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A reactive nitrogen budget for Lake Michigan
Rowe, M., R. Kreis, AND D. Dolan. A reactive nitrogen budget for Lake Michigan. JOURNAL OF GREAT LAKES RESEARCH. International Association for Great Lakes Research, Ann Arbor, MI, 40(1):192-201, (2014).
A multimedia mass balance model is described which has been applied to nitrogen in the Lake Michigan ecosystem. This manuscript reflects the first time a historical record of nitrogen external loads has been compiled for Lake Michigan and the first time a modeled budget of Lake Michigan has been computed. The effort reflects the regional trends in reactive nitrogen but is parallel to the Agency efforts to quantify loads, trends, and impacts across the nation.
The reactive nitrogen budget for Lake Michigan was reviewed and updated, making use of recent estimates of watershed and atmospheric nitrogen loads. The updated total N load to Lake Michigan was approximately double the previous estimate from the Lake Michigan Mass Balance study owing to recent estimates of watershed loads being greater than previous estimates, and due to inclusion of estimated atmospheric dry deposition and atmospheric deposition of organic N in our budget. Atmospheric and watershed total N loads were nearly equal. The estimated loss due to denitrification at the sediment surface was at least equal to, and possibly much greater than, the combined loss due to outflow and net sediment accumulation. The updated loads were used to force the LM3-PP biogeochemical water quality model. Simulated water column concentrations of nitrate and organic nitrogen were consistent with available observational data when denitrification was included at the sediment surface at a rate that is consistent with literature values. The model simulation confirmed that the budget is plausible, and that the estimated denitrification rate does not exceed the availability of settling organic N mass.