A new biogeochemical model for Chesapeake Bay has been developed by merging two published models – the ECB model of Da et al. (2018) that has been calibrated for the Bay but only simulates nitrogen, carbon and oxygen and the BioRedoxCNPS model of al Azhar et al. (2014) and Hantsoo et al. (2018) that includes cryptic sulfur cycling. Comparison between these models shows that judicious choices are required for key processes and parameters. This manuscript documents the sources of differences between the two published models in order to select the most realistic configuration for our new model. • This study focuses on three sets of differences–processes only included in ECB (burial and dissolved organic matter), processes only included in BioRedoxCNPS (explicit dynamics for hydrogen sulfide, sulfate and nitrite, light attenuation that does not include CDOM or sediments), and differences in parameters common to the two codes. • Sensitivity studies that highlight particular choices (absorption by dissolved organic matter, nitrification rates, stoichiometric ratios) are also shown. • The new model includes sulfur cycling and has comparable skill in predicting oxygen as ECB, but also has improved simulation of nitrogen species compared with both original codes.