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, biochemical and ecosystem models and represents a significant multiagency 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 water 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 WIPs include 

management practices for agricultural, urban, and forested land and infrastructure improvements affecting

storm water and wastewater management. The WIPs can be viewed at 

http://www.chesapeakebay.net/about/programs/watershed.

Chesapeake Bay Water 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 generated 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-model 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 aimed 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 Fisheries Model (CBFEM)

The CBFEM is a fisheries-oriented trophic network model for the Bay using a widely 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 module for 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/ecosystemmodeling/chesapeake-bay-fisheries-ecosystem-model.