartmouth's estuaries, known as Turn-The-Tide. This program is a partnership between the Town of Dartmouth, the Coalition for Buzzards Bay, the Lloyd Center for the Environment and the Coastal Systems Program at the School for Marine Science and Technology - University of Massachusetts Dartmouth. The goal is to restore water quality and living resources in Dartmouth's three major estuarine systems. Much of the present effort was conducted under this partnership, which greatly enhanced information and data transfers with the Town and its Departments. The Town of Dartmouth and its citizens have expended "extra" effort in the stewardship of these critical coastal systems and are to be commended. Departments and staff from the Town of Dartmouth have provided essential insights toward this effort, particularly the Department of Public Works and its commissioners who oversaw the Turn-The-Tide Project and specifically the help provided by David Hickox; Water and Sewer Division, Steve Sullivan; Animal Control, Sandra Gosselin and Wendy Henderson Board of Health. The technical team would like to specifically acknowledge the efforts of Mike O'Reilly, Dartmouth's Environmental Affairs Coordinator, who worked tirelessly as the Town interface with the Turn-The-Tide Project and was key in facilitating the overall effort. Other individuals of particular note include Mark Rasmussen, Executive Director CBB and Darcy McMahon Director of the Lloyd Center, who helped to guide and disseminate the information from the Turn-The-Tide effort. In addition to local contributions, technical, policy and regulatory support has been freely and graciously provided by Bill Napolitano and Karen Porter from SRPEDD; MaryJo Feurbach and Art Clark of the USEPA; and our MassDEP colleagues: Arleen O’Donnell, Art Screpetis, Rick Dunn, Steve Halterman, and Russ Issacs. 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. © [2007] University of Massachusetts All Rights Reserved Support for this project was provided by the Town of Dartmouth through the Turn the Tide Project, private donations from citizens of the Town of Dartmouth, the MassDEP, and the USEPA. This Nutrient Threshold Technical Report to be used by the Town of Dartmouth in the restoration of two of its key estuarine systems is dedicated to Don Tucker former Director of the Lloyd Center, who helped to establish the Turn the Tide partnership project but passed away suddenly before its completion. CITATION Howes B.L., N.P. Millham, S.W. Kelley, J. S. Ramsey, R.I. Samimy, D.R. Schlezinger, E.M. Eichner (2007). Linked Watershed-Embayment Model to Determine Critical Nitrogen Loading Thresholds for the Slocum’s and Little River Estuaries, Dartmouth, Massachusetts. SMAST/DEP Massachusetts Estuaries Project, Massachusetts Department of Environmental Protection. Boston, MA. © [2007] University of Massachusetts All Rights Reserved MASSACHUSETTS ESTUARIES PROJECT TABLE OF CONTENTS I. INTRODUCTION .......................................................................................................................1 I.1 THE MASSACHUSETTS ESTUARIES PROJECT APPROACH ........................................4 I.2 SITE DESCRIPTION...........................................................................................................8 I.3 NITROGEN LOADING ......................................................................................................17 I.4 WATER QUALITY MODELING.........................................................................................18 I.5 REPORT DESCRIPTION..................................................................................................19 II. PREVIOUS STUDIES RELATED TO NITROGEN MANAGEMENT.....................................21 III. DELINEATION OF WATERSHEDS .....................................................................................25 III.1 BACKGROUND...............................................................................................................25 III.2 WATERSHED DELINEATION APPROACH ...................................................................26 IV. WATERSHED NITROGEN LOADING TO EMBAYMENT: LAND USE, STREAM INPUTS, AND SEDIMENT NITROGEN RECYCLING...................................................................31 IV.1 WATERSHED LAND USE BASED NITROGEN LOADING ANALYSIS .........................31 IV.1.1 Land Use and Water Use Database Preparation.....................................................35 IV.1.2 Nitrogen Loading Input Factors................................................................................37 IV.1.3 Calculating Nitrogen Loads ......................................................................................48 IV.2 ATTENUATION OF NITROGEN IN SURFACE WATER TRANSPORT.........................54 IV.2.1 Background and Purpose.........................................................................................54 IV.2.2 Surface water Discharge and Attenuation of Watershed Nitrogen: Stream Discharge from Paskamanset River to head of Slocums River ...............................59 IV.2.3 Surface water Discharge and Attenuation of Watershed Nitrogen: Stream Discharge from Destruction Brook to the head of Slocums River............................70 IV.2.4 Surface water Discharge and Attenuation of Watershed Nitrogen: Stream Discharge Barneys Joy (north) Creek to head of Slocums River.............................76 IV.2.4 Surface water Discharge and Attenuation of Watershed Nitrogen: Stream Discharge Giles Creek to the head of the Slocums River........................................78 IV.3 BENTHIC REGENERATION OF NITROGEN IN BOTTOM SEDIMENTS......................83 IV.3.1 Sediment-Watercolumn Exchange of Nitrogen ........................................................83 IV.3.2 Method for determining sediment-watercolumn nitrogen exchange.........................84 IV.3.3 Rates of Summer Nitrogen Regeneration from Sediments ......................................87 V. HYDRODYNAMIC MODELING ............................................................................................91 V.1 INTRODUCTION..............................................................................................................91 V.2 GEOMORPHIC AND ANTHROPOGENIC EFFECTS TO THE ESTUARINE SYSTEM..92 V.3 FIELD DATA COLLECTION AND ANALYSIS .................................................................92 V.3.1 Data Acquisition ........................................................................................................93 V.3.1.1 Water Elevation ..................................................................................................93 V.3.1.2 Bathymetry..........................................................................................................97 V.3.1.3 Current Measurements .......................................................................................98