Methods and Approaches for Deriving Numeric Criteria for Nitrogen/Phosphorus Pollution in Florida’s Estuaries, Coastal Waters, and Southern Inland Flowing Waters November 17, 2010 Methods and Approaches for Deriving Numeric Criteria for Nitrogen/Phosphorus Pollution in Florida’s Estuaries, Coastal Waters, and Southern Inland Flowing Waters Disclaimer This document is intended to provide technical support to EPA in developing and establishing numeric water quality criteria under the Clean Water Act (CWA) pursuant to Section 303(c)(4), in order to support the applicable designated uses in the State of Florida from effects of nitrogen/phosphorus pollution. The information provided herein does not substitute for the CWA or EPA’s regulations; nor is this document a regulation itself. Thus, this document cannot and does not impose any legally binding requirements on EPA, States, Authorized Tribes, the regulated community, or any other party, and might not apply to a particular situation or circumstance. 1 Methods and Approaches for Deriving Numeric Criteria for Nitrogen/Phosphorus Pollution in Florida’s Estuaries, Coastal Waters, and Southern Inland Flowing Waters Contributing Authors Jim Carleton, U.S. Environmental Protection Agency Tiffany Crawford, U.S. Environmental Protection Agency Ed Decker, U.S. Environmental Protection Agency Edward Dettman, U.S. Environmental Protection Agency Erica Fleisig, U.S. Environmental Protection Agency Richard Greene, U.S. Environmental Protection Agency James Hagy, U.S. Environmental Protection Agency Galen Kaufman, U.S. Environmental Protection Agency Jacques Oliver, U.S. Environmental Protection Agency Blake Schaeffer, U.S. Environmental Protection Agency Mario Sengco, U.S. Environmental Protection Agency Dana Thomas, U.S. Environmental Protection Agency Timothy Wool, U.S. Environmental Protection Agency Steven Davie, Tetra Tech Jeroen Gerritsen, Tetra Tech Jon Harcum, Tetra Tech John Hochheimer, Tetra Tech Michael Paul, Tetra Tech Steven Davie, Tetra Tech 2 Methods and Approaches for Deriving Numeric Criteria for Nitrogen/Phosphorus Pollution in Florida’s Estuaries, Coastal Waters, and Southern Inland Flowing Waters Contents Contributing Authors ...................................................................................................................... 2 Abbreviations and Acronyms ....................................................................................................... 15 Executive Summary ...................................................................................................................... 18 1 Introduction ........................................................................................................................... 21 1.1 Purpose of the Document ............................................................................................. 21 1.2 Document Organization ............................................................................................... 21 1.3 Background: Clean Water Act Requirements and Florida’s Current Water Quality Standard for Nitrogen/Phosphorus Pollution ............................................................... 22 1.4 Nature of the Chemical Stressor: Nitrogen/Phosphorus Pollution ............................... 24 1.4.1 Stressor Source and Distribution .......................................................................... 24 1.4.2 Aquatic Ecosystem Effects of Nitrogen/Phosphorus Pollution ............................ 24 1.5 Purpose of this Effort ................................................................................................... 27 2 Approach ............................................................................................................................... 29 2.1 Overview ...................................................................................................................... 29 2.1.1 Nutrient Criteria Development Guidance ............................................................. 30 2.1.2 General Approach ................................................................................................. 30 2.2 Conceptual Model ........................................................................................................ 31 2.3 Review of Scientific Basis and Selection of Potential Assessment Endpoints and Indicator Variables ....................................................................................................... 33 2.3.1 Selecting Assessment Endpoints and Water Quality Indicator Variables ............ 33 2.3.2 Selected Biological Assessment Endpoints .......................................................... 37 2.3.3 Water Quality Indicator Variables for Expressing Criteria .................................. 39 2.4 Potential Data Sources .................................................................................................. 40 3 Numeric Nutrient Criteria Development in Florida Estuaries .............................................. 45 3.1 Delineating Estuaries .................................................................................................... 46 3.2 Selection of Assessment Endpoints and Indicator Variables ....................................... 48 3.3 Numeric Criteria Approaches ....................................................................................... 49 3.3.1 Reference Condition Approaches ......................................................................... 51 3.3.2 Stressor Response Relationships ........................................................................... 52 3.3.3 Water Quality Simulation Models ........................................................................ 54 3.3.4 Evaluating Water Quality Simulation Models ...................................................... 64 3.4 Seagrass Depth Targets ................................................................................................ 65 3 Methods and Approaches for Deriving Numeric Criteria for Nitrogen/Phosphorus Pollution in Florida’s Estuaries, Coastal Waters, and Southern Inland Flowing Waters 3.5 Example Application: Pensacola Bay .......................................................................... 69 3.5.1 Selection of Assessment Endpoints ...................................................................... 70 3.5.2 Numeric Criteria Development ............................................................................. 71 3.5.3 Details on the Pensacola Bay Water Quality Model ............................................. 72 4 Numeric Nutrient Criteria Development for Florida Coastal Waters ................................... 77 4.1 Analysis Plan and Delineation of Coastal Areas .......................................................... 77 4.1.1 Use of Remote Sensing Data ................................................................................ 79 4.2 Deriving Numeric Criteria ............................................................................................ 81 4.2.1 Satellite Chlorophyll Data Evaluation .................................................................. 82 4.2.2 Comparison of Satellite Chlorophyll to Field Collected Chlorophyll .................. 83 4.2.3 ChlRS-a Criteria from Statistical Distributions ...................................................... 87 4.3 Uncertainties and Data Gaps ........................................................................................ 90 5 Numeric Nutrient Criteria Development in South Florida Marine and Inland Flowing Waters ................................................................................................................................... 91 5.1 Analysis Plan for South Florida ................................................................................... 91 5.1.1 Inland Flowing Waters .......................................................................................... 92 5.1.2 Marine Waters ....................................................................................................... 93 5.2 Inland Flowing Waters: Classification ......................................................................... 93 5.2.1 Existing TP Criterion for the EvPA ...................................................................... 97 5.3 Inland Flowing Waters: Inventory ............................................................................... 98 5.4 Inland Flowing Waters: Data Sources and Assessment Endpoints ............................ 102 5.4.1 Deriving Numeric Criteria .................................................................................. 104 5.5 Marine Waters: Classification and Data Sources ....................................................... 113 5.6 Marine Waters: Numeric Criteria Derivation ............................................................. 116 5.6.1 Reference Condition Approach—Least Disturbed Sites .................................... 116 5.7 Uncertainties and Data Gaps ...................................................................................... 120 6 Numeric Nutrient Criteria Development for the Protection of Downstream Estuaries ...... 122 6.1 Analysis Plan .............................................................................................................. 122 6.2 Estimating Protective TN and TP Loading ................................................................ 123 6.3 Computing DPVs for Terminal Reaches .................................................................... 123 6.4 Computing DPVs for Upstream Reaches