## Attachment 17 **– Description of models used to choose attribute levels** 

Forecasting the attribute levels under different baseline and policy scenarios requires combining the results of different hydrological, bioche mical and ecosystem models and represents a significant multi agency effort. In summary, plans for land use and management practices are used in a hydrological model to forecast nutrient and sediment loadings to watershed streams, rivers and the Bay. Forecasts for the wate r clarity attribute can be taken directly from the hydrological model. Nutrient loadings from the hydrological model are used in a fisheries ecosystem model to forecast the striped bass, blue crab and oyster population attributes. Nutrient loadings from the hydrological model are also used in a hydrological - biochemical model to forecast levels for the watershed lakes attribute. The data, models, and resulting output used to forecast future conditions and choose the attribute levels in the choice questions are described in more detail below. **Watershed Implementation Plans (WIPs)** Each of the seven Chesapeake Bay Watershed jurisdictions created WIPs that document how the jurisdiction will meet the water quality standards of the Chesapeake Bay TMDLs. The WI Ps include management practices for agricultural, urban, and forested land and inf rastructure improvements affecting storm water and wastewater management. The WIPs can be viewed at http://www.chesapeakebay.net/about/programs/watershed . **Chesapeake Bay W**  **ater Quality Model** The Chesapeake Bay Program Office and other stakeholders use a suite of computer models that project pollution loads and flow. The component models that work together to form the Chesapeake Bay Water Quality Model are described below. More on the Water Quality Model can be found at http://www.chesapeakebay.net/about/programs/modeling . Watershed Model The Watershed Model incorporates information about land use, fertilizer applications, wastewater plant discharges, septic systems, air deposition, farm animal populations, weather and other variables to estimate the amount of nutrients and sediment reaching the Chesapeake Bay and where these pollutants originate.Estuary Model

The Estuary Model examines the effects that pollution loads g enerated by the Watershed Model have on water quality. In the Estuary Model, the Chesapeake Bay is represented by more than 57,000 computational cells and is built on two sub - models:  The hydrodynamic sub - mo del simulates the mixing of waters in the Bay and its tidal tributaries.  The water quality sub - model calculates the Bay’s biological, chemical and physical dynamics. Scenario Builder Scenario Builder can generate simulations of the past, present or future state of the Chesapeake Bay watershed to explore potential impacts of management actions and evaluate alternatives. Scenario Builder produces inputs for the Watershed Model based on factors from a wide range of land uses and management actions. For example, information such as acres of different crops, numbers of animals and extent of conservation practices is used to generate Watershed Model inputs for agricultural land use types. Airshed Model The Airshed Model uses information about nitrogen emissions from power plants, vehicles and other sources to estimate the amount of and location where these pollutants are deposited on the Chesapeake Bay and its watershed. That information is fed into the Watershed Model. Land Change Model The Land Change Model analyzes and forecasts the effects of urban land use and population on sewer and septic systems in the Chesapeake Bay watershed. **Northeast Lakes Model** The Northeast Lakes model was designed specifically to model changes in the eutrophication of freshwater lakes as the result of management practices aime d at improving the water quality of coastal estuaries. Combining data from the National Lakes Assessment and results from the Spatially Referenced Regressions On Watershed Attributes (SPARROW) nutrient models , the Northeast Lakes model uses nutrient loads to watershed streams and rivers to forecast eutrophication of lakes in the watershed. The Northeast Lakes Model places every lake in the Chesapeake Bay watershed into one of four eutrophication categories. The “low algae growth” lakes on the survey refer to the lower three categories. The Northeast lakes model is described in more detail in the following peer reviewed publications:Moore, R. B., C. M. Johnston, R. A. Smith and B. Milstead (2011). "Source and Delivery of Nutrients to

Receiving Waters in the Northeastern and Mid - Atlantic Regions of the United States." JAWRA Journal of the American Water Resources Association **47** (5): 965 - 990.http://dx.doi.org/10.1111/j.1752 - 1688.2011.00582.x Booth, N. L., E. J. Everman, I. L. Kuo, L. Murphy and L. Sprague (2011). "A Web - Based Decision Support System for Assessing Regional Water - Quality Conditions and Management Actions." J. Am. Water Resour. Assoc. Journal of the American Water Resources Association **47** (5): 1136 - 1150 **Chesapeake Bay Ecosystem Fisheri es Model**  **(CBFEM)** The CBFEM is a fisheries - oriented trophic network model for the Bay using a w idely applied software package, Ecopath with Ecosim, or EwE. Ecopath is a static, mass - balanced snapshot of the system and Ecosim is a time dynamic simulation mo dule fo r policy exploration. The major species for the CBFEM application of EwE include the multi - stanza (or life - stage) representations of commercially important species (striped bass, bluefish, weakfish, white perch, Atlantic menhaden, blue crab, and oyster) as well as single biomass pool groups of other commercially important species including American eel, Atlantic croaker, summer flounder, spot, alewife, American shad, black drum, catfish, and bivalves. CBFEM forecasts changes in relative biomass that can be used with current populations to forecast populations in the future. Documentation for the CBFEM can be found at http://chesapeakebay.noaa .gov/ecosystem modeling/chesapeake -bay - fisheries - ecosystem - model .