Water quality models are important tools used by the Maryland Department of the Environment (MDE) in developing Total Maximum Daily Loads (TMDLs), which serve as water quality standards. The MDE tool, which spatially interpolates output from the Chesapeake Bay Program Watershed Model (WSM), is often used because it requires little time, data, or training. In contrast, the WSM requires extensive time, data, and training to run.

This study examines if the MDE tool provides accurate estimates of pollutant loads and whether the mid-level complexity model AVGWLF provides comparatively more accurate estimates.  The accuracy of the models was assessed based on qualitative comparisons, t-tests, and Nash-Sutcliffe coefficients.  The MDE tool was found to more accurately predict total nitrogen and total sediment loads and the AVGWLF model was found to more accurately predict total phosphorus loads.  The study also found that a consistent method for calculating observed loads needs to be developed.