United States Office of Water EPA-822-R-08-023 Environmental Protection Office of Science and Technology December 2008 Agency Washington, DC 20460 www.epa.gov METHODS FOR EVALUATING WETLAND CONDITION #19 Nutrient Loading United States Office of Water EPA-822-R-08-023 Environmental Protection Office of Science and Technology December 2008 Agency Washington, DC 20460 www.epa.gov METHODS FOR EVALUATING WETLAND CONDITION #19 Nutrient Loading Major Contributors Iowa State University U. Sunday Tim and William Crumpton Prepared jointly by: The U.S. Environmental Protection Agency Health and Ecological Criteria Division (Office of Science and Technology) and Wetlands Division (Office of Wetlands, Oceans, and Watersheds) Notice The material in this document has been subjected to U.S. Environmental Protection Agency (EPA) technical review and has been approved for publication as an EPA document. The information contained herein is offered to the reader as a review of the “state of the science” concerning wetland bioassessment and nutrient enrichment and is not intended to be prescriptive guidance or firm advice. Mention of trade names, products or services does not convey, and should not be interpreted as conveying official EPA approval, endorsement, or recommendation. Appropriate Citation U.S. EPA. 2008. Methods for Evaluating Wetland Condition: Nutrient Loading. Office of Water, U.S. Environmental Protection Agency, Washington, DC. EPA-822-R-08-023. Acknowledgements EPA acknowledges the contributions of the following people in the writing of this module: U. Sunday Tim and William Crumpton both of Iowa Sate University. This entire document can be downloaded from the following U.S. EPA websites: http://www.epa.gov/water science/criteria/wetlands/ http://www.epa.gov/owow/wetlands/bawwg/publicat.html iii CONTENTS FORE W ORD ����������������������������������������������������������������������������������������������������������������V LIST OF “METHODS FOR EVALUATING WETLAND CONDITION ” MODULES VI NUTRIENT LOADING ��������������������������������������������������������������������������������������������������1 SU mm ARY ������������������������������������������������������������������������������������������������������������������1 PUR P OSE 1 INTRODU C TION �����������������������������������������������������������������������������������������������������������1 LOADING FUN C TION MODELS 2 PRO C ESS -ORIENTED MODELS 7 LI M ITATIONS AND MODEL VALIDATION 25 CHOOSING A SUITABLE MODEL 31 REFEREN C ES ���������������������������������������������������������������������������������������������������������34 LIST OF TABLES TABLE 1: IN P UT P ARA M ETERS REQUIRED BY GWLF M ODEL . .4 TABLE 2: IN P UT P ARA M ETERS REQUIRED BY AGNPS M ODEL . 8 TABLE 3: IN P UT P ARA M ETERS REQUIRED BY HSPF . 15 TABLE 4: SWAT/SWAT 200 IN P UT P ARA M ETERS . 19 LIST OF FIGURES FIGURE 1: MODEL QUALITY ASSURAN C E C O mp ONENTS . 26 iv FORE W ORD In 1999, the U.S. Environmental Protection Agency (EPA) began work on this series of reports entitled Methods for Evaluating Wetland Condition. The purpose of these reports is to help States and Tribes develop methods to evaluate (1) the overall ecological condition of wetlands using biological assessments and (2) nutrient enrichment of wetlands, which is one of the pri- mary stressors damaging wetlands in many parts of the country. This information is intended to serve as a starting point for States and Tribes to eventually establish biological and nutrient water quality criteria specifically refined for wetland waterbodies. This purpose was to be accomplished by providing a series of “state of the science” modules concerning wetland bioassessment as well as the nutrient enrichment of wetlands. The individual module format was used instead of one large publication to facilitate the addition of other reports as wetland science progresses and wetlands are further incorporated into water quality programs. Also, this modular approach allows EPA to revise reports without having to reprint them all. A list of the inaugural set of 20 modules can be found at the end of this section. This last set of reports is the product of a collaborative effort between EPA’s Health and Ecological Criteria Division of the Office of Science and Technology (OST) and the Wetlands Division of the Office of Wetlands, Oceans and Watersheds (OWOW). The reports were initiated with the support and oversight of Thomas J. Danielson then of OWOW, Amanda K. Parker and Susan K. Jackson (OST), and seen to completion by Ifeyinwa F. Davis (OST). EPA relied on the input and expertise of the contributing authors to publish the remaining modules. More information about biological and nutrient criteria is available at the following EPA website: http://www.epa.gov/ost/standards More information about wetland biological assessments is available at the following EPA website: http://www.epa.gov/owow/wetlands/bawwg v LIST Of “METHODS FOR EValUATING WETlanD CONDITION” MODULES MODULE # MODULE TITLE 1 ................. INTRODU C TION TO WETLAND BIOLOGIC AL ASSESS M ENT 2 ................. INTRODU C TION TO WETLAND NUTRIENT ASSESS M ENT 3 ................. THE STATE OF WETLAND SC IEN C E 4 ................. STUDY DESIGN FOR MONITORING WETLANDS 5 ................. AD M INISTRATIVE FRA M E W ORK FOR THE Imp LE M ENTATION OF A WETLAND BIOASSESS M ENT PROGRA M 6 ................. DEVELO P ING METRI C S AND INDEXES OF BIOLOGIC AL INTEGRITY 7 ................. WETLANDS CLASSIFIC AT ION 8 ................. VOLUNTEERS AND WETLAND BIO M ONITORING 9 ................. DEVELO P ING AN INVERTEBRATE INDEX OF BIOLOGIC AL INTEGRITY FOR WETLANDS 10 ............... USING VEGETATION TO ASSESS ENVIRON M ENTAL CONDITIONS IN WETLANDS 11 ............... USING ALGAE TO ASSESS ENVIRON M ENTAL CONDITIONS IN WETLANDS 12 ............... USING A mp HIBIANS IN BIOASSESS M ENTS OF WETLANDS 13 ............... BIOLOGIC AL ASSESS M ENT METHODS FOR BIRDS 14 ............... WETLAND BIOASSESS M ENT CASE STUDIES 15 ............... BIOASSESS M ENT METHODS FOR FISH 16 ............... VEGETATION -BASED INDI C ATORS OF WETLAND NUTRIENT ENRI C H M ENT 17 ............... LAND -USE CHARA C TERIZATION FOR NUTRIENT AND SEDI M ENT RISK ASSESS M ENT 18 ............... BIOGEO C HE M I C AL INDI C ATORS 19 ............... NUTRIENT LOADING 20 .............. WETLAND HYDROLOGY vi NUTRIENT LOADING PUR P OSE he purpose of this module is to describe he purpose of this module is to provide T and discuss the general hydrologic prop- T an overview of hydrologic and contami- erties that make wetlands unique, and to pro- nant transport models that can be used to es- vide an overview of the processes that control timate nutrient loads to wetlands. wetland hydrologic behavior. The intent is to provide a general discussion of wetland hy- drologic processes and methods in the hope INTRODU C TION of fostering an understanding of the impor- tant attributes of wetland hydrology relevant ver the past three decades, considerable to the monitoring and assessment of these Oeffort has been expended in developing systems. As such, it is not intended to address models to simulate watershed hydrology and the narrower definition of wetland hydrology nutrient transport, particularly the estima- for jurisdictional or classification purposes. tion of cumulative field/watershed contribu- Also, this module should not replace more tions of flow, sediment, nutrients, and other advanced wetland texts. If the need arises to contaminants of interest. Appropriately used, obtain more specific information, the reader existing models may apply when in evaluat- is advised to refer to wetland books or ar- ing wetland reference conditions or establish- ticles, including those referenced within this ing nutrient criteria for wetlands or guiding document. management decisions once nutrient criteria are established. U mm ARY S Several reviews have summarized the char- acteristics, features, strengths, and limitations utrient loading to wetlands is deter- of models that are used for estimating wa- N mined primarily by surface and subsur- tershed hydrology and water quality (Doni- face transport from the contributing land- gian, et al., et al. 1991b, 1995b; DeVries and scape, and varies significantly as a function Hromadka 1993; Novotny and Olem 1994; of weather and landscape characteristics such Tim 1996a, 1996b). These models vary wide- as soils, topography, and land use. In the ab- ly in structure and in spatial and temporal sence of sufficient measurements, nutrient scale, and can be classified as (i) empirical or loading can only be estimated using an appro- semi-empirical loading function models and priate loading model. This module provides ii) process-oriented simulation models. an overview of hydrologic and contaminant transport models that can be used to estimate nutrient loads to wetlands. 1 LOADING to the screening model Regression models are used to obtain preliminary estimates of pollut- FUN C TION MODELS ant load under limiting and incomplete data. These models require primary input param- oading function models are based on em- eters such as drainage area, percent impervi- Lpirical or semi-empirical relationships that ousness, mean annual precipitation, land use provide estimates of pollutant loads based on pattern, and ambient temperature. Regression long-term measurements of flow